OCCURRENCE OF LISTERIA MONOCYTOGENES IN FRESH MEAT AND OFFAL SOLD FOR HUMAN CONSUMPTION IN ZARIA METROPOLIS, NIGERIA

ABSTRACT

Listeriosis is a disease caused by a gram positive, non-spore forming intracellular pathogenic bacteria of the genus Listeria, commonly associated with food. To determine the presence of Listeria monocytogenes and some of its associated virulence genes in fresh meat samples sold for human consumption, 240 samples were obtained comprising of 156 beef, 26 liver, 25 reproductive tract and 33 intestinal parts sold at various locations in Zaria from July to November, 2013. Sixty six (27.5%) isolates of Listeria species were obtained and characterised through conventional biochemicaltests, out of which, 8 (3.3%) were Listeria monocytogenes, but only one was subsequently confirmed using the Microgen^R 12L ID kit. Beef had the highest occurrence of 66.7% followed by reproductive tract (13.6%), intestines (10.6%) and liver (9.1%). Antibiotic susceptibility testing of the eight isolates by Kirby-Bauer disk diffusion method revealed that 100% of the L. monocytogenes isolates were resistant to ampicillin, 87.5% to tetracycline and cefixime, 75% to amoxicillin/clavulanic acid, 62.5% to erythromycin, 50% to chloramphenicol, nitrofurantoin and sulfamethoxazole, 37.5% to ciprofloxacin and kanamycin and 12.5% to gentamicin,. The least resistance frequency was to gentamicin 12.5%. However, all the isolates were resistant to at least 3 antimicrobial agents. Antibiotic resistance profiles of the isolates revealed 6 different antimicrobial resistance patterns. Isolates were subjected to a multiplex PCR to detect the presence of the haemolysin (hylA), internalin (inlA) and invasiveness associated protein (iap) virulence genes. None (0%) of the eight isolates was found to harbour haemolysin hylA, 1(12.5%) was positive for both internalin inlA and invasiveness associated proteins iap while 5(62.5%) harboured iap gene. The findings of this study showed the occurrence of Listeria monocytogenes in fresh meat samples in Zaria metropolis which displayed multiple antibiotic resistance and possessed virulence genes in lA, and iap. This finding is of public health significance.