Comparison of examination of milk samples using the real-time polymerase chain reaction assay Mastit 4A and enriched bacteriological culturing

Test systems for quantitative polymerase chain reaction (gPCR) play an increasingly important role in the analysis of mastitis pathogens in raw milk samples. The aim of the study was an assessment of the quality parameters sensitivity and specificity of the commercial qPCR-Assay Mastit 4A on cow level (pooled udder quarter samples) with bacteriological culturing (BC) after enrichment of quarter milk samples as reference method in a pre-stratified approach. The qPCR assay was applied on pooled udder quarter samples of 50 (Sc. agalactiae, Sc. dysgalactiae, S. aureus) or 48 (Sc. uberis) BC positive cows and 50 (Sc. agalactiae, Sc. dysgalactiae, S. aureus) or 52 (Sc. uberis) BC negative cows. Sensitivities of 96.0 % respectively 94.0 % were calculated for Sc. agalactiae und Sc. dysgalactiae, the corresponding specificities were 74.0 % respectively 88.0%. For the detection of S. aureus and Sc. uberis the qPCR-examination showed specificities of 98.0 % and 94.2 %, while sensitivities of 70.0 % and 79.2 % were found. An optimization of the cycle of threshold limits, carried out separately for each of the four investigated mastitis pathogens using the receiver operating characteristic improved sensitivity and specificity for Sc. dysgalactioe (94.0%, 94.0%), S. aureus (70.0%, 100.0%) and Sc. agalactioe (92.0%, 92.0%). In conclusion, by qPCR testing similar results as by bacteriological culturing after enrichment were achieved. The calculated estimates for the quality parameters can be used as prior information for further studies without preselection of sampled animals.