Simple detection of small amounts of Pseudomonas cells in milk by using a microfluidic device

Lett Appl Microbiol. 2006 Dec;43(6):631-6. doi: 10.1111/j.1472-765X.2006.02013.x.

Abstract

Aims: Flow cytometry offers rapid and reliable analyses of bacteria in milk. However, a flow cytometer is relatively expensive and operation is rather complicated for an unskilled operator. We applied flow cytometry using a microfluidic device (on-chip flow cytometry) in detection of small amounts of milk-spoiling bacteria.

Methods and results: Pseudomonas cells in milk were in situ hybridized with Cy5-labelled probe specific for Pseudomonas spp. under optimized condition. Numbers of Pseudomonas cells in the stationary phase and in the starved state determined by on-chip flow cytometry were compared with those determined by conventional plate counting, and on-chip flow cytometry detected targeted cells in milk that were undetectable as colony forming units(CFU) on Standards Methods Agar.

Conclusions: The contamination in milk with fewer than 10 CFU ml(-1) of targeted cells in starved state was detectable with simple procedure (0.5 h milk-clearing, 1 h fixation, 2 h hybridization and 0.5 h on-chip flow cytometry following 12 h enrichment of cells).

Significance and impact of the study: On-chip flow cytometry following fluorescence in situ hybridization could be applicable to simple detection of milk-spoiling bacteria.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Animals
  • Colony Count, Microbial
  • Flow Cytometry / methods*
  • Food Microbiology*
  • In Situ Hybridization, Fluorescence / methods*
  • Microfluidic Analytical Techniques / methods*
  • Milk / microbiology*
  • Pseudomonas / genetics
  • Pseudomonas / growth & development
  • Pseudomonas / isolation & purification*