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Surface Layer Protein EA1 Is Not a Component of Bacillus anthracis Spores but Is a Persistent Contaminant in Spore Preparations. David D. Williams, 2004.EA1 is an abundant, highly antigenic, surface layer protein of Bacillus anthracis vegetative cells . Recent studies indicate that EA1 is also a component of B . anthracis spores and a potential marker for spore detection . We show here that EA1 is not a spore component but a persistent contaminant in spore preparations . Listeria monocytogenes  B Regulates Stress Response and Virulence Functions.Mark J. Kazmierczak, 2003.While the stress-responsive alternative sigma factor B
has been identified in different species of Bacillus,
Listeria, and Staphylococcus, the
B regulon has been extensively characterized only
in B . subtilis. We combined biocomputing and microarray-based
strategies to identify
B-dependent genes in the
facultative intracellular pathogen Listeria monocytogenes.
Hidden Markov model (HMM)-based searches identified 170 candidate
B-dependent promoter sequences in the strain EGD-e
genome sequence . These data were used to develop a specialized,
208-gene microarray, which included 166 genes downstream of
HMM-predicted
B-dependent promoters as well as
selected virulence and stress response genes . RNA for the microarray
experiments was isolated from both wild-type and
 sigB
null mutant L . monocytogenes cells grown to stationary phase
or exposed to osmotic stress (0.5 M KCl) . Microarray analyses
identified a total of 55 genes with statistically significant
B-dependent expression under the conditions used in
these experiments, with at least 1.5-fold-higher expression in the wild
type over the sigB mutant under either stress condition (51
genes showed at least 2.0-fold-higher expression in the wild type) . Of
the 55 genes exhibiting
B-dependent expression, 54
were preceded by a sequence resembling the
B
promoter consensus sequence . Rapid amplification of cDNA ends-PCR was
used to confirm the
B-dependent nature of a subset
of eight selected promoter regions . Notably, the
B-dependent L . monocytogenes genes
identified through this HMM/microarray strategy included both stress
response genes (e.g., gadB, ctc, and the glutathione
reductase gene lmo1433) and virulence genes (e.g.,
inlA, inlB, and bsh) . Our data demonstrate
that, in addition to regulating expression of genes important for
survival under environmental stress conditions,
B
also contributes to regulation of virulence gene expression in L.
monocytogenes. These findings strongly suggest that
B contributes to L . monocytogenes gene
expression during
infection .
Characterization of the RpoS Status of Clinical Isolates of Salmonella enterica. Véronique Robbe-Saule, 2003.The stationary-phase-inducible sigma factor,  S (RpoS), is the master regulator of the general stress response in Salmonella and is required for virulence in mice . rpoS mutants can frequently be isolated from highly passaged laboratory strains of Salmonella . We examined the rpoS status of 116 human clinical isolates of Salmonella, including 41 Salmonella enterica serotype Typhi strains isolated from blood, 38 S . enterica serotype Typhimurium strains isolated from blood, and 37 Salmonella serotype Typhimurium strains isolated from feces . We examined the abilities of these strains to produce the
S protein, to express RpoS-dependent catalase activity, and to resist to oxidative stress in the stationary phase of growth . We also carried out complementation experiments with a cloned wild-type rpoS gene . Our results showed that 15 of the 41 Salmonella serotype Typhi isolates were defective in RpoS . We sequenced the rpoS allele of 12 strains . This led to identification of small insertions, deletions, and point mutations resulting in premature stop codons or affecting regions 1 and 2 of
S, showing that the rpoS mutations are not clonal . Thus, mutant rpoS alleles can be found in freshly isolated clinical strains of Salmonella serotype Typhi, and they may affect virulence properties . Interestingly however, no rpoS mutants were found among the 75 Salmonella serotype Typhimurium isolates . Strains that differed in catalase activity and resistance to hydrogen peroxide were found, but the differences were not linked to the rpoS status . This suggests that Salmonella serotype Typhimurium rpoS mutants are counterselected because rpoS plays a role in the pathogenesis of Salmonella serotype Typhimurium in humans or in the transmission cycle of the disease .
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