Corynebacterium diphtheriae is one of the most prominent human pathogens and the causative agent of the communicable disease diphtheria. The genomes of 12 strains isolated from patients with classical diphtheria, endocarditis, and pneumonia were completely sequenced and annotated. Including the genome of C. diphtheriae NCTC 13129, we herewith present a comprehensive comparative analysis of 13 strains and the first characterization of the pangenome of the species C. diphtheriae . Comparative genomics showed extensive synteny and revealed a core genome consisting of 1,632 conserved genes. The pangenome currently comprises 4,786 protein-coding regions and increases at an average of 65 unique genes per newly sequenced strain. Analysis of prophages carrying the diphtheria toxin gene tox revealed that the toxoid vaccine producer C. diphtheriae Park-Williams no. 8 has been lysogenized by two copies of the ω tox + phage, whereas C. diphtheriae 31A harbors a hitherto-unknown tox + corynephage. DNA binding sites of the tox -controlling regulator DtxR were detected by genome-wide motif searches. Comparative content analysis showed that the DtxR regulons exhibit marked differences due to gene gain, gene loss, partial gene deletion, and DtxR binding site depletion. Most predicted pathogenicity islands of C. diphtheriae revealed characteristics of horizontal gene transfer. The majority of these islands encode subunits of adhesive pili, which can play important roles in adhesion of C. diphtheriae to different host tissues. All sequenced isolates contain at least two pilus gene clusters. It appears that variation in the distributed genome is a common strategy of C. diphtheriae to establish differences in host-pathogen interactions.

BackgroundCorynebacterium ulcerans has been detected as a commensal in domestic and wild animals that may serve as reservoirs for zoonotic infections. During the last decade, the frequency and severity of human infections associated with C. ulcerans appear to be increasing in various countries. As the knowledge of genes contributing to the virulence of this bacterium was very limited, the complete genome sequences of two C. ulcerans strains detected in the metropolitan area of Rio de Janeiro were determined and characterized by comparative genomics: C. ulcerans 809 was initially isolated from an elderly woman with fatal pulmonary infection and C. ulcerans BR-AD22 was recovered from a nasal sample of an asymptomatic dog.ResultsThe circular chromosome of C. ulcerans 809 has a total size of 2,502,095 bp and encodes 2,182 predicted proteins, whereas the genome of C. ulcerans BR-AD22 is 104,279 bp larger and comprises 2,338 protein-coding regions. The minor difference in size of the two genomes is mainly caused by additional prophage-like elements in the C. ulcerans BR-AD22 chromosome. Both genomes show a highly similar order of orthologous coding regions; and both strains share a common set of 2,076 genes, demonstrating their very close relationship. A screening for prominent virulence factors revealed the presence of phospholipase D (Pld), neuraminidase H (NanH), endoglycosidase E (EndoE), and subunits of adhesive pili of the SpaDEF type that are encoded in both C. ulcerans genomes. The rbp gene coding for a putative ribosome-binding protein with striking structural similarity to Shiga-like toxins was additionally detected in the genome of the human isolate C. ulcerans 809.ConclusionsThe molecular data deduced from the complete genome sequences provides considerable knowledge of virulence factors in C. ulcerans that is increasingly recognized as an emerging pathogen. This bacterium is apparently equipped with a broad and varying set of virulence factors, including a novel type of a ribosome-binding protein. Whether the respective protein contributes to the severity of human infections (and a fatal outcome) remains to be elucidated by genetic experiments with defined bacterial mutants and host model systems.

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Aims:  This investigation aimed to isolate enteric rods from subgingival sites of patients presenting chronic periodontitis lesions, and to assess antimicrobial resistance and expression of hydrolytic enzymes. Methods and Results:  Enterobacteriaceae were isolated from 20% patients, and assayed for antimicrobial susceptibility and hydrolytic enzymes with specificity to different substrates. Isolates comprised seven Enterobacter cloacae (43·75%), five Serratia marcescens (31·25%), one Klebsiella pneumoniae (6·25%), one Enterobacter aerogenes (6·25%), one Pantoea agglomerans (6·25%), and one Citrobacter freundii (6·25%). Gelatinase activity was observed for 75% strains; caseinase and elastase was produced by six and two strains, respectively. DNase, lecithinase and lipase were expressed by S. marcescens. Most of strains were resistant to ampicillin (93·75%) and amoxicillin/clavulanic acid (81·25%). The majority of strains were susceptible to cephalosporins and aztreonam. Enterobacteria remained susceptible to imipenem, streptomycin and fluoroquinolones. Resistance to gentamicin, amikacin, sulfamethoxazole/thrimethoprim, tetracycline, and chloramphenicol were also observed. Eight strains presented multiple drug resistance. Conclusions:  Subgingival sites from periodontal diseases contain multi‐resistant and hydrolytic enzyme‐producing enterobacteria that may contribute to overall tissue destruction and spreading. Significance and Impact of the Study:  Enterobacteria isolated from patients generally considered as healthy individuals poses periodontal diseases as reservoir for systemic infections particularly in immunocompromised and hospitalized hosts.

Endodontic E. faecalis isolates exhibit high level of resistance to tetracycline, an antibiotic that has use in local treatment of dental infections. This opens up a much-needed debate on the role and efficacy of this antibiotic for oral infections. Furthermore, these isolates were shown to possess genes that could contribute to pathogenicity in the pulp cavity.