Development of a semi-automated procedure for high throughput screening of microbial sensitivity to inhibitory substances

A semi-automated procedure for the evaluation of microbial sensitivity to biocides and antibiotics was developed in a 384 well plates. The procedure allow to test simultaneously 16 strains in triplicate against six different concentration of an antimicrobial substance. The coupling of a 384 well plate micro-dilution method with a spectrophotometer evaluation of the cellular density allowed the measurement of growth kinetic parameters useful to describe the microbial growth response in presence of different concentrations of antimicrobials. The semi-automated procedure was applied to evaluate the sensitivity of 200 lactic acid bacteria strains of dairy and non-dairy origin towards four biocides and four antibiotics. Moreover, the versatility of the procedure developed was useful to characterize the phenotype of S. thermophilus mutants showing a reduced susceptibility to chlorhexidine and ethidium bromide by the over expression of pmrAB multidrug resistance efflux pump system.