Analyses of the putative Crp/Fnr family of transcriptional regulators of a serotype 4b strain of Listeria monocytogenes.

A whole-genome sequence analysis of Listeria monocytogenes strain F2365 revealed 15 potential members of the Crp/Fnr family of transcriptional regulatory proteins. Each gene and the flanking regions were cloned, subjected to in vitro transpositional mutagenesis, and recombined into strain F2365. Mutant strains, produced for 14 of the family members, were compared to strain F2365 for differences in carbon utilization, resistance to oxidative stress, and growth under reduced oxygen conditions that would signal an Fnr- or Crp-like function for these proteins.

Survival of Listeria monocytogenes strain H7762 and resistance to simulated gastric fluid following exposure to frankfurter exudate.

Listeria monocytogenes strain H7762, a frankfurter isolate, was tested to determine whether it was able to survive at 4 degrees C in frankfurter pack fluid (exudate) and to determine whether food exposure affects its acid sensitivity. Cultures were sampled and tested for acid sensitivity by challenge with simulated gastric fluid (SGF). SGF challenges performed immediately after inoculation revealed that between 20 and 26% of the cells survived the full 30 min of SGF challenge regardless of whether the cells were inoculated into brain heart infusion broth (BHI) or exudate.

Whole genome comparisons of serotype 4b and 1/2a strains of the food-borne pathogen Listeria monocytogenes reveal new insights into the core genome components of this species.

The genomes of three strains of Listeria monocytogenes that have been associated with food-borne illness in the USA were subjected to whole genome comparative analysis. A total of 51, 97 and 69 strain-specific genes were identified in L.monocytogenes strains F2365 (serotype 4b, cheese isolate), F6854 (serotype 1/2a, frankfurter isolate) and H7858 (serotype 4b, meat isolate), respectively.

The htrA (degP) gene of Listeria monocytogenes 10403S is essential for optimal growth under stress conditions.

This report describes a mutant of Listeria monocytogenes strain 10403S (serotype 1/2a) with a defective response to conditions of high osmolarity, an environment that L. monocytogenes encounters in some ready-to-eat foods. A library of L.

Use of pulsed-field gel electrophoresis to monitor a five-strain mixture of Listeria monocytogenes in frankfurter packages.

In a previous study, the viability of a five-strain mixture of Listeria monocytogenes (including Scott A [serotype 4b, clinical isolate], 101M [serotype 4b, beef-pork sausage isolate], F6854 [serotype 1/2a, turkey frankfurter isolate], H7776 [serotype 4b, frankfurter isolate], and MFS-2 [serotype 1/2a, pork plant isolate]) was monitored during refrigerated storage of frankfurters prepared with and without 3.0% added potassium lactate. Throughout a 90-day period of storage at 4 degrees C, the initial inoculum level of 20 CFU per package remained relatively constant in packages containing frankfurters prepared with potassium lactate, but pathogen counts increased to 4.

Use of pulsed-field gel electrophoresis to characterize the heterogeneity and clonality of salmonella isolates obtained from the carcasses and feces of swine at slaughter.

Salmonella enterica isolates were recovered from swine at a collaborating processing plant over a 2-month period in the spring of 2000. In the present study, molecular subtyping by pulsed-field gel electrophoresis (PFGE) was performed on the 581 confirmed Salmonella isolates from the 84 Salmonella-positive samples obtained from the previous study. A total of 32 different PFGE pulsotypes were observed visually, and a BioNumerics software analysis clustered those pulsotypes into 12 PFGE groups.

GcvA binding site 1 in the gcvTHP promoter of Escherichia coli is required for GcvA-mediated repression but not for GcvA-mediated activation.

GcvA binds to three sites in the gcvTHP control region, from base -34 to -69 (site 1), from base -214 to -241 (site 2) and from base -242 to -271 (site 3). Previous results suggested that sites 3 and 2 are required for both GcvA-dependent activation and repression of a gcvT::lacZ fusion. However, the results were less clear as to the role of site 1.