Study on Listeria Monocytogenes and Other Listeria Species in Milk and Meat Products in Retail Markets of Addis Ababa, Ethiopia
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2005-06
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Abstract
A cross sectional study of Listeria monocytogenes and other Listeria species was undertaken in major supermarkets, pastry shops and restaurants in Addis Ababa, Ethiopia from September 2004 to March 2005. The study was conducted on milk and milk products (pasteurized cows’ milk, cottage cheese, soft cheese, creamed cakes, and ice cream) and meat products (minced beef, chicken carcass, and pork). A total of 711 food samples consisting of 50 pasteurized milk, 101 soft cheeses, 80 cottage cheeses, 103 ice creams, 107 creamed cakes, 109 minced beef, 80 pork and 81 chicken carcasses were collected for analysis during the study period. Listeria monocytogenes and other Listeria species were identified and isolated according to the techniques recommended by the International Organization for Standardization (ISO 11290-1, 1996). Serotyping of L. monocytogenes strains was carried out at the French Authority for Food Safety (AFSSA), Ploufragan, France.
Out of the total of 711 food samples examined in this study, 189 food samples (26.6%) were positive for Listeria species. Of the samples examined, pork was the most contaminated food item with Listeria species with an overall prevalence of 62.5%. Of the examined samples, 52 (47.7%) minced beef, 44 (42.7%) ice cream, 17 (16.8%) soft cheese, 13 (16.0%) chicken carcasse and 13 (12.1%) cake samples were also positive for Listeria species. All pasteurized milk and cottage cheese samples were negative for all Listeria species in this study. Listeria innocua was the predominant species (17.7%) isolated from the food samples examined in the current study. Its prevalence was higher in pork with a prevalence of 53.8%, followed by 31.2% in minced beef and 25.2% in ice cream. Chicken, soft cheese and cakes were also found contaminated with this species with a prevalence of 11.1%, 9.9% and 3.7% respectively. Listeria monocytogenes was the second most predominant Listeria species isolated (4.8%) in the food items examined. Considering the prevalence of L. monocytogenes in each food item, ice cream was the most contaminated food item with a prevalence of 11.7% followed by cakes (6.5%) and pork (5.0%). Soft cheese, chicken carcass and minced beef were also found contaminated with L. monocytogenes with a prevalence of 3.9%, 3.7% and 3.7% respectively. Other Listeria species isolated from the different food samples examined include, L. welshimeri (1.8%), L. murrayi (0.8%), L. seeligeri (0.7%), L. ivanovii (0.6%) and L. grayi (0.1%). Only two samples from each of minced beef and soft cheese food items were found contaminated with L. ivanovii. Other food items were found free from L. ivanovii. Listeria murrayi was found in ice cream, pork and minced beef. Among the 32 isolates of L. monocytogenes sent to Ploufragan, France for serotyping, 32 (96%) isolates were serotypes 4b/4e and the rest were 4c and 4e.
The microbiological examination in our current study suggested that L. monocytogenes is found in the different fooditems examined with the exception of pasteurized milk and cottage cheese. This indicates the possible risk of foodborne listeriosis particularly for the pregnant women, the elderly and immuno-compromised individuals in Ethiopia. The responsible veterinary and public health authorities should make efforts to raise the awareness of the food producers, suppliers, retailers and the public at large through various ways about the methods of safe food production, storage and handling. Awareness should also be created about the risks of foodborne diseases and the methods of preventing such diseases so that a considerable part of the population can be protected from many foodborne diseases including listeriosis.
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Listeria monocytogenes, Listeria species, serotype, milk and meat products