Performance evaluation of disinfectant formulations using poloxamer-hydrogel biofilm-constructs

Poloxamer F127 is a di-block co-polymer of polyoxyethylene and polyoxypropylene. Aqueous solutions show thermo-reversible gelation, being liquid at temperatures < 15 degrees C and robust gels at temperatures > 15 degrees C. Chilled poloxamer solutions (30% w/v) were inoculated with approximately 10(4-5) cfu ml-1 of stationary phase cultures of Pseudomonas aeruginosa, Ps. fluorescens, Pantoea agglomerans, Micrococcus luteus, Staphylococcus epidermidis, Bacillus subtilis or Listeria innocua. Drops (200 microliters) of the inoculated poloxamers were placed on stainless steel coupons held in Petri dishes containing moistened cotton wool and incubated at 30 degrees C for 5 h. All strains grew well giving between 10(6-7) cfu ml-1 at 5-6 h. The cultured gels were readily applied to tests of biocide effectiveness as the stainless steel coupons could be removed and flooded with biocide solution for fixed exposure times. Provided that the temperature of the biocide solutions was > 15 degrees C, the integrity of the gels could be maintained during exposure. After exposure, the gels and their supports were removed to separate tubes containing neutralizer solution (< 15 degrees C). The gels rapidly dispersed within 5 min to ensure a complete recovery of the sample population. Biofilm-constructs and cell suspensions (10(7) cfu ml-1) were exposed to four commercial disinfectant formulations, based on hypochlorite, alcohol, hydrogen peroxide and a tenside, at recommended use levels. Cell suspensions, in the presence of bovine serum albumen (BSA; 0.03% w/v), were subject to a > 5-log kill within 5 min while the killing effected against the biofilm-constructs varied between 0.4 and 2-log reductions. The results indicate a high degree of reproducibility between replicate samples, with patterns of susceptibility varying both as a function of organism, biocide type and concentration. The experiments strongly support the view that poloxamer-constructs are suitable for application in trials and testing of disinfectant formulations.