doi:10.1038/nindia.2013.119 Published online 9 September 2013
Researchers have developed amino-acid-modified magnetic particles that can detect bacteria causing mastitis, a disease that damages milk-secreting tissues in the mammary glands of cattle . These magnetic particles can be used to determine the most suitable antibiotic to treat mastitis.
Staphylococcus aureus, Escherichia coli and Streptococcus agalactiae are the most prevalent mastitis-initiating bacteria in cattle. To identify them, the researchers synthesized magnetic iron oxide particles and modified them with amino acid glycine. They compared the efficacy of these particles in trapping and detecting bacteria with that of unmodified magnetic iron oxide particles. The modified magnetic particles were exposed to cultured samples of S. aureus, E. coli and S. agalactiae and 25 milk samples from mastitis-affected cattle.
Glycine-modified magnetic particles showed a higher capacity for trapping E. coli, S. aureus and S. agalactiae than unmodified magnetic particles. The milk samples contained at least one bacterial species — Enterobacteriaceae sp., Streptococcus sp. or Staphylococcus sp.
The bacteria-bound magnetic particles were then isolated using a magnetic separator. They were used for antibiotic selection based on how they changed the colour of the indicator methylene blue. For a sample mostly containing living bacteria, the reductase enzyme in the bacteria cell membranes reduced methylene blue to a colourless compound. The indicator retained its blue colour for a sample mostly containing dead bacteria.
The kit will be useful for field vets to identify the right antibiotic for treating mastitis, says one of the co-authors Gopal Dhinakar Raj.