Summary auto-generated
This study developed a molecular method for rapidly identifying bacterial causes of bovine mastitis using 16S-23S rRNA spacer sequences. Researchers determined spacer region sequences from nine mastitis-causing species: six Staphylococcus species (aureus, chromogenes, epidermidis, hyicus, simulans, xylosus) and three Streptococcus species (agalactiae, dysgalactiae, uberis). Spacer lengths varied from 240 to 461 base pairs, with significant sequence variation between species enabling primer design. Species-specific oligonucleotide primer pairs were created for each organism, along with genus-specific primers. Testing on 31 bacterial species and 51 clinical mastitis isolates showed the primers successfully identified target pathogens with high specificity. The method detected as little as 50 picograms of purified DNA and worked on mastitic milk samples containing only 40 colony-forming units of Staphylococcus aureus. While conventional microbiological identification requires 24+ hours, this PCR-based approach offers rapid, species-level identification. The method showed 90% accuracy with conventional laboratory identifications and 73% success with coagulase-negative staphylococci, which are traditionally difficult to identify.
Key findings
- The 16S-23S rRNA spacer region shows significant sequence variation (53-85% identity within genera) suitable for species-specific primer design for nine bovine mastitis pathogens.
- Species-specific PCR primer pairs successfully identified target bacteria with high specificity, with minimal cross-reactivity among 31 tested bacterial species.
- The method detected as few as 50 pg of purified bacterial DNA and successfully amplified from mastitic milk samples containing only 40 colony-forming units, demonstrating high sensitivity.
- Testing on 51 clinical mastitis isolates achieved 90% correct species identification and showed particular utility for coagulase-negative staphylococci (73% detection), which are traditionally difficult to identify.
- PCR-based identification can be completed in hours compared to 24+ hours for conventional microbiological methods, enabling rapid pathogen detection and potential simultaneous antibiotic resistance screening.
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Abstract
Bovine mastitis is caused mainly by certain Staphylococcus and Streptococcus species. The sequences of the 16S-23S rRNA spacer regions were determined for the nine species which cause mastitis: Staphylococcus aureus, Staphylococcus chromogenes, Staphylococcus epidermidis. Staphylococcus hyicus, Staphylococcus simulans, Staphylococcus xylosus. Streptococcus agalactiae, Streptococcus dysgalactiae and Streptococcus uberis. Significant variation was found between the spacer sequences of different species with the lengths of the spacers varying from 240 to 461 bp. Between genera the spacers shared only short conserved regions (8-9 bp) and within genera the sequence identities varied from 53 to 85%. This variation made it possible to construct specific primer pairs for these species and genera. The specificities of these primers were tested with 25 bacterial species and 51 isolates from cattle with clinical mastitis. The DNA-based identification of the mastitis species was mostly successful.