Occurrence and characterization of biofilm-forming and multidrug-resistant Shigella spp. in retail poultry meat and associated environments in Sylhet, Bangladesh.

Abstract

Shigella spp. are important foodborne pathogens increasingly associated with antimicrobial resistance (AMR) and contamination within retail poultry-handling environments. This study investigated the prevalence, antimicrobial resistance profiles, extended-spectrum β-lactamase (ESBL) determinants, virulence-associated genes, efflux pump genes, and biofilm-forming ability of Shigella spp. isolated from retail poultry meat and associated environments in Sylhet, Bangladesh. A total of 300 samples, including cloacal swabs, meat, handler hand swabs, utensil swabs, and wastewater samples, were collected and analyzed using culture-based methods, biochemical tests, and species-specific PCR. We also performed antimicrobial susceptibility testing (AST) and molecular characterization. Overall, 50.0% (150/300) of samples were culture-positive for Shigella. Among the 150 culture-positive samples, 144 (96.0%) were confirmed by species-specific PCR, including 98 Shigella flexneri and 46 S. dysenteriae isolates. When calculated against the total number of samples tested, Shigella flexneri and S. dysenteriae were present in 32.67% (98/300) and 15.33% (46/300) of samples, respectively, with the highest prevalence observed in cloacal swabs (46.38% and 21.74%, respectively). AST revealed high resistance to trimethoprim-sulfamethoxazole (92.9% and 84.8%), tetracycline (87.7% and 87.0%), azithromycin (86.7% and 76.1%), and levofloxacin (76.5% and 56.5%) among S. flexneri and S. dysenteriae, respectively. In contrast, cefixime and gentamicin remained the most effective agents, showing susceptibility rates of 82.7% and 80.6% in S. flexneri and 67.4% and 58.7% in S. dysenteriae. The predominant resistance genes were tetA (72.45; 78.26%), qnrS (80.61; 89.13%), sul1 (50.0; 69.57%), and bla_TEM (38.78; 45.65%), while efflux pump genes acrAB (60.20; 80.43%) and tolC (77.55; 86.96%) were widely distributed. Biofilm formation was detected in 37.76% and 56.52% of isolates by Congo red agar and in 27.55% and 36.96% by microtiter plate assay for S. flexneri and S. dysenteriae, respectively. All isolates exhibited MAR indices >0.20, while MDR and possible XDR (P-XDR) phenotypes were detected in 38.78% and 61.22% of S. flexneri and 58.70% and 41.30% of S. dysenteriae isolates, respectively. These findings highlight the occurrence of antimicrobial-resistant and biofilm-forming Shigella spp. within the investigated retail poultry-handling environment and underscore the need for strengthened biosecurity, antimicrobial stewardship, and One Health surveillance strategies.