Pre-processed bovine milk quality in Trinidad: Prevalence and characteristics of bacterial pathogens and occurrence of antimicrobial residues in milk from collection centres

ABSTRACT

The study was conducted to assess the impact of the changes in the milk collection system in Trinidad (from twice daily collection to once, introduction of chilling facilities to the collection centres and transportation of milk to the processing plant in insulated truck instead of in metal churns at ambient temperature) on the microbial load and antimicrobial residue quality of the milk as well as the temperature and pH of milk, using standard methods. The presence of antimicrobial residues was detected using the Delvo test kit. Of a total of 266 milk samples from churns, the mean ñ sd temperature and log10 ñ sd TAPC per ml was 20.36 ñ 7.91 øC and 6.3 ñ 1.09 respectively. For 20 milk samples from the chillers, the mean temperature and log10 ñ sd TAPC per ml was 15.10 ñ 2.73 øC and 7.04 ñ 0.33 respectively compared with corresponding values for 36 samples collected from the truck, 11.64 ñ 4.22 øC and 7.11 ñ 0.62 respectively (P < 0.05; X2). The mean TAPC, staphylococcal and E. coli counts per ml of milk from churns were significantly (P < 0.05; X2) higher for milk at low temperature (0–20 øC) compared with milk at high temperature (>30 øC). Eight (4.2 per cent) of 192 milk samples tested contained antimicrobial residues. Of 168 S. aureus isolates tested, 24 (14.3 per cent) were enterotoxigenic while 53 (45.3 per cent) of 117 isolates tested exhibited resistance to various antimicrobial agents while of 386 isolates of E. coli tested, 3 (0.8 per cent) were O157 strain and 129 (64.5 per cent) of 200 isolates exhibited resistance to antimicrobial agents. It was concluded that despite the changes, the microbial load of milk was still high suggesting poor sanitary practices at the farm level. The detection of antimicrobial residues agents coupled with toxigenic S. aureus and E. coli isolates could pose health hazards to consumers.