Haemophilus influenzae
Haemophilus influenzae :
Haemophilus influenzae is a type of bacteria that can cause various infections, particularly respiratory tract infections. It is best known for causing pneumonia, meningitis, and otitis media (middle ear infections), especially in children.
There are two main types:
Type b (Hib): This type is associated with serious diseases, including meningitis and epiglottitis. Vaccination has significantly reduced the incidence of Hib infections in many parts of the world.
Non-typeable strains: These are not covered by the Hib vaccine and can cause milder infections, including sinusitis and bronchitis.
Infections are typically treated with antibiotics, though some strains have developed resistance. Vaccination is key in preventing serious infections caused by Hib.
Haemophilus influenzae:
General Characteristics:
Classification: Gram-negative bacterium
Shape: Coccobacillus
Oxygen Requirement: Facultatively anaerobic
Size: 0.5 to 1.0 micrometers in diameter
Types:
Type b (Hib): Most pathogenic; associated with severe diseases.
Non-typeable strains: Generally cause milder infections and are not included in the Hib vaccine.
Pathogenesis:
Transmission: Primarily spread through respiratory droplets. Carriers often harbor the bacteria in their nasopharynx without showing symptoms.
Virulence Factors:
Capsule: The polysaccharide capsule of Hib helps evade the immune system
Adhesins: Allow adherence to respiratory epithelial cells.
Endotoxins: Contribute to inflammation and tissue damage.
Meningitis: Most serious, particularly in children under five. Symptoms include fever, headache, stiff neck, and altered mental status.
Pneumonia: Common in individuals with underlying lung disease or compromised immune systems.
Otitis Media: Frequent cause of middle ear infections in children.
Sinusitis and Bronchitis: Can lead to exacerbations in patients with chronic obstructive pulmonary disease (COPD).
Epidemiology:
Incidence: Prevalence of Hib infections has dramatically decreased in vaccinated populations.
At-Risk Populations: Unvaccinated children, elderly individuals, and those with weakened immune systems.
Diagnosis
Culture: Isolation from sterile sites (e.g., blood, cerebrospinal fluid).
Gram Stain: Shows Gram-negative coccobacilli.
PCR: Molecular techniques for rapid identification.
Treatment:
Antibiotics: Commonly used include:
Beta-lactams (e.g., ampicillin)
Ceftriaxone (for severe infections)
Macrolides (for penicillin-resistant strains)
Resistance: Some strains exhibit resistance to multiple antibiotics, making susceptibility testing crucial.
Prevention
Vaccination: The Hib vaccine is effective in preventing severe infections and is part of routine childhood immunization schedules.
Hygiene Practices: Handwashing and respiratory hygiene can reduce transmission.
Conclusion :
Haemophilus influenzae remains an important pathogen, particularly in specific populations. Vaccination has drastically reduced the burden of disease caused by Hib, but awareness of non-typeable strains and antibiotic resistance is essential for effective management and treatment.
pertussis and B parapertussis cause whooping cough (pertussis) in humans. Other members of the genus are B bronchiseptica, which causes respiratory disease in various animals and is only occasionally found in humans. Recent additions to the genus are B avium and B hinzii, which both cause respiratory disease in poultry and are very rarely found in humans.
Clinical Manifestations:
After an incubation period of 1 to 2 weeks, whooping cough begins with the catarrhal phase. This phase lasts 1 to 2 weeks and is usually characterized by low-grade fever, rhinorrhea, and progressive cough; the patient is highly infectious. The subsequent paroxysmal phase, lasting 2 to 4 weeks, is characterized by severe and spasmodic cough episodes. At the end of the catarrhal phase, a leukocytosis with an absolute and relative lymphocytosis frequently begins, reaching its peak at the height of the paroxysmal stage. At this time, the total blood leukocyte levels may resemble those of leukemia (≥ 100,000/mm3), with 60 to 80 percent being lymphocytes. The convalescent phase, lasting 1 to 3 weeks, is characterized by a continuous decline of the cough before the patient returns to normal. Serious complications, sometimes fatal, are bronchopneumonia and acute encephalopathy, the latter being characterized primarily by convulsions and frequently resulting in death or lifelong brain damage.
Classification and Antigenic Types
The genus Bordetella contains species of serologically related bacteria with similar morphology, size, and staining reactions. B pertussis and B parapertussis are genomically extremely closely related. Other members of the genus are B bronchiseptica, which by DNA-DNA and DNA-rRNA hybridization is also closely related. Recent additions to the genus are B avium (formerly designated Alcaligenes faecalis) and B hinzii (formerly designated A faecalis type II), which cause respiratory disease in poultry and are very rarely found in humans.
Bordetella pertussis was first isolated in pure culture in 1906 and was long considered the sole agent of whooping cough. Later studies revealed that this disease also can be caused in a mild form by B parapertussis and occasionally by B bronchiseptica. A phenomenon of B pertussis organisms is their variation during growth on agar plates: the antigenically competent, smooth, virulent form (phase I) can mutate to the antigenically incomplete, nonvirulent, rough form (phase IV). This change is associated with a loss of capacity to synthesize pertussis toxin, filamentous hemagglutinin, heat-labile toxin, adenylate cyclase toxin, agglutinogens, and certain outer membrane proteins. There are also two intermediate forms, called phases II and III.
In addition to this spontaneous phase variation, B pertussis undergoes antigenic modulation in response to changes in environmental conditions, such as growth at low temperatures or on agar plates with high concentrations of MgSO4 or nicotinic acid. Bordetella pertussis organisms grown under such conditions are avirulent and are characterized by the loss of the capacity to synthesize the numerous toxic factors and other structural components. Both phase variation and antigenic modulation are reversible and also occur in B parapertussis and B bronchiseptica. Both phenomena are under the control of a single genetic locus. The virulent strains are therefore designated Bvg+, and the avirulent strains Bvg–. Phase variation has been observed in vivo. Another type of serotype variation in B pertussis—the loss of one or more agglutinogens—occurs independently of phase variation.
Pathogenesis :
The agent of whooping cough is transmitted primarily via droplets. Infection results in colonization and rapid multiplication of the bacteria on the mucous membranes of the respiratory tract. Bacteremia does not occur. Electron microscopic studies have demonstrated that phase I strains of B pertussis adhere only to the tuft of ciliated cells in the mucosa of the human respiratory tract; no attachment to nonciliated cells was observed. Convincing experimental data indicate that the adherence of B pertussis to human cilia is effected by a synergistic action of pertussis toxin and filamentous hemagglutinin, each acting as a bivalent bridge between the bacterium and the ciliary receptor.
Epidemiology:
The mucous membranes of the human respiratory tract are the natural habitat for B pertussis and B parapertussis. Although B pertussis can survive outside the body for a few days and so may be transmitted by contaminated objects, most infections occur after direct contact with diseased persons—specifically, by inhalation of bacteria-bearing droplets expelled in cough spray. The patient is most infectious during the early catarrhal phase, when clinical symptoms are relatively mild and noncharacteristic. Subclinical cases may have similar epidemiologic significance. Healthy carriers of B pertussis or B parapertussis are assumed to play no significant epidemiologic role. The natural habitat of B bronchiseptica is the respiratory tract of smaller animals such as rabbits, cats, and dogs. Therefore, human infections with B bronchiseptica are extremely rare and occur only after close contact with carrier animals.
Relationship of B pertussis to the developing antibody response during whooping cough.
Relationship of B pertussis to the developing antibody response during whooping cough.
Whooping cough, a highly communicable, worldwide infection, was once common and dangerous, killing many thousands of children per year. Widespread vaccination has caused a continuous decrease in incidence and mortality over the years, but large numbers of patients still die in countries where vaccination is inadequate. Whooping cough is mainly an infection of infants and children, although susceptibility is general. The disease is especially dangerous in the first 6 months of life. Neither season nor climate seems to affect the morbidity rate.
Diagnosis:
Bordetellae can be cultured from nasopharyngeal swabs or nasopharyngeal secretions. The sensitivity of the method depends mainly on the technique of taking the swabs or secretions. Swabs (one for each nostril) should be introduced deeply into the nose as to reach the nasopharynx. Swabs should be made of dacron or calcium alginate, and they should be transported in half strength charcoal blood agar. Secretions should be from the nasopharynx using a suction device with a mucus trap. Nasopharyngeal secretions should be immediately plated onto Regan-Lowe medium, which has replaced Bordet-Gengou medium as the medium of choice. The transportation time for both materials should be kept as short as possible. For culture isolation, Bordet-Gengou agar containing blood, potato extract, and glycerol remains one of the effective means, although minor modifications regarding blood concentrations and addition of penicillin and nicotinamide have been recommended. For routine use, charcoal-blood agar (REGAN-LOWE medium) is most widely used. A (2,6-O-dimethyl)-b-cyclodextrin supplemented STAINER-SCHOLTE broth can be used as an enrichment medium. The Bordetella species do not need factors X and V (NAD+ and hemin).
Bordetella pertussis usually grows after 3 to 4 days of incubation at 37° C. The small, transparent colonies are indistinguishable from those of B bronchiseptica, but usually are smaller than those of B parapertussis. All three species produce hemolysis. Biochemically they are relatively inert and do not ferment carbohydrates or produce H2S and indole. An important characteristic of B parapertussis is its capacity to produce brown pigmentation on blood-free peptone agar. B pertussis and B parapertussis can be distinguished by certain biochemical and culture characteristics (Table 31-1) in addition to slide agglutination with specific antisera. B bronchiseptica as well as B avium and B hinzii can be differentiated by conventional methods for typing gram-negative nonfermenting rods (such as API-NE).
Haemophilus influenzae
