Studies on the Role of Virulence Factors of S. enterica and its Pathogenicity in Dairy Farms

Abstract

1-Field investigation of clinical mastitic cows and clinical diarrhic calves by clinical examination. 2- Bacteriological isolation and identification of Salmonella spp. from collecting samples. 3- Serological identification for serotype of isolated Salmonella strains. 4- Using of polymerase chain reaction technique (PCR) for detection of some virulence genes in salmonella isolates. 5- Antimicrobial sensitivity testing of Salmonella isolates. 6-Epidemiological studies and some risk factors associated with significant effect on Salmonella prevalence. The prevalence of Salmonella were investigated in a total number of 313 samples divided into188 milk samples (124 from bulk tank milk and 64 from individual mastitic milk) and 125 fecal samples (100 diarrheic fecal samples and 25 from apparently normal calves in contact with the diseased ones) which collected from different localities of governorates in Egypt.

The results obtained revealed that: The bacteriological examination showed that, 30 out of 313 total samples were found positive for isolation of Salmonella. Using XLD and S.S. media. The results of Salmonella identification by traditional biochemical methods revealed that 25 isolates (8%) were Salmonella spp. By using serotyptyping method for 25 of Salmonella spp. revealed that 18(5.8%) of Salmonella isolates were typed, fifteen of them were typed as S. typhimurium, two as S. sekondi and only one as S. chester in percentage of 83.3%, 11.1% and 5.6% respectively, while 7 strains were untyped. By using PCR technique for Salmonella isolates for detection of virulence genes (invA, bcfC, stn, pefA, mgtC, csgD, and fimH) detected in 18 (100%), 18(100%), 16(88.9%), 14(77.7%), 3(16.7%), 1(5.5%) and 0(0%) respectively. All isolates of S.typhimurium were sensitive to antibiotic discs in percentage of (80%) for amoxicillin +clavulanic acid, (85%) for ceftifoure, (%100) for cefiquinom and florfenicol but (86.6%) for levofloxacin, the isolates was sensitive (80%) to norfloxacin but the isolate was resistant to erythromycine, gentamycin and tetracycline 100%, 33.3% and 66.7% respectively. Results showed that the isolates of S.sekondi were sensitive to amoxicillin +clavulanic acid, cefiquinom, cefitifour, florfenicol, levofloxacin and norfloxacin antibiotic while moderately sensitive to tetracycline (50%) and resistant to gentamycin and erythromycin respectively. Results showed that the isolates of S.chester were sensitive to ceftiofur, Cefquinome, gentamicin, levofloxacin, norfloxacin and florfenicol (100%) but resistant to amoxicillin + clavulinic acid, tetracycline and erthromycin .