Major gram-negative bacterial pathogens Flashcards
-Morphology, growth requirements and classification of key Gram-negative bacteria. Neisseria infections and pathogenicity. -Haemophilus infections and pathogenicity. -Yersinia and Pseudomonas infections and pathogenicity, epidemiology and spread. - Control of Gram-negative bacterial infections including antibiotic treatment, prophylaxis and use of vaccines, as appropriate.
Gram negative cell surface antigens
H-antigen (flagellum)
K-antigen (capsule)
Peptidoglycan
O antigen (outer membrane LPS)
The gram-negative cell envelope
Outer membrane:
-LPS is intimately attached to the outer membrane
-capsule is loosely attached
-both are antigens confer some resistance to immune system
-lipoproteins link OM to peptidoglycan layer - gives cell rigidity
Inner membrane:
-contains many transport proteins and components of bacterial respiratory chain
-these enable bug to get energy from growth substrate
LPS O-antigens
Deters complement c567 - Membrane Attack Complex precusors
-membrane pore in target cell
Capsule evades antibody binding
Meningitis and gonorrhoea gram-negative genera
Neisseria
Meningitis, pneumonia gram-negative genera
Haemophilus influenzae
plague – millions of deaths in medieval times
Gram-negative genera
Yersinia pestis
Burn infections and lung infections of CF patients
Gram-negative genera
Pseudomonas aeruginosa
GI tract gram-negative genera
Salmonella spp.- gastroenteritis
Shigella spp.- gastroenteritis
Vibrio cholera- cholera – GI lecture
Helicobacter pylori- stomach ulcers- GI lecture
Camplylobacter jejuni- food poisioning- GI lecture
Whooping cough gram-negative genera
Bordetella
Legionnaires disease gram-negative genera
Legionella
‘The Clap’ syphilis gram-negative genera
Treponema pallidum
Neisseria spp.
Gram-negative diplococci
N. meningitidis - meningococcus
N. gonorrhoeae - gonococcus
Both fastidious - growth (heated blood [chocolate]) + CO2
N. meningitidis - meningococcus
Meningitis/ meningococcal septicaemia
Infection of CSF and meninges
Commensal carriage in pharynx/nasopharynx
Capsular, serotyping based on polysaccharides
N. gonorrhoeae - gonococcus
Gonorrhoea
STI, genital and oral infection
Neonatal transfer- eye infections
Lipooligosaccharide capsule often sialylated> STI lecture
The meninges
Pia mater, arachnoid mater, dura mater
Symptoms of meningitis
Floppy child/ difficulty supporting own weight Fever, vomiting, diarrhoea Confusion and drowsiness Severe headache Stiff neck Dislike of bright light Body stiffness/ jerky movements
N. meningitidis
10 - 25% nasopharynx commensal carriage rate
During disease episodes, carriage rate may rise to 90%
5 Serogroups:
-dependent on polysaccharide capsular antigen
-serogroups A,B,C,Y,W135- account for almost all cases worldwide
N. meningitidis UK
Serogroup B- 90% confirmed cases
(since introduction of Group C vaccine, now replaced with ACYW vaccine from 2015)
Serogroups A, C,and W135 comprise others
N. meningitidis pathogenesis: spread
either directly to subarachnoid space or through nasopharyngeal mucosa to enter the bloodstream
N. meningitidis pathogenesis
Possess IgA protease for serum resistance
In most first infection leads to ab production without development of clinical disease
Bactericidal antibody against capsule is most important protective factor
-meningitis still relatively rare in UK
N. meningitidis epidemiology
Occurs worldwide and is WHO and NHS notifiable
Outbreaks occur in winter months
Approx. 2000 cases and 80 deaths per year in UK (4%)
2/3 of cases occur in first 5 years of life
Peak prevalence is in first year of life, second peak 16-23 years
Frequent outbreaks among
young adult population (military, university)
Worldwide picture: meningitis
Highest occurrence of meningitis is in a region of sub-saharan Africa- ‘meningitis belt’
During outbreaks can cause infection of up to 10% of population – mainly Serogroup A
Diagnosis and treatment of meningitis
Speed is the key: 6-24hr onset
CSF
-many PMNLs, presence of bacteria- diplococci
Blood culture
-sub-culture on chocolate agar
-sugar fermentation tests – maltose & glucose +ve
-oxidase positive
Penicillin, cefotaxime (chloramphenicol)
-followed by eradicative treatment: rifampicin or ciprofloxacin often accompanied by corticosteroids
Vaccines available for group A, C, Y and W135; - tetravalent conjugate given since 2015
Introduction of 4CMenB vaccine (Bexsero) in 2015 for infants and at-risk groups.
But expensive – I.e. for non-developed countries, and even in UK MenB was a tricky sell to UK-JCVI
Haemophilus influenzae G -ve cocco-bacillus
Originally isolated from influenza sufferers (1892 Pfeiffer), thus H. influenzae
Thought to be causative agent of flu until 1933!
Non-invasive disease : otitis media, sinusitis
(2 - 4 yrs old)
Causes septicaemia, pneumonia and meningitis
-meningitis and pneumonia (4 months - 2 years 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)
-capsule major virulence factor avoidance of c3b binding
-99% invasive disease caused by type b capsule type
Commensal carriage of type b approximately 5-10% - nasopharynx
(non-capsulate 25-80%)
-other factors include fimbriae, IgA proteases
H. influenzae epidemiology
Serious systemic disease in children worldwide
350,000- 450,000 deaths per year- mainly in developing countries
Meningitis more common in winter months
Pneumonia more common in third world
Outbreaks in nursery schools etc.
Hib vaccine
Hib vaccine introduced 1992 in UK
- given at 2, 3, 4 months
- infection in <5y declined 95% in developed world
Cost of vaccine approx. $20 per dose, (need 3 doses) too high for many countries
Problems with increasing antibiotic resistance strengthens need for vaccine
Diagnosis and treatment of H. influenzae
Sputum, throat swabs, blood culture Chocolate agar, 5-10% CO2 Haemophili require either factor X or factor V for growth -Factor X = haemin -Factor V = NAD or NADH -H. influenzae requires both X + V -H. ducreyi requires only Factor X Meningitis - antigen detection/ PCR Cefotaxime (chloramphenicol) Non-invasive disease – amoxycillin Chemoprophylaxis for contacts - rifampicin
Yersinia Pestis: THE PLAGUE
Background
First recorded pandemic began in Egypt 250 AD
Second pandemic- THE BLACK DEATH
spread from Asia (China) to Europe in the 1300s
Development of pneumonic plague is highly contagious and mortality rates ~100%, 50% for bubonic plague
Killed 25% of European population, and 30% in England, 50% of vicars!!
Infectious cycle
Bubonic plague and animal vector
Infected flea bites human
Bubonic plague - 75% death - no person to person spread
If there is profuse bacterial growth in lung –> pneumonic plague (90% death) –> rapid person-to person spread
Virulence factors - plague
Gram negative- so LPS
Contains three large virulence plasmids
Encode type III secretion needle for injection of toxins into host cells: suppress immune response, promote bacterial invasion and survival inside host cells
pCP1- plasminogen activator: helps dissemination in host- degrades complement components C3b and C5a
pMT1- antiphagocytic capsule and TTSS host evasion
Type III secretion system (TTSS)
Protein Needles or ‘injectisomes’ that directly inject toxins into the host cytosol
Eyam: quarantine
Disease arrived summer 1665
Infected cloth from London
By October 1666: 250 of 350 villagers were dead
Prevented spread by self-imposed quarantine, no-one entered, food dropped at perimeter, money in a well
of vinegar
May have saved many thousands in northern
England
Plague: present day
Easily treated by antibiotics: Streptomycin or Tetracycline
Formalin-killed vaccine
Very few cases in developed countries
- But is endemic in rodents in western USA so isolated cases and outbreaks do occur in Hunters – mainly sylvatic plague
Some outbreaks in third world – large one in 2005 in Democratic Republic of Congo and some cases still in western US states each year.
Pseudomonas aeruginosa
Common environmental isolate and human commensal
Gram –ve, motile rod motile, strictly aerobic
Colonies on agar with characteristic green spreading shape and grapey smell?
Often multiply antibiotic resistant
Major cause of infection after burns
-well adapted to the warm moist environment in a burn wound
-many extracellular proteases breakdown tissues
-can lead to septicaemia- Ecythma gangrenosum lesions
P. Aeruginosa and Cystic Fibrosis patients
Major cause of lung infections in cystic fibrosis patients- productive cough, no fever, causes lung damage (1 in 2500 live births)
Mucoid slime made of alginate- complex polysaccharide- left of picture
Growth in microcolony biofilms in lung
Increased resistance to Antibiotics
Damage due to virulence factors and immune reaction to alginate and antigens
Combination Ab therapy reduces load but never eradicate
ESKAPE
Most antibiotic resistant pathogens
4 of the 6 are gram negative
One of these is pseudomonas
-increasingly resistant to Carbepenam which is one of the last drugs of resort
Enterococcus faecium, Staphylococcus aureus, Klebsiella pneumoniae, Acinetobacter baumannii, Pseudomonas aeruginosa, and Enterobacter species
