Major gram-negative bacterial pathogens

Question 1

Gram negative cell surface antigens

Answer 1

H-antigen (flagellum)
K-antigen (capsule)
Peptidoglycan
O antigen (outer membrane LPS)

Question 2

The gram-negative cell envelope

Answer 2

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

Question 3

LPS O-antigens

Answer 3

Deters complement c567 - Membrane Attack Complex precusors
-membrane pore in target cell
Capsule evades antibody binding

Question 4

Meningitis and gonorrhoea gram-negative genera

Answer 4

Neisseria

Question 5

Meningitis, pneumonia gram-negative genera

Answer 5

Haemophilus influenzae

Question 6

plague – millions of deaths in medieval times

Gram-negative genera

Answer 6

Yersinia pestis

Question 7

Burn infections and lung infections of CF patients

Gram-negative genera

Answer 7

Pseudomonas aeruginosa

Question 8

GI tract gram-negative genera

Answer 8

Salmonella spp.- gastroenteritis
Shigella spp.- gastroenteritis
Vibrio cholera- cholera – GI lecture
Helicobacter pylori- stomach ulcers- GI lecture
Camplylobacter jejuni- food poisioning- GI lecture

Question 9

Whooping cough gram-negative genera

Answer 9

Bordetella

Question 10

Legionnaires disease gram-negative genera

Answer 10

Legionella

Question 11

‘The Clap’ syphilis gram-negative genera

Answer 11

Treponema pallidum

Question 12

Neisseria spp.

Answer 12

Gram-negative diplococci
N. meningitidis - meningococcus
N. gonorrhoeae - gonococcus
Both fastidious - growth (heated blood [chocolate]) + CO2

Question 13

N. meningitidis - meningococcus

Answer 13

Meningitis/ meningococcal septicaemia
Infection of CSF and meninges
Commensal carriage in pharynx/nasopharynx
Capsular, serotyping based on polysaccharides

Question 14

N. gonorrhoeae - gonococcus

Answer 14

Gonorrhoea
STI, genital and oral infection
Neonatal transfer- eye infections
Lipooligosaccharide capsule often sialylated> STI lecture

Question 15

The meninges

Answer 15

Pia mater, arachnoid mater, dura mater

Question 16

Symptoms of meningitis

Answer 16

Floppy child/ difficulty supporting own weight
Fever, vomiting, diarrhoea
Confusion and drowsiness
Severe headache
Stiff neck
Dislike of bright light
Body stiffness/ jerky movements

Question 17

N. meningitidis

Answer 17

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

Question 18

N. meningitidis UK

Answer 18

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

Question 19

N. meningitidis pathogenesis: spread

Answer 19

either directly to subarachnoid space or through nasopharyngeal mucosa to enter the bloodstream

Question 20

N. meningitidis pathogenesis

Answer 20

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

Question 21

N. meningitidis epidemiology

Answer 21

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)

Question 22

Worldwide picture: meningitis

Answer 22

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

Question 23

Diagnosis and treatment of meningitis

Answer 23

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

Question 24

Haemophilus influenzae G -ve cocco-bacillus

Answer 24

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

Question 25

H. influenzae pathogenesis

Answer 25

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

Question 26

H. influenzae epidemiology

Answer 26

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.

Question 27

Hib vaccine

Answer 27

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

Question 28

Diagnosis and treatment of H. influenzae

Answer 28

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

Question 29

Yersinia Pestis: THE PLAGUE

Background

Answer 29

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!!

Question 30

Infectious cycle

Answer 30

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

Question 31

Virulence factors - plague

Answer 31

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

Question 32

Type III secretion system (TTSS)

Answer 32

Protein Needles or ‘injectisomes’ that directly inject toxins into the host cytosol

Question 33

Eyam: quarantine

Answer 33

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

Question 34

Plague: present day

Answer 34

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.

Question 35

Pseudomonas aeruginosa

Answer 35

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

Question 36

P. Aeruginosa and Cystic Fibrosis patients

Answer 36

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

Question 37

ESKAPE

Answer 37

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