Biofilm formation by the Enterobacteriaceae: a comparison between Salmonella enteritidis, Escherichia coli and a nitrogen-fixing strain of Klebsiella pneumoniae

A simple laboratory reactor, which simulates biofilm formation in pipes, was used to compare biofilm formation by three members of the Enterobacteriaceae, namely, an environmental, nitrogen-fixing strain of Klebsiella pneumoniae , a pathogen, Salmonella enteritidis , and a faecal indicator, Escherichia coli. All three attached to CVCP pipe surfaces in the reactor and formed substantial biofilm populations of over a million bacteria cm^-2 within 24 h. These populations increased by approximately 10-fold over the next 48 h. Estimates of the numbers of metabolically active cells and the ratios of viable to direct counts showed that Kl. pneumoniae formed the densest and most metabolically active biofilms, followed by Salm. enteritidis and E. coli , respectively. Nitrogen fixation and polysaccharide production (EPS) by Kl. pneumoniae occurred only in mature biofilms and were of no selective advantage in the initiation of biofilms. Despite producing more EPS the rate of attachment of Salm. enteritidis was lower than for Kl. pneumoniae .