diagnostic microbiology lecture: 13 gram positive, non endospore-forming bacilli corynebacterium

Diagnostic microbiologylecture: 13

Gram Positive, Non Endospore-Forming Bacilli

CORYNEBACTERIUM

Abed ElKader Elottol MSc. Microbiology

2010

1 abed elkader elottol

Medically Important SPECIES:1. Corynebacterium diphtheria2. Corynebacterium ulcerans3. Corynebacterium ovis (pseudotuberculosis)


Corynebacterium diphtheria

Clinical manifestation:•Local lesions in the nose and throat.•Primary infection may affect ear, conjuctiva, umbilicus and vagina.•The classic form of the disease is characterized by a local pseudomembraneous.•lesion covering the tonsils, pharynx or in the nose.• The pseudomembrane can extend into trachea and completely obstruct the air passage, causing the patient to die of suffocation.•Diphtheria toxin produced in the local lesion which is absorbed systematically can damage such distant organs and tissues such as heart, liver, kidneys and central nervous system. •Death is usually results from heart failure.


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Sign and SymptomsSign and Symptoms•The respiratory form has an incubation period of 2-5 days.

•The onset of disease is usually gradual.• Symptoms include fatigue, fever, a mild sore throat and

problems swallowing.Children infected have symptoms that include nausea, vomiting,

chills, and a high fever, although some do not show symptoms until the infection has progressed further.

• In 10% of cases, patients experience neck swelling, informally referred to as "bull neck."

•These cases are associated with a higher risk of death.

http://en.wikipedia.org/wiki/Incubation_period

General Characteristics:•Gram-positive bacilli, Pleomorphic (Curved or straight).• Non-motile, non-acid fast and aerobic.•Club-shaped forms = Swelled end• Chinese characters “Cell arrangement L or V shapes are also observed ).•Ability to grow on selective media containing potassium tellurite.Specimen Collection:•Throat and nasopharengeal.• When diagnosis is confirmed, patient contacts must be subjected to the same procedures.• Moisten swabs with Normal saline and collect in the usual manner.



Media Pai MediumComposition per 1620.0mL:Glucose...............................................................5.0gHomogenized whole egg...................................1.0LGlycerol......................................................120.0mLpH 6.75 ± 0.2 at 25°CUse: For the isolation and cultivation of Corynebacterium spp.


Tinsdale AgarComposition per 1100.0mL:peptone............................................................20.0gAgar..................................................................15.0gNaCl....................................................................5.0gYeast extract........................................................5.0gL-Cystine...........................................................0.24gTinsdale Supplement:Composition per 100.0mL: Na2S2O3(Sodium Thiosulphate )................... 0.43gK2TeO3(Potassium Tellurite) ....................... 0.35gSerum..........................................................100.0mLUse: For the primary isolation and identification of Corynebacterium diphtheriae. The formation of black to brown halos surrounding the colony results from the reduction of potassium tellurite to metallic tellurite.


Loeffler MediumComposition per liter:Beef serum........................................................70.0gEgg, dried............................................................7.5gHeart muscle, solids from infusion...................0.72gGlucose.............................................................0.71gPeptic digest of animal tissue...........................0.71gNaCl..................................................................0.36gpH 7.6 ± 0.2 at 25°CUse: For the cultivation of Corynebacterium diphtheriae. For demonstration of pigment production and proteolysis by Corynebacterium diphtheriae


Hoyle Medium BaseComposition per liter:Agar..................................................................15.0gBeef extract.......................................................10.0gPeptone.............................................................10.0gNaCl....................................................................5.0gBlood…………....................................................50.0mLTellurite solution...........................................10.0mLpH 7.8 ± 0.2 at 25°CTellurite Solution:Composition per 100.0mL:K2TeO33.5g................................................................Caution: Potassium tellurite is toxic.Use: For the isolation and differentiation of Corynebacterium diphtheriae

Pai medium and Loeffler medium provides good growth of C.diphtheria and stained smears prepared from both media may show the characteristic Chinese letters blue bacillus.Colony Morphology:Gray to black with irregular edges on Loeffler medium. Based on colony morphology Corynebacteria are divided into 3 groups on Tinsdale Agar and Hoyle Medium1. Gravis: Large, flat, gray to black, non-hemolytic2. Mitis: Smaller, more convex, darker with dull surface3. Intermedius: The smallest of all.Note: Gravis strain hydrolysis starch and glycogen while mitis and intermedius do not.


Diphtheria toxin:1.Structure:• It is a heat-labile polypeptide that can be lethal in a dose of 0.1 ug/kg.• If disulfide bond are broken, the molecule can give two fragments. (A & B). •Fragment B has no independent action but it is required for the transport of fragment A.2. Mechanism of Action: •Fragment A inhibits polypeptide chain elongation by inactivating the elongation factor 2 "EF2".• This factor is required for translocation of polypeptidyl-transfere RNA from the acceptor to the donor site on the eukaryotic ribosome. •Thus preventing protein synthesis leading to cell death.14 abed elkader elottol

Biochemical tests:The colonial morphology of C. diphtheria on Tinsdale medium is the most important characteristics in differentiating it from other species of corynebacteria.=Urease Negative=Nitrate Positive=Gelatin liquefaction: NegativeFermentation reactions of various carbohydrates.


Toxigenicity Tests:1. In-Vivo toxigenicity test:1. From a pure culture of an isolate, inoculate a 10-ml tube of BHIB, incubate at 370C for 48 hours.2. Inject one guinea pig with diphtheria antitoxin to serve as a control.3. After 2 hours, inject 5 ml of the broth into both the control and test animals.4.Observe after 48 hours.Results and interpretation•If the test animal dies and the control survives= It is C. diphtheria• If both the test and control show illness or die= It is another organism.


2. In Vitro toxigenicity test:Principle: This test is based on a precipitin reaction between diphtheria toxin produced by the test culture and diphtheria antitoxin in the medium. The reaction produces insoluble products that precipitate.Procedures:1. Paper strip is saturated with diphtheria antitoxin.2. The medium contained in a petridish is streaked with the test organism or organisms if more than one strain are to be tested.3. Place the paper strip perpendicular to the organism streaks.4. Incubate the plates for 24 hours at 37 oC.5. Examine the line of precipitation that extend out from the line of bacterial growth.6. The presence of line of precipitation is considered positive and it confirms that the test organism as a toxigenic.


Skin test = Schick testTo determine whether The patient is susceptible to diphtheria infection or not by detecting the presence or absence of antibodies.Procedures:1. 0.1 ml of toxin is injected intradermally in one arm.2. 0.1 ml of heated (inactivated) toxin as a control is injected in the other arm.3. Read after 24-48 hours.Positive: (Susceptible)Redness and swelling that increases for several days and then fades, leaving brownish pigmented area. The control site shows no reaction.Negative:(Not susceptible) Neither injection site shows any reaction).


Treatment:1.Antibiotic therapy: Penicillin or erythromycin To eradicate the organism.2. Anti-toxin: To neutralize the effect of diphtheria toxin.Control: By immunization with inactivated or attenuated toxin of toxigenic C.diphtheria.


Erysipelothrix insidiosaE. Rhusiopathiae

25 Abed ElKader ElOttol

Disease: Erysipleoid (red skin) it has three distinct clinical entities:1. Erysipeloid : Localized cutaneous infection usually on the finger and hands.2. Generalized cutaneous infection.3. SepticemiaMicroorganism:- Gram-positive rods.- Non-motile.- Non-spore forming.- Facultative anaerobe.


Specimen and media:• Usually skin biopsy from the advancing borders of the lesion.• Blood specimen if septicemia is suspected.•-Culture media: 1% glucose broth and blood agar.NB: Make gram staining for the organism from the clinical specimen and the growth on blood agar.Biochemical tests used in the identification:•Test tube brush appearance in gelatine stabs.• H2S production.• Acidification of slant and butt in TSIA with no gas production.• To differentiate this organism from Listeria monocytogenes, perform the catalase test. Listeria monocytogenes is catalase Positive.Treatment:- Penicillin is the drug of choice.


Listeria monocytogenes


Disease: Listerosis = it has four forms1. Non-specific flu-like illness during pregnancy or puerperal sepsis.2. Neonatal sepsis and later meningitis.3. Sepsis or meningitis in immunocompromised patients.4. Food poisoning.Microorganism:- Gram-positive rods (Shorter & Thinner).- Non-spore forming- Facultative anaerobe- Beta hemolytic on Blood agar.


Biochemical Characteristics: Motile (Umbrella-type growth in semi-solid media) Motile (Tumbling motility as seen by the hanging drop technique) Catalase positive V.P positiveSpecimen and Culture media:Blood, cerebrospinal fluid (CSF) and genital tract secretion.Media : BHIA + 5% sheep blood and BHIB. Selective Listeria Agar SLA = Brownish to black discoloration is usually seen around the colonies of Listeria monocytogenes.


Identification:1. The demonstration of Gram-positive bacilli from stained smears (CSF and other fluids or food samples).2. Culture and Isolation: On Blood Agar or Selective Listeria Agar.3. Biochemical tests: Catalase test, V.P, and motility test.4. Serological test: Agglutination with specific sera.

Treatment: Combined therapy of penicillin plus aminoglycosides. Tetracycline also may be used as a second line if the patient is sensitive to penicilllin or aminoglycosides.



Pinpoint to small, semi-transparent colonies.

The same Blood Agar plate examined with transmitted light. The colonies are surrounded by a narrow haemolytic zone. This zone is more easily seen if the culture is grown on thin Blood Agar plates.


Listeria monocytogenes grows as brown-green colored colonies with a black halo (esculin splitting).

END of LECTURE


diagnostic microbiology lecture: 13 gram positive, non endospore-forming bacilli corynebacterium

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