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Praseeda Ajitkumar Jeroen De Buck Herman Barkema Department of Production Animal Health

Rapid identification of Bovine Mastitis pathogens by High Resolution Melt Analysis of 16S rDNA sequences. CAHLN 2010. Praseeda Ajitkumar Jeroen De Buck Herman Barkema Department of Production Animal Health. Background.

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Praseeda Ajitkumar Jeroen De Buck Herman Barkema Department of Production Animal Health

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  1. Rapid identification of Bovine Mastitis pathogens by High Resolution Melt Analysis of 16S rDNA sequences CAHLN 2010 PraseedaAjitkumar Jeroen De Buck Herman Barkema Department of Production Animal Health

  2. Background • Mastitis: persistent problem and the most expensive disease of dairy cows • Coagulase-negative staphylococci (CNS) are a frequent cause of bovine mastitis in many countries. • CNS are not identified further by species but are treated as a uniform group

  3. Identification of mastitis pathogens • Bacteriological culture- gold standard • PCR based assays- to complement or replace conventional identification methods • DNA sequencing

  4. High Resolution Melt (HRM) • Rapid molecular technique introduced in 2002 • Generation of melting curves after PCR amplification • Based on differences in the thermal stability of DNA • Genotyping of several organisms (Chlamydia psittaci, Mycoplasmapneumoniae, Mycobacterium tuberculosis , M. aviumsubsp.paratuberculosis(Castellanos et al.,2010a and 2010b), Influenza A virus)

  5. HRM versus Melt curve HRM is an extended analysis of melt curve • Requires additional analysis software - Normalize melt curves - Apply an optional temperature shift - Plot curves in a difference graph for easy visualization - Clusters curves into groups representing different genotypes/sequences

  6. HRM versus Melt curve • “Saturation” dyes are less inhibitory to PCR than SYBR (Evagreen, LC green dyes) • Observed melting behaviour is characteristic of a particular DNA sample • Target - 16S rRNA gene • Gold standard for broad-range microbial identification • Feasibility of using high-precision melting for bacterial speciation (Cheng et al., 2006) • Highly specific species identification of clinically relevant biothreat bacterial agents (Yang et al., 2009)

  7. Hypothesis • High resolution analysis of melting curves generated after PCR amplification can lead to rapid speciation of mastitis pathogens

  8. Objective • Development of novel and rapid assays to speciate major and minor mastitis pathogens based on real-time PCR and HRM

  9. Pathogens in Clinical Mastitis n-3,024 OldeRiekerink et al., 2008

  10. Bacterial species included in HRM

  11. Coagulase-negative staphylococci

  12. Materials & Methods Extraction of bacterial genomic DNA • 7 bacterial strains from ATCC and 6 isolates from mastitis milk samples subjected to DNA extraction • 14 coagulase-negative staphylococci isolates from CBMRN • Genomic DNA extracted with the DNeasy Blood and Tissue Kit (Qiagen)

  13. Materials& methods (contd…) • Amplification of 16S rRNA gene using real-time PCR • Real-time PCR amplification of 16S rRNA gene using BioRad CFX thermal cycler • Cycling conditions 1: 98.0°C for 2:00 min 2: 98.0°C for 0:05 3: 55.0°C for 0:10 Plate Read 4: GOTO 2, 39 more times 5: 95.0°C for 1:00 6: 70.0°C for 1:00 7: Melt Curve 70°C to 95°C : Increment 0.2°C for 0:10 Clustering

  14. Result HRM-common mastitis pathogens • 1. A. pyogenes • 2. C. bovis • 3. S. agalactiae • 4. S. dysgalactiae • 5. E. coli • 6. K. pneumoniae • 7. S. uberis • 8. P. melaninogenica • 9. F. necrophorum • 10. S. aureus • 11. B. fragilis • 12. M. bovis 1 3 2 4 5 6,7 8 9 12 10,11 13

  15. Result HRM- coagulase-negative staphylococci • 1. S. auricularis • 2. S. chromogenes • 3. S. intermedius • 4. S. hyicus • 5. S. aureus • 6. S. capitis • 7. S. epidermidis • 8. S. sciuri • 9. S. simulans • 10. S. warneri • 11. S. saprophyticus • 12. S. cohnii • 13. S. xylosus • 14. S. haemolyticus • 15. S. hominis

  16. Advantages of HRM • Inexpensive • High sensitivity & specificity • Rapid-completed in about 1 h 30 min

  17. Conclusions • High resolution melt analysis is a rapid molecular tool for the identification of mastitis pathogens • Validation of the technique is necessary • Applicability of the technique in speciation of pathogens in mastitis milk samples needs to be evaluated

  18. Future Directions • Test and validate HRM assays on DNA extracts of subclinical and clinical mastitis cases (CNS and other mastitis pathogens) • Culture-negative mastitis samples

  19. Acknowledgements • Supervisors Herman Barkema & JeroenDe Buck • John Middleton, Faculty of Vet. Med, Missouri • Lab mates Elena Castellanos Amanda Reith Nick Mackenzie VineetSaini RienskeMortier Joel David • Faculty of Veterinary Medicine, University of Calgary for the UCVM scholarship • National Mastitis Research Foundation

  20. Thanks

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