RESUMEN
BACKGROUND: Coagulase negative Staphylococcus (CNS) species are currently the most prevalent intra-mammary pathogens causing subclinical mastitis and occasional clinical mastitis or persistent infection in lactating dairy cattle. More than 10 CNS species have been identified, but they are generally managed as one group on most dairies in the United States. However, improved management decisions and treatment outcomes may be achieved with better understanding of the prevalent species, pathogenicity and strain diversity within and across dairies. METHODOLOGY: A total of 604 CNS isolates were cultured from milk samples collected during a dry-cow treatment clinical trial conducted on 6 dairy herds in 4 states in the US. All the study cows were randomized to receive 1 of the 3 different intra-mammary antimicrobial infusions (Quatermaster, Spectramast DC or ToMorrow Dry Cow) at dry-off. Milk samples were collected at dry-off, calving (0-6 days in milk, DIM), post-calving (7-13 DIM) and at mastitis events within the first 100 DIM. The CNS isolates were identified to species level by partial sequencing of the rpoß gene, and genetic relatedness within species was investigated by phylogenetic analysis of the pulse-field gel electrophoresis profiles of the isolates. RESULTS: The major CNS species identified were S. chromogenes (48.3%), S. haemolyticus (17.9%), S. simulans and S. epidermidis (each at 6.5%). Other CNS species identified at lower frequencies included S. hominis, S. auricularis, S. sciuri, S. spp KS-SP, S. capitis, S. cohnii, S. warneri, S. pasteuri, S. xylosus, S. hyicus, S. equorum, S. microti, S. rostri, S. gallinarum, S. saprophyticus and S. succinus. Phylogenetic analyses of the major species types demonstrated an association between genetic relatedness and epidemiological distributions of S. chromogenes, S. simulans, S. haemolyticus and S. auricularis. Additionally, identical strains of S. chromogenes and S. simulans were isolated from the same udder quarter of several cows at consecutive sample stages. The rest of the minor species had no deducible genetic-epidemiological link. DISCUSSION: The observed association between genetic and epidemiological distributions indicated animal-adapted nature of four CNS species, suggesting possible host-adapted and environmental transmission of these species. Multi-stage isolation of the same udder quarter strain was evidence for chronic intra-mammary infection. CONCLUSION: The different CNS species and strains circulating on US dairy herds were genetically diverse. Four species identified were likely udder-adapted pathogens, 2 of which caused persistent infection. Our findings are important in guiding the design of effective mastitis control strategies.
RESUMEN
A simple, cow-side test for the presence of drug residues in live animal fluids would provide useful information for tissue drug residue avoidance programs. This work describes adaptation and evaluation of rapid screening tests to detect drug residues in serum and urine. Medicated heifers had urine, serum, and tissue biopsy samples taken while on drug treatment. Samples were tested by rapid methods and high-performance liquid chromatography (HPLC). The adapted microbial inhibition method, kidney inhibition swab test, was useful in detecting sulfadimethoxine in serum, and its response correlated with the prescribed withdrawal time for the drug, 5 to 6 days posttreatment. The lateral flow screening method for flunixin and beta-lactams, adapted for urine, was useful in predicting flunixin in liver detected by HPLC, 96 h posttreatment. The same adapted methods were not useful to detect ceftiofur in serum or urine due to a lack of sensitivity at the levels of interest. These antemortem screening test studies demonstrated that the method selected, and the sampling matrix chosen (urine or serum), will depend on the drug used and should be based on animal treatment history if available. The live animal tests demonstrated the potential for verification that an individual animal is free of drug residues before sale for human consumption.