Respiratory Bacterial Infections. Dr Amin Aqel Respiratory system. In lower respiratory system usually no permanent residents are present. Bordetella pertussis Basics. Aerobic, small, Gram negative encapsulated coccobacillus Specific to Humans Colonizes the respiratory tract
Steele, R.W. Pertussis: Is Eradication Achievable. Pediatric Annals. Aug 2004. 33(8):525-534
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.
Incubation 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)
Gram-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
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 seen
Tellurite: tellurium dioxide (TeO2).
Organisms are streaked on media with low Fe content to maximize toxin production.
protease peptone agar + serum (horse or bovine)
1 and 4 positive