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

Erika Korzune Ganda,Rodrigo Carvalho Bicalho,Dean Harrison Decter,Rafael Sisconeto Bisinotto,Horacio Bach

doi:10.1371/journal.pone.0155314

Erika Korzune Ganda, Rodrigo Carvalho Bicalho + Show 3 more

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https://doi.org/10.1371/journal.pone.0155314

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Abstract

The present study aimed evaluate an on-farm culture system for identification of milk pathogens associated with clinical mastitis in dairy cows using two different gold standard approaches: standard laboratory culture in study 1 and 16S rRNA sequencing in study 2. In study 1, milk from mastitic quarters (i.e. presence of flakes, clots, or serous milk; n = 538) was cultured on-farm using a single plate containing three selective chromogenic media (Accumast—FERA Animal Health LCC, Ithaca, NY) and in a reference laboratory using standard culture methods, which was considered the gold standard. In study 2, mastitic milk was cultured on-farm and analyzed through 16S rRNA sequencing (n = 214). In both studies, plates were cultured aerobically at 37°C for 24 h and read by a single technician masked to gold standard results. Accuracy, sensitivity, specificity, positive (PPV) and negative predictive value (NPV) were calculated based on standard laboratory culture in study 1, and PPV was calculated based on sequencing results in study 2. Overall accuracy of Accumast was 84.9%. Likewise, accuracy for identification of Gram-negative bacteria, Staphylococcus sp., and Streptococcus sp. was 96.4%, 93.8%, and 91.5%, respectively. Sensitivity, specificity, PPV, and NPV were 75.0%, 97.9%, 79.6%, and 97.3% for identification of E. coli, 100.0%, 99.8%, 87.5%, and 100.0% for S. aureus, 70.0%, 95.0%, 45.7%, and 98.1% for other Staphylococcus sp., and 90.0%, 92.9%, 91.8%, and 91.2% for Streptococcus sp. In study 2, Accumast PPV was 96.7% for E. coli, 100.0% for Enterococcus sp., 100.0% for Other Gram-negatives, 88.2% for Staphylococcus sp., and 95.0% for Streptococcus sp., respectively. In conclusion, Accumast is a unique approach for on-farm identification pathogens associated with mastitis, presenting overall sensitivity and specificity of 82.3% and 89.9% respectively.

Highlights

Clinical mastitis remains an important animal health issue and leads to major economic losses to the dairy industry worldwide
Rapid on-farm identification of milk pathogens is critical for targeted antimicrobial therapy, which helps avoid the indiscriminate use of antibiotics in livestock and reduces the economic burden of clinical mastitis
The most prevalent pathogens in the milk of cows diagnosed with clinical mastitis according to results from Quality Milk Production Services (QMPS) standard laboratory culture were S. uberis, Streptococcus sp., and E. coli (Table 1)

Summary

Introduction

Clinical mastitis remains an important animal health issue and leads to major economic losses to the dairy industry worldwide. From 20% to 30% of dairy cows are diagnosed with clinical mastitis at least once during lactation [1, 2]. Estimated costs per case of clinical mastitis range between $179 and $488 depending upon milk prices, level of production in affected cows, culling policies, and stage of lactation when the disease occurred [3, 4]. Fungi and algae have been observed in the milk of cows diagnosed with clinical mastitis, inflammation of the mammary gland is caused predominantly by bacterial infections. The use of an intramammary antibiotic is not recommended for cows with mastitis associated with E. coli [9]. Rapid on-farm identification of milk pathogens is critical for targeted antimicrobial therapy, which helps avoid the indiscriminate use of antibiotics in livestock and reduces the economic burden of clinical mastitis

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