Comparative analysis of four commercial on-farm culture methods to identify bacteria associated with clinical mastitis in dairy cattle

Abstract

Several multiple-media culture systems have become commercially available for on-farm identification of mastitis-associated pathogens. However, the accuracy of these systems has not been thoroughly and independently validated against microbiological evaluations performed by referral laboratories. Therefore, the purpose of the present study was to evaluate the performance of commercially available culture plates (Accumast, Minnesota Easy System, SSGN and SSGNC Quad plates) to identify pathogens associated with clinical mastitis in dairy cows. Milk samples from the affected quarter with clinical mastitis were aerobically cultured with the on-farm culture systems and by two additional reference laboratories. Agreeing results from both standard laboratories were denoted as the reference standard (RS). Accuracy (Ac), sensitivity (Se), specificity (Sp), positive and negative predictive values (PPV and NPV, respectively) and Cohen’s kappa coefficient (k) of on-farm plates were determined based on the RS culture of 211 milk samples. All four plate-systems correctly identified ≥ 84.9% of milk samples with no bacterial growth. Accumast had greater values for all overall predictive factors (Ac, Se, Sp, PPV and NPV) and a substantial agreement (k = 0.79) with RS. The inter-rater agreements of Minnesota, SSGN, and SSGNC with RS were moderate (0.45 ≤ k ≤ 0.55). The effectiveness to categorize bacterial colonies at the genus and species was numerically different amongst the commercial plates. Our findings suggest that Accumast was the most accurate on-farm culture system for identification of mastitis-associated pathogens of the four systems included in the analysis.

Multiple Bacteria Identification in the Point-of-Care: an Old Method Serving a New Approach

“…In comparison to microbial culture, POC PCR-based systems are expected to bring improvements in terms of time of analysis, sample volume, and the ability to analyze multiple targets in the same assay. While bacterial culturing-based detection of pathogens requires sample incubation for at least 18 h [6], result times can be significantly reduced to a couple of hours using fully integrated systems that comprise miniaturized sample preparation and amplification units [2].…”

Graduate Student Literature Review: Understanding the genetic mechanisms underlying mastitis

“…The importance of pathogen diagnosis and targeted treatment has long been recognized, and on-farm culture systems have been used despite varied sensitivity and specificity reports (McCarron et al, 2009;Ganda et al, 2016;Ferreira et al, 2018). Although the incorporation of microbial sequencing techniques is not yet practical on farm, it would allow for the most precise phenotyping of mastitis, and dissecting mastitis by specific etiology may clarify the genetic mechanisms at play given the pathogen-specific immunological responses often observed (Yang et al, 2008;Bannerman, 2009;Buitenhuis et al, 2011).…”

Evaluation of Chromogenic Culture Media for Rapid Identification of Gram-Positive Bacteria Causing Mastitis

“…The performance indicators of Acc, Se, Sp, Positive Predictive Value (PPV), and Negative Predictive Value (NPV) of the chromogenic media were calculated based on the following results: True Positive (TP; when there was microbial growth and the result of visual microbiological identification of the chromogenic media was corresponding to that of the gold standard method), True Negative (TN; when there was no growth of any microorganism in the chromogenic culture media and blood agar), False Positive (FP; when there was a growth of any microorganism whose result was different between the microbiological identification of the gold standard method and the visual microbiological identification of the chromogenic media), False Negative (FN; when there was no growth of microorganisms in the chromogenic media and there was a growth of any microorganism in the gold standard method) (12).…”

“…Chromogenic culture media are alternatives for rapid microbiological identification, as they make it possible to presumptively differentiate bacterial species and/or groups according to colony color, reducing the need for biochemical tests (11). These culture media outperform other conventional microbiological rapid methods (e.g., Minnesota Easy System Triplets; Mastitis SSGN Quad Culture Plates) concerning specificity (Sp), sensitivity (Se), and accuracy (Acc) (12), in addition to identifying contamination in the samples more efficiently (13), which minimizes the occurrence of false positives in the identification of agents.…”