Dr Amin AqelRespiratory system

Respiratory Bacterial Infections

In lower respiratory system usually no permanent residents are present

Bordetella pertussis Basics

Aerobic, small, Gram negative encapsulated coccobacillus

Specific to HumansColonizes the respiratory

tract Whooping Cough

(Pertussis)Bordetella parapertussis

is the most closely related to Bordetella pertussis .

It can cause a milder pertussis-like disease in humans

http://www.hhmi.princeton.edu/sw/2002/psidelsk/Microlinks.htm

http://microvet.arizona.edu/Courses/MIC420/lecture_notes/bordetella_pertussis/gram_pertussis.html

TransmissionVery ContagiousTransmission occurs via respiratory dropletsOutbreaks first described in the 16th CenturyMajor cause of childhood fatality prior to

vaccination

http://www.ratbags.com/rsoles/history/2000/12december.htmhttp://www.universityscience.ie/imgs/scientists/whoopingcough.gif

Virulence

Steele, R.W. Pertussis: Is Eradication Achievable. Pediatric Annals. Aug 2004. 33(8):525-534

AdhesionsFilamentous hemagglutininPertactinFimbriae

http://www.rivm.nl/infectieziektenbulletin/bul1306/kinkhoest.jpghttp://www.my-pharm.ac.jp/~yishibas/research/Pertussis1.jpg

ToxinsPertussis Toxin: Colonizing factor and

endotoxinAdenylate Cyclase Toxin: Invasive toxin,

Impairment of immune effector cellsTracheal cytotoxin: inhibits cilia

movementDermonecrotic toxin: vasoconstriction and

ischemic necrosis

www.ibl.fr/u447/u447.htm

Pertussis Pathogenesis

Primarily a toxin-mediated diseaseBacteria attach to cilia of respiratory

epithelial cellsproduce toxins that paralyze the cilia, and

cause inflammation of the respiratory tractInflammation will interferes with clearance of

pulmonary secretionsPertussis antigens allow evasion of host

defenses (lymphocytosis promoted but impaired chemotaxis)

Pertussis Infection and Clinical Features

Incubation period 4-21 days3 Stages

1st Stage- Catarrhal Stage 1-2 weeks

2nd Stage- Paroxysmal Stage 1-6 weeks

3rd Stage- Convalescent Stage weeks-months

http://www.cdc.gov/nip/publications/pertussis/chapter1.pdf

DiagnosisIsolation by culturePCRDirect fluorescent antibodySerological testing

TreatmentAntibiotic therapy

ErythromycinAzithromycin and clarithromycinTrimethoprim-sulfamethoxazole

http://medinfo.ufl.edu/year2/mmid/bms5300/images/d7053.jpg

Pertussis Vaccine1st Pertussis vaccine- whole cellAcellular vaccine now usedCombination vaccines

http://www.nfid.org/publications/clinicalupdates/pediatric/pertussis.html

http://www.tdh.state.tx.us/immunize/providers.htm

Corynebacterium SpeciesGeneral characteristics

Found as free-living saprophytes in fresh and salt water, in soil and in the air

Members of the usual flora of humans and animals(often dismissed as contaminants)

Often called “diphtheroids”Corynebacterium diphtheriae is the most significant

pathogenOther species may cause infections in the

immunocompromised hosts

General CharacteristicsMorphology

Gram-positive, non–spore-forming rods, Non-motile; noncapsulate

Arrange in palisades:“L-V” shape; “Chinese characters”

Pleomorphic: “club-ends” or coryneform

Beaded, irregular stainingMetachromatic granules (often

near the poles) give the rod a beaded appearance.

Strains of this genus contain short mycolic acid in the cell wall.

.

C. diphtheriae: Agent of Diphtheria

Toxigenic Corynebacterium diphtheriaeWorldwide distribution but rare in places where

vaccination programs exist

Exotoxin, Diphtheria toxin, as the virulence factorNot all C. diphtheriae strains produce toxinToxin is produced by certain strainsToxin is antigenic

C. diphtheriae

Pathogenesis and Immunity

C. diphtheriae occurs in the respiratory tract, in wounds, or on the skin of infected persons or normal carriers. It is spread by droplets or skin contact.

Portal of entry: respiratory tract or skin abrasions.

Diphtheria bacilli colonize and grow on mucous membranes, and start to produce toxin, which is then absorbed into the mucous membranes, and even spread by the bloodstream.

Local toxigenic effects: elicit inflammatory response and necrosis of the faucial mucosa cells-- formation of "pseudo-membrane“ (composed of bacteria, lymphocytes, plasma cells, fibrin, and dead cells), causing respiratory obstruction.

Systemic toxigenic effects: necrosis in heart muscle, liver, kidneys and adrenals. Also produces neural damage.

Toxigenic Corynebacterium diphtheriae

Toxin consists of two fragments (heat labile)A: Active fragment

Inhibits protein synthesis Leads to cell/tissue death

B: BindingBinds to specific cell membrane receptorsMediates entry of fragment A into cytoplasm of host

cell

Clinical Forms of Diphtheria

RespiratoryRespiratoryAcquired by droplet spray

or hand to mouth contactNon-immunized

individuals are susceptible

Non-respiratoryNon-respiratorySystemicSkin and cutaneous forms

Bull-neck appearance

Diphtheria

Respiratory disease–diphtheriaIncubation period–2 to 5 days

Symptoms: sore throat, fever, malaise

Toxin is produced locally, usually in the pharynx or tonsils

Toxin causes tissue necrosis, can be absorbed to produce systemic effects

Forms a tough, thick, adherent grey to white pseudo-membrane which may cause suffocation(WBC + RBCs +organism +fibrin +dead cells)

Treatment

Infected patients treated with anti-toxin and antibioticsAnti-toxin produced in horsesAntibiotics have no effect on circulating toxin, but

prevent spread of the toxin by bacteial killingPenicillin drug of choice, erythromycin

Prevention: DPT immunization

Laboratory Diagnosis

Microscopic morphologyGram-positive, non–spore-

forming rods, club-shaped, can be beaded

Appear in palisades and give "Chinese letter" arrangement

Produce metachromatic granules or “Babes’ Ernst” bodies (food reserves) which stain more darkly than remainder of organism

Corynebacterium diphtheriae gram stain

Laboratory Diagnosis: Cultural Characteristics

Loeffler's slant used to demonstrate pleomorphism and metachromatic granules ("Babes’ Ernst bodies“)

Growth on Serum Tellurite or modified Tinsdale exhibits brown or grayish→ to black halos around the colonies

Blood agar plate, grey translucent colonies

Small zone of b- hemolysis also seenTellurite: tellurium dioxide (TeO2).

Laboratory Diagnosis

Toxigenicity testingElek test Immunodiffusion test

Organisms are streaked on media with low Fe content to maximize toxin production.

protease peptone agar + serum (horse or bovine)1 and 4 positive

Streptococcus pyogenes in chains

Bacillus anthracis

TB/ Löwenstein–Jensen medium

Pseudomonas/ Pigments in Nutrient Agar