Aerobic Mesophilic Bacteria Associated With Irish Potato (Solanum Tuberosum L.) Spoilage and Their Susceptibility Pattern to Lactic Acid Bacteria and Antibiotics.

Abstract

A total of 15 samples of spoilt Irish potatoes (Solanum tuberosum L.) were collected from five grocery shops in Ile-Ife, Osun State, Nigeria and were analysed for aerobic mesophilic bacterial load. The isolated aerobic mesophilic bacteria were phenotypically characterized by biochemical tests and their susceptibility to antibiotics was assessed. In addition, lactic acid bacteria (Lactobacillus casei, Enterococcus faecalis and Lactobacillus cellobiosus) previously isolated from yoghurt showing inhibitory activities against indicator organisms were screened for antimicrobial activities against the isolated spoilage bacteria. The population of aerobic mesophilic bacteria ranged from 5.18 7.74 log c.f.u g^-1 . A total of five strains of bacteria were isolated and identified as Bacillus sp. (A₁ ), Bacillus sp. (B₁ ), Bacillus sp. (B₂), Erwinia chrysanthemi and Pseudomonas sp. The isolated bacterial strains showed multiple antibiotics resistance. Of significant note is the high multiple resistance pattern of Bacillus sp. strain B2 which showed resistance to five out of the eight antibiotics tested. The multiple antibiotic resistance (MAR) index of the isolated bacterial strains ranged from 0.4 to 0.6. Of the lactic acid bacteria screened, only Enterococcus faecalis showed inhibitory activity due to the effect of organic acid against Erwinia sp. and Bacillus sp. (A₁ ). The results indicated the high prevalence of antibiotic resistant strains associated with the spoilage of Irish potato.

Key words: Irish Potato, Aerobic Mesophilic Bacteria, Antimicrobial Agents, Lactic Acid Bacteria,