The Aminoglycoside Resistance Genes, pehX, blaCTXM, blaAmpC, and npsB among Klebsiella oxytoca Stool Samples

Abstract

Background: Klebsiella oxytoca may cause various infections, including respiratory, urinary, and bloodstream infections, often with multidrug-resistant strains posing challenges in treatment. The aim of this study was for molecular identification of K. oxytoca and to assess the existence of aminoglycoside resistance genes in biofilm and in toxin-producing and AmpC-positive isolates. Methods and Results: A total of 400 non-duplicate stool samples were collected from patients with colitis from 2019 to 2020 and were immediately cultured onto McConkey and blood agar (Merk, Germany). Antibiotic discs and Mueller-Hinton agar (MHA) culture medium (Merck, Germany) were used for antimicrobial susceptibility testing. The disk diffusion was done for susceptibility examination of them using CLSI 2020. Phenotypic detection of AmpC enzymes and biofilm formation were also determined. The PCR was performed to detect polygalacturonase (pehX) gene, blaCTX-M gene, npsB toxin-encoding gene, blaAmpC gene, and the aac(6′)-lb and aac(3′)-IIa AMEs genes. A total of 100 K. oxytoca were identified from stool samples. Most isolates were not susceptible to tetracycline, cotrimoxazole, or cefoxitin disks. Moreover, most were susceptible to amikacin and piperacillin-tazobactam disks. Among 100 isolates, 54% produced the AmpC enzyme in the combined disk method. Among them, 30 isolates were resistant to gentamicin. Strong biofilm formation was determined in 66% of isolates, and 30% of them produced moderate biofilms. Moreover, 4% of the isolates had weak biofilms. Among the 60 gentamicin-resistant K. oxytoca, 32 isolates had strong biofilms, and 11 isolates produced moderate ones. The pehX was used for the molecular identification of K. oxytoca; the results showed the presence of this gene in all isolates. The majority (98%) of K. oxytoca amplified the npsB toxin-encoding gene. The rate of blaCTX-M, blaAmpC, aac(6′)-lb, and aac(3)-IIa genes were 62%, 45%, 12%, 24%, respectively. Conclusion: In our study, more than half of K. oxytoca showed MDR phenotype. Moreover, half of the isolates carried the blaAmpC and blaCTX-M genes. Strong biofilm formation was observed in more than 60% of them.