Semi-Quantitative Method for Streptococci Magnetic Detection in Raw Milk

Biosensors (Basel). 2016 Apr 27;6(2):19. doi: 10.3390/bios6020019.


Bovine mastitis is the most costly disease for dairy farmers and the most frequent reason for the use of antibiotics in dairy cattle; thus, control measures to detect and prevent mastitis are crucial for dairy farm sustainability. The aim of this study was to develop and validate a sensitive method to magnetically detect Streptococcus agalactiae (a Group B streptococci) and Streptococcus uberis in raw milk samples. Mastitic milk samples were collected aseptically from 44 cows with subclinical mastitis, from 11 Portuguese dairy farms. Forty-six quarter milk samples were selected based on bacterial identification by conventional microbiology. All samples were submitted to PCR analysis. In parallel, these milk samples were mixed with a solution combining specific antibodies and magnetic nanoparticles, to be analyzed using a lab-on-a-chip magnetoresistive cytometer, with microfluidic sample handling. This paper describes a point of care methodology used for detection of bacteria, including analysis of false positive/negative results. This immunological recognition was able to detect bacterial presence in samples spiked above 100 cfu/mL, independently of antibody and targeted bacteria used in this work. Using PCR as a reference, this method correctly identified 73% of positive samples for streptococci species with an anti-S. agalactiae antibody, and 41% of positive samples for an anti-GB streptococci antibody.

Keywords: Streptococcus agalactiae; Streptococcus uberis; immunogenic recognition; magnetic nanoparticle (NP); magnetoresistive sensors; microfluidic; milk.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Animals
  • Biosensing Techniques*
  • Cattle
  • Food Microbiology / methods*
  • Food Safety
  • Humans
  • Magnetite Nanoparticles*
  • Microfluidics
  • Milk / microbiology*
  • Reproducibility of Results
  • Sensitivity and Specificity
  • Streptococcus agalactiae / genetics
  • Streptococcus agalactiae / isolation & purification
  • Streptococcus* / genetics
  • Streptococcus* / isolation & purification


  • Magnetite Nanoparticles