Phenotypic Characterisation and Virulence Profiling of Bacterial Contaminants in Traditional Unpasteurized Soft Cheese (Wara) Sold in Urban Nigerian Markets: A Bio-Surveillance Framework

Abstract

This study focuses on the characterisation and safety assessment of bacterial isolates recovered from Wara, a locally produced soft cheese sold in Ojoo Main Market in Ibadan, Oyo State, Nigeria. Wara is a traditional dairy product widely consumed across West Africa, but artisanal processing methods, unpasteurized milk, plant-derived coagulants (Calotropis procera), and ambient market handling conditions present significant foodborne transmission risks. A total of 40 bacterial isolates were recovered and characterised using morphological examination, Gram staining, biochemical profiling, sugar fermentation assays, and in vitro safety markers (beta-haemolysis on 5% sheep blood agar, gelatinase liquefaction, and DNase production). To translate qualitative phenotypic findings into reproducible risk metrics, a computational Virulence Scoring Index (VSI) was formulated on a 0 to 100 scale. Eleven distinct species spanning five microbial groups were identified. Beta-haemolytic activity was documented in 52.5% of isolates (21/40), gelatinase production in 52.5% (21/40), and DNase activity in 30.0% (12/40). The population-wide mean VSI was 49.88 out of 100, with 57.5% of isolates categorized as potential or opportunistic pathogens. Staphylococcus aureus, Pseudomonas aeruginosa, and Bacillus cereus demonstrated the highest virulence scores. Lactic acid bacteria (LAB) represented 40.0% of isolates, highlighting an indigenous reservoir of beneficial fermenters alongside pathogenic contaminants. An open-source bio-surveillance platform was developed to store, query, and visualise isolate-level risk data in real time. These findings underscore the urgency of standardised hygiene interventions in traditional dairy value chains and establish a digital bio-surveillance framework for food safety monitoring in resource-limited settings.