Phenotypic characterisation of Listeria monocytogenes in cow milk from three catchment areas of Goliati Area in Thyolo District, Malawi

Abstract

Background: Listeria monocytogenes is one of the food borne pathogens that cause an illness known as Listeriosis upon ingestion of contaminated food. Outbreaks of Listeriosis have been reported in Canada, USA, Europe, South Africa, Ghana and other countries but there is limited data on outbreaks due to Listeria monocytogenes and its isolation from contaminated foods in Malawi. This prompted our interest to determine the presence of Listeria monocytogenes in cow milk from Goliati area, Thyolo district in Malawi. Objectives: To determine the presence and concentration of Listeria monocytogenes in cow milk from daily farmers around Goliati area in Thyolo district in Malawi. Methodology: Nine raw milk samples from three bulk centers and two processed milk samples were cultured on both Nutrient Agar and Brain Heart Infusion agar as primary cultures. A pure culture of Listeria monocytogenes was obtained by sub culturing the primary culture on Brain Heart Infusion agar media. Colonies from the pure culture were further identified using Gram staining, Catalase test, Motility test and Beta hemolysis test on blood agar to phenotypically identify Listeria monocytogenes. Results: There was a 100% growth rate of colonies suggestive of Listeria monocytogenes on all the nine samples. These colonies were observed to contain Gram positive, purple, short, rod shaped bacteria which was motile and catalase positive and it caused complete beta hemolysis on blood agar. Conclusion: In this study, isolates of Listeria monocytogenes were phenotypically identified in cow milk that is produce from Goliath Area in Thyolo district. This is a major public health concern for milk farmers and consumers in the area and beyond. The findings from this work calls for improved hygienic practices in the handling of milk and milk products to reduce contamination.