HOME HELP FEEDBACK SUBSCRIPTIONS ARCHIVE SEARCH TABLE OF CONTENTS		QUICK SEARCH:   [advanced] Author: Keyword(s): Year:  Vol:  Page:

This Article Full Text Full Text (PDF) Interpretive Summary Alert me when this article is cited Alert me if a correction is posted Services Similar articles in this journal Similar articles in PubMed Alert me to new issues of the journal Download to citation manager Citing Articles Citing Articles via Google Scholar Google Scholar Articles by Kirk, J. H. Articles by Cullor, J. S. Search for Related Content PubMed PubMed Citation Articles by Kirk, J. H. Articles by Cullor, J. S.

Association of Minimum Inhibitory Concentration Cluster Patterns with Dairy Management Practices for Environmental Bacteria Isolated from Bulk Tank Milk^*

¹ Veterinary Medicine Extension, and
² Department of Population Health and Reproduction, School of Veterinary Medicine, University of California Davis, Tulare 93274
³ University of California Cooperative Extension, Fresno and Madera Counties, Fresno 93702
⁴ University of California Cooperative Extension, Kings County, Hanford 93230
⁵ University of California Cooperative Extension, Merced County, Merced 95340
⁶ University of California Cooperative Extension, Glenn County, Orland 95963
⁷ University of California Cooperative Extension, San Bernardino County, San Bernardino 92415

Corresponding author: E. R. Atwill; e-mail: ratwill{at}vmtrc.ucdavis.edu.

Environmental bacteria have emerged over the past few years to become significant causes of mastitis. Bacteria in this group are often reported by practicing veterinarians to be increasingly resistant to intramammary therapy and responsible for elevated bulk tank somatic cell counts. The purpose of this study was to determine the extent of association of the minimum inhibitory concentrations for selected antimicrobial agents with environmental bacteria isolated from bulk tank milk on California dairies and their housing facilities, husbandry practices, and antimicrobic-use strategies. Bulk tank milk samples were collected from 2 dairy cooperatives that had their milk cultured at the Milk Quality Laboratory, University of California Davis, Veterinary Medicine Teaching and Research Center in Tulare, CA. Samples were collected from July 2001 through March 2002 on 88 d; and 404 environmental bacteria isolated from 93 dairies were found. Minimum inhibitory concentrations were determined on 337 of the isolates for 10 antimicrobial agents. Cluster analysis was performed on the minimum inhibitory concentration values for each organism, and 4 antimicrobial clusters with varying degrees of resistance were found.

A 69-question survey questionnaire was completed on-farm for 49 of the 73 dairies that had at least 3 environmental bacterial isolates. The questionnaire sought information on housing facilities, milking management, mastitis prevention, antimicrobial usage strategies, and owner/veterinary involvement in disease control and prevention. Multinomial logistic regression analysis found significant associations between the antimicrobial agent-resistance cluster groups and some of the housing and bedding practices, failure to dry udders before milking, and antimicrobial treatment of nonmastitis conditions. No association was noted for antimicrobial agent treatment of mastitis and the resistance cluster patterns.

Key Words: minimum inhibitory concentration • cluster pattern • environmental bacteria • bulk tank milk

Abbreviation key: MIC₉₀ = MIC for 90% of isolates tested, MQL = Milk Quality Laboratory, RR = relative risk.