Microbiological Quality of Raw Cow's Milk at Collection Centers in Trinidad

The microbial quality, pH and presence of selected pathogens in milk at eight collection centers in Trinidad were determined. The enterotoxigenicity and susceptibility of Staphylococcus aureus strains to antimicrobial agents and bacteriophages were investigated while the antibiograms and ability of Escherichia coli isolates to agglutinate O157 antiserum were also assessed. Of the 287 milk samples tested, the mean pH was 6.80 ± 0.10 and 207 (72.1%) were California mastitis test (CMT) positive. All (100.0%) milk samples contained S. aureus , and 217 (75.6%) were positive for E. coli . The ranges of mean counts per ml for total aerobic bacteria, S. aureus and E. coli were 3.3 ¥ 10⁶ to 9.8 ¥ 10⁷, 1.4 ¥ 10⁴ to 1.2 ¥ 10⁵ and 4.2 ¥ 10⁴ to 1.6 ¥ 10⁶, respectively. Ninety-three (40.4%) of 230 strains of S. aureus tested were enterotoxigenic producing staphylococcal enterotoxins A, B, C, D or a combination with SEC being predominantly elaborated. Of the 245 strains of S. aureus phage-typed, 123 (50.2%) were susceptible to international phage set (IPS) of bacteriophages. Overall, 49 (49.0%) of 100 strains of S. aureus tested were resistant to 1 or more of the 8 antimicrobial agents with resistance high to penicillin (48.0%), ampicillin (45.0%) and methicillin (21.0%). Among 100 strains of E. coli tested, 98 (98.0%) exhibited resistance to antimicrobial agents with high prevalence of resistance detected for cephalothin (79.0%), ampicillin (73.0%) and streptomycin (47.0%). Thirteen (6.9%) of 188 strains of E. coli agglutinated with O157 antiserum. It was concluded that the presence of some pathogens in milk in fairly high counts coupled with toxigenicity of some strains pose a health hazard to consumers.