Gram negative bacteria Flashcards
1
Q
What differentiates Shigella from E. coli and salmonella?
A
Shigella is non-motile, the rest are motile
2
Q
What differentiates E. coli from Shigella and Salmonella and describe what the appearance of colonies on MacConkey agar would be
A
E. coli ferments lactose (lac+) so is red on MacConkey-lactose agar and the rest form yellow colonies
3
Q
What are the three types of cell surface antigens of G- bacteria?
A
K, H, O antigen
4
Q
What is K antigen?
A
the capsule of the bacteria
5
Q
What is H antigen?
A
flagella
6
Q
What is O antigen?
A
LPS
7
Q
Does shigella have flagella?
A
No
8
Q
What system do shigella, salmonella and E. coli all affect?
A
GIT
9
Q
Give the principal infections caused by E. coli
A
wound infections UTIs gastroenteritis traveller's diarrhoea bacteraemia meningitis in infants
10
Q
Why are some strains of E.coli pathogenic, even though E.coli is a commensal?
A
Pathogenicity islands - acquisition of genes (by lateral and horizontal transmission) from other pathogens or other organisms which confer and advantage and are maintained
11
Q
How does heat labile toxin cause ETEC (traveller’s diarrhoea)
A
- E.coli adheres
- produces toxin
- toxin taken up by epithelial cell
- toxin modifies the G protein by adding ADP ribose group
- This locks the G protein into an active form that is on all the time
- stimulates adenylate cyclase continuously
- cAMP levels increase and protein kinase phosphorylates CFTR
- CFTR pumps chlorine into the gut lumen and Na and h20 follows
12
Q
How does heat stable toxin lead to ETEC?
A
- ST binds to guanylyl cyclase on epithelial cell as mimics guanylyl
- results in formation of cGMP
- protein kinase activated and phosphorylates CFTR and causes Cl- to enter lumen of gut
- water and Na follow
13
Q
How do EHEC and EPEC cause pathogenicity?
A
overall attachment and effacement
1. bundle forming pilli adhere to villi on epithelial cells
2. type 3 secretion system is switched on which injects toxins into the epithelial cell
3. rearrangement of actin filaments = effacement of microvilli
actin reorganised into a pedestal
14
Q
How is Shigella related to E..coli?
A
Shigella = E.coli + virulence plasmid
15
Q
What are the features/signs of shigellosis?
A
e.g. dystentery severe bloody diarrhoea frequent passage of stools pus, blood prostrating cramps, pain in straining fever self-limiting
16
Q
How is shigella transmitted?
A
person-person
faeco-oral
contaminated water and food
17
Q
Which cells in the colon sample antigens?
A
colonic M cells (overlay lymphoid follicles)
18
Q
How does shigella damage the colonic mucosa?
A
- neutrophils - release mediators that cause damage and their migration through the mucosa damages cells too
- M cells transcytose antigens for macrophages to sample them. the macrophages apoptose so releases cytokines that damage the epithelium
- shigella can move laterally through the epithelium
19
Q
How does the Shiga toxin work?
A
cleaves a bond in rRNA
so protein synthesis doesn’t work
eventually all ribosomes will be inactive
20
Q
What is the main Salmonella sp that causes infection in humans?
A
S. enterica
21
Q
Which serovars of Salmonella enterica cause gastroenteritis?
A
serovar Enteritidis
serovar Typhimurium
22
Q
Which serovars of Salmonella cause enteric fever (typhoid)?
A
serovar Typhi
serovar Paratyphi
23
Q
Describe the pathogenesis of Salmonellosis
A
- ingestion of contained food/water
- invasion of s. intestine epithelium
- transcytosed to basolateral membrane
- enters submucosal macrophages
- survival and replication in intracellular macrophages
- dissemination of macrophages –> systemic [ONLY in typhoid not gastroenteritis]
gastroenteritis also involves chemokine release that causes neutrophils to migrate and cause injury
24
Q
Which damages the gut mucosa more initially - gastroenteritis or typhoid?
A
gastroenteritis
25
describe how enteric fever spreads around the body
1. dissemination of macrophages
2. enter lymph nodes
3. enter blood through throacic duct (transient/primary bacteraemia)
4. enter liver, spleen, bone marrow and multiply here
5. secondary bacteraemia --> i.e. septicaemia causing fever and kidney infection
6. reenters s.intestine from liver through the bile in gall bladder
26
What infection does Proteus mirabilis cause?
opportunistic UTIs
| leads to pyelonephritis (kidney infection) and septicaemia
27
What is the virulence factor of Proteus mirabilis and what does this cause?
urease - causes kidney stones
28
What infections does Klebsiella pneumoniae cause?
```
opportunistic nosocomial infection:
pneumonia
wound/surgical infection
meningitis
very common in hospital ICU
```
29
How is Vibrio cholerae transmitted?
faecal-oral
e.g. faecal contaminated water or food
shellfish
the bacterium itself is found in water, but can also contaminate food
30
What is a key treatment in Vibrio cholerae?
ORS
31
What are the two virulence factors of V. cholerae
1. TCP (toxin-coregulated pili) - colonisation
2. cholera toxin - adds ADP ribose to to G protein, so its locked in the on state
uncontrolled cAMP production
protein kinases are activated that phosphorylate CFTR - loss of Cl- ions
i.e. like heat labile LT
32
Pseudomonas aeruguinosa is an opportunistic infection. T or F
T
33
Give examples of situations where Pseudomonas causes acute infections
1. surgical wounds/ burns
2. UTIs from catheters
3. keratitis from contacts
4. bacteraemia in neutropenic pts due to leukaemia, chemo, AIDS
5. nosocomial pneumonia in ICU pts
34
Give 2 pt groups that are susceptible to chronic infection with Pseudomonas a.
CF
| brochiectasis
35
What percentage of the population carrier H. inluenzae in their nasopharynx?
25-80%
36
Give examples of infections caused by H. influenzae
```
infant meningitis
epiglotitis
sinusitis
otitis media
bacteraemia
CF and COPD lung infections
```
37
Who are most vulnerable to infection by H. influenzae?
young children and adult smokers
38
Which agar can H. influenza not grow on and so which agar has to be used?
cannot grow on blood agar so grown on chocolate agar
| so fastidious
39
What are the 3 virulence factors of H. influenzae?
1. pili - to adhere to epithelial cells
2. capsule - cause of invasive infections e.g. meningitis
3. LPS endotoxin - causes inflammation
40
What type of agar does Legionella pneumophila need to be cultured on?
charcoal agar - fastidious
41
What is legionnaires' disease?
severe inflammatory pneumonia
42
Who is most susceptible to Legionnaires' disease?
elderly
alcoholics
smokers
43
Where is L. pneumophila present?
```
man-made aquatic environments:
air-con
shower heads
nebulisers
humidifiers
```
44
Explain the pathogenesis of Legionella
1. infects alveolar macrophages
2. avoids phagosome-lysosome fusion
3. unregulated proinflammtory genes in alveolar macrophages
4. causes XS influx of neutrophils into the lungs
45
What shape is Bordetella pertussis?
short/oval rods (coccobacilli)
46
Are humans the only known reservoir for pertussis and Neisseria?
yes
47
How is pertussis transmitted?
aerosol transmission e.g. coughing
48
What are the symptoms of pertussis?
non-specific flu -like symptoms
| paroxysmal coughing
49
What two toxins are released by Bordetella pertussis and what do both of these cause?
pertussis toxin
adenylate cyclase haemolysin toxin
both increase
50
What are the two medically important species of Neisseria?
N. meningitidis
| N. gonorrhoeae
51
Where is Neisseria present in infection?
CNS - meningitis
| urethral discharge - gonorrhoeae
52
Is N. meningitidis present int he nasopharynx of the population asymptomatically?
Yes - 5-10% popln
53
How is N. meningitidis spread?
aerosol person-person
| e.g. in uni and other crowded places
54
How does N. meningitidis enter the CSF?
crosses the BBB
55
What can meningitis lead to?
septicaemia - very high mortality
56
What are the virulence determinants of N. meningitidis?
capsule - antiphagocytic
pili - adherence and colonisation
LPS - cytokine cascade and sepsis (DIC, MOF)
57
What can N. gonorrhoeae cause?
1. STD - urethritis with infection of female genitalia, can lead to salpingitis and infertility and pelvic inflammatory disease
2. oral infections if oral sex
3. conjunctivitis of the newborn of infected mother
58
What does campylobacter junk and coli cause?
food poisoning
mild to severe diarrhoea with blood
self limiting (1 week)
59
How does Campylobacter enter the body?
ingestion of unpasteurised milk or undercooked poultry
60
What 4 problems does H. pylori cause?
gastritis
peptic ulcer disease
gastric adenocarcinoma
MALT lymphoma
61
What is the most abundant flora of the large intestine?
Bacteroides
62
Where are the bacteroides found in the body normally?
large intestine
vagina
cervix
63
What do the bacteroides cause?
opportunistic infections after tissue injury in surgery, perforated appendix or ulcer
this leads to pelvic cavity infections
64
Are bacteroides aerobic or anaerobic?
strictly anaerobic
65
Give an example of a bacteroides sp.
B. fragilis
66
What is the virulence factor of Bacteroides
antiphagocytic capsule
67
Can chlamydia be cultured on agar plates?
No it is an obligate intracellular parasite
68
How can we detect chlamydia?
serum Abs
| PCR
69
Describe the life cycle of chlamydia
1. elementary bodies enter the endocervical cells/ urethral cells
2. the elementary body prevents phagolysosome fusion
3. elementary body converted to reticulate body
4. multiplication of RB within inclusion
5. the RGB converted back into an EB
6. cell lysis and release of EBs to infect another cell
70
What organism causes the most common STD?
Chlamydia trachomatis
71
Chlamydia trachomatis is usually asymptomatic. T or F
T
72
What areas can Chlamydia trachomatis infect?
```
urethra
vagina
uterus
ovaries - PID
conjunctivitis
trachoma --> blindness
```
73
What is a key feature of the Spirochaetes?
the endoflagellum
an internal flagellum that allows the bacteria to move through viscous fluids e.g. ECM
propels bacterium in a corkscrew motion
74
What are the 3 medically important genera of Spirochaetes?
Treponema pallidum
Borrelia burgdoferi
Leptospira interrogans
75
What disease does Borrelia burgdoferi cause?
Lyme's disease
76
What are the signs and symptoms of Lyme's disease?
bull's eye rash
flu-like symptoms
dissemination via lymph/blood to other organs causing neurological problems and arthritis
77
What is the case of leptospirosis and how is it transmitted?
animal urine - spread by mammals e.g. rodents whose urine comes into contact with mucous membranes or broken skin
78
What infection does Treponema palladium cause?
syphilis
79
What are the stages of syphilis?
1˚ - days/weeks post infection, localised infection - ulcer, highly transmissible
2˚ - 1-3 months post infection - systemic infection, skin, lymph nodes, joints, muscles
3˚ - several years post infection, gummas in bone and soft tissue, cardiovascular syphilis and neurosyphilis
80
What is the morphology of Proteobacteria?
rod-shaped bacilli
| EXCEPT - Neisseria - diplococci and Campylobacter/Helicopbacter = spiral
81
What is the morphology of Bacteroides?
rod-shaped bacilli
82
What is the morphology of Chlamydia?
EB- round
| RB- pleomorphic
83
What is the morphology of Spirochaetes?
spiral
84
What conditions do gut bacteria need to be able to survive?
Low oxygen
| so they are obligate anaerobes, facultative anaerobes and microaerophiles
85
Name two organelles which originated from bacteria
chloroplasts and mitochondria
86
which G- bacteria are easily cultured?
Enterobacteria
Vibrio
Pseudomonas
87
Which G- bacteria cannot be cultured in vitro?
```
Chlamydia (obligate intracellular parasite)
Treponema pallidum (obligate parasite)
```
88
Which G- bacteria are fastidious?
```
Legionella (charcoal)
Haemophilus (chocolate)
Bordetella
Neisseria
Campylobacter
Helicobacter
```
89
Name 3 G- organisms that can cause meningitis?
Neisseria meningitidis
some E. coli
Haemophilus influenzae
90
Name G- sp. that can cause resp tract infections
```
Bordetella pertussis
Haemophilus influenzae
Pseudomonas aeruginosa
Legionella pneumophila
Chlamydia pneumoniae
Klebsiella pneumoniae
```
91
Name 3 G- sp. that cause UTIs
E. coli
Proteus mirabilis
Pseudomonas aeruginosa
92
Name some G- sp. that cause wound infections
E. coli
Bacteroides fragilis
Pseudomonas aeruginosa
Klebsiella pneumoniae
93
Which three organisms cause STIs?
Neisseria gonorrhoeae
Chlamydia trachomatis
Trepnoema pallidium
94
Which G- bacteria are zoonoses (infectious diseases of animals that can be transmitted to humans)?
Leptospira interrogans - leptospirosis
| Borrelia burgdorferi- Lyme's
95
Which G- bacteria can cause systemic infections (i.e. is invasive)?
E. coli
Salmonella Typhi
Treponema pallidum
96
Which G- bacteria cause GIT infections?
```
Vibrio cholerae
Shigella dysenteriae
Salmonella enterica
E. coli
Campylobacter jejuni and coli
Helicobacter pylori
Bacteroides fragilis (abdominal wound infections)
```
