Susceptibility of suspended and surface-attached Salmonella enteritidis to biocides and elevated temperatures

Effect of flagella on initial attachment of Listeria monocytogenes to stainless steel

At 22 degrees C a flagellin mutant of Listeria monocytogenes was found to attach to stainless steel at levels 10-fold lower than wild-type cells, even under conditions preventing active motility. At 37 degrees C, when flagella are not produced, attachment of both strains was identical. Therefore, flagella per se facilitate the early stage of attachment.

Engineering the luxCDABE genes from Photorhabdus luminescens to provide a bioluminescent reporter for constitutive and promoter probe plasmids and mini-Tn5 constructs

The luxCDABE operon of Photorhabdus luminescens has been cloned and engineered as an easily mobilisable cassette flanked by sites for commonly used restriction enzymes. Constitutive and promoter probe plasmids utilising the P. luminescens luxCDABE have been constructed using a number of compatible replicons and antibiotic markers. Complementary to these plasmids, a range of promoterless and constitutive luxCDABE mini-Tn5 derivatives has been constructed. The potential of coupling mini-Tn5 luxCDABE promoter probe transposons with automated luminometry and photometry to screen for mutants that exhibit growth phase variation in gene expression is demonstrated.

Thin aggregative fimbriae enhance Salmonella enteritidis biofilm formation

Salmonella enteritidis enteropathogens produce a variety of potentially adherent fimbrial types including SEF14, SEF17, SEF18 and SEF21 (type I). In a simplified, pure culture, biofilm generating system the virulent isolate, S. enteritidis 3b, readily adhered to Teflon (polytetrafluoroethylene) and stainless steel forming thick cell aggregates. The inability of an isogenic SEF17-deficient mutant to form thick biofilms suggested a role for SEF17 in stabilizing cell-cell interactions during biofilm formation. Epifluorescent detection of SEF17 in biofilms confirmed the association of these fimbriae with aggregated cells but not with adherent mutants unable to produce SEF17. The reduced adherence observed with an isogenic SEF14/SEF21-deficient strain implicated the involvement of additional cell surface adherence factors, possibly including SEF21 (type I) fimbriae in the adherence of S. enteritidis to stainless steel or Teflon. The role of SEF17 fimbriae in biofilm formation and the contributions of SEF17 to the persistence of Salmonellae on surfaces and in food are discussed.

Challenging food microbiology from a molecular perspective

Summary: Two key themes within food microbiology are bacterial detection and control. There is a raft of sub-headings under each of these themes, but in the last decade molecular approaches within each have made a significant contribution to the field. This is a personal review of the author’s past and present contributions and future ideas for challenging food microbiology from a molecular perspective.

Synergism in biofilm formation between Salmonella enteritidis and a nitrogen-fixing strain of Klebsiella pneumoniae

A laboratory reactor, which simulates biofilm formation in water pipes, was used to study interactions in biofilm formation between a nitrogen-fixing strain of Klebsiella pneumoniae and Salmonella enteritidis. The level of attachment of Salm. enteritidis was higher in the binar biofilm than in the single species biofilm. In the initial colonization phase the binary biofilm contained a much higher proportion of metabolically active cells than in single species biofilms formed by either Salm. enteritidis or Kl. pneumoniae. When a pulse of Salm. enteritidis was passed over an already established biofilm of Kl. pneumoniae it rapidly became integrated into the biofilm, from where it was subsequently released into the water column, along with Kl. pneumoniae. Klebsiella pneumoniae fixed nitrogen in the presence of Salm. enteritidis in both types of biofilm.

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.

Use of bioluminescence to model the thermal inactivation of Salmonella typhimurium in the presence of a competitive microflora

The survival of Salmonella typhimurium was investigated by bioluminescence and standard plating techniques in pure cultures and in the presence of competitors after the cultures were heated to 55 degrees C for increasing lengths of time. Decimal reduction (D) values increased from 0.43 to 2.09 min in the presence of 10(8) CFU of competitors ml-1, indicating a significant protective effect.