Identification of Clostridium innocuum hypothetical protein that is cross-reactive with C. difficile anti-toxin antibodies.

OBJECTIVES: Previously considered solely an opportunistic pathogen, Clostridium innocuum (CI) was recently reported in Taiwan to be an emerging cause of antibiotic-associated diarrhea and clinically indistinguishable from Clostridioides difficile (CD) infection. We previously identified CI culture supernatant being cross-reactive with commercial CD toxin enzyme immunoassays. We aimed to identify and characterize the cross-reacting protein and determine whether it functioned as a human toxin. METHODS: We performed western blots using CI culture supernatants and CD anti-toxin antibodies and identified interacting bands. We identified protein(s) using tandem mass spectrometry and evaluated them by cytotoxicity assays. RESULTS: CI, but not CD, was isolated from stool of 12 children and adults with diarrhea. Culture supernatant from 6/12 CI isolates, and an ATCC reference strain, tested positive for CD toxins (total 7/13 isolates) by commercial EIA. Using two of these isolates, we identified two ∼40 kDa hypothetical proteins, CI_01447 and CI_01448, and confirmed cross-reactivity with CD anti-toxin antibodies by enzyme immunoassay and Western blot. Whole-genome sequencing confirmed all 13 isolates contained both genes, which were highly conserved. We observed no cytopathic or cytotoxic effects to HeLa cells when treated with these proteins. We identified amino acid sequence similarity to the NlpC/P60 family of proteins. CONCLUSIONS: Our findings do not suggest CI proteins CI_01448 and CI_01447, which cross-react with antibodies against CD toxins A and B, are toxic to HeLa cells. Further studies are needed to determine the function of these cross-reacting proteins and the potential virulence factors that could be responsible for CI diarrheal disease.

Complete Genome Sequence of Clostridium innocuum Strain LC-LUMC-CI-001, Isolated from a Patient with Recurrent Antibiotic-Associated Diarrhea.

Here, we report the complete genome sequence of Clostridium innocuum strain LC-LUMC-CI-001. As recently as 2018, C. innocuum was generally considered a benign gastrointestinal microorganism. This strain was isolated from the stool of a patient with recurrent Clostridioides difficile infection-like illnesses.

Complete Genome Sequence of Clostridium innocuum Strain ATCC 14501.

We report the complete genome sequence of Clostridium innocuum ATCC 14501, which was isolated in 1962 from an appendiceal abscess. At that time, the isolated strain was designated C. innocuum, given its suspected lack of virulence, but recent reports suggest that C. innocuum is an emerging pathogen.

Elevated levels of the second messenger c-di-GMP contribute to antimicrobial resistance of Pseudomonas aeruginosa.

Biofilms are highly structured, surface-associated communities. A hallmark of biofilms is their extraordinary resistance to antimicrobial agents that is activated during early biofilm development of Pseudomonas aeruginosa and requires the regulatory hybrid SagS and BrlR, a member of the MerR family of multidrug efflux pump activators. However, little is known about the mechanism by which SagS contributes to BrlR activation or drug resistance. Here, we demonstrate that ΔsagS biofilm cells harbour the secondary messenger c-di-GMP at reduced levels similar to those observed in wild-type cells grown planktonically rather than as biofilms. Restoring c-di-GMP levels to wild-type biofilm-like levels restored brlR expression, DNA binding by BrlR, and recalcitrance to killing by antimicrobial agents of ΔsagS biofilm cells. We likewise found that increasing c-di-GMP levels present in planktonic cells to biofilm-like levels (≥ 55 pmol mg(-1) ) resulted in planktonic cells being significantly more resistant to antimicrobial agents, with increased resistance correlating with increased brlR, mexA, and mexE expression and BrlR production. In contrast, reducing cellular c-di-GMP levels of biofilm cells to ≤ 40 pmol mg(-1) correlated with increased susceptibility and reduced brlR expression. Our findings suggest that a signalling pathway involving a specific c-di-GMP pool regulated by SagS contributes to the resistance of P. aeruginosa biofilms.