Major gram neg bacterial pathogens Flashcards
(31 cards)
Name the gram negative surface antigens
H-antigen = flagellum
K-antigen = capsule
Peptidoglycan
O-antigen = outer membrane lipopolysaccharide (LPS)
Both gram neg and gram pos bac have a capsule - what is it’s purpose?
Protection and help it stick down to surface
What does PS o-antigen do?
Deters complement c567 - Membrane attack precursors (MAC)
Structure of gram neg bac?
2 membranes OM connected to LPS layer Thin PG layer Does NOT retain gram stain = pink Outer layers and released are LPS major antigens LPS and capsule help immune evasion
Give examples of medically important gram neg bac
Neisseria - meningitis and gonorrhoea
Haemophilus influenza - meningitis, pneumonia
Pseudomonas aeruginosa - burn infecs and lung infecs of CF pts
Yersinia pestis - plague
Bordetella - whooping cough
Legionella - legionnaires disease
Treponema pallidum - syphilis
GI: Salmonella spp - gastroenteritis Shigella spp - gastroenterits Virbio cholera - cholera Helicobacter pylori - stomach ulcers Campylobacter jejuni - food poisoning
What is neisseria spp?
Gram neg diplococci
Name the pathogens of neisseria spp and what do they do?
N-meningitidis;
- Meningitis/meningococcal septicaemia
- Infec of CSF and meninges
- Commensal carriage in pharynx/nasopharynx
- Capsular, serotyping based on polysaccharides
N/gonorrhoeae;
- Gonorrhoea
- STI, genital and oral infec
- Neonatal transfer - eye infecs
- Lipopolysaccharide capsule often sialylated
Both fastidious - Growth (Heated blood [chocolate}) + CO2
What is meningitis?
Inflam of the meninges
Bac replicates in cerebrospinal fluid, produce lots of protein = meninges inflamed = pressure on brain = aching
Also gives rash, leg pain, cold hands and feet, vomiting, confusion
What is N.meningitidis carriage rate? When may the carriage rate increase?
10-25% nasopharynx commensal carriage rate
During disease = carriage rate may rise to 90%
What do N.meningitidis’ serogrpoups depend on? Name the 5 serogroups
Dependent on polysaccharide capsular antigen
A, B, C, Y, W135 - account for almost all cases worldwide
UK - 90% serogroup B
A, C and W135 comprise others
N.meningitidis pathogenesis - how does it enter the body?
Name 1 virulence factor of it and the most important Ab in protecting against ti
Directly to subarachnoid space or through nasopharyngeal mucosa to enter the bloodstream
Mucosal spread - kissing
Protease IgA for serum resistance
Bactericidal antibody against capsule is most important protective factor
N.meningitidis epidemiology?
Outbreak in winter
2000 cases and 80 deaths in UK per yr
2/3 of cases occur in 1st 5yrs of life
Peak prevalence = 1st yr of life, 2nd peak = 16-23
Frequent in young adult pop - uni, military
Where is the highest occurrence of meningitis?
In a region of sub-saharan Africa - meningitis belt
Infec of up to 10% of pop - mainly serogroup A
How to diagnose meningitis?
CSF - many PMNLs, presence of bac - diplococci
Blood culture;
- Sub-culture on chocolate agar
- Sugar fermentation tests - maltose and glucose positive (red to yellow)
- Oxidase positive (purple)
How to treat meningitis?
Penicillin, cefotaxime
- followed by eradicative treatment (rifampicin or ciproflaxacin often with corticosteroids
- Vaccines available for group A, C, Y and W135
- 4CMenB vaccine in 2015 for infants and at-risk groups
- Expensive
What does haemophilus influenzae (gram neg cocco-bacillus) cause? Complications? Survival percentage?
Non-invasive disease: otitis media, sinusitis (2-4yrs old)
Cause septicaemia, pneumonia and meningitis
- Meningitis and pneumonia (4 months to 2 yrs old)
- Invasion - penetration of submucosa of nasopharynx
- Complications; epiglottitis, bacteraemia, cellulitis
- 15-35% survivors with disability
H.influenzae pathogenesis?
6 capsular types (a-f`)
Some strains non-capsulate (commensals)
- capsular major virulence factor avoidance of c3b binding
- 99% invasive disease caused by type b capsular type
Commensal carriage of type b 5-10% nasopharynx, non-capsular 25-80%
H.influenzae epidemiology?
Serious systemic disease in children
300,000 deaths per yr in 2008 - mainly in dev countries
Outbreaks in nursery
H.influenzae vaccine?
Hib vaccine given at 2, 3, 4 months
Cost of vaccine has been reduced
Increasing antibiotic resistance = vaccine needed more
How to diagnose presence of H.influenzae?
Sputum, throat swabs, blood culture
Chocolate gar 5-10% CO2
What does haemophil need for growth?
Factor X (haemin) or V (NAD or NADH) H.influenzae = needs both X and V H.ducreyi needs X
How to diagnose meningitis - H influenzae?
Antigen detection/PCR
How to treat H.influenzae?
Cefotaxime
Non-invasive disease - amoxycillin
Chemoprophylaxis for contacts - rifampicin
What causes the plague?
How is it spread?
Yersina pestis
Infected flea bites human
