The prevalence and characteristics of Staphylococcus aureus strains isolated from bulk and composite milk and from cattle handlers on dairy farms in Trinidad were determined. S. aureus strains were isolated from all 175 bulk milk samples tested (100%) while 280 of 287 composite milk samples (97.6%) yielded S. aureus. The mean counts of S. aureus in bulk milk ranged from 5.9 x 10(3) to 1.2 x 10(5) CFU/ml compared with mean S. aureus counts in composite milk which ranged from 2.4 x 10(3) to 3.0 x 10(4) CFU/ml. Of the 105 strains of S. aureus from bulk milk tested, 45 (42.9%) were enterotoxigenic elaborating staphylococcal enterotoxin A (SEA), SEB, SEC, SED, or a combination compared to 69 of 146 strains (47.3%) recovered from composite milk which were enterotoxigenic, but the difference was not statistically significant (P > = 0.05; chi 2). Twenty-two of 42 bulk milk samples containing enterotoxigenic S. aureus (52.4%) had counts of the organism which exceeded 10(4) CFU/ml. For S. aureus strains isolated from cattle handlers, 66 of 146 (45.2%) were enterotoxigenic. Prevalence of resistance to nine antimicrobial agents tested was 18.7% and 12.9% among bulk milk and composite milk isolates, respectively, compared to 49.3% and 69.5%. among isolates from human anterior nares and hand swabs, respectively. Resistance to ampicillin and penicillin was highest among both milk (12.2%) and human (53.6%) isolates of S. aureus, and the difference was statistically significant (P < or = 0.001; chi 2). It was concluded that bulk milk containing relatively high counts of enterotoxigenic S. aureus may constitute a health hazard to consumers.

The prevalence, counts, and characteristics of Escherichia coli isolated from bulk milk, composite milk, and feces of dairy cows in eight milking centers were determined. The microbial quality of water used during milking was also investigated. Of a total of 175 bulk milk samples studied, 83 (47.4%) contained E. coli compared to only 14 (4.9%) of 287 composite milk samples and the difference was statistically significant (P ≤ 0.001; χ2). The ranges in mean counts of E. coli per milliliter of bulk milk and composite milk were 8.4 × 103 to 2.0 × 105 and 2.1 × 101 to 2.0 × 102, respectively. The prevalences and mean counts of E. coli and mean pH values for bulk milk from farms with and without subclinically mastitic cows were not significantly different (P ≥ 0.05; χ2). A total of 204 (65.2%) of 313 fecal samples of dairy cows were positive for E. coli. Of the samples of water used during milking collected from 171 dairy farms, 80 (46.8%) were free of coliforms while 59 (34.5%), 12 (7.0%), and 8 (4.7%) had ranges of coliform counts per 100 ml of 1 to 50, 51 to 100, and over 250, respectively. Twenty-six (27.7%) and 17 (18.5%) of 94 strains of E. coli isolated from bulk milk were enteropathogenic E. coli (EPEC) and verocytotoxigenic E. coli (VTEC) strains, respectively. Compared with 204 fecal strains of E. coli, 16 (7.8%) and 68 (35.6%) were EPEC and VTEC strains, respectively, and the differences were statistically significant (P ≤ 0.01; χ2). Similarly, the difference in prevalence of resistance to one or more of nine antimicrobial agents between bulk milk isolates (69.6%) and fecal isolates (25.9%) was statistically significant (P ≤ 0.001; χ2), and resistance to ampicillin was the most prevalent type of resistance for strains of E. coli from bulk milk isolates. It was concluded that the relatively high counts of toxigenic E. coli in bulk milk originating from dairy farms in Trinidad could pose a health risk to consumers. The poor microbial quality of water used on farms may be an important source of contamination of milk.

A cross-sectional study was conducted on dairy farms in eight milking centres in Trinidad to determine the prevalence of risk factors for mastitis and to assess their relationship to occurrence of subclinical mastitis. The California mastitis test (CMT) was used to determine the prevalence of subclinical mastitis by estimating the somatic cell counts in bulk and composite milk. Of a total of 177 dairy farms studied, 121 (68.4%), 39 (22.0%) and 17 (9.6%) practised semi-intensive, extensive and intensive management systems, respectively. A total of 129 (72.9%), 37 (20.9%) and 11 (6.2%) farms milked cows in parlours, stanchions and pasture/out-on-field, respectively. Based on sanitary practices, 40 (22.6%), 123 (69.5%), and 14 (7.9%) farms were classified as good, fair, and poor, respectively, while 76 (42.9%) and 60 (33.9%) farms reported to rarely experience and frequently experience water shortages, respectively. Amongst the 177 farms, only seven (4.0%) used machine-milking primarily, 152 (85.9%) screened for mastitis as a routine, 18 (10.2%) teat dipped, and 49 (27.7%) practised dry cow therapy. To detect mastitis, of 152 farms involved, 20 (13.2%) used the strip cup while only two (1.3%) employed the CMT. Pipe-borne water delivered directly from the hose was the only source of water to 91 (51.4%) farms while seven (4.0%) and eight (4.5%) farms used only well and surface water (ponds and rivers), respectively. Based on bulk milk samples, the farm prevalence of subclinical mastitis was 60.5% (107 of 177) with a range from 33.3% (centre 5H) to 100.0% (centre 2B). The difference was statistically significant (P < 0.01; chi 2). However, using composite milk, the farm prevalence of subclinical mastitis was 52.5% (93 of 177) with a range from 21.2% (centre 5H) to 92.9% (centre 2B) and again, the difference in prevalence was statistically significant (P < 0.001; chi 2). Subclinical mastitis was detected in 150 (45.0%) of 333 lactating cows screened and the range of prevalence was from 17.9% (centre 5H) to 56.3% (centre 1C). The difference was statistically significant (P < 0.001; chi 2). Of a total of 14 risk factors for mastitis studied which were related to animal husbandry, personnel, mastitis control and water, only two, the herd size and practice of dry cow therapy were significantly (P < 0.05; chi 2) associated with subclinical mastitis. It was concluded that the high prevalence of subclinical mastitis in Trinidad dairy herds could significantly reduce milk production with associated economic loss. Although a majority of the risk factors studied were not found to be significantly associated with the occurrence of subclinical mastitis possibly due to confounding factors, the need to eliminate or reduce these risk factors cannot be over-emphasized.

The susceptibility of .\: aurws strains isolatcd from milk and human handlers in dairy farms in Trinidad to bacteriophages was determined. O f the 110 strains isolated from bulk milk, 73 (66.4 Yo) were typable cithcr at routine test dilution (RTD) or 100-RIY1' compared to 108 (72.5 'Yo) of 149 strains from compositc milk sensitive but the difference was not statistically significant ( l ' > 0.05; x'). Strains of .% uurezis from human handlers had significantly ( I ' d 0.05; x2) lower sensitivity, with only 90 (59.6%) of 151 strains typable. Phages in various groups were predominantly more active on both milk isolates, 54.1 '%I (98 of 181) and human strains, 73.3 "/ n (66 of 90). Phage 42D alone lysed 22 (12.2 '!I) hut with other phages typed 90 (49.7'51) o f 181 t)Tpable strains from milk compared to a lytic activity of only 1.1 "/ o (1 of 90) alone and 35 (38.9 Yo) with other phages for strains isolated from human handlers. The differences were however not statistically significant (r, 2 0.05; x'). Relatedness of .i: uureus strains isolated from bulk milk, composite milk and human handlers o n each farm was demonstrated in 21 (46.7 ' / n) of 45 dairy farms using the phage patterns detected. Similarly, the relatedness of .C aureus strains isolated from the anterior narcs and hands o f each human milker was dctccted on 10 (35.7 %I) of 28 dairy farms studied.It was concluded that J aureu.r strains from human milkers contaminated both composite and bulk milk o n the farms studied while bovine strains of S. aureus were also acquired by humans during milking.

La prévalence de Listeria, Salmonella, Campylobacter, Yersinia et Cryptosporidium dans du lait en vrac, les matières fécales des vaches laitières et des effluents à lait des fermes laitières de l'île de la Trinité, a été evaluée. Des 177 échantillons de lait en vrac testés, 3 (1,7 %), 3 (1,7 %) et 2 (1,2 %) étaient positifs respectivement pour Listeria monocytogenes, Salmonella spp. et Yersinia enterocolitica mais négatifs pour Campylobacter spp. et Cryptosporidium spp. Des 333 échantillons fécaux testés, L. monocytogenes, Campylobacter spp. et Cryptosporidium spp. étaient présents dans respectivement 11 (3,3 %), 19 (5,7 %) et 7 (2,1 %) des cas. Ces taux étaient significativement (P < 0,05; chi2) plus élevés, que le taux de détection (0 %) pour Yersinia spp. Salmonella spp. a été detectée dans 3 (0,9 %) échantillons fécaux. Des 168 échantillons prélevés des effluents à lait, Campylobacter spp. était présent dans 7 (4,2 %) échantillons alors que Salmonella spp. l'était dans seulement 1 (0,6 %) échantillon. Aucun échantillon n'était positif pour Yersinia spp. et Listeria spp. (différence significative, P<= 0,05; chi2). En conclusion, les cinq espèces entero-pathogènes testées étaient présentes dans les fermes laitières de l'île de la Trinité.