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Objective

To determine frequency and antibiotic susceptibility patterns of bacterial pathogens from cows with mastitis treated at a private practice during a 2-year period.

Design

Observational study.

Animals

Lactating dairy cows from 47 herds of 40 to 600 cows each.

Procedure

Bacteria isolated from milk samples were identified as coliforms. Staphylococcus spp, or Streptococcus spp, using selective media. Antibiotic susceptibility testing was performed, using the disk diffusion method with the following antibiotics: gentamicin, amikacin sulfate, penicillin G, penicillin G-novobiocin, ampicillin, cephalothin sodium, ticarcillin, ceftiofur, lincomycin, erythromycin, pirlimycin hydrochloride, sulfonamide, tetracycline, and polymyxin B.

Results

Of 354 samples tested, 82 (23.2%) yielded no growth. Of bacteria isolated, 54 (15.3%) were coliforms, 96 (27.1%) were Staphylococcus spp, and 94 (26.6%) were Streptococcus spp. Antibiotic susceptibility testing was performed on 62.4% of all samples cultured. For Staphylococcus isolates, cephalothin was the most effective antibiotic in vitro for which a commercially available preparation exists. Penicillin G-novobiocin was the most effective antibiotic in vitro for Streptococcus isolates. Commercial antibiotic preparations approved for intramammary use were not effective in vitro against coliforms that were found to cause mastitis.

Clinical Implications

Mastitis caused by coliform organisms does not respond to commercial preparations intended for intramammary use; however, it may respond to parenterally administered antibiotics. Mastitis caused by Staphylococcus spp or Streptococcus spp should be treated first with a cephalothin or penicillin G-novobiocin preparation. (J Am Vet Med Assoc 1998; 212:404-406)

Free access
in Journal of the American Veterinary Medical Association
in Journal of the American Veterinary Medical Association
in Journal of the American Veterinary Medical Association
in Journal of the American Veterinary Medical Association

Summary

A total of 21 calves were inoculated IV with 1 of the following isolates of bovine viral diarrhea virus (BVDV); CD87 (n = 10), NY-1 (n = 3), NADL (n = 5), or were sham-inoculated with virus-free medium (n = 3). Subsequent to inoculation, platelet counts were monitored to detect differences between noncytopathic (CD87, NY-1) and cytopathic (NADL) isolates in their ability to induce thrombocytopenia. Platelet count decrease throughout infection was statistically analyzed by comparing the slope of the line drawn from the count on the day of infection to the lowest count achieved by that calf. Significant difference was observed in the CD87-inoculated calves and in the NY-1-inoculated calves, compared with those of the same control group. Significant difference was not observed in the slope of platelet count decrease between the cytopathic NADL-infected calves and control-group calves. The data indicate that noncytopathic BVDV isolates may more easily induce thrombocytopenia than do cytopathic isolates in immune-naive, immunocompetent calves; acute infection with 1 cytopathic BVDV isolate (NADL) did not induce thrombocytopenia. In addition, although each calf seroconverted, virus was rarely isolated from mononuclear cells obtained from calves with cytopathic infections. At some point after infection, virus was always isolated from each of the calves undergoing noncytopathic infections, and occasionally, transient association of noncytopathic BVDV antigen with platelets was observed during these infections.

Free access
in American Journal of Veterinary Research

Summary

The relationship between bovine viral diarrhea virus (bvdv) infection and thrombocytopenia was studied in 18 veal calves experimentally infected with bvdv. All calves were free of bvdv, and 13 calves were free of serum neutralizing antibodies to bvdv before virus inoculation. Calves were inoculated at approximately 10 days of age, and platelet counts were monitored over a period of several weeks. Ten additional calves housed in close proximity were kept as uninoculated controls. A profound decrease in platelet counts by 3 to 11 days after inoculation was seen in all calves that had neutralizing antibody titers < 1:32 before infection. Severe thrombocytopenia (<5,000 platelets/μl) was seen in 12 calves, 11 of which also developed hemorrhages. Necropsy findings in 3 severely thrombocytopenic calves that died included multiple hemorrhages throughout the body. Calves that recovered had increased platelet counts, and in most instances, a corresponding increase in neutralizing antibody titers to bvdv. At 11 days after inoculation, bvdv was detected on platelets by use of immunofluorescence, but evidence of surface-bound immunoglobulin was not found. The results suggest that a nonimmunoglobulin-mediated method of platelet destruction or sequestration develops as a sequela to bvdv infection.

Free access
in Journal of the American Veterinary Medical Association