CORYNEBACTERIUM

 

                                       

     In the 4th century B.C., Hippocrates provided the first clinical description of diphtheria. Bretonneu (1821), a French army surgeon, described the disease's unique clinical characteristics and coined the term "dipht'erie" to refer to the tough leathery pseudo membrane that occurs in the oropharynx and occasionally in the nasopharynx.

    Corynebacteria, often known as "Coryneform bacteria," are a type of positive bacillus that does not produce spores. They're usually clubbed or unevenly formed; coryne means "club" in Greek. Diphtheria's causal agent, Corynebacterium diphtheria, is the most common pathogen in this group. C. Ulcerans, a pathogenic corynebacterium that causes diphtheria-like sores, is another pathogenic corynebacterium. C. minutissimum and C. tenuis are Corynebacteria that cause superficial skin diseases. Normal commensals in the throat, skin, and conjunctiva are caused by diphtheria.

    Slender Gram-positive rods, pleomorphic, and readily decolonized Corynebacterium diphtheria. They are not capsule-forming, sporing, or motile. Polymetaphosphate granules can be detected in the cells. When stained with Loeffler's Methylene Blue, they take on a bluish purple appearance against faintly stained cytoplasm, earning the name 'Metachromatic granules.' 'Volatin granules' or 'Babes Ernst granules' are other names for these granules. They are frequently found at the poles, referred to as 'polar bodies.'

      Special stains for demonstrating the granules are Albert’s stain, Neisser’s stain, Ponder’s stain.

The bacilli are arranged in pairs, palisades or small groups; the bacilli lie at various angles to each other, resembling the letters, V or L. This is called, “Chinese letter pattern” or “cuneiform pattern.

     They are both facultative anaerobes and aerobes. The ideal temperature is 370 degrees Celsius. On conventional media, growth is scarce. For proper growth, blood, serum, or eggs are required. Potassium tellurite (0.04%) is a'selective agent,' inhibiting the growth of most oral commensals while slowing the growth of Candida albicans and Staphylococcus aureus.

       Cultures remain viable for 2-3 wks at 25-300C. Can be destroyed by heat. Resistant to light, desiccation or freezing. Easily destroyed by antiseptics. Susceptible to Penicillin, erythromycin and broad spectrum antibiotics.