Pan-drug, colistin, streptomycin, erythromycin, clindamycin resistant Salmonella enterica serovars isolated from slaughtered cattle and human in mansoura, Egypt.

Objectives: Salmonella is recognized globally as a significant foodborne pathogen associated with foodborne outbreaks in both humans and animal. The rise of multidrug-resistant (MDR) Salmonella isolates poses a critical public health challenge. Given that the isolation of Salmonella within abattoirs is a prominent source of community infection especially through the consumption of contaminated meat. This study aims to determine the prevalence of Salmonella, the occurrence of virulence genes (invA, spvC), and specific resistance genes (tetA, sul1, aadA1, aac(3)- IV) in Salmonella isolates isolated from cattle in abattoirs. Additionally, the investigation assesses the potential exposure risks for abattoir workers in Mansoura City, Egypt.

Methods: In a study conducted from May to July 2024, a total of 150 samples were collected to investigate the presence of Salmonella in healthy Egyptian Baladi cattle and abattoir workers at the Mansoura abattoir, Mansoura City, Egypt. The sample collection comprised rectal swabs (n = 50) and meat swabs (n = 50) from cattle, in addition to 50 hand swabs obtained from abattoir workers. Salmonella isolation was done following standard microbiological techniques. Initially, pre-enrichment of the samples was conducted using buffered peptone water. Subsequently, selective enrichment was executed using Rappaport Vassiliadis broth, followed by cultivation on xylose-lysine-deoxycholate (XLD) agar to isolate suspected Salmonella colonies. These colonies were then subjected to a series of identification tests, including biochemical assays, slide agglutination tests, and polymerase chain reaction (PCR) targeting the invA gene, which is indicative of Salmonella presence. Furthermore, molecularly identified isolates were tested for the virulence gene spvC, which is related to the pathogenicity of Salmonella. The antimicrobial susceptibility of the isolates was assessed using the Kirby-Bauer disc diffusion method, providing insight into the resistance profiles of the observed isolates. In addition, a subset of 19 Salmonella isolates underwent multiplex PCR analysis to evaluate the presence of specific resistance genes: tetA, sul1, aadA1, and aac(3)-IV.

Results: The overall occurrence of Salmonella isolates across all examined samples was 12.7%. This included 4% from cattle carcass swabs, 12% from rectal swabs, and a notable 22% from workers' hands. The most prevalent serotypes identified were Salmonella Enteritidis and Salmonella Typhimurium, exhibiting incidences of 26.3% (n = 5) and 21% (n = 4), respectively. Other serotypes included Salmonella Infantis at 15.8% (n = 3), Salmonella Kentucky and Salmonella Tsevie each at 10.5% (n = 2), and Salmonella Paratyphi A, Salmonella Haifa, and Salmonella Virchow at 5.3% ((n = 1) each). From the tested Salmonella isolates, 100% (19/19) were positive for the invA and 89.5% (17/19) carried Spvc genes. Resistance profiling categorized the isolates into pandrug-resistant (PDR) at 5.3%, extensively drug-resistant (XDR) at 5.3%, multidrug-resistant (MDR) at 63.1%, and low drug-resistant at 26.3%. Notably, Salmonella Enteritidis exhibited complete resistance to all tested antimicrobial agents, resulting in a Multiple Antibiotic Resistance (MAR) index of 1. Conversely, S. Typhimurium was classified as XDR, with a MAR index of 0.937. Resistance rates were alarmingly high, with 100% against streptomycin, 89.5% against erythromycin, 73.7% against clindamycin, and 63.2% against ampicillin. Among the resistance genes, the aadA1 gene was most prevalent at 100%, followed by sul1 and tetA at 42.1% (n = 8) and 31.6% (n = 6), respectively. The aac(3)-IV gene was the least prevalent, noticed in 15.8% (n = 3) of the isolates.

Conclusion: The high occurrence of multidrug-resistant (MDR) Salmonella serovars among the tested isolates is concerning. These antibiotics are crucial for effectively treating severe salmonellosis, highlighting the crucial need for strict antimicrobial regulation in both veterinary and human medicine.