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The dangers of sublethal carvacrol exposure: increases in virulence of Bacillus cereus during endophthalmitis.

ABSTRACT: Bacillus cereus can cause endophthalmitis through secretion of virulence factors, including hemolysin BL (Hbl) and nonhemolytic entertoxin (Nhe). Carvacrol is an extract from oregano oil, with potential for curtailing B. cereus endophthalmitis, due to antimicrobial and anti-inflammatory qualities. However, sublethal levels of carvacrol increases B. cereus virulence. The goal of this study was to investigate the increase in B. cereus virulence potential in response stress induced by a subinhibitory concentration (SIC) of carvacrol. Enterotoxin production and tissue damage were examined during ocular infections in vitro and in vivo. We hypothesized that the SIC of carvacrol would significantly increase toxin production in B. cereus without progressing systemically. RT-PCR determined SIC carvacrol-treated B. cereus had significantly higher hblC and nheA mRNA expression levels than controls in vitro. ELISA and RPLA analysis revealed a 46.8% and 50% increase in NheA and HblC toxin levels, respectively, in SIC-treated cultures. Caenorhabditis elegans-fed SIC carvacrol-treated B. cereus had a significantly higher mean mortality rate than nematodes fed untreated B. cereus. Significantly higher TNF-? levels were observed in SIC carvacrol-treated B. cereus mice compared to other treatment groups except for mice infected with B. cereus alone. Significantly higher IL-6 levels were also found in SIC-B. cereus mice. Histological analysis using Rose-Bengal and DAPI determined that the eyes of mice infected with SIC carvacrol-treated B. cereus had significantly more damage than eyes treated with B. cereus alone. The SIC of carvacrol increased B. cereus virulence in vitro and in vivo, with a mild systemic infection noted.

SUBMITTER: Rajabli N

PROVIDER: S-EPMC6261914 | biostudies-literature | 2018

REPOSITORIES: biostudies-literature

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The dangers of sublethal carvacrol exposure: increases in virulence of Bacillus cereus during endophthalmitis.

Rajabli Niloofar N Williamson Lauren L Nimmer Pierre S PS Kelly-Worden Marie M Bange Jill S JS Ho Yenling Y McKillip John L JL

International journal of biochemistry and molecular biology 20181008 2

Bacillus cereus can cause endophthalmitis through secretion of virulence factors, including hemolysin BL (Hbl) and nonhemolytic entertoxin (Nhe). Carvacrol is an extract from oregano oil, with potential for curtailing B. cereus endophthalmitis, due to antimicrobial and anti-inflammatory qualities. However, sublethal levels of carvacrol increases B. cereus virulence. The goal of this study was to investigate the increase in B. cereus virulence potential in response str ...[more]

PMID: 30515347

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Project description:BackgroundEndophthalmitis is a serious intraocular infection that frequently results in significant inflammation and vision loss. Because current therapeutics are often unsuccessful in mitigating damaging inflammation during endophthalmitis, more rational targets are needed. Toll-like receptors (TLRs) recognize specific motifs on invading pathogens and initiate the innate inflammatory response. We reported that TLR4 contributes to the robust inflammation which is a hallmark of Bacillus cereus endophthalmitis. To identify novel, targetable host inflammatory factors in this disease, we performed microarray analysis to detect TLR4-dependent changes to the retinal transcriptome during B. cereus endophthalmitis.ResultsC57BL/6 J and TLR4-/- mouse eyes were infected with B. cereus and retinas were harvested at 4 h postinfection, a time representing the earliest onset of neutrophil infiltration. Genes related to acute inflammation and inflammatory cell recruitment including CXCL1 (KC), CXCL2 (MIP2-α), CXCL10 (IP-10), CCL2 (MCP1), and CCL3 (MIP1-α)) were significantly upregulated 5-fold or greater in C57BL/6 J retinas. The immune modulator IL-6, intercellular adhesion molecule ICAM1, and the inhibitor of cytokine signal transduction SOCS3 were upregulated 25-, 11-, and 10-fold, respectively, in these retinas. LIF, which is crucial for photoreceptor cell survival, was increased 6-fold. PTGS2/COX-2, which converts arachidonic acid to prostaglandin endoperoxide H2, was upregulated 9-fold. PTX3, typically produced in response to TLR engagement, was induced 15-fold. None of the aforementioned genes were upregulated in TLR4-/- retinas following B. cereus infection.ConclusionsOur results have identified a cohort of mediators driven by TLR4 that may be important in regulating pro-inflammatory and protective pathways in the retina in response to B. cereus intraocular infection. This supports the prospect that blocking the activation of TLR-based pathways might serve as alternative targets for Gram-positive and Gram-negative endophthalmitis therapies in general.

Project description:Bacillus endophthalmitis is a devastating eye infection that causes rapid blindness through extracellular tissue-destructive exotoxins. Despite its importance, knowledge of the phylogenetic relationships and population structure of intraocular Bacillus spp. is lacking. In this study, we sequenced the whole genomes of eight Bacillus intraocular pathogens independently isolated from 8/52 patients with posttraumatic Bacillus endophthalmitis infections in the Eye Hospital of Wenzhou Medical University between January 2010 and December 2018. Phylogenetic analysis revealed that the pathogenic intraocular isolates belonged to Bacillus cereus, Bacillus thuringiensis and Bacillus toyonensis To determine the virulence of the ocular isolates, three representative strains were injected into mouse models, and severe endophthalmitis leading to blindness was observed. Through incorporating publicly available genomes for Bacillus spp., we found that the intraocular pathogens could be isolated independently but displayed a similar genetic context. In addition, our data provide genome-wide support for intraocular and gastrointestinal sources of Bacillus spp. belonging to different lineages. Importantly, we identified five molecular signatures of virulence and motility genes associated with intraocular infection, namely, plcA-2, InhA-3, InhA-4, hblA-5, and fliD using pangenome-wide association studies. The characterization of overrepresented genes in the intraocular isolates holds value to predict bacterial evolution and for the design of future intervention strategies in patients with endophthalmitis.IMPORTANCE In this study, we provided a detailed and comprehensive clinicopathological and pathogenic report of Bacillus endophthalmitis over the 8 years of the study period. We first reported the whole-genome sequence of Bacillus spp. causing devastating endophthalmitis and found that Bacillus toyonensis is able to cause endophthalmitis. Finally, we revealed significant endophthalmitis-associated virulence genes involved in hemolysis, immunity inhibition, and pathogenesis. Overall, as more sequencing data sets become available, these data will facilitate comparative research and will reveal the emergence of pathogenic "ocular bacteria."

Project description:BackgroundBacillus cereus (Bc) can cause self-limiting gastrointestinal infections, but when infecting the eye, can cause rapid and irreversible blindness. This study investigated whether clinical ocular and gastrointestinal Bc isolates differed in terms of virulence-related genotypes and endophthalmitis virulence.MethodsTwenty-eight Bc ocular, gastrointestinal, and laboratory reference isolates were evaluated. Hemolysis assays were performed to assess potential differences in hemolytic activity. The presence of twenty Bc virulence-related genes was assessed by PCR. A subset of ocular and gastrointestinal isolates differing in PCR positivity for 5 virulence genes was compared to strain ATCC14579 in an experimental murine model of endophthalmitis. At 8 hours post infection, retinal function was evaluated by electroretinography, and intraocular bacterial concentrations were determined by plate counts.ResultsGastrointestinal Bc isolates were more hemolytic than the Bc ocular isolates and ATCC14579 (p < 0.0001). Bc ocular isolates were more frequently PCR-positive for capK, cytK, hblA, hblC, and plcR compared to the gastrointestinal isolates (p ≤ 0.0002). In the endophthalmitis model, mean A-wave retention did not differ significantly between eyes infected with ATCC14579 and eyes infected with the selected ocular or gastrointestinal isolates (p ≥ 0.3528). Similar results were observed for mean B-wave retention (p ≥ 0.0640). Only one diarrheal isolate showed significantly greater B-wave retention when compared to ATCC14579 (p = 0.0303). No significant differences in mean A-wave (p ≥ 0.1535) or B-wave (p ≥ 0.0727) retention between the selected ocular and gastrointestinal isolates were observed. Intraocular concentrations of ATCC14579 were significantly higher than the selected ocular isolate and 3 of the gastrointestinal isolates (p ≤ 0.0303). Intraocular concentrations of the selected ocular isolate were not significantly different from the gastrointestinal isolates (p ≥ 0.1923).ConclusionsAmong the subset of virulence-related genes assessed, 5 were significantly enriched among the ocular isolates compared to gastrointestinal isolates. While hemolytic activity was higher among gastrointestinal isolates, retinal function retention and intraocular growth was not significantly different between the selected ocular and gastrointestinal isolates. These results suggest that Bc strains causing gastrointestinal infections, while differing from ocular isolates in hemolytic activity and virulence-related gene profile, are similarly virulent in endophthalmitis.

Project description:Bacillus endophthalmitis is a severe intraocular infection. Hallmarks of Bacillus endophthalmitis include robust inflammation and rapid loss of vision. We reported that the absence of Bacillus surface layer protein (SLP) significantly blunted endophthalmitis severity. Here, we further investigated SLP in the context of Bacillus-retinal cell interactions and innate immune pathways to explore the mechanisms by which SLP contributes to intraocular inflammation. We compared phenotypes of Wild-type (WT) and SLP deficient (?slpA) Bacillus thuringiensis by analyzing bacterial adherence to and phagocytosis by human retinal Muller cells and phagocytosis by mouse neutrophils. Innate immune receptor activation by the Bacillus envelope and purified SLP was analyzed using TLR2/4 reporter cell lines. A synthetic TLR2/4 inhibitor was used as a control for this receptor activation. To induce endophthalmitis, mouse eyes were injected intravitreally with 100 CFU WT or ?slpA B. thuringiensis. A group of WT infected mice was treated intravitreally with a TLR2/4 inhibitor at 4 h postinfection. At 10 h postinfection, infected eyes were analyzed for viable bacteria, inflammation, and retinal function. We observed that B. thuringiensis SLPs contributed to retinal Muller cell adherence, and protected this pathogen from Muller cell- and neutrophil-mediated phagocytosis. We found that B. thuringiensis envelope activated TLR2 and, surprisingly, TLR4, suggesting the presence of a surface-associated TLR4 agonist in Bacillus. Further investigation showed that purified SLP from B. thuringiensis activated TLR4, as well as TLR2 in vitro. Growth of WT B. thuringiensis was significantly higher and caused greater inflammation in untreated eyes than in eyes treated with the TLR2/4 inhibitor. Retinal function analysis also showed greater retention of A-wave and B-wave function in infected eyes treated with the TLR2/4 inhibitor. The TLR2/4 inhibitor was not antibacterial in vitro, and did not cause inflammation when injected into uninfected eyes. Taken together, these results suggest a potential role for Bacillus SLP in host-bacterial interactions, as well as in endophthalmitis pathogenesis via TLR2- and TLR4-mediated pathways.

Dataset Information

The dangers of sublethal carvacrol exposure: increases in virulence of Bacillus cereus during endophthalmitis.

Publications

The dangers of sublethal carvacrol exposure: increases in virulence of <i>Bacillus cereus</i> during endophthalmitis.

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