The production of fibrinous exudates may play an important role in determining the outcome of bacterial infection. Although pseudomembrane formation is a characteristic feature of diphtheria, little is known about the fibrinogen (Fbn)-binding properties of Corynebacterium diphtheriae strains and the influence of the gene that codes for diphtheria toxin (tox gene) in this process. In this study we demonstrated the ability of C. diphtheriae strains to bind to Fbn and to convert Fbn to fibrin. Bacterial interaction with rabbit plasma was evaluated by both slide and tube tests. Interaction of microorganisms with human Fbn was evaluated by both enzyme linked immunosorbent assay (ELISA) and fluorescein isothiocyanate-conjugated (FITC) Fbn binding assays. Nontoxigenic and toxigenic strains formed bacterial aggregates in the presence of plasma in the slide tests. The ability to convert Fbn to a loose web of fibrin in the plasma solution in the tube tests appeared to be a common characteristic of the species, including strains that do not carry the tox gene. Fbn binding to C. diphtheriae strains occurred at varying intensities, as demonstrated by the FITC-Fbn and ELISA binding assays. Our data suggest that the capacity to bind to Fbn and to convert Fbn to fibrin may play a role in pseudomembrane formation and act as virulence determinants of both nontoxigenic and toxigenic strains.

The increasing problems with multidrug resistance in relation to Corynebacterium, including C. diphtheriae, are examples of challenges confronting many countries. For this reason, Brazilian C. diphtheriae strains were evaluated by the E-Test for their susceptibility to nine antibacterial drugs used in therapy. Resistance (MIC < 0.002; 0.38 µg/ml) to penicillin G was found in 14.8% of the strains tested. Although erythromycin (MIC90 0.75 µg/ml) and azithromycin (MIC90 0.064 µg/ml) were active against C. diphtheriae in this study, 4.2% of the strains showed decreased susceptibility (MIC 1.0 µg/ml) to erythromycin. Multiple resistance profiles were determined by the disk diffusion method using 31 antibiotics. Most C. diphtheriae strains (95.74%) showed resistance to mupirocin, aztreonam, ceftazidime, and/or oxacillin, ampicillin, penicillin, tetracycline, clindamycin, lincomycin, and erythromycin. This study presents the antimicrobial susceptibility profiles of Brazilian C. diphtheriae isolates. The data are of value to practitioners, and suggest that some concern exists regarding the use of penicillin.

Um caso de difteria ocorreu, em 1999, em mulher de 32 anos de idade. A paciente iniciou episódio de dor de garganta imediatamente após participação em reunião com profissionais europeus durante cinco dias consecutivos, no Rio de Janeiro. Ela declarou ter sido submetida ao esquema completo de imunização contra difteria (DTP-tríplice bacteriana) na infância e a doses de reforço (dT-dupla adulto) há dois anos. O diagnóstico clínico da doença só foi firmado após o laboratório de microbiologia ter confirmado a capacidade de produção de toxina pela amostra isolada de Corynebacterium diphtheriae var. gravis, biotipo não fermentador de sacarose comumente encontrado em diversos países europeus e responsável pela atual epidemia na região correspondente a antiga União Soviética. Na era da vacinação antidiftérica, indivíduos adultos de nossa comunidade podem apresentar-se potencialmente susceptíveis a difteria.

In 1999, a case of diphtheria in a 32-year-old woman was reported. The patient developed a sore throat immediately after participating of a five-day meeting with European workers in Rio de Janeiro. Her history included complete pediatric immunization (DTP) and three doses of adult formulation tetanus and diphtheria toxoid (dT) two years earlier. Clinical diagnosis of diphtheria was not made until microbiologic examination of specimens confirmed toxigenicity of Corynebacterium diphtheriae var. gravis, a biotype currently found circulating within Europe where diphtheria remains epidemic. This case reinforces the potential susceptibility of Brazilian adults to epidemic diphtheria in the vaccine era.