scholarly journals Finding of Agr Phase Variants in Staphylococcus aureus

mBio ◽  
2019 ◽  
Vol 10 (4) ◽  
Author(s):  
Vishal Gor ◽  
Aya J. Takemura ◽  
Masami Nishitani ◽  
Masato Higashide ◽  
Veronica Medrano Romero ◽  
...  
Keyword(s):  
Staphylococcus Aureus ◽  
Virulence Factors ◽  
Phase Variation ◽  
Accessory Gene ◽  
Content Type ◽  
Accessory Gene Regulator ◽  
Immune Mediated ◽  
A Minor ◽  
First Time ◽  
Phase Variants

ABSTRACT Staphylococcus aureus is an important human pathogen whose success is largely attributed to its vast arsenal of virulence factors that facilitate its invasion into, and survival within, the human host. The expression of these virulence factors is controlled by the quorum sensing accessory gene regulator (Agr) system. However, a large proportion of clinical S. aureus isolates are consistently found to have a mutationally inactivated Agr system. These mutants have a survival advantage in the host but are considered irreversible mutants. Here we show, for the first time, that a fraction of Agr-negative mutants can revert their Agr activity. By serially passaging Agr-negative strains and screening for phenotypic reversion of hemolysis and subsequent sequencing, we identified two mutational events responsible for reversion: a genetic duplication plus inversion event and a poly(A) tract alteration. Additionally, we demonstrate that one clinical Agr-negative methicillin-resistant S. aureus (MRSA) isolate could reproducibly generate Agr-revertant colonies with a poly(A) tract genetic mechanism. We also show that these revertants activate their Agr system upon phagocytosis. We propose a model in which a minor fraction of Agr-negative S. aureus strains are phase variants that can revert their Agr activity and may act as a cryptic insurance strategy against host-mediated stress. IMPORTANCE Staphylococcus aureus is responsible for a broad range of infections. This pathogen has a vast arsenal of virulence factors at its disposal, but avirulent strains are frequently isolated as the cause of clinical infections. These isolates have a mutated agr locus and have been believed to have no evolutionary future. Here we show that a fraction of Agr-negative strains can repair their mutated agr locus with mechanisms resembling phase variation. The agr revertants sustain an Agr OFF state as long as they exist as a minority but can activate their Agr system upon phagocytosis. These revertant cells might function as a cryptic insurance strategy to survive immune-mediated host stress that arises during infection.

scholarly journals Prevalence of Agr phase variants in Staphylococcus aureus

2020 ◽  
Vol 2 (7A) ◽  
Author(s):  
Vishal Gor ◽  
Mitsuaki Hoshi ◽  
Aya Takemura ◽  
Masato Higashide ◽  
Veronica Romero ◽  
...  
Keyword(s):  
Staphylococcus Aureus ◽  
Quorum Sensing ◽  
Virulence Factors ◽  
Human Pathogen ◽  
Accessory Gene ◽  
Accessory Gene Regulator ◽  
Inversion Event ◽  
First Time ◽  
Phase Variants ◽  
Phenotypic Reversion

Staphylococcus aureus is an important human pathogen whose success is largely attributed to its vast arsenal of virulence factors that facilitate its invasion into, and survival within, the human host. The expression of these virulence factors is controlled by the quorum sensing Accessory Gene Regulator (Agr) system. However, a large proportion of clinical S. aureus isolates are consistently found to have a mutationally inactivated Agr system. These mutants have a survival advantage in the host but are considered irreversible mutants. Here we show, for the first time, that a fraction of Agr-negative mutants can revert their Agr activity. By serially passaging Agr negative strains and screening for phenotypic reversion of haemolysis and subsequent sequencing, we identified two mutational events responsible for reversion: a genetic duplication plus inversion event and a poly(A) tract alteration. Additionally, we demonstrate that one clinical Agr-negative MRSA isolate could reproducibly generate Agr-revertant colonies with a poly(A) tract genetic mechanism. We also show that these revertants activate their Agr system upon phagocytosis. To assess the significance of our findings we screened a series of primary clinical isolates, which had undergone minimal handling post-isolation, and successfully identified a fraction which were Agr phase variants. Taken together, we propose a model where some Agr-negative S. aureus strains are phase variants who can revert their Agr activity and may act as a cryptic insurance strategy against host-mediated stress.

scholarly journals Generation of Virulence Factor Variants in Staphylococcus aureus Biofilms

2007 ◽  
Vol 189 (22) ◽  
pp. 7961-7967 ◽  
Author(s):  
Jeremy M. Yarwood ◽  
Kara M. Paquette ◽  
Ilya B. Tikh ◽  
Esther M. Volper ◽  
E. Peter Greenberg
Keyword(s):  
Staphylococcus Aureus ◽  
Virulence Factors ◽  
Hemolytic Activity ◽  
Bacterial Species ◽  
Phase Variation ◽  
Accessory Gene ◽  
Altered Expression ◽  
Sensing System ◽  
Accessory Gene Regulator ◽  
Different Strains

ABSTRACT Several serious diseases are caused by biofilm-associated Staphylococcus aureus. Colonial variants occur in biofilms of other bacterial species, and S. aureus variants are frequently isolated from biofilm-associated infections. Thus, we studied the generation of variants with altered expression of virulence factors in S. aureus biofilms. We observed that the number of variants found in biofilms, as measured by hemolytic activity, varied for different strains. Further study of hemolytic activity and signaling by the accessory gene regulator (Agr) quorum-sensing system in one S. aureus strain revealed three primary biofilm subpopulations: nonhemolytic (Agr deficient), hemolytic (Agr positive), and hyperhemolytic (also Agr positive). The nonhemolytic variant became the numerically dominant subpopulation in the biofilm. The nonhemolytic variant phenotype was stable and heritable, indicating a genetic perturbation, whereas the hyperhemolytic phenotype was unstable, suggesting a phase variation. Transcription profiling revealed that expression of the agr locus and many extracellular virulence factors was repressed in the nonhemolytic variant. Expression of the agr-activating gene, sarU, was also repressed in the nonhemolytic variant, suggesting one potential regulatory pathway responsible for the Agr-deficient phenotype. We suggest that the development of these variants in biofilms may have important clinical implications.

scholarly journals Impact of agr Functionality on the Outcome of Patients with Methicillin-Susceptible Staphylococcus aureus Bacteremia

2021 ◽  
Author(s):  
Jeong Eun Lee ◽  
Shinwon Lee ◽  
Sohee Park ◽  
Soon O. Lee ◽  
Sun H. Lee
Keyword(s):  
Staphylococcus Aureus ◽  
Accessory Gene ◽  
Content Type ◽  
Accessory Gene Regulator ◽  
Staphylococcus Aureus Bacteremia ◽  
Mssa Infection

Few studies have examined the association between methicillin-susceptible Staphylococcus aureus (MSSA) infection and accessory gene regulator ( agr ) functionality. We evaluated the association between agr dysfunction and mortality in patients with MSSA bacteremia.

scholarly journals Contribution of Lactococcus lactis Reducing Properties to the Downregulation of a Major Virulence Regulator in Staphylococcus aureus, theagrSystem

2014 ◽  
Vol 80 (22) ◽  
pp. 7028-7035 ◽  
Author(s):  
Sébastien Nouaille ◽  
Lucie Rault ◽  
Sophie Jeanson ◽  
Pascal Loubière ◽  
Yves Le Loir ◽  
...  
Keyword(s):  
Staphylococcus Aureus ◽  
Lactic Acid ◽  
Lactococcus Lactis ◽  
Response Regulator ◽  
Food Poisoning ◽  
Accessory Gene ◽  
Content Type ◽  
Accessory Gene Regulator ◽  
Virulence Regulator ◽  
Reducing Properties

ABSTRACTStaphylococcus aureusis a major cause of food poisoning outbreaks associated with dairy products, because of the ingestion of preformed enterotoxins. The biocontrol ofS. aureususing lactic acid bacteria (LAB) offers a promising opportunity to fight this pathogen while respecting the product ecosystem. We had previously established the ability ofLactococcus lactis, a lactic acid bacterium widely used in the dairy industry, to downregulate a major staphylococcal virulence regulator, the accessory gene regulator (agr) system, and, as a consequence,agr-controlled enterotoxins. In the present paper, we have shown that the oxygen-independent reducing properties ofL. lactiscontribute toagrdownregulation. Neutralizing lactococcal reduction by adding potassium ferricyanide or maintaining the oxygen pressure constant at 50% releasedagrdownregulation in the presence ofL. lactis. This downregulation still occurred in anS. aureus srrAmutant, indicating that the staphylococcal respiratory response regulator SrrAB was not the only component in the signaling pathway. Therefore, this study clearly demonstrates the ability ofL. lactisreducing properties to interfere with the expression ofS. aureusvirulence, thus highlighting this general property of LAB as a lever to control the virulence expression of this major pathogen in a food context and beyond.

scholarly journals Staphylococcal Virulence Factors on the Skin of Atopic Dermatitis Patients

mSphere ◽  
2019 ◽  
Vol 4 (6) ◽  
Author(s):  
Mary C. Moran ◽  
Michael P. Cahill ◽  
Matthew G. Brewer ◽  
Takeshi Yoshida ◽  
Sara Knowlden ◽  
...  
Keyword(s):  
Staphylococcus Aureus ◽  
Atopic Dermatitis ◽  
Virulence Factors ◽  
Virulence Factor ◽  
Protein Level ◽  
Content Type ◽  
Factor Production ◽  
First Time ◽  
Virulence Factor Production ◽  
Specific Virulence

ABSTRACT Staphylococcus aureus is the leading cause of skin and soft tissue infections, bacteremia, infective endocarditis, osteoarticular, pleuropulmonary, and device-related infections. Virulence factors secreted by S. aureus, including superantigens and cytotoxins, play significant roles in driving disease. The ability to identify virulence factors present at the site of infection will be an important tool in better identifying and understanding how specific virulence factors contribute to disease. Previously, virulence factor production has been determined by culturing S. aureus isolates and detecting the mRNA of specific virulence factors. We demonstrated for the first time that virulence factors can be directly detected at the protein level from human samples, removing the need to first culture isolated bacteria. Superantigens and cytotoxins were detected and quantified with a Western dot blot assay by using reconstituted skin swabs obtained from patients with atopic dermatitis. This methodology will significantly enhance our ability to investigate the complex host-microbe environment and the effects various therapies have on virulence factor production. Overall, the ability to directly quantify virulence factors present at the site of infection or colonization will enhance our understanding of S. aureus-related diseases and help identify optimal treatments. IMPORTANCE For the first time, we show that secreted staphylococcal virulence factors can be quantified at the protein level directly from skin swabs obtained from the skin of atopic dermatitis patients. This technique eliminates the need to culture Staphylococcus aureus and then test the strain’s potential to produce secreted virulence factors. Our methodology shows that secreted virulence factors are present on the skin of atopic patients and provides a more accurate means of evaluating the physiological impact of S. aureus in inflammatory diseases such as atopic dermatitis.

scholarly journals Virulence Reversion in Staphylococcus aureus

Proceedings ◽  
2021 ◽  
Vol 66 (1) ◽  
pp. 24
Author(s):  
Vishal Gor ◽  
Mitsuaki Hoshi ◽  
Aya J. Takemura ◽  
Masato Higashide ◽  
Veronica Medrano Romero ◽  
...  
Keyword(s):  
Staphylococcus Aureus ◽  
Regulatory System ◽  
Opportunistic Pathogen ◽  
Accessory Gene ◽  
Genetic Changes ◽  
Accessory Gene Regulator ◽  
Heavy Burden ◽  
The Common ◽  
Phase Variants ◽  
Inactivating Mutations

Staphylococcus aureus is a Gram-positive opportunistic pathogen that imposes a heavy burden on society. What sets this pathogen apart is the sheer spectrum of infections it can cause, which range from benign skin and soft tissue infections to lethal endocarditis and bacteraemia. The ability of S. aureus to cause this gamut of infections is conferred by its arsenal of virulence factors that are under the control of the Accessory Gene Regulator (Agr) system. However, a large proportion of clinical isolates have inactivating mutations in this important regulatory system. We previously showed that, contrary to the common dogma, not all these mutations are evolutionary ‘dead-ends’ and a fraction are phase variants which can revert to an Agr active state. Here we report that some Agr deficient isolates can revert a haemolytic phenotype without repairing their Agr system. We collected a series of 30 Agr negative primary patient samples in order to assess the significance of our previous findings on the existence of Agr phase variants. We used primary samples to avoid strains that had undergone multiple clonal expansions before being tested for reversibility. We assessed Agr reversibility by serially passaging strains and screening for phenotypic reversion of haemolysis. We show that two strains reverted haemolysis and one reverted alpha haemolysin activity without any genetic changes in agr (and hla for the alpha revertant). These results add further complexity to the phenomenon of Agr shutdown observed in the clinical setting and corroborate recent findings of compensatory mutations arising in Agr deficient clinical strains.

scholarly journals Accessory Gene Regulator (agr) Dysfunction in Staphylococcus aureus Bloodstream Isolates from South Korean Patients

2012 ◽  
Vol 57 (3) ◽  
pp. 1509-1512 ◽  
Author(s):  
Yong Pil Chong ◽  
Eun Sil Kim ◽  
Su-Jin Park ◽  
Ki-Ho Park ◽  
Tark Kim ◽  
...  
Keyword(s):  
Staphylococcus Aureus ◽  
Tertiary Care ◽  
Hospital Setting ◽  
Care Hospital ◽  
Accessory Gene ◽  
Content Type ◽  
South Korean ◽  
Accessory Gene Regulator ◽  
Clonal Spread ◽  
Hospital Acquired

ABSTRACTWe describe the genetic and microbiological characteristics of methicillin-resistantStaphylococcus aureus(MRSA) bloodstream isolates withagrdysfunction from a tertiary-care hospital in Korea. Of these, ST5-SCCmectype II-agrgroup II MRSA isolates, which are known to be prevalent in hospital-acquired infections in Korea, were the most abundant, because of the clonal spread of a specificagr-defective lineage. This finding suggests that the loss ofagrfunction may confer a potential advantage in a hospital setting. Clonal spread of a specific defective-agrstrain was not observed among community-associated MRSA or methicillin-susceptibleS. aureusclones, regardless of community or hospital acquisition of infection.agr-defective clones, including ST5 and ST239 MRSA, were enriched for heteroresistant vancomycin-intermediateS. aureus.

scholarly journals Front-Loaded Linezolid Regimens Result in Increased Killing and Suppression of the Accessory Gene Regulator System of Staphylococcus aureus

2012 ◽  
Vol 56 (7) ◽  
pp. 3712-3719 ◽  
Author(s):  
Brian T. Tsuji ◽  
Tanya Brown ◽  
Ridhi Parasrampuria ◽  
Daniel A. Brazeau ◽  
Alan Forrest ◽  
...  
Keyword(s):  
Staphylococcus Aureus ◽  
Growth Control ◽  
Study Endpoint ◽  
Infection Model ◽  
Accessory Gene ◽  
Bacterial Killing ◽  
Content Type ◽  
Accessory Gene Regulator ◽  
Pharmacodynamic Profile ◽  
The Impact

ABSTRACTFront loading is a strategy used to optimize the pharmacodynamic profile of an antibiotic through the administration of high doses early in therapy for a short duration. Our aims were to evaluate the impact of front loading of linezolid regimens on bacterial killing and suppression of resistance and on RNAIII, the effector molecule of the accessory gene regulator system (encoded byagr) in methicillin-resistantStaphylococcus aureus(MRSA). Time-killing experiments over 48 h were utilized for linezolid against four strains of MRSA: USA100, USA300, USA400, and ATCC 29213. A hollow-fiber infection model simulated traditional and front-loaded human therapeutic regimens of linezolid versus USA300 at 106CFU/ml over 240 h. Over 48 h in time-kill experiments, linezolid displayed bacteriostatic activity, with reductions of >1 log10CFU/ml for all strains. Front-loaded regimens that were administered over 5 days, 1,200 mg every 12 h (q12h) (total, 10 doses) and 2,400 mg q12h (total, 10 doses) followed by 300 mg q12h thereafter, resulted in sustained bactericidal activity, with reductions of the area under the CFU curve of −6.15 and −6.03, respectively, reaching undetectable limits at the 10-day study endpoint. All regimens displayed a reduction in RNAIII relative expression at 24 h and 240 h compared with that of the growth control. Monte Carlo simulations predicted a <1.27× increase in the fractional decreases in platelets for all front-loaded regimens versus the 600 mg q12h regimen, except for the highest-dose front-loaded regimen. Front-loading strategies for linezolid are promising and may be of utility in severe MRSA infections, where early aggressive therapy is necessary.

scholarly journals Identification and characterization of msa (SA1233), a gene involved in expression of SarA and several virulence factors in Staphylococcus aureus

Microbiology ◽  
2006 ◽  
Vol 152 (9) ◽  
pp. 2559-2572 ◽  
Author(s):  
Karthik Sambanthamoorthy ◽  
Mark S. Smeltzer ◽  
Mohamed O. Elasri
Keyword(s):  
Staphylococcus Aureus ◽  
Virulence Factors ◽  
Protein A ◽  
Laboratory Strain ◽  
Reporter System ◽  
Accessory Gene ◽  
Accessory Gene Regulator ◽  
Genes Encoding ◽  
Membrane Spanning ◽  
The Impact

The staphylococcal accessory regulator (sarA) plays a central role in the regulation of virulence in Staphylococcus aureus. To date, studies involving sarA have focused on its activity as a global regulator that modulates transcription of a wide variety of genes (>100) and its role in virulence. However, there is also evidence to suggest the existence of accessory elements that modulate SarA production and/or function. A reporter system was developed to identify such elements, and a new gene, msa (SA1233), mutation of which results in reduced expression of SarA, was identified and characterized. Additionally, it was shown that mutation of msa resulted in altered transcription of the accessory gene regulator (agr) and the genes encoding several virulence factors including alpha toxin (hla) and protein A (spa). However, the impact of mutating msa was different in the laboratory strain RN6390 and the clinical isolate UAMS-1. For instance, mutation of msa caused a decrease in spa and hla transcription in RN6390 but had a different effect in UAMS-1. The strain-dependent effects of the msa mutation were similar to those observed previously, which suggests that msa may modulate the production of specific virulence factors through its impact on sarA. Interestingly, sequence analysis of Msa suggests that it is a putative membrane protein with three membrane-spanning regions, indicating that Msa might interact with the environment. The findings show that msa is involved in the expression of SarA and several virulence factors.

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