Bacteria are capable of existence in two separate lifestyles: sessile and planktonic. Sessile bacteria grow in surface-associated communities enmeshed in an extracellular matrix know as biofilms. Biofilms confer upon constituent bacteria a heightened resistance to physical and chemical stress and represent the preferred mode of growth. Early studies of biofilm development were limited by the shortcomings inherent in microscopic techniques of the 1980's. Subsequent improvement however, particularly the use of confocal scanning laser microscopy, allowed for the observation of fully hydrated, living biofilms which contributed to the running theory of what constitutes biofilm structure, particularly at maturity. And while useful, the model of biofilm development and structure is based largely upon the study of Pseudomonas aeruginosa- an obvious shortcoming when one endeavors to study biofilm formation in other bacteria. Indeed, studies have examined biofilm development of E. coli but focus on either O157:H7, a pathogenic isolate responsible for causing gastrointestinal disease in humans, as well as K-12, a standard laboratory strain and are almost always carried out in defined laboratory media. Additionally, growing evidence indicates that E. coli are capable of existence in aqueous environments beyond the protective mammalian host. Thus, an examination of biofilm formation of not only clinical, but of environmental isolates of E. coli, was undertaken here.;Enterohemorrhagic serogroups O157, O111 and O26 as well as environmental biofilm strains collected from three Northwestern Ontario water bodies were screened for their respective abilities to form biofilm in optimal laboratory medium. DNA-fingerprinting was then used in an effort to identify genetic diversity of the strains employed. Subsequently, one representative each from the O157 and environmental biofilm groups of E. coli, along with K-12, were selected for microscopic examination of biofilm development in optimal lab medium as well as filter-sterilized sewage-contaminated and uncontaminated lake water. Planktonic development was similarly monitored. When screened for biofilm formation in optimal laboratory medium, it was obvious that the environmental biofilm E. coli were significantly better formers than the others. Moreover, the O157 and O26 strains were nearly incapable of forming biofilm. It was further discovered that DNA fingerprint was not predictive of biofilm forming ability. Microscopic examination of the three representative E. coli selected revealed vastly differing biofilm phenotypes between organisms in the same medium as well as for the same organism in different media. The only bacterium to reach maturity was the environmental isolate, and then, only when grown in laboratory medium. Also noteworthy was the semi-mature biofilm formed by H32 in the sewage contaminated lake water. This presents public health concerns as it indicates that pathogenic E. coli have the capacity to adhere to abiotic surfaces, potentially in waters that see public use. In rich laboratory medium, planktonic and biofilm trends were very similar. However, in the poor environmental media, plankotnic cell densities fell over time while biofilm populations remained constant suggesting that indeed, the formation of biofilm provides a protective measure for bacteria when faced with poor environmental conditions. In addition to being the first to examine biofilm structure and development of pathogenic E. coli alongside natural varieties isolated from temperate water bodies, this research provides a useful foundation for the further study of biofilm formation of E. coli in temperate water bodies.
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