Incidence and bacterial load of vegetative Bacillus species in dried milk-based products sold in Upper Egypt

Abstract

Bacillus spp. are foodborne pathogens important in food contamination, especially in dried milk products. They are associated with foodborne outbreaks, spoilage of dairy products (sweet curdling and bitterness), and bovine mastitis. This study investigated the contamination rate of Bacillus spp. in a total of 105 samples of the dried milk products kishk, Cerelac and whole milk powder, marketed in Assiut city, Upper Egypt. The identification of the Bacillus spp. strains was completed using conventional biochemical methods and PCR protocols for the confirmation of isolates. Bacillus spp. were isolated from 57 out of 105 (54%) [95% CI: 44.6-64.0%] of the examined samples at levels of up to 7.7 log10 cfu/g. The prevalence of Bacillus spp. was significantly (P<0.05) higher in kishk (74%) than in the other food categories with a mean count of 4.04±0.49 log10 cfu/g. Regarding the species of Bacillus detected, 39.05% of the examined samples contained B. cereus, 8.57% contained B. subtilis, 2.86%: B. pumilus, another 2.86%: B. megatrium and 0.95%: B. licheniformis. B. cereus was isolated from 18 (51.43%) of the kishk samples, 9 (25.71%) of the Cerelac samples and 14 (40%) of the whole milk powder samples. Out of the 41 B. cereus strains previously identified by biochemical tests, 19 (46.34%) isolates were also confirmed using PCR (61.11%, 42.86% and 22.22% for kishk, whole milk powder and Cerelac, respectively). In conclusion, incorporating preventive measures to reduce bacterial contamination in the Egyptian dairy environment are warranted in order to avoid the contamination of milk products with these life-threatening pathogens.