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

Abstract

The present study aimed to evaluate the diagnostic performance specificity (Sp), sensitivity (Se), positive predictive value (PPV), negative predictive value (NPV), and accuracy (Acc) of two chromogenic culture media for rapid identification of Gram-positive bacteria causing subclinical mastitis (SCM) in dairy cows. For this, the performance of chromogenic culture media Gram-positive (GP) and Staphylococcus (Staph) (CHROMagar ™, Paris—France) was evaluated in milk samples collected from: (1) lactating cows with SCM (n = 504), and (2) cows in the post-partum period (PP) (7 ± 3 days post-partum; n = 536). Rapid identification of Gram-positive bacteria in chromogenic media was performed by visual inspection of colony colors after 24 h of incubation at 37°C. Bacterial identification by MALDI-TOF mass spectrometry was considered the reference methodology for calculating: Acc, Se, Sp, PPV, NPV, and Cohen's Kappa coefficient of agreement (k). The chromogenic media GP showed high Acc for Strep. agalactiae/dysgalactiae identification in both samples of SCM (Se: 89.1%; Sp: 96.3% and Acc: 95.6%) and of cows in PP (Se: 100%; Sp: 99.0% and Acc: 99.1%). Similar results were observed for Strep. uberis/Enterococcus spp. identification (Se: 90.5%; Sp: 92.5% and Acc: 92.3%) in SCM samples and Se: 100%; Sp: 99.6% and Acc: 99.6% in samples of PP cows using the GP media. However, the GP chromogenic media showed low Se (25.0% in SCM samples and 50.0% in samples of cows in PP) for Staph. aureus identification, despite Sp and Acc were high (Sp: 98.3% and Acc: 95.4% in SCM and Sp samples: 99.4% and Acc: 98.9% in PP cow samples). Staph culture media showed high Acc for Staph. aureus identification (Se: 80.0%; Sp: 98.8% and Acc: 98.0% in SCM samples and Se: 66.7%; Sp: 100% and Acc: 99.6% in PP cow samples), although the low prevalence of Staph. epidermidis and Staph. saprophyticus limit inferences about the performance of identifying these pathogens in Staph media. In conclusion, despite the limitation of the GP media for identification of Staph. aureus, GP, and Staph chromogenic media obtained satisfactory diagnostic performance results for the rapid identification of the main Gram-positive pathogens associated with SCM.

Pathogen and severity-dependent immune responses in bovine mastitis: highlight the dynamics of differential somatic cell count

“…Staphylococcus aureus (SA) was differentiated from coagulase-negative staphylococci (CNS) based on hemolysis patterns and a tube coagulase test. A presumptive diagnosis of streptococcal isolates was made by culturing bacteria on a chromogenic agar (CHROMagar™ Orientation, BD Japan) [ 15 ], a sorbitol-containing andrade peptone broth, and an SF broth ( Streptococcus uberis diagnosis kit; Kanto Chemical, Tokyo, Japan). Isolates presumed to be Streptococcus uberis (SU) and Streptococcus dysgalactiae (SD) were confirmed using API 20 Strep ® (BioMérieux Japan Ltd., Tokyo, Japan), and the other streptococci-like isolates were categorized into other streptococci and related genera (OS).…”

Assessment of listing and categorisation of animal diseases within the framework of the Animal Health Law (Regulation (EU) No 2016/429): antimicrobial‐resistant Staphylococcus aureus in cattle and horses

“…It has characteristic small white‐yellow β‐haemolytic colonies on blood agar. Recently, selective chromogenic culture media for rapid identification of microorganisms, including S. aureus , specifically from samples of bovine mastitis have been tested (Garcia et al., 2021 ; Granja et al., 2021 ). Also for selective growth of MRSA, chromogenic agars are commercially available (Pletinckx et al., 2013 ).…”