Diphtheria remains a threat to health in the developing world: an overview

Discovery of natural bispecific antibodies: Is psoriasis induced by a toxigenic Corynebacterium simulans and maintained by CIDAMPs as autoantigens?

The high abundance of Corynebacterium simulans in psoriasis skin suggests a contribution to the psoriasis aetiology. This hypothesis was tested in an exploratory study, where western blot (WB) analyses with extracts of heat-treated C. simulans and psoriasis serum-derived IgG exhibited a single 16 kDa-WB-band. Proteomic analyses revealed ribosomal proteins as candidate C. s.-antigens. A peptidomic analysis unexpectedly showed that psoriasis serum-derived IgG already contained 31 immunopeptides of Corynebacteria ssp., suggesting the presence of natural bispecific antibodies (BsAbs). Moreover, peptidomic analyses gave 372 DECOY-peptides with similarity to virus- and phage proteins, including Corynebacterium diphtheriae phage, and similarity to diphtheria toxin. Strikingly, a peptidomic analysis for human peptides revealed 64 epitopes of major psoriasis autoantigens such as the spacer region of filaggrin, hornerin repeats and others. Most identified immunopeptides represent potential cationic intrinsically disordered antimicrobial peptides (CIDAMPs), which are generated within the epidermis. These may form complexes with bacterial disordered protein regions, representing chimeric antigens containing discontinuous epitopes. In addition, among 128 low-abundance immunopeptides, 48 are putatively psoriasis-relevant such as epitope peptides of PGE2-, vitamin D3- and IL-10-receptors. Further, 47 immunopeptides originated from tumour antigens, and the endogenous retrovirus HERV-K. I propose that persistent infection with a toxigenic C. simulans initiates psoriasis, which is exacerbated as an autoimmune disease by CIDAMPs as autoantigens. The discovery of natural BsAbs allows the identification of antigen epitopes from microbes, viruses, autoantigens and tumour-antigens, and may help to develop epitope-specific peptide-vaccines and therapeutic approaches with antigen-specific regulatory T cells to improve immune tolerance in an autoimmune disease-specific-manner.

Insights of OxyR role in mechanisms of host-pathogen interaction of Corynebacterium diphtheriae

Corynebacterium diphtheriae, the leading causing agent of diphtheria, has been increasingly related to invasive diseases, including sepsis, endocarditis, pneumonia, and osteomyelitis. Oxidative stress defense is required not only for successful growth and survival under environmental conditions but also in the regulation of virulence mechanisms of human pathogenic species, by promoting mucosal colonization, survival, dissemination, and defense against the innate immune system. OxyR, functioning as a negative and/or positive transcriptional regulator, has been included among the major bacterial coordinators of antioxidant response. OxyR was first reported as a repressor of catalase expression in C. diphtheriae. However, the involvement of OxyR in C. diphtheriae pathogenesis remains unclear. Accordingly, this work aimed to investigate the role of OxyR in mechanisms of host-pathogen interaction of C. diphtheriae through the disruption of the OxyR of the diphtheria toxin (DT)-producing C. diphtheriae CDC-E8392 strain. The effects of OxyR gene disruption were analyzed through interaction assays with human epithelial cell lines (HEp-2 and pneumocytes A549) and by the induction of experimental infections in Caenorhabditis elegans nematodes and Swiss Webster mice. The OxyR disruption exerted influence on NO production and mechanism accountable for the expression of the aggregative-adherence pattern (AA) expressed by CDC-E8392 strain on human epithelial HEp-2 cells. Moreover, invasive potential and intracytoplasmic survival within HEp-2 cells, as well as the arthritogenic potential in mice, were found affected by the OxyR disruption. In conclusion, data suggest that OxyR is implicated in mechanisms of host-pathogen interaction of C. diphtheriae.

Cutaneous infection by non-diphtheria-toxin producing and penicillin-resistant Corynebacterium diphtheriae strain in a patient with diabetes mellitus

Diphtheria is a potentially fatal infection, mostly caused by diphtheria toxin (DT)-producing Corynebacterium diphtheriae strains. During the last decades, the isolation of DT-producing C. diphtheriae strains has been decreasing worldwide. However, non-DT-producing C. diphtheriae strains emerged as causative agents of cutaneous and invasive infections. Although endemic in countries with warm climates, cutaneous diphtheria is rarely reported in Brazil. Presently, an unusual case of skin lesion in a Brazilian elderly diabetic patient infected by a penicillin-resistant non-DT-producing C. diphtheriae strain was reported. Laboratory diagnosis included mass spectrometry and multiplex PCR analyses. Since cutaneous diphtheria lesions are possible sources of secondary diphtheria cases and systemic diseases and considering that penicillin is the first line of antimicrobial agent for the treatment of these infections, the detection of penicillin-resistant strains of diphtheria bacilli should be a matter of concern. Thus, cases similar to the presently reported should be appropriately investigated and treated, particularly in patients with risk factor (s) for the development of C. diphtheriae invasive infections, such as diabetes. Moreover, health professionals must be aware of the presence of C. diphtheriae in cutaneous lesions of lower limbs, a common type of morbidity in diabetic patients, especially in tropical and subtropical countries.

Production of IgY polyclonal antibody against diphtheria toxin and evaluation of its neutralization effect by Vero cell assay

BACKGROUND

Diphtheria is a bacterial disease which is caused by Corynebacterium diphtheriae. The symptoms are due to the diphtheria toxin produced by the bacteria. Antibiotic therapy and the use of diphtheria antitoxin is a recommended strategy to control diphtheria. Although mammalian antibodies are used to treat patients, IgY antibody has advantages over mammalian ones, including cost-effectiveness and production through non-invasive means. Moreover, in contrast to mammalian antibodies, IgY does not bind to the rheumatoid factor and does not activate the complement system. The objective of this study was to evaluate the in vitro neutralizing effect of IgY against diphtheria toxin.

RESULTS

Anti-DT IgY was produced by immunization of the laying white leghorn chickens. Indirect enzyme-linked immunosorbent assay revealed successful immunization of the animals, and the IgY was purified with a purity of 93% via polyethylene glycol precipitation method. The neutralizing activity of the purified IgY was evaluated by Vero cell viability assay. This assay confirmed that 1.95 μg (8.6 μg/ml of culture medium) of anti-DT IgY would neutralize 10 fold of cytotoxic dose 99% of DT, which was 0.3 ng (1.33 ng/ml of culture medium).

CONCLUSION

This anti-DT IgY may be applicable for diphtheria treatment and quality controls in vaccine production.

New approach for the identification of potentially toxigenic Corynebacterium sp. using a multiplex PCR assay

In diphtheria laboratory examinations, the PCR test can be applied to isolates and clinical specimens. This study aimed to develop a PCR assay to identify the species and toxigenicity of diphtheria-causing bacteria, including the prediction of some NTTB types. Seven reference isolates, four synthetic DNA samples, 36 stored isolates, and 487 clinical samples used for PCR optimization. The PCR results was confirmed by DNA sequence analysis. The results of the PCR examination of the 7 reference isolates and 36 stored isolates were similar to the results obtained using conventional methods as gold standard, both for diphtheria-causing and non-diphtheria-causing bacteria. The validation of the PCR results using DNA sequence analysis showed that there was no mispriming or misamplification. The multiplex PCR assay developed in this study could correctly identify the species and toxigenicity of diphtheria-causing bacteria, including the prediction of some NTTB types not yet covered by established PCR methods.

First-line antibiotic susceptibility pattern of toxigenic Corynebacterium diphtheriae in Indonesia

BACKGROUND

Diphtheria has been reported as an outbreak in some regions in Indonesia, most especially in East Java Province. Resistance to penicillin, erythromycin, and other antibiotics, single or multiple, has been reported in several studies. This study aims to evaluate the first-line antibiotic susceptibility pattern of toxigenic Corynebacterium diphtheriae isolates.

METHODS

This descriptive observational study was performed from August to November 2018. C. diphtheriae isolates were collected from diphtheria patients and carriers in East Java from 2012 to 2017 and kept at the Balai Besar Laboratorium Kesehatan Daerah Surabaya or the Public Health Laboratory of Surabaya. Sample selection was done by random cluster sampling. The sensitivity test by E-test®of the five antibiotics (penicillin, oxacillin, erythromycin, azithromycin, and clarithromycin) was done to determine the minimum inhibitory concentration (MIC). The Clinical and Laboratory Standards Institute M45A (2015) Corynebacterium spp. for penicillin and erythromycin was used as standard.

RESULTS

From 114 targeted isolates, 108 were viable and toxigenic. The E-test was performed on the viable isolates. The majority of the hosts were male (58.3%), with median (range) age of 6.5 (1-14) years. Half of the samples were from the 1 to 5-year-old age group. The isolates were acquired much more from patients (78.7%) than carriers (21.3%) and from pharyngeal swab (74.1%). Most of these isolates were from Madura Island (47.2%) and the northern and eastern parts of the province (horseshoe area). Mitis isolates were the major variant (76.9%). The susceptibility pattern of C. diphtheriae to erythromycin was better than that to penicillin. The E-test result for penicillin was 68.52% susceptible, 31.48% intermediate, and 0% resistant (MIC range, < 0.016 to 2 μg/L) and for erythromycin (MIC range, < 0.016 to > 256 μg/L) was 85.2% susceptible, 12% intermediate, and 2.8% resistant The MIC range for oxacillin was 1 to 96 μg/L, while for both azithromycin and clarithromycin were <  0.016 to > 256 μg/L.

CONCLUSION

The susceptibility rate of C. diphtheriae to erythromycin is higher than that to penicillin. The regular update of antibiotic selection to the national guidelines is recommended. The MIC reference standard to azithromycin and clarithromycin is also needed.

Molecular epidemiology and antimicrobial susceptibility of outbreak-associated Corynebacterium diphtheriae in Thailand, 2012

Infections caused by Corynebacterium diphtheriae remain endemic in many countries. Since the implementation of the DTP (Diphtheria-Tetanus-Pertussis) vaccination program in 1977, only sporadic diphtheria cases have been reported in Thailand. In 2012, a diphtheria outbreak occurred in rural Thailand and 38 cases were reported, with the majority being adults (mean 22.1 years, range 5-72 years). The current study determined the genetic diversity of C. diphtheriae isolated from 83 individuals associated with either sporadic (n = 34) from 1994, 1996, 1997, 1998, 1999, 2000, 2012, and 2018, or 2012 outbreak (n = 49) diphtheria occurrences in Thailand. Antimicrobial susceptibility testing was performed on 41/83 isolates using broth microdilution. All sporadic (n = 27) and epidemic (n = 14) C. diphtheriae isolates (41/41; 100%) were susceptible to erythromycin (≤0.5 μg/ml), clindamycin (≤0.5 μg/ml), gentamicin (≤ 4 μg/ml), ciprofloxacin (≤1 μg/ml), and vancomycin (2 μg/ml), except tetracycline with a resistance rate of 34.1% (14/41 isolates). All isolates were intermediately resistant to penicillin (MIC range, 0.25-2 μg/ml). Multilocus sequence typing (MLST) revealed 17 sequence types (STs) among 83C. diphtheriae isolates. For the 2012 outbreak isolates, the predominant ST was ST243 (n = 34/49; 69.4%), followed by ST245 (n = 5/49; 10.2%) and ST244 (n = 4/49; 8.1%), whereas the main STs among the sporadic isolates were ST248 (n = 15/34; 44.1%), followed by ST209 (n = 7/34; 20.6%) and ST258 (n = 3/34; 8.8%). The ST243 outbreak strain was a single-locus variant of sporadic ST258. Phylogenetic analysis using concatenated sequences of 7 MLST genes from 17 STs revealed that ST243, ST248, and ST258 were located in the same cluster and ST243 appeared to have evolved from ST258, an endemic strain. This study highlights the importance of epidemiological surveillance together with characterization of C. diphtheriae strains to help inform the future control and prevention of diphtheria.

Characterization of Corynebacterium diphtheriae, C. confusum and C. amycolatum isolated from sows with genitourinary infection

Porcine Corynebacterium infection is still poorly studied, even though the pig has been described as an asymptomatic carrier of Corynebacterium species, including the zoonotic species C. ulcerans, C. confusum and C. amycolatum. Here we present the identification, molecular and antimicrobial susceptibility characterization of coryneform bacteria isolated from sows with urinary tract infection. C. diphtheriae, C. confusum and C. amycolatum were isolated from sows with urinary infection and metritis. Corynebacterium species were identified by MALDI-TOF MS and confirmed by 16S rRNA and rpoB sequencing. All porcine C. diphtheriae strains were further characterized as non-toxigenic (tox^-). SE-AFLP genotyping was also performed and enabled not only Corynebacterium species differentiation but also the assessment of C. amycolatum genetic heterogeneity. All studied porcine Corynebacterium strains presented alarming resistance profiles with high MIC values for macrolides/lincosamide, tetracyclines and quinolones, which can be related with high usage in both veterinary and human medicine. Isolation of zoonotic Corynebacterium species from commercial swine is important for assessing the potential zoonotic risk for farmers and further implication for both human and animal treatment.

An isolated outbreak of diphtheria in South Africa, 2015

An outbreak of respiratory diphtheria occurred in two health districts in the province of KwaZulu-Natal in South Africa in 2015. A multidisciplinary outbreak response team was involved in the investigation and management of the outbreak. Fifteen cases of diphtheria were identified, with ages ranging from 4 to 41 years. Of the 12 cases that were under the age of 18 years, 9 (75%) were not fully immunized for diphtheria. The case fatality was 27%. Ninety-three household contacts, 981 school or work contacts and 595 healthcare worker contacts were identified and given prophylaxis against Corynebacterium diphtheriae infection. A targeted vaccination campaign for children aged 6-15 years was carried out at schools in the two districts. The outbreak highlighted the need to improve diphtheria vaccination coverage in the province and to investigate the feasibility of offering diphtheria vaccines to healthcare workers.

Pathogenic properties of a Corynebacterium diphtheriae strain isolated from a case of osteomyelitis

Corynebacterium diphtheriae is typically recognized as a colonizer of the upper respiratory tract (respiratory diphtheria) and the skin (cutaneous diphtheria). However, different strains of Corynebacteriumdiphtheriae can also cause invasive infections. In this study, the characterization of a non-toxigenic Corynebacteriumdiphtheriae strain (designated BR-INCA5015) isolated from osteomyelitis in the frontal bone of a patient with adenoid cystic carcinoma was performed. Pathogenic properties of the strain BR-INCA5015 were tested in a Caenorhabditis elegans survival assay showing strong colonization and killing by this strain. Survival rates of 3.8±2.7 %, 33.6±7.3 % and 0 % were observed for strains ATCC 27010T, ATCC 27012 and BR-INCA5015, respectively, at day 7. BR-INCA5015 was able to colonize epithelial cells, showing elevated capacity to adhere to and survive within HeLa cells compared to other Corynebacteriumdiphtheriae isolates. Intracellular survival in macrophages (THP-1 and RAW 264.7) was significantly higher compared to control strains ATCC 27010T (non-toxigenic) and ATCC 27012 (toxigenic). Furthermore, the ability of BR-INCA5015 to induce osteomyelitis was confirmed by in vivo assay using Swiss Webster mice.

Tetanus-diphtheria-acellular pertussis vaccination for adults: an update

Although tetanus and diphtheria have become rare in developed countries, pertussis is still endemic in some developed countries. These are vaccine-preventable diseases and vaccination for adults is important to prevent the outbreak of disease. Strategies for tetanus, diphtheria, and pertussis vaccines vary from country to country. Each country needs to monitor consistently epidemiology of the diseases and changes vaccination policies accordingly. Recent studies showed that tetanus–diphtheria–acellular pertussis vaccine for adults is effective and safe to prevent pertussis disease in infants. However, vaccine coverage still remains low than expected and seroprevalence of protective antibodies levels for tetanus, diphtheria, and pertussis decline with aging. The importance of tetanus–diphtheria–acellular pertussis vaccine administration should be emphasized for the protection of young adult and elderly people also, not limited to children.

Heme Binding by Corynebacterium diphtheriae HmuT: Function and Heme Environment

The heme uptake pathway (hmu) of Corynebacterium diphtheriae utilizes multiple proteins to bind and transport heme into the cell. One of these proteins, HmuT, delivers heme to the ABC transporter HmuUV. In this study, the axial ligation of the heme in ferric HmuT is probed by examination of wild-type (WT) HmuT and a series of conserved heme pocket residue mutants, H136A, Y235A, and M292A. Characterization by UV-visible, resonance Raman, and magnetic circular dichroism spectroscopies indicates that H136 and Y235 are the axial ligands in ferric HmuT. Consistent with this assignment of axial ligands, ferric WT and H136A HmuT are difficult to reduce while Y235A is reduced readily in the presence of dithionite. The FeCO Raman shifts in WT, H136A, and Y235A HmuT-CO complexes provide further evidence of the axial ligand assignments. Additionally, these frequencies provide insight into the nonbonding environment of the heme pocket. Ferrous Y235A and the Y235A-CO complex reveal that the imidazole of H136 exists in two forms, one neutral and one with imidazolate character, consistent with a hydrogen bond acceptor on the H136 side of the heme. The ferric fluoride complex of Y235A reveals the presence of at least one hydrogen bond donor on the Y235 side of the heme. Hemoglobin utilization assays showed that the axial Y235 ligand is required for heme uptake in HmuT.

Tellurite resistance: a putative pitfall in Corynebacterium diphtheriae diagnosis?

Corynebacterium diphtheriae strains continue to circulate worldwide causing diphtheria and invasive diseases, such as endocarditis, osteomyelitis, pneumonia and catheter-related infections. Presumptive C. diphtheriae infections diagnosis in a clinical microbiology laboratory requires a primary isolation consisting of a bacterial culture on blood agar and agar containing tellurite (TeO3(2-)). In this study, nine genome sequenced and four unsequenced strains of C. diphtheriae from different sources, including three samples from a recent outbreak in Brazil, were characterized with respect to their growth properties on tellurite-containing agar. Levels of tellurite-resistance (Te(R)) were evaluated by determining the minimum inhibitory concentrations of potassium tellurite (K2TeO3) and by a viability reduction test in solid culture medium with K2TeO3. Significant differences in Te(R) levels of C. diphtheriae strains were observed independent of origin, biovar or presence of the tox gene. Data indicated that the standard initial screening with TeO3(2-)-selective medium for diphtheria bacilli identification may lead to false-negative results in C. diphtheriae diagnosis laboratories.

The re-emergency and persistence of vaccine preventable diseases

The introduction of vaccination worldwide dramatically reduced the incidence of pathogenic bacterial and viral diseases. Despite the highly successful vaccination strategies, the number of cases among vaccine preventable diseases has increased in the last decade and several of those diseases are still endemic in different countries. Here we discuss some epidemiological aspects and possible arguments that may explain why ancient diseases such as, measles, polio, pertussis, diphtheria and tuberculosis are still with us.

Determination of the presence of diphtheria toxin in the myocardial tissue of rabbits and a female subject by using an immunofluorescent antibody method

BACKGROUND

Clinical diagnosis of diphtheria is often difficult, in particular in countries where the disease is rarely observed, such as Turkey. In 2011, after 12 years of no recorded diphtheria cases in Turkey, a 34-year-old woman was diagnosed with diphtheria; she later died of myocarditis. In this study, we aimed to demonstrate the diagnostic potential of an immunofluorescent antibody method to determine the presence of diphtheria toxin (DT) in the myocardial cells of DT-injected rabbits and the female subject.

METHODS

We randomly divided rabbits into two groups: a control group and a DT-injected group. Diphtheria intoxication was simulated in the rabbits by intravenous injection of DT. The myocardium of the rabbits and the female subject were harvested for histopathologic and immunofluorescence examination. A mouse monoclonal anti-DT antibody was used for the immunofluorescent antibody method.

RESULTS

The presence of DT in the myocardial cells of both the rabbits and the female subject was visualized using the immunofluorescent method.

CONCLUSIONS

Laboratory diagnosis of diphtheria is challenging because of non-toxigenic C. diphtheriae strains and/or the dysfunction of DT. However, visualizing the presence of DT in the myocardial tissue may act as an indicator of biologically active DT. We validated that an immunofluorescent method, which utilizes a monoclonal anti-DT (A-subunit specific) antibody, is a useful diagnostic tool to determine the presence of DT in the myocardium of rabbits and human.

Diphtheria outbreak in Maranhão, Brazil: microbiological, clinical and epidemiological aspects

We describe microbiological, clinical and epidemiological aspects of a diphtheria outbreak that occurred in Maranhão, Brazil. The majority of the 27 confirmed cases occurred in partially (n = 16) or completely (n = 10) immunized children (n = 26). Clinical signs and characteristic symptoms of diphtheria such as cervical lymphadenopathy and pseudomembrane formation were absent in 48% and 7% of the cases, respectively. Complications such as paralysis of lower limbs were observed. Three cases resulted in death, two of them in completely immunized children. Microbiological analysis identified the isolates as Corynebacterium diphtheriae biovar intermedius with a predominant PFGE type. Most of them were toxigenic and some showed a decrease in penicillin G susceptibility. In conclusion, diphtheria remains endemic in Brazil. Health professionals need to be aware of the possibility of atypical cases of C. diphtheriae infection, including pharyngitis without pseudomembrane formation.

Diphtheria outbreak with high mortality in northeastern Nigeria

SUMMARY A diphtheria outbreak occurred from February to November 2011 in the village of Kimba and its surrounding settlements, in Borno State, northeastern Nigeria. We conducted a retrospective outbreak investigation in Kimba village and the surrounding settlements to better describe the extent and clinical characteristics of this outbreak. Ninety-eight cases met the criteria of the case definition of diphtheria, 63 (64.3%) of whom were children aged <10 years; 98% of cases had never been immunized against diphtheria. None of the 98 cases received diphtheria antitoxin, penicillin, or erythromycin during their illness. The overall case-fatality ratio was 21.4%, and was highest in children aged 0-4 years (42.9%). Low rates of immunization, delayed clinical recognition of diphtheria and absence of treatment with antitoxin and appropriate antibiotics contributed to this epidemic and its severity.

Multiplex polymerase chain reaction to identify and determine the toxigenicity of Corynebacterium spp with zoonotic potential and an overview of human and animal infections

Corynebacterium diphtheriae, Corynebacterium ulcerans and Corynebacterium pseudotuberculosis constitute a group of potentially toxigenic microorganisms that are related to different infectious processes in animal and human hosts. Currently, there is a lack of information on the prevalence of disease caused by these pathogens, which is partially due to a reduction in the frequency of routine laboratory testing. In this study, a multiplex polymerase chain reaction (mPCR) assay that can simultaneously identify and determine the toxigenicity of these corynebacterial species with zoonotic potential was developed. This assay uses five primer pairs targeting the following genes: rpoB (Corynebacterium spp), 16S rRNA (C. ulcerans and C. pseudotuberculosis), pld (C. pseudotuberculosis), dtxR (C. diphtheriae) and tox [diphtheria toxin (DT) ]. In addition to describing this assay, we review the literature regarding the diseases caused by these pathogens. Of the 213 coryneform strains tested, the mPCR results for all toxigenic and non-toxigenic strains of C . diphtheriae, C. ulcerans and C. pseudotuberculosis were in 100% agreement with the results of standard biochemical tests and PCR-DT. As an alternative to conventional methods, due to its advantages of specificity and speed, the mPCR assay used in this study may successfully be applied for the diagnosis of human and/or animal diseases caused by potentially toxigenic corynebacterial species.

Preventing the preventable through effective surveillance: the case of diphtheria in a rural district of Maharashtra, India

BACKGROUND

Epidemic diphtheria is still poorly understood and continues to challenge both developing and developed countries. In the backdrop of poor immunization coverage, non-existent adult boosters, weak case based surveillance and persistence of multiple foci, there is a heightened risk of re-emergence of the disease in epidemic forms in India. Investigating each outbreak to understand the epidemiology of the disease and its current status in the country is therefore necessary. Dhule a predominantly tribal and rural district in Northern Maharashtra has consistently recorded low vaccination coverages alongside sporaidic cases of diphtheria over the last years.

METHODS

This study reports the findings of an onsite survey conducted to assess a recent outbreak of diphtheria in Dhule district and the response mounted to it. Secondary data regarding outbreak detection and response were obtained from the district surveillance office. Clinical data were extracted from hospital records of eleven lab confirmed cases including one death case. Frequency distributions were calculated for each identified clinical and non- clinical variable using Microsoft™ Excel® 2010.

RESULTS

Our findings suggest a shift in the median age of disease to adolescents (10-15 years) without gender differences. Two cases (18%) reported disease despite immunization. Clinical symptoms included cough (82%), fever (73%), and throat congestion (64%). About 64% and 36% of the 11 confirmed cases presented with a well defined pseudomembrane and a tonsillar patch respectively. Drug resistance was observed in all three culture positive cases. One death occurred despite the administration of Anti-Diphtheric Serum in a partially immunized case (CFR 9%). Genotyping and toxigenicity of strain was not possible due to specimen contamination during transport as testing facilities were unavailable in the district.

CONCLUSIONS

The outbreak raises several concerns regarding the epidemiology of diphtheria in Dhule. The reason for shift in the median age despite consistently poor immunization coverage (below 50%) remains unclear. Concomitant efforts should now focus on improving and monitoring primary immunization and booster coverages across all age groups. Gradually introducing adult immunization at ten year intervals may become necessary to prevent future vulnerabilities. Laboratory networks for genotyping and toxigenicity testing are urgently mandated at district level given the endemicity of the disease in the surrounding region and its recent introduction in remote Dhule. Contingency funds with pre- agreements to obtain ADS and DT/Td vaccines at short notice and developing standard case management protocols at district level are necessary. Monitoring the disease, emerging strains and mutations, alongside drug resistance through robust and effective surveillance is a pragmatic way forward.

Tetanus: still a public health problem in India - observations in an infectious diseases hospital in Kolkata

BACKGROUND

Tetanus is a major health problem in many developing countries, including India, with significant morbidity and mortality due to lack of environmental hygiene and health education, incomplete vaccination, high case prevalence and inadequate intensive care facilities.

OBJECTIVES

To observe the demography, clinical profile and outcomes of tetanus patients.

MATERIALS AND METHODS

A total of 282 tetanus patients were screened and closely observed prospectively from January 2010 to December 2011.

RESULTS

The mean age of the study patients was 31.15 years (± 14.26) and the majority were unvaccinated or incompletely vaccinated against tetanus. Patients were mainly farmers (140, 49.64%) and children (102, 36.17%). The sources of infection identified were mainly thorn/pin prick in 129 cases (45.7%), cut/lacerated injury in 83 cases (29.4%) and ear infection in 47 cases (16.7%), while definite injurywas not detected/remembered in 42 cases (14.8%). The average duration of hospital stay was 17.2 ± (4.7) days and autonomic nervous system dysfunction was the most common complication observed in this study. Death was the outcome in a total of 58 patients (20.6%) mostly due to aspiration pneumonia-induced sepsis, respiratory failure or cardiac complications.

CONCLUSION

Environmental hygiene, basic health education, increased in immunization coverage, proper wound care - even following minor injuries - and more facilities for intensive care units, may reduce the overall incidence of tetanus and mortality following onset of the disease.

Corynebacterium ulcerans diphtheria: an emerging zoonosis in Brazil and worldwide

The article is a literature review on the emergence of human infections caused by Corynebacterium ulcerans in many countries including Brazil. Articles in Medline/PubMed and SciELO databases published between 1926 and 2011 were reviewed, as well as articles and reports of the Brazilian Ministry of Health. It is presented a fast, cost-effective and easy to perform screening test for the presumptive diagnosis of C. ulcerans and C. diphtheriae infections in most Brazilian public and private laboratories. C. ulcerans spread in many countries and recent isolation of this pathogen in Rio de Janeiro, southeastern Brazil, is a warning to clinicians, veterinarians, and microbiologists on the occurrence of zoonotic diphtheria and C. ulcerans dissemination in urban and rural areas of Brazil and/or Latin America.

Complete genome sequence, lifestyle, and multi-drug resistance of the human pathogen Corynebacterium resistens DSM 45100 isolated from blood samples of a leukemia patient

BACKGROUND

Corynebacterium resistens was initially recovered from human infections and recognized as a new coryneform species that is highly resistant to antimicrobial agents. Bacteremia associated with this organism in immunocompromised patients was rapidly fatal as standard minocycline therapies failed. C. resistens DSM 45100 was isolated from a blood culture of samples taken from a patient with acute myelocytic leukemia. The complete genome sequence of C. resistens DSM 45100 was determined by pyrosequencing to identify genes contributing to multi-drug resistance, virulence, and the lipophilic lifestyle of this newly described human pathogen.

RESULTS

The genome of C. resistens DSM 45100 consists of a circular chromosome of 2,601,311 bp in size and the 28,312-bp plasmid pJA144188. Metabolic analysis showed that the genome of C. resistens DSM 45100 lacks genes for typical sugar uptake systems, anaplerotic functions, and a fatty acid synthase, explaining the strict lipophilic lifestyle of this species. The genome encodes a broad spectrum of enzymes ensuring the availability of exogenous fatty acids for growth, including predicted virulence factors that probably contribute to fatty acid metabolism by damaging host tissue. C. resistens DSM 45100 is able to use external L-histidine as a combined carbon and nitrogen source, presumably as a result of adaptation to the hitherto unknown habitat on the human skin. Plasmid pJA144188 harbors several genes contributing to antibiotic resistance of C. resistens DSM 45100, including a tetracycline resistance region of the Tet W type known from Lactobacillus reuteri and Streptococcus suis. The tet(W) gene of pJA144188 was cloned in Corynebacterium glutamicum and was shown to confer high levels of resistance to tetracycline, doxycycline, and minocycline in vitro.

CONCLUSIONS

The detected gene repertoire of C. resistens DSM 45100 provides insights into the lipophilic lifestyle and virulence functions of this newly recognized pathogen. Plasmid pJA144188 revealed a modular architecture of gene regions that contribute to the multi-drug resistance of C. resistens DSM 45100. The tet(W) gene encoding a ribosomal protection protein is reported here for the first time in corynebacteria. Cloning of the tet(W) gene mediated resistance to second generation tetracyclines in C. glutamicum, indicating that it might be responsible for the failure of minocycline therapies in patients with C. resistens bacteremia.

Plasticity of Corynebacterium diphtheriae pathogenicity islands revealed by PCR

Despite the existence of a vaccine against diphtheria, this disease remains endemic and is reemerging in several regions due to many factors, including variations in genes coding for virulence factors. One common feature of virulence factors is their high concentration in pathogenicity islands (PAIs), very unstable regions acquired via horizontal gene transfer, which has lead to the emergence of various bacterial pathogens. The 13 putative PAIs in Corynebacterium diphtheriae NCTC 13129 and the reemergence of this disease point to the great variability in the PAIs of this species, which may reflect on bacterial life style and physiological versatility. We investigated the relationships between the large number of PAIs in C. diphtheriae and the possible implications of their plasticity in virulence. The GenoFrag software was used to design primers to analyze the genome plasticity of two pathogenicity islands of the reference strain (PiCds 3 and 8) in 11 different strains. We found that PiCd 3 was absent in only two strains, showing genes playing putative important roles in virulence and that only one strain harbored PiCd 8, due to its location in a putative "hotspot" for horizontal gene transfer events.

Multilocus sequence types of invasive Corynebacterium diphtheriae isolated in the Rio de Janeiro urban area, Brazil

Invasive infections caused by Corynebacterium diphtheriae in vaccinated and non-vaccinated individuals have been reported increasingly. In this study we used multilocus sequence typing (MLST) to study genetic relationships between six invasive strains of this bacterium isolated solely in the urban area of Rio de Janeiro, Brazil, during a 10-year period. Of note, all the strains rendered negative results in PCR reactions for the tox gene, and four strains presented an atypical sucrose-fermenting ability. Five strains represented new sequence types. MLST results did not support the hypothesis that invasive (sucrose-positive) strains of C. diphtheriae are part of a single clonal complex. Instead, one of the main findings of the study was that such strains can be normally found in clonal complexes with strains related to non-invasive disease. Comparative analyses with C. diphtheriae isolated in different countries provided further information on the geographical circulation of some sequence types.

A dominant-negative approach that prevents diphthamide formation confers resistance to Pseudomonas exotoxin A and diphtheria toxin

Diphtheria toxin (DT), Pseudomonas aeruginosa Exotoxin A (ETA) and cholix toxin from Vibrio cholerae share the same mechanism of toxicity; these enzymes ADP-rybosylate elongation factor-2 (EF-2) on a modified histidine residue called diphthamide, leading to a block in protein synthesis. Mutant Chinese hamster ovary cells that are defective in the formation of diphthamide have no distinct phenotype except their resistance to DT and ETA. These observations led us to predict that a strategy that prevents the formation of diphthamide to confer DT and ETA resistance is likely to be safe. It is well documented that Dph1 and Dph2 are involved in the first biochemical step of diphthamide formation and that these two proteins interact with each other. We hypothesized that we could block diphthamide formation with a dominant negative mutant of either Dph1 or Dph2. We report in this study the first cellular-targeted strategy that protects against DT and ETA toxicity. We have generated Dph2(C-), a dominant-negative mutant of Dph2, that could block very efficiently the formation of diphthamide. Cells expressing Dph2(C-) were 1000-fold more resistant to DT than parental cells, and a similar protection against Pseudomonas exotoxin A was also obtained. The targeting of a cellular component with this approach should have a reduced risk of generating resistance as it is commonly seen with antibiotic treatments.

Expression and purification of the immunogenically active fragment B of the Park Williams 8 Corynebacterium diphtheriae strain toxin

The construction of a hexahistidine-tagged version of the B fragment of diphtheria toxin (DTB) represents an important step in the study of the biological properties of DTB because it will permit the production of pure recombinant DTB (rDTB) in less time and with higher yields than currently available. In the present study, the genomic DNA of the Corynebacterium diphtheriae Park Williams 8 (PW8) vaccine strain was used as a template for PCR amplification of the dtb gene. After amplification, the dtb gene was cloned and expressed in competent Escherichia coli M15 cells using the expression vector pQE-30. The lysate obtained from transformed E. coli cells containing the rDTB PW8 was clarified by centrifugation and purified by affinity chromatography. The homogeneity of the purified rDTB PW8 was confirmed by immunoblotting using mouse polyclonal anti-diphtheria toxoid antibodies and the immune response induced in animals with rDTB PW8 was evaluated by ELISA and dermonecrotic neutralization assays. The main result of the present study was an alternative and accessible method for the expression and purification of immunogenically reactive rDTB PW8 using commercially available systems. Data also provided preliminary evidence that rabbits immunized with rDTB PW8 are able to mount a neutralizing response against the challenge with toxigenic C. diphtheriae.

Implications from predictions of HLA-DRB1 binding peptides in the membrane proteins of Corynebacterium diphtheriae

The aerobic gram positive bacterium Corynebacterium diphtheriae causes diphtheria, a respiratory tract illness characterized by symptoms such as sore throat, low fever, and an adherent membrane on the tonsils, pharynx, and/or nasal cavity. Therefore, it is important to develop preventive vaccines for diphtheria. The availability of the 2,488,635 bp long complete sequence for the C. diphtheriae genome provides an opportunity to understand cell mediated immune response using Computational Biology tools from the bacterial proteome sequence data. We selected 355 membrane proteins from the C. diphtheriae proteome using annotation data to identify potential HLA-DRB1 binding short peptide using modeling, simulations and predictions. This exercise identified 30 short peptides in membrane proteins showing binding capability to HLA-DRB1 alleles. These peptides serve as outline for the understanding of cell mediated immune response to C. diphtheriae. It should be noted that the predicted data to be verified using binding assays for further consideration.

Ins and outs of glucose transport systems in eubacteria

Glucose is the classical carbon source that is used to investigate the transport, metabolism, and regulation of nutrients in bacteria. Many physiological phenomena like nutrient limitation, stress responses, production of antibiotics, and differentiation are inextricably linked to nutrition. Over the years glucose transport systems have been characterized at the molecular level in more than 20 bacterial species. This review aims to provide an overview of glucose uptake systems found in the eubacterial kingdom. In addition, it will highlight the diverse and sophisticated regulatory features of glucose transport systems.

Novel lipoarabinomannan-like lipoglycan (CdiLAM) contributes to the adherence of Corynebacterium diphtheriae to epithelial cells

The genus Corynebacterium is part of the phylogenetic group nocardioform actinomycetes. Members of this group have a characteristic cell envelope structure composed primarily of branched long-chain lipids, termed mycolic acids, and a rich number of lipoglycans such as lipoarabinomanans (LAM) and lipomannans. In this study, we identified a novel LAM variant isolated from Corynebacterium diphtheriae named CdiLAM. The key structural features of CdiLAM are a linear alpha-1-->6-mannan with side chains containing 2-linked alpha-D-Manp and 4-linked alpha-D-Araf residues. The polysaccharide backbone is linked to a phosphatidylinositol anchor. In contrast to the LAMs of other members of actinomycetales, CdiLAM presents an unusual substitution at position 4 of alpha-1-->6-mannan backbone by alpha-D-Araf. Unlike the non-fimbrial adhesin 62-72p, CdiLAM did not function as a hemagglutinin to human red blood cells. Experimental evidences pointed to CdiLAM as an adhesin of C. diphtheriae to human respiratory epithelial cells, thereby, contributing to the pathogenesis of diphtheria.

Evaluation of human antibody responses to diphtheria toxin subunits A and B in various age groups

This study aimed to evaluate human antibody responses to diphtheria toxin subunits in various age groups. Antibodies against the intact diphtheria toxin and the diphtheria toxin subunits A and B were evaluated in 1319 individuals using a double-antigen ELISA. Although high levels of protection (83.6%, 95% CI 79.2-87.4) were found in children and adolescents, the middle-aged adult population was less protected (28.8%, 95% CI 24.3-33.6). An increase in age was associated with a decrease in the frequency of protected individuals in the 0-39-year age group (p <0.001). Anti-subunit B levels correlated well (p <0.01) with levels of antibodies against the intact toxin. In children aged < or =16 years, the intervals at which the peaks in geometric mean titres of anti-subunit B antibodies were observed were found to correlate with the ages at which booster doses are administered. Overall, males appeared to be more protected than females (OR 1.67, 95% CI 1.34-2.08, p <0.001). A small group of individuals had antibody levels of > or =0.1 IU/mL against the intact toxin, but did not have protective antibody against subunit B. Determination of anti-subunit B antibody levels should help in evaluating the effectiveness of diphtheria boosters and other aspects of diphtheria immunity.

Bacteriophage-based vectors for site-specific insertion of DNA in the chromosome of Corynebacteria

In Corynebacterium diphtheriae, diphtheria toxin is encoded by the tox gene of some temperate corynephages such as beta. beta-like corynephages are capable of inserting into the C. diphtheriae chromosome at two specific sites, attB1 and attB2. Transcription of the phage-encoded tox gene, and many chromosomally encoded genes, is regulated by the DtxR protein in response to Fe(2+) levels. Characterizing DtxR-dependent gene regulation is pivotal in understanding diphtheria pathogenesis and mechanisms of iron-dependent gene expression; although this has been hampered by a lack of molecular genetic tools in C. diphtheriae and related Coryneform species. To expand the systems for genetic manipulation of C. diphtheriae, we constructed plasmid vectors capable of integrating into the chromosome. These plasmids contain the beta-encoded attP site and the DIP0182 integrase gene of C. diphtheriae NCTC13129. When these vectors were delivered to the cytoplasm of non-lysogenic C. diphtheriae, they integrated into either the attB1 or attB2 sites with comparable frequency. Lysogens were also transformed with these vectors, by virtue of the second attB site. An integrated vector carrying an intact dtxR gene complemented the mutant phenotypes of a C. diphtheriae DeltadtxR strain. Additionally, strains of beta-susceptible C. ulcerans, and C. glutamicum, a species non-permissive for beta, were each transformed with these vectors. This work significantly extends the tools available for targeted transformation of both pathogenic and non-pathogenic Corynebacterium species.

Molecular epidemiology of C. diphtheriae strains during different phases of the diphtheria epidemic in Belarus

BACKGROUND

The reemergence of epidemic diphtheria in Belarus in 1990s has provided us with important information on the biology of the disease and the diversity of the causative agent Corynebacterium diphtheriae. Molecular investigations were conducted with the aim to analyze the genetic variability of C diphtheriae during the post-epidemic period.

METHODS

The biotype and toxigenicity status of 3513 C. diphtheriae strains isolated from all areas in Belarus during a declining period of diphtheria morbidity (1996-2005) was undertaken. Of these, 384 strains were isolated from diphtheria cases, 1968 from tonsillitis patients, 426 from contacts and 735 from healthy carriers. Four hundred and thirty two selected strains were ribotyped.

RESULTS

The C diphtheriae gravis biotype, which was prevalent during 1996-2000, was "replaced" by the mitis biotype during 2001-2005. The distribution of toxigenic C. diphtheriae strains also decreased from 47.1% (1996) to 5.8% (2005). Changes in the distribution of the epidemic ribotypes Sankt-Peterburg and Rossija were also observed. During 2001-2005 the proportion of the Sankt-Peterburg ribotype decreased from 24.3% to 2.3%, in contrast to the Rossija ribotype, that increased from 25.1% to 49.1%. The circulation of other toxigenic ribotypes (Otchakov, Lyon, Bangladesh), which were prevalent during the period of high diphtheria incidence, also decreased. But at the same time, the proportion of non-toxigenic strains with the Cluj and Rossija ribotypes dramatically increased and accounted for 49.3% and 30.1%, respectively.

CONCLUSION

The decrease in morbidity correlated with the dramatic decrease in the isolation of the gravis biotype and Sankt Peterburg ribotype, and the prevalence of the Rossija ribotype along with other rare ribotypes associated with non-toxigenic strains (Cluj and Rossija, in particular).

Mapping and comprehensive analysis of the extracellular and cell surface proteome of the human pathogen Corynebacterium diphtheriae

Secreted proteins of the human pathogen Corynebacterium diphtheriae might be involved in important pathogen-host cell interactions. Here, we present the first systematic reference map of the extracellular and cell surface proteome fractions of the type strain C. diphtheriae C7s(-)tox-. The analysis window of 2-DE covered the pI range from 3 to 10 along with a MW range from 8 to 150 kDa. Computational analysis of the 2-D gels detected almost 150 protein spots in the extracellular proteome fraction and about 80 protein spots of the cell surface proteome. MALDI-TOF-MS and PMF with trypsin unambiguously identified 107 extracellular protein spots and 53 protein spots of the cell surface, representing in total 85 different proteins of C. diphtheriae C7s(-)tox-. Several of the identified proteins are encoded by pathogenicity islands and might represent virulence factors of C. diphtheriae. Additionally, four solute-binding proteins (HmuT, Irp6A, CiuA, and FrgD) of different iron ABC transporters were identified, with the hitherto uncharacterized FrgD protein being the most abundant one of the cell surface proteome of C. diphtheriae C7s(-)tox-.

Diphtheria-neutralizing antibody levels in healthy adults from Rio de Janeiro, Brazil

In Brazil, until 2004, the immunization policy against diphtheria involved childhood vaccination with no official routine booster dose administered after 15 years of age. This study assessed functional antibody levels against diphtheria among blood donors. A total of 140 blood samples were collected, and diphtheria antitoxin levels were evaluated by Vero cell neutralization test. The mean age of the population was 34 years old (range: 18-61 years); 37.8% females and 62.2% males. Overall, 30.7% (95%, CI: 23.4-38.7) individuals presented neutralizing antitoxin antibody titers < 0.01 IU/ml; 42.1% (95%, CI: 34.1-50.4) showed values between 0.01-0.09 IU/ml and, 27.1% (95%, CI: 20.2-34.9) had (3) 0.1 IU/ml. In the subgroup of individuals with history of diphtheria immunization during childhood (85%), a number of 28.5% showed unprotective levels of circulating neutralizing antibody (< 0.01 IU/ml). Despite the continuous progress of immunization programs directed to Brazilian population, currently healthy adults remain susceptible to diphtheria.

Stealth and mimicry by deadly bacterial toxins

Diphtheria toxin and exotoxin A are well-characterized members of the ADP-ribosyltransferase toxin family that function as virulence factors in the pathogenic bacteria Corynebacterium diphtheriae and Pseudomonas aeruginosa. Recent high-resolution structural data of the Michaelis (enzyme-substrate) complex of the P. aeruginosa toxin with an NAD(+) analog and eukaryotic elongation factor 2 (eEF2) have provided insights into the mechanism of inactivation of protein synthesis caused by these protein factors. In addition, rigorous steady-state and stopped-flow kinetic analyses of the toxin-catalyzed reaction, in combination with inhibitor studies, have resulted in a quantum leap in our understanding of the mechanistic details of this deadly enzyme mechanism. It is now apparent that these toxins use stealth and molecular mimicry in unleashing their toxic strategy in the infected host eukaryotic cell.

The life and death of translation elongation factor 2

eEF2 (eukaryotic elongation factor 2) occupies an essential role in protein synthesis where it catalyses the translocation of the two tRNAs and the mRNA after peptidyl transfer on the 80 S ribosome. Recent crystal structures of eEF2 and the cryo-electron microscopy reconstruction of its 80 S complex now provide a substantial structural framework for dissecting the functional properties of this factor. The factor can be modified by either phosphorylation or ADP-ribosylation, which results in cessation of translation. We review the structural and functional properties of eEF2 with particular emphasis on the unique diphthamide residue, which is ADP-ribosylated by diphtheria toxin from Corynebacterium diphtheriae and exotoxin A from Pseudomonas aeruginosa.

Expression of diphtheria toxin inStreptococcus mutansand induction of toxin-neutralizing antisera

The nontoxic full-length diphtheria toxin (DTX), fragment A (DTA), and fragment B (DTB) were each genetically fused to the major surface protein antigen P1 (SpaP) of Streptococcus mutans. Repeated attempts to express the recombinant DTX and DTB in the live oral vaccine candidate Streptococcus gordonii were unsuccessful, whereas DTA could be readily expressed in this bacterium. However, the recombinant DTX, DTB, and DTA could be expressed in the related oral bacterium S. mutans. Western blotting and enzyme-linked immunosorbant assay (ELISA) using anti-DTX and anti-P1 antibodies demonstrated the expression of the three fusion proteins in S. mutans. Mouse antisera raised against the recombinant S. mutans recognized the native DTX in Western immunoblotting. The antibodies raised against S. mutans expressing the recombinant DTX and DTA neutralized the cytotoxicity of the native toxin in a Vero cell assay, but the neutralization titers were relatively low. The potential of using S. gordonii as a live vaccine against diphtheria faces major challenges in the expression of DTX in this organism and in the induction of high-titer toxin-neutralizing antibodies.Key words: diphtheria toxin, Streptococcus mutans, Streptococcus gordonii.

Exotoxin A-eEF2 complex structure indicates ADP ribosylation by ribosome mimicry

The bacteria causing diphtheria, whooping cough, cholera and other diseases secrete mono-ADP-ribosylating toxins that modify intracellular proteins. Here, we describe four structures of a catalytically active complex between a fragment of Pseudomonas aeruginosa exotoxin A (ETA) and its protein substrate, translation elongation factor 2 (eEF2). The target residue in eEF2, diphthamide (a modified histidine), spans across a cleft and faces the two phosphates and a ribose of the non-hydrolysable NAD+ analogue, betaTAD. This suggests that the diphthamide is involved in triggering NAD+ cleavage and interacting with the proposed oxacarbenium intermediate during the nucleophilic substitution reaction, explaining the requirement of diphthamide for ADP ribosylation. Diphtheria toxin may recognize eEF2 in a manner similar to ETA. Notably, the toxin-bound betaTAD phosphates mimic the phosphate backbone of two nucleotides in a conformational switch of 18S rRNA, thereby achieving universal recognition of eEF2 by ETA.

Complete genome sequence and analysis of the multiresistant nosocomial pathogen Corynebacterium jeikeium K411, a lipid-requiring bacterium of the human skin flora

Corynebacterium jeikeium is a "lipophilic" and multidrug-resistant bacterial species of the human skin flora that has been recognized with increasing frequency as a serious nosocomial pathogen. Here we report the genome sequence of the clinical isolate C. jeikeium K411, which was initially recovered from the axilla of a bone marrow transplant patient. The genome of C. jeikeium K411 consists of a circular chromosome of 2,462,499 bp and the 14,323-bp bacteriocin-producing plasmid pKW4. The chromosome of C. jeikeium K411 contains 2,104 predicted coding sequences, 52% of which were considered to be orthologous with genes in the Corynebacterium glutamicum, Corynebacterium efficiens, and Corynebacterium diphtheriae genomes. These genes apparently represent the chromosomal backbone that is conserved between the four corynebacteria. Among the genes that lack an ortholog in the known corynebacterial genomes, many are located close to transposable elements or revealed an atypical G+C content, indicating that horizontal gene transfer played an important role in the acquisition of genes involved in iron and manganese homeostasis, in multidrug resistance, in bacterium-host interaction, and in virulence. Metabolic analyses of the genome sequence indicated that the "lipophilic" phenotype of C. jeikeium most likely originates from the absence of fatty acid synthase and thus represents a fatty acid auxotrophy. Accordingly, both the complete gene repertoire and the deduced lifestyle of C. jeikeium K411 largely reflect the strict dependence of growth on the presence of exogenous fatty acids. The predicted virulence factors of C. jeikeium K411 are apparently involved in ensuring the availability of exogenous fatty acids by damaging the host tissue.

The individual and common repertoire of DNA-binding transcriptional regulators of Corynebacterium glutamicum, Corynebacterium efficiens, Corynebacterium diphtheriae and Corynebacterium jeikeium deduced from the complete genome sequences

Background

The genus Corynebacterium includes Gram-positive microorganisms of great biotechnologically importance, such as Corynebacterium glutamicum and Corynebacterium efficiens, as well as serious human pathogens, such as Corynebacterium diphtheriae and Corynebacterium jeikeium. Although genome sequences of the respective species have been determined recently, the knowledge about the repertoire of transcriptional regulators and the architecture of global regulatory networks is scarce. Here, we apply a combination of bioinformatic tools and a comparative genomic approach to identify and characterize a set of conserved DNA-binding transcriptional regulators in the four corynebacterial genomes.

Results

A collection of 127 DNA-binding transcriptional regulators was identified in the C. glutamicum ATCC 13032 genome, whereas 103 regulators were detected in C. efficiens YS-314, 63 in C. diphtheriae NCTC 13129 and 55 in C. jeikeium K411. According to amino acid sequence similarities and protein structure predictions, the DNA-binding transcriptional regulators were grouped into 25 regulatory protein families. The common set of DNA-binding transcriptional regulators present in the four corynebacterial genomes consists of 28 proteins that are apparently involved in the regulation of cell division and septation, SOS and stress response, carbohydrate metabolism and macroelement and metal homeostasis.

Conclusion

This work describes characteristic features of a set of conserved DNA-binding transcriptional regulators present within the corynebacterial core genome. The knowledge on the physiological function of these proteins should not only contribute to our understanding of the regulation of gene expression but will also provide the basis for comprehensive modeling of transcriptional regulatory networks of these species.