Ecology and epidemiology of multidrug-resistant Salmonella in synanthropic small mammals in Bangladesh

Multidrug resistant (MDR) organisms pose a significant global concern, affecting both human and animal health.
Synanthropic small mammals, such as rodents and shrews can serve as environmental reservoirs and vectors for
MDR organisms, including Salmonella spp. Hence, a cross-sectional study was conducted to estimate the prevalence, risk factors, and MDR patterns of Salmonella spp. in wild rodents and shrews across diverse ecological
settings in Bangladesh. Throat and rectal/fecal swab samples were collected from a total of 350 mammals (203
wild rodents and 147 shrews) and tested for Salmonella spp. using selective culturing, biochemical properties and
PCR. All isolates were tested for culture susceptibility using the Kirby-Bauer disc diffusion method for 17 antimicrobials. Our findings revealed the overall prevalence of MDR Salmonella spp. was 38.6 % (95 % CI:
33.5–44.0). Prevalence was highest in S. murinus (61.2 %), followed by B. bengalensis (35.9 %), M. musculus (29.4
%) and R. rattus (29.0 %). The resistance of the isolated Salmonella strains in descending order was: 100 % to
ampicillin and oxytetracycline, followed by 94 % to sulfamethoxazole-trimethoprim, 92.0 % to doxycycline, and
89.0 % to ciprofloxacin. Shrews had significantly higher odds of carrying MDR Salmonella (OR = 3.8, p < 0.01)
compared to rodents. Moreover, small mammals from human dwellings had greater odds (OR = 2.4, p < 0.01) of
carrying MDR Salmonella than agricultural lands. Resistance to ceftriaxone and azithromycin is particularly
concerning, as these are critical for treating human infections with third generation cephalosporin and macrolides. These findings underscore the importance of enhanced reduced environmental contamination and judicious use of antibiotics to prevent spillovers of MDR organisms from wildlife to people and livestock.