title: 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.
authors.affiliation: Department of Veterinary Population Medicine, College of Veterinary Medicine, University of Minnesota, Saint Paul 55108. Electronic address: royster@umn.edu.
authors.forename: E
authors.initials: E
authors.lastname: Royster
authors.affiliation: Department of Veterinary Population Medicine, College of Veterinary Medicine, University of Minnesota, Saint Paul 55108.
authors.forename: S
authors.initials: S
authors.lastname: Godden
authors.affiliation: Department of Food Science, University of Wisconsin, Madison 53706.
authors.forename: D
authors.initials: D
authors.lastname: Goulart
authors.affiliation: Department of Veterinary Population Medicine, College of Veterinary Medicine, University of Minnesota, Saint Paul 55108.
authors.forename: A
authors.initials: A
authors.lastname: Dahlke
authors.affiliation: Department of Veterinary Population Medicine, College of Veterinary Medicine, University of Minnesota, Saint Paul 55108.
authors.forename: P
authors.initials: P
authors.lastname: Rapnicki
authors.affiliation: Department of Veterinary Population Medicine, College of Veterinary Medicine, University of Minnesota, Saint Paul 55108.
authors.forename: J
authors.initials: J
authors.lastname: Timmerman
mesh_terms: D000818:Animals; D015373:Bacterial Typing Techniques / Q000379:methods*; D002417:Cattle; D003470:Culture Media / Q000737:chemistry; D016983:Enterococcus / Q000302:isolation & purification; D004926:Escherichia coli / Q000302:isolation & purification; D005260:Female; D005506:Food Contamination / Q000032:analysis; D005516:Food Microbiology; D007709:Klebsiella / Q000302:isolation & purification; D008321:Mammary Glands, Animal / Q000382:microbiology; D008414:Mastitis, Bovine / Q000175:diagnosis* / Q000382:microbiology*; D008892:Milk / Q000382:microbiology*; D008910:Minnesota; D012680:Sensitivity and Specificity; D013211:Staphylococcus aureus / Q000302:isolation & purification; D013291:Streptococcus / Q000302:isolation & purification; D013292:Streptococcus agalactiae / Q000302:isolation & purification
chemical_list: D003470:Culture Media
keywords: bi-plate; clinical mastitis; on-farm culture; selective treatment; tri-plate