Corynebacterium and other Gram-positive rods

미생물학교실

권 형 주

Corynebacterium : coryne, a club; bakterion, a small rod (a small, club-shaped rod) C. Diphtheriae : diphthera, leather or skin (reference to the leathery membrane

that forms initially on the pharynx) – 가죽피부 , pseudomembrane 형성

Coryneform group : Corynebacterium and related genera : non-spore-forming, : non-acid-fast, Short-chain mycolic acids : gram-positive rods with a high guanine plus cytosine content. : metachromatic granules : catalase-positive : Ferment carbohydrates

Genus CatalaseFermentation/Oxidation Motility Cell Wall Gram Stain

       Mycolic Acids

Diamino Acid  

Corynebacterium + Ferm/Oxid - + meso-DAP Club-shaped rods

Arcanobacterium - Ferm - - Lysine Irregularly shaped rods

Brevibacterium - Oxid - - meso-DAP Short coccobacilli

Oerskovia - Ferm Variable - Lysine Long branching rods

Turicella - Oxid - - meso-DAP Long rods

Table. Characteristic properties of selected Coryneform generaGram stain of C. diphtheriae

Organism Diseases

C. diphtheriae Diphtheria (respiratory, cutaneous); pharyngitis and endocarditis (nontoxigenic strains)

C. jeikeium (group JK) Septicemia, endocarditis, wound infections, foreign body (catheter, shunt, prosthesis) infections

C. urealyticum (group D2)

Urinary tract infections (including pyelonephritis and alkaline-encrusted cystitis), septicemia, endocarditis, wound infections

C. amycolatum Wound infections, foreign body infections, septicemia, urinary tract infections, respiratory tract infections

C. macginleyi Eye infections

C. minutissimum Wound infections, respiratory tract infections

C. pseudodiphtheriticum Respiratory tract infections, endocarditis

C. pseudotuberculosis Lymphadenitis, ulcerative lymphangitis, abscess formation

C. riegelii Genitourinary tract infections (females)

C. striatum Wound infections, respiratory tract infections, foreign body infections

C. ulcerans Respiratory diphtheria

Corynebacterium species associated with human disease

Corynebacterium diphtheriae

PHYSIOLOGY AND STRUCTURE - Pleomorphic rod (0.3 to 0.8 × 1.0 to 8.0 μm) : irregular shape- Metachromatic granules( 이염소체 ) : rods stained with methylne blue - 1- to 3-mm colonies are observed on blood agar medium- Subdivision : belfanti, gravis, intermedius, mitis

PATHOGENESIS AND IMMUNITY - Classic model of bacterial virulence. - Toxicity in diphtheria : exotoxin secreted by the bacteria at the focus of infection : tox gene – lysogenic bacteriophage (-phage)- The organism does not need to enter the blood to produce the systemic signs of disease

Diphtheria toxin : Two processing steps (1) proteolytic cleavage of the leader sequence from the tox protein during secretion from the bacterial cell; and (2) cleavage of the toxin molecule into two polypeptides (A and B) that remain attached by a disulfide bond. This 58,300-Da protein is an example of the classic A-B exotoxin.

- B subunit : receptor-binding region, translocation region - receptor : heparin-binding epidermal growth factor- A subunit : catalytic region-Toxin entry : the toxin becomes attached to the host cells, facilitating the movement of the catalytic region into the cytosol. - cytotoxicity : The A subunit terminates host cell protein synthesis by inactivating elongation factor 2 (EF-2) – ADP-ribosylation - Toxin synthesis regulation : chromosomally encoded element, diphtheria toxin repressor (DTxR) - activated in the presence of high-iron concentrations- tox gene : transduction, lysogenic bacteriophage (-phage)

EPIDEMIOLOGY Diphtheria : found worldwide- Respiratory droplets or skin contact transmit- Humans are the only known reservoir for this organism -C. diphtheriae maintenance : asymptomatic carriage in the oropharynx or on the skin of immune people (after either exposure to C. diphtheriae or immunization)- uncommon in the United States as the result of an active immunization program

CLINICAL DISEASES The clinical presentation of diphtheria

(1) the site of infection, (2) the immune status of the

patient, (3) the virulence of the organism.

BOX 26-3. Corynebacterium diphtheriae: Clinical Diseases

Respiratory diphtheria: Multiply on epithelial cells (pharynx). Sudden onset with exudative pharyngitis, sore throat, low-grade fever, and malaise; a thick pseudomembrane develops over the pharynx; in critically ill patients, breathing obstruction, cardiac arrhythmia, coma, and death can develop

Cutaneous diphtheria: A papule can develop on the skin that progresses to a nonhealing ulcer (chronic); systemic signs can develop

Thick pseudomembrane : bacteria, lymphocytes, plasma cells, fibrin, dead cells tonsils, uvula, palate, nasopharynx, larynx system complication : myocarditis-> heart failure, cardiac arrhythmias, death - Neurotoxicity neuropathy

This child has diphtheria resulting in a thick gray coating over back of throat. This coating can eventually expand down through airway and, if not treated, the child could die from suffocation CDC

LABORATORY DIAGNOSIS

The initial treatment of a patient with diphtheria is instituted on the basis of the clinical diagnosis, not laboratory results, because definitive results are not available for at least a week

Microscopy - Metachromatic granules : stained with methylene blue - appearance is not specific to C. diphtheriae, and interpretation of the smear requires technical expertise

Culture Specimens for the recovery : nasopharynx and the throat - enriched blood agar plate and a medium developed specifically (e.g., cysteine-tellurite agar, serum tellurite agar). Tellurite, Löffler's medium

Toxigenicity Testing o Test for the production of exotoxin : in vitro immunodiffusion assay (Elek test), : a tissue culture neutralization assay using specific antitoxin, : in vivo neutralization assay using guinea pigs injected subcutaneously with the isolate from the patient.o PCR-based nucleic acid amplication method

TREATMENT, PREVENTION, AND CONTROL

- Diphtheria antitoxin : neutralize the exotoxin before it is bound by the host cell. - Antibiotic therapy : penicillin or erythromycin   is also used to eliminate C. diphtheriae and terminate toxin production- After the patient has recovered, immunization with toxoid is required : most patients fail to develop protective antibodies after a natural infection.

Prevention : children - five injections of diphtheria with pertussis and tetanus antigens (DPT vaccine) at ages 2, 4, 6, 15 to 18 months, and at 4 to 6 years.

- Penicillin, erythromycin

Other Corynebacterium Species

Box 26-4. Summary: Other Corynebacterium Species

• Biology, Virulence, and Disease - Gram-positive pleomorphic rods - Some clinically important species require lipids such as Tween 80 for good growth (e.g., C. jeikeium, C. urealyticum). - Diphtheria A-B exotoxin may be carried by C. ulcerans and C. pseudotuberculosis. - Urinary tract pathogens produce urease (e.g., C. urealyticum). - Many species able to adhere to foreign bodies (e.g., catheters, shunts, prosthetic devices) - Some species resistant to most antibiotics (e.g., C. amycolatum, C. jeikeium, C. urealyticum) - Diseases include septicemia, endocarditis, foreign body infections, wound infections, urinary tract infections, respiratory infections, including diphtheria. • Epidemiology - Most infections are endogenous (produced by species that are part of the host's normal bacterial population on the skin surface and mucosal membranes). • Diagnosis - Culture on nonselective media is reliable, although growth may be slow, and media may require supplementation with lipids. •Treatment, Prevention, and Control - Treatment with effective antibiotics to eliminate the organism - Removal of foreign body

Other Corynebacterium Genera

Table 26-2. Less Common Coryneform Gram-Positive Rods Associated with Human Disease

Organism Diseases

Arcanobacterium Pharyngitis, cellulitis, wound infections, abscess formation, septicemia, endocarditis

Brevibacterium Septicemia, osteomyelitis, foreign body (catheter, shunt, prosthesis) infections

Rothia Endocarditis, foreign body infections

Tropheryma Whipple disease