Very rapid flow cytometric assessment of antimicrobial susceptibility during the apparent lag phase of microbial (re)growth

Microbiology (Reading). 2019 Apr;165(4):439-454. doi: 10.1099/mic.0.000777. Epub 2019 Feb 11.


Rapid changes in the number and flow cytometric behaviour of cells of E. coli taken from a stationary phase and inoculated into rich medium.Cells of E. coli were grown in LB medium, taken from a stationary phase of 2-4 h, and re-inoculated into fresh media at a concentration (105 ml-1 or lower) characteristic of bacteriuria. Flow cytometry was used to assess how quickly we could detect changes in cell size, number, membrane energization (using a carbocyanine dye) and DNA distribution. It transpired that while the lag phase observable macroscopically via bulk OD measurements could be as long as 4 h, the true lag phase could be less than 15-20 min, and was accompanied by many observable biochemical changes. Antibiotics to which the cells were sensitive affected these changes within 20 min of re-inoculation, providing the possibility of a very rapid antibiotic susceptibility test on a timescale compatible with a visit to a GP clinic. The strategy was applied successfully to genuine potential urinary tract infection (UTI) samples taken from a doctor's surgery. The methods developed could prove of considerable value in ensuring the correct prescription and thereby lowering the spread of antimicrobial resistance.

Keywords: antimicrobial susceptibility testing; carbocyanine; flow cytometry; proliferation.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Anti-Bacterial Agents / pharmacology*
  • Anti-Bacterial Agents / therapeutic use
  • Bacteria / drug effects*
  • Bacteria / growth & development*
  • Bacteria / isolation & purification
  • Bacteriuria / drug therapy
  • Bacteriuria / microbiology
  • Culture Media
  • Flow Cytometry*
  • Humans
  • Microbial Sensitivity Tests / methods*
  • Urinary Tract Infections / drug therapy
  • Urinary Tract Infections / microbiology*


  • Anti-Bacterial Agents
  • Culture Media