Inactivation of () induces the SOS response and MGEs mobilization and silences the general stress response and virulence program in .

Bacteria have evolved numerous regulatory pathways to survive in changing environments. The SOS response is an inducible DNA damage repair system that plays an indispensable role in bacterial adaptation and pathogenesis. Here we report a discovery of the previously uncharacterized protein Lmo0946 as an SOS response interfering factor (Sif) in the human pathogen Functional genetic studies demonstrated that is indispensable for normal growth of in stress-free as well as multi-stress conditions, and contributes to susceptibility to β-lactam antibiotics, biofilm formation and virulence.

Experimental Validation of RNA-RNA Interactions by Electrophoretic Mobility Shift Assay.

Regulatory RNAs in bacteria are known to act by base pairing with other RNAs. Interactions between two partner RNAs can be investigated by electrophoretic mobility shift assays. The regions predicted to be engaged in base pairing are analyzed by introducing mutations in one RNA that prevent RNA-RNA complex formation.

Anti-infective activities of long-chain fatty acids against foodborne pathogens.

Free fatty acids (FFAs) have long been acknowledged for their antimicrobial activity. More recently, long-chain FFAs (>12 carbon atoms) are receiving increased attention for their potent antivirulence activity against pathogenic bacteria. In the gastrointestinal tract, foodborne pathogens encounter a variety of long-chain FFAs derived from the diet, metabolic activities of the gut microbiota, or the host.

Chitin Attenuates Expression of Virulence Genes .

External signals are crucial for bacteria to sense their immediate environment and fine-tune gene expression accordingly. The foodborne pathogen senses a range of environmental cues in order to activate or deactivate the virulence-inducing transcriptional factor PrfA during transition between infectious and saprophytic lifecycles. Chitin is an abundant biopolymer formed from linked β-(1-4)-N-acetyl-D-glucosamine residues associated with fungi, the exoskeleton of insects and often incorporated into foods as a thickener or stabilizer.

The LhrC sRNAs control expression of T cell-stimulating antigen TcsA in Listeria monocytogenes by decreasing tcsA mRNA stability.

The bacterial pathogen Listeria monocytogenes encodes seven homologous small regulatory RNAs, named the LhrC family of sRNAs. The LhrCs are highly induced under infection-relevant conditions and are known to inhibit the expression of multiple target mRNAs encoding virulence-associated surface proteins. In all cases studied so far, the LhrCs use their CU-rich regions for base pairing to complementary AG-rich sequences of the ribosomal binding site (RBS) of specific target mRNAs.

Relies on the Heme-Regulated Transporter to Resist Heme Toxicity and Uses Heme as a Signal to Induce Transcription of , Encoding Adhesion Protein.

For pathogenic bacteria, host-derived heme represents an important metabolic cofactor and a source for iron. However, high levels of heme are toxic to bacteria. We have previously shown that excess heme has a growth-inhibitory effect on the Gram-positive foodborne pathogen , and we have learned that the LhrC1-5 family of small RNAs, together with the two-component system (TCS) LisRK, play a role in the adaptation of to heme stress conditions.

The Small Regulatory RNAs LhrC1-5 Contribute to the Response of to Heme Toxicity.

The LhrC family of small regulatory RNAs (sRNAs) is known to be induced when the foodborne pathogen is exposed to infection-relevant conditions, such as human blood. Here we demonstrate that excess heme, the core component of hemoglobin in blood, leads to a strong induction of the LhrC family members LhrC1-5. The heme-dependent activation of relies on the response regulator LisR, which is known to play a role in virulence and stress tolerance.

Mutational Analysis of sRNA-mRNA Base Pairing by Electrophoretic Mobility Shift Assay.

Small regulatory RNAs (sRNAs) in bacteria often act by base pairing to mRNAs. Direct interactions between an sRNA and its target mRNA can be investigated by electrophoretic mobility shift assay. In this assay, regions engaged in base pairing are analyzed by introducing mutations in one of the RNAs that prevent sRNA-mRNA complex formation, followed by the introduction of complementary mutations in its partner RNA that restore base pairing.

Thioridazine potentiates the effect of a beta-lactam antibiotic against Staphylococcus aureus independently of mecA expression.

The neuroleptic antipsychotic derivate thioridazine has been shown to increase the susceptibility of a methicillin-resistant Staphylococcus aureus (MRSA) isolate towards dicloxacillin. The aim of this study was to investigate the combinatorial effect of the two drugs on a broad selection of staphylococcal strains by analyzing a large collection of MRSA strains carrying different types of SCCmec, as well as MSSA strains. Transcription and translation of the resistance marker PBP2a encoded by mecA within the SCCmec cassette were analyzed by primer extension and western blotting.

A small RNA controls expression of the chitinase ChiA in Listeria monocytogenes.

In recent years, more than 60 small RNAs (sRNAs) have been identified in the gram-positive human pathogen Listeria monocytogenes, but their putative roles and mechanisms of action remain largely unknown. The sRNA LhrA was recently shown to be a post-transcriptional regulator of a single gene, lmo0850, which encodes a small protein of unknown function. LhrA controls the translation and degradation of the lmo0850 mRNA by an antisense mechanism, and it depends on the RNA chaperone Hfq for efficient binding to its target.