Phenotypic and molecular characterization of Salmonella serotypes in cow raw milk and milk products in Nigeria

Abstract

The presence of Salmonella and human pathogens in unpasteurized milk remains a public health hazard. The study reported the phenotypic and molecular characterization of Salmonella serotypes in cow raw milk, cheese and traditional yoghurt marketed for man’s consumption in Nigeria. Isolation of Salmonella was done on Salmonella and Shigella agar by pour plate method at 37°C. Susceptibility to antibiotics was determined by the disc diffusion method. Molecular characterization of the Salmonella serotypes and detection of some target genes was done by the polymerase chain reaction. All the isolates were sensitive to ofloxacin and nalidixic acid. Resistance to antibiotics was in varying proportions with amoxicillin (95.2%), tetracycline (90.4%) and augumentin (28.5%). Ten (10) different multiple antibiotic resistance patterns were observed among the serotypes. The serotypes identified include Salmonella typhi, Salmonella typhimurium and Salmonella enteritidis, and the serogroups include D (28.6%), B (52.4%), D₁ (28.6%), respectively. The invA genes were amplified in all the Salmonella serotypes while fliC and fliB genes were absent. The rfbJ gene was detected only in S. Typhimurium. The recovery of multiple antibiotic resistant pathogenic Salmonella serotypes in cheese and yoghurt samples in the study is of great health concern.

Keywords: Salmonella serotype, molecular characterization, virulence genes, antibiotics

African Journal of Biotechnology, Vol 13(37) 3774-3789