Corynebacteria Balsam Miri

Morphology Corynebacteria are small, Gram-positive, generally nonmotile, non-sporulating bacteria; they possess irregular swelling at one end that give them the "club-shaped" appearance. Due to their snapping type of division, cells often lie in clusters resembling chinese letters. Corynebacteria are aerobic, or facultatively anaerobic, and they exhibit a fermentative metabolism (carbohydrates to lactic acid) under certain conditions. They are fastidious organisms, growing slowly on even an enriched medium.

Ecology Many species of Corynebacteria can be isolated from various places such as soil, water, blood, and human skin. Pathogenic strains of Corynebacteria can infect plants, animals, or humans. Though humans are now the only known reservoir for the disease. The bacterium is generally found in temperate zones but may also be found in other parts of the world. Nondiptherial Corynebacteria are ubiquitous in nature, and are commonly found in human mucous membranes and skin.

Species C. amycolatum C. aquaticum C. bovis C. diphtheriae C. equi (now Rhodococcus equi) C. flavescens C. glutamicum C. haemolyticum C. jeikeium (group JK) C. minutissimum C. parvum (Propionibacterium acnes) C. pseudodiphtheriticum (C. hofmannii) C. pesudotuberculosis (C. ovis) C. pyogenes C. urealyticum (group D2) C. renale C. striatum C. tenuis C. ulcerans C. xerosis

Culture Corynebacteria grow slowly, even on enriched media. In terms of nutritional requirements, all need biotin in order to grow. Some strains also need thiamine . The bacteria grow in Loeffler's media, blood agar, and trypticase soy agar (TSA). It forms small grayish colonies with a granular appearance, mostly translucent but with opaque centers, convex, with continuous borders and may have small zone of hemolysis on blood agar. The color tends to be yellowish white in Loeffler's media. In TSA, it can form grey colonies with black centers .On agar containing potassium tellurite the colonies are brown to black.

Role in disease 1-The most notable human infection is diphtheria, caused by Corynebacterium diphtheriae. It is an acute and contagious infection characterized by pseudomembranes of dead epithelial cells, white blood cells, red blood cells, and fibrin that form around the tonsils and back of the throat. It is an uncommon illness that tends to occur in un-vaccinated individuals especially school-aged children, those in developing countries, elderly, neutropenic or immunocompromised patients. It can occasionally infect wounds, the vulva, the conjunctiva, and the middle ear. It can be spread within a hospital. The virulent and toxigenic strains are lysogenic and produce an exotoxin .

Pathology The pathogenesis capabilities of diphtheria are dependent on its ability to colonize the nasopharyngeal cavity or skin and its ability to produce the diphtheria toxin. C. diphtheriae usually colonize a local lesion in the upper respiratory tract, where the toxin secreted by the bacteria cases necrotic injury to epithelial cells. As a result, blood plasma leaks into the area and forms a fibrin network called a pseudomembrane, which is full of rapidly growing C. diphtheriae cells.

Pathology At the site of the lesion the diphtheria toxin is absorbed and disseminated throughout the body via lymph channels. Most commonly affected areas include heart, muscle, peripheral nerves, adrenal glands, kidneys, liver, and spleen.

Pathology The diphtheria toxin works by causing the death of eukaryotic cells and tissues by inhibiting protein synthesis in the cells. Two key factors aid C. diphtheriae in the production of this systemic toxin: low extracellular concentrations of iron and the presence of a lysogenic prophage .

pathology There are three different strains of C. diphtheriae which are differentiated by the severity of the disease they cause in humans. The three strains are gravis, intermedius, and mitis (you can distinguish the severity of each strain based on its name). The difference in virulence of the three strains can be attributed to their relative abilities to manufacture the diphtheria toxin (in both rate and quantity), and their respective growth rates. The mitis strain has a generation time of about 180 minutes while the gravis strain has a generation time of about 60 minutes. This faster growth rate may allow colonies to deplete iron supplies in colonized areas faster, letting them produce toxin in greater quantities sooner.

2-Corynebacterium bovis Is a pathogenic veterinary bacterium that causes mastitis and pyelonephritis in cattle. In mastitis infections C. bovis is spread from cow to cow most commonly through improper milking technique. However it is usually a mild infection resulting in elevated somatic cell count (SCC). The bacterium is sensitive to the majority of antibiotics, such as the penicillins, ampicillin, cephalosporins, quinolones, chloramphenicol, tetracyclines, cefuroxime and trimethoprim

3-Rhodococcus equi Is a Gram-positive coccobacillus bacterium. The organism is commonly found in dry and dusty soil and can be important for diseases of domesticated animals (horses and goats). R. equi is an important pathogen causing pneumonia in foals. Since 2008, it is known that R. equi can infect wild boar as well as domestic pigs. In addition, R. equi can infect humans. At risk groups are immunocompromised people, such as HIV-AIDS-patients or transplant recipients. Rhodococcus infection in these groups of patients resembles clinical and pathological signs of pulmonary tuberculosis.

Virulence The most common route of infection in horses is via inhalation of contaminated dust particles. Inhaled virulent strains of R. equi are phagocytosed by alveolar macrophages. During normal phagocytosis, bacteria are enclosed by the phagosome, which fuses with the lysosome to become a phagolysosome. The internal environment of the phagolysosome contains nucleases and proteases, which are activated by the low pH. The macrophage produces bacteriocidal compounds (e.g., oxygen radicals) following the respiratory burst. However, like its close relative Mycobacterium tuberculosis, R. equi prevents the fusion of the phagosome with the lysosome and acidification of the phagosome.

Additionally, the respiratory burst is inhibited. This allows R Additionally, the respiratory burst is inhibited. This allows R. equi to multiply within the phagosome where it is shielded from the immune system by the very cell that was supposed to kill it. After about 48 hours, the macrophage is killed by necrosis, not apoptosis. Necrosis is pro-inflammatory attracting additional phagocytic cells to the site of infection, eventually resulting in massive tissue damage.

4-Corynebacterium renale Is opportunistic pathogens of the urinary tract of cattle and other domestic animals. These organisms cause cystitis and ascending pyelonephritis in cattle .Disease occurs most frequently in mature cows, and one quarter to one third of cases are fatal. Transmission may be venereal, but C. renale survive well in soil, possibly facilitating indirect transmission. The urease –positive nature of the organism leads to production of ammonia, with resulting mucosal inflammation .The clinical presentation of acute pyelonephritis include fever, anorexia, polyuria, hematuria and abnormal posture (arched back).

5-Corynebacterium pseudotuberculosis (C. ovis) Which is responsible for a number of diseases of animals, including caseous lymphadenitis of sheep and goats, and ulcerative lymphangitis of horses, and formation of abscesses in many other animal species. Grows well on blood-agar medium, producing circular, opaque surface colonies which are frequently surrounded by a narrow zone of haemolysis

The main source of infection and potential spread of the organism is via the rupture of affected lymph nodes and abscesses with the discharge of thick caseous pus containing millions of organisms into the environment.

DIAGNOSIS From clinical signs. Swabs from the suspected lesions must be collected and should then be placed in semi-solid transport media. Smears stained with methylene blue or Gram stain. Specimens should be inoculated to a blood agar plate, Loffler slant and a tellurite plate and incubated at 37 c .Tellurite media is the agar of choice for isolation of Corynebacteria, which produce jet black colonies. PCR  

Treatment Antimicrobial drugs (penicillin ,erythromycin) inhibit the growth of corynebacteria ,they arrest toxin production. The treatment of diphtheria depend on rapid suppression of toxin –producing bacteria by antimicrobial drugs and early administration of specific antitoxin .Diphtheria antitoxin is produced in various animals (horses, sheep, goats and rabbits)by the repeated injection of toxoid.