Gram-Negative Coccobacilli Lecture Notes PDF

The Gram-Negative Coccobacilli  The Gram-Negative Coccobacilli This group includes: Haemophilus Bordetella Brucella  GRAM-NEGATIVE COCCOBACILLI Genus Species H. influenzae Haemophilus H. parainfluenzae Most commonly Haemophilus influenzae (b...

The Gram-Negative Coccobacilli  The Gram-Negative Coccobacilli This group includes: Haemophilus Bordetella Brucella  GRAM-NEGATIVE COCCOBACILLI Genus Species H. influenzae Haemophilus H. parainfluenzae Most commonly Haemophilus influenzae (blood lover) Bordetella B. pertussis B. parapertussis  Haemophilus influenzae Morphology Gram negative - Coccobacillus, 1 m Cultivation Growth factors chocolate agar, X= Haem, V= NAD, Satellite-phenomenon; Satellitism Blood agar plate culture showing Haemophilus influenzae satelliting around Staphylococcus aureus.  Haemophilus influenzae Virulence factors: PRP (polyribitol phosphate PRP) capsule – antiphagocytic. LPS = endotoxin (fever, inflammation), impairs ciliary function of respiratory epithelial cells. IgA1 protease – role in colonization Pili & nonpilus adhesin – colonization of the oropharynx. Survival in respiratory epithelial cells  Haemophilus influenzae Reservoir: humans (carriers, infected individuals) – mostly endogenous/exogenous Transmission: close contact, via respiratory droplets (air-borne route) Enters upper respiratory tract: attaches to cells (fimbriae, IgA1 protease) Endotoxin stops respiratory tract cilia from beating & clearing the bacterial cells, & induces inflammation Local spread (ears, sinuses, lungs, soft tissues) Systemic spread (blood & brain) Haemophilus are broadly classified into encapsulated and non-encapsulated types. The encapsulated bacterium is further subdivided into 'a' through ‘ f ' subtypes based on capsule type. The most familiar and predominant form is H. influenzae type b (Hib), which infects mostly children and immunocompromised individuals.  Haemophilus Endogenous and exogenous infections Endogenous H. influenzae infections Encapsulated strains Unencapsulated a, b, c, d, e, f strains invasive (otitis media, sinusitis, infections in young bronchitis, children: tracheobronchitis), pneumonia, arthritis Other: sinusitis, otitis Other species: otitis media, media, bronchitis conjunctivitis, sinusitis, endocarditis, dental abscesses, meningitis  Haemophilus influenzae Sepsis An infant with severe vasculitis with disseminated Periorbital cellulitis intravascular coagulation (DIC) with gangrene of the hand secondary to Haemophilus influenzae type b septicemia - prior to the availability of the Hib vaccine.  Genus: Bordetella Reservoir: humans Transmission: air-borne droplets Whooping cough – occur primarily in non-immune children Adults with waning immunity: milder disease misdiagnosed as cold or flu  Bordetella pertussis Morphology Gram-negative Coccobacillus, 1m  Bordetella pertussis Culture: Special Medium Bordet – Gengou agar B. pertussis Inflammation of respiratory mucosal memb. or death Most infectious, but generally not yet diagnosed Prophylaxis: azithromycin  Brucella & brucellosis Zoonosis = a disease of animals that may be transmitted to humans under natural conditions Examples: brucellosis Medically important species named for the livestock they commonly come from Brucella abortus (cattle) Brucella melitensis (goats/sheep) Brucella canis (dogs) Brucella suis (pigs) Facultative intracellular pathogen  Brucella Morphology: Gram-negative coccobacilli non-motile, non - capsulate Cultivation: Agar : nutrient rich (Serum, Glycerin) Atmosphere: CO2 aerobic to microaerophilic Incubation: days-weeks Description: Brucella spp. Colony Characteristics: A. Fastidious, usually not visible at 24h. Brucella colonies are visible after 3-5 days incubation period at 37ºC. B. Grows slowly on most standard laboratory media (e.g. sheep blood, chocolate and trypticase soy agars). Pinpoint, smooth, entire translucent, non-hemolytic at 48h  Brucella & brucellosis Human brucellosis usually presents as an acute febrile illness Most cases are caused by B. melitensis All age groups are affected Complications may affect any organ system The disease may persist as relapse, chronic localized infection or delayed convalescence  Brucella & brucellosis Cattle, sheep, goats and pigs are the main reservoirs of Brucella Transmission to humans occurs through occupational or environmental contact with infected animals or derived food products Food of animal’s origin is a major source of infection Brucellosis can be a travel-associated disease Blood or organ/tissue transfer are possible sources of infection Person-to-person transmission is extremely rare (inhalation) DIAGNOSIS : A- Demonstration by fluorescent antibody of organism in clinical specimen. B- Blood culture: - It is important in the acute phase of the infection. - It should be carried out repeatedly because the organisms may enter the blood intermittently. - It is +ve in only 30-50% of cases, mainly in the first 2-3 weeks of the disease C- Serological tests “agglutination reaction” : The most common serological test: 1. Rose Bengal Test (RBT). The significant titer = 1/160 or higher. 2. Standard Tube Agglutination Test (STAT). 3. Enzyme Linked Immuno Sorbent Assay (ELISA) Treatment: The drug of choice is tetracycline+ Rifampin  macrophages macrophages macrophagesmacrophages brucellosis