Classical microbiology techniques are relatively slow in comparison to othe
r analytical techniques, in many cases due to the need to culture the micro
organisms. Furthermore, classical approaches are difficult with unculturabl
e microorganisms. More recently, the emergence of molecular biology techniq
ues, particularly those on antibodies and nucleic acid probes combined with
amplification techniques, has provided speediness and specificity to micro
biological diagnosis Flow cytometry (FCM) allows single- or multiple-microb
e detection in clinical samples in an easy, reliable, and fast way. Microbe
s can be identified on the basis of their peculiar cytometric parameters or
by means of certain fluorochromes that can be used either independently or
bound to specific antibodies or oligonucleotides. FCM has permitted the de
velopment of quantitative procedures to assess antimicrobial susceptibility
and drug cytotoxicity in a rapid, accurate, and highly reproducible way. F
urthermore, this technique allows the monitoring of in vitro antimicrobial
activity and of antimicrobial treatments ex vivo. The most outstanding cont
ribution of FCM is the possibility of detecting the presence of heterogeneo
us populations with different responses to antimicrobial treatments. Despit
e these advantages, the application of FCM in clinical microbiology is not
yet widespread, probably due to the lack of access to flow cytometers or th
e lack of knowledge about the potential of this technique. One of the goals
of this review is to attempt to mitigate this latter circumstance. We are
convinced that in the near future, the availability of commercial kits shou
ld increase the use of this technique in the clinical microbiology laborato
ry.