Researchers have discovered that common disinfectants face an uphill battle killing Salmonella once it has had the time to form a biofilm – a community of cells that attach to each other and a surface, increasing the density of bacterial growth and providing support from harsh environments. Researchers at the National University of Ireland, Galway, allowed Salmonella enterica cells to grow for seven days before applying three types of disinfectant — sodium hypochlorite, sodium hydroxide and benzalkonium chloride. They found that none of the disinfectants was able to kill the cells after that amount of time. Even soaking the biofilms in disinfectant for an hour and a half failed to kill them. “Once Salmonella cells are allowed to become established on a surface, the number of cells will increase over time, resulting in difficulty – if not impossible – to completely eliminate or kill all cells once part of a mature biofilm,” said Mary Corcoran, one of the authors of the study published in the journal Applied and Environmental Microbiology. The strains she tested were able to form a biofilm on glass, steel, polycarbonate plastic, glazed tile and concrete. “In terms of ‘real world’ environments, it is estimated that most organisms are capable of this, and that a high percentage of micro-organisms will form a biofilm to optimize growth and survival,” Corcoran said. Once biofilms grow, it is possible that abrasive cleaning or higher concentrations of disinfectants could reduce the pathogen count, Corcoran said, but “the recommended concentrations – frequently used in industry – did not kill the biofilm cells, particularly, after seven days biofilm growth.” To help put the issue of biofilms into context, the study referenced two outbreaks of the Agona serotype of Salmonella where the pathogen remained in the food processing facility for 10 years “despite intensive cleaning and decommissioning of contaminated equipment.” Corcoran’s tests used three Salmonella serotypes – Agona, Typhimurium and Enteritidis – and a Pseudomonas aeruginosa organism. “However, it is most likely that a similar pattern is true for other serotypes of Salmonella and other organisms such as E. coli,” Corcoran said. She also called the results an opportunity for food manufacturers to become more aware of possible biofilm formation. “People should be aware that cleaning with disinfectants may not eliminate all cells – particularly if they have been given an opportunity to form a biofilm over time,” Corcoran said. To head off an issue of resistance, Corcoran strongly recommended “appropriate and frequent cleaning to prevent the buildup of bacteria on surfaces” and “improving handling practices such as ensuring raw food is prepared in a separate area from cooked food” to reduce the risk of cross-contamination.

  • Marco Polo

    Ugh….I didn’t want to know this creepy news. So much for all my counter-top spray bottles of disinfectant. I do clean up quickly but the idea of a biofilm forming to increase and protect colonies disgusts me.

  • Cosimo Barruffo

    Were ever made of tests of effectiveness of biofilm removal through the use of solutions of chlorine dioxide ?

  • flame4justice

    I always clean up as soon as I’m done with each item of food to be prepared . After reading this I will become more vigilant then I already am. Everyone in my household who prepares any food will be required to read this article and clean the way I want them to.

  • Box Car Willard

    Silver Dihydrogen citrate works. Don’t be fooled.

  • Gertrude “Trudy”

    A recent health news article reported a study which found that copper or copper alloy kills resistant microbes including MRSA in seconds upon contact, whereas the same microbes survived up to 3 weeks on stainless steel, despite cleansing. So I keep a copper-plated scrub pad to dry-wipe my hands as needed and each time after I wash them and dry them. I seem not to have had as many illnesses this winter since I started doing that. Dry wiping avoids pad rust. And since the study showed that even touching a copper alloy door knob killed resistant germs, dry wiping is just as good as wet wiping, and preserves the pad longer. I began with a bowl of copper pennies…but the pad doesn’t spill all over the floor or go down the drain.

  • ellyanah

    I would like to know if they cleaned with soap/detergent before applying the disinfectant? And if that makes a difference in the results. That is the standard in food preparation after all. And if they did not then perhaps this is just fear mongering?

  • the germ guy

    Really think they missed the boat by not including hydrogen peroxide. In my teaching of college microbiology labs, we found it to destroy most of the common pathogens employed in standard lab exercises, including salmonella. We grew the organisms solid on plated media (which I believe constitutes biofilm) and it was effective there.