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

Poloxamer F127 is a di-block co-polymer of polyoxyethylene and polyoxypropy lene. Aqueous solutions show thermo-reversible gelation, being liquid at te mperatures <15 degrees C and robust gels at temperatures >15 degrees C. Chi lled poloxamer solutions (30% w/v) were inoculated with approximately 10(+5 ) cfu ml(-1) of stationary phase cultures of Pseudomonas aeruginosa, Ps. fl uorescens, Pantoea agglomerans, Micrococcus luteus, Staphylococcus epidermi dis, Bacillus subtilis or Listeria innocua. Drops (200 mu l) of the inocula ted 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 stainle ss steel coupons could be removed and flooded with biocide solution for fix ed exposure times. Provided that the temperature of the biocide solutions w as > 15 degrees C, the integrity of the gels could be maintained during exp osure. After exposure, the gels and their supports were removed to separate tubes containing neutralizer solution (< 15 degrees C). The gels rapidly d ispersed within 5 min to ensure a complete recovery of the sample populatio n. Biofilm-constructs and cell suspensions (10(7) cfu ml(-1)) were exposed to four commercial disinfectant formulations, based on hypochlorite, alcoho l, hydrogen peroxide and a tenside, at recommended use levels. Cell suspens ions, in the presence of bovine serum albumen (BSA; 0.03% w/v), were subjec t to a > 5-log kill within 5 min while the killing effected against the bio film-constructs varied between 0.4 and 2-log reductions. The results indica te a high degree of reproducibility between replicate samples, with pattern s of susceptibility varying both as a function of organism, biocide type an d concentration. The experiments strongly support the view that poloxamer-c onstructs are suitable for application in trials and testing of disinfectan t formulations.