Detection of Streptococcus agalactiae from raw milk samples

Abstract

Streptococcus agalactiae (S. agalactiae) is one of the most important microorganisms associated with bovine mastitis, a disease that causes great economic losses and represents a risk for human and animal health. Microbiological cultures constitute the "gold standard technique" for the diagnosis of S. agalactiae; however, they require intensive work to obtain the results. An alternative to the microbiological testing is the detection of S. agalactiae through amplification by Polymerase Chain Reaction (PCR) from DNA extracted from raw milk, which reduces the diagnosis time of the pathogen and decreases the occurrence of false positive results associated with the culture. The objective of this work was the identification of S. agalactiae by PCR from DNA extracted from raw milk samples. DNA extraction was performed by organic extraction. In parallel, the microbiological culture of the samples was carried out and their subsequent analysis by the Christie-Atkins-Munch-Peterson test (CAMP). For the PCR assay, primers amplifying a 153pb fragment of the cfb gene, encoding for the CAMP factor, were used. Thirteen samples were positive to the CAMP test. The PCR assay amplified the extracted DNA in 10 of the 50 samples, which coincided with the positive samples of the CAMP test. Three samples positive to CAMP were negative by PCR. The use of PCR allowed the detection of S. agalactiae in cows with mastitis.