Morphology-Independent Virulence of Candida Species during Polymicrobial Intra-abdominal Infections with Staphylococcus aureus

Abstract

c Intra-abdominal polymicrobial infections cause significant morbidity and mortality. An experimental mouse model of Candida albicans-Staphylococcus aureus intra-abdominal infection (IAI) results in 100% mortality by 48 to 72 h postinoculation, while monomicrobial infections are avirulent. Mortality is associated with robust local and systemic inflammation without a requirement for C. albicans morphogenesis. However, the contribution of virulence factors coregulated during the yeast-tohypha transition is unknown. This also raised the question of whether other Candida species that are unable to form hyphae are as virulent as C. albicans during polymicrobial IAI. Therefore, the purpose of this study was to evaluate the ability of non-albicans Candida (NAC) species with various morphologies and C. albicans transcription factor mutants (efg1/efg1 and cph1/cph1) to induce synergistic mortality and the accompanying inflammation. Results showed that S. aureus coinoculated with C. krusei or C. tropicalis was highly lethal, similar to C. albicans, while S. aureus-C. dubliniensis, S. aureus-C. parapsilosis, and S. aureus-C. glabrata coinoculations resulted in little to no mortality. Local and systemic interleukin-6 (IL-6) and prostaglandin E 2 (PGE 2 ) levels were significantly elevated during symptomatic and/or lethal coinfections, and hypothermia strongly correlated with mortality. Coinoculation with C. albicans strains deficient in the transcription factor Efg1 but not Cph1 reversed the lethal outcome. These results support previous findings and demonstrate that select Candida species, without reference to any morphological requirement, induce synergistic mortality, with IL-6 and PGE 2 acting as key inflammatory factors. Mechanistically, signaling pathways controlled by Efg1 are critical for the ability of C. albicans to induce mortality from an intra-abdominal polymicrobial infection. I ntra-abdominal infection (IAI) is a broad term used to describe numerous infections caused by the invasion of microorganisms into the abdominal cavity. These infections can range from appendicitis to complicated peritonitis and are initiated by microbes entering the abdominal cavity through a variety of routes, including bowel perforation, laparotomy, intestinal hernias, and insertion of medical devices such as peritoneal catheters (reviewed in reference 1). These infections often are polymicrobial in nature, which complicates diagnosis and treatment. Accordingly, infections with multiple microbes can result in amplified pathogenicity, also known as "infectious synergism" (2-4), which may accelerate disease progression or protect microbes from host responses (5), resulting in higher morbidity and mortality (6, 7).Polymicrobial IAIs involving fungi result in mortality rates between 50 and 75%, compared to 10 to 30% for polymicrobial bacterial infections (8-11). The majority of polymicrobial fungal IAIs are caused by Candida albicans (12, 13). However, IAIs caused by non-albicans Candida (NAC) species are becoming more common (14). C. al...

Candida albicans and Pseudomonas aeruginosa Interact To Enhance Virulence of Mucosal Infection in Transparent Zebrafish

“…However, the enhanced virulence is consistent with most mouse C. albicans-bacterial coinfection models, including organotypic models, which result in enhanced virulence, cytokine production, and/or fungal invasion (22,23,26,27,(56)(57)(58). The fact that the same strains of C. albicans and P. aeruginosa were used in these in vivo experiments as have been used in vitro suggests that the switch from antagonism to synergy is due to the host environment.…”

“…(C) Larvae were injected and monitored as described above with the following groups: PVP control, C. albicans (2.5 ϫ 10 7 CFU/ml) plus UV-inactivated (UV-x) P. aeruginosa (2.5 ϫ 10 8 CFU/ml), P. aeruginosa (2.5 ϫ 10 8 CFU/ml) plus UV-x C. albicans (2.5 ϫ 10 7 CFU/ml), or C. albicans plus P. aeruginosa at 2.5 ϫ 10 7 CFU/ml and 2.5 ϫ 10 8 CFU/ml, respectively. Data are representative of six (Continued on next page) IL-6 is produced by several cell types and has been linked to edema, sepsis, and increased mortality in both monoinfections and C. albicans-S. aureus coinfection (22)(23)(24)46). Interestingly, this proinflammatory cytokine was significantly upregulated in C. albicans-P. aeruginosa coinfection compared to the C. albicans monoinfection (Fig.…”

“…The inflammatory role of IL-6 in immunopathology is well established, including its association with lethal C. albicans-bacterial intraperitoneal infections (22,23,61), but it is not known if this cytokine's action is necessary or sufficient to enhance C. albicans pathogenesis. Mucosal polymicrobial infections in humans stimulate immune cell infiltration, pulmonary edema, acute lung injury, and alveolar collapse, all phenotypes that are associated with severe morbidity and mortality (33,(62)(63)(64)(65).…”

S. oralis activates the Efg1 filamentation pathway in C. albicans to promote cross-kingdom interactions and mucosal biofilms

“…3 The role of this pathway in fungalbacterial synergy was also demonstrated in an intraabdominal staphylococcal-C. albicans mixed infection model where Efg1 was required for synergistic virulence. 42 The finding that filamentation was not promoted by S. oralis in the efg1 mutant shows that this regulatory pathway is required for hyphal growth in Candida-streptococcal biofilms. Interestingly, S. oralis was able to promote the oral colonization of the efg1D/D strain, suggesting that the requirement for Efg1 in these interactions in vivo is modified by the mucosal environment and perhaps by the presence of commensal microorganisms other than S. oralis.…”

Candida albicans Pathogenesis: Fitting within the Host-Microbe Damage Response Framework

“…These findings indicate that the host response is a key mediator of host damage, emphasizing the class 3 designation. Furthermore, a recent study examining the role of C. albicans morphogenesis in the disease process indicated that, unlike in the majority of C. albicans infections, hyphal formation is not a major contributor to the pathogenesis of C. albicans-bacterial pathogen peritonitis, although the signaling pathways governing morphogenesis are required (96,98). Further, studies using a sublethal monomicrobial inoculum demonstrated a role for a secreted aspartyl protease (Sap6) in mediating peritoneal organ invasion and tissue damage independent of hyphal formation, supporting the concept that morphogenesis per se is not a virulence determinant during peritoneal infection (99).…”