Occurrence and antimicrobial susceptibility of Salmonella in feces and milk samples of lactating dairy cows in Addis Ababa, Ethiopia

Salmonella is one of the major causes of foodborne diseases that remained important public health concerns worldwide. Antimicrobial resistance in Salmonella is also a global concern. Establishing the status of Salmonella in dairy farms and antimicrobial susceptibility of circulating isolates particularly where animals and humans live in close proximity is vital to devise appropriate intervention. A cross-sectional study was conducted from December 2019 to May 2020 to determine the prevalence of Salmonella and antimicrobial susceptibility of isolates among lactating dairy cows in Addis Ababa. A total of 151 fecal and 151 milk samples were collected from lactating dairy cows and cultured for Salmonella. Salmonella isolation and identification was conducted using standard microbiological techniques and further confirmation was carried out using Salmonella genus-specific PCR. An antimicrobial susceptibility test was performed using the Kirby-Bauer disk diffusion technique. Salmonella was isolated from 4 fecal samples (4/151) (2.7%) whereas none of the 151 milk samples were positive for Salmonella. One isolate was multidrugresistant (MDR) to seven antimicrobials namely: ampicillin, amoxicillin, ceftriaxone, cephalothin, tetracycline, and sufamethoxazole+ trimethoprim and    two isolates were resistant to either tetracycline or sulfisoxazole. All Salmonella isolates were susceptible to ciprofloxacin, amikacin, chloramphenicol, nalidixic acid, and gentamicin. In conclusion, a low prevalence of Salmonella among lactating dairy cattle was recorded in this study and it was not detected in milk samples. However, the observed resistance to commonly used antimicrobials particularly third-generation cephalosporin, ceftriaxone in one of the isolates pose a public health concern. Thus, appropriate measures should be instituted to protect the public and animals from infection with multidrug-resistant strains of Salmonella.