Diphtheria carriers in Manchester: simultaneous infection with toxigenic and non-toxigenic mitis strains

Fatal Case of Diphtheria and Risk for Reemergence, Singapore

We report a fatal autochthonous diphtheria case in a migrant worker in Singapore. This case highlights the risk for individual cases in undervaccinated subpopulations, despite high vaccination coverage in the general population. Prompt implementation of public health measures and maintaining immunization coverage are critical to prevent reemergence of diphtheria.

Diagnosis in France of a Non-Toxigenic tox Gene-Bearing Strain of Corynebacterium diphtheriae in a Young Male Back From Senegal

Cutaneous diphtheria is uncommon in Europe. In this study, we report a case of imported cutaneous infection due to a non-toxigenic but tox gene-bearing (NTTB) strain of Corynebacterium diphtheriae. The NTTB strains are recognized as emerging pathogens across Europe, and physicians and bacteriologists should be aware of the circulation of these strains.

[Diphtheria and infections caused by Corynebacterium diphtheriae in 1997]

INTRODUCTION

Diphtheria is a reemerging disease. Two epidemics recently occurred in Algeria and Independent States Community, not so far from Europe. Imported cases were diagnosed in contiguous European countries. This review focuses on the data obtained from these epidemics, with particular emphasis on new clinical forms of Corynebacterium diphtheriae infections. CURRENTS KNOWLEDGE AND KEY POINTS: Sore throat with membranes is no longer the only clinical feature of diphtheria. However, patients' management is identical, with combination of antibiotics, injection of specific antisera, and immunization of patients' close contacts and relatives. French and American sero-epidemiological studies showed that antibody levels does not provide protection, particularly in the elderly. Adult populations would therefore be at risk every 10 years. Recent advances in molecular biology led to the development of gene amplification with polymerase chain reaction, that may be used for the detection of the toxin gene. They also promoted epidemiological surveys of circulating strains via ribotyping. Although this technic evidenced predominant strains in the various countries, genotypes encountered during an epidemics may differ. Besides diphtheria which has apparently been eradicated in France, systemic infections with non-toxigenic strains of C diphtheriae, such as endocarditis, septicemia and arthritis, are evenly diagnosed.

FUTURE PROSPECTS AND PROJECTS

A French national reference center for C diphtheriae has been recently created. This center collects most of the strains isolated in France, clinical data and assesses the toxigenicity of bacteria, allowing strict epidemiological survey.

Characterization of bacteriophages from tox-containing, non-toxigenic isolates of Corynebacterium diphtheriae

Non-toxigenic strains of Corynebacterium diphtheriae continue to cause disease within immunized populations. A subset of these corynebacteria carry the diphtheria toxin gene but in a cryptic form. To determine whether such strains might contribute to the re-emergence of functional toxin genes, the phages and tox mutations within three clone types were examined. tox-containing, beta-related phages were isolated from two of the strain types. The third isolate appeared to harbour a defective prophage. One of the tox- phages encoded truncated, yet enzymatically-active, forms of diphtheria toxin, suggesting that it had sustained a point mutation within the latter half of its toxin gene. In contrast, the other mutant phage did not elicit the production of either a cross-reacting material or an ADP-ribosylating activity. Complementation tests employing a series of double lysogens confirmed that the mutations responsible for the non-toxigenic phenotype of all of the phages were cis dominant. Given these findings, it is reasonable to hypothesize that tox+ genes can arise within human populations by either homologous recombination between two distinct tox- phages or spontaneous reversion within a single mutant allele.

The return of Corynebacterium diphtheriae: the rise of non-toxigenic strains

With the decline in incidence of diphtheria in Europe and the USA, many laboratories no longer routinely culture throat swabs for Corynebacterium diphtheriae. However, there is an outbreak of infection with toxigenic strains in Russia and most adults do not have protective levels of antibody. Non-toxigenic strains are known to cause local disease and lysogenic conversion probably occurs in vivo as well as in vitro. Non-toxigenic C. diphtheriae var. gravis, formerly quite rare, has been isolated with increasing frequency in the UK over the last five years. During prospective screening at one Sexually Transmitted Disease Clinic, six (1%) of 578 homosexual men were found to harbour the organism in the throat, four of them with clinical pharyngitis. Only one of 1696 heterosexual men and women were found to be carriers. Seven cases of endocarditis due to this organism were reported in a single year in Sydney, Australia and non-toxigenic C. diphtheriae var. mitis has caused four cases of endocarditis in Switzerland. Non-toxigenic strains are responsible for pharyngitis and occasional invasive disease and should be treated. Routine screening of throat swabs should not be abandoned.

[Cutaneous diphtheria]

Cutaneous diphtheria, frequently seen in tropical areas, is uncommon in developed countries. As seen in the recent epidemics in western countries, where it turned out to be an important factor of dissemination, there is a persisting risk of diphtheria. A perfect knowledge of the clinical manifestations and factors of risk and consequent vaccination is necessary to eradicate diphtheria.

Polymerase chain reaction assay for diagnosis of potentially toxinogenic Corynebacterium diphtheriae strains: correlation with ADP-ribosylation activity assay

We have developed a polymerase chain reaction assay for the clinical diagnosis of potentially toxinogenic strains of Corynebacterium diphtheriae, the causative agent of diphtheria. A 910-bp amplification product, overlapping a DNA portion encoding both fragments of the diphtheria toxin, has been found in 28 among the 36 strains tested. In addition, effective toxin production, as evidenced by the ability of bacterial culture supernatants to ADP ribosylate eukaryotic elongation factor 2, was determined. In every case, the presence of an amplification product correlated with an ADP-ribosylation activity, thus confirming the diagnosis. The polymerase chain reaction assay herein described is very rapid (2 h) compared with the Elek immunodiffusion test or the guinea pig lethality test. It can provide a convenient and reliable method for laboratories involved in the identification of toxinogenic corynebacteria.

Molecular epidemiology of nasopharyngeal corynebacteria in healthy adults from an area where diphtheria vaccination has been extensively practiced

In addition to conventional biochemical tests, a DNA probe specific for Corynebacterium diphtheriae was used to characterize 53 cystinase-positive and urease-negative corynebacteria strains isolated from pharyngeal and nasal swabs obtained from 515 healthy adults living in an urban area of central Italy. No Corynebacterium diphtheriae strain was found. Six "atypical" strains were isolated, which could not be classified in any of the species so far defined in the Corynebacterium genus. These strains appeared to be biochemically close to Corynebacterium pseudodiphtheriticum and genetically close to Corynebacterium diphtheriae, since their DNAs strongly hybridized, under relatively low stringency conditions, with a Corynebacterium diphtheriae-specific probe and since insertion sequences which are usually found in Corynebacterium diphtheriae genomes were also found to be present in their genomes. No one of these six strains was either toxigenic or susceptible to lysogenization by beta-corynephage carrying the tox gene. Therefore, they do not seem to have any epidemiological relevance as possible hosts for beta-phages.

Immunity to diphtheria, six to 15 years after a basic three-dose immunization schedule

The results of a study of the immunity to diphtheria of 283 girls (9-18 years of age) vaccinated at the age of two years with three doses of vaccine, are reported. The rabbit skin test was used to determine the titre of serum diphtheria antitoxin. 55.8% of the subjects were found to be protected (titre greater than or equal to 0.1 IU/ml), 38.9% were only relatively immune (titre greater than or equal to 0.01- less than 0.01 IU/ml), and 5.3% were unprotected (titre less than 0.01 IU/ml). The antitoxin titres showed a tendency to decrease with time. Even so, 6-15 years after vaccination, the percentages of protected and partially protected subjects were still high (95%).

Epidemiological typing of Corynebacterium diphtheriae isolated in Sweden 1984-1986

From September 1984 to December 1986 121 cases of culture-positive diphtheria were reported to the National Bacteriological Laboratory in Stockholm. Toxigenic Corynebacterium diphtheriae nongravis was isolated from all but one of 33 patients with disease and from 69 healthy carriers. 63/65 toxigenic isolates, available for epidemiological typing, had the same phage type, 20, and the same restriction enzyme pattern, RE2. This included strains isolated both from patients inside and outside of the traditional risk groups of people abusing alcohol and drugs. Non-toxigenic strains gave different phage types and RE patterns.

Double-antibody sandwich enzyme-linked immunosorbent assay for rapid detection of toxin-producing Corynebacterium diphtheriae

An enzyme-linked immunosorbent assay for determining the toxigenicity of Corynebacterium diphtheriae is presented. The assay uses hyperimmune horse diphtheria antitoxin as a capture antibody and mouse monoclonal diphtheria antitoxin as a detecting antibody. Growth of bacteria and capture of diphtheria toxin by antitoxin are carried out in one step. Toxin produced by as little as 100 toxin-producing corynebacteria is detectable, corresponding to a sensitivity of 10 ng of diphtheria toxin per ml. Demonstration of toxin after incubation of the bacteria for 4.75 h, as well as after 18 h, was in accordance with the modified Elek gel diffusion method and the guinea pig inoculation test. However, heavy inocula incubated overnight produced significantly lower optical density than did diluted inocula; thus, the higher optical density was used as an indicator of toxin production. A decrease in optical density was also seen by shortening the incubation time. For laboratory safety, ethanol was added to the microtiter plate wells before washing out of the bacteria. This resulted in a further decrease in optical density. Using 4.75-h incubation time gave a single false-negative result. No false-positive results were ever seen. Incubation for 18 h is suitable for large-scale screening, and 4.75 h of incubation is suitable for rapid identification of toxin-producing C. diphtheriae.

DNA element of Corynebacterium diphtheriae with properties of an insertion sequence and usefulness for epidemiological studies

The segment of DNA which is inserted within the tox gene of bacteriophage gamma and is responsible for its Tox- phenotype was found to be present and repeated approximately 30 times in the chromosome of Corynebacterium diphtheriae Belfanti 1030. Other C. diphtheriae strains contained a variable number of copies (1 to 25) of the same element. Sequence analysis showed that this repeated and interspersed DNA element was flanked by 9-base-pair direct repeats and that the 5' and 3' ends of the insertion contained sequences forming an imperfect inverted repeat. Therefore, the DNA segment here described has most of the typical structural features of a bacterial insertion sequence element. We show that different C. diphtheriae isolates derived from the same outbreak of diphtheria have an identical genomic distribution of this DNA element and that such DNA can be useful for epidemiological studies.

Prevalence of diphtheria carriers in a population with disappearing clinical diphtheria

Ten years ago the incidence of diphtheria was relatively high in Greece and a survey of school children had revealed a carrier prevalence of non-toxigenic Corynebacterium diphtheriae of 3,4%. A similar survey undertaken now has revealed that the disease seems to be disappearing. Among 895 school children (6-13 years-old) in seven primary schools of different socioeconomic levels, only seven were carriers of non-toxigenic C. diphtheriae strains, corresponding to a prevalence of 0.8%. Toxigenic strains were not found. All carriers were pupils of the same school, and the carrier state was more frequent during the first three school years. All the carriers were found in a school serving a socioeconomically deprived area. A statistically significant association was found between the prevalence of C. diphtheriae and of other non-pathogenic Corynebacteria.

Studies on the molecular epidemiology of diphtheria

DNA was extracted from toxigenic and nontoxigenic (tox+ and tox-) diphtheria bacilli isolated during a carrier survey that followed recovery of a tox+ Corynebacterium diphtheriae mitis from a baby with membranous tonsillitis. The electrophoretic gel patterns of restriction enzyme digests were indistinguishable from one another. They were, however, readily distinguishable from similar gels of DNAs extracted from diphtheria bacilli associated with outbreaks elsewhere. Hybridisation of a labelled nick-translated corynephage-beta c-DNA probe to nitrocellulose blots of these gels occurred only to blots from tox+ strains. Other hybridisation studies showed that all of seven strains, each isolated from a diphtheria case or carrier in a different part of the world, carried a prophage with DNA closely related to phage beta tox+. When an individual carrying a tox+ diphtheria bacillus arrives in an immunised community, spread of the tox gene to other individuals may be via phage conversion of tox- C diphtheriae already prevalent among the nasopharyngeal bacterial flora of the local populace, rather than by colonisation with the tox+ strain itself.

The role of adherence in determining the site of infection by Corynebacterium diphtheriae

Twenty-nine strains of Corynebacterium diphtheriae isolated from throats and 29 strains from skin lesions, the latter mainly from communities of low socio-economic status in tropics and cold climates, have been examined for the property of adherence to human buccal epithelial cells. All throat strains showed adherence. In contrast, strains from skin lesions were predominantly poor adherers. These results indicate that strains of C. diptheriae from throats must now be added to the important group of pathogens which possess the property of adherence to surface epithelial cells of mucous membranes, thus providing an essential first step in the process of colonizing their hosts. The possible role of this phenomenon of adherence to bucco-pharyngeal epithelial cells in the evolution of the host-parasite relationship of C. diphtheriae is discussed.

Diphtheria immunization in adolescents and adults with reduced doses of adsorbed diphtheria toxoid

A study was undertaken in Schick-positive university students and schoolchildren to determine the diphtheria antitoxin response to vaccines containing a reduced dose of adsorbed diphtheria toxoid. It was found that the majority of participants, apparently previously sensitized, responded with an increase in antitoxin titre to protective levels after performance of the Schick test, or after the first dose of vaccine. A group of non-immune students required three doses of vaccine to reach adequate antitoxin levels to ensure durable immunity. Only one local reaction was observed in the group of 51 students, and this was attributed to an Arthus-type reaction involving the tetanus toxoid component of a combined adsorbed diphtheria and tetanus vaccine.