Molecular detection of genes encoding resistance to tetracycline and quinolones among Shigella strains isolated from children with acute diarrhea in southwest Iran

An increase in the antibiotic resistance of Shigella isolates has caused major global challenges in antimicrobial therapy. Knowledge of local antibiotic resistance trends is essential for selecting appropriate antibiotic treat- ment regimens. This study aimed to evaluate the frequency of efflux-mediated tetracycline resistance (tet) and plasmid-me- diated quinolone resistance (qnr) genes among Shigella isolates.

This survey investigated 91 Shigella isolates, obtained from children with acute diarrhea. The iso- lates were identified using standard biochemical tests and confirmed by polymerase chain reaction (PCR) assay. Besides, the susceptibility of isolates to six selected antibiotics was assessed by the disk diffusion method. All tetracycline-resistant and nalidixic acid and ciprofloxacin resistant strains were screened for tet and qnr genes by a multiplex PCR assay.

According to the results of antibiotic susceptibility tests, the highest level of antibiotic resistance was related to tet- racycline (80.2%) and doxycycline (78.1%), respectively. All isolates were sensitive to tigecycline. The PCR results showed that 40.6%, 3.1%, 21.8%, 61.6% and 28.7% of the isolates carried qnrA, qnrB, qnrS, tetA, and tetB genes, respectively. None of the isolates contained tetC and tetD genes.

The current findings revealed that tetA and qnrA genes might play a key role in conferring tetracycline and quinolone resistance.