Major Gram-Negative Bacterial Pathogens Flashcards
(15 cards)
What are the gram-negative cell surface antigens
K-ANTIGEN: Capsule
- Capsule can help evade detection by the immune system to complement and antibodies so that processes such as opsonisation are avoided
H-ANTIGEN: Flagellum
O-ANTIGEN: Outer membrane lipopolysaccharide (LPS)
- The LPS can be bound by mac precursors.
Gram -ve bacteria membrane structure
- Gram -ve bacteria have two membranes with the outer membrane connected to the LPS layer
- Thin peptidoglycan layer
- Do not retain gram stain
- LPS & Capsule help immune evasion
List of medically important Gram -ve bacteria
Neisseria - Meningitis & Gonnorhoea
Haemophilus Influenza - meningitis, pneumonia
Yersinia pestis - Plague
GI TRACT:
Salmonella spp. & Shigella spp. - Gastroenteritis
Vibrio cholera - Cholera
Helicobacter pylori - Stomach ulcers
Camphylobacter jejuni - Food poisoning
OTHERS:
Bordetella - Whooping cough
Legionella - legionnaires disease
Treponema pallidum - Syphils
Describe the two pathogens of Nesseria spp. (gram -ve diplococci)
• N.MENINGITIS (meningococcus)
- Meningitis
- Infection of CSF and meninges
- Commensal carriage in pharynx/nasopharynx
- Capsular, serotyping based on polysaccharides
• N.GONORRHOEAE (gonococcus)
- Gonorrhoea
- STI, genital & oral infection
- Neonatal transfer - eye infections
- Lipooligosaccharide capsule often sialylated
Symptoms of Meningitis
Inflammation of the meninges:
- Intense headache
- fever
- malaise
- photophobia
- stiff muscles (neck)
- can lead to convulsions and death
- Loads of neutrophuls in CSF - lumbar puncture
Describe the pathogenesis of N.meningitidis
•SPREAD either directly to subarachnoid space or through nasopharyngeal mucosa to enter the bloodstream (mucosal - kissing)
• POSSESS IgA protease for serum resistance.
- 1st infection leads to ab production w/o development of clinical disease
- Bactericidal antibody against capsule (very variable) is most important protective factor
Diagnosis of Meningitis Speed is key (6-24hr onset)
- Presence of many PMNLs and diplococci bacteria in CSF
- BLOOD CULTURE:
- Sub-culture on chocolate agar
- Sugar fermentation tests (maltose & glucose +ve)
Salt solution w/ pH indicator. Goes from red to yellow as acid is produced
Treatment of Meningitis
• Penicillin, cefotaxime
- followed by eradicative treatment:
- Rifampicin often accompanied with corticosteroids
• Vaccines available for group A,C, Y and W135
- expensive
Haemophilus Influenzae - Gram -ve cocco-bacillus
- Causes septicaemia, pneumonia and meningitis (4 months - 2 yrs for P & M)
- Invasion via the penetration of submucosa of nasopharynx
- Complications: epiglottitis, bacteraemia, cellulitis
H.influenzae Pathogenesis
• 6 capsular types (a-f), some strains non-capsulate (commensals)
- Capsule major virulence factor avoidance of c3b binding
- 99% invasive disease caused by type b capsule type
• Uncontrolled growth leads to septic shock.
- Disabilities of mental retardations ad deafness which is more prevalent in men or pneumonia
300,000 deaths per year
Diagnosis of H.influenzae
- Sputum, throat swabs, blood culture
- Chocolate agar, 5-10% CO2
- Haemophili require EITHER factor X (haemin) or factor V (NAD/NADH) for growth
- H.infuenzae requires BOTH factors X & V
- H.ducreyi requires ONLY factor X
Treatment of H.influenzae
- Cefotaxime (chloramphenicol)
- Non-invasive disease - amoxycillin
- Chemoprophylaxis for contacts - rifampicin
Virulence factors of Yersinia pestis
- Gram -ve so LPS
- Contains three large virulence plasmids
- Encode type III secretion for injection of toxins into host cells: suppress immune response, promote bacterial invasion and survival inside host cells
- pCPI - plasminogen activator: helps dissemination in host. Degrades complement components C3b & C5a
- pMTI - antiphagocytic capsule and TTSS host evasion
What is Pseudomonas aeruginosa
- Gram -ve motile road, strictly aerobic
- Colonies on agar with characteristic green spreading shape and grapey smell
- Often multiply antibiotic resistance
- Major cause of infections after burns
- Well adapted to warm moist environment in a burn wound
- Many extracellular proteases breakdown tissues
- Can lead to septicaemia - Ecythma gangrenous lesions
- Major killer of cystic fibrosis patients who become chromosomal infected
- Treatment by antibiotic
What is ESKAPE?
Group of the most antibiotic resistant pathogens with HIGHEST risk in clinical & hospital situations
- Enterococcus faecium
- Staph aureus
- Acinetobacter
- Pseudomonas
- Enterobacter
