Complete Genome Sequence of Streptococcus pyogenes emm28 Clinical Isolate M28PF1, Responsible for a Puerperal Fever

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.

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.

Streptococcus pyogenes infects human endometrium by limiting the innate immune response

Group A Streptococcus (GAS), a Gram-positive human-specific pathogen, yields 517,000 deaths annually worldwide, including 163,000 due to invasive infections and among them puerperal fever. Before efficient prophylactic measures were introduced, the mortality rate for mothers during childbirth was approximately 10%; puerperal fever still accounts for over 75,000 maternal deaths annually. Yet, little is known regarding the factors and mechanisms of GAS invasion and establishment in postpartum infection. We characterized the early steps of infection in an ex vivo infection model of the human decidua, the puerperal fever portal of entry. Coordinate analysis of GAS behavior and the immune response led us to demonstrate that (a) GAS growth was stimulated by tissue products; (b) GAS invaded tissue and killed approximately 50% of host cells within 2 hours, and these processes required SpeB protease and streptolysin O (SLO) activities, respectively; and (c) GAS impaired the tissue immune response. Immune impairment occurred both at the RNA level, with only partial induction of the innate immune response, and protein level, in an SLO- and SpeB-dependent manner. Our study indicates that efficient GAS invasion of the decidua and the restricted host immune response favored its propensity to develop rapid invasive infections in a gynecological-obstetrical context.

The Emergence of Successful Streptococcus pyogenes Lineages through Convergent Pathways of Capsule Loss and Recombination Directing High Toxin Expression

Gene transfer and homologous recombination in Streptococcus pyogenes has the potential to trigger the emergence of pandemic lineages, as exemplified by lineages of emm1 and emm89 that emerged in the 1980s and 2000s, respectively. Although near-identical replacement gene transfer events in the nga (NADase) and slo (streptolysin O) loci conferring high expression of these toxins underpinned the success of these lineages, extension to other emm genotype lineages is unreported. The emergent emm89 lineage was characterized by five regions of homologous recombination additional to nga-slo, including complete loss of the hyaluronic acid capsule synthesis locus hasABC, a genetic trait replicated in two other leading emm types and recapitulated by other emm types by inactivating mutations. We hypothesized that other leading genotypes may have undergone similar recombination events. We analyzed a longitudinal data set of genomes from 344 clinical invasive disease isolates representative of locations across England, dating from 2001 to 2011, and an international collection of S. pyogenes genomes representing 54 different genotypes and found frequent evidence of recombination events at the nga-slo locus predicted to confer higher toxin genotype. We identified multiple associations between recombination at this locus and inactivating mutations within hasAB, suggesting convergent evolutionary pathways in successful genotypes. This included common genotypes emm28 and emm87. The combination of no or low capsule and high expression of nga and slo may underpin the success of many emergent S. pyogenes lineages of different genotypes, triggering new pandemics, and could change the way S. pyogenes causes disease.IMPORTANCEStreptococcus pyogenes is a genetically diverse pathogen, with over 200 different genotypes defined by emm typing, but only a minority of these genotypes are responsible for the majority of human infection in high-income countries. Two prevalent genotypes associated with disease rose to international dominance following recombination of a toxin locus that conferred increased expression. Here, we found that recombination of this locus and promoter has occurred in other diverse genotypes, events that may allow these genotypes to expand in the population. We identified an association between the loss of hyaluronic acid capsule synthesis and high toxin expression, which we propose may be associated with an adaptive advantage. As S. pyogenes pathogenesis depends both on capsule and toxin production, new variants with altered expression may result in abrupt changes in the molecular epidemiology of this pathogen in the human population over time.

Capsule-Negative emm Types Are an Increasing Cause of Pediatric Group A Streptococcal Infections at a Large Pediatric Hospital in Texas

BACKGROUND

Bacterial infections caused by group A Streptococcus (GAS) are common in childhood. Few study reports have provided data on pediatric-specific trends in the epidemiology and bacterial strain characteristics of GAS infections.

METHODS

We prospectively collected GAS isolates from the clinical microbiology laboratory at Texas Children's Hospital between July 1, 2013, and June 30, 2017. Patient characteristics and GAS disease categories were determined through chart review. GAS isolates were obtained from patients in either the inpatient or outpatient setting, and cases were defined as pharyngeal disease, skin and soft-tissue infection (SSTI), or invasive disease on the basis of predefined criteria. All isolates were emm typed to determine trends over time.

RESULTS

We identified 930 cases over the 4-year period, including 432 (46.4%) pharyngeal, 235 (25.3%) SSTI, and 263 (28.3%) invasive disease types. The most frequently encountered emm types were emm1 (21.4%), emm12 (15.7%), emm89 (14.6%), emm4 (9.2%), and emm3 (8.2%). We observed significant changes over the 4-year period in the relative frequency of infections caused by emm1 (-17.7%; P = .046), emm4 (8.7%; P = .023), or emm6 (-7.9%; P = .024). Using bioinformatic analyses and targeted gene sequencing, we also discovered that all GAS emm28 and emm87 types harbored mutations that rendered them incapable of producing capsule. The relative frequency of GAS disease cases caused by capsule-negative GAS emm types (emm4, emm22, emm28, emm87, and emm89) increased over the 4-year period (32.2%-44.4%), although the difference was statistically significant for only nonpharyngeal disease types (27.1%-43.9%; P = .038).

CONCLUSIONS

Our data suggest an evolving epidemiology of GAS in the Houston pediatric population characterized by an increase in the frequency of capsule-negative emm types.

The N-terminal domain of the R28 protein promotes emm28 group A Streptococcus adhesion to host cells via direct binding to three integrins

Group A Streptococcus (GAS) is a human-specific pathogen responsible for a wide range of diseases, ranging from superficial to life-threatening invasive infections, including endometritis, and autoimmune sequelae. GAS strains express a vast repertoire of virulence factors that varies depending on the strain genotype, and many adhesin proteins that enable GAS to adhere to host cells are restricted to some genotypes. GAS emm28 is the third most prevalent genotype in invasive infections in France and is associated with gyneco-obstetrical infections. emm28 strains harbor R28, a cell wall-anchored surface protein that has previously been reported to promote adhesion to cervical epithelial cells. Here, using cellular and biochemical approaches, we sought to determine whether R28 supports adhesion also to other cells and to characterize its cognate receptor. We show that through its N-terminal domain, R28_Nt, R28 promotes bacterial adhesion to both endometrial-epithelial and endometrial-stromal cells. R28_Nt was further subdivided into two domains, and we found that both are involved in cell binding. R28_Nt and both subdomains interacted directly with the laminin-binding α3β1, α6β1, and α6β4 integrins; interestingly, these bindings events did not require divalent cations. R28 is the first GAS adhesin reported to bind directly to integrins that are expressed in most epithelial cells. Finally, R28_Nt also promoted binding to keratinocytes and pulmonary epithelial cells, suggesting that it may be involved in supporting the prevalence in invasive infections of the emm28 genotype.