A-102 Trends in antimicrobial resistance and carbapenemase genes in Gram-negative bacteria in Chilpancingo de los Bravo, Guerrero, México (2021–2025).

Abstract

Antimicrobial resistance (AMR) in Gram-negative bacteria represents one of the major threats to global public health, particularly due to the emergence and dissemination of carbapenem-resistant microorganisms. In Mexico, longitudinal local surveillance integrating phenotypic resistance patterns and the detection of carbapenemase genes remains limited. The aim of this study was to evaluate temporal trends in antimicrobial resistance and to detect carbapenemase-encoding genes in Gram-negative bacteria isolated in Chilpancingo de los Bravo, Guerrero, Mexico, during the period 2021–2025. An observational, analytical, ambispective study was conducted using clinical isolates obtained from urine, blood, and lower respiratory tract samples from patients within the public healthcare sector. Antimicrobial susceptibility testing was performed using automated systems (Vitek 2 and MicroScan) and interpreted according to Clinical and Laboratory Standards Institute (CLSI) criteria. Resistance data were standardized and analyzed using WHONET 2025 software. Multidrug-resistant (MDR), extensively drug-resistant (XDR), and pandrug-resistant (PDR) phenotypes were classified according to international definitions. Temporal resistance trends were assessed using the Cochran–Armitage test. Meropenem-resistant isolates were analyzed by polymerase chain reaction (PCR) for the detection of carbapenemase genes, including blaNDM, blaVIM, blaIMP, blaGES, blaKPC, blaOXA-48, blaOXA-23, and blaOXA-24. A total of 2,617 Gram-negative bacterial isolates were analyzed, corresponding to Escherichia coli (n=1,999), Klebsiella pneumoniae (n=359), Pseudomonas aeruginosa (n=175), Enterobacter cloacae (n=60), and Acinetobacter baumannii (n=24). E. coli was the most frequent species (76.4%), predominantly isolated from urine samples and female patients. High resistance rates were observed in E. coli to third-generation cephalosporins and fluoroquinolones; however, significant downward trends were identified for several antimicrobials, including ceftriaxone, cefepime, amikacin, and levofloxacin (p<0.05). Carbapenem resistance among Enterobacterales remained low throughout the study period (=5.4%). In contrast, P. aeruginosa showed persistently high resistance to ciprofloxacin (>30%), with an increase in resistance to ceftazidime and gentamicin in 2025, as well as notable proportions of MDR (31%), possible XDR (31%), and possible PDR (17%) phenotypes. A. baumannii exhibited the highest frequencies of MDR (71%) and XDR (63%). Molecular analysis identified blaNDM as the predominant carbapenemase determinant in Enterobacterales. In P. aeruginosa, greater genetic diversity was detected, including the presence of blaVIM, and blaGES, while blaOXA-23 and blaOXA-24 were identified in A. baumannii. The blaKPC and blaOXA-48 genes were not detected. Gram-negative bacteria circulating in Chilpancingo de los Bravo, Mexico exhibit a high burden of antimicrobial resistance, characterized by a high frequency of MDR and possible XDR phenotypes and the presence of diverse carbapenemase genes, particularly among non-fermenting bacteria. Although carbapenem resistance in Gram-negative bacteria remained low, the detection of critical genetic determinants underscores the need to maintain continuous phenotypic and molecular surveillance programs to support rational antimicrobial use and infection control strategies.