Enterobacterales carrying chromosomal AmpC ß-lactamases in Europe (EuESCPM): Epidemiology and antimicrobial resistance burden from a cohort of 27 hospitals, 2020-2022.

INTRODUCTION: The ESCPM group (Enterobacter species including Klebsiella aerogenes - formerly Enterobacter aerogenes, Serratia species, Citrobacter freundii complex, Providencia species and Morganella morganii) has not yet been incorporated into systematic surveillance programs. METHODS: We conducted a multicentre retrospective observational study analysing all ESCPM strains isolated from blood cultures in 27 European hospitals over a 3-year period (2020-2022). Diagnostic approach, epidemiology, and antimicrobial susceptibility were investigated. RESULTS: Our study comprised 6,774 ESCPM isolates. MALDI-TOF coupled to mass spectrometry was the predominant technique for bacterial identification. Susceptibility to new ß-lactam/ß-lactamase inhibitor combinations and confirmation of AmpC overproduction were routinely tested in 33.3% and 29.6% of the centres, respectively. The most prevalent species were E. cloacae complex (44.8%) and S. marcescens (22.7%). Overall, third-generation cephalosporins (3GC), combined third- and fourth-generation cephalosporins (3GC + 4GC) and carbapenems resistance phenotypes were observed in 15.7%, 4.6%, and 9.5% of the isolates, respectively. AmpC overproduction was the most prevalent resistance mechanism detected (15.8%). Among carbapenemase-producers, carbapenemase type was provided in 44.4% of the isolates, VIM- (22.9%) and OXA-48-enzyme (16%) being the most frequently detected. E. cloacae complex, K. aerogenes and Providencia species exhibited the most notable cumulative antimicrobial resistance profiles, with the former displaying 3GC, combined 3GC + 4GC and carbapenems resistance phenotypes in 15.2%, 7.4%, and 12.8% of the isolates, respectively. K. aerogenes showed the highest rate of both 3GC resistant phenotype (29.8%) and AmpC overproduction (32.1%), while Providencia species those of both carbapenems resistance phenotype (42.7%) and carbapenemase production (29.4%). ESCPM isolates exhibiting both 3GC and combined 3GC + 4GC resistance phenotypes displayed high susceptibility to ceftazidime/avibactam (98.2% and 95.7%, respectively) and colistin (90.3% and 90.7%, respectively). Colistin emerged as the most active drug against ESCPM species (except those intrinsically resistant) displaying both carbapenems resistance phenotype (85.8%) and carbapenemase production (97.8%). CONCLUSIONS: This study presented a current analysis of ESCPM species epidemiology in Europe, providing insights to inform current antibiotic treatments and guide strategies for antimicrobial stewardship and diagnostics.

Evaluating the drop test method in measuring colistin susceptibility of Klebsiella pneumoniae, Escherichia coli and Pseudomonas aeruginosa.

Introduction. Colistin is an antibiotic used to treat Gram-negative bacterial infections, particularly those caused by multidrug-resistant bacteria.Hypothesis/Gap Statement. The broth microdilution (BMD) reference method is the recommended protocol for detecting colistin susceptibility; however, it is laborious and expensive and cannot be performed in all laboratories.Aim. To evaluate the colistin susceptibility in Klebsiella pneumoniae, Escherichia coli and Pseudomonas aeruginosa using an alternative method, which has been referred to as the drop test.Methodology. A 16 µg ml-1 colistin solution was deposited on a Mueller-Hinton agar plate previously swabbed with the strain and incubated overnight, and the presence or absence of an inhibition zone was observed.Results. The categorical agreement (CA) of the drop test with respect to BMD was 100 % when 190 Enterobacterales (19 E. coli and 171 K. pneumoniae) were used, and no major errors (MEs) or very major errors (VMEs) were detected. The CA of the drop test with respect to the BMD was 99.2 % for 119 P. aeruginosa isolates, while no ME was detected and only 1 VME (6.7%) was observed.Conclusion. The drop test is an alternative method for antimicrobial susceptibility testing of colistin against K. pneumoniae and E. coli. It is an adequate method for detecting resistant strains of P. aeruginosa, but susceptible isolates should be confirmed using BMD. The drop test is a simpler alternative to the BMD that does not require additional equipment and allows for the testing of numerous isolates in a short period of time.