Microbial composition, including the incidence of pathogens, of goat milk from the Bergamo region of Italy during a lactation year

Abstract

Sixty samples of raw goat milk intended for Caprino cheese-making were collected from ten farms in the Bergamo area over a 6-month period. Analyses of main microbial groups, somatic cell count (SCC) and pH were performed to determine the effect of origin (farm) and lactation period (April – September) on microbial composition and the incidence of pathogens in milk. Overall mean values were: standard plate count (SPC), 5.0×104 cfu/ml; yeasts, 2.5×102 cfu/ml; coliforms, 9.1×102 cfu/ml; Escherichia coli, 2.9 cells/ml; enterococci, 1.1×102 cfu/ml; lactococci, 3.4×103 cfu/ml; lactobacilli, 3.0×103 cfu/ml; halotolerant bacteria, 8.2×103 cfu/ml; spores of mesophilic aerobic bacteria, 11 cfu/ml; SSC, 9.9×105 cells/ml; pH, 6.63. Moulds and spores of sulphite-reducing clostridia were found intermittently. Neither Salmonella spp. nor Listeria monocytogenes was detected, while Esch. coli O157[ratio ]H7 was isolated from one milk sample (an incidence of 1.7%). Staphylococcus aureus was discovered at a level >102 cfu/ml in 26 samples (43%) with an overall mean of 1.2×103 cfu/ml, whereas coagulase-negative staphylococci were found in 54 samples (90%) with an overall mean of 1.3×103 cfu/ml. Of Staph. aureus strains, 23% proved to be enterotoxinogenic with a prevalence of enterotoxin C producers. Staph. caprae was the coagulase-negative species most frequently isolated; none of the coagulase-negative staphylococci strains synthesized any of the enterotoxins tested for.Sample source was the major factor affecting the microbial composition of goat milk: significant differences (P<0.01) were observed among samples from different farms for SPC, coliforms, lactococci, lactobacilli and halotolerant bacteria. Period of lactation had a significant effect (P<0.025) on SCC and pH. SPC correlated well with coliforms, lactococci and lactobacilli; SSC did not reveal positive interactions with any microbial groups or pH.