|FENG, DORIS - US Department Of Agriculture (USDA)|
Submitted to: Food Microbiology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 1/21/2016
Publication Date: 1/22/2016
Citation: Carter, M.Q., Louie, J.W., Feng, D., Zhong, W.W., Brandl, M. 2016. Curli fimbriae are conditionally required in Escherichia coli O157:H7 for initial attachment and biofilm formation. Food Microbiology. 57: 81-89.
Interpretive Summary: Shiga toxin-producing Escherichia coli (STEC) serotype O157 is one of the major STEC groups associated with enteric diseases. We used two E. coli O157:H7 outbreak strains and their mutant lack of long aggregative fimbriae, curli, to understand the role of curli in surface attachment and biofilm maturation. Contribution of curli to biofilm formation on abiotic surfaces was conditional, depending on cell physiology, abiotic surface, and local physiochemical condition. Although curli fimbriae were not required for E. coli O157:H7 biofilm formation on abiotic surfaces in sterile spinach lysates, they enhanced the initial attachment of E. coli O157:H7 to spinach leaves and stainless steel, and contributed to the formation of mixed biofilms by the enteric pathogen and plant-associated bacterial species on abiotic surfaces in spinach-wash water. Such mixed biofilms may enhance environmental survival of E. coli O157:H7 and serve as a contamination source in produce-processing environments.
Technical Abstract: Several species of enteric pathogens produce curli fimbriae, which may affect their interaction with surfaces and other microbes in nonhost environments. Here we used two E. coli O157:H7 outbreak strains with distinct genotypes to understand the role of curli in surface attachment and biofilm formation in several systems relevant to fresh produce production and processing. Curli significantly enhanced the initial attachment of E. coli O157:H7 to spinach leaf and stainless steel surfaces by 5-fold. Curli also was required for E. coli O157:H7 biofilm formation on stainless steel and enhanced biofilms on glass by 19-27 fold in LB no-salt broth. However, this contribution was not observed when cells were grown in sterile spinach lysates. Furthermore, both strains of E. coli O157:H7 produced minimal biofilms on polypropylene in LB no-salt broth, but considerable amounts in spinach lysates. Under the latter conditions, curli appeared to slightly increase the biofilm production. Notably, curli played an important role in the formation of mixed biofilm by E. coli O157:H7 and plant-associated microorganisms in spinach leaf washes, as revealed by confocal microscopy. No or little E. coli O157:H7 biofilms were detected at 4°C, supporting the importance of temperature control in postharvest and produce processing environments.