Sensitivity of Planktonic Cells and Biofilm of Wild-Type and Pressure-Stressed Cronobacter sakazakii and Salmonella enterica Serovars to Sodium Hypochlorite

Aggregate cells are the predominant physiological mode of bacterial proliferation in food processing areas and clinical settings, and microbial biofilms are responsible for the vast majority of all bacterial infections. The current study was conducted to determine whether sodium hypochlorite, validated in the past against planktonic cells, is also efficacious for decontamination of biofilms of wild-type and pressure-stressed nontyphoidal Salmonella enterica serovars and Cronobacter sakazakii. A four-strain mixture of wild-type and pressure-stressed pathogens was used for biofilm formation of up to 14 days on the surface of stainless steel coupons at 7 and 25°C. Experiments were conducted in two biologically independent repetitions (blocking factors) in a randomized complete block design. Similar biofilm formation trends were observed for wild-type and pressure-stressed phenotypes of C. sakazakii. Treatment with sodium hypochlorite was efficacious (P < 0.05) only against the planktonic cells and was unable to completely eliminate 1- and 2-week-mature bacterial biofilms of the pathogens. These findings illustrate that, whereas after a typical sanitization with sodium hypochlorite up to >3-log reduction of planktonic pathogens is achievable, >6 log of viable pathogens per cm2 of an abiotic surface may survive if bacteria had the opportunity to anchor onto the surface and form biofilm prior to treatment.