Corynebacterium Species

Corynebacterium Species  Gram-positive  Non–spore-forming rods  Arrange in palisades: “Y-V” shape; “Chinese characters”  Pleomorphic: “club-ends”  Metachromatic granules with special stains  Aerobic  or facultatively anaerobic Nonmotile, Catalase-positive short-chain mycolic acids (22 to 36 carbon) (not acid fast) 3 Corynebacterium Species Normally colonize  Skin  Upper respiratory tract  Gastrointestinal tract  Urogenital tract  Opportunistic pathogens  Corynebacterium diphtheriae Corynebacterium diphtheriae Physiology and Structure   Often stain irregularly [Especially with methylene blue] Loeffler medium   Metachromatic granules (Babes-Ernst granules) Cystine-tellurite blood agar (CTBA)  Produce a brown halo Corynebacterium diphtheriae  Four biotypes:   belfanti, gravis, intermedius, and mitis Most disease : gravis and mitis 6 Pathogenesis and Immunity Does not need to enter blood stream  Exotoxin as virulence factor  Lysogenized by bacteriophage (beta-phage) with toxin gene (tox)  Toxin is antigenic Pathogenesis and Immunity  Three functional regions exist on toxin molecule  a receptor-binding region on B subunit  a translocation region on B subunit  a catalytic region on A subunit  Toxin receptor: heparin binding epidermal growth factor  Present on surface of many eukaryotic cells, particularly Heart and nerve cells 8 Pathogenesis and Immunity Toxin is regulated by Diphtheria toxin repressor (DTxR) [Chromosomally]  In high iron concentrations DTxR activated prevent toxin production  Toxin; inactivating elongation factor 2 (EF -2) Because turnover of EF-2 is very slow, and approximately only one molecule per ribosome is present in a cell: cell death  Diphtheria Toxin: Mode of Action • Heparin-binding epidermal growth factor • Acidification of endocytic vesicle allows exposing translocation domain (T domain) of toxin • T domain inserts into endosome membrane translocating A subunit into cytoplasm where it regains its enzymatic configuration • Enzymatic A subunit inactivates elongation factor 2 (EF-2) and terminates host cell protein synthesis • One EF-2 molecule per ribosome in a cell, so one exotoxin molecule can completely turn off protein synthesis Epidemiology  Worldwide distribution  Humans are only known reservoir  Carriage in oropharynx or on skin surface  Rare in places where vaccination programs exist  Spread person to person by respiratory droplets or skin contact  Disease observed in unvaccinated people living in crowded urban Clinical Diseases 1- Respiratory Diphtheria  Acquired by droplet spray, 2- to 6-day incubation period  Multiply locally on epithelial cells in pharynx  Toxin is produced locally, usually in pharynx or tonsils  Initially cause localized damage Onset    is sudden; Malaise, sore throat, exudative pharyngitis Pseudomembrane: Bacteria, lymphocytes, plasma cells, fibrin, and dead cells Difficult to dislodge without making tissue bleed (unique to diphtheria) Recovers after approximately 1-week Respiratory Diphtheria Myocarditis: mostly occur Neurotoxicity: depend on severity Respiratory Diphtheria Clinical Diseases 2- Cutaneous Diphtheria  Tropical disease Organism  A papule Systemic    colonizes skin and Entry into subcutaneous tissue Chronic non healing ulcer signs by exotoxin Affects kidneys, heart, and nervous system Death occurs due to cardiac failure Staphylococcus aureus or Streptococcus pyogenes is also frequently present in wound 15 Laboratory Diagnosis 1- Microscopy  Dacron swabs from nose, throat semisolid transport media such as Amies Initial treatment is instituted on basis of clinical diagnosis Results of microscopic examination of clinical material are unreliable 16 Laboratory Diagnosis 2- Culture  Nasopharynx and throat  Inoculated onto nonselective media + selective media  On tellurite containing media  Cysteine-tellurite blood agar (CTBA) Tinsdale medium Loeffler's serum medium 17 Laboratory Diagnosis  Loeffler's serum medium  Corynebacteria grow much more readily than other respiratory organisms  Morphology of organisms is typical in smears 18 Laboratory Diagnosis Colony of Corynebacterium diphtheriae on Tinsdale's agar. Note black colonies with brown halo. Detection of toxin  C. diphtheriae isolate should testing for toxigenicity  (1) Elek: A filter paper disk containing antitoxin is placed on an agar plate.  (2) Detection of diphtheria toxin gene (tox) by PCR used directly on patient specimens  (3) ELISA from clinical C diphtheriae isolates to detect toxin Laboratory Diagnosis Toxigenicity Testing Elek test; Immunodiffusion test sterile filter paper with C. diphtheriae antitoxin Ab-Ag precipitation line bacteria PCR of toxin gene on clinicl isolated or swabs from diphtheritic membrane or biopsy material is diagnostic test of choice Treatment, Prevention, and Control  Early administration of diphtheria antitoxin  Penicillin or erythromycin : eliminate C. diphtheriae  Bed rest  Isolation to prevent secondary spread Diphtheria toxoid : DPT vaccine Antimicrobial prophylaxis with penicillin or erythromycin Schick test Immunity to diphtheria determined by measuring neutralizing antibodies in a person Intradermal injection of diphtheria toxin If neutralizing antibodies are present; No skin reaction is observed If neutralizing antibodies are absent; localized edema with necrosis occurs Other Corynebacterium Species  Opportunistic infections, such as pneumonia, endocarditis, and soft tissue and bone infections, in immunocompromised patients. C. jeikeium: sepsis, endocarditis, wound infections, foreign body infections. C. urealyticum causes UT infections. It is a strong urease producer, infection of UT may lead to formation of stones. C. ulcerans is closely related to C. diphtheriae. May cause diphtheria-like disease.  Resistant to many antibiotics.