The growth and resistance to sodium hypochlorite of Listeria monocytogenes in a steady-state multispecies biofilm

Abstract

. GI LM O UR . 2000. A constant-depth film fermenter (CDFF) was used to culture a steady-state multispecies biofilm consisting of one strain each of Listeria monocytogenes, Pseudomonas fragi and Staphylococcus xylosus. These bacteria were initially grown together in a conventional chemostat to achieve a steady state before being inoculated into the CDFF over an 18-h period. A dilute tryptone soya broth (TSB) medium was supplied to the CDFF and the biofilm allowed to develop over a 28-d period. This mature biofilm was then subjected to increasing levels of sodium hypochlorite solution to measure any antimicrobial effect. The three organisms were seen to reach a steady state after 6 d in the chemostat before being transferred to the CDFF where the mature multispecies biofilm reached steady state at 17 d. Listeria monocytogenes in both planktonic and biofilm growth stabilized at 1·8 and 1·5%, respectively, of the total plate counts, while Ps. fragi and Staph. xylosus were the predominant organisms in the biofilm at 59% and 39·5%, respectively, of the total microbial population. Steady-state biofilms in the CDFF were exposed to increasing strengths of sodium hypochlorite; 200, 500 and 1000 p.p.m. free chlorine, but a substantial two-log cycle drop in bacterial numbers was only achieved at 1000 p.p.m. free chlorine. In planktonic culture all three organisms were completely eliminated when exposed to 10 p.p.m. free chlorine for a 30-s period.

Irradiation Sensitivity of Planktonic and Biofilm-Associated Escherichia coli O157:H7 Isolates Is Influenced by Culture Conditions

“…As increased contact time did not increase penetration in that study, it was concluded that the lack of penetration is a primary mechanism for the reduced efficacy of antimicrobials when applied against biofilms (2,3). Biofilms of Listeria monocytogenes showed an exceptional tolerance for sodium hypochlorite treatment, with only a 2-log reduction following a treatment that was significantly more aggressive (1,000 ppm, 20 min) than that which yielded an 8-log reduction of planktonic cells (10 ppm, 0.5 min) (16). Treatment with alkaline hypochlorite, chlorsulfamates, and trisodium phosphate yielded similar results (20,23).…”

Resistance mechanisms of bacteria to antimicrobial compounds

“…Inplanktonic culture a 100% kill was achieved when exposed to 10 p.p.m. free chlorine for 30s (Norwood and Gilmour, 2000). Furthermore, the penetration of positively charged hydrophilic drugs such as aminoglycosides and polypeptides was inhibited by the glycocalyx, whilst that of B-lactams, quinolones, and macrolides was not inhibited.…”

Shewanella putrefaciens Adhesion and Biofilm Formation on Food Processing Surfaces

“…Despite rigorous cleaning and disinfection procedures, pathogenic bacteria and spoilage microorganisms may be isolated from many types of surfaces in food processing plants (B. Fonnesbech Vogel, personal communication). This may at least partly be explained by an increased resistance of adherent bacteria to adverse conditions like disinfection (21,32,41).…”