Attempts to kill seven-day old Salmonella biofilms is ‘extraordinarily difficult’ if not ‘impossible’, according to researchers who used different disinfectants.
The difficulty of eradicating the biofilm places emphasis on preventing its access to post-cook areas of food production facilities, said Corcoran et al.
Researchers attempted to kill Salmonella biofilms on hard surfaces including concrete, glass, steel, tile and polycarbonate using three types of disinfectant.
They assessed biofilm density at 168 hours compared with 48 hours on multiple surfaces and the activity of chemical disinfectants against early (48 hour) and more mature (168 hour) Salmonella biofilm for a subset of strains representing common serovars on a concrete substratum.
Not possible to kill
Mary Corcoran, one of the researchers, said it was not possible to kill Salmonella cells using the three disinfectants, if the biofilm was able to grow for seven days before the disinfectant was applied.
Using the CDC biofilm reactor, the activity of sodium hypochlorite, sodium hydroxide and benzalkonium chloride were examined against an early and relatively mature biofilm.
All three agents result in reduction in viable counts of Salmonella, however only sodium hydroxide resulted in eradication of the early biofilm.
None of the agents achieved eradication of mature biofilm, even with 90-minutes contact time.
The impetus for the study was a European outbreak which sickened 160 people in 10 countries from the Agona serotype of Salmonella traced to meat from a food-processing facility.
“We found that all of the types of Salmonella we looked at were able to adopt the specialized biofilm lifestyle on all of the surfaces we looked at, including glass, stainless steel, glazed tile, and plastic, and that the biofilm of Salmonella gets more dense over time, and becomes more firmly attached to the surface,” said Corcoran.
“People need to question whether disinfectants that are promoted as killing various types of bacteria are really as effective in real life situations where biofilms can form as they are claimed to be based on experiments that do not use biofilms.”
E.coli was reprogrammed to seek out and fight certain biofilms, in a study for ACS Synthetic Biology .
Harvard Scientists have also developed a coating (called SLIPS ) to prevent biofilms forming in food processing machinery.
The researchers said that the properties of S. entericabiofilm on most surfaces relevant to the food processing environment change over time.
Results were based on static exposure to the three disinfectants and did not address disinfectant activity associated with abrasive or mechanical cleaning, used in real world settings.
“…our data suggest[s] there are substantial differences between 48 hour and 168 hour biofilm…and that none of the three disinfectants studied are capable, on their own, of eradicating an established 168 hour Salmonella biofilm,” said the study.
Source: Applied and Environmental Microbiology
Online ahead of print, doi: 10.1128/AEM.03109-13
“Commonly used disinfectants fail to eradicate Salmonella enterica biofilm from food contact surface materials”
Authors: Corcoran, M, Morris, D, De Lappe, N, O’Connor, J, Lalor, P, Dockery, P, Cormican, M