Evidence for Rho-dependent control of a virulence switch in .

is a significant cause of infections in the healthcare setting. More recently, has been a leading cause of secondary bacterial pneumonia in patients infected with SARS-CoV-2 and the overall frequency of infection increased 78% during the COVID-19 pandemic. can exist in virulent or avirulent subpopulations and this interconversion is mediated by the expression of a family of TetR-type transcriptional regulators.

Stochastic activation of a family of TetR type transcriptional regulators controls phenotypic heterogeneity in .

Phenotypic heterogeneity is an important mechanism for regulating bacterial virulence, where a single regulatory switch is typically activated to generate virulent and avirulent subpopulations. The opportunistic pathogen can transition at high frequency between virulent opaque (VIR-O) and avirulent translucent subpopulations, distinguished by cells that form opaque or translucent colonies. We demonstrate that expression of 11 TetR-type transcriptional regulators (TTTRs) can drive cells from the VIR-O opaque subpopulation to cells that form translucent colonies.

Extraction and Visualization of Capsular Polysaccharide from Acinetobacter baumannii.

Methods to determine the presence of a bacterial capsule typically involve the use of stains specific for capsule, the exclusion of a dye by the capsule or by electron microscopy. However, these procedures require equipment that may not be readily available to all researchers. Here we describe a method for extraction, visualization, and quantification of extracellular capsular polysaccharide from Acinetobacter baumannii with commonly used reagents and equipment.

Role of Capsule in Resistance to Disinfectants, Host Antimicrobials, and Desiccation in Acinetobacter baumannii.

strain AB5075 forms two cell types distinguished by their opaque (VIR-O) or translucent (AV-T) colonies. VIR-O cells possess a thicker capsule and are more resistant to a variety of stressors than AV-T cells. However, the direct role of the capsule in these stressors was unknown.

A high-frequency phenotypic switch links bacterial virulence and environmental survival in Acinetobacter baumannii.

Antibiotic-resistant infections lead to 700,000 deaths per year worldwide . The roles of phenotypically diverse subpopulations of clonal bacteria in the progression of diseases are unclear. We found that the increasingly pathogenic and antibiotic-resistant pathogen Acinetobacter baumannii harbours a highly virulent subpopulation of cells responsible for disease.

An Two-Component System Ortholog Regulates Phase Variation, Osmotic Tolerance, Motility, and Virulence in Acinetobacter baumannii Strain AB5075.

Recently, a novel phase-variable colony opacity phenotype was discovered in strain AB5075, where colonies interconvert between opaque and translucent variants. Opaque colonies become mottled or sectored after 24 h of growth due to translucent variants arising within the colony. This easily distinguishable opaque-colony phenotype was used to screen for random transposon insertions that increased the frequency of sectoring at a time point when wild-type colonies were uniformly opaque.

Multiple roles for a novel RND-type efflux system in Acinetobacter baumannii AB5075.

Colony opacity phase variation in Acinetobacter baumannii strain AB5075 is regulated by a reversible high-frequency switch. Transposon mutagenesis was used to generate mutations that decreased the opaque to translucent switch and a gene encoding a predicted periplasmic membrane fusion component of a resistance-nodulation-cell division (RND)-type efflux system was isolated. This gene was designated arpA and immediately downstream was a gene designated arpB that encodes a predicted membrane transporter of RND-type systems.

Phase-Variable Control of Multiple Phenotypes in Acinetobacter baumannii Strain AB5075.

Unlabelled: Acinetobacter baumannii strain AB5075 produces colonies with two opacity phenotypes, designated opaque and translucent. These phenotypes were unstable and opaque and translucent colony variants were observed to interconvert at high frequency, suggesting that a phase-variable mechanism was responsible. The frequency of phase variation both within colonies and in broth cultures increased in a cell density-dependent manner and was mediated by the accumulation of an extracellular factor.

Post-transcriptional regulation of gene PA5507 controls Pseudomonas quinolone signal concentration in P. aeruginosa.

Pseudomonas aeruginosa can sense and respond to a myriad of environmental signals and utilizes a system of small molecules to communicate through intercellular signaling. The small molecule 2-heptyl-3-hydroxy-4-quinolone (Pseudomonas Quinolone Signal [PQS]) is one of these signals and its synthesis is important for virulence. Previously, we identified an RpiR-type transcriptional regulator, QapR, that positively affects PQS production by repressing the qapR operon.

QapR (PA5506) represses an operon that negatively affects the Pseudomonas quinolone signal in Pseudomonas aeruginosa.

Pseudomonas aeruginosa is a Gram-negative, opportunistic pathogen that can cause disease in varied sites within the human body and is a significant source of morbidity and mortality in those afflicted with cystic fibrosis. P. aeruginosa is able to coordinate group behaviors, such as virulence factor production, through the process of cell-to-cell signaling.