Corynebacteria
The corynebacteria are gram-positive rods which arrange themselves in palisades, possess club-shaped swellings at their poles and stain irregularly. C. diptheriae is responsible for diptheria.
Gram positive bacilli, tend to arrange in pallisades
Obligate aerobe, grows well on simple media
Loeffler’s coagulated serum medium is still useful
Diptheria toxin is produced by strains that are lysogenic for B-prophage
The toxin gene resides in the phage genome
Diptheria begins in the upper respiratory tract where an inflammatory response results in the characteristic diptheritic pseudomembrane appearing on the tonsils or posterior pharynx. This may then spread into the nasal passages or into the larynx and trachea. Mechanical obstruction of the larynx may occur resulting in suffocation. Persons who recover from diptheria may continue to harbor the organism in the nose or throat for weeks or months. Such carriers act as the reservoir for infection.
A definitive diagnosis are diptheria can be made be isolating toxigenic diptheria bacilli from the primary lesion. Exudate taken from the lesion should be immediately transferred to a Loeffler slant or blood agar plate. In suspected cases of diptheria, antitoxin should be given early before results of laboratory tests are available.
Diptheria toxoid is available for immunisation and as a result, diptheria has become rare in countries which practice immunisation. It is still prevalent in those which do not. Individuals can be tested for immunity against diptheria by the Schick test, where a small amount of toxin is administered intradermally.
Bordetella are minute aerobic gram-negative bacteria. B. pertussis is the causative agent of whooping cough. Pertussis has two phases. The first phase is an upper respiratory tract illness with fever, cough, and malaise. After a period of around 10 days, the second toxaemic phase develops, characterised by prolonged and paraxysmal coughing with inspiratory whoops. The coughing may be so severe that it leads to vomiting and aspiration. During the first phase, the organism can be readily recovered from respiratory secretions and the severity of the disease can be reduced by antimicrobial therapy. During the second phase of the disease, the organism is rarely recovered and antimicrobials do not alter the course of the disease.
Laboratory diagnosis can be made by culturing nasopharyngeal secretions on Bordet-Gengou medium. B. pertussis is recovered in about 80% of cases in the first 2 weeks but rarely after 4 weeks of symptoms. Erythromycin given in the initial stage is effective in reducing the symptoms. An inactivated vaccine is available which is given as part of DPT at 2, 4, and 6 months of age.