Efficacy of a quaternary ammonium compound against planktonic and sessile populations of differentLegionella pneumophila strains

Abstract

Efficacy of Gemacide PN-50 TM (a quaternary ammonium compound) as a commercial formulation recommended for disinfecting heat exchangers was determined for both planktonic and sessile populations of various Legionella pneumophila strains. The quaternary ammonium compound (QAC) was preferred as an alternative due to the emerging resistance of potentially pathogenic bacteria against different biocides. Planktonic L. pneumophila strains were suspended in tap water while sessile ones were grown on stainless steel that is used in construction of the cooling towers, then both group of strains were exposed to the biocide. The sensitivity of both planktonic and sessile populations of L. pneumophila strains to the biocide was different. The biocide was found effective below recommended dosages (1000-2000 mg/L) against planktonic populations of L. pneumophila, whereas it was determined that higher than the recommended dosages were required for sessile populations. The environmental isolates were more resistant to the biocide than the ATCC isolate was. The results indicated that studying only the planktonic populations of L. pneumophila for biocide tests might not be sufficient to provide the optimum dosage and contact time information for field trials. Therefore, biocidal activity of a water treatment chemical must be evaluated in terms of dosage and contact times on both planktonic and sessile bacteria.

Selection and Transmission of Antibiotic-Resistant Bacteria

“…However, since bacteria (and notably environmental/clinical isolates) grown as a biofilm are more resilient to antimicrobial action (Kimiran-Erdem et al 2007), one of the problems associated with biofilm efficacy test, apart the type of protocol to be used, is that higher a concentration of a biocide will most probably have to be used to ensure efficacy. This will lead to increase in costs for the manufacturer and increase in levels of biocide released in the environment.…”

Efficacy of Colloidal Silver-Hydrogen Peroxide and 2-Bromo-2-nitroporopane-1,3-diol Compounds Against Different Serogroups of Legionella pneumophila Strains

“…In general, oxidizing biocides were found to be more effective than non-oxidizing ones against legionellae [5,16,17]. In the present study oxidizing biocide (CSHP) was found more effective than non-oxidizing biocide (BNPD) in terms of contact times, log reductions and recommended concentrations.…”

“…At the time points given above, biocide-bacteria suspensions were incubated at 37°C and aliquots were processed as described above. The controls consisted of Legionella bacteria in Cl 2 -free sterile tap water containing no biocide [16,17]. All of the experiments were done in triplicates.…”