Characterization of multi-resistant Shigella species isolated from raw cow milk and milk products.

This study was organized to investigate the prevalence, antibiotic and disinfectant resistance phenotypes and genotypes as well as plasmid profiles of Shigella species isolated from raw cow milk and milk products in Egypt. Genotypic analysis was performed to determine the presence of ß-lactamase encoding genes (blaTEM, blaCTX-M, blaOXA-1 and blaSHV), tet(A) and qacE∆. Forty-two (7%) Shigella isolates (S. dysenteriae, S. flexneri, and S. sonnei) were recovered, with S. dysenteriae as the predominant type. Antibiotic sensitivity tests showed that 71.4% of Shigella isolates were resistant to three or more antibiotic classes (multidrug-resistant). High resistance rates were observed against tetracyclines (100%), ampicillin, amoxicillin-clavulanate (90.5%, each) and cefaclor (66.7%), while no resistance was detected against imipenem, sulfamethoxazole/trimethoprim, and azithromycin. Disinfectant susceptibility test of Shigella isolates revealed resistance to phenolic compound (vanillic acid), while 85.7% of the Shigella isolates were resistant to benzalkonium chloride. Uniplex PCR analysis declared the existence of ß-lactamase encoding genes (blaTEM in all isolates and blaCTX-M in 28.6% of isolates) and, tet(A) in all isolates and 85.7% of the isolates were positive for qacE∆1, while all isolates were negative for blaOXA-1 and blaSHV. All Shigella extended spectrum ß-lactamases (ESBL) producers (12, 100%) were positive for the blaTEM, blaCTX-M, and qacE∆1 genes. Furthermore, plasmid profiling revealed seven distinct plasmid patterns (P1-P7), ranging from 1.26 to 33.61 kb, among all the Shigella strains; S. dysenteriae exhibited the greatest variance. The co-transfer of ß-lactamase genes (blaTEM and blaCTX-M) and qacE∆1 genes was observed by conjugation from all ESBL producers to a recipient strain. These findings indicate the emergence of Shigella species in Egypt that exhibited multi-resistance to either antibiotics (particularly ESBL producer strains) or disinfectants. Thus, the resistance of Shigella species should regularly be monitored and appropriate measures should be taken to manage this problem.