Isolation and Antimicrobial Susceptability of Listeria Monocytogenes from Raw Milk and Milk Products in Northern Kaduna State, Nigeria

Abstract

Listeria (L.) monocytogenes is an ‘emerging food borne pathogen’ that poses threat to global food safety. Its occurrence in milk and milk products constitute a negative impact to the dairy industry. Despite its veterinary public health significance, only few studies are available on the prevalence and characteristics of the organism from milk and milk products in Nigeria. The main objectives of this study were to isolate, identify and determine the antibiotic susceptibility patterns of the Listeria monocytogenes isolated from raw milk and milk product in Kaduna state Nigeria. A total of 550 samples of raw milk and milk products (fermented milk “Kindrimo” and milk butter “Manshanu”) were collected during a cross-sectional study. Of these 550 samples, 193 (35.10%) samples were positive for Listeria species- like growth when plated on chromogenic Listeria agar, 91 (47.15%) from raw milk, 65 (33.67%) from ‘Manshanu’ and 37 (19.15%) ‘Kindrimo’. A total of 36 (6.55%) were found to be L. monocytogenes based on conventional biochemical tests. However, when further subjected to MicrobactTM Listeria 12L detection Kit (Oxoid, MB1128A) only 3 (8.3%) of the 36 isolates were identified as L. monocytogenes, while the others were L. grayi 4 (11.1%), L. ivanovii 27 (75.0%) and L. seeligeri 2 (5.6%). The multiplex PCR assay identified 9 Listeria (L.) monocytogenes isolates harbouring the hly A gene. The susceptibility of 36 L. monocytogenes isolates to 10 antibiotics was evaluated using the disk diffusion method. Isolates from milk samples had an overall resistance of 64.09% to the antibiotics, followed by isolates from ‘Kindrimo’ (61.67%), and least resistance was observed in isolates from ‘Manshanu” (58.33%). Overall, L. monocytogenes isolates showed the highest frequency of resistance to ampicillin (100%), followed by penicillin (95%) and cloxacillin (90%). In conclusion, the isolation of L. monocytogenes and other Listeria species in this study calls for an improved hygienic practices in the milk and milk products production channels and for the enlightment of the Fulani herds men and women by agricultural extension workers. Also, the resistance pattern shown by the isolates is an indication that the use of antibiotics should be regulated to minimize the incidence of antibiotic resistance.