Antimicrobial Susceptibility and Genetic Prevalence of Extended-Spectrum β-Lactamases in Gram-Negative Rods Isolated from Clinical Specimens in Pakistan

The prevalence of extended-spectrum β-lactamase (ESBL) genes has increased remarkably, resulting in multidrug-resistant gram-negative rods (GNRs) in clinical specimens. This cross-sectional study aimed to determine the antimicrobial susceptibility of ESBL-producing GNRs and its correlation with corresponding genes. Two hundred and seventy-two (n = 272) samples were evaluated for the molecular identification of ESBL genes by polymerase chain reaction after confirmation with the modified double-disc synergy test. E. coli 64.0% (n = 174) was the most prevalent ESBL producer, followed by Klebsiella species 27.2% (n = seventy-four), Acinetobacter species 6.6% (n = eighteen) and others 2.2% (n = six). These ESBL-producing isolates showed resistance to β-lactam antibiotics, i.e., sulbactam/cefoperazone (41.5%), piperacillin/tazobactam (39.3%), meropenem (36.0%), imipenem (34.2%) and non- β-lactam antibiotics, i.e., nalidixic acid (89.0%), co-trimoxazole (84.9%), ciprofloxacin (82.4%), gentamicin (46.3%), nitrofurantoin (24.6%), amikacin (19.9%) and fosfomycin (19.9%). The incidences of the ESBLs-producing genes blaCTX-M, blaTEM, blaOXA and blaSHV were 91.2%, 61.8%, 39.3% and 17.6%, respectively. Among nine multiple-gene combinations, blaCTX-M + blaTEM (30.5%) was the most prevalent combination, followed by blaCTX-M + blaOXA + blaTEM (14.0%), blaCTX-M + blaOXA (13.6%), blaCTX-M + blaTEM + blaSHV (7.0%), blaCTX-M + blaSHV (2.2%), blaCTX-M + blaOXA + blaSHV (2.2%) and blaOXA + blaTEM (1.8%). ESBLs producing GNRs carrying blaCTX-M, blaTEM, blaOXA and blaSHV showed resistances to β-lactam antibiotics, i.e., ampicillin, amoxillin-clavulanic acid, cefotaxime and ceftazidime but were susceptible to carbapenems (meropenem and imipenem), β-lactam-β-lactamase inhibitor combination (piperacillin/tazobactam) and non-β-lactam antibiotics i.e., aminoglycoside (amikacin and gentamicin), nitrofurantoin and fosfomycin. These antibiotics that demonstrated activity may be used to treat infections in clinical settings.