Relevance of spontaneousfabTmutations to a streptococcal toxic shock syndrome to non-streptococcal toxic shock syndrome transition in the novel-typeStreptococcus pyogenesisolates that lost asalRK

The double-edged role of FASII regulator FabT in Streptococcus pyogenes infection

In Streptococcus pyogenes, the type II fatty acid (FA) synthesis pathway FASII is feedback-controlled by the FabT repressor bound to an acyl-Acyl carrier protein. Although FabT defects confer reduced virulence in animal models, spontaneous fabT mutants arise in vivo. We resolved this paradox by characterizing the conditions and mechanisms requiring FabT activity, and those promoting fabT mutant emergence. The fabT defect leads to energy dissipation, limiting mutant growth on human tissue products, which explains the FabT requirement during infection. Conversely, emerging fabT mutants show superior growth in biotopes rich in saturated FAs, where continued FASII activity limits their incorporation. We propose that membrane alterations and continued FASII synthesis are the primary causes for increased fabT mutant mortality in nutrient-limited biotopes, by failing to stop metabolic consumption. Our findings elucidate the rationale for emerging fabT mutants that improve bacterial survival in lipid-rich biotopes, but lead to a genetic impasse for infection.

Pangenome evaluation of gene essentiality in Streptococcus pyogenes

Bacterial species often consist of strains with variable gene content, collectively referred to as the pangenome. Variations in the genetic makeup of strains can alter bacterial physiology and fitness. To define biologically relevant genes of a genome, genome-wide transposon mutant libraries have been used to identify genes essential for survival or virulence in a given strain. Such phenotypic studies have been conducted in four different genotypes of the human pathogen Streptococcus pyogenes, yet challenges exist in comparing results across studies conducted in different genetic backgrounds and conditions. To advance genotype to phenotype inferences across different S. pyogenes strains, we built a pangenome database of 249 S. pyogenes reference genomes. We systematically re-analyzed publicly available transposon sequencing datasets from S. pyogenes using a transposon sequencing-specific analysis pipeline, Transit. Across four genetic backgrounds and nine phenotypic conditions, 355 genes were essential for survival, corresponding to ~24% of the core genome. Clusters of Orthologous Genes (COG) categories related to coenzyme and lipid transport and growth functions were overrepresented as essential. Finally, essential operons across S. pyogenes genotypes were defined, with an increased number of essential operons detected under in vivo conditions. This study provides an extendible database to which new studies can be added, and a searchable html-based resource to direct future investigations into S. pyogenes biology.IMPORTANCEStreptococcus pyogenes is a human-adapted pathogen occupying restricted ecological niches. Understanding the essentiality of genes across different strains and experimental conditions is important to direct research questions and efforts to prevent the large burden of disease caused by S. pyogenes. To this end we systematically reanalyzed transposon sequencing studies in S. pyogenes using transposon sequencing-specific methods, integrating them into an extendible meta-analysis framework. This provides a repository of gene essentiality in S. pyogenes which was used to highlight specific genes of interest and for the community to guide future phenotypic studies.

Acyl-AcpB, a FabT corepressor in Streptococcus pyogenes

Membranes are a universal barrier to all cells. Phospholipids, essential bacterial membrane components, are composed of a polar head and apolar fatty acid (FA) chains. Most bacterial FAs are synthesized by the Type II FA synthesis pathway (FASII). In Streptococcaceae, Enterococci, and Lactococcus lactis, a unique feedback mechanism controls the FASII gene expression. FabT, encoded in the FASII main locus, is the repressor, and it is activated by long-chain acyl-acyl carrier protein (acyl-ACP). Many Streptococci, Enterococcus faecalis, but not L. lactis, possess two ACPs. The AcpA-encoding gene is within the FASII locus and is coregulated with the FASII genes. Acyl-AcpA is the end product of FASII. The AcpB-encoding gene is in operon with plsX encoding an acyl-ACP:phosphate acyltransferase. The role of acyl-AcpB as FabT corepressor is controversial. Streptococcus pyogenes, which causes a wide variety of diseases ranging from mild non-invasive to severe invasive infections, possesses AcpB. In this study, by comparing the expression of FabT-controlled genes in an acpB-deleted mutant with those in a wild-type and in a fabT mutant strain, grown in the presence or absence of exogenous FAs, we show that AcpB is the S. pyogenes FabT main corepressor. Its deletion impacts membrane FA composition and bacterial adhesion to eucaryotic cells, highlighting the importance of FASII control. Importance Membrane composition is crucial for bacterial growth or interaction with the environment. Bacteria synthesize fatty acids (FAs), membrane major constituents, via the Type II FAS (FASII) pathway. Streptococci control the expression of the FASII genes via a transcriptional repressor, FabT, with acyl-acyl carrier proteins (ACPs) as corepressor. Streptococcus pyogenes that causes a wide variety of diseases ranging from mild non-invasive to severe invasive infections possesses two ACPs. acpA, but not acpB, is a FASII gene. In this study, we show that acyl-AcpBs are FabT main corepressors. Also, AcpB deletion has consequences on the membrane FA composition and bacterial adhesion to host cells. In addition to highlighting the importance of FASII control in the presence of exogeneous FAs for the adaptation of bacteria to their environment, our data indicate that FASII gene repression is mediated by a corepressor whose gene expression is not repressed in the presence of exogenous FAs.

General Phenotype of NADase Induction by CLI Treatment in Streptococcus pyogenes

The administration of high-dose clindamycin (CLI) along with penicillin is recommended for the treatment of streptococcal toxic-shock syndrome (STSS). However, we previously reported that a “subinhibitory dose” of CLI induced the expression of the NAD-glycohydrolase (NADase) exotoxin in an emm1-type Streptococcus pyogenes 1529 strain isolated from an STSS patient. In this study, we examine NADase induction by CLI treatment using an extracellular NADase activity assay instead of the previous two-dimensional gel electrophoresis assay. The examination revealed that CLI administration can induce NADase expression in a dose-dependent manner. We analyzed 23 CLI-susceptible strains (5 emm1 strains, 6 emm3 strains, 3 emm4 strains, 1 emm6 strain, 3 emm12 strains, 1 emm28 strain, and 4 emm89 strains), and 19 of the 23 strains showed similar NADase induction phenotypes to that shown in strain 1529. These results indicate that NADase induction by CLI treatment is not restricted to specific strains and it could be a standard phenotype among CLI-susceptible S. pyogenes strains. We also analyzed four CLI-resistant strains. All four strains showed increased extracellular NADase activities at high concentrations of CLI that did not inhibit bacterial growth. These results indicated that the subinhibitory dose of CLI was not the critical factor for NADase induction.

FabT, a Bacterial Transcriptional Repressor That Limits Futile Fatty Acid Biosynthesis

Phospholipids are vital membrane constituents that determine cell functions and interactions with the environment. For bacterial pathogens, rapid adjustment of phospholipid composition to changing conditions during infection can be crucial for growth and survival. Fatty acid synthesis (FASII) regulators are central to this process. This review puts the spotlight on FabT, a MarR-family regulator of FASII characterized in streptococci, enterococci, and lactococci. Roles of FabT in virulence, as reported in mouse and nonhuman primate infection models, will be discussed. We present FabT structure, the FabT regulon, and changes in FabT regulation according to growth conditions. A unique feature of FabT concerns its modulation by an unconventional corepressor, acyl-acyl-carrier protein (ACP). Some bacteria express two ACP proteins, which are distinguished by their interactions with endogenous or exogenous fatty acid sources, one of which causes strong FabT repression. This system seems to allow preferred use of environmental fatty acids, thereby saving energy by limiting futile FASII activity. Control of fabT expression and FabT activity link various metabolic pathways to FASII. The various physiological consequences of FabT loss summarized here suggest that FabT has potential as a narrow range therapeutic target.

A case of streptococcus necrotizing fasciitis secondary to acute tonsillitis and review of literatures

Necrotizing fasciitis, officially named by Wilson in 1952, was a rare potentially life-threatening necrotizing soft tissue infections disease. The main lesions showed subcutaneous fat and fascia layer in progressive necrosis, generally not involving muscles. It was characterized by acute onset, rapid progress, and dangerous condition, often accompanied by systemic toxin shock, which was a relatively rare clinical acute critical disease with high mortality rate. Necrotizing fasciitis is a rare but clinical critical disease. The overall incidence of necrotizing fasciitis is approximately 0.04 cases per 1000 persons in the United States, the 30-day mortality is 27%, and necrotizing fasciitis–related mortality in Asian region is about 28%. Streptococcus pyogenes (group A streptococcus) are human-specific pathogens that can cause upper respiratory tract infection such as tonsillitis, associated with post-infection diseases such as rheumatic fever, and also can induce severe invasive diseases such as necrotizing fasciitis and streptococcus toxin shock syndrome. This article reports a case of streptococcus necrotizing fasciitis secondary to suppurative tonsillitis, which was seldom reported before and our successful management with delayed debridement. This study was anonymous and was approved by the local Research Ethics Committee. Informed consent was obtained from the patient.

Complete Genome Sequence of emm 1 Streptococcus pyogenes 10-85, a Strain Isolated from a Patient with Streptococcal Toxic Shock Syndrome in Japan

Here, we announce the complete genome sequence of Streptococcus pyogenes strain 10-85 (type emm1), isolated from a patient with streptococcal toxic shock syndrome (STSS). The strain lacks the genomic regions encoding SalR-SalK, a two‐component regulatory system, and the adjacent type I restriction modification system.

Here, we announce the complete genome sequence of Streptococcus pyogenes strain 10-85 (type emm1), isolated from a patient with streptococcal toxic shock syndrome (STSS). The strain lacks the genomic regions encoding SalR-SalK, a two‐component regulatory system, and the adjacent type I restriction modification system.

Enterococcus faecalis Encodes an Atypical Auxiliary Acyl Carrier Protein Required for Efficient Regulation of Fatty Acid Synthesis by Exogenous Fatty Acids

Acyl carrier proteins (ACPs) play essential roles in the synthesis of fatty acids and transfer of long fatty acyl chains into complex lipids. The Enterococcus faecalis genome contains two annotated acp genes, called acpA and acpB AcpA is encoded within the fatty acid synthesis (fab) operon and appears essential. In contrast, AcpB is an atypical ACP, having only 30% residue identity with AcpA, and is not essential. Deletion of acpB has no effect on E. faecalis growth or de novo fatty acid synthesis in media lacking fatty acids. However, unlike the wild-type strain, where growth with oleic acid resulted in almost complete blockage of de novo fatty acid synthesis, the ΔacpB strain largely continued de novo fatty acid synthesis under these conditions. Blockage in the wild-type strain is due to repression of fab operon transcription, leading to levels of fatty acid synthetic proteins (including AcpA) that are insufficient to support de novo synthesis. Transcription of the fab operon is regulated by FabT, a repressor protein that binds DNA only when it is bound to an acyl-ACP ligand. Since AcpA is encoded in the fab operon, its synthesis is blocked when the operon is repressed and acpA thus cannot provide a stable supply of ACP for synthesis of the acyl-ACP ligand required for DNA binding by FabT. In contrast to AcpA, acpB transcription is unaffected by growth with exogenous fatty acids and thus provides a stable supply of ACP for conversion to the acyl-ACP ligand required for repression by FabT. Indeed, ΔacpB and ΔfabT strains have essentially the same de novo fatty acid synthesis phenotype in oleic acid-grown cultures, which argues that neither strain can form the FabT-acyl-ACP repression complex. Finally, acylated derivatives of both AcpB and AcpA were substrates for the E. faecalis enoyl-ACP reductases and for E. faecalis PlsX (acyl-ACP; phosphate acyltransferase).IMPORTANCE AcpB homologs are encoded by many, but not all, lactic acid bacteria (Lactobacillales), including many members of the human microbiome. The mechanisms regulating fatty acid synthesis by exogenous fatty acids play a key role in resistance of these bacteria to those antimicrobials targeted at fatty acid synthesis enzymes. Defective regulation can increase resistance to such inhibitors and also reduce pathogenesis.