Bacteriological quality and associated public health risk of pre-processed bovine milk in Trinidad

The bacteriological quality of pre-processed raw milk originating from all 16 milk collection centres in Trinidad was evaluated. The mean total aerobic counts for bacteria, Staphylococcus aureus and Escherichia coli were determined. The pH and presence of somatic cells in milk were also determined. Of the 507 milk samples collected, 454 (89.5%) were California mastitis test (CMT)-positive and the mean pH was 6.50 +/- 0.13. The total aerobic plate count per ml was generally high for all samples ranging from 5.8 x 10(5) +/- 3.1 x 10(5) to 5.7 x 10(8) +/- 1.5 x 10(9). S. aureus was isolated from 478 (94.3%) samples and the mean counts per ml ranged from 1.5 x 10(5) +/- 1.1 x 10(5) to 9.4 x 10(5) +/- 1.3 x 10(6). Nine (7.7%) of 117 strains of S. aureus produced staphylococcal enterotoxins A(SEA), B(SEB), D(SED) or a combination. E. coli was isolated from 105 (20.7%) samples and the mean counts per ml ranged from 6.6 x 10(2) +/- 1.1 x 10(2) to 4.0 x 10(5) +/- 4.6 x 10(5). Twenty-five (23.6%) of the 106 strains of E. coli tested produced verocytotoxin (VT) but none was positive for heat-labile (LT) toxin. It was concluded that pre-processed milk in Trinidad is of poor bacteriological quality. The detection of high counts of S. aureus in milk with some producing heat stable enterotoxins, coupled with the isolation of some verocytotoxigenic E. coli, are of public health significance to consumers.