Pediatric Infections and H. influenzae Quiz

Medical Microbiology

• Medical microbiology is the study of microorganisms that cause illness.
• Microorganisms studied include bacteria, viruses, fungi, and parasites.

Haemophilus

• The genus Haemophilus contains many species, H. influenzae is the most common clinically significant species relating to immuno-competent humans.
• H. ducreyi causes chancroid, a sexually transmitted disease (STD), characterized by a comparatively soft ulcer on the external genitalia.
• H. influenzae aegyptius is a biotype of H. influenzae, often associated with purulent conjunctivitis and Brazilian purpuric fever, a life-threatening childhood infection.
• H. parainfluenzae is a rare cause of pneumonia and endocarditis.
• Haemophilus influenzae is gram negative, non-motile, facultative anaerobe, pleomorphic small coccobacilli.
• Requires hemin (factor X) and nicotinamide adenine dinucleotide (NAD+) (factor V) for growth on chocolate agar. Growth is enhanced by high CO2 concentration (5%).
• It does not grow on normal blood agar.
• H. influenzae requires factors V and X, H. parainfluenzae requires factor V only, and H. ducreyi requires factor X only.

Serotypes of H. influenzae

• Two major categories: encapsulated smooth strains and unencapsulated strains.
• Encapsulated smooth strains, classified by distinct capsular antigens. Six types are recognized (a-f). Type b capsule is composed of polyribitol phosphate (PRP).
• Unencapsulated strains are termed non-typable (NTHI).

Virulence Factors

• H. influenzae, important virulence factors: IgA protease (degrades secretory IgA), and polysaccharide capsule (important for encapsulated strains, particularly type b "Hib").

Pathogenesis of Haemophilus

• Encapsulated strains resist phagocytosis and complement-mediated lysis in the non-immune host.
• Unencapsulated strains are typically less invasive but can cause inflammatory responses in humans, leading to various symptoms.
• Hib infection initially causes runny nose, low-grade fever, and headache. Due to its invasive nature, it rapidly disseminates, crosses the blood-brain barrier, and causes meningitis (stiff neck), convulsions, coma, and potentially death.

Diagnosis of Haemophilus

• Culture: A bacterial culture of H. influenzae is often performed on chocolate agar, supplemented with X and V factors, in an enriched CO2 incubator at 37°C. H. influenzae grows best as a satellite around other bacteria in the hemolytic zone of Staphylococcus aureus on Blood Agar plates. The hemolysis of cells by Staph. aureus releases nutrients vital for H. influenzae growth.
• Catalase and oxidase tests are often positive.
• Serological tests differentiate between H. influenzae b and non-encapsulated species.
• PCR assays for more sensitive diagnosis.

Treatment and Prevention

• Cefotaxime and ceftriaxone are the preferred antibiotics for severe cases, while ampicillin, sulbactam, cephalosporins of the second and third generation, or fluoroquinolones are used for less severe cases.
• Erythromycin can be used for H. ducreyi and H. influenzae aegyptius.
• A vaccine containing the capsular polysaccharide of Hib conjugated to diphtheria toxoid provides effective prevention.

Bordetella pertussis

• Causes pertussis (whooping cough) in infants and young children.
• Gram-negative, capsulated, non-motile, aerobic coccobacillus.
• It is a fastidious organism, does not grow on common laboratory media, oxidase positive, but urease negative.
• Grows aerobically on special culture media at 37°C for 3-5 days.
• Colonies appear grayish-white with a shiny convex surface (“mercury drop”) appearance.
• Grows on Bordet-Gengou agar.

Pertussis Pathogenesis

• B. pertussis colonizes lung epithelial cells without blood invasion.
• The bacterium contains a surface protein: filamentous hemagglutinin (FHA) (agglutinogens).
• These are not exotoxins but contribute to binding to ciliated epithelial cells.
• Tracheal cytotoxin stops cilia beating and causes epithelial destruction when in higher concentrations.
• The pertussis toxin (PTx) contributes to bacterial binding and increased mucus secretion. Adenylate cyclase (CyaA) prevents phagocytes.

Pertussis Signs and Symptoms

• Three stages:
• Catarrhal: resembles a common cold (runny nose, sneezing, mild cough, low-grade fever). Adults might have milder symptoms.
• Paroxysmal: characterized by the inspiratory sound (whoop), prolonged and distressing inspiratory gasp; hypoxia during protracted attacks can lead to seizure or coma.
• Convalescent: the cough gradually diminishes and recovery takes 3–16 weeks.
• Possible secondary complications: pneumonia, otitis media, and meningo-encephalitis.

Pertussis Diagnosis

• Isolation of the organism in the catarrhal and early paroxysmal phases by nasopharyngeal swab for Gram stain.
• Growth on complex enriched media like Bordet-Gengou agar showing characteristic colonies.
• Direct immunofluorescence, PCR, and serologic detection for antibodies.

Pertussis Treatment and Prevention

• Macrolides (erythromycin) are the drugs of choice during catarrhal and early paroxysmal phases.
• Oxygen inhalation and sedation during paroxysms to prevent hypoxia and brain damage.
• A heat-killed vaccine (pertussis component part of DTaP vaccine) provides safety.
• An acellular vaccine made of filamentous hemagglutinins (and detoxified pertussigen) is part of DTap.

Legionella

• Facultative intracellular pathogens, staining poorly as gram-negative, motile rods.
• Fastidious, do not grow well on conventional agar.
• Grows on buffered charcoal yeast extract (BCYE) agar at 35°C for 3-7 days.
• Oxidase positive and catalase positive, does not ferment sugars.

Legionella Pathogenesis

• L. pneumophila lives in stagnant water.
• Often infects hot water towers and air conditioning systems.
• Legionella are phagocytosed into monocytes, but prevent phagosome-lysosome fusion, replicate inside, and escape.
• Causes two distinct diseases: Legionnaires' disease (community-acquired or nosocomial pneumonia)
• Pontiac fever (flu-like illness).

Legionella Diagnosis, Prevention, and Treatment

• Culture: using pleural fluid or lung biopsy on BCYE agar aerobically
• Serology: Detection of IgM or rising titer of IgG by ELISA.
• PCR tests for detection.
• Treatment: Erythromycin alone or in combination with rifampin is the treatment of choice. If erythromycin is not usable then doxycycline.
• Prevention: Elimination of aerosols from water sources and reducing the incidence of legionella in hospital water supplies by using temperature and hyperchlorination.

Francisella tularensis

• Small, gram-negative, non-motile, encapsulated, pleomorphic coccobacillus.
• Facultative intracellular parasite.
• Requires careful handling due to low infectious dose. Causes tularemia (rabbit fever).
• Has a low infectious dose, so causing disease after inhaling or being injected intradermally.
• Primarily in rabbits, hares, and ticks.
• Humans infected from insect bites or from handling infected animal tissues.
• Symptoms include a skin papule at the entry site, ulceration, fever, chills, malaise, fatigue, and lymphadenopathy; bacteremia.

Francisella tularensis Treatment and Prevention

• Primarily using streptomycin.
• Live attenuated organism vaccine is available.

Pasteurella multocida

• Animal pathogen (zoonotic), especially mice and rabbits.
• Causes localized infections (e.g., cat scratches, animal bites), systemic infections (e.g., bacteremia, meningitis), or respiratory infections.
• Self-limiting but treated with aminoglycosides, penicillin, or cephalosporins.

Gardnerella vaginalis

• Gram-negative rods, non-capsulated, and non-motile.
• Causes bacterial vaginosis (non-specific vaginitis), characterized by a grayish-white vaginal discharge with a fishy odor.
• KOH drop test and microscopic analysis of discharge to confirm. Can be cultured on blood agar.
• Treatment: Metronidazole.

Bacteroides

• Gram-negative, capsulated coccobacilli.
• Common cause of serious anaerobic infections like sepsis, peritonitis, and abscesses.
• B. fragilis and B. melanogenicus are common species.
• Predisposition factors include trauma, necrosis or impaired blood supply.
• The presense of facultative anaerobes utilizes oxygen and allows anaerobic growth.
• Treatment and prevention is often associated with metronidazole and surgical interventions to drain pus; sometimes used in combined treatment with aminoglycosides.

Acid-Fast Bacteria (Mycobacteria)

• Mycobacteria are obligate aerobes, non-motile, lack endospores and capsules.
• Resists decolorization with acid-alcohol due to a thick cell wall containing mycolic acids/mycolates.
• Main families: M. tuberculosis, M. leprae, atypical mycobacteria, and saprophytic mycobacteria.

Mycobacterium tuberculosis

• Causes tuberculosis (TB).
• Characteristic staining, typically thin rods arranged singly or in small groups seen on Zeil-Neelsen stain.
• Culture in egg-enriched media (Lowenstein-Jensen (L-J)), shows slow growth, generation time around 12−18 hours, requires weeks before visible growth.
• Resistant to acids, alkali, and dryness.
• Survives in dried sputum, transmitted via aerosol.
• Killed by the pasteurization of milk

Tuberculosis Pathogenesis

• M. tuberculosis infects the lung and is distributed within macrophages; survives intracellularly.
• Inhibits phagosome-lysosome fusion leading to intracellular replication and substance production that interferes with phagosome and lysosome.
• Prevents generation of H2O2.
• Primary infection: exudative lesion in lungs causing Ghon's complex characterized by:
• Acute exudative lesion
• Caseous lymph nodes

Tuberculosis Clinical Findings and Diagnosis

• Fever, fatigue, and night sweats are common symptoms.
• Pulmonary TB causes chronic cough and coughing up blood.
• Military TB: multiple disseminated lesions and a high fatality rate.
• Diagnosis involves:
• Direct methods: sputum examination, urine sample, or acid-fast bacilli detection.

Tuberculosis Treatment

• First-line treatment: Isoniazid (INH), rifampicin, ethambutol, and pyrazinamide.
• Infections with multiple drug resistance: use second-line drugs (e.g., streptomycin, para-aminosalicylic acid, ethionamide, cycloserine).
• BCG vaccine: an attenuated strain of M. bovis that immunizes against tuberculosis and M. bovis.

Mycobacterium leprae

• Causative agent of leprosy.
• Chronic disease affecting the mucous membrane of the nose, skin, and nerve fibers, often with physical disfigurement.
• Low temperature infecting the skin.

Leprosy Pathogenesis

• Ingestion of lepra-containing material induces characteristic lesions on footpads of mice.
• Infection frequently acquired by prolonged contact with lepromatous leprosy patients.
• The incubation period: 2-10 years, insidious onset, intracellular replication within skin histiocytes, endothelial cells, and nerve cells

Leprosy Clinical Forms and Diagnosis

• Lepromatous: progressive, malignant; many skin lesions and nerve involvement showing abundant acid-fast bacilli and negative lepromin test.
• Tuberculoid: benign, non-progressive; fewer skin lesions and nerve involvement, less severe with few organisms, positive lepromin test.
• Diagnosis:
• Clinical picture (e.g., suspected lesions and distribution)
• Acid fast staining with the Z-N stain.
• Skin or nasal-smear examination to evaluate bacteria density (bacterial index).
• Tuberculin (Lepromin) test

Leprosy Treatment and Prevention

• Treatment: Dapsone and rifampicin.
• No specific vaccine; chemoprophylaxis (dapson) for exposed children.
• Isolation for lepromatous patients.

Test your knowledge on the causes, symptoms, and treatments of infections caused by Haemophilus influenzae and Bordetella pertussis, particularly in young children. This quiz covers essential facts about antibiotic choices, diagnostic methods, and associated pathogens.