Increased detection of mastitis pathogens by real-time PCR compared to bacterial culture.

Rapid and accurate identification of mastitis pathogens is important for disease control. Bacterial culture and isolate identification is considered the gold standard in mastitis diagnosis but is time consuming and results in many culture-negative samples. Identification of mastitis pathogens by PCR has been proposed as a fast and sensitive alternative to bacterial culture. The results of bacterial culture and PCR for the identification of the aetiological agent of clinical mastitis were compared. The pathogen identified by traditional culture methods was also detected by PCR in 98 per cent of cases indicating good agreement between the positive results of bacterial culture and PCR. A mastitis pathogen could not be recovered from approximately 30 per cent of samples by bacterial culture, however, an aetiological agent was identified by PCR in 79 per cent of these samples. Therefore, a mastitis pathogen was detected in significantly more milk samples by PCR than by bacterial culture (92 per cent and 70 per cent, respectively) although the clinical relevance of PCR-positive culture-negative results remains controversial. A mixed infection of two or more mastitis pathogens was also detected more commonly by PCR. Culture-negative samples due to undetected Staphylococcus aureus infections were rare. The use of PCR technology may assist in rapid mastitis diagnosis, however, accurate interpretation of PCR results in the absence of bacterial culture remains problematic.

Pathogen profile of clinical mastitis in Irish milk-recording herds reveals a complex aetiology.

Effective mastitis control requires knowledge of the predominant pathogen challenges on the farm. In order to quantify this challenge, the aetiological agents associated with clinical mastitis in 30 milk-recording dairy herds in Ireland over a complete lactation were investigated. Standard bacteriology was performed on 630 pretreatment quarter milk samples, of which 56 per cent were culture-positive, 42 per cent culture-negative and 2 per cent contaminated. Two micro-organisms were isolated from almost 5 per cent of the culture-positive samples. The bacteria isolated were Staphylococcus aureus (23 per cent), Streptococcus uberis (17 per cent), Escherichia coli (9 per cent), Streptococcus species (6 per cent), coagulase-negative Staphylococci (4 per cent) and other species (1 per cent). A wide variety of bacterial species were associated with clinical mastitis, with S aureus the most prevalent pathogen overall, followed by S uberis. However, the bacterial challenges varied widely from farm to farm. In comparison with previous reports, in the present study, the contagious pathogens S aureus and Streptococcus agalactiae were less commonly associated with clinical mastitis, whereas, the environmental pathogens S uberis and E coli were found more commonly associated with clinical mastitis. While S aureus remains the pathogen most commonly associated with intramammary infection in these herds, environmental pathogens, such as S uberis and E coli also present a considerable challenge.