Jaglic Z., Cervinkova D., Vlkova H., Michu E., Kunova G., Babak V. (2012): Bacterial biofilms resist oxidising agents due to the presence of organic matter. Czech J. Food Sci., 30: 178–187. This study evaluated the susceptibility of planktonic and biofilm cells of Staphylococcus spp. (n = 87), klebsiella spp. (n = 30), and escherichia coli (n = 74) isolates originating from food contact surfaces of milk and meat processing plants to benzalkonium chloride (BAC), sodium hypochlorite (NaClO), chloramine B (CAB), and peracetic acid (PAA). Bacterial growth and reduction of viable cells in the presence of disinfectants were determined in tryptone soya broth (TSB) and water, respectively. Biofilm positive isolates ( n = 73) were tested for the presence of selected qac genes. Unlike BAC, chlorine‑based disinfectants and PAA were poorly efficient in TSB, especially in the case of biofilms. However, when tested in water, the efficacy of NaClO, CAB and PAA substantially increased, which was particularly evident in biofilms. In water, staphylococcal biofilms were even more susceptible to CAB than planktonic cells. A part (23.3%) of the biofilm positive staphylococci carried the qac genes but did not express an increased resistance to BAC. This study showed that bacterial biofilms protected with organic matter could be one of the main reasons for disinfection failure.

The adherence of microorganisms to surfaces is a critical precondition for biofilm development. In this study, we evaluated the adherence (in amounts capable of biofilm formation) of Staphylococcus epidermidis in milk to stainless steel. During a 6-h time frame, the effect of milk temperature and laminar flow on adherence was analysed. In amounts capable of biofilm formation, the cells adhered within 0.5 h; however, at the milk temperatures promoting cell growth (25 and 28 °C), the cells proceeded to detach from the surface when bacteria started to grow (after 2 h), but only during the milk flow. When the temperatures were below the growth limit (6 and 22 °C) or under static conditions, the cells remained attached during the whole monitoring period. This study showed that temperatures which are suboptimal for growth and static conditions support the adhesion S. epidermidis in amounts capable of biofilm formation. On the contrary, at temperatures allowing the growth, adhered cells of S. epidermidis can easily be washed away from the stainless steel surface when bacteria begin to grow.

Staphylococcus epidermidis may form biofilms in milk processing plants and secondarily contaminate milk products. In this study, the ability of S. epidermidis to form a biofilm in milk and the influence of glucose and NaCl on biofilm formation were analysed. Biofilm production on stainless steel was investigated at 30°C in pasteurized milk and in milk containing glucose, NaCl or both glucose and NaCl. Biofilm formation was evaluated by monitoring of colony-forming units (cfu) on stainless chips and by real-time quantitative PCR analysis of the icaA and σB transcripts. An increase in cfu and icaA transcription was observed after 20h incubation, especially in milk containing glucose and NaCl. NaCl alone was shown to present a greater risk of biofilm development in milk than glucose alone, but the NaCl/glucose combination represented the highest risk. The σB factor did not seem to be involved in biofilm formation under the conditions of this study.