Longitudinal Analysis of the Microbiological Quality of Raw Cow's Milk Samples Collected from Three Small Family Dairy Farms in Mexico over a 2-Year Period.

In Mexico, the total milk production that family dairy farms (FDF) contribute is ca. 35%, but this milk is not evaluated for microbiological quality. Forty percent of the milk and dairy products consumed by Mexicans is unpasteurized. In total, 24 raw cow's milk samples from three FDF (one sample per each season from each FDF for two sequent years) were characterized for the presence of food quality indicator organisms, and spp., by standard procedures. presence was also evaluated by a direct count method and diarrheagenic (DEC) by molecular methods. On the basis of Mexican guidelines for raw milk entering production, 42% of samples exceeded the aerobic mesophilic bacteria limits. A total of 83% raw milk samples were positive for total coliforms, 54% for fecal coliforms, and 46% for . Forty-three isolates were selected and characterized for the presence of 11 DEC loci; of theses, 40 isolates were negative for all DEC loci, and 3 isolates, all collected from the same sample, were Shiga toxin 2 () positive and O157 antigen negative, and one isolate was resistant to 6 of the 16 antibiotics tested. None of the 24 raw milk samples were positive for or staphylococcal enterotoxin. was isolated from nine samples, of which only three samples harbored resistant isolates. From three samples, four nontuberculous mycobacterial isolates were recovered ( and two ). All four isolates produced biofilm and had sliding motility, and three isolates ( and two ) were resistant to the two antibiotics tested (clarithromycin and linezolid). FDF provide raw milk to a large proportion of the Mexican population, but its consumption could be harmful to health, emphasizing the need to implement national microbiological quality guidelines for raw milk intended for direct human consumption.