Ecology and epidemiology of multidrug resistance Salmonella in fruit Bats and shared water sources in Bangladesh

Antimicrobial resistance (AMR) is a growing global threat to both animal and human health, underscoring the importance of AMR surveillance across all sectors of the One Health triad, including wildlife. Fruit bats in Bangladesh frequently inhabit areas in close proximity to human settlements and livestock facilities, creating ecological conditions that facilitate the co-occurrence of AMR bacteria through direct contact or shared contaminated environments. A cross-sectional study was conducted to determine the prevalence of Salmonella spp. isolation and the proportion of antimicrobial-resistant isolates among confirmed positives, characterize resistance patterns across multiple antimicrobial classes, and identify associated risk factors in fruit bat populations and environmental water sources in Bangladesh. We collected 369 fecal samples from the roosts of two bat species, Pteropus medius and Rousettus leschenaultii, along with 22 water samples from water bodies utilized by humans, livestock, and bats. Salmonella spp. isolates were identified using selective agar culture, followed by biochemical testing and confirmation via polymerase chain reaction (PCR). Confirmed isolates underwent antimicrobial susceptibility testing via the Kirby-Bauer disc diffusion method against 12 antimicrobials. The prevalence of AMR Salmonella spp. was 7.9% (95% CI: 5.3-11.1%) in bat's roost fecal samples and 31.8% (95% CI: 13.9-54.9%) in environmental water samples. Bat-derived isolates showed high resistance to tetracycline (93%), nalidixic acid (86%), sulfamethoxazole-trimethoprim (80%), and azithromycin (76%). Among the identified AMR isolates, 28 (96.5%) met the criteria for multidrug resistance (MDR), defined as resistance to three or more antimicrobial classes. Water-derived isolates also demonstrated high resistance, particularly to tetracycline (86%), amoxicillin-clavulanic acid (75%), azithromycin (73%), ceftriaxone (72%), and ciprofloxacin (71%). Multivariable logistic regression analysis revealed that the odds ratio (OR) of detection of MDR Salmonella spp. in fruit bats was 5.1 times higher during the summer season compared to winter. These findings highlight the evidence of MDR Salmonella spp. in fruit bats and shared environmental water sources in Bangladesh. The co-occurrence of resistant isolates across wildlife and environmental samples highlights the need for integrated AMR surveillance encompassing wildlife reservoirs and shared ecological interfaces. Strengthened antimicrobial stewardship, improved wastewater management, and coordinated One Health surveillance strategies are essential to mitigate the risk of zoonotic spillover and reduce further ecological overlap of MDR bacteria at the wildlife-livestock-human interface in Bangladesh and the broader South Asian region.