Prevalence, Molecular Characterization And Antibiotic Sensitivity Of Listeria Monocytogenes Isolated From Foods Of Animal Origin In Nairobi And Its Environs, Kenya

ABSTRACT

Food borne infections are an important public health concern worldwide with most being caused by pathogens that are zoonotic in nature. Among the most common food borne infection is listeriosis, caused by Listeria monocytogenes, a bacterium that is widely distributed in nature and which has been isolated in a wide array of foods. It mainly affects immunocompromised individuals including pregnant women, neonates and the elderly. Currently, in Kenya, there is no published data on the presence of this organism in ready to eat foods. The aim of this study was therefore to determine the prevalence, serotypes, virulence factors, genetic relationship and antibiotic susceptibility of L. monocytogenes from ready to eat meat products and milk products in Nairobi and its environs. A total of 570 samples; 350 milk products and 220 meat products were collected from selected retail markets in the study area. Isolation and identification was done as per the Bacteriological Analytical Manual protocol, and out of the 570 samples, 49 (8.59%) tested positive for Listeria spp after amplification of a 370 bp region of the prs gene. Twenty-one (42.8%) of these isolates were from milk products namely; milk powder (4.76%), short life pasteurized milk (4.76%), long life pasteurized milk (14.29%) and pasteurized milk from dispensing machines (76.19%). The rest, 28/49 (57.2%) were isolated from meat products namely; ham (7.14%), brawn (46.43%), polony (28.57%), salami (3.57%) and ready to eat meat bites (14.29%). Speciation of the Listeria isolates was done through multiplex PCR and of the 49 isolates, 22 were confirmed as L. monocytogenes through the amplification of a 509 bp region of the Lmo1030 gene. Of these L. monocytogenes isolates, 77.27% were from milk products while 22.72% were from meat products. The highest prevalence, 68.18 % was from dispensed milk while the lowest, 4.54% was from short life milk, long life milk and ham. Of the other 27 Listeria spp isolates, two were identified as L. welshimeri by amplification of a 281 bp region of the scrA gene while three were identified as L. innocua by amplification of a 749 bp region of the Lin0464 gene. The rest of the isolates, (22/27) were unidentified Listeria spp. The overall prevalence of L. monocytogenes was 3.86% (22/570). Molecular serotyping of the 22 L. monocytogenes isolates showed that 95.45% of the isolates carried both the ORF 2110 and the ORF 2819 genes characteristic of serotypes 4b,4d and 4e. A majority of these isolates (68.18%) were from milk collected from dispensing machines, two isolates from polony and an isolate each (4.55%) from long life milk, short life milk, brawn and ham. The remaining isolate (4.55%) carried the ORF2819 gene only, characteristic of serotype 1/2b, 3b, 4b, 4d, 4e and 7 and was isolated from brawn. All the isolates possessed hlyA, inlA, inlC, iap and actA virulence genes. Almost all the isolates (21/22) had the inlJ gene while inlB was only detected in 10/22 (45.45%) of the isolates. All L. monocytogenes were resistant to penicillin, 9.09% resistant to erythromycin and 4.54% resistant to sulfamethoxazole trimethoprim. All isolates were susceptible to gentamycin, chloramphenicol and tetracycline. The study concluded that processed ready to eat meat and milk products available to consumers were contaminated with the virulent form of L. monocytogenes that is responsible for up to 95% of Listeriosis cases reported worldwide. It is recommended that strict regulation of the processing and storage conditions of ready to eat foods be done to ensure they reach consumers pathogen free.