Phenotypic and Genotypic Characterization of Histamine-producing Bacillus Species and Enterobacter cloacae Isolated from Fermented African Locust Beans in Enugu State, Nigeria

Abstract

Bacillus and Enterobacter species contaminate many types of food products. This study aimed to determine the prevalence, histamine-producing ability and antibiotic resistance profiles of Bacillus and Enterobacter species in African locust beans in Enugu State, Nigeria. One hundred and fifty fermented locust bean samples were used in this study. Bacillus and Enterobacter species were isolated and confirmed by molecular method and subsequently screened for histamine production. Presence of histamine in the fermented samples was screened for, using HPLC. The isolates were further subjected to antibiotic sensitivity tests using appropriate methods. PCR techniques were used to dectect virulence factors in the isolates. Seventy (48.7%) of the 150 samples screened harbours Bacillus species out of which 51, belonging to the strains:1. anthracis KPRR6, B. subtilis RO-NN-1, B.subtilis 557and B. subtilis J732 and Enterobacter cloacae JL1112 were histamine producers. The susceptibility patterns show that more than 70% of the Bacillus strains were resistant to at least 50% of the antibiotics used while sensitivity levels were less than 20% in more than 90% of the strains. Gene encoding virulence factor: nheA gene  in Bacillus and Gaplley ProofapC gene in Enterobacter  were detected at 480bp and 200bp  respectively. The high prevalence of histamine producing, multidrug resistant Bacillus and Enterobacter strains, with virulence factor gene, makes consumption of traditionally fermented locust bean unsafe. Deliberate efforts to select appropriate fermenting strains and proper regulation of fermentation conditions are therefore necessary to improve the safety of the product.