Cohort profile: GRACE - a residential aged care cohort examining factors influencing antimicrobial resistance carriage.

BACKGROUND: The emergence of antimicrobial-resistant bacteria represents a considerable threat to human health, particularly for vulnerable populations such as those living in residential aged care. However, antimicrobial resistance carriage and modes of transmission remain incompletely understood. The Generating evidence on antimicrobial Resistance in the Aged Care Environment (GRACE) study was established to determine principal risk factors of antimicrobial resistance carriage and transmission in residential aged care facilities (RACFs). This article describes the cohort characteristics, national representation, and planned analyses for this study. METHODS: Between March 2019 and March 2020, 279 participants were recruited from five South Australian RACFs. The median age was 88.6 years, the median period in residence was 681 days, and 71.7% were female. A dementia diagnosis was recorded in 54.5% and more than two thirds had moderate to severe cognitive impairment (68.8%). 61% had received at least one course of antibiotics in the 12 months prior to enrolment. RESULTS: To investigate the representation of the GRACE cohort to Australians in residential aged care, its characteristics were compared to a subset of the historical cohort of the Registry of Senior Australians (ROSA). This included 142,923 individuals who were permanent residents of RACFs on June 30th, 2017. GRACE and ROSA cohorts were similar in age, sex, and duration of residential care, prevalence of health conditions, and recorded dementia diagnoses. Differences were observed in care requirements and antibiotic exposure (both higher for GRACE participants). GRACE participants had fewer hospital visits compared to the ROSA cohort, and a smaller proportion were prescribed psycholeptic medications. CONCLUSIONS: We have assembled a cohort of aged care residents that is representative of the Australian aged care population, and which provides a basis for future analyses. Metagenomic data isolated from participants and built environments will be used to determine microbiome and resistome characteristics of an individual and the facility. Individual and facility risk exposures will be aligned with metagenomic data to identify principal determinants for antimicrobial resistance carriage. Ultimately, this analysis will inform measures aimed at reducing the emergence and spread of antimicrobial resistant pathogens in this high-risk population.

Assessment of Long-Term Macrolide Exposure on the Oropharyngeal Microbiome and Macrolide Resistance in Healthy Adults and Consequences for Onward Transmission of Resistance.

While the use of long-term macrolide therapy to prevent exacerbations in chronic respiratory diseases is widespread, its impact on the oropharyngeal microbiota and macrolide resistance, and the potential for onward transmission of resistance to close contacts are poorly understood. We determined the effects of long-term exposure to azithromycin or erythromycin on phenotypic and genotypic macrolide resistance within the oropharyngeal microbiome of healthy adults and their close contacts in a randomized, single-blinded, parallel-group trial of 4 weeks of twice-daily oral 400 mg erythromycin ethylsuccinate or twice-daily oral 125 mg azithromycin. Using oropharyngeal swabs collected from 20 index healthy adults and 20 paired close contacts, the oropharyngeal microbial composition and macrolide resistance in streptococci were assessed by 16S rRNA sequencing and antibiotic susceptibility testing of oropharyngeal cultures, respectively, at baseline and weeks 4 and 8 (washout). Targeted quantitative PCR of antibiotic resistance genes was performed to evaluate paired changes in resistance gene levels in index patients and close contacts and to relate the potential transmission of antibiotic resistance. Neither azithromycin nor erythromycin altered oropharyngeal microbiota characteristics significantly. Proportional macrolide resistance in oropharyngeal streptococci increased with both erythromycin and azithromycin, remaining above baseline levels for the azithromycin group at washout. Levels of resistance genes increased significantly with azithromycin[erm(B) and mef] and erythromycin (mef), returning to baseline levels at washout only for the erythromycin group. We found no evidence of onward transmission of resistance to close contacts, as indicated by the lack of concomitant changes in resistance gene levels detected in close contacts. (This study has been registered with the Australian and New Zealand Clinical Trials Registry under identifier ACTRN12617000278336.).

Ear microbiota and middle ear disease: a longitudinal pilot study of Aboriginal children in a remote south Australian setting.

BACKGROUND: Otitis media (OM) is a major disease burden in Australian Aboriginal children, contributing to serious long-term health outcomes. We report a pilot analysis of OM in children attending an outreach ear and hearing clinic in a remote south Australian community over a two-year period. Our study focuses on longitudinal relationships between ear canal microbiota characteristics with nasopharyngeal microbiota, and clinical and treatment variables. RESULTS: Middle ear health status were assessed in 19 children (aged 3 months to 8 years) presenting in remote western South Australia and medical interventions were recorded. Over the two-year study period, chronic suppurative OM was diagnosed at least once in 7 children (37%), acute OM with perforation in 4 children (21%), OM with effusion in 11 children (58%), while only 1 child had no ear disease. Microbiota analysis of 19 children (51 sets of left and right ear canal swabs and nasopharyngeal swabs) revealed a core group of bacterial taxa that included Corynebacterium, Alloiococcus, Staphylococcus, Haemophilus, Turicella, Streptococcus, and Pseudomonas. Within-subject microbiota similarity (between ears) was significantly greater than inter-subject similarity, regardless of differences in ear disease (p = 0.0006). Longitudinal analysis revealed changes in diagnosis to be associated with more pronounced changes in microbiota characteristics, irrespective of time interval. Ear microbiota characteristics differed significantly according to diagnosis (P (perm) = 0.0001). Diagnoses featuring inflammation with tympanic membrane perforation clustering separately to those in which the tympanic membrane was intact, and characterised by increased Proteobacteria, particularly Haemophilus influenzae, Moraxella catarrhalis, and Oligella. While nasopharyngeal microbiota differed significantly in composition to ear microbiota (P (perm) = 0.0001), inter-site similarity was significantly greater in subjects with perforated tympanic membranes, a relationship that was associated with the relative abundance of H. influenzae in ear samples (rs = - 0.71, p = 0.0003). Longitudinal changes in ear microbiology reflected changes in clinical signs and treatment. CONCLUSIONS: Children attending the ear and hearing clinic in a remote Aboriginal community present with a broad spectrum of OM conditions and severities, consistent with other remote Aboriginal communities. Ear microbiota characteristics align with OM diagnosis and change with disease course. Nasopharyngeal microbiota characteristics are consistent with the contribution of acute upper respiratory infection to OM aetiology.

Targeted reduction of airborne viral transmission risk in long-term residential aged care.

COVID-19 has demonstrated the devastating consequences of the rapid spread of an airborne virus in residential aged care. We report the use of CO2-based ventilation assessment to empirically identify potential 'super-spreader' zones within an aged care facility, and determine the efficacy of rapidly implemented, inexpensive, risk reduction measures.

National Trends in Antibiotic Use in Australian Residential Aged Care Facilities, 2005-2016.

BACKGROUND: Understanding current patterns of antibiotic use in residential aged care facilities (RACFs) is essential to inform stewardship activities, but limited utilization data exist. This study examined changes in prevalence and consumption of antibiotics in Australian RACFs between 2005-2006 and 2015-2016. METHODS: This population-based, repeated cross-sectional analysis included all long-term permanent residents of Australian RACFs between July 2005 and June 2016 who were aged ≥ 65 years. The yearly prevalence rate of antibiotic use and number of defined daily doses (DDDs) of systemic antibiotics per 1000 resident-days were determined annually from linked pharmaceutical claims data. Trends were assessed using ordinary least squares regression. RESULTS: This study included 502 752 residents from 3218 RACFs, with 424.9 million resident-days analyzed. Antibiotics were dispensed on 5 608 126 occasions during the study period, of which 88% were for oral use. Cefalexin, amoxicillin-clavulanic acid, and trimethoprim were the most commonly dispensed antibiotics. The annual prevalence of antibiotic use increased from 63.8% (95% confidence interval [CI], 63.3%-64.4%) to 70.3% (95% CI, 69.9%-70.7%) between 2005-2006 and 2015-2016 (0.8% average annual increase, P < .001). There was a 39% relative increase in total consumption of systemic antibiotics, with utilization increasing from 67.6 to 93.8 DDDs/1000 resident-days during the study period (average annual increase of 2.8 DDDs/1000 resident-days, P < .001). CONCLUSIONS: This nationwide study showed substantial increases in both prevalence of use and total consumption of antibiotics in Australian RACFs between 2005 and 2016. The increasingly widespread use of antibiotics in Australian RACFs is concerning and points to a need for enhanced efforts to optimize antibiotic use in this setting.

Contribution of facility level factors to variation in antibiotic use in long-term care facilities: a national cohort study.

OBJECTIVES: To examine national variation in systemic antibiotic use in long-term care facilities (LTCFs) and identify facility characteristics associated with antibiotic utilization. METHODS: This retrospective cohort study included 312 375 residents of 2536 Australian LTCFs between 2011 and 2016. LTCFs were categorized as low, medium or high antibiotic use facilities according to tertiles of DDDs of systemic antibiotics dispensed per 1000 resident-days. Multivariable logistic regression estimated the associations between facility characteristics (ownership, size, location, medication quality indicator performance, prevalence of after-hours medical practitioner services) and antibiotic use (low versus high). RESULTS: LTCFs in the lowest and highest antibiotic use categories received a median of 54.3 (IQR 46.5-60.5) and 106.1 (IQR 95.9-122.3) DDDs/1000 resident-days, respectively. Compared with not-for-profit LTCFs in major cities, government-owned non-metropolitan LTCFs were less likely to experience high antibiotic use [adjusted OR (aOR) 0.47, 95% CI 0.24-0.91]. LTCFs with 69-99 residents were less likely to experience high antibiotic use (aOR 0.69, 95% CI 0.49-0.97) than those with 25-47 residents annually. Greater prevalence of medical practitioner services accessed after-hours was associated with high antibiotic use [aOR 1.10 (per 10% increase in after-hours services), 95% CI 1.01-1.21]. South Australian LTCFs (aOR 2.17, 95% CI 1.38-3.39) were more likely, while Queensland (0.43, 95% CI 0.30-0.62) and Western Australian (aOR 0.34, 95% CI 0.21-0.57) LTCFs were less likely to experience high antibiotic use than New South Wales LTCFs. CONCLUSIONS: Considerable facility level variation in systemic antibiotic use was observed across Australian LTCFs. Identification of facility characteristics associated with antibiotic use provides a basis for targeted stewardship initiatives.

Conventional myelosuppressive chemotherapy for non-haematological malignancy disrupts the intestinal microbiome.

BACKGROUND: The gut microbiota influences many aspects of host physiology, including immune regulation, and is predictive of outcomes in cancer patients. However, whether conventional myelosuppressive chemotherapy affects the gut microbiota in humans with non-haematological malignancy, independent of antibiotic exposure, is unknown. METHODS: Faecal samples from 19 participants with non-haematological malignancy, who were receiving conventional chemotherapy regimens but not antibiotics, were examined prior to chemotherapy, 7-12 days after chemotherapy, and at the end of the first cycle of treatment. Gut microbiota diversity and composition was determined by 16S rRNA gene amplicon sequencing. RESULTS: Compared to pre-chemotherapy samples, samples collected 7-12 days following chemotherapy exhibited increased richness (mean 120 observed species ± SD 38 vs 134 ± 40; p = 0.007) and diversity (Shannon diversity: mean 6.4 ± 0.43 vs 6.6 ± 0.41; p = 0.02). Composition was significantly altered, with a significant decrease in the relative abundance of gram-positive bacteria in the phylum Firmicutes (pre-chemotherapy median relative abundance [IQR] 0.78 [0.11] vs 0.75 [0.11]; p = 0.003), and an increase in the relative abundance of gram-negative bacteria (Bacteroidetes: median [IQR] 0.16 [0.13] vs 0.21 [0.13]; p = 0.01 and Proteobacteria: 0.015 [0.018] vs 0.03 [0.03]; p = 0.02). Differences in microbiota characteristics from baseline were no longer significant at the end of the chemotherapy cycle. CONCLUSIONS: Conventional chemotherapy results in significant changes in gut microbiota characteristics during the period of predicted myelosuppression post-chemotherapy. Further study is indicated to link microbiome changes during chemotherapy to clinical outcomes.

Prevention of SARS-CoV-2 (COVID-19) transmission in residential aged care using ultraviolet light (PETRA): a two-arm crossover randomised controlled trial protocol.

BACKGROUND: SARS-CoV-2 poses a considerable threat to those living in residential aged care facilities (RACF). RACF COVID-19 outbreaks have been characterised by the rapid spread of infection and high rates of severe disease and associated mortality. Despite a growing body of evidence supporting airborne transmission of SARS-CoV-2, current infection control measures in RACF including hand hygiene, social distancing, and sterilisation of surfaces, focus on contact and droplet transmission. Germicidal ultraviolet (GUV) light has been used widely to prevent airborne pathogen transmission. Our aim is to investigate the efficacy of GUV technology in reducing the risk of SARS-CoV-2 infection in RACF. METHODS: A multicentre, two-arm double-crossover, randomised controlled trial will be conducted to determine the efficacy of GUV devices to reduce respiratory viral transmission in RACF, as an adjunct to existing infection control measures. The study will be conducted in partnership with three aged care providers in metropolitan and regional South Australia. RACF will be separated into paired within-site zones, then randomised to intervention order (GUV or control). The initial 6-week period will be followed by a 2-week washout before crossover to the second 6-week period. After accounting for estimated within-zone and within-facility correlations of infection, and baseline infection rates (10 per 100 person-days), a sample size of n = 8 zones (n = 40 residents/zone) will provide 89% power to detect a 50% reduction in symptomatic infection rate. The primary outcome will be the incidence rate ratio of combined symptomatic respiratory infections for intervention versus control. Secondary outcomes include incidence rates of hospitalisation for complications associated with respiratory infection; respiratory virus detection in facility air and fomite samples; rates of laboratory confirmed respiratory illnesses and genomic characteristics. DISCUSSION: Measures that can be deployed rapidly into RACF, that avoid the requirement for changes in resident and staff behaviour, and that are effective in reducing the risk of airborne SARS-CoV-2 transmission, would provide considerable benefit in safeguarding a highly vulnerable population. In addition, such measures might substantially reduce rates of other respiratory viruses, which contribute considerably to resident morbidity and mortality. Trial registration Australian and New Zealand Clinical Trials Registry ACTRN12621000567820 (registered on 14th May, 2021).

Australian consensus statements for the regulation, production and use of faecal microbiota transplantation in clinical practice.

OBJECTIVE: Faecal microbiota transplantation (FMT) has proved to be an extremely effective treatment for recurrent Clostridioides difficile infection, and there is interest in its potential application in other gastrointestinal and systemic diseases. However, the recent death and episode of septicaemia following FMT highlights the need for further appraisal and guidelines on donor evaluation, production standards, treatment facilities and acceptable clinical indications. DESIGN: For these consensus statements, a 24-member multidisciplinary working group voted online and then convened in-person, using a modified Delphi approach to formulate and refine a series of recommendations based on best evidence and expert opinion. Invitations to participate were directed to Australian experts, with an international delegate assisting the development. The following issues regarding the use of FMT in clinical practice were addressed: donor selection and screening, clinical indications, requirements of FMT centres and future directions. Evidence was rated using the GRADE (Grading of Recommendations Assessment, Development and Evaluation) system. RESULTS: Consensus was reached on 27 statements to provide guidance on best practice in FMT. These include: (1) minimum standards for donor screening with recommended clinical selection criteria, blood and stool testing; (2) accepted routes of administration; (3) clinical indications; (4) minimum standards for FMT production and requirements for treatment facilities acknowledging distinction between single-site centres (eg, hospital-based) and stool banks; and (5) recommendations on future research and product development. CONCLUSIONS: These FMT consensus statements provide comprehensive recommendations around the production and use of FMT in clinical practice with relevance to clinicians, researchers and policy makers.

Influence of antimicrobial susceptibility reporting on junior doctors' decision to prescribe antimicrobials inappropriately.

Objectives: Inappropriate antimicrobial use drives antimicrobial resistance and is a global public health problem. This study examined whether withholding antimicrobial susceptibilities in combination with interpretive comments on microbiological reports influenced the decision to inappropriately prescribe antibiotics in a controlled survey. Methods: Seventy junior doctors attending educational sessions were given one of two surveys describing four clinical case vignettes (scenarios) in which antimicrobial treatment was not indicated. They were asked to select their preferred treatment from multiple choices. In the scenarios labelled 'A', the laboratory report did not report antibiotic susceptibilities, but included comments from the microbiologist. In the scenarios labelled 'B', the laboratory report included full organism identification and susceptibility results without additional comments. Results: For scenarios 1, 2 and 3 there was a significantly higher probability ( P < 0.01) that the doctor selected an answer involving antibiotic treatment if he/she received the 'B' version of the scenario where reports included antimicrobial susceptibilities, but no interpretive comments. This was significant in both interns and more senior doctors. In scenario 4, of which there were two versions, there was no difference seen in the answers between the groups given scenario A or B. Conclusions: The results of this survey suggest that withholding antimicrobial susceptibility results in combination with interpretive comments on microbiology reports significantly influences the decision of junior doctors to prescribe antibiotics in low-acuity outpatient setting scenarios (represented in scenarios 1-3), but not in inpatient scenarios (represented in scenario 4).

Performance of phenotypic tests for detection of penicillinase in Staphylococcus aureus isolates from Australia.

Recent studies have shown that chromogenic cephalosporin tests are inferior to disc zone edge tests in detecting penicillinase in Staphylococcus aureus isolates, resulting in a change to CLSI and EUCAST guidelines in 2012. We sought to confirm these findings using Australian isolates and compare the performance of the CLSI and EUCAST methods, which use different disc strengths, penicillin at 10 units (P10) and 1 unit (P1), respectively. Using blaZ PCR as the reference standard, the sensitivities of the tests for detection of penicillinase production were as follows: Cefinase disc test, 24/38 isolates (63%); P10 disc zone edge test, 34/38 isolates (89%); P10 disc diameter test, 25/38 isolates (66%); P1 disc zone edge test, 38/38 isolates (100%); and P1 disc diameter test, 38/38 isolates (100%). We also found that the P10 disc zone edge test reading was interpreted differently by the clinical laboratory and the study investigators in 11% of instances. Our findings support those of previous studies showing that chromogenic cephalosporin-based ß-lactamase tests are inferior to disc methods in detecting S. aureus penicillinase. We also conclude that the EUCAST method using the P1 disc has the best performance, particularly because the P1 disc zone diameter reading closely correlated with penicillinase production and reading of the disc zone diameter is less subjective than reading of the zone edge.

Direct whole-genome sequencing of HIV-1 for clinical drug-resistance analysis and public health surveillance.

BACKGROUND: Human Immunodeficiency virus type 1 (HIV-1) remains a significant global health threat partly due to its ability to develop resistance to anti-retroviral therapies. HIV-1 genotype and drug resistance analysis of the polymerase (pol) sequence is a mainstay of its clinical and public health management. However, as new treatments and resistances evolve, analysis methods must change accordingly. In this study, we outline the development and implementation of a direct whole-genome sequencing approach (dWGS) using probe-capture target-enrichment for HIV-1 genotype and drug resistance analysis. METHODS: We implemented dWGS and performed parallel pol Sanger sequencing for clinical samples, followed by comparative genotype and drug-resistance analysis. These HIV-1 WGS sequences were also utilised for a novel partitioned phylogenetic analysis. RESULTS: Optimised nucleic acid extraction and DNAse I treatment significantly increased HIV-1 whole-genome coverage and depth, and improved recovery of high-quality genomes from low viral load clinical samples, enabling routine sequencing of viral loads as low as 1000 copies/mL. Overall, dWGS was robust, accurate and more sensitive for detecting low-frequency variants at drug-resistance sites compared to Sanger sequencing. Analysis of multiple sequence regions improved phylogenetic reconstruction for recombinant HIV-1 sequences compared to analysis of pol sequence alone. CONCLUSIONS: These findings demonstrate dWGS enhances HIV-1 drug-resistance analysis by quantitative variant detection and improves reconstruction of HIV-1 phylogenies compared to traditional pol sequencing. This work supports that HIV-1 dWGS is a viable option to replace Sanger sequencing for clinical and public health applications.

Intestinal persistence of Bifidobacterium infantis is determined by interaction of host genetics and antibiotic exposure.

Probiotics have gained significant attention as a potential strategy to improve health by modulating host-microbe interactions, particularly in situations where the normal microbiota has been disrupted. However, evidence regarding their efficacy has been inconsistent, with considerable interindividual variability in response. We aimed to explore whether a common genetic variant that affects the production of mucosal α(1,2)-fucosylated glycans, present in around 20% of the population, could explain the observed interpersonal differences in the persistence of commonly used probiotics. Using a mouse model with varying α(1,2)-fucosylated glycans secretion (Fut2WT or Fut2KO), we examined the abundance and persistence of Bifidobacterium strains (infantis, breve, and bifidum). We observed significant differences in baseline gut microbiota characteristics between Fut2WT and Fut2KO littermates, with Fut2WT mice exhibiting enrichment of species able to utilize α(1,2)-fucosylated glycans. Following antibiotic exposure, only Fut2WT animals showed persistent engraftment of Bifidobacterium infantis, a strain able to internalize α(1,2)-fucosylated glycans, whereas B. breve and B. bifidum, which cannot internalize α(1,2)-fucosylated glycans, did not exhibit this difference. In mice with an intact commensal microbiota, the relationship between secretor status and B. infantis persistence was reversed, with Fut2KO animals showing greater persistence compared to Fut2WT. Our findings suggest that the interplay between a common genetic variation and antibiotic exposure plays a crucial role in determining the dynamics of B. infantis in the recipient gut, which could potentially contribute to the observed variation in response to this commonly used probiotic species.

Atmospheric CO2 monitoring to identify zones of increased airborne pathogen transmission risk in hospital settings.

Measures to reduce airborne pathogen transmission in health care settings, such as increased air exchange, air decontamination, and reductions in peak occupancy, can be expensive and disruptive, particularly when employed in an untargeted manner. We report the empirical identification of high transmission risk zones in a tertiary hospital, using carbon dioxide-based assessments of air exchange. This rapid, cost-effective, and unobtrusive approach led to the targeted remediation of a high transmission risk zone.

Intestinal microbiology and urinary tract infection associated risk in long-term aged care residents.

BACKGROUND: Urinary tract infections (UTI) are the most frequently diagnosed infection in residents of long-term care and are a major risk factor for urosepsis, hospitalisation, and death. Translocation of gut pathobionts into the urinary tract is the presumed cause of most UTIs. While specific gut microbiota characteristics have been linked to UTI risk in younger adults, their relevance in aged care residents remains uncertain. METHODS: The faecal microbiome was assessed in 54 long-term aged care residents with a history of UTIs and 69 residents without a UTI history. Further comparisons were made to microbiome characteristics in 20 younger adults without UTIs. Microbiome characteristics were examined in relation to prior and subsequent UTIs, as well as antibiotic therapy. RESULTS: In long-term aged care residents, prior UTI history and exposure to UTI-exclusive antibiotics do not significantly affect microbiome composition or functional capacity. However, exposure to antibiotics unrelated to UTI treatment is associated with distinct microbiota compositional traits. Adjustment for dementia, incontinence, diabetes, and prior antibiotic use finds no microbiota characteristic linked to UTI development. However, prior UTI is identified as a predictor of future UTIs. Comparison with younger adults identifies greater within-participant dispersion in aged care residents, as well as lower microbiota diversity and altered microbiome functional potential. CONCLUSIONS: No association between the gut microbiome and UTI incidence, as has been reported in younger individuals, is evident in long-term aged care residents. Considerable variability in gut microbiome characteristics, relating to high antibiotic exposure and age-related physiological and immunological factors, could mask such a relationship. However, it cannot be discounted that increased UTI risk in the elderly is independent of microbiome-mediated mechanisms.

Urinary tract infections (UTIs) are common in residents of long-term aged care facilities, posing serious health risks. Harmful bacteria moving from the gut to the urinary tract is thought to cause most UTIs. It is still unclear, however, how differences in gut bacteria contribute to UTI risk in older adults. Here, we investigate the gut bacteria of aged care residents, both with and without a history of UTIs, and compare them to younger adults. While prior UTIs did not alter gut bacteria, antibiotic use did. We observed greater variability in gut bacteria among aged care residents compared to younger adults. These observations suggest that both high antibiotic exposure and age-related factors may mask any potential relationship between gut bacteria and UTI risk in this population. Understanding these factors could lead to improved UTI prevention and treatment strategies for elderly individuals.

Exposure to doxycycline increases risk of carrying a broad range of enteric antimicrobial resistance determinants in an elderly cohort.

OBJECTIVES: High rates of antibiotic prescription in residential aged care are likely to promote enteric carriage of antibiotic-resistant pathogens and increase the risk of antibiotic treatment failure. Despite their importance, relationships between antibiotic exposures and patterns of enteric resistance carriage in this population remain poorly understood. METHODS: We conducted a cross-sectional metagenomic cohort analysis of stool samples from residents of five long-term aged-care facilities in South Australia. Taxonomic composition was determined, and enteric carriage of antibiotic resistance genes (ARGs) was identified and quantified against the Comprehensive Antibiotic Resistance Database. Both the detection and abundance of stool taxa and ARGs were related to antibiotic exposures up to 12 months prior. Factors associated with the abundance of ARGs of high clinical concern were identified. RESULTS: Stool samples were provided by 164 participants (median age: 88 years, IQR 81-93; 72% female). Sixty-one percent (n = 100) of participants were prescribed antibiotics at least once in the prior 12 months (median prescriptions: 4, range: 1-52), most commonly a penicillin (n = 55, 33.5%), cephalosporin (n = 53, 32.3%), diaminopyrimidine (trimethoprim) (n = 36, 22%), or tetracycline (doxycycline) (n = 21, 12.8%). More than 1100 unique ARGs, conferring resistance to 38 antibiotic classes, were identified, including 20 ARGs of high clinical concern. Multivariate logistic regression showed doxycycline exposure to be the greatest risk factor for high ARG abundance (adjusted odds ratio [aOR]=14.8, q<0.001) and a significant contributor to inter-class selection, particularly for ARGs relating to penicillins (aOR=3.1, q=0.0004) and cephalosporins (aOR=3.4, q=0.003). High enteric ARG abundance was associated with the number of separate antibiotic exposures (aOR: 6.4, q<0.001), exposures within the prior 30 days (aOR: 4.6, q=0.008) and prior 30-100 days (aOR: 2.6, q=0.008), high duration of antibiotic exposure (aOR: 7.9, q<0.001), and exposure to 3 or more antibiotic classes (aOR: 7.4, q<0.001). Carriage of one or more ARGs of high clinical concern was identified in 99% of participants (n = 162, median: 3, IQR: 2-4), involving 11 ARGs conferring resistance to aminoglycosides, four to beta-lactams, one to glycopeptides, three to fluoroquinolones, and one to oxazolidinones. Carriage of ARGs of high clinical concern was positively associated with exposure to doxycycline (aminoglycoside, fluoroquinolone, and oxazolidinone ARGs) and trimethoprim (fluoroquinolone and beta-lactam ARGs). Analysis of doxycycline impact on microbiota composition suggested that observed resistome changes arose principally through direct ARG selection, rather than through the antibiotic depletion of sensitive bacterial populations. CONCLUSIONS: The gut microbiome of aged care residents is a major reservoir of antibiotic resistance. As a critical antibiotic in medical practice, a comprehensive understanding of the impact of doxycycline exposure on the gut resistome is paramount for informed antibiotic use, particularly in an evolving landscape of prophylactic applications. Near-universal asymptomatic carriage of clinically critical resistance determinants is highly concerning and reinforces the urgent need for improved management of antibiotic use in long-term aged care.

Preventing empirical antibiotic treatment failure in migrant populations: screening by infection risk, not ethnic background.

Multidrug-resistant organisms (MDROs) are a major international health threat. In many low and middle-income countries poorly regulated antibiotic use, limited surveillance, and inadequate sanitation give rise to high rates of antibiotic resistance. A resulting reliance on last-line antibiotic options further contributes to the emergence of MDROs. The potential for these pathogens to spread across international borders is a matter of considerable concern. However, this problem is commonly framed as primarily a threat to the health security of countries where resistance is not yet endemic. In fact, it is little acknowledged that those at greatest risk from antibiotic treatment failure are individuals who move from regions of high MDRO prevalence to settings where standard empirical treatment options remain largely effective. In this perspective, we highlight the poor treatment outcomes for disseminated bacterial infections in individuals who have moved from settings in which MDROs are common to those where MDROs are currently less common. We discuss MDRO screening strategies that could avoid stigmatizing vulnerable populations by focusing on future risk of disseminated infection, rather than past risk of acquisition. In practical terms, this means screening individuals before childbirth, immunosuppressive treatments, major surgery, or other events associated with disseminated infection risk, rather than prioritizing screening for individuals from regions with high carriage rates. We argue that such measures would reduce antibiotic treatment failure and improve outcomes while protecting migrant populations from the divisive consequences of targeted screening programs.

Carriage and Transmission of Macrolide Resistance Genes in Patients With Chronic Respiratory Conditions and Their Close Contacts.

BACKGROUND: Long-term macrolide therapy has been shown to provide benefit to those with a range of chronic respiratory conditions. However, concerns remain about the impact of macrolide exposure on the carriage and abundance of antibiotic resistance genes within the oropharynx. The potential for onward transmission of resistance from macrolide recipients to their close contacts also is poorly understood. RESEARCH QUESTION: Does long-term macrolide use impact carriage of resistance within the oropharyngeal microbiota in people with chronic respiratory conditions and risk of onward transmission to their close contacts? STUDY DESIGN AND METHODS: Oropharyngeal swabs were collected from 93 individuals with chronic respiratory conditions, 53 of whom were receiving long-term macrolide therapy. An oropharyngeal swab also was collected from a close cohabiting contact of each patient. Detection and abundance of 10 macrolide-associated resistance genes with the potential to disseminate via horizontal gene transfer were assessed by quantitative polymerase chain reaction analysis. RESULTS: Detection of resistance genes in macrolide recipients was comparable with that in nonrecipients. However, the normalized gene abundance of erm(B) was significantly higher in the macrolide recipient group (P = .045). Among the close contacts, no between-group differences in resistance gene detection or abundance were identified. Within-group analysis showed that the detection of erm(F) and mef in macrolide recipients, but not nonrecipients, was associated significantly with detection in close contacts (P = .003 and P = .004, respectively). However, between-group analysis showed that treatment group did not predict cocarriage between patients and their close contacts (P > .05 for each gene). INTERPRETATION: Although levels of erm(B) were higher in those receiving long-term macrolide therapy and evidence of gene cocarriage with close contacts was found, no evidence was found that macrolide use increased the onward transmission risk to their close contacts. This study therefore addresses concerns that long-term macrolide therapy could promote the dissemination of transmissible macrolide resistance.

The cystic fibrosis gut as a potential source of multidrug resistant pathogens.

BACKGROUND: The emergence of multidrug resistant (MDR) pathogens represents a profound threat to global health. Individuals with CF have amongst the highest cumulative antibiotic exposure of any patient group, including to critically-important last-line agents. While there is little evidence that antibiotic resistance in airway pathogens results in worse clinical outcomes for CF patients, the potential emergence of MDR pathogens in non-respiratory systems, as a consequence of CF care, represents a potential health threat to the wider population, including family and carers. METHODS: Stool from 19 adults with CF and 16 healthy adult controls was subjected to metagenomic sequencing, to assess faecal resistome, and culture-based analysis. Resistant isolates were identified phenotypically, and genetic determinants of resistance characterised by whole genome sequencing. RESULTS: CF and control faecal resistomes differed significantly (P = 0.0003). The proportion of reads that mapped to mobile genetic elements was significantly higher in CF (P = 0.014) and the composition was significantly different (P = 0.0001). Notably, CF patients displayed higher carriage of plasmid-mediated aminoglycoside-modifying genes ant(6)-Ib, aac(6')-Ip, and aph(3')-IIIa (P < 0.01). Culture-based analysis supported higher aminoglycoside resistance, with a higher proportion of aminoglycoside-resistant, Gram-negative bacteria (P < 0.0001). Isolated extended spectrum beta lactamase (ESBL)-positive Escherichia coli from CF stool exhibited phenotypic resistance to tobramycin and gentamicin. Genomic analysis showed co-localisation of both aminoglycoside resistance and ESBL genes, consistent with MDR emergence through horizontal gene transfer. CONCLUSIONS: The carriage of potentially transmissible resistance within the adult CF gut microbiome is considerably greater than in healthy individuals and could contribute to the emergence and dissemination of MDR pathogens.