Resistance of Gram-Negative Bacteria Isolated from Blood Cultures in the Post-COVID Era

Abstract

 Introduction: Gram-negative bacilli (GNB) are common causes of sepsis in intensive care units. The proportion of multidrug-resistant (MDR), extensively drug-resistant (XDR), and pandrug-resistant (PDR) strains is increasing. A higher number of hospitalizations and increased antibiotic use during the COVID-19 pandemic may have influenced resistance patterns.

 Aim: The aim of this study was to determine the antimicrobial resistance profile, the frequency of MDR, XDR, and PDR categories among isolated GNB, and to examine the association between MDR status and basic demographic characteristics of patients.

 Materials and Methods: In this retrospective study conducted at the Institute for Pulmonary Diseases of Vojvodina during 2022 and 2023, a total of 213 GNB isolated from positive blood cultures were analyzed. Bacterial identification was performed using the Vitek 2 Compact system. Antimicrobial susceptibility testing was carried out by the disk diffusion method according to EUCAST guidelines.

 Results: The following species were isolated: K. pneumoniae (48.0%), A. baumannii complex (30.0%), P. aeruginosa (8.0%), E. coli (5.0%), E. cloacae complex (2.0%), P. stuartii (2.0%), P. mirabilis (2.0%), Citrobacter spp. (1.0%), S. marcescens (1.0%), M. morganii (1.0%). Among Enterobacterales isolates, 82.6% were resistant to 3rd- and 4th-generation cephalosporins, 77.3% to carbapenems—most commonly K. pneumoniae—and 45.0% to colistin. PDR Enterobacterales accounted for 12.1%, all K. pneumoniae. Among A. baumannii isolates, 98% were carbapenem-resistant, and 6.2% were PDR. A total of 35% of P. aeruginosa isolates were carbapenem-resistant, while 71% remained susceptible to piperacillin/tazobactam. Younger patients (< 65) more often developed infections with MDR Enterobacterales (98.3%) (χ² = 4.226, p < 0.05). MDR P. aeruginosa infections were more common in 2023 (55.6%) (χ² = 7.269, p < 0.05).

 Conclusion: A high proportion of MDR GNB strains was observed, including PDR Enterobacterales and A. baumannii. MDR Enterobacterales infections were significantly more frequent in younger patients, while MDR P. aeruginosa increased in 2023.