Costi D. Sifri et al. (2007) International Worm Meeting "Immune evasion by staphylococcal exopolysaccharide during C. elegans infection."

Jakob Begun, Dietrich Mack, Costi D. Sifri, Jessica M. Gaiani, Frederick M. Ausubel, Holger Rohde, Stephen B. Calderwood

[International Worm Meeting, 2007]

We have previously shown that C. elegans can serve as a model host for the study of S. aureus pathogenesis and host innate immunity. Here we characterize nematode killing by S. epidermidis. C. elegans fed S. epidermidis survive 3-5 days, which is ~1 day longer than their lifespan on S. aureus. Inactivation of the ica operon (the biofilm exopolysaccharide [PIA] biosynthetic operon and Yersinia hms homolog) in S. epidermidis strain M10 greatly reduces nematode killing compared to the isogenic parental strain 9142 and a plasmid complemented mutant. In S. aureus, overproduction of PIA due to derepression of ica augments nematocidal activity. FITC-WGA labeling confirmed the presence of PIA within the digestive tracts of worms fed 9142 but not M10. Attachment of bacteria or bacterial matrix to the nematode cuticle was not observed. Nematodes briefly exposed to 9142 could not be rescued by transfer to M10, and worms fed dilutions of 9142 in M10 at ratios as low as 1:10e4, respectively, still die. Pulse/chase experiments using 9142, M10, and a second PIA-deficient strain, ATCC 12228, showed that durable colonization requires an intact ica operon. Disruption of N2 worms fed 1:100 9142/M10 mixtures for 20h confirmed significant enrichment of 9142 within the digestive tract of N2 but not sek-1 animals. Moreover, sek-1 and pmk-1 animals were found to be equally sensitive to M10- and 9142-mediated killing, in contrast to wild-type N2 worms. Several conclusions can be drawn from these studies. (a) S. epidermidis can infect and kill worms. (b) Disruption of PIA biosynthesis abrogates S. epidermidis virulence, while overproduction of PIA in S. aureus augments virulence. (c) PIA-producing S. epidermidis has a competitive advantage over PIA-deficient S. epidermidis within the nematode digestive tract. (d) Genetic analysis suggests that PIA may protect luminal staphylococci from SEK-1 p38 MAPK-regulated immune responses.

Hodgson SD et al. (2014) Transfusion "Enhanced pathogenicity of biofilm-negative Staphylococcus epidermidis isolated from platelet preparations."

Ramirez-Arcos S, Hodgson SD, Sifri CD, Jimenez CS, Brassinga AK, Greco-Stewart V

[Transfusion, 2014]

BACKGROUND: The platelet (PLT) storage environment triggers the formation of surface-attached aggregates known as biofilms by the common PLT contaminant Staphylococcus epidermidis. The biofilm matrix is largely composed of polysaccharide intercellular adhesin (PIA) mediated by the icaADBC operon. However, PIA-negative S.epidermidis has been reported to form biofilms in PLT concentrates (PCs). Since biofilm formation is associated with increased virulence, this study was aimed at determining if PIA-negative S.epidermidis grown in PCs presents enhanced virulence using the nematode Caenorhabditis elegans as a host model for bacterial pathogenesis. STUDY DESIGN AND METHODS: Biofilm-positive S.epidermidisATCC 35984 and 9142, which carry the icaADBC operon, and biofilm-negative S.epidermidisATCC 12228 and 9142 icaA were grown in regular media and in PCs and biofilm formation was quantified using a crystal violet assay. The virulence of these strains after passage through PCs was tested using nematode killing assays. Nematode survival was calculated using the Kaplan-Meier method and statistical differences were determined by log-rank analysis. RESULTS: All S.epidermidis strains were able to form biofilms in PCs. Although persistence of a biofilm-positive phenotype in the biofilm-negative strains grown in PCs was not observed after passage in regular medium, the virulence of all strains was significantly increased as demonstrated by shortened life spans of the nematodes in C.elegans killing assays. CONCLUSION: Our findings highlight the potential of an increased risk of nosocomial infections caused by S.epidermidis in transfusion recipients since PC storage conditions promote biofilm formation, and possibly pathogenicity, of strains traditionally known to be attenuated for virulence.

Begun J et al. (2007) PLoS Pathog "Staphylococcal biofilm exopolysaccharide protects against Caenorhabditis elegans immune defenses."

Calderwood SB, Sifri CD, Begun J, Mack D, Rohde H, Ausubel FM, Gaiani JM

[PLoS Pathog, 2007]

Staphylococcus epidermidis and Staphylococcus aureus are leading causes of hospital-acquired infections that have become increasingly difficult to treat due to the prevalence of antibiotic resistance in these organisms. The ability of staphylococci to produce biofilm is an important virulence mechanism that allows bacteria both to adhere to living and artificial surfaces and to resist host immune factors and antibiotics. Here, we show that the icaADBC locus, which synthesizes the biofilm-associated polysaccharide intercellular adhesin (PIA) in staphylococci, is required for the formation of a lethal S. epidermidis infection in the intestine of the model nematode Caenorhabditis elegans. Susceptibility to S. epidermidis infection is influenced by mutation of the C. elegans PMK-1 p38 mitogen-activated protein (MAP) kinase or DAF-2 insulin-signaling pathways. Loss of PIA production abrogates nematocidal activity and leads to reduced bacterial accumulation in the C. elegans intestine, while overexpression of the icaADBC locus in S. aureus augments virulence towards nematodes. PIA-producing S. epidermidis has a significant survival advantage over ica-deficient S. epidermidis within the intestinal tract of wild-type C. elegans, but not in immunocompromised nematodes harboring a loss-of-function mutation in the p38 MAP kinase pathway gene sek-1. Moreover, sek-1 and pmk-1 mutants are equally sensitive to wild-type and icaADBC-deficient S. epidermidis. These results suggest that biofilm exopolysaccharide enhances virulence by playing an immunoprotective role during colonization of the C. elegans intestine. These studies demonstrate that C. elegans can serve as a simple animal model for studying host-pathogen interactions involving staphylococcal biofilm exopolysaccharide and suggest that the protective activity of biofilm matrix represents an ancient conserved function for resisting predation.

Chauve, Laetitia et al. (2019) International Worm Meeting "Inter-individual variability in neuronal stress creates phenotypic variability."

Marioni, John, Hastings, Janna, Chauve, Laetitia, Biggins, Laura, Todtenhaupt, Pia, Murdoch, Sharlene, Vallejos, Catalina, Casanueva, Olivia

[International Worm Meeting, 2019]

We use isogenic C. elegans to study non-genetic influences on phenotypic heterogeneity. Heat shock proteins (hsps) are collectively controlled by the transcription factor HSF-1 and are essential to maintain protein-folding homeostasis. Despite their essentiality, previous works has shown that upon exposure to stress, hsp induction is variable across worms dictating an individual's ability to both cope with stress and to reproduce. The dose-sensitive and critical nature of these phenotypes for survival, prompted us to study inter-individual transcriptional variability under normal, unstressed conditions. We developed a sensitive high-throughput quantitative PCR method and incorporated a Bayesian statistical approach to accurately quantify inter-individual steady-state transcript variability in single worms. We find that hsp transcripts are highly variable across worms even in the absence of exogenous stress. Surprisingly we observed that in vivo, inter-individual variability stems primarily from head neurons (n-hsp). It has been previously shown that ectopic hsf-1 expression in head neurons (n-hsf-1) protects better against exogenous stress. We find a similar phenotype happens to individual worms with greater number of n-hsps under physiological conditions. In addition, we observe that the number of n-hsps is temperature sensitive, suggesting that neuronal stress could modulate adaptation to ambient temperatures. We find that n-hsps anti-correlate with fat desaturases, known to contribute unsaturated fatty acids (UFAs) to both fat storages and membranes. Negative regulation of UFAs is also caused by n-HSF-1, demonstrating causality. We have identified the neurons and the signals critical to relay information across tissues and propose a model where neurons act as a sensitive thermostat that orchestrates homeo-viscous adaptation. The variable activation of the thermostat at normal ambient temperatures creates phenotypic heterogeneity with potential adaptive value.