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inhibatory concentration PBP2a Penicillin-binding protein 2a PFGE Pulsed-field gel electrophoresis PFP Pulsed-field profile a. Microbank, ProLab Diagnostics, Austin, Tex. b. MicroScan Walkaway 40 PC20 gram-positive combo-panel, Dade Behring

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in American Journal of Veterinary Research
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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)

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in Journal of the American Veterinary Medical Association

Findings section that the rabbit had previously responded to treatment that included oral administration of penicillin G potassium. Penicillin had been administered SC in the rabbit.

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in Journal of the American Veterinary Medical Association

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)

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in Journal of the American Veterinary Medical Association

Summary

A longitudinal study was conducted over 2 years to identify types of antibiotics and sulfonamides used in Michigan dairy herds for disease prevention and treatment, to determine patterns of use of antibiotics and sulfonamides by herd size and animal age group, and to determine the influence of veterinary presence during diagnosis on the types of antimicrobials used for disease treatments.

In order of frequency, the most commonly used preventive antibiotic and sulfonamides were penicillins, tetracyclines, aminoglycosides, and cephalosporins, making up over 86% of all antimicrobials used for disease prevention. The most commonly used therapeutic antibiotics and sulfonamides were penicillins, tetracyclines, aminoglycosides, and sulfonamides, making up over 81% of all antimicrobial drugs used for disease treatment. Cows received the greatest number of drugs, followed by calves (cattle from birth to weaning). Young stock (cattle from weaning to first calving) received the lowest number of drugs. All herds had similar patterns of drug use for the 3 age groups, regardless of herd size.

With the exception of polymyxin and chloramphenicol, producers used antibiotics on their own more than with a veterinarian present or on the advice of a veterinarian. Overall, veterinary presence was significantly associated with increased use of tetracyclines, sulfonamides, and nitrofurans, and decreased use of penicillins and aminoglycosides. Implications for drug residue prevention strategies are discussed, with emphasis on the role of the practicing veterinarian.

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in Journal of the American Veterinary Medical Association

Summary

A prospective clinical trial was conducted on 2 large dairies in the San Joaquin Valley of California to determine whether a single intrauterine infusion with procaine penicillin G or oxytetracycline reduced the calving-to-conception interval in cows with endometritis. Cows with endometritis were randomly assigned to a treatment or a control group. The uterus of treated cows on 1 dairy was infused with 0.8 to 1.0 million U of procaine penicillin G in 40 ml of sterile water, and the uterus of treated cows on the other dairy was infused with 500 mg of Oxytetracycline in 20 ml of sterile water, both of which were typical doses used on dairies in the area. A difference was not observed in the cumulative proportion of cows remaining nonpregnant between 87 penicillin-treated and 77 control cows on the 1 dairy (P = 0.356), or between 74 oxytetracycline-treated and 62 control cows on the other dairy (P = 0.174). Results suggest that routine infusion of antibiotics to treat endometritis, as commonly practiced, may not be efficacious.

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in Journal of the American Veterinary Medical Association

Summary

A single preoperative dose of antibiotic proved as effective as a preoperative and 7-day postoperative course in reducing complications following rumenotomy in cattle. Exploratory rumenotomy was performed on 29 healthy Angus steers, which were allotted to the following treatment groups: (1) no antibiotic therapy, (2) single-dose, preoperative, antibiotic prophylaxis, using potassium penicillin G, and (3) preoperative potassium penicillin G prophylaxis, followed by a 7-day postoperative course of procaine penicillin G. Steers receiving antibiotics had significantly greater postoperative feed intake, lower rectal temperatures, and fewer abscesses at the surgical site than those receiving no antibiotics. There was no significant difference between animals receiving a single preoperative dose of antibiotic and those treated for an additional 7 days after surgery. In human medicine, it is generally agreed that a single preoperative dose of antibiotic offers effective prophylaxis. There are few published reports on antimicrobial prophylaxis in the veterinary literature, particularly in regard to large animals. Considering USDA requirements for milk withholding times and withdrawal times prior to slaughter for food animals receiving antibiotics, the findings of this study have medical as well as economic value.

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in Journal of the American Veterinary Medical Association

SUMMARY

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.

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in American Journal of Veterinary Research

Summary

Minimal inhibitory concentration of 42 antimicrobial agents was determined against 57 field strains of Actinobacillus pleuropneumoniae isolated from pigs in Spain. Penicillins, aminoglycosides, and tetracyclines had irregular activity; ticarcillin, tobramycin, and doxycycline were the most active of each group, respectively. Macrolides, vancomycin, dapsone, and tiamulin, to which strains had high rate of resistance, were almost ineffective. Thiamphenicol, colistin, rifampin, fosfomycin, mupirocin, and metronidazole had good activity, with resistance ranging between 0 and 8.8%. Finally, cephalosporins (except cephalexin) and quinolones (especially ciprofloxacin, enrofloxacin, and sparfloxacin) were the most active antibiotics against A pleuropneumoniae.

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in American Journal of Veterinary Research

Objective

To determine whether perioperative antimicrobial prophylaxis would reduce incidence of postoperative infection among dogs undergoing elective orthopedic procedures.

Design

Randomized, controlled, blinded, intention clinical trial.

Animals

Dogs of any breed, sex, or age undergoing elective orthopedic surgery at a veterinary teaching hospital.

Procedures

Dogs were randomly assigned to 1 of 3 groups: treatment with saline solution, treatment with potassium penicillin G, and treatment with cefazolin. Treatments were intended to be administered within 30 minutes prior to surgery; a second dose was administered if surgery lasted > 90 minutes. Dogs were monitored for 10 to 14 days after surgery for evidence of infection.

Results

After the first 112 dogs were enrolled in the study, it was found that infection rate for control dogs (5/32 dogs) was significantly higher than the rate for dogs treated with antimicrobials (3/80 dogs). Therefore, no more dogs were enrolled in the study. A total of 126 dogs completed the study. Monte Carlo simulations indicated that compared with dogs that received antimicrobials prophylactically, dogs that received saline solution developed infections significantly more frequently. Difference in efficacy, however, was not observed between the 2 antimicrobial drugs used.

Conclusions and Clinical Relevance

Results indicated that perioperative antimicrobial prophylaxis decreased postoperative infection rate in dogs undergoing elective orthopedic surgery, compared with infection rate in control dogs. Cefazolin was not more efficacious than potassium penicillin G in these dogs. (J Am Vet Med Assoc 1999;215:212–216)

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in Journal of the American Veterinary Medical Association