This study was conducted to investigate the demography, management, and production practices on layer chicken farms in Trinidad and Tobago, Grenada, and St. Lucia and the frequency of risk factors for Salmonella infection. The frequency of isolation of Salmonella from the layer farm environment, eggs, feeds, hatchery, and imported day-old chicks was determined using standard methods. Of the eight risk factors (farm size, age group of layers, source of day-old chicks, vaccination, sanitation practices, biosecurity measures, presence of pests, and previous disease outbreaks) for Salmonella infection investigated, farm size was the only risk factor significantly associated (P = 0.031) with the prevalence of Salmonella; 77.8% of large farms were positive for this pathogen compared with 33.3 and 26.1% of medium and small farms, respectively. The overall isolation rate of Salmonella from 35 layer farms was 40.0%. Salmonella was isolated at a significantly higher rate (P < 0.05) from farm environments than from the cloacae. Only in Trinidad and Tobago did feeds (6.5% of samples) and pooled egg contents (12.5% of samples) yield Salmonella; however, all egg samples from hotels, hatcheries, and airports in this country were negative. Salmonella Anatum, Salmonella group C, and Salmonella Kentucky were the predominant serotypes in Trinidad and Tobago, Grenada, and St. Lucia, respectively. Although Salmonella infections were found in layer birds sampled, table eggs appear to pose minimal risk to consumers. However, the detection of Salmonella -contaminated farm environments and feeds cannot be ignored. Only 2.9% of the isolates belonged to Salmonella Enteritidis, a finding that may reflect the impact of changes in farm management and poultry production in the region.

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.

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.

This investigation determined the frequency of resistance of 84 isolates of Salmonella comprising 14 serotypes recovered from layer farms in three Caribbean countries (Trinidad and Tobago, Grenada, and St. Lucia) to eight antimicrobial agents, using the disc diffusion method. Resistance among isolates of Salmonella was related to the country of recovery, type of sample, size of layer farms, and isolate serotype. Overall, all (100.0%) of the isolates exhibited resistance to one or more of seven antimicrobial agents tested, and all were susceptible to chloramphenicol. The resistance detected ranged from 11.9% to sulphamethoxazole-trimethoprim (SXT) to 100.0% to erythromycin. The difference was, however, not statistically significant (P = 0.23). Across countries, for types of samples that yielded Salmonella, significant differences in frequency of resistance were detected only to SXT (P = 0.002) in Trinidad and Tobago and to gentamycin (P = 0.027) in St. Lucia. For the three countries, the frequency of resistance to antimicrobial agents was significantly different for ampicillin (P = 0.001) and SXT (P = 0.032). A total of 83 (98.8%) of the 84 isolates exhibited 39 multidrug resistance patterns. Farm size significantly (P = 0.032) affected the frequency of resistance to kanamycin across the countries. Overall, among the 14 serotypes of Salmonella tested, significant (P < 0.05) differences in frequency of resistance were detected to kanamycin, ampicillin, and SXT. Results suggest that the relatively high frequency of resistance to six of the antimicrobial agents (erythromycin, streptomycin, gentamycin, kanamycin, ampicillin, and tetracycline) tested and the multidrug resistance detected may pose prophylactic and therapeutic concerns for chicken layer farms in the three countries studied.