Evaluation of the Minnesota Easy Culture System II Bi-Plate and Tri-Plate for identification of common mastitis pathogens in milk

Abstract

The objective of this study was to validate use of the Minnesota Easy Culture System II Bi-Plate and Tri-Plate (University of Minnesota Laboratory for Udder Health, St. Paul) to identify common mastitis pathogens in milk. A total of 283 quarter and composite milk samples submitted to the University of Minnesota Laboratory for Udder Health during the spring of 2010 were cultured simultaneously using 3 methods: standard laboratory culture (reference method) and the Minnesota Easy Culture System II Bi-Plate and Tri-Plate methods. Bi-Plate and Tri-Plate cultures were incubated for 18 to 24h and interpreted by 2 independent, untrained readers within 5h of each other. An experienced technician completed the standard laboratory culture. For each sample, all 3 study personnel recorded the culture result (yes/no) for each of the following diagnostic categories: no bacterial growth (NG), mixed (2 organisms), contaminated (3 or more organisms), gram-positive (GP), gram-negative (GN), Staphylococcus spp., Streptococcus spp., Streptococcus agalactiae, Streptococcus dysgalactiae, Streptococcus uberis, Enterococcus spp., Staphylococcus aureus, coagulase-negative staphylococci, Escherichia coli, Klebsiella spp., and other. For each category, the prevalence, sensitivity, specificity, accuracy, and predictive values of a positive and negative test were calculated, and the agreement between readers and between each reader and the laboratory was assessed. Specificity, overall accuracy, and negative predictive values were generally high (>80%) for the Bi-Plate and Tri-Plate for each category. Sensitivity and positive predictive values were intermediate (>60%) or high (>80%) for the broad categories of NG, GP, GN, Staphylococcus spp. and Streptococcus spp., and for Staph. aureus, but were generally lower (<60%) for other more specific categories. Similarly, interreader agreement (kappa value) was moderate to substantial (40-80%) for the broad categories of NG, GP, GN, Staphylococcus spp. and Streptococcus spp., and for Staph. aureus and E. coli, but was lower for other categories. The Tri-Plate had a higher sensitivity, accuracy, and negative predictive value for Streptococcus spp., and higher interreader agreement for some of the more specific categories. Our conclusion was that Bi-Plate and Tri-Plate results will be most reliable when used to classify infections in broad diagnostic categories such NG, GP, or GN. The Bi-Plate and Tri-Plate will have intermediate ability to identify infections as being caused by Staphylococcus spp., Streptococcus spp., or Staph. aureus.

Negatively controlled, randomized clinical trial to evaluate intramammary treatment of nonsevere, gram-negative clinical mastitis

“…(Rowbotham and Ruegg, 2016). Although previous research has shown that culture-based systems can only accurately differentiate gram-positive from gram-negative bacteria (Royster et al, 2014), before the study began, veterinarians and managers employed on both farms commonly used OFC to guide mastitis treatment decisions, and at the beginning of the study, they were confident in their ability to differentiate E. coli from Klebsiella spp. Our results indicated that differentiation of E. coli from Klebsiella spp.…”

Evaluation of an On-Farm Culture System (Accumast) for Fast Identification of Milk Pathogens Associated with Clinical Mastitis in Dairy Cows

“…and Streptococcus sp. and evaluation of Staphylococcus aureus presence in milk [ 12 ]. Nevertheless, using these other techniques the assessment of colony appearance is required for detailed identification of milk pathogens and may reduce the predictive value of on-farm culture systems when conducted by farm personnel.…”

Dutch dairy farmers’ need for microbiological mastitis diagnostics

“…Although several laboratory tools for microbiological diagnosis of IMI for dairy farmers and their veterinarians are available currently, these are rarely used to support treatment decisions (Owens et al, 1997;Lago et al, 2011a). The small number of milk samples submitted to bacteriological laboratories can be explained by the related costs, by the required effort of the farmer involved (Royster et al, 2014), and by the time-to-result (Neeser et al, 2006;Lago et al, 2011a). The current laboratory microbiological diagnostic methods are not considered suitable to base targeted treatment of CM in practice on, because of a time lag of >24 h between sampling and result (Viora et al, 2014).…”

“…To overcome the delay due to the long time-to-result, the use of onfarm mastitis diagnostics has expanded in countries such as the United States and Canada (Roberson, 2003;Cameron et al, 2013). With on-farm mastitis diagnostics, different categories of mastitis pathogens may be identified (Viora et al, 2014), leading to faster treatment decisions (Lago et al, 2011a,b;Royster et al, 2014) and selective use of antimicrobial agents in CM (Pinzón-Sánchez et al, 2011). In many countries in Europe, however, it is still common practice to treat all cases of CM with antimicrobial agents (Viora et al, 2014), which may be due to the lack of microbiological mastitis diagnostic tests considered suitable by farmers for making treatment decisions.…”