Emergence of Resistance in Klebsiella aerogenes to Piperacillin-Tazobactam and Ceftriaxone

Activity of meropenem/vaborbactam and comparators against non-carbapenemase-producing carbapenem-resistant Enterobacterales isolates from Europe

Background

Carbapenem-resistant Enterobacterales (CRE) isolates have disseminated worldwide. CREs usually produce a carbapenemase; however, some isolates are negative for known carbapenemases. In this study, we evaluated the activity of meropenem/vaborbactam and comparators against CREs without a carbapenemase (nonCP CREs) collected from European hospitals from 2016 to 2019.

Materials and methods

23 043 Enterobacterales clinical isolates were collected in 41 hospitals located in 20 countries. Susceptibility (S) testing was performed using the broth microdilution method. CLSI/EUCAST (2021) interpretive criteria were used. 978 CREs were identified with MICs >2 mg/L to meropenem or imipenem. Whole-genome sequencing was performed on each CRE isolate. 125 isolates were negative for carbapenemase genes, including blaKPC, blaNDM, blaIMP, blaVIM and blaOXA-48-like. NonCP CRE isolates were analysed for the presence of other β-lactamases, multilocus sequence types (ST) and mutations in outer membrane protein (OMP) sequences.

Results

Most nonCP CRE were Klebsiella pneumoniae (KPN; n = 97/125). 84.0% of nonCP CRE (n = 105) were from Poland, including 88 KPN. The most common β-lactamase was blaCTX-M-15 in 92/125 isolates. OMP disruptions or alterations were noted among 76 KPN. Among KPN isolates that had MLST typing, 30 belonged to ST11, 18 to ST152 and 17 to ST147, while 13 other STs were observed. Susceptibility to meropenem/vaborbactam was 96.0/97.6% (CLSI/EUCAST) while meropenem was 2.4/8.0%S.

Conclusions

Meropenem/vaborbactam had potent in vitro activity against CRE isolates that lacked known carbapenemases. Resistance mechanisms observed among nonCP CREs included acquired β-lactamases and OMP alterations. These results indicate that meropenem/vaborbactam may be a useful treatment for infections caused by nonCP CREs.

Emerging resistance to ceftriaxone treatment owing to different ampD mutations in Enterobacter roggenkampii

OBJECTIVES

The Enterobacter cloacae complex is responsible for a variety of infections in hospitalized patients and is resistant to β-lactam antibiotics owing to the expression of AmpC β-lactamase. We report emerging resistance in Enterobacter roggenkampii exposed to ceftriaxone and explore the mechanism underlying mutations responsible for this resistance.

METHODS

Three strains were derived from different samples from one patient (blood and liver abscess fluid). Antimicrobial susceptibility was evaluated by standard broth microdilution, while ampC expression was determined via RT-PCR. Genetic relatedness was evaluated via pulsed-field gel electrophoresis (PFGE). Species identification and comparative genome analysis were performed via genome sequencing. Mutation rate testing and selection of AmpC-derepressed mutants were conducted to explore the mutation mechanism.

RESULTS

E. roggenkampii F1247 was susceptible to third-generation cephalosporins (3GCs); F95 and F1057, found in blood sample on day 11 and liver abscess drainage fluid on day 25, were resistant. ampC expression was 341- and 642-fold higher in F95 and F1057, respectively, than in F1247. Three isolates were the same PFGE and sequence types (ST1778) and were highly homologous (2 and 4 core genome single nucleotide polymorphism differences). Compared to F1247, F95 possessed a 575 bp deletion, including 537 bp of ampD, whereas F1057 harbored only one amino acid mutation (Leu140Pro in ampD). The mutation rates from F1247 exposure to cefotaxime, ceftazidime, ceftriaxone, piperacillin-tazobactam, and cefepime were (1.90 ± 0.21) × 10^-8, (3.18 ± 0.43) × 10^-8, (2.00 ± 0.20) × 10^-8, (2.92 ± 0.29) × 10^-9, and zero, respectively. In vitro-selected mutations responsible for resistance were identified in ampD, ampR, and dacB.

CONCLUSIONS

E. roggenkampii may develop resistance in vivo and in vitro upon exposure to 3GCs and to a lesser extent to piperacillin-tazobactam. 3GCs should not be used as a monotherapy for E. roggenkampii infections. Therapy using cefepime or carbapenems may be preferred to piperacillin-tazobactam in the treatment of E. roggenkampii, especially if source control is difficult.