Streptococcal species isolated from dairy cows with clinical mastitis were obtained from mastitis research workers in Florida, Louisiana, New York, Vermont, Washington, and West Virginia. Seventy-one streptococcal isolates were tested, including 39 strains of Streptococcus agalactiae, 21 strains of S dysgalactiae, and 11 strains of S uberis. The minimal inhibitory concentration of erythromycin, lincomycin, oxytetracycline, penicillin, spectinomycin, streptomycin, and tetracycline was determined for each isolate. Differences were not detected among strains with respect to geographic origin. None of the strains was resistant to penicillin. Lincomycin was the next most effective antimicrobial, with only 2 resistant strains of each streptococcal species. There were no differences among the streptococcal species with respect to resistance to either penicillin or lincomycin. Streptococcus uberis was more likely to be resistant to erythromycin than were S agalactiae and S dysgalactiae (P < 0.02). Streptococcus agalactiae and S uberis had similar distributions for resistance to oxytetracycline, tetracycline, spectinomycin, and streptomycin. Strains of S dysgalactiae were more likely to have intermediate resistance to oxytetracycline and streptomycin than were strains of S agalactiae and S uberis, which were highly resistant to oxytetracycline and streptomycin (P < 0.001). Differences were not detected among the streptococcal species with respect to resistance to spectinomycin. Resistance to multiple antimicrobials was observed in all streptococcal species tested. Although S dysgalactiae appeared to have a greater percentage of strains (73%) that were resistant to multiple antimicrobials than did S agalactiae (31%) or S uberis (45%), differences were not statistically significant.

Six primiparous Holstein cows were fed a Se-deficient diet, beginning at least 90 days before their first calving, and 6 other primiparous cows were given the same diet plus a supplement of 2 mg of Se/cow/d as sodium selenite. All cows were fed their diets for the duration of the experimental period. One uninfected quarter of each cow was injected with 25 microgram of Escherichia coli endotoxin at postpartum week 5. Leukocytes were isolated by centrifugation from milk collected at postinjection hour 16. Isolated cells were 92 +/- 3% neutrophils and were incubated with Staphylococcus aureus or E coli in a 1:300 ratio. Phagocytosis and intracellular killing by neutrophils were assessed after 0, 30, 60, and 90 minutes by a fluorochrome assay, using acridine orange. Viability of neutrophils was assessed by use of trypan blue. Superoxide anion production and hydrogen peroxide production by neutrophils also were determined. Cows fed Se-deficient diets had significantly (P < 0.05) lower blood Se concentration and blood glutathione peroxidase activity than cows fed Se-supplemented diets. Selenium status had no effect on the phagocytic capacity of neutrophils. Neutrophils obtained from cows fed Se-supplemented diets killed a significantly (P < 0.05) higher percentage of ingested bacteria than did neutrophils from cows fed the Se-deficient diet. Viability was significantly (P < 0.05) reduced by incubation with S aureus in neutrophils from both groups of cows, with neutrophils from Se-deficient cows having lower viability. Superoxide anion production did not differ significantly between neutrophils from the 2 groups, but extracellular hydrogen peroxide concentration was significantly (P < 0.05) higher in neutrophils harvested from milk of cows fed the Se-deficient diet.