Abstract

Sixteen foods borne bacteria were isolated from raw food samples including okro, carrot, spinach, pepper, tomato, onion and cooked food samples (rice, yam, beans, meat and plantain). The isolates were characterized and identified asBacillus brevis, Bacillus congulans, Bacillus polymyxa, Bacillus lentus, Bacillus megaterium, Bacillus subtilis, Acinetobacter spp., Citrobacter freundii,Klebsiella aerogenes, Streptococcus agalactiae, Alcaligenes spp.,Corynebacterium spp., Enterobacter aerogenes, Enterobacter spp. andStaphylococcus epidermidis. These isolates were screened on egg yolk agar for toxigenic properties and thirteen of the sixteen were positive for toxin production while three were negative. Six out of the thirteen toxigenic bacterial were selected for further work. These were; E. coli, K. aerogenes, C. freundii, B. polymyxa, S. epidermidis and E. aerogenes. The effect of pH, thermal treatment and chemical preservatives on the growth rate and toxin elaboration of E. coli, K. aerogenes, C. freundii, B. polymyxa, S. epidermidis and E. aerogenes was studied. It was observed that E. coli had no viable growth until 48 h of incubation, while the other five isolates had visible growth right from the 24 h of incubation. Also E. coli did not produce toxin until the 96^th hour of incubation; K. aerogenesand E. aerogenes were able to produce toxin at 24 h of incubation, while C. freundii, B. polymyxa and S. epidermidis produced toxin at 48 h of incubation. Also, 44°C was not suitable for toxin production. pH 3 and 5 were less favorable for toxin production despite the fact that isolates were able to grow at different temperature and pH ranges. The isolate were more sensitive to sodium metabisulfite than benzoic acid. Also, E. coli and K. aerogenes were able to elaborate toxin in their dormant state with 750 mg of sodium metabisulfite.

Key words: Toxin production, viable growth, raw food sample, cooked food sample, E. coli, K. aerogenes, C. freundii, B. polymyxa, S. epidermidis and E. aerogenes.