Evaluation of Streptococcus agalactiae detection by PCR in Milk and its comparison to other microbiological methods

The development of molecular biological techniques provide a method for direct detection and identification of pathogens. This study attempted to compare bacterial culture and PCR to detect S. agalactiae in cattle milk samples. The PCR method was based on using primers V1 and V2 derived from the 16s rRNA gene. One hundred milk samples were collected from individual cattle herds of Urmia, Iran. Direct bacterial DNA extraction was attempted from100 milk samples. The PCR method was based on using primers V1and V2 derived from the 16s rRNA gene. In addition, two sets of positive control primer pairs (C1 and C2) were used to identify false negatives obtained with primers V1 and V2. In bacteriological culture, biochemical tests were carried out on suspected isolates. S. agalactiae was isolated from 8% of the 100 samples and 15% were positive in amplification of the 16S rRNA gene and all of the positive samples gave the expected size fragment of approximately 120bp. All isolates which were diagnosed as S. agalactiae in microbiological methods were also positive with PCR detection. Compared with culture, PCR is less time consuming. It takes less than 24h to complete, while identification of bacteria by conventional microbiological and biochemical methods requires more than 48h. The findings of our study revealed that PCR is more sensitive than culture for the detection of S. agalactiae in milk.