Multidrug-Resistant Salmonella Spp. Isolated From Cloacal Swab of Healthy Layer Chickens and Egg Surface at Selected Farms in Bangladesh.

Multidrug-resistant (MDR) Salmonella spp. is regarded as a perilous menace of public health significance. This research finding was carried out to investigate the prevalence of MDR Salmonella spp. in cloacal swabs of healthy layer birds and egg surface washing along with their resistance patterns and some associated resistance gene detection. In total, 120 samples consisting of 60 cloacal swabs and 60 eggs were collected from three different layer farms located at Mymensingh, Bangladesh, and subjected to various classical and molecular approaches. Antibiotic resistance patterns were investigated phenotypically using the Kirby-Bauer disk diffusion method and genotypically by detection of respective resistance genes. The overall prevalence rate of Salmonella spp. was 29% (95% CI: 18.077%-33.255%) and sample-wise prevalence was 23% (95% CI: 14.415%-26.918%) in cloacal swab and 35% (95% CI: 22.043%-39.956%) in egg surface washing, respectively. Antibiotic susceptibility test revealed that the highest resistance was found to ampicillin 94.29% (95% CI: 86.65%-99.96%) followed by oxytetracycline 80.00%, (95% CI: 65.23%-98.03%), and erythromycin 65.72% (95% CI: 56.73%-75.41%), 45.71%, (95% CI: 33.039%-58.08%) to streptomycin, whereas the highest sensitivity was observed against florfenicol 74.29% (95% CI: 62.91%-85.28%), followed by ciprofloxacin (68.57%, 95% CI: 62.80%-73.66%), and sulphamethoxazole (68.57%, 95% CI: 53.48%-78.97%). The isolates were also found to be MDR as 80% (28/35) isolates (95% CI: 75.80%-86.69%) possessed a MAR index ranging between 0.33 and 0.89. On average, 19 isolates (54.28%; 95% CI: 26.90%-85.17%) were resistant to 5 - 8 antibiotics of seven classes, which is really alarming for public health significance. Based on PCR results, different resistant genes blaTEM, tetA, aadA1, cat1, and flo-R were amplified from 100%, 85.71%, 77.14%, 62.86%, and 37.14% of the isolates. Due to increased drug resistance, antibiotics and other antimicrobial drugs are becoming ineffective for the medication of both human and animal infections. Further investigations are also suggested to cope with antimicrobial resistance through this research study.