Activity of aztreonam/avibactam and ceftazidime/avibactam against Enterobacterales with carbapenemase-independent carbapenem resistance.

Enterobacterales with carbapenemase-independent resistance to carbapenems are sometimes selected during therapy and, on rare occasions, cause outbreaks. Most have extended-spectrum or AmpC ß-lactamases, together with changes to permeability or penicillin-binding proteins (PBPs). Newer ß-lactam-ß-lactamase inhibitor combinations may present useful options for infections due to these organisms. Accordingly, Clinical and Laboratory Standards Institute/European Committee on Antimicrobial Susceptibility Testing broth-microdilution was used to measure the minimum inhibitory concentrations (MICs) of ceftazidime/avibactam and aztreonam/avibactam for 51 carbapenemase-negative Enterobacterales with resistance or reduced susceptibility to carbapenems: genomic sequencing of the least-susceptible organisms was also undertaken. MICs of the two avibactam combinations cross-correlated closely, but with fewer MICs (2/51 vs. 10/51) exceeding 8+4 mg/L in the case of ceftazidime/avibactam. Raised MICs for Escherichia coli were associated with PBP3 inserts together with CMY-42 ß-lactamase; correlates among Enterobacter cloacae complex isolates remain elusive, with AmpC and PBP3 sequences found to be species specific. In the case of Klebsiella spp., no MICs exceeding 2 mg/L were seen for either combination. It appears that these avibactam combinations have potential against Enterobacterales with carbapenemase-independent carbapenem resistance or reduced susceptibility, with ceftazidime/avibactam being more reliably active than aztreonam/avibactam.

UK clinicians' attitudes towards the application of molecular diagnostics to guide antibiotic use in ICU patients with pneumonias: a quantitative study.

BACKGROUND: Molecular diagnostic tests may improve antibiotic prescribing by enabling earlier tailoring of antimicrobial therapy. However, clinicians' trust and acceptance of these tests will determine their application in practice. OBJECTIVES: To examine ICU prescribers' views on the application of molecular diagnostics in patients with suspected hospital-acquired and ventilator-associated pneumonia (HAP/VAP). METHODS: Sixty-three ICU clinicians from five UK hospitals completed a cross-sectional questionnaire between May 2020 and July 2020 assessing attitudes towards using molecular diagnostics to inform initial agent choice and to help stop broad-spectrum antibiotics early. RESULTS: Attitudes towards using molecular diagnostics to inform initial treatment choices and to stop broad-spectrum antibiotics early were nuanced. Most (83%) were positive about molecular diagnostics, agreeing that using results to inform broad-spectrum antibiotic prescribing is good practice. However, many (58%) believed sick patients are often too unstable to risk stopping broad-spectrum antibiotics based on a negative result. CONCLUSIONS: Positive attitudes towards the application of molecular diagnostics to improve antibiotic stewardship were juxtapositioned against the perceived need to initiate and maintain broad-spectrum antibiotics to protect unstable patients.

Activity of aztreonam/avibactam against metallo-ß-lactamase-producing Enterobacterales from the UK: Impact of penicillin-binding protein-3 inserts and CMY-42 ß-lactamase in Escherichia coli.

Aztreonam/avibactam is being developed on the rationale that aztreonam evades metallo-ß-lactamases (MBLs) whilst avibactam protects aztreonam against co-produced serine ß-lactamases. This study measured the activity of aztreonam/avibactam against MBL-producing Enterobacterales referred to the UK Health Security Agency in 2015, 2017 and 2019. Minimum inhibitory concentrations (MICs) were determined by broth microdilution, and genome sequences were determined with Illumina technology. For Klebsiella and Enterobacter spp. with NDM, IMP or VIM enzymes, the MICs of aztreonam/avibactam were distributed unimodally, with >90% of isolates inhibited at 1+4 mg/L, and all inhibited at 8+4 mg/L. Over 85% of Escherichia coli with NDM carbapenemases were inhibited at 8+4 mg/L, but their MIC distribution was multi-modal with major peaks at 0.12 and 8 mg/L. Forty-eight of 50 NDM E. coli with high aztreonam/avibactam MICs (defined as ≥8 mg/L) had YRIK inserted after amino acid 333 of penicillin-binding protein (PBP)3, or had a YRIN insert plus an acquired AmpC ß-lactamase, commonly CMY-42. Ten of 15 E. coli with moderately raised aztreonam/avibactam MICs (defined as 0.5-4 mg/L) had YRIN inserts without acquired AmpC. Twenty-two of 24 E. coli isolates with normal MICs (defined as 0.03-0.25 mg/L) lacked PBP3 inserts. YRIK inserts were associated with E. coli ST405, and YRIN inserts with ST167; however, many isolates with high or moderately raised MICs were clonally diverse. No substantive MIC distribution shifts occurred across the three survey years; ST405 isolates with YRIK comprised more high-MIC organisms in 2019 compared with earlier years, but the apparent increase lacked significance (P>0.05).

Activity of ertapenem/zidebactam (WCK 6777) against problem Enterobacterales.

BACKGROUND: Secondary healthcare will remain pressured for some years, both because SARS-CoV-2 will circulate as a nosocomial pathogen, and owing to backlogs of patients awaiting delayed elective procedures. These stresses will drive the use of Outpatient Parenteral Antibiotic Therapy (OPAT), which will need to cover increasingly resistant Gram-negative opportunists. We evaluated the activity of ertapenem/zidebactam, proposed for 2 + 2 g q24h administration. MATERIALS AND METHODS: MICs were determined, by BSAC agar dilution, for 1632 Enterobacterales submitted to the UK national reference laboratory for investigation of antimicrobial resistance. RESULTS: Over 90% of Escherichia coli with AmpC, ESBLs, KPC, metallo- or OXA-48 carbapenemases were inhibited by ertapenem/zidebactam 1:1 at ertapenem's current 0.5 mg/L breakpoint. For other major Enterobacterales, the proportions inhibited by ertapenem/zidebactam 1:1 at 0.5 mg/L were mostly 65% to 90% but were lower for Klebsiella pneumoniae/oxytoca with metallo- or OXA-48 ß-lactamases. However, animal studies support an 8 mg/L breakpoint for ertapenem/zidebactam, based on a shortened T>MIC being needed compared with ertapenem alone. On this basis ertapenem/zidebactam would count as active against 90%-100% of isolates in all groups except K. pneumoniae/oxytoca with MBLs (±OXA-48), where MICs and percent susceptibility vary substantially even with inocula within the BSAC acceptable range. CONCLUSIONS: Ertapenem/zidebactam has a proposed once-daily regimen well suited to OPAT. Even on highly conservative breakpoint projections, it has potential against MDR E. coli, including metallo-carbapenemase producers. If trial data sustain the 8 mg/L breakpoint indicated by animal experiments, its potential will extend widely across infections due to ESBL-, AmpC- and carbapenemase-producing Enterobacterales.

OXA-48-Like ß-Lactamases: Global Epidemiology, Treatment Options, and Development Pipeline.

Modern medicine is threatened by the rising tide of antimicrobial resistance, especially among Gram-negative bacteria, where resistance to ß-lactams is most often mediated by ß-lactamases. The penicillin and cephalosporin ascendancies were, in their turn, ended by the proliferation of TEM penicillinases and CTX-M extended-spectrum ß-lactamases. These class A ß-lactamases have long been considered the most important. For carbapenems, however, the threat is increasingly from the insidious rise of a class D carbapenemase, OXA-48, and its close relatives. Over the past 20 years, OXA-48 and "OXA-48-like" enzymes have proliferated to become the most prevalent enterobacterial carbapenemases across much of Europe, Northern Africa, and the Middle East. OXA-48-like enzymes are notoriously difficult to detect because they often cause only low-level in vitro resistance to carbapenems, meaning that the true burden is likely underestimated. Despite this, they are associated with carbapenem treatment failures. A highly conserved incompatibility complex IncL plasmid scaffold often carries blaOXA-48 and may carry other antimicrobial resistance genes, leaving limited treatment options. High conjugation efficiency means that this plasmid is sometimes carried by multiple Enterobacterales in a single patient. Producers evade most ß-lactam-ß-lactamase inhibitor combinations, though promising agents have recently been licensed, notably ceftazidime-avibactam and cefiderocol. The molecular machinery enabling global spread, current treatment options, and the development pipeline of potential new therapies for Enterobacterales that produce OXA-48-like ß-lactamases form the focus of this review.

Inoculum effects of cefepime/zidebactam (WCK 5222) and ertapenem/zidebactam (WCK 6777) for Enterobacterales in relation to ß-lactamase type and enhancer effect, as tested by BSAC agar dilution.

OBJECTIVES: Combinations of PBP3-active ß-lactams with developmental diazabicyclooctanes (DBOs), e.g. zidebactam, remain active against many MBL producers via an enhancer effect. We explored how this activity is affected by inoculum. MATERIALS AND METHODS: MICs of zidebactam and its cefepime and ertapenem combinations (WCK 5222 and WCK 6777, respectively) were determined by BSAC agar dilution at inocula from 3-6 × 103 to 3-6 × 105 cfu/spot. Isolates, principally Klebsiella spp., were chosen as having previously tested resistant to zidebactam or its cefepime combination, and by ß-lactamase type. RESULTS: MICs of zidebactam, tested alone, were strongly inoculum dependent regardless of ß-lactamase type; MICs of its cefepime and ertapenem combinations likewise were strongly inoculum dependent-rising ≥32-fold across the inoculum range tested-but only for MBL producers. Combination MICs for isolates with non-MBLs, including those with OXA-48 (where the enhancer effect remains critical for ertapenem/zidebactam) were much less inoculum dependent, particularly for cefepime/zidebactam. MBL producers frequently moved between putative 'susceptible' (MIC ≤ 8 + 8 mg/L) and 'resistant' (MIC > 8 + 8 mg/L) categories according to whether the inoculum was at the high or low end of BSAC's acceptable (1-4 × 104 cfu/spot) range. CONCLUSIONS: The activity of zidebactam combinations against MBL producers, which strongly depends on the enhancer effect, is inoculum dependent. Animal data suggest consistent in vivo activity even in high-inoculum pneumonia models. Contingent on this being supported by clinical experience, the combination behaviour may be best represented by the MICs obtained at the lower end of BSAC's inoculum range.

SUsceptibility and Resistance to Fosfomycin and other antimicrobial agents among pathogens causing lower urinary tract infections: findings of the SURF study.

Urinary tract infections (UTIs) are prevalent worldwide, particularly among women. Their incidence increases with age, and treatment is increasingly challenging owing to antibiotic resistance and the lack of new agents. We investigated the susceptibility of current urinary isolates to fosfomycin and other antibiotics across Europe. This cross-sectional study collected consecutive urinary isolates from non-hospitalised women at 20 centres in Belgium, the UK, Italy, Spain and Russia. Bacteria were tested by disk diffusion with relevant antibiotics. As a quality control, a central laboratory re-tested, by agar dilution, (i) isolates found resistant to fosfomycin and (ii) every tenth isolate; all non-Russian sites were included. A total of 2848 isolates were analysed, principally Escherichia coli (2064; 72.5%), Klebsiella spp. (275; 9.7%) and Proteus spp. (103; 3.6%). For E. coli, agents active against >90% of isolates were nitrofurantoin (98.5%), fosfomycin (96.4%) and mecillinam (91.8%). Fosfomycin and nitrofurantoin remained active against >90% of cephalosporin-resistant E. coli. Among 143 E. coli recorded as susceptible locally by disk tests, 138 (96.5%) were confirmed susceptible by minimum inhibitory concentration (MIC) tests, however resistance was only confirmed in 29/58 (50.0%) of those reported resistant by local disk tests. Escherichia coli was found to be the most common uropathogen isolated and was highly susceptible to fosfomycin, nitrofurantoin and mecillinam, all used effectively for more than 30 years. Guidelines advocating fosfomycin for uncomplicated UTIs in women remain microbiologically valid.

Multicentre evaluation of two multiplex PCR platforms for the rapid microbiological investigation of nosocomial pneumonia in UK ICUs: the INHALE WP1 study.

BACKGROUND: Culture-based microbiological investigation of hospital-acquired or ventilator-associated pneumonia (HAP or VAP) is insensitive, with aetiological agents often unidentified. This can lead to excess antimicrobial treatment of patients with susceptible pathogens, while those with resistant bacteria are treated inadequately for prolonged periods. Using PCR to seek pathogens and their resistance genes directly from clinical samples may improve therapy and stewardship. METHODS: Surplus routine lower respiratory tract samples were collected from intensive care unit patients about to receive new or changed antibiotics for hospital-onset lower respiratory tract infections at 15 UK hospitals. Testing was performed using the BioFire FilmArray Pneumonia Panel (bioMérieux) and Unyvero Pneumonia Panel (Curetis). Concordance analysis compared machine and routine microbiology results, while Bayesian latent class (BLC) analysis estimated the sensitivity and specificity of each test, incorporating information from both PCR panels and routine microbiology. FINDINGS: In 652 eligible samples; PCR identified pathogens in considerably more samples compared with routine microbiology: 60.4% and 74.2% for Unyvero and FilmArray respectively vs 44.2% by routine microbiology. PCR tests also detected more pathogens per sample than routine microbiology. For common HAP/VAP pathogens, FilmArray had sensitivity of 91.7%-100.0% and specificity of 87.5%-99.5%; Unyvero had sensitivity of 50.0%-100.0%%, and specificity of 89.4%-99.0%. BLC analysis indicated that, compared with PCR, routine microbiology had low sensitivity, ranging from 27.0% to 69.4%. INTERPRETATION: Conventional and BLC analysis demonstrated that both platforms performed similarly and were considerably more sensitive than routine microbiology, detecting potential pathogens in patient samples reported as culture negative. The increased sensitivity of detection realised by PCR offers potential for improved antimicrobial prescribing.

AmpC hyperproduction in a Cedecea davisae implant-associated bone infection during treatment: a case report and therapeutic implications.

BACKGROUND: Data on antimicrobial resistance mechanisms are scanty for Cedecea spp., with very variable antibiotic resistance patterns documented. Here we report the first in vivo resistance evolution of a C. davisae clinical isolate in a patient with a complex hand trauma and provide insight in the resistance mechanism, leading to therapeutic implications for this pathogen. CASE PRESENTATION: Cedecea davisae was isolated from a patient with hand trauma during a first surgical debridement. Six days after primary surgical treatment and under antimicrobial treatment with amoxicillin-clavulanic acid and later cefepime, follow up cultures yielded C. davisae which demonstrated a resistance development. The susceptible parental isolate and its resistant derivative were characterized by whole genome sequencing, ampC, ompC and ompF by RT- PCR. The resistant derivative demonstrated an A224G SNP in ampD, the transcriptional regulator of ampC, leading to a His75Arg change in the corresponding AmpD protein. AmpC transcription of the resistant derivative was 362-times higher than the susceptible isolate. Transcription levels of ompF and ompC were 8.5-fold and 1.3-fold lower, respectively, in the resistant derivative. Downregulation of OmpF putatively resulted from a mutation in the presumed promoter region upstream of the dusB-Fis operon, a proposed regulator for ompF. CONCLUSIONS: This case demonstrates the in vivo resistance development of C. davisae within 7 days similar to that of the members of the Enterobacter cloacae complex. Our findings add valuable information for future therapeutic management of these opportunistic pathogens as they warrant the same empirical treatment as AmpC producers.

Understanding decisions about antibiotic prescribing in ICU: an application of the Necessity Concerns Framework.

BACKGROUND: Antibiotics are extensively prescribed in intensive care units (ICUs), yet little is known about how antibiotic-related decisions are made in this setting. We explored how beliefs, perceptions and contextual factors influenced ICU clinicians' antibiotic prescribing. METHODS: We conducted 4 focus groups and 34 semistructured interviews with clinicians involved in antibiotic prescribing in four English ICUs. Focus groups explored factors influencing prescribing, whereas interviews examined decision-making processes using two clinical vignettes. Data were analysed using thematic analysis, applying the Necessity Concerns Framework. RESULTS: Clinicians' antibiotic decisions were influenced by their judgement of the necessity for prescribing/not prescribing, relative to their concerns about potential adverse consequences. Antibiotic necessity perceptions were strongly influenced by beliefs that antibiotics would protect patients from deterioration and themselves from the ethical and legal consequences of undertreatment. Clinicians also reported concerns about prescribing antibiotics. These generally centred on antimicrobial resistance; however, protecting the individual patient was prioritised over these societal concerns. Few participants identified antibiotic toxicity concerns as a key influencer. Clinical uncertainty often complicated balancing antibiotic necessity against concerns. Decisions to start or continue antibiotics often represented 'erring on the side of caution' as a protective response in uncertainty. This approach was reinforced by previous experiences of negative consequences ('being burnt') which motivated prescribing 'just in case' of an infection. Prescribing decisions were also context-dependent, exemplified by a lower perceived threshold to prescribe antibiotics out-of-hours, input from external team members and local prescribing norms. CONCLUSION: Efforts to improve antibiotic stewardship should consider clinicians' desire to protect with a prescription. Rapid molecular microbiology, with appropriate communication, may diminish clinicians' fears of not prescribing or of using narrower-spectrum antibiotics.

Fosfomycin Trometamol for the Prevention of Infectious Complications After Prostate Biopsy: A Consensus Statement by an International Multidisciplinary Group.

CONTEXT: Transrectal ultrasound-guided prostate biopsy (TRPB) has been a standard of care for diagnosing prostate cancer but is associated with a high incidence of infectious complications. OBJECTIVE: To achieve an expert consensus on whether fosfomycin trometamol provides adequate prophylaxis in TRPB and discuss its role as prophylaxis in transperineal prostate biopsy (TPPB). EVIDENCE ACQUISITION: An international multidisciplinary group of experts convened remotely to discuss how to best use fosfomycin in various clinical settings and patient situations. Six statements related to prostate biopsy and the role of fosfomycin were developed, based on literature searches and relevant clinical experience. EVIDENCE SYNTHESIS: Consensus was reached for all six statements. The group of experts was unanimous regarding fosfomycin as a preferred candidate for antimicrobial prophylaxis in TRPB. Fosfomycin potentially also meets the requirements for empiric prophylaxis in TPPB, although further clinical studies are needed to confirm or refute its utility in this setting. There is a risk of bias due to sponsorship by a pharmaceutical company. CONCLUSIONS: Antimicrobial prophylaxis is mandatory in TRPB, and fosfomycin trometamol is an appropriate candidate due to low rates of resistance, a good safety profile, sufficient prostate concentrations, and demonstrated efficacy in reducing the risk of infectious complications following TRPB. PATIENT SUMMARY: Patients undergoing transrectal ultrasound-guided prostate biopsy (TRPB) have a high risk of infectious complications, and antimicrobial prophylaxis is mandatory. However, increasing antimicrobial resistance, as well as safety concerns with fluoroquinolones, has restricted the number of antimicrobial options. Fosfomycin trometamol meets the requirements for a preferred antimicrobial in the prophylaxis of TRPB.

Therapeutic Potential of Injectable Nano-Mupirocin Liposomes for Infections Involving Multidrug-Resistant Bacteria.

Antibiotic resistance is a global health threat. There are a few antibiotics under development, and even fewer with new modes of action and no cross-resistance to established antibiotics. Accordingly, reformulation of old antibiotics to overcome resistance is attractive. Nano-mupirocin is a PEGylated nano-liposomal formulation of mupirocin, potentially enabling parenteral use in deep infections, as previously demonstrated in several animal models. Here, we describe extensive in vitro profiling of mupirocin and Nano-mupirocin and correlate the resulting MIC data with the pharmacokinetic profiles seen for Nano-mupirocin in a rat model. Nano-mupirocin showed no cross-resistance with other antibiotics and retained full activity against vancomycin-, daptomycin-, linezolid- and methicillin- resistant Staphylococcus aureus, against vancomycin-resistant Enterococcus faecium, and cephalosporin-resistant Neisseria gonorrhoeae. Following Nano-mupirocin injection to rats, plasma levels greatly exceeded relevant MICs for >24 h, and a biodistribution study in mice showed that mupirocin concentrations in vaginal secretions greatly exceeded the MIC90 for N. gonorrhoeae (0.03 µg/mL) for >24 h. In summary, Nano-mupirocin has excellent potential for treatment of several infection types involving multiresistant bacteria. It has the concomitant benefits from utilizing an established antibiotic and liposomes of the same size and lipid composition as Doxil®, an anticancer drug product now used for the treatment of over 700,000 patients globally.

Replacement of Enterococcus faecalis by Enterococcus faecium as the predominant enterococcus in UK bacteraemias.

OBJECTIVES: To review temporal changes in the proportions of different Enterococcus species recorded in two UK bacteraemia surveillance systems. Antibiotic resistance trends were also considered. METHODS: We reviewed data for enterococci from 2001 to 2019 in: (a) the BSAC Resistance Surveillance Programme, which collected up to 7-10 bloodstream enterococci every year from each of 23-39 hospitals in the UK and Ireland and tested these centrally; and (b) PHE bacteraemia surveillance, using routine results from NHS microbiology laboratories in England. RESULTS: BSAC surveillance, based upon 206-255 enterococci each year (4486 in total), indicated that the proportion of Enterococcus faecium rose from 31% (212/692) in the period 2001-3 to 51% (354/696) in the period 2017-19, balanced by corresponding falls in the proportion of Enterococcus faecalis. PHE surveillance provided a larger dataset, with >5000 enterococcus reports per year; although its identifications are less precise, it too indicated a rise in the proportion of E. faecium. BSAC surveillance for E. faecium indicated no consistent trends in resistance to ampicillin (≥86% in all years), vancomycin (annual rates 19%-40%) or high-level resistance to gentamicin (31%-59%). Resistance to vancomycin remained <4% in E. faecalis in all years, whilst high-level resistance to gentamicin fell, perhaps partly reflecting the decline of two initially prevalent gentamicin- and ciprofloxacin-resistant clones. CONCLUSIONS: Both surveillance systems indicate a growing proportion of E. faecium in enterococcal bloodstream infections. This is important because fewer therapeutic options remain against this frequently multiresistant species than against E. faecalis.

INHALE: the impact of using FilmArray Pneumonia Panel molecular diagnostics for hospital-acquired and ventilator-associated pneumonia on antimicrobial stewardship and patient outcomes in UK Critical Care-study protocol for a multicentre randomised controlled trial.

BACKGROUND: Hospital-acquired and ventilator-associated pneumonias (HAP and VAP) are common in critical care and can be life-threatening. Rapid microbiological diagnostics, linked to an algorithm to translate their results into antibiotic choices, could simultaneously improve patient outcomes and antimicrobial stewardship. METHODS: The INHALE Randomised Controlled Trial is a multi-centre, parallel study exploring the potential of the BioFire FilmArray molecular diagnostic to guide antibiotic treatment of HAP/VAP in intensive care units (ICU); it identifies pathogens and key antibiotic resistance in around 90 min. The comparator is standard care whereby the patient receives empirical antibiotics until microbiological culture results become available, typically after 48-72 h. Adult and paediatric ICU patients are eligible if they are about to receive antibiotics for a suspected lower respiratory infection (including HAP/VAP) for the first time or a change in antibiotic because of a deteriorating clinical condition. Breathing spontaneously or intubated, they must have been hospitalised for 48 h or more. Patients are randomised 1:1 to receive either antibiotics guided by the FilmArray molecular diagnostic and its trial-based prescribing algorithm or standard care, meaning empirical antibiotics based on local policy, adapted subsequently based upon local microbiology culture results. Co-primary outcomes are (i) non-inferiority in clinical cure of pneumonia at 14 days post-randomisation and (ii) superiority in antimicrobial stewardship at 24 h post-randomisation (defined as % of patients on active and proportionate antibiotics). Secondary outcomes include further stewardship reviews; length of ICU stay; co-morbidity indicators, including septic shock, change in sequential organ failure assessment scores, and secondary pneumonias; ventilator-free days; adverse events over 21 days; all-cause mortality; and total antibiotic usage. Both cost-effectiveness of the molecular diagnostic-guided therapy and behavioural aspects determining antibiotic prescribing are being explored. A sample size of 552 will be required to detect clinically significant results with 90% power and 5% significance for the co-primary outcomes. DISCUSSION: This trial will test whether the potential merits of rapid molecular diagnostics for pathogen and resistance detection in HAP/VAP are realised in patient outcomes and/or improved antibiotic stewardship. TRIAL REGISTRATION: ISRCTN Registry ISRCTN16483855 . Retrospectively registered on 15 July 2019.

Selection and characterization of mutational resistance to aztreonam/avibactam in ß-lactamase-producing Enterobacterales.

BACKGROUND: Aztreonam/avibactam is being developed for its broad activity against carbapenemase-producing Enterobacterales, including those with metallo-ß-lactamases (MBLs). Its potential to select resistance in target pathogens was explored. Findings are compared with previous data for ceftazidime/avibactam and ceftaroline/avibactam. METHODS: Single-step mutants were sought from 52 Enterobacterales with AmpC, ESBL, KPC, MBL and OXA-48-like enzymes. Mutation frequencies were calculated. MICs were determined by CLSI agar dilution. Genomes were sequenced using Illumina methodology. RESULTS: Irrespective of ß-lactamase type and of whether avibactam was used at 1 or 4 mg/L, mutants could rarely be obtained at >4× the starting MIC, and most MIC rises were correspondingly small. Putative resistance (MIC >8 + 4 mg/L) associated with changes to ß-lactamases was seen only for mutants of AmpC, where it was associated with Asn346Tyr and Tyr150Cys substitutions. Asn346Tyr led to broad resistance to avibactam combinations; Tyr150Cys significantly affected only aztreonam/avibactam. MIC rises up to 4 + 4 mg/L were seen for producers of mutant KPC-2 or -3 enzymes, and were associated with Trp105Arg, Ser106Pro and Ser109Pro substitutions, which all reduced the MICs of other ß-lactams. For producers of other ß-lactamase types, we largely found mutants with lesions in baeRS or envZ, putatively affecting drug accumulation. Single mutants had lesions in ampD, affecting AmpC expression or ftsI, encoding PBP3. CONCLUSIONS: The risk of mutational resistance to aztreonam/avibactam appears smaller than for ceftazidime/avibactam, where Asp179Tyr arises readily in KPC enzymes, conferring frank resistance. Asn346 substitutions in AmpC enzymes may remain a risk, having been repeatedly selected with multiple avibactam combinations in vitro.

Antibiotic resistance during and beyond COVID-19.

Antibiotics underpin the 'modern medicine' that has increased life expectancy, leading to societies with sizeable vulnerable elderly populations who have suffered disproportionately during the current COVID-19 pandemic. Governments have responded by shuttering economies, limiting social interactions and refocusing healthcare. There are implications for antibiotic resistance both during and after these events. During spring 2020, COVID-19-stressed ICUs relaxed stewardship, perhaps promoting resistance. Counterpoised to this, more citizens died at home and total hospital antibiotic use declined, reducing selection pressure. Restricted travel and social distancing potentially reduced community import and transmission of resistant bacteria, though hard data are lacking. The future depends on the vaccines now being deployed. Unequivocal vaccine success should allow a swift return to normality. Vaccine failure followed by extended and successful non-pharmaceutical suppression may lead to the same point, but only after some delay, and with indefinite travel restrictions; sustainability is doubtful. Alternatively, failure of vaccines and control measures may prompt acceptance that we must live with the virus, as in the prolonged 1889-94 'influenza' (or coronavirus OC43) pandemic. Vaccine failure scenarios, particularly those accepting 'learning to live with the virus', favour increased outpatient management of non-COVID-19 infections using oral and long t ½ antibiotics. Ultimately, all models-except those envisaging societal collapse-suggest that COVID-19 will be controlled and that hospitals will revert to pre-2020 patterns with a large backlog of non-COVID-19 patients awaiting treatment. Clearing this will increase workloads, stresses, nosocomial infections, antibiotic use and resistance. New antibiotics, including cefiderocol, are part of the answer.

Intensivists' beliefs about rapid multiplex molecular diagnostic testing and its potential role in improving prescribing decisions and antimicrobial stewardship: a qualitative study.

BACKGROUND: Rapid molecular diagnostic tests to investigate the microbial aetiology of pneumonias may improve treatment and antimicrobial stewardship in intensive care units (ICUs). Clinicians' endorsement and uptake of these tests is crucial to maximise engagement; however, adoption may be impeded if users harbour unaddressed concerns or if device usage is incompatible with local practice. Accordingly, we strove to identify ICU clinicians' beliefs about molecular diagnostic tests for pneumonias before implementation at the point-of-care. METHODS: We conducted semi-structured interviews with 35 critical care doctors working in four ICUs in the United Kingdom. A clinical vignette depicting a fictitious patient with signs of pneumonia was used to explore clinicians' beliefs about the importance of molecular diagnostics and their concerns. Data were analysed thematically. RESULTS: Clinicians' beliefs about molecular tests could be grouped into two categories: perceived potential of molecular diagnostics to improve antibiotic prescribing (Molecular Diagnostic Necessity) and concerns about how the test results could be implemented into practice (Molecular Diagnostic Concerns). Molecular Diagnostic Necessity stemmed from beliefs that positive results would facilitate targeted antimicrobial therapy; that negative results would signal the absence of a pathogen, and consequently that having the molecular diagnostic results would bolster clinicians' prescribing confidence. Molecular Diagnostic Concerns included unfamiliarity with the device's capabilities, worry that it would detect non-pathogenic bacteria, uncertainty whether it would fail to detect pathogens, and discomfort with withholding antibiotics until receiving molecular test results. CONCLUSIONS: Clinicians believed rapid molecular diagnostics for pneumonias were potentially important and were open to using them; however, they harboured concerns about the tests' capabilities and integration into clinical practice. Implementation strategies should bolster users' necessity beliefs while reducing their concerns; this can be accomplished by publicising the tests' purpose and benefits, identifying and addressing clinicians' misconceptions, establishing a trial period for first-hand familiarisation, and emphasising that, with a swift (e.g., 60-90 min) test, antibiotics can be started and refined after molecular diagnostic results become available.