Elucidation of Mechanisms of Ceftazidime Resistance among Clinical Isolates of Pseudomonas aeruginosa by Using Genomic Data

Abstract

Ceftazidime is one of the few cephalosporins with activity against Pseudomonas aeruginosa. Using whole-genome comparative analysis, we set out to determine the prevalent mechanism(s) of resistance to ceftazidime (CAZ) using a set of 181 clinical isolates. These isolates represented various multilocus sequence types that consisted of both ceftazidime-susceptible and -resistant populations. A presumptive resistance mechanism against ceftazidime was identified in 88% of the nonsusceptible isolates using this approach. Pseudomonas aeruginosa is an opportunistic pathogen associated with numerous nosocomial infections, where ␤-lactam antibiotics remain key in treatment (1, 2). One of the major antimicrobials used to fight P. aeruginosa infections is ceftazidime (CAZ), a well-known cephalosporin that acts primarily as a penicillin-binding protein 3 (PBP3) inhibitor (3,4).A significant proportion of ceftazidime-resistant isolates arise through the horizontal acquisition of ␤-lactamases or altered expression of the chromosomal drug-inducible wide-spectrum class C ␤-lactamase AmpC (reviewed in reference 5). The overproduction of AmpC can result from mutations affecting the peptidoglycan (PG) recycling process, where accumulation of cell wall intermediates ultimately induces ampC overexpression (5).We focused our study on a panel of 181 clinical P. aeruginosa isolates, where comparative analysis between multiple isolates belonging to the same multilocus sequence types (MLSTs) allowed for identification of chromosomal gene variants unique to the ceftazidime-resistant population (6).The initial MIC to ceftazidime was determined using frozen plates (Thermo Scientific) following the Clinical and Laboratory Standards Institute guidelines (7,8). Of the 181 isolates in the analysis set, 99 (55%) were resistant to ceftazidime (MIC, Ն16 g/ml), and 82 were susceptible (MIC, Յ8 g/ml) ( Table 1; see Table S1 in the supplemental material).Genomic analysis (see Table S1 in the supplemental material) was performed using CLC Genomic Workbench 7.0.4 (CLCBio). Unique sequence variants exclusive to the resistant population of each MLST group were flagged for further analysis as outlined in the summary column of Table S1. To account for resistance in the 99 ceftazidime-resistant isolates in a parsimonious manner, we followed a triage process-accounting first for resistance-inducing ␤-lactamases, second for mechanisms allowing for derepression of ampC, and third for other candidate causes of resistance.Forty-six isolates had ␤-lactamases that have been reported to hydrolyze ceftazidime (Table 1). Analysis of the ampC regulon and additional cephalosporin targets was also completed for these isolates (see Table S1 in the supplemental material); however, resistance was attributed primarily to the presence of the ␤-lactamases, as clinically, detection of such an element would rule out treatment with ceftazidime. It was apparent that certain MLST lineages were enriched in ␤-lactamases, particularly sequence type 111 (ST111) and ST233, which were t...

Correlation between phenotypic antibiotic susceptibility and the resistome in Pseudomonas aeruginosa

“…Class 1 integrons, already before shown to often carry metallo-beta-lactamase genes [119], were identified as important elements and integration and conjugation as important evolutionary processes facilitating resistance flexibility [121]. Even more recently a detailed study described the successful detection of presumptive ceftazidime resistance markers in 88% of all P. aeruginosa genomes studied [118]. Here we successfully introduce a method that does not only allow for monitoring resistance but which is even able to categorize strains on the basis of elevated MICs, even below the clinically relevant resistance level.…”

Seçilen Bitkilerin DMSO Özütlerinin Antibiyotik Dirençli Klinik İzolatlara Karşı Antibakteriyel Aktivitesi

“…P. aeruginosa (PA1) was resistant to piperacillin, piperacillin/tazobactam, meropenem and ceftazidime. Piperacillin, cefotaxime and ceftazidime resistant E.coli isolates and piperacillin/tazobactam, meropenem and ceftazidime resistant P. aeruginosa isolates have been reported in previos studies (Tavío et al, 2014;Hunter et al, 2010;Akova, 2016;Andersen et al, 2005;Direkel et al, 2017;Mirsalehian et al, 2017;Rostami et al, 2018;Kos et al, 2016). These isolates restricts treatment options and cause problems in clinical settings.…”

Prevalence of ESBL-producing Pseudomonas aeruginosa isolates in Warsaw, Poland, detected by various phenotypic and genotypic methods

“…The primary cause of cephalosporin resistance in P . aeruginosa isolates is the overexpression of the chromosomal AmpC enzyme (mainly resistant to ceftazidime) and the production of the metallo-β-lactamases, MBLs (resistant to cephalosporins and carbapenems) [ 3 , 4 ]. However, ESBL-positive P .…”