Efficacy of benzalkonium chloride against bioluminescent P. aeruginosa ATCC9027 constructs

Whole cell biosensors have been seldom used in the pharmaceutical and cosmetics industries for preservative efficacy testing (PET). According to several pharmacopoeias, preservatives should be tested for microbial activity using traditional viable count techniques; the use of whole cell microbial biosensors potentially provides an alternative, fast, and efficient method. The aim of the study was to assess the applicability of Pseudomonas aeruginosa ATCC9027 and its validated bioluminescent strains for preservative efficacy tests using benzalkonium chloride (BKC). Applicability of five constitutively-expressed bioluminescent strains was evaluated for preservative efficacy tests (PET) using bacterial replication, bioluminescence and fluorescence in a three-way study. PET using BKC showed no significant difference between bioluminescence and enumeration. Good correlations between bioluminescence, colony-forming units (CFU) count and fluorescence were obtained for BKC concentrations (R>0.9) between 0.0003-0.0025% against strains containing the constructs lys-pMElux, lpp-pMElux and tat-pMElux. Furthermore, two-way ANOVA analysis showed that the bioluminescent method and traditional plate counting method were equivalent for concentrations of BKC (0.0003-0.01%) during preservative efficacy tests. PET testing with BKC showed that tat-pMElux (R>0.9) had consistently high correlation coefficients between CFU and relative bioluminescence; P. aeruginosa ATCC9027 tatH5-pMElux is the best construct for testing various antimicrobial agents.