Gram -ve Respiratory Tract Rods

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             Diseases H influentae used to be the leading cause of meningitis in young children, but the use of the highly effective "conjugate" vaccine has greatly reduced the incidence of meningitis caused by this organism.

It is still an important cause of upper respiratory tract infections (olitis media, si-- nusitis, and epiglottitis) and sepsis in children.

It also causes pneumonia in adults, particularly in those with chronic obstructive lung disease.

Important Properties H influenzae is a small gram-negative rod (coccobacillus) with a polysaccharide capsule.

It enters the body through the upper respiratory tract, resulting in either asymptomatic colonization or infections such as otitis media, sinusitis, or pneumonia.

Pathogenesis involves the antiphagocytic capsule and endotoxin; no exotoxin is produced.

This age distribution is attributed to a decline in maternal IgG in the child coupled with the inability of the child to generate sufficient antibody against the polysaccharide capsular antigen until the age of approximately 2 years.

Laboratory Diagnosis Laboratory diagnosis depends on isolation of the organism on heatedblood ("chocolate") agar enriched with two growth factors required for bacterial respiration, namely, factor X (a heme compound) and factor V (NAD).

Treatment The treatment of choice for meningitis or other serious systemic infections caused by H influenzae is ceftriaxone.

Prevention The vaccine contains the capsular polysaccharide of H influenzae type b conjugated to diphtheria toxoid or other carrier protein.

Important Properties Legionellae are gram-negative rods that stain faintly with the standard Gram stain.

Patients with AIDS, cancer, or transplants (especially renal transplants) or patients being treated with corticosteroids are predisposed to Legionella pneumonia, which indicates that cell-mediated immunity is the most important defense mechanism.

Although cough is a prominent symptom, sputum is frequently scanty and nonpurulent.

If tissue is available, it is possible to demonstrate Legionella antigens in infected lung tissue by using fluorescent-antibody staining.

Prevention Prevention involves reducing cigarette and alcohol consumption, eliminating aerosols from water sources, and reducing the incidence of Legionella in hospital water supplies by using high temperatures and hyperchlorination.

Pertussis toxin stimulates adenylate cyclase by catalyzing the addition of ADP-ribose to the inhibitory subunit of the G protein complex (Gi protein).