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. We conducted a multicentre retrospective observational study analysing all ESCPM strains isolated from blood cultures in 27 European hospitals over a three-year period (2020-2022). Diagnostic approach, epidemiology, and antimicrobial susceptibility were investigated. Our study comprised 6,774 ESCPM isolates. MALDI-TOF coupled to mass spectrometry was the predominant technique for bacterial identification. Susceptibility to new β-lactam/β-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%). 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.

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.

Introduction. Imipenemase (IMI) enzymes are an uncommon class A carbapenemases that have been isolated from aquatic environments and, occasionally, from clinical isolates of Enterobacterales. Aim. We describe a cluster of three patients infected by IMI-1 carbapenemase-producing Enterobacter ludwigii (IMI-1-Elud) in a tertiary university hospital in Gran Canaria, Spain. Methodology. Antimicrobial susceptibility was determined using the Vitek2 AST-N355 card and antibiotic gradient strips. The modified carbapenem inactivation method (CIM) test was performed in cases where the ertapenem MIC value was higher than 0.125 mg l⁻¹. The carbapenemase was identified by PCR and DNA microarray and later characterized by whole-genome next-generation sequencing (NGS) with Illumina. Results. Three patients presented thoracic or abdominal infections caused by IMI-1-Elud ST1677 from 14 June 2022 to 14 July 2022. All patients underwent at least one gastroscopy during their admission, and two of them were located in adjoining rooms. Isolates were resistant to carbapenems, colistin and fosfomycin but susceptible to ciprofloxacin. IMI/NMC-A carbapenemase was detected by PCR and hybridization test and confirmed by NGS as IMI-1. All patients underwent at least one gastroscopy, and two of them were in nearby rooms. Patients showed microbiological and clinical improvement following focus drainage and targeted antibiotic treatment with a fluoroquinolone. Conclusions. This study reports the first documented global outbreak of patients infected with IMI-1-Elud. The source appeared to be related to endoscopes. Contact transmission may also have played a role. A screening method such as the modified CIM test is crucial for detecting less common carbapenemases that might not be identified by rapid molecular or immunochromatographic tests, as these often do not include bla _IMI genes, which could lead to the undetected dissemination of carbapenemase-producing Enterobacterales. Effective infection source control and targeted treatment are essential for achieving a favourable clinical outcome.

Background: Antibiotic resistance is a worldwide concern. This study retrospectively analyzed patients admitted to the ICU of a tertiary hospital over a period of 7 months who were rectally colonized by multidrug-resistant microorganisms. The incidence of concomitant nosocomial infections was estimated, thus providing the risk of a colonizing microorganism producing a nosocomial infection. Methods: Infections with the same microorganism (concomitant) or different microorganisms (non-concomitant) were analyzed in order to adjust the empirical antibiotic treatment. Patients with rectal colonization by at least one multidrug-resistant bacterium (MDRB) on admission or after ICU admission were included. All patients had complete selective digestive decontamination (SDD) prophylaxis. For univariate analysis, categorical variables are expressed as frequencies and percentages and continuous variables as means and standard deviations, or as medians and interquartile ranges. For multivariate analysis, the model is summarized with p-values and hazard ratios with 95% confidence intervals. Survival analysis was conducted using the Kaplan–Meier method, which was performed to evaluate the time elapsed from colonization to infection by the same bacteria. Statistical significance was considered at p < 0.05. Results: Of the 130 patients with MDRB bacterial colonization analyzed, 98 remained free of infection, while 22 developed non-concomitant infections and 10 had infections concomitant to rectal colonizing bacteria. OXA-48-producing bacteria and MDR-Pseudomonas spp. incidences were 18.9% (95% CI: 7.96–35.2) and 44.4% (CI: 13.7–78.8), respectively. Conclusions: OXA-48-producing bacteria and MDR-Pseudomonas spp. were the only bacteria associated with the development of infections concomitant to rectal colonization in an SDD setting. The incidence of MDRB infections was low.