Safety, efficacy and utility of methods of transferring adhesive and cohesive Escherichia coli cells to microplates to avoid aerosols

The virtual colony count (VCC) microbiological assay has been utilized for over a decade to measure the antimicrobial activity of peptides such as defensins and LL-37 against biosafety level (BSL)-1 and BSL-2 bacteria including Escherichia coli, Staphylococcus aureus, Bacillus cereus, and Enterobacter aerogenes. In addition, a modified pipetting technique was presented in a 2011 study of defensin activity against the BSL-3 pathogen Bacillus anthracis. Both studies were published in the journal Antimicrobial Agents and Chemotherapy. Here I report that the method can also detect cross-contamination caused by aerosols utilizing the VCC method of data analysis by quantitative growth kinetics (QGK). The QGK threshold time, or T (t), equivalent to the cycle time C (t) reported in 1996 by Heid et al., precisely identifies when wells were inoculated.