Christopher Weidenmaier

Role of teichoic acids in Staphylococcus aureus nasal colonization, a major risk factor in nosocomial infections

Colonization of the anterior nares in ∼37% of the population is a major risk factor for severe Staphylococcus aureus infections. Here we show that wall teichoic acid (WTA), a surface-exposed staphylococcal polymer, is essential for nasal colonization and mediates interaction with human nasal epithelial cells. WTA-deficient mutants were impaired in their adherence to nasal cells, and were completely unable to colonize cotton rat nares. This study describes the first essential factor for S. aureus nasal colonization.

Teichoic acids and related cell-wall glycopolymers in Gram-positive physiology and host interactions.

Abstract | Most Gram-positive bacteria incorporate membrane- or peptidoglycan-attached carbohydrate-based polymers into their cell envelopes. Such cell-wall glycopolymers (CWGs) often have highly variable structures and have crucial roles in protecting, connecting and controlling the major envelope constituents. Further important roles of CWGs in host-cell adhesion, inflammation and immune activation have also been described in recent years. Identifying and harnessing highly conserved or species-specific structural features of CWGs offers excellent opportunities for developing new antibiotics, vaccines and diagnostics for use in the fight against severe infectious diseases, such as sepsis, pneumonia, anthrax and tuberculosis.

Staphylococcus aureus Strains Lacking d-Alanine Modifications of Teichoic Acids Are Highly Susceptible to Human Neutrophil Killing and Are Virulence Attenuated in Mice

Staphylococcus aureus is resistant to alpha-defensins, antimicrobial peptides that play an important role in oxygen-independent killing of human neutrophils. The dlt operon mediates d-alanine incorporation into teichoic acids in the staphylococcal cell envelope and is a determinant of defensin resistance. By using S. aureus wild-type (WT) and Dlt- bacteria, the relative contributions of oxygen-dependent and -independent antimicrobial phagocyte components were analyzed. The Dlt- strain was efficiently killed by human neutrophils even in the absence of a functional respiratory burst, whereas the killing of the WT organism was strongly diminished when the respiratory burst was inhibited. Human monocytes, which do not produce defensins, inactivated the WT and Dlt- bacteria with similar efficiencies. In addition, mice injected with the Dlt- strain had significantly lower rates of sepsis and septic arthritis and fewer bacteria in the kidneys, compared with mice infected with the WT strain.

d-Alanylation of Teichoic Acids Promotes Group A Streptococcus Antimicrobial Peptide Resistance, Neutrophil Survival, and Epithelial Cell Invasion

Group A streptococcus (GAS) is a leading cause of severe, invasive human infections, including necrotizing fasciitis and toxic shock syndrome. An important element of the mammalian innate defense system against invasive bacterial infections such as GAS is the production of antimicrobial peptides (AMPs) such as cathelicidins. In this study, we identify a specific GAS phenotype that confers resistance to host AMPs. Allelic replacement of the dltA gene encoding d-alanine-d-alanyl carrier protein ligase in an invasive serotype M1 GAS isolate led to loss of teichoic acid d-alanylation and an increase in net negative charge on the bacterial surface. Compared to the wild-type (WT) parent strain, the GAS DeltadltA mutant exhibited increased susceptibility to AMP and lysozyme killing and to acidic pH. While phagocytic uptake of WT and DeltadltA mutants by human neutrophils was equivalent, neutrophil-mediated killing of the DeltadltA strain was greatly accelerated. Furthermore, we observed the DeltadltA mutant to be diminished in its ability to adhere to and invade cultured human pharyngeal epithelial cells, a likely proximal step in the pathogenesis of invasive infection. Thus, teichoic acid d-alanylation may contribute in multiple ways to the propensity of invasive GAS to bypass mucosal defenses and produce systemic infection.

Lack of Wall Teichoic Acids in Staphylococcus aureus Leads to Reduced Interactions with Endothelial Cells and to Attenuated Virulence in a Rabbit Model of Endocarditis

Wall teichoic acids (WTAs) are major surface components of gram-positive bacteria that have recently been shown to play a key role in nasal colonization by Staphylococcus aureus. In the present study, we assessed the impact that WTAs have on endovascular infections by using a WTA-deficient S. aureus mutant ( Delta tagO). There were no significant differences detected between the isogenic parental strain (SA113) and the Delta tagO mutant in polymorphonuclear leukocyte-mediated opsonophagocytosis; killing by a prototypic platelet microbicidal protein; or binding to platelets, fibronectin, or fibrinogen. However, compared with the parental strain, the Delta tagO mutant adhered considerably less well to human endothelial cells, especially under flow conditions (70.3% reduction; P<.05). Beads coated with WTA bound to endothelium in a dose-dependent manner, suggesting that WTA contributes specifically to this interaction. These in vitro data closely paralleled those from a rabbit model of infective endocarditis in which the Delta tagO mutant was compared with the parental strain. Clearances of staphylococcus from the bloodstream were equivalent, but the Delta tagO mutant showed a significantly reduced capacity to both colonize sterile cardiac vegetations (P<.05) and proliferate within these vegetations, the kidneys, and the spleen (P<.001). We conclude that WTA is an important factor in the induction and progression of endovascular S. aureus infection, likely through a specific interaction with endothelial cells.

Human commensals producing a novel antibiotic impair pathogen colonization

The vast majority of systemic bacterial infections are caused by facultative, often antibiotic-resistant, pathogens colonizing human body surfaces. Nasal carriage of Staphylococcus aureus predisposes to invasive infection, but the mechanisms that permit or interfere with pathogen colonization are largely unknown. Whereas soil microbes are known to compete by production of antibiotics, such processes have rarely been reported for human microbiota. We show that nasal Staphylococcus lugdunensis strains produce lugdunin, a novel thiazolidine-containing cyclic peptide antibiotic that prohibits colonization by S. aureus, and a rare example of a non-ribosomally synthesized bioactive compound from human-associated bacteria. Lugdunin is bactericidal against major pathogens, effective in animal models, and not prone to causing development of resistance in S. aureus. Notably, human nasal colonization by S. lugdunensis was associated with a significantly reduced S. aureus carriage rate, suggesting that lugdunin or lugdunin-producing commensal bacteria could be valuable for preventing staphylococcal infections. Moreover, human microbiota should be considered as a source for new antibiotics.

Influence of Wall Teichoic Acid on Lysozyme Resistance in Staphylococcus aureus

Staphylococcus aureus peptidoglycan (PG) is completely resistant to the hydrolytic activity of lysozyme. Here we show that modifications in PG by O acetylation, wall teichoic acid, and a high degree of cross-linking contribute to this resistance.

DltABCD- and MprF-mediated cell envelope modifications of Staphylococcus aureus confer resistance to platelet microbicidal proteins and contribute to virulence in a rabbit endocarditis model.

ABSTRACT The DltABCD and MprF proteins contribute a net positive charge to the Staphylococcus aureus surface envelope by alanylating and lysinylating teichoic acids and membrane phosphatidylglycerol, respectively. These surface charge modifications are associated with increased in vitro resistance profiles of S. aureus to a number of endogenous cationic antimicrobial peptides (CAPs), such as α-defensins. The current study investigated the effects of dltA and mprF mutations on the following host factors relevant to endovascular infections: (i) in vitro susceptibility to the CAP thrombin-induced platelet microbicidal protein 1 (tPMP-1), (ii) in vitro adherence to endothelial cells (EC) and matrix proteins, and (iii) in vivo virulence in an endovascular infection model (rabbit endocarditis) in which tPMP-1 is felt to play a role in limiting S. aureus pathogenesis. Both mutations resulted in substantial increases in the in vitro susceptibility to tPMP-1 compared to that of the parental strain. The dltA (but not the mprF) mutation resulted in a significantly reduced capacity to bind to EC in vitro, while neither mutation adversely impacted in vitro binding to fibronectin, fibrinogen, or platelets. In vivo, both mutations significantly attenuated virulence in terms of early colonization of sterile vegetations and subsequent proliferation at this site (versus the parental strain). However, only the dltA mutation significantly reduced metastatic infections in kidneys and spleens compared to those in animals infected with the parental strain. These data underscore the importance of resistance to distinct CAPs and of teichoic acid-dependent EC interactions in the context of endovascular infection pathogenesis.

Staphylococcus aureus determinants for nasal colonization

Approximately 20% of the healthy human population is persistently colonized in the nasal cavity with Staphylococcus aureus, which constitutes a major risk for infection. S. aureus seems to predominantly colonize the anterior part of the nasal cavity by adhering to nasal surface structures and escaping the host innate and adaptive immune responses. Several bacterial and host factors that play a role in these processes have been identified in the past few years and were in part functionally evaluated in appropriate colonization models. However, the dynamics of host-pathogen crosstalk is only partially understood.

Differential roles of sortase-anchored surface proteins and wall teichoic acid in Staphylococcus aureus nasal colonization

Most of the severe bacterial infections originate from the endogenous microflora of human body surfaces. However, the molecular basis of colonization, e.g. of the human nose by Staphylococcus aureus, has remained incompletely understood. Several surface-exposed proteins and wall teichoic acid (WTA) polymers have previously been implicated in S. aureus attachment to nasal epithelial cells. Here we dissect the role of these molecules in colonization using S. aureus sortase A (srtA) and tagO mutants deficient in surface protein and WTA display, respectively. Although the two mutants were similarly affected in attachment to nasal cells they were abrogated in binding to different types of epithelial ligands. Surface protein sorting, but not WTA, were required for keratin- or fibronectin-mediated interactions while only WTA-mediated binding to nasal cells was effectively inhibited by polyinosinic acid, indicating a possible role of scavenger receptor-like molecules in WTA-dependent epithelial interactions. Both mutants exhibited profound colonization defects in a cotton rat nasal colonization model, albeit at different stages of colonization (>90% reduced bacterial counts at 24h or several days after inoculation with the tagO or srtA mutant, respectively). These data indicate that S. aureus nasal colonization is a multifactorial process with various ligands affecting initial colonization and prolonged persistence in different ways. Our studies should be useful in the development of new preventive and therapeutic strategies.