Role of extracellular polymeric substances in polymicrobial biofilm infections of Staphylococcus epidermidis and Candida albicans modelled in the nematode Caenorhabditis elegans

Abstract

Biofilms are formed by communities of microorganisms living in a self-produced extracellular polymeric matrix attached to a surface. When living in a biofilm microorganisms change phenotype and thus are less susceptible to antibiotic treatment and biofilm infections can become severe. The aim of this study was to determine if the presence of multikingdom microorganisms alters the virulence of a biofilm infection in a host organism. The coexistence of Candida albicans and Staphylococcus epidermidis in biofilm was examined in the nematode model Caenorhabditis elegans. It was evaluated if the hyphal form of C. albicans and extracellular polymeric substances (EPS) formed by S. epidermidis increases biofilm virulence. Survival assays were performed, where C. elegans nematodes were exposed to S. epidermidis and C. albicans. Single inoculation assays showed a decreased survival rate after 2 days following exposure, while dual inoculation assays showed that a clinical S. epidermidis strain together with C. albicans significantly increased the virulence and decreased nematode survival. EPS seem to interfere with the bacterial attachment to hyphae, since the EPS overproducing S. epidermidis strain was most virulent. The clinical S. epidermidis paired with C. albicans led to a severe infection in the nematodes resulting in reduced survival.

The staphylococcal exopolysaccharide PIA – Biosynthesis and role in biofilm formation, colonization, and infection

“…In mixed in-vitro biofilms of S. epidermidis strain RP62A and C. albicans , slime, which is mainly composed of PIA in that strain [52] , protected C. albicans from fluconazole penetration [168] . EPS produced by S. epidermidis also increased the overall virulence of a mixed S. epidermidis and C. albicans challenge in C. elegans , resulting in reduced survival of the infected worms [169] . In S. aureus , MSSA and MRSA grew synergistically with C. albicans within biofilms [170] , and C. albicans increased S. aureus resistance to vancomycin [171] , suggesting mutual benefit.…”

Candida albicans and Staphylococcus Species: A Threatening Twosome

“…Additionally, Holt et al used a polymicrobial biofilm model of S. epidermidis and C. albicans in the nematode Caenorhabditis elegans to show that S. epidermidis exhibits a significantly increased virulence and induced mortality in dual infections. Extracellular polymeric substances (EPSs) produced by S. epidermidis may play a role in this enhanced virulence (Holt et al, 2017). The infectious synergism of these species highlights the importance of both the treatment and surveillance of mixed species infections (Figure 1C).…”

Do Mixed-Species Biofilms Dominate in Chronic Infections?–Need for in situ Visualization of Bacterial Organization

“…However, chronic infections often harbor many species residing in biofilms, but interactions across species boundaries are poorly understood. The impact of microbial diversity and interspecific interactions on severity and treatment of chronic infections is unclear, but recent experimental studies indicate that the presence of two or more species enhance resistance and virulence compared to single species infections (Holt et al, 2017 ; Reddinger et al, 2018 ). In addition, it has been demonstrated in a porcine wound model that acute wounds co-inoculated with S. aureus and P. aeruginosa healed more slowly than both non-inoculated wounds and those containing only one of the species (Pastar et al, 2013 ).…”