Emergence of gyrA and aac(6′)-Ib-cr Mediated Quinolone Resistance in Salmonella Typhi Isolated from Blood Samples in a Tertiary Care Hospital, Bangladesh

Abstract

Antibiotic resistance among Salmonella Typhi poses a growing challenge in Bangladesh. A cross-sectional study was conducted in the Department of Microbiology, Dhaka Medical College, Dhaka, Bangladesh, from July 2019 to June 2020, to assess the prevalence of gyrA and aac(6′)-Ib-cr quinolone-resistance genes in isolates from blood cultures of enteric fever patients. Blood cultures were processed using standard methods. Primary culture was done in trypticase soya broth, followed by subculture on blood agar and MacConkey agar. Identification was performed by biochemical tests and confirmed by serotyping with S. Typhi antisera. Disc diffusion was performed as per CLSI guidelines using commercial antibiotic discs. PCR assays targeted gyrA, qnrA, qnrB, qnrS, qnrC, qnrD, and aac(6′)-Ib-cr. S. Typhi was identified by biochemical testing and 16S rRNA PCR. PCR was further used to detect gyrA, qnrB, qnrS, and aac(6′)-Ib-cr genes. Out of 83 culture-positive samples, 50 were Salmonella spp., of which 40 were confirmed as S. Typhi. 12 isolates showed ciprofloxacin resistance. Among these, gyrA was detected in 8 (66.7%), aac(6′)-Ib-cr in 2 (16.7%), and qnrB and qnrS in 1 each (8.3%). A high frequency of gyrA mutations and detection of plasmid-mediated aac(6′)-Ib-cr indicates emerging quinolone resistance in S. Typhi. This highlights the urgent need for routine molecular surveillance and strengthened antimicrobial stewardship.  

CBMJ 2026 July: Vol. 15 No. 02 P:4-9