Probing fosfomycin's potential: a study on susceptibility testing and resistance in Staphylococcus epidermidis from prosthetic joint infections.

BACKGROUND: There are limited treatment options for prosthetic joint infections (PJI) due to multidrug-resistant Staphylococcus epidermidis (MDRSE). Fosfomycin (FOF) has gained attention as a potential therapy, but there is a paucity of information on the phenotypic and genotypic susceptibility amongst S. epidermidis, including MDRSE. OBJECTIVES: To investigate phenotypical and genotypical susceptibility to FOF in S. epidermidis isolates prospectively collected from PJIs in Sweden. METHODS: MIC determination was performed using in-house agar dilution (AD) and a commercial AD panel. Genes and gene variants associated with FOF resistance were analysed. RESULTS: Multidrug resistance was common [74/89 (83%) isolates were MDRSE].FOF inhibited all isolates except one, which had an MIC > 256 mg/L. The commercial AD panel demonstrated good overall performance but tended to overestimate the MIC, resulting in 84% essential agreement with the gold standard. Genomic analysis with publically available tools for whole-genome sequencing (WGS) data suggested genotypic FOF resistance in all isolates, but in-depth analysis revealed that fosB, associated with FOF resistance, was only present in the phenotypically resistant isolate. No other genes or gene variants associated with FOF resistance were detected. CONCLUSIONS: Phenotypic resistance to FOF and presence of fosB were rare in this collection, indicating FOF's potential as a treatment option for S. epidermidis. The commercial AD panel demonstrated high reproducibility, but EA with the reference method was less than optimal. Findings of genotypic FOF resistance using common tools for WGS data should be critically evaluated and appropriately verified with relevant fosB references for S. epidermidis.

The Epidome - a species-specific approach to assess the population structure and heterogeneity of Staphylococcus epidermidis colonization and infection.

BACKGROUND: Although generally known as a human commensal, Staphylococcus epidermidis is also an opportunistic pathogen that can cause nosocomial infections related to foreign body materials and immunocompromized patients. Infections are often caused by multidrug-resistant (MDR) lineages that are difficult and costly to treat, and can have a major adverse impact on patients' quality of life. Heterogeneity is a common phenomenon in both carriage and infection, but present methodology for detection of this is laborious or expensive. In this study, we present a culture-independent method, labelled Epidome, based on an amplicon sequencing-approach to deliver information beyond species level on primary samples and to elucidate clonality, population structure and temporal stability or niche selection of S. epidermidis communities. RESULTS: Based on an assessment of > 800 genes from the S. epidermidis core genome, we identified genes with variable regions, which in combination facilitated the differentiation of phylogenetic clusters observed in silico, and allowed classification down to lineage level. A duplex PCR, combined with an amplicon sequencing protocol, and a downstream analysis pipeline were designed to provide subspecies information from primary samples. Additionally, a probe-based qPCR was designed to provide valuable absolute abundance quantification of S. epidermidis. The approach was validated on isolates representing skin commensals and on genomic mock communities with a sensitivity of < 10 copies/µL. The method was furthermore applied to a sample set of primary skin and nasal samples, revealing a high degree of heterogeneity in the S. epidermidis populations. Additionally, the qPCR showed a high degree of variation in absolute abundance of S. epidermidis. CONCLUSIONS: The Epidome method is designed for use on primary samples to obtain important information on S. epidermidis abundance and diversity beyond species-level to answer questions regarding the emergence and dissemination of nosocomial lineages, investigating clonality of S. epidermidis communities, population dynamics, and niche selection. Our targeted-sequencing method allows rapid differentiation and identification of clinically important nosocomial lineages in low-biomass samples such as skin samples.

Pivmecillinam with Amoxicillin/Clavulanic acid as step down oral therapy in febrile Urinary Tract Infections caused by ESBL-producing Enterobacterales (PACUTI).

BACKGROUND: Oral treatment alternatives for febrile urinary tract infections are limited in the era of increasing antimicrobial resistance. We aim to evaluate if the combination of pivmecillinam and amoxicillin/clavulanic acid is non-inferior to current alternatives for step-down therapy in adult patients with febrile urinary tract infection. METHODS: We plan to perform an investigator-initiated non-inferiority trial. Adult hospitalised patients treated with 1-5 days of intravenous antibiotics for acute febrile urinary tract infection caused by extended spectrum beta-lactamase (ESBL) producing Enterobacterales will be randomised 1:1 to either control (7-10 days of either oral ciprofloxacin 500 mg twice daily or oral trimethoprim-sulfamethoxazole 800 mg/160 mg twice daily or intravenous ertapenem 1 g once daily, depending on sex, drug allergy, glomerular filtration rate and susceptibility testing) or intervention (10 days of pivmecillinam 400 mg three times daily and amoxicillin/clavulanic acid 500/125 mg three times daily). The primary outcome will be clinical cure 10 days (+/- 2 days) after antibiotic treatment completion. Clinical cure is defined as being alive with absence of fever and return to non-infected baseline of urinary tract symptoms without additional antibiotic treatment or re-hospitalisation (for urinary tract infection) based on a centralised allocation-blinded structured telephone interview. We plan to recruit 330 patients to achieve 90% power based on a sample size simulation analysis using a two-group comparison, one-sided alpha of 2.5%, an absolute non-inferiority margin of 10% and expecting 93% clinical cure rate and 10% loss to follow-up. The primary endpoint will be analysed using generalised estimated equations and reported as risk difference for both intention-to-treat and per protocol populations. Patients are planned to be recruited from at least 10 centres in Sweden from 2023 to 2026. DISCUSSION: If the combination of pivmecillinam and amoxicillin/clavulanic acid is found to be non-inferior to the control drugs there are potential benefits in terms of tolerability, frequency of interactions, outpatient treatment, side effects, nosocomial infections and drive for further antimicrobial resistance compared to existing drugs. TRIAL REGISTRATION: NCT05224401. Registered on February 4, 2022.

Long-lasting T-cell response to SARS-CoV-2 antigens after vaccination-a prospective cohort study of HCWs working with COVID-19 patients.

BACKGROUND: Vaccination against SARS-CoV-2 reduces the risk of hospitalisation and death, but vaccine-induced IgG antibodies against the spike protein (IgG S) decline over time. Less is known about the nature of the vaccine-induced T-cell response to SARS-CoV-2 antigens. METHODS: IgG antibodies against nucleocapsid protein (IgG N), IgG S, and T-cell response towards SARS-CoV-2 antigens were determined in samples taken between November 2020 and November 2021 from a cohort of healthcare workers at an Infectious Diseases Department. RT-PCR screening for SARS-CoV-2 was encouraged once every four weeks in addition to testing when symptomatic or identified through contact tracing. Vaccination data were collected at the end of the study. RESULTS: At inclusion, T-cell response to SARS-CoV-2 antigens was found in 10/15 (66.7%) of participants with a previous/current COVID-19 infection and in 9/54 (16.7%) of participants with no prior/current history of COVID-19 infection. All participants with complete follow-up (n = 59) received two doses of a SARS-CoV-2 vaccine during the study. All participants demonstrated detectable IgG (S) antibodies at the end of the study, in median 278 days (IQR 112) after the second vaccine dose. All but four participants displayed T-cell responses towards SARS-CoV-2 antigens. IgG S antibody levels correlated with time since the second vaccine dose. In addition, previous COVID-19 infection and the strength of the S1 T-cell response correlated with IgG S antibody levels. However, no correlation was demonstrated between the strength of the T-cell response and time since the second vaccine dose. CONCLUSION: COVID-19 vaccination induces robust T-cell responses that remain for at least nine months.

High prevalence of persistent symptoms and reduced health-related quality of life 6 months after COVID-19.

Background: The long-term sequelae after COVID-19 constitute a challenge to public health and increased knowledge is needed. We investigated the prevalence of self-reported persistent symptoms and reduced health-related quality of life (HRQoL) in relation to functional exercise capacity, 6 months after infection, and explored risk factors for COVID-19 sequalae. Methods: This was a prospective, multicenter, cohort study including 434 patients. At 6 months, physical exercise capacity was assessed by a 1-minute sit-to-stand test (1MSTST) and persistent symptoms were reported and HRQoL was evaluated through the EuroQol 5-level 5-dimension (EQ-5D-5L) questionnaire. Patients with both persistent symptoms and reduced HRQoL were classified into a new definition of post-acute COVID syndrome, PACS+. Risk factors for developing persistent symptoms, reduced HRQoL and PACS+ were identified by multivariable Poisson regression. Results: Persistent symptoms were experienced by 79% of hospitalized, and 59% of non-hospitalized patients at 6 months. Hospitalized patients had a higher prevalence of self-assessed reduced overall health (28 vs. 12%) and PACS+ (31 vs. 11%). PACS+ was associated with reduced exercise capacity but not with abnormal pulse/desaturation during 1MSTST. Hospitalization was the most important independent risk factor for developing persistent symptoms, reduced overall health and PACS+. Conclusion: Persistent symptoms and reduced HRQoL are common among COVID-19 survivors, but abnormal pulse and peripheral saturation during exercise could not distinguish patients with PACS+. Patients with severe infection requiring hospitalization were more likely to develop PACS+, hence these patients should be prioritized for clinical follow-up after COVID-19.

The clinical and microbiological efficacy of temocillin versus cefotaxime in adults with febrile urinary tract infection, and its effects on the intestinal microbiota: a randomised multicentre clinical trial in Sweden.

BACKGROUND: Use of third-generation cephalosporins, such as cefotaxime, is associated with an increased risk of selection for antimicrobial resistance, so alternative antibiotics need to be considered. The aim of the present study was to evaluate intestinal colonisation with third-generation cephalosporin-resistant pathogens following use of temocillin-an alternative antibiotic to cefotaxime that is potentially less prone to disturbing the intestinal microbiota-in empirical treatment of febrile urinary tract infection (UTI). METHODS: We did a randomised, multicentre, superiority, open-label phase 4 trial in patients who had been admitted to inpatient care in 12 Swedish hospitals with suspected or diagnosed febrile UTI (complicated or uncomplicated). To meet inclusion criteria, a patient was required to have at least one sign or symptom of pyelonephritis (ie, flank pain; costovertebral angle tenderness; and changes to urinary frequency or urgency or dysuria), a fever of 38·0°C or higher, and a positive urine dipstick (for nitrites, white blood cells, or both). Participants were also required to have an indication for intravenous antibiotic treatment. Participants were randomly assigned (1:1) to receive either 2 g temocillin or 1-2 g cefotaxime, by local investigators opening consecutive sealed randomisation envelopes that were generated centrally in advance. Both drugs were administered intravenously every 8 h. The trial was open label for investigators and patients, but those doing the microbiological analyses were masked to the groups. Participants were treated with antibiotics for 7-10 days (or up to 14 days if they had bacteraemia), at least 3 days of which were on the study drug; at day 4 and later, participants who were showing improvement could be given an oral antibiotic (ciprofloxacin, ceftibuten, cefixime, or co-trimoxazole). Patients not showing improvement were regarded as having treatment failures. Rectal swabs were collected at three timepoints: at baseline (before the first dose), after the last dose of study drug, and 7-10 days after treatment stopped. The composite primary outcome was colonisation with Enterobacterales with reduced susceptibility to third-generation cephalosporins, or colonisation with toxin-producing Clostridioides difficile, or both, to evaluate disturbance of the intestinal microbiota. The study is registered in the EU Clinical Trials Register (EudraCT 2015-003898-15). FINDINGS: Between May 20, 2016, and July 31, 2019, 207 patients were screened for eligibility, of whom 55 patients were excluded. 152 participants were randomly assigned to groups: 77 (51%) patients received temocillin, 75 (49%) patients received cefotaxime. The composite primary endpoint was met by 18 (26%) of 68 participants receiving temocillin versus 30 (48%) of 62 patients receiving cefotaxime (risk difference -22% [95% CI -42% to -3%]), showing superiority of temocillin versus cefotaxime (ie, less disturbance of the intestinal microbiota). 43 adverse events were reported in 40 (52%) of 77 patients in the temocillin group, versus 46 adverse events in 34 (45%) of 75 patients in the cefotaxime group. Most events were of mild to moderate severity. 21 (27%) patients in the temocillin and 17 (23%) patients in the cefotaxime group had an adverse event that was considered to be associated with the study drug. INTERPRETATION: Temocillin was found to be less selective than cefotaxime of Enterobacterales with reduced susceptibility to third-generation cephalosporins, and it could therefore be a favourable alternative in the empirical treatment of febrile UTI. Use of this antibiotic could reduce hospital transmission and health-care-associated infections by these pathogens. FUNDING: Public Health Agency of Sweden.

Characteristics and definitive outcomes of COVID-19 patients admitted to a secondary hospital intensive care unit in Sweden.

BACKGROUND AND AIMS: Most published reports of COVID-19 Intensive Care Unit (ICU) patients are from large tertiary hospitals and often present short-term or incomplete outcome data. There are reports indicating that ICUs with fewer beds are associated with higher mortality. This study aimed to investigate the definitive outcome and patient characteristics of the complete first wave of COVID-19 patients admitted to ICU in a secondary hospital. METHODS: In this prospective observational study, all patients with respiratory failure and a positive SARS-CoV-2 test admitted to Västerås Hospital ICU between 24 March and July 22, 2020 were included. The primary outcome was defined as 90-day mortality. Secondary outcomes included ICU length of stay, hospital length of stay, number of days with invasive ventilation, need for vasopressors/inotropes, and use of renal replacement therapy. RESULTS: Fifty-three patients were included. Median age (range) was 59 (33-76) and 74% were men. Obesity and hypertension were the most common comorbidities and 45% of the patients were born outside Europe. Ninety-day mortality was 30%. Median ICU length of stay (interquartile range) was 14 (5-24) days and the duration of invasive mechanical ventilation 16 (12-26) days. No patients received dialysis at 90-day follow-up. CONCLUSION: In this cohort of COVID-19 patients treated in a secondary hospital ICU, mortality rates were low compared to early studies from China, Italy, and the United States, but similar to other government-funded hospitals in Scandinavia. A preparatory reorganization enabled an increase in ICU capacity, hence avoiding an overwhelmed intensive care organization.

Low rate of COVID-19 seroconversion in health-care workers at a Department of Infectious Diseases in Sweden during the later phase of the first wave; a prospective longitudinal seroepidemiological study.

Background: Health-care workers are at risk of contracting and transmitting SARS-CoV-2. The aim of this study was to investigate the prevalence of SARS-CoV-2 IgG antibodies and the rate of seroconversion in an environment with high exposure to SARS-CoV-2. Methods: 131 health-care workers at the Department of Infectious Diseases in Västerås, Sweden, were included in the study. Abbott's SARS-COV-2 IgG immunoassay was used with a signal cut-off ratio of ≥1.4. Every third week from the beginning of May, blood samples were drawn, and the participants completed a questionnaire regarding symptoms consistent with COVID-19 and the result of any SARS-CoV-2 PCR performed since the last sampling occasion. Participants with IgG antibodies against SARS-CoV-2 were re-sampled only on the sixth and last occasion. Results: At the start of the study, 18 (15%) participants had SARS-CoV-2 IgG antibodies. At the end, 25 (19%) of 131 participants were seropositive. One case of asymptomatic infection was detected, and two cases with PCR-confirmed COVID-19 did not develop IgG antibodies. Conclusion: The low rate of seroconversion during the study suggests that it is possible to prevent transmission of SARS-COV-2 in a high-exposure environment. Compliance with adequate infection control guidelines is the likely explanation of our findings.

Comparative genomics of Staphylococcus epidermidis from prosthetic-joint infections and nares highlights genetic traits associated with antimicrobial resistance, not virulence.

There is increased awareness of the worldwide spread of specific epidemic multidrug-resistant (MDR) lineages of the human commensal Staphylococcus epidermidis. Here, using bioinformatic analyses accounting for population structure, we determined genomic traits (genes, SNPs and k-mers) that distinguish S. epidermidis causing prosthetic-joint infections (PJIs) from commensal isolates from nares, by analysing whole-genome sequencing data from S. epidermidis from PJIs prospectively collected over 10 years in Sweden, and contemporary S. epidermidis from the nares of patients scheduled for arthroplasty surgery. Previously suggested virulence determinants and the presence of genes and mutations linked to antimicrobial resistance (AMR) were also investigated. Publicly available S. epidermidis sequences were used for international extrapolation and validation of findings. Our data show that S. epidermidis causing PJIs differed from nasal isolates not by virulence but by traits associated with resistance to compounds used in prevention of PJIs: ß-lactams, aminoglycosides and chlorhexidine. Almost a quarter of the PJI isolates did not belong to any of the previously described major nosocomial lineages, but the AMR-related traits were also over-represented in these isolates, as well as in international S. epidermidis isolates originating from PJIs. Genes previously associated with virulence in S. epidermidis were over-represented in individual lineages, but failed to reach statistical significance when adjusted for population structure. Our findings suggest that the current strategies for prevention of PJIs select for nosocomial MDR S. epidermidis lineages that have arisen from horizontal gene transfer of AMR-related traits into multiple genetic backgrounds.

Methicillin-Resistant Staphylococcus epidermidis Lineages in the Nasal and Skin Microbiota of Patients Planned for Arthroplasty Surgery.

Staphylococcus epidermidis, ubiquitous in the human nasal and skin microbiota, is a common causative microorganism in prosthetic joint infections (PJIs). A high proportion of PJI isolates have been shown to harbor genetic traits associated with resistance to/tolerance of agents used for antimicrobial prophylaxis in joint arthroplasties. These traits were found within multidrug-resistant S. epidermidis (MDRSE) lineages of multiple genetic backgrounds. In this study, the aim was to study whether MDRSE lineages previously associated with PJIs are present in the nasal and skin microbiota of patients planned for arthroplasty surgery but before hospitalization. We cultured samples from nares, inguinal creases, and skin over the hip or knee (dependent on the planned procedure) taken two weeks (median) prior to admittance to the hospital for total joint arthroplasty from 66 patients on agar plates selecting for methicillin resistance. S. epidermidis colonies were identified and tested for the presence of mecA. Methicillin-resistant S. epidermidis (MRSE) were characterized by Illumina-based whole-genome sequencing. Using this method, we found that 30/66 (45%) of patients were colonized with MRSE at 1-3 body sites. A subset of patients, 10/66 (15%), were colonized with MDRSE lineages associated with PJIs. The qacA gene was identified in MRSE isolates from 19/30 (63%) of MRSE colonized patients, whereas genes associated with aminoglycoside resistance were less common, found in 11/30 (37%). We found that MDRSE lineages previously associated with PJIs were present in a subset of patients' pre-admission microbiota, plausibly in low relative abundance, and may be selected for by the current prophylaxis regimen comprising whole-body cleansing with chlorhexidine-gluconate containing soap. To further lower the rate of S. epidermidis PJIs, the current prophylaxis may need to be modified, but it is important for possible perioperative MDRSE transmission events and specific risk factors for MDRSE PJIs to be investigated before reevaluating antimicrobial prophylaxis.

Alteration of Bacterial Communities in Anterior Nares and Skin Sites of Patients Undergoing Arthroplasty Surgery: Analysis by 16S rRNA and Staphylococcal-Specific tuf Gene Sequencing.

The aim was to study alterations of bacterial communities in patients undergoing hip or knee arthroplasty to assess the impact of chlorhexidine gluconate soap decolonisation and systemic antibiotic prophylaxis. A Swedish multicentre, prospective collection of samples obtained from elective arthroplasty patients (n = 83) by swabbing anterior nares, skin sites in the groin and the site of planned surgery, before and after arthroplasty surgery, was analysed by 16S rRNA (V3-V4) gene sequencing and a complementary targeted tuf gene sequencing approach to comprehensively characterise alterations in staphylococcal communities. Significant reductions in alpha diversity was detected for both bacterial (p = 0.04) and staphylococcal (p = 0.03) groin communities after arthroplasty surgery with significant reductions in relative Corynebacterium (p = 0.001) abundance and Staphylococcus hominis (p = 0.01) relative staphylococcal abundance. In nares, significant reductions occurred for Staphylococcus hominis (p = 0.02), Staphylococcus haemolyticus (p = 0.02), and Staphylococcus pasteuri (p = 0.003) relative to other staphylococci. Staphylococcus aureus colonised 35% of anterior nares before and 26% after arthroplasty surgery. Staphylococcus epidermidis was the most abundant staphylococcal species at all sampling sites. No bacterial genus or staphylococcal species increased significantly after arthroplasty surgery. Application of a targeted tuf gene sequencing approach provided auxiliary staphylococcal community profiles and allowed species-level characterisation directly from low biomass clinical samples.

Mammographic casting-type calcifications is not a prognostic factor in unifocal small invasive breast cancer: a population-based retrospective cohort study.

BACKGROUND AND OBJECTIVES: The role of mammographic casting-type microcalcifications as a prognostic factor in breast cancer has been debated. We studied the relation between mammographic features and prognosis in a population-based cohort. METHODS: In 515 women with 1-15 mm invasive breast cancer mammograms were re-classified according to Tabar et al. The relation to breast cancer death was studied. RESULTS: During the follow-up (median 155 months) 44 of 515 women died from breast cancer. Twenty-nine of 515 presented with casting-type calcifications and three of these died from breast cancer. The adjusted odds ratio for breast cancer death was 1.6 (0.5-5.8) for patients presenting with casting-type calcifications and 4.8 (1.8-12.7) for crushed stone-like (pleomorphic) calcifications using stellate tumors as a reference group. CONCLUSIONS: Except for patients with crushed stone-like microcalcifications breast cancer survival was excellent, 87-95% after 15 years. Casting-type calcifications were not a statistically significant prognostic factor. Tumors with casting-type calcifications were more often of high grade, hormone receptor negative, and HER2 positive but this was not statistically significant either. However, microcalcifications may be more prevalent in tumors with extensive ductal cancer in situ (DCIS) containing multiple foci of invasive cancer and in this study we only included unifocal cancer.

Lower activation of caspase-1 by Staphylococcus epidermidis isolated from prosthetic joint infections compared to commensals.

Nosocomial sequence types of Staphylococcus epidermidis dominate in prosthetic joint infections. We examined caspase-1 activation in human neutrophils after incubation with Staphylococcus epidermidis isolated from prosthetic joint infections and normal skin flora. Active caspase-1 was lower after incubation with isolates from prosthetic joint infections than after incubation with commensal isolates. Both host and isolate dependent differences in active caspase-1 were noted. Our results indicate that there might be a host-dependent incapacity to elicit a strong caspase-1 response towards certain strains of S. epidermidis. Further experiments with a larger number of individuals are warranted.

Staphylococcus epidermidis from prosthetic joint infections induces lower IL-1ß release from human neutrophils than isolates from normal flora.

The aim of this study was to test the hypothesis that Staphylococcus epidermidis isolated from prosthetic joint infections (PJIs) differs from S. epidermidis isolated from normal flora in terms of its capacity to induce activation of caspase-1 and release of IL-1ß in human neutrophils. The amount of active caspase-1 was determined over 6 h by detecting Ac-YVAD-AMC fluorescence in human neutrophils incubated with S. epidermidis isolates from PJIs (ST2) or normal flora. The amount of IL-1ß was detected by ELISA in neutrophil supernatants after 6 h of incubation. Mean IL-1ß release was lower after incubation with S. epidermidis from PJIs compared to isolates from normal flora, but no statistically significant difference was found in active caspase-1. Substantial inter-individual differences in both active caspase-1 and IL-1ß were noted. These results suggest that evasion of innate immune response, measured as reduced capacity to induce release of IL-1ß from human neutrophils, might be involved in the predominance of ST2 in S. epidermidis PJIs, but that other microbe-related factors are probably also important.

Staphylococcus epidermidis isolates from nares and prosthetic joint infections are mupirocin susceptible.

The objective of the present study was to investigate the antibiotic susceptibility including mupirocin among Staphylococcus. epidermidis isolated from prosthetic joint infections (PJIs) (n=183) and nasal isolates (n=75) from patients intended to undergo prosthetic joint replacements. Susceptibility to mupirocin (used for eradication of nasal carriership of Staphylococcus aureus) was investigated by gradient test, and susceptibility to various other antimicrobial agents was investigated by disc diffusion test. All isolates, except three from PJIs and one from the nares, were fully susceptible to mupirocin. Multi-drug resistance (≥3 antibiotic classes) was found in 154/183 (84.2%) of the PJI isolates but only in 2/75 (2.7%) of the nares isolates, indicating that S. epidermidis causing PJIs do not originate from the nares.

Genomic relatedness of Staphylococcus pettenkoferi isolates of different origins.

PURPOSE: The aim of the study was to characterize clinical and environmental Staphylococcus pettenkoferi isolates with regard to genomic diversity and antibiotic susceptibility pattern. Repetitive-sequence-based PCR and core genome phylogenetic analysis of whole-genome sequencing (WGS) data verified the presence of distinct clades comprising closely related S. pettenkoferi isolates from different geographical locations and origins. METHODOLOGY: Phylogenetic relationships between 25 S. pettenkoferi isolates collected from blood cultures and intra-operative air sampling were determined by repetitive-sequence-based PCR typing and analysis of ~157 000 SNPs identified in the core genome after WGS. Antibiotic susceptibility testing and tests for biofilm production (microtitre plate assay) were performed. RESULTS: Repetitive-sequence-based PCR as well as WGS data demonstrated the close relatedness of clinically significant blood culture isolates to probable contaminants, as well as to environmental isolates. Antibiotic-susceptibility testing demonstrated a low level of antimicrobial resistance. The mecA gene was present in two cefoxitin-resistant isolates. No isolates were found to produce biofilm. CONCLUSION: Close genomic relatedness of S. pettenkoferi isolates from different geographical locations and origins were found within clades, but with substantial genomic difference between the two major clades. The ecological niche of S. pettenkoferi remains unconfirmed, but the presence of S. pettenkoferi in the air of the operating field favours the suggestion of a role in skin flora. Identification of S. pettenkoferi in clinical samples should, in a majority of cases, most likely be regarded as a probable contamination, and its role as a possible pathogen in immunocompromised hosts remains to be clarified.

Sequence types of Staphylococcus epidermidis associated with prosthetic joint infections are not present in the laminar airflow during prosthetic joint surgery.

Molecular characterization of Staphylococcus epidermidis isolates from prosthetic joint infections (PJIs) has demonstrated a predominance of healthcare-associated multi-drug resistant sequence types (ST2 and ST215). How, and when, patients acquire these nosocomial STs is not known. The aim was to investigate if sequence types of S. epidermidis associated with PJIs are found in the air during prosthetic joint surgery. Air sampling was undertaken during 17 hip/knee arthroplasties performed in operating theaters equipped with mobile laminar airflow units in a 500-bed hospital in central Sweden. Species identification was performed using MALDI-TOF MS and 16S rRNA gene analysis. Isolates identified as S. epidermidis were further characterized by MLST and antibiotic susceptibility testing. Seven hundred and thirty-five isolates were available for species identification. Micrococcus spp. (n = 303) and coagulase-negative staphylococci (n = 217) constituted the majority of the isolates. Thirty-two isolates of S. epidermidis were found. S. epidermidis isolates demonstrated a high level of allelic diversity with 18 different sequence types, but neither ST2 nor ST215 was found. Commensals with low pathogenic potential dominated among the airborne microorganisms in the operating field during prosthetic joint surgery. Nosocomial sequence types of S. epidermidis associated with PJIs were not found, and other routes of inoculation are therefore of interest in future studies.