The quorum sensing com system regulates pneumococcal colonisation and invasive disease in a pseudo-stratified airway tissue model

Streptococcus pneumoniae (Spn) colonises respiratory epithelia but can also invade lung cells causing pneumonia. We developed an ex vivo model with human airway epithelial (HAE) cells harvested from lung biopsies to study Spn colonisation and translocation. Flow-cytometry, confocal imaging and electron microscopy studies identified the epithelial lineage with signs of differentiation (beating cilia, mucus, and tight junctions). HAE cells were challenged with Spn wild-type TIGR4 (wtSpn) or its isogenic ΔcomC quorum sensing-deficient mutant. ΔcomC mutant colonised significantly less than wtSpn at 6 h post-inoculation but at significantly higher levels at 19 h and 30 h. Translocation correlated inversely with colonisation density. Transepithelial electric resistance (TEER) decreased after pneumococcal infection and correlated with increased translocation for both strains. Confocal imaging illustrated colocalisation of intracellular Spn with both cilia and zonulin-1 and prominent microcolony formation with wtSpn but disintegration of microcolony structures over time with ΔcomC mutant. ΔcomC caused a more pronounced release of both zonulin-1 and lactate dehydrogenase into the supernatant at later time points than wtSpn, suggesting that cytotoxicity is likely not the mechanism leading to translocation. There was a density- and time-dependent increase of inflammatory cytokines from human HAE cells infected with ΔcomC compared with wtSpn, including increased levels of the NLRP3 inflammasome-related IL-18. In conclusion, our experiments indicate that ComC system allows a higher organisational level of population structure resulting in microcolony formation, increased early colonisation and subsequent translocation. We propose that ComC inactivation unleashes a very different and possibly more virulent phenotype that merits further investigation.

The Roseobacter-group bacterium Phaeobacter as safe probiotic solution for aquaculture

Phaeobacter inhibens has been assessed as a probiotic bacterium for application in aquaculture. Studies addressing the efficacy and safety indicate that P. inhibens maintains it antagonistic activity against pathogenic vibrios in aquaculture live cultures (live feed and fish egg/larvae), while having no or a positive effect on the host organisms, and a minor impact on the host microbiomes. While producing antibacterial and algicidal compounds, no study has so far found a virulent phenotype of P. inhibens cells against higher organisms. Additionally, an in silico search for antibiotic resistance genes using published genomes of representative strains did not raise concern regarding the risk for antimicrobial resistance. P. inhibens occurs naturally in aquaculture systems supporting its safe usage in this environment. Concluding, at the current state of knowledge, P. inhibens is a “safe-to-use” organism.

Genotyping, Assessment of Virulence and Antibacterial Resistance of the Rostov Strain of Mycobacterium tuberculosis Attributed to the Central Asia Outbreak Clade

The Central Asia Outbreak (CAO) clade is a growing public health problem for Central Asian countries. Members of the clade belong to the narrow branch of the Mycobacterium tuberculosis Beijing genotype and are characterized by multidrug resistance and increased transmissibility. The Rostov strain of M. tuberculosis isolated in Russia and attributed to the CAO clade based on PCR-assay and whole genome sequencing and the laboratory strain H37Rv were selected to evaluate the virulence on C57Bl/6 mice models by intravenous injection. All mice infected with the Rostov strain succumbed to death within a 48-day period, while more than half of the mice infected by the H37Rv strain survived within a 90-day period. Mice weight analysis revealed irreversible and severe depletion of animals infected with the Rostov strain compared to H37Rv. The histological investigation of lung and liver tissues of mice on the 30th day after injection of mycobacterial bacilli showed that the pattern of pathological changes generated by two strains were different. Moreover, bacterial load in the liver and lungs was higher for the Rostov strain infection. In conclusion, our data demonstrate that the drug-resistant Rostov strain exhibits a highly virulent phenotype which can be partly explained by the CAO-specific mutations.

Tornadic shear stress induces a transient, calcineurin-dependent hyper-virulent phenotype in Mucorales molds

Trauma-related necrotizing myocutaneous mucormycosis (NMM) has a high morbidity and mortality in victims of combat-related injuries, geo-meteorological disasters, and severe burns. Inspired by the observation that several recent clusters of NMM have been associated with extreme mechanical forces (e.g. during tornados), we studied the impact of mechanical stress on Mucoralean biology and virulence in a Drosophila melanogaster infection model. In contrast to other experimental procedures to exert mechanical stress, tornadic shear challenge (TSC) by magnetic stirring induced a hyper-virulent phenotype in several clinically relevant Mucorales species but not in Aspergillus or Fusarium. Whereas fungal growth rates, morphogenesis, and susceptibility to noxious environments or phagocytes were not altered by TSC, soluble factors released in the supernatant of shear-challenged R. arrhizus spores rendered static spores hyper-virulent. Consistent with a rapid decay of TSC-induced hyper-virulence, minimal transcriptional changes were revealed by comparative RNA sequencing analysis of static and shear-challenged Rhizopus arrhizus. However, inhibition of the calcineurin/heat shock protein 90 (hsp90) stress response circuitry by cyclosporine A (CsA) and tanespimycin abrogated the increased pathogenicity of R. arrhizus spores following TSC. Similarly, calcineurin loss-of-function mutants of Mucor circinelloides displayed no increased virulence capacity in flies after undergoing TSC. Collectively, these results establish that TSC induces hyper-virulence specifically in Mucorales and point out the calcineurin/hsp90 pathway as a key orchestrator of this phenotype. Our findings invite future studies of topical calcineurin inhibitor treatment of wounds as an adjunct mitigation strategy for NMM following high-energy trauma.SignificanceGiven the limited efficacy of current medical treatments in trauma-related necrotizing mucormycosis, there is a dire need to better understand the Mucoralean pathophysiology in order to develop novel strategies to counteract fungal tissue invasion following severe trauma. Here, we describe that tornadic shear stress challenge transiently induces a hyper-virulent phenotype in various pathogenic Mucorales species but not in other molds known to cause wound infections. Our data support a model whereby shear stress-induced hyper-virulence is primarily driven by soluble factors and orchestrated by the calcineurin/hsp90 pathway. Importantly, pharmacological and genetic inhibition of calcineurin signaling abrogated hyper-virulence in shear stress-challenged Mucorales, encouraging further evaluation of (topical) calcineurin inhibitors to improve therapeutic outcomes of NMM after combat-related blast injuries or violent storms.

Analysis of Codon Usage and Nucleotide Bias in Middle East Respiratory Syndrome Coronavirus Genes

The Middle East Respiratory Syndrome (MERS) is an emerging disease caused by a recently identified human coronavirus (CoV). Over 2494 laboratory-confirmed cases and 858 MERS-related deaths have been reported from 27 countries. MERS-CoV has been associated with a high case fatality rate, especially in patients with pre-existing conditions. Despite the fatal nature of MERS-CoV infection, a comprehensive study to explore its evolution and adaptation in different hosts is lacking. We performed codon usage analyses on 4751 MERS-CoV genes and determined underlying forces that affect the codon usage bias in the MERS-CoV genome. The current analyses revealed a low but highly conserved, gene-specific codon usage bias in the MERS-CoV genome. The codon usage bias is mainly shaped by natural selection, while mutational pressure emerged as a minor factor affecting codon usage in some genes. Other contributory factors included CpG dinucleotide bias, physical and chemical properties of encoded proteins and gene length. Results reported in this study provide considerable insights into the molecular evaluation of MERS-CoV and could serve as a theoretical basis for optimizing MERS-CoV gene expression to study the functional relevance of various MERS-CoV proteins. Alternatively, an attenuated vaccine strain containing hundreds of silent mutations could be engineered. Codon de-optimization will not affect the amino acid sequence or antigenicity of a vaccine strain, but the sheer number of mutations would make viral reversion to a virulent phenotype extremely unlikely.

Phenylacetyl Coenzyme A, Not Phenylacetic Acid, Attenuates CepIR-Regulated Virulence in Burkholderia cenocepacia

ABSTRACT During phenylalanine catabolism, phenylacetic acid (PAA) is converted to phenylacetyl coenzyme A (PAA-CoA) by a ligase, PaaK, and then PAA-CoA is epoxidized by a multicomponent monooxygenase, PaaABCDE, before further degradation through the tricarboxylic acid (TCA) cycle. In the opportunistic pathogen Burkholderia cenocepacia, loss of paaABCDE attenuates virulence factor expression, which is under the control of the LuxIR-like quorum sensing (QS) system, CepIR. To further investigate the link between CepIR-regulated virulence and PAA catabolism, we created knockout mutants of the first step of the pathway (PAA-CoA synthesis by PaaK) and characterized them in comparison to a paaABCDE mutant using liquid chromatography-tandem mass spectrometry (LC-MS/MS) and virulence assays. We found that while loss of PaaABCDE decreased virulence, deletion of the paaK genes resulted in a more virulent phenotype than that of the wild-type strain. Deletion of either paaK or paaABCDE led to higher levels of released PAA but no differences in levels of internal accumulation compared to the wild-type level. While we found no evidence of direct cepIR downregulation by PAA-CoA or PAA, a low-virulence cepR mutant reverted to a virulent phenotype upon removal of the paaK genes. On the other hand, removal of paaABCDE in the cepR mutant did not impact its attenuated phenotype. Together, our results suggest an indirect role for PAA-CoA in suppressing B. cenocepacia CepIR-activated virulence. IMPORTANCE The opportunistic pathogen Burkholderia cenocepacia uses a chemical signal process called quorum sensing (QS) to produce virulence factors. In B. cenocepacia, QS relies on the presence of the transcriptional regulator CepR which, upon binding QS signal molecules, activates virulence. In this work, we found that even in the absence of CepR, B. cenocepacia can elicit a pathogenic response if phenylacetyl-CoA, an intermediate of the phenylacetic acid degradation pathway, is not produced. Instead, accumulation of phenylacetyl-CoA appears to attenuate pathogenicity. Therefore, we have discovered that it is possible to trigger virulence in the absence of CepR, challenging the classical view of activation of virulence by this QS mechanism. Our work provides new insight into the relationship between metabolism and virulence in opportunistic bacteria. We propose that in the event that QS signaling molecules cannot accumulate to trigger a pathogenic response, a metabolic signal can still activate virulence in B. cenocepacia.

1725. Shear Forces Induce a Transient, Calcineurin-Dependent Hyper-Virulent Phenotype in Mucorales via Soluble Factors

Background Myocutaneous mucormycosis is encountered in settings of extreme mechanical forces such as combat-related blast injuries or natural catastrophes. It is unclear whether the virulence of Mucorales is affected by mechano-biological factors such as shear forces (SF). Methods Spores of clinical strains of Rhizopus arrhizus, Rhizomucor pusillus, and Mucor circinelloides (107/mL in PBS) were either kept in static culture (control) or exposed to shear forces (SF) by magnetic stirring for 30 minutes. Mycelial expansion was monitored in the IncuCyte time-lapse microscopy system. For in vivo studies, the dorsal thorax of wild-type Drosophila melanogaster flies (n = 66–76 per condition) was pricked with a needle dipped in control or SF-exposed spore solutions. Flies were also infected with non-exposed spores suspended in cell-free supernatant taken from SF-exposed spores. Survival was monitored for 7 days post-infection. Results Growth rates and morphogenesis of all isolates were not altered by SF. However, SF-exposed spores of all tested Mucorales isolates exhibited increased pathogenicity in the fly model (7-day survival: SF 8–14%, control 36–44%, P < 0.001). Introducing different resting periods after SF resulted in gradual attenuation of the hyper-virulent phenotype, with survival rates of infected flies returning to the level seen with non-SF-exposed spores after 120 min post-SF resting (Panel A). To gain a mechanistic insight, we added cyclosporine A (CsA, 100 µg/mL) during shear challenge. Compared with SF-exposed spores, CsA addition improved 7-day survival of R. arrhizus-infected flies from 1% to 29% (P < 0.001), whereas the pathogenicity of non-SF-exposed spores was not influenced by CsA. Interestingly, supernatants from SF-exposed R. arrhizus rendered non-exposed spores hyper-virulent (Panel B, P = 0.003). Conclusion SF induces a transient hypervirulent phenotype of Mucorales. Our findings suggest that soluble mediators contribute to increased pathogenicity. Largely attenuated hyper-virulence in the presence of CsA corroborated the previously described relevance of the calcineurin pathway in fungal mechano-biology. RNA sequencing studies are in progress to identify epigenetic alterations in Mucorales following SF. Disclosures All authors: No reported disclosures.

Phenylacetyl-CoA, not phenylacetic acid, attenuates CepIR-regulated virulence in Burkholderia cenocepacia

During phenylalanine catabolism, phenylacetic acid (PAA) is converted to phenylacetyl-CoA (PAA-CoA) by a ligase, PaaK, and then epoxidized by a multicomponent monooxygenase, PaaABCDE, before further degradation to the TCA cycle. In the opportunistic pathogen Burkholderia cenocepacia, loss of paaABCDE attenuates virulence factor expression, which is under control of the LuxIR-like quorum sensing system, CepIR. To further investigate the link between CepIR-regulated virulence and PAA catabolism, we created knockout mutants of the first step of the pathway (PAA-CoA synthesis by PaaK) and characterized them in comparison to a paaABCDE mutant using liquid chromatography/mass spectrometry (LC-MS/MS) and virulence assays. We found that while loss of PaaABCDE decreased virulence, deletion of the paaK genes resulted in a more virulent phenotype than the wild type strain. Deletion of either paaK or paaABCDE led to higher levels of released PAA but no differences in internal accumulation, compared to wild type. While we found no evidence of direct cepIR downregulation by PAA-CoA or PAA, a low virulence cepR mutant reverted to a virulent phenotype upon removal of the paaK genes. On the other hand, removal of paaABCDE in the cepR mutant did not impact its attenuated phenotype. Together, our results suggest an indirect role for PAA-CoA in supressing B. cenocepacia CepIR-activated virulence.ImportanceThe opportunistic pathogen Burkholderia cenocepacia uses a chemical signal process called quorum sensing (QS) to produce virulence factors. In B. cenocepacia, QS relies on the presence of the transcriptional regulator CepR, which upon binding QS signal molecules, activates virulence. In this work, we found that even in the absence of CepR, B. cenocepacia can elicit a pathogenic response if phenylacetyl-CoA, an intermediate of the phenylacetic acid degradation pathway, is not produced. Instead, accumulation of phenylacetyl-CoA appears to attenuate pathogenicity. Therefore, we have discovered that it is possible to trigger virulence in the absence of CepR, challenging the classical view of activation of virulence by this QS mechanism. Our work provides new insight into the relationship between metabolism and virulence in opportunistic bacteria. We propose that, in the event that QS signaling molecules cannot accumulate to trigger a pathogenic response, a metabolic signal can still activate virulence in B. cenocepacia.