Isolation and characterization of Lactic Acid Bacteria and indicator microorganisms of food safety from Omaere, a traditionally fermented milk product in Botswana

Abstract

Botswana has many traditional foods and beverages that are prepared by means of natural/spontaneous fermentation. The traditional preparation of these foods is for the most part largely undocumented and the microorganisms involved in the fermentation process unknown. The main objective of this study was to isolate and characterize dominant culturable lactic acid bacteria (LAB) strains associated with the end-product fermentation of Omaere, a fermented milk product popular with the Herero tribe in Botswana. In addition to this, the study also aimed to investigate the presence of selected pathogens and microbial indicators of poor sanitary quality in the Omaere samples. Twelve Omaere samples were collected from domestic households in two geographical regions of Botswana (Ghanzi and North-Western districts of Botswana). MRS agar was used to isolate lactic acid bacteria, and standard microbiological, biochemical and morphological tests were used to categorize the isolates into 14 phenotypic groups based on similar biochemical, physiological and morphological characteristics. These isolates were further identified to species level using the API 50 CH system (bioMerieux, France). The isolates that had low identification percentages using the API 50 CH system, were subjected to 16S rRNA gene sequence analysis to confirm their identity. Bacterial pathogens, fungi and microbial indicators of sanitary quality were isolated using seven selective media; Eosin Methylene Blue Agar (EMBA) for the detection of coliforms, Mannitol Salt Agar (MSA) for isolation of Staphylococcus aureus, Sabouraud Dextrose Agar (SDA), Dichloran Glrycerol agar (DG-18) and Dichloran Rose Bengal Chlorotetracycline (DRBC) for isolation of fungi and some yeasts. Corn meal Agar was used for isolation of yeasts while Bacillus cereus Agar was used for isolation of Bacillus cereus. Lactobacillus plantarum was found to be the most dominant species of lactic acid bacteria in the Omaere samples, having been isolated from all the samples, with Lactobacillus rhamnosus being the second most dominant LAB species with 58% percentage distribution across samples. Other bacterial species commonly associated with Omaere fermentation were Enterococcus faecium and Lactobacillus helveticus with 25% and 17% distributions, respectively. No pathogens or bacterial indicators of poor sanitary quality specific to the seven selective media used were isolated from the Omaere samples. No yeast and fungi were isolated from the traditional fermented milk product.