MAJOR GRAM NEGATIVE BACTERIA

what is the difference in structure between gram negative and gram positive bacteria

state the gram-negative cell surface antigens

• H-antigen

• K-antigen

• O-antigen

what are the H, K and O antigens

another diagram showing gram negative cell wall structure

• capsule extends from surface, loosely attached

• LPS attached to outer membrane

do gram negative bacteria retain gram stain

no, they are therefore counterstained to become pink

what do O-antigens do

immune evasion

what does the capsule do

evades antibody binding (immune evasion)

list of medically important gram negative bacteria

• Neiserria - meningitis and gonorrhoea

• Yersinia pestis

• Pseudomonas aeruginosa

—

GI tract - enterobacteria

• Salmonella spp. (gastroenteritis)

• Shigella spp. (gastroenteritis)

• Vibrio cholera

• Escherichia coli

• Helicobacter pylori

• Campylobacter jejuni (food poisoning)

extra gram negative bacteria

• Bordetella (whooping cough)

• Legionella

• Treponema pallidum (syphilis)

• Klebsiella (major hospital resistant pathogen)

what shape is Neisseria spp.

gram negative diplococci

where are Neisseria spp. often seen

inside PMNLs of infected individuals

• this is an observation diagnostic of infection

which two diseases are Neisseria spp. most associated with

• meningitis (N.meningitidis)

• gonorrhoea (N.gonorrhoeae)

outline N.meningitidis/ meningococcus

infection of CSF and meninges

• commensal carriage in pharynx/ nasopharynx

• capsular

• serotyping based on polysaccharides

outline N.gonorrhoeae/ gonococcus

• STI - genital and oral infection

• neonatal transfer manifests as eye infections

• lipo-oligosaccharide capsule often sialylated

both N.meningitidis and N.gonorrhoeae are fastidious bacteria, what does this mean?

• they need specific nutritional requirements

  • heated blood (chocolate agar) + CO₂

what is meningitis and its symptoms

inflammation of the meninges

• intense headache

• fever

• malaise

• photophobia

• stiff muscles and neck

what can meningitis lead to

convulsions and death

on darker skin tones, where should a rash be identified as being associated with meningococcal septicaemia

• lighter areas: palms, soles of feet, conjunctiva, palate

outline the epidemiology of N.meningitidis

• occurs worldwide often in the winter months

• 2/3 of cases occur in first 4yrs of life

  • peak prevalence is 1st yr of life

  • second peak: 16-23yo (onset of large gatherings)

why does meningitis often occur during winter

• dryness of air and thus the breakdown in mucosal barriers

  • this makes it easier for bacteria to access the body

why is the peak prevalence of meningitis in the first year of life

• the initial protection from maternal antibodies is lost so the infant becomes susceptible

how is N.meningitidis spread

• either directly to subarachnoid space

or

• through nasopharyngeal mucosa to enter the bloodstream

points on N.meningitidis pathogenesis

30,000 annual deaths (reduced from 300,000 in 2000)

describe the onset of meningitis

• onset of meningitis is very fast

• 6-24h onset

(therefore speed is the key to successful treatment)

points showing diagnosis of meningitis

what medications are used to treat meningitis

antibiotics

• ceftriaxone

• cefotaxime + ampicillin

often accompanied by corticosteroids

which antibiotics is prescribed as a prophylaxis for meningitis

ciprofloxacin

what are the chances of passing on meningitis through close contacts

1 in 300

Neisseria summary slide

what other type of bacteria causes meningitis

Haemophilus influenzae (also gram negative)

• originally from influenza sufferers

what shape is Haemophilus influenzae

coccobacillus (between a sphere and a rod)

what other conditions can Haemophilus influenzae cause (4)

• septicaemia

• pneumonia

• otitis media (mild infection)

• sinusitis (mild infection)

and

• meningitis

which strains of H.influenzae are non-capsular

the commensals

how many capsular types of H.influenzae are there

6 capsular types (a-f)

• 99% of disease is caused by type b capsule type (Hib vaccine combats this)

what is the purpose of the H.influenzae capsule

capsule is a major virulence factor for avoiding C3b (opsonin) binding

• incl. fimbriae, IgA proteases

antimicrobial resistance and the WHO list of critical pathogens

outline Pseudomonas aeruginosa

• gram negative

• common environmental isolate and human commensal

• strictly aerobic

• rod motile

• often multiply to become antibiotic resistant

outline Pseudomonas aeruginosa colonies on agar (appearance and smell)

• characteristic green spreading shape

• grapey smell

Pseudomonas aeruginosa is a major cause of infection after _____

Pseudomonas aeruginosa is a major cause of infection after burns

why does P.aeruginosa cause infection after burns

• well adapted to the warm moist environment in a burn wound

• many extracellular proteases breakdown tissues

infection by P.aeruginosa can cause…

septicaemia - ecthyma gangrenosum lesions

how is P.aeruginosa linked to cystic fibrosis patients

P.aeruginosa is the major killer of CF patients - who then develop chronic lung infections and die

name some Klebsiella spp.

• Klebsiella pneumoniae

• Klebsiella oxytoca

what do Klebsiella spp. cause

• hospital sepsis

• pneumonia

• wound infections (diabetic foot ulcer)

• meningitis

antibiotics effective against Klebsiella spp.

• colistin

  • many strains are becoming resistant to last resort antibiotics e.g. carbapenem

where do Klebsiella spp. normally reside

human gut resident

how is Klebsiella spread (infection route)

fecal-oral spread

list of gram negative bacilli (enterobacteria)

summary