Upper Respiratory Infections and Diphtheria

Upper Respiratory Tract Infections

• Upper respiratory tract infections include pharyngitis, croup, and epiglottitis. A key pathogen in these infections is Haemophilus influenzae.

Corynebacterium Diphtheriae

• Corynebacterium diphtheriae is a gram-positive bacillus with an irregular shape, sometimes appearing clubbed at one or both ends.
• It's highly pleomorphic, showing varied shapes resembling Chinese letters or cuneiform patterns.
• Useful media include Loeffler's serum slope tellurite blood agar.
• Sugar fermentations are typically done in Hiss's serum peptone water.
• C. diphtheriae is H2S positive and reduces nitrate to nitrite.
• Toxigenic strains produce a potent exotoxin.
• Toxogenicity depends on the presence of corynephages (tox+).
• Diphtheria toxin is a heat-labile protein with two fragments. It inhibits protein synthesis.
• Clinical forms include respiratory and cutaneous.
• Microscopy, culture, and virulence tests are used for diagnosis, with in vivo and in vitro methods for virulence testing.
• Diphtheria presents as a sore throat, localized pain, fever, pharyngitis, and oozing fluid.
• The fluid thickens to form a thick pseudomembrane.
• The pseudomembrane adheres tightly to the tonsils, uvula, roof of mouth, pharynx, and larynx, potentially causing bleeding and airway obstruction. Severe cases can lead to suffocation.
• In vivo tests include subcutaneous and intracutaneous tests.
• In vitro tests include precipitation tests, tissue culture, ELISA, and PCR.
• Prophylaxis involves DPT vaccinations; doses at 6, 10, 14 weeks with boosters at 5-6 years.

Diphtheroids

• Some Corynebacterium species resemble C. diphtheriae and are called diphtheroids. These are normal commensals in the throat and skin.
• Common diphtheroids include C. Pseudodiphtheriticum and C. xerosis.

Bordetella Pertussis

• Bordetella pertussis is a minute, gram-negative, non-acid-fast, non-spore-forming coccobacillus.
• Important species include B. pertussis, B. parapertussis, and B. bronchiseptica.
• Bordetella pertussis is extremely small, ovoid, gram-negative coccobacilli, exhibiting pleomorphism, and is nonmotile and nonsporing.
• Key factors include filamentous hemagglutinin and pertussis toxin. This bacterium also produces several toxins (Pertussis toxin, Adenylate cyclase toxin, Dermonecrotic toxin, and Tracheal cytotoxin).
• The pertussis toxin interferes with ciliated epithelial cells, increasing mucus production.
• Adenylate cyclase toxin promotes mucus production and inhibits leukocyte function.
• Dermonecrotic toxin causes localized constriction and hemorrhage.
• Tracheal cytotoxin inhibits cilia movement.
• Patients have three stages: catarrhal, paroxysmal, and convalescent. Younger children are most at risk.
• Diagnosis includes microscopy, culture, and PCR.
• Treatment involves macrolides like erythromycin or azithromycin. Erythromycin is used for prophylaxis.
• Vaccination with whole-cell vaccines or acellular vaccines is effective. Whole cell vaccines have more side effects compared to acellular vaccines.
• Incubation period is 6-20 days, with an average of 7-10 days.

Haemophilus influenzae

• Haemophilus influenzae is a small gram-negative coccobacillus requiring factors X (hemin) and V (NAD) for growth.
• Type b causes the majority of invasive disease (around 95%). The capsule is polyribitol phosphate.
• The bacterium lives in the upper respiratory tract and is spread by respiratory droplets.
• The capsule is the most critical virulence determinant. Non-capsulated strains cause mucosal infections but not invasive infections, and IgA protease is produced.
• Common diseases include sinusitis, otitis media, and pneumonia; however, epiglottitis is an uncommon but important complication. The vaccine has largely reduced the incidence of meningitis associated with this bacterium.

Epiglottitis

• Epiglottitis is inflammation of the epiglottis.
• Symptoms include rapidly worsening sore throat, pain on swallowing, and difficulty swallowing.
• Haemophilus influenzae type B is the most frequent cause. Vaccines have dramatically reduced its occurrence.
• Severe cases present with airway obstruction and are an urgent medical emergency.
• Other pathogens include H. influenzae types other than B, S. pneumoniae, S. pyogenes, and S. aureus.

Vaccination and Treatment

• Vaccination schedules vary across organisms and diseases.
• Treatment options depend on the specific pathogen.

This quiz covers upper respiratory tract infections such as pharyngitis and croup, alongside a focus on Corynebacterium diphtheriae, its characteristics, and the diagnostic methods involved. Explore the microbes, their pathogenicity, and the clinical implications of infections. Test your knowledge on this important area of microbiology.