Abstract

The likelihood of contamination and spread of pathogenic bacteria increases when infant foods are consumed without adequate heating, which helps to effectively control or eliminate potentially harmful bacteria that might cause food-borne illnesses. Food-borne pathogens encounter multiple obstacles such as acidic conditions in the stomach and bile in the small intestine, which serves as a protective mechanism against infections in humans. The aim of this study was to determine the acid, bile salt, thermotolerance and antibiotic susceptibility pattern of Enterobacteriaceae isolates of infant food origin. Thirty Enterobacteriaceae isolates of infant food origin were used in this study. The isolates were screened for acid, bile salt and thermotolerance. Antibiotic sensitivity test was done using the Kirby-Bauer disc diffusion method and multiple antibiotic resistance index was evaluated. Thereafter, molecular techniques were used to carry out the plasmid profiling of the isolates with the highest MAR index. Results of the acid tolerance assay revealed that Raoultella ornithinolytica and Cronobacter sakazakii recorded highest viabilities of 89.40% and 84.41% at pH 4.5 and 3.0 respectively, while all isolates showed bile salt tolerance ranging from 84% to 99.32%. Thermotolerance studies showed that Proteus mirabilis (6.64 min) and Klebsiella spp. (5.70 min) had the highest D-values at 45℃ and 60℃ respectively. All isolates recorded MAR index (0.24 – 0.60) higher than the permissible limit of 0.20. The presence of multiple antibiotic-resistant bacteria isolates with a high level of tolerance to heat, acid and bile salt, in food products intended for infant consumption is of significant health concern.

Keywords: Acid and bile salt tolerance, Antibiotic susceptibility profile, Cronobacter sakazakii, Infant food, Thermotolerance, Raoultella ornithinolytica