Spectrum and transferability of beta-lactam resistance in hospital strains of Enterobacter isolated in Bratislava and Innsbruck

Analysis of Extended Spectrum Beta Lactamase (ESBL) Genes of Non-Invasive ESBL Enterobacterales in Southeast Austria in 2017

Extended spectrum beta lactamases producing Enterobacteriaceae are a major player in the antibiotic resistance challenge. In general, the situation regarding antibiotic resistance in Austria is very good compared to many other countries. Perhaps this is why there is a lack of data on the distribution of ESBL genes in the clinical setting. The aim of this study was to collect data on ESBL genes from a larger sample of human non-invasive clinical isolates from one region in Austria. In total, 468 isolates from different sample materials isolated at the Medical University of Graz from 2017 were examined. The most frequent organisms were Escherichia coli and Klebsiella pneumoniae. Among the enzymes produced, CTX-M-15 was clearly dominant, exotic ESBLs were only represented by three Proteus mirabilis isolates harboring genes for VEB-6 and one P. mirabilis for CTX-M-2, respectively. Compared to other countries, the results are in line with the expectations. The data help to better classify the many studies from the non-clinical field in Austria and to shift the focus slightly away from the exotic results and sample sites.

Influence of vancomycin minimum inhibitory concentration on the treatment of methicillin-resistant Staphylococcus aureus bacteremia

BACKGROUND

Vancomycin treatment failure in methicillin-resistant Staphylococcus aureus (MRSA) bacteremia is not uncommon, even when MRSA is susceptible to vancomycin. The aim of our study was to evaluate whether vancomycin minimum inhibitory concentration has any influence on the mortality associated with MRSA bacteremia.

METHODS

A total of 414 episodes of MRSA bacteremia were prospectively followed-up from 1991 through 2005. MIC of vancomycin for the first isolate was determined by E-test. Clinical variables recorded were age, comorbidity, prior administration of vancomycin, use of corticosteroids, prognosis of underlying disease, source of bacteremia, the need for mechanical ventilation, shock, and mortality. A "treatment group" variable was created and defined as follows: (1) receipt of empirical vancomycin and an isolate with a vancomycin MIC of 1 microg/mL (38 episodes), (2) receipt of empirical vancomycin and an isolate with a vancomycin MIC of 1.5 microg/mL (90 episodes), (3) receipt of empirical vancomycin and an isolate with a vancomycin MIC of 2 microg/mL (40 episodes), and (4) receipt of inappropriate empirical therapy (246 episodes). Univariate and multivariate analyses were performed.

RESULTS

Episodes caused by strains with a vancomycin MIC of 2 microg/mL were independently associated with a lower risk of shock (odds ratio [OR], 0.33; 95% confidence interval [CI], 0.15-0.75). Multivariate analysis selected receipt of empirical vancomycin and an isolate with a vancomycin MIC of 2 microg/mL (OR, 6.39; 95% CI, 1.68-24.3), receipt of inappropriate empirical therapy (OR, 3.62; 95% CI, 1.20-10.9), increasing age (OR, 1.02; 95% CI, 1.00-1.04), use of corticosteroids (OR, 1.85; 95% CI, 1.04-3.29), an ultimately (OR, 10.2; 95% CI, 2.85-36.8) or rapidly (OR, 1.81; 95% CI, 1.06-3.10) fatal underlying disease, high-risk (OR, 3.60; 95% CI, 1.89-6.88) and intermediate-risk (OR, 2.18; 95% CI, 1.17-4.04) sources of bacteremia, and shock (OR, 7.38; 95% CI, 4.11-13.3) as the best predictors of mortality.

CONCLUSIONS

Mortality associated with MRSA bacteremia was significantly higher when the empirical antibiotic was inappropriate and when vancomycin was empirically used for treatment of infection with strains with a high vancomycin MIC (>1 microg/mL).

Extended double disc synergy testing reveals a low prevalence of extended-spectrum β-lactamases in Enterobacter spp. in Vienna, Austria

OBJECTIVES

The aims of this study were to determine the prevalence of extended-spectrum beta-lactamases (ESBLs) in AmpC-carrying Enterobacter spp. in a tertiary care university hospital in Vienna, Austria, and to implement a cost-effective strategy to detect ESBLs in this particular genus on a routine basis.

METHODS

Clinical Enterobacter isolates (n=208) were investigated by means of (i) an inhibitor-potentiated diffusion test using cefpodoxime, (ii) an expanded double disc diffusion synergy test (discs of cefotaxime, ceftazidime, cefpodoxime and cefepime placed around amoxicillin/clavulanic acid), (iii) the Etest ESBL screening method and (iv) the cefoxitin-cefotaxime antagonist test. Cefepime MICs were determined by separate Etests.

RESULTS

Of 208 isolates, 76 (37%), 18 (9%) and 92 (44%) were derepressed, partially derepressed and inducible AmpC producers, respectively. Eight (4%) ESBL-producing Enterobacter strains could be detected, all of which would have been detected using disc-based tests. Six out of eight strains were genetically not related, as assessed by random amplification of polymorphic DNA. Typing results were confirmed by means of enterobacterial repetitive intergenic consensus PCR. The MIC(90) of cefepime was not different in ESBL carriers (range 2-4 mg/L), and was especially low in inducible AmpC producers (0.125 mg/L). More than half of all Enterobacter isolates (n=110; 53%) were partly derepressed or fully inducible AmpC producers. In the absence of cefoxitin, they appeared susceptible or intermediately susceptible to cefazolin (n=8; 9%), cefuroxime (n=75; 81.5%), ceftazidime (n=91; 99%), cefotaxime (n=92; 100%), cefpodoxime (n=75; 81.5%) and cefepime (n=91; 99%).

CONCLUSIONS

Susceptibility to third-generation cephalosporins would have been falsely assumed in more than half of all Enterobacter isolates, but ESBL in Enterobacter is currently rare in our institution. Integration of multiple double disc tests into the routine antibiogram seems a reliable approach to screen for emerging resistance mechanisms. Etests did not provide additional information in this study.

Accessory gene regulator group II polymorphism in methicillin-resistant Staphylococcus aureus is predictive of failure of vancomycin therapy

We studied methicillin-resistant Staphylococcus aureus (MRSA) isolates to determine if the group II polymorphism at the accessory gene regulator (agr) locus demonstrated any relationship with the clinical efficacy of vancomycin. One hundred twenty-two MRSA isolates from 87 patients treated with vancomycin were evaluated. Forty-five of 87 patients had no clinical or bacteriological response to vancomycin. Among the 36 clinically evaluable patients with the agr group II polymorphism, 31 had an infection that failed to respond to vancomycin, whereas only 5 had an infection that responded successfully to vancomycin. This finding is of interest in light of our previous findings that glycopeptide-intermediately resistant S. aureus (GISA) and hetero-GISA clinical isolates in the United States and Japan are enriched for the agr group II polymorphism, and it suggests a possible intrinsic survival advantage of some S. aureus clones with this genetic marker under vancomycin selective pressure.

Occurrence and transferability of beta-lactam resistance in Enterobacteriaceae isolated in Children's University Hospital in Bratislava

Occurrence and transferability of beta-lactam resistance in 30 multi-resistant Escherichia coli, Klebsiella spp., Enterobacter spp., Pantoea agglomerans, Citrobacter freundii and Serratia marcescens strains isolated from children between 0 and 3 years of age is presented. The strains were resistant to ampicillin (30), cefoxitin (22), cefotaxime (30), ceftriaxone (30), ceftazidime (30) and aztreonam (28), but susceptible to cefepime (30) and imipenem (26). Twenty-eight of 30 isolates possessed a transferable resistance confirmed by conjugation and isolation of 79-89-kb plasmids. The beta-lactam resistance was due to production of beta-lactamases and ceftazidime proved to be stronger beta-lactamase inductor than ceftriaxone. Twenty-five clinical isolates expressed transferable extended spectrum beta-lactamases, and chromosomally encoded AmpC beta-lactamase.