Search Results

Abstract

Objective—To determine whether there was any association between results of in vitro antimicrobial susceptibility testing of pathogens isolated from cows with mild or moderate clinical mastitis and outcome of treatment.

Design—Observational study.

Animals—133 cows with mild or moderate mastitis in a single quarter.

Procedure—Cows were treated by means of intramammary infusion of pirlimycin (50 mg) in the affected quarter once daily for 2 days; additional intramammary treatments with the same product were administered if the milk continued to appear abnormal. Duration of treatment and days until clinical cure were recorded. Bacterial isolates were tested for antimicrobial susceptibility by means of a broth micro-dilution technique.

Results—Environmental streptococci, coliforms, and coagulase-negative Staphylococcus spp were the most commonly isolated pathogens. Duration of treatment and days until clinical cure were not significantly different for cows from which pathogens that were susceptible or resistant to pirlimycin were isolated. Bacteriologic cure rates 14 and 21 days after treatment were not significantly different for cows with mastitis caused by susceptible or resistant bacteria. Similar results were found when data only from cows with mastitis caused by gram-positive isolates were analyzed.

Conclusions and Clinical Relevance—In the present study, differences in clinical outcome for cows with mild or moderate mastitis that could be attributed to differences in results of in vitro susceptibility testing were not identified. The use of in vitro susceptibility testing to guide intramammary mastitis treatment cannot be recommended on the basis of results of this study. (J Am Vet Med Assoc 2005;227:1461–1468)

Abstract

Objective—To determine the association between results of in vitro antimicrobial susceptibility tests and outcomes in cows that received intramammary treatment with pirlimycin hydrochloride for subclinical mastitis associated with gram-positive pathogens.

Design—Case-control study.

Animals—132 dairy cows (178 mammary glands with subclinical mastitis caused by 194 pathogen isolates).

Procedures—Cows with positive results for a California mastitis test (CMT) were assigned to receive 50 mg of pirlimycin via intramammary administration into each CMT-positive mammary gland every 24 hours for 2 consecutive days or no treatment. Duplicate milk samples were collected before treatment and approximately 21 days later. Target pathogens included coagulase-negative Staphylococcus spp (n = 118 isolates), Streptococcus spp (28), Staphylococcus aureus (7), and other gram-positive cocci (30). Antimicrobial susceptibilities were determined via broth microdilution.

Results—Overall treatment success rate was 66% (128/194) for both groups. In vitro resistance to pirlimycin ranged from 0% (0/7 isolates of S aureus) to 50% (13/26 isolates of other gram-positive cocci). For the treated group, 62 of 94 (66%) target pathogens were classified as treatment successes and 32 (34%) were classified as failures. Similarly for the control group, 66 of 100 (66%) target pathogens were classified as treatment successes, whereas 34 (34%) were classified as failures.

Conclusions and Clinical Relevance—Many target pathogens from cows with subclinical mastitis were eliminated without treatment, and treatment with pirlimycin did not improve the treatment success rate. Results of in vitro antimicrobial susceptibility tests were not useful as predictors of treatment success following intramammary treatment with pirlimycin.

Abstract

Objective—To determine whether antimicrobial resistance patterns of major mastitis pathogens isolated from milk samples from dairy cows have changed over time.

Design—Retrospective study.

Sample Population—8,905 bacterial isolates obtained from milk samples submitted to the Wisconsin Veterinary Diagnostic Laboratory between January 1994 and June 2001.

Procedure—Antimicrobial susceptibility was determined by means of the Kirby-Bauer disk diffusion method. Logistic regression was used to determine whether percentages of isolates resistant to various antimicrobials changed over time.

Results—For the gram-positive mastitis pathogens, percentages of isolates resistant to various β-lactam antimicrobials did not increase over the course of the study. Percentage of Staphylococcus aureus isolates resistant to penicillin decreased from 49 to 30%; percentage of Streptococcus isolates resistant to penicillin decreased from 6 to 1%. Percentage of isolates resistant to erythromycin increased for S aureus, Escherichia coli, Enterobacter spp, Enterococcus spp, and Pasteurella spp. Percentage of isolates resistant to lincomycin increased for S aureus and Staphylococcus spp. Percentage of coagulase-negative Staphylococcus isolates resistant to pirlimycin increased from 6 to 19%. For several pathogens, percentages of isolates resistant to sulfisoxazole and to trimethoprim-sulfamethoxazole decreased. No pathogens had a significant increase in the percentage of isolates resistant to novobiocin-penicillin.

Conclusions and Clinical Relevance—Results did not indicate a trend toward increased antimicrobial resistance among mastitis pathogens isolated from milk samples from dairy cows between 1994 and 2001. Reduced resistance to β-lactam antimicrobials was identified for several gram-positive mastitis pathogens. (J Am Vet Med Assoc 2003;222:1582–1589)

Abstract

Objective—To evaluate enterotoxin production, enterotoxin gene distribution, and genetic diversity of Staphylococcus aureus in milk obtained from cows with subclinical mastitis.

Sample—Milk samples obtained from 350 cows (1,354 mammary glands) on 11 Wisconsin dairy farms.

Procedures—Of 252 S aureus isolates obtained from 146 cows, 83 isolates (from 66 cows with subclinical mastitis) were compared genotypically by use of pulsed-field gel electrophoresis and via PCR identification of toxic shock syndrome toxin 1 (TSST-1) and classical S aureus enterotoxin genes (sea, seb, sec, sed, and see).

Results—Among the 83 S aureus isolates, ≥ 1 enterotoxin genes were identified in 8 (9.6%). Enterotoxin gene distribution was as follows: TSST-1, 7 isolates (8.4%); sec, 5 isolates (6.0%); and sed, 2 isolates (2.4%). Enterotoxin genes sea, seb, and see were not identified. Twelve pulsotypes and 5 subtypes were identified among the 83 isolates; 5 of the 12 pulsotypes were represented by only 1 isolate. In cows of 1 herd, only a single S aureus pulsotype was detected; in cows on most other farms, a variety of pulsotypes were identified. One pulsotype was recovered from 4 farms (n = 23 cows) and another from 5 other farms (16). Isolates with an enterotoxin gene were represented by 6 pulsotypes.

Conclusions and Clinical Relevance—S aureus classical enterotoxins and TSST-1 were rarely recovered from milk samples obtained from cows with subclinical mastitis in Wisconsin. Diverse pulsotypes of S aureus were detected within and among farms, indicating that different strains of S aureus cause subclinical mastitis in dairy cows.

Abstract

Objective—To identify management factors associated with veterinary usage by organic and conventional dairy farms.

Design—Prospective case-control study.

Sample—292 farms.

Procedures—Organic farms in New York, Oregon, and Wisconsin were matched to conventional farms on the basis of location and herd size. During a single herd visit, a questionnaire was administered, information about animal disease incidence and number of veterinarian visits in the preceding 60 days was collected, and forms to record similar information during the 60 days after the visit were left for the herd manager to complete. For analysis, conventional herds were classified as either grazing or nongrazing. Multiple correspondence analysis was used to assess relationships among management factors and selected outcomes for frequency of veterinary usage.

Results—Intensive management practices were closely associated with frequent veterinary usage. Generally, organic management practices were associated with less frequent veterinary usage than were conventional management practices. Conventional grazing practices were associated with intermediate veterinary usage (more than organic practices but less than intensive practices), whereas conventional nongrazing practices were associated with frequent veterinary usage. Cost of routinely scheduled veterinarian visits/45 kg (100 lb) of milk produced/y was greater for small farms than that for large farms.

Conclusions and Clinical Relevance—Results suggested that management intensiveness was more closely associated with frequency of veterinary usage than was organic status; therefore, veterinarians should characterize farms by factors other than organic status when investigating which farms are most likely to use their services. Economic factors substantially affected routine veterinary usage on small farms.

Abstract

Objective—To compare the minimum inhibitory concentration (MIC) of cephapirin and ceftiofur with MICs of their active metabolites (desacetylcephapirin and desfuroylceftiofur) for selected mastitis pathogens.

Sample—488 mastitis pathogen isolates from clinically and subclinically affected cows in commercial dairy herds in Wisconsin.

Procedures—Agar dilution was used to determine MICs for Staphylococcus aureus (n = 98), coagulase-negative staphylococci (99), Streptococcus dysgalactiae (97), Streptococcus uberis (96), and Escherichia coli (98).

Results—All S aureus isolates were susceptible to cephapirin and ceftiofur. Most coagulase-negative staphylococci were susceptible to cephapirin and ceftiofur. For E coli, 50 (51.0%; cephapirin) and 93 (94.95%; ceftiofur) isolates were susceptible to the parent compounds, but 88 (89.8%) were not inhibited at the maximum concentration of desacetylcephapirin. All S dysgalactiae isolates were susceptible to ceftiofur and cephapirin, and consistent MICs were obtained for all compounds. Most S uberis isolates were susceptible to cephapirin and ceftiofur. Of 98 S aureus isolates classified as susceptible to ceftiofur, 42 (42.9%) and 51 (52%) were categorized as intermediate or resistant to desfuroylceftiofur, respectively. For 99 coagulase-negative staphylococci classified as susceptible to ceftiofur, 45 (45.5%) and 17 (17.2%) isolates were categorized as intermediate or resistant to desfuroylceftiofur, respectively. For all staphylococci and streptococci, 100% agreement in cross-classified susceptibility outcomes was detected between cephapirin and desacetylcephapirin. No E coli isolates were classified as susceptible to desacetylcephapirin.

Conclusions and Clinical Relevance—Differences in inhibition between parent compounds and their active metabolites may be responsible for some of the variation between clinical outcomes and results of in vitro susceptibility tests.

Abstract

Abstract

Objective—To describe the occurrence of fecal shedding, persistence of shedding over time, and serogroup classification of Salmonella spp on a large number of dairy farms of various sizes.

Design—Longitudinal study.

Sample Population—22,417 fecal samples from cattle and 4,570 samples from the farm environment on 110 organic and conventional dairy farms in Minnesota, Wisconsin, Michigan, and New York.

Procedure—5 visits were made to each farm at 2-month intervals from August 2000 to October 2001. Fecal samples from healthy cows, calves, and other targeted cattle groups and samples from bulk tank milk, milk line filters, water, feed sources, and pen floors were collected at each visit. Bacterial culture was performed at 1 laboratory.

Results—Salmonella spp were isolated from 4.8% of fecal samples and 5.9% of environmental samples; 92.7% of farms had at least 1 Salmonella-positive sample. The 75th percentile for median within-herd prevalence of Salmonella spp in cattle for 5 sampling visits to a given farm was 2.0% and for maximum within-herd prevalence of Salmonella spp was 13.6%. Farms with a median within-herd prevalence of Salmonella spp of ≥ 2.0% accounted for 76.3% of Salmonella-positive samples. There was no significant difference in the prevalence of Salmonella spp between conventional and organic farms. Seasonal differences in Salmonella shedding were observed. More farms had at least 1 serogroup B isolate than any other serogroup, whereas serogroup E1 was the most common among all Salmonella-positive samples. More than 1 serogroup was isolated on 76.4% of Salmonella-positive farms.

Conclusions and Clinical Relevance—Salmonella spp were isolated from > 90% of dairy farms; however, 25% of farms accounted for > 75% of Salmonella-positive samples. This information is critical for the direction of intervention strategies to decrease the prevalence of Salmonella spp on dairy farms. (J Am Vet Med Assoc 2004;225:567–573)

Abstract

Objective—To describe antimicrobial susceptibility patterns in Campylobacter spp isolated from dairy cattle and farms managed organically and conventionally in the midwestern and northeastern United States.

Design—Longitudinal study.

Sample Population—128 farms.

Procedure—Samples and data were collected every 2 months from August 2000 to October 2001. Fecal samples were collected from calves and cows. Milk samples were obtained from the bulk tank and milk line filters. Environmental samples were obtained from a water source, feed bunks of lactating cows, and cattle housing areas. Campylobacter identification and antimicrobial susceptibility testing were performed at a central laboratory by use of microbroth dilution with 2 customized antimicrobial susceptibility panels.

Results—460 and 1,570 Campylobacter isolates were obtained from organic and conventional dairy farms, respectively. Most isolates from both farm types were susceptible to most antimicrobial agents tested, and antimicrobial susceptibility of conventional dairy isolates was decreased, compared with organic dairy isolates. Low proportions of isolates resistant to ampicillin (< 10%) and moderate proportions resistant (30% to 60%) to kanamycin, sulfamethoxazole, and tetracycline were observed on both farm types. The proportion of isolates resistant to tetracycline was higher for conventional than organic farms.

Conclusions and Clinical Relevance—Campylobacter isolates from dairy cattle and farms managed organically and conventionally had similar patterns of antimicrobial resistance; the proportion of resistant isolates was higher for conventional than organic farms.