Gastrointestinal infections 1 Flashcards
Bacterial agents in GI infection,
split into two groups according to mechanism by which they cause illness:
(1) - _______
= bacteria develop in ___ after ingestion of contaminated food
Examples: 3
[incubation time ?]
(2) - _________ (poisoning)
= bacteria grow in foods and produce _____
Examples: 2
[incubation time?]
Bacterial agents in GI infection,
split into two groups according to mechanism by which they cause illness:
(1) - Infection
= bacteria develop in gut after ingestion of contaminated food
Examples: salmonella, campylobacter, E.coli
[incubation time ~12hr]
(2) - Intoxication (poisoning)
= bacteria grow in foods and produce toxins
Examples: bacillus cereus, staph aureus
[short incubation as toxin already made]
Clinical terminology
Have a think about what each of these are and their symptoms:
Diarrhoea
Gastroenteritis
Dysentery
Enterocolitis
Clinical terminology
Diarrhoea
- increased freq and fluid stool
- fluid n electrolyte loss
Gastroenteritis
- inflamm of stomach and intestines
- nausea, vomiting, diarrhoea, ab discomfort
Dysentery
- inflamm of large bowel
- blood and pus in faeces
- pain, fever, ab cramps
Enterocolitis
- inflamm affecting small and large bowel
- diarrhoea, nausea/vomting, ab cramps/pain, fever
Manifestations of GI infection
within GI tract
- toxin effect
- inflamm due to microbial invasion
outwith GI tract
- systemic effects of toxins
- invasive infection of GI tract with wider dissemination (spread)
Think of an example for each.
Manifestations of GI infection
within GI tract
- toxin effect e.g. severe diarrhoea from cholera
- inflamm due to microbial invasion e.g. shigellosis (shigella infection) [causes bloody diarrhoea]
outwith GI tract
- systemic effects of toxins e.g. STEC (Shiga Toxin producing E.Coli)
- invasive infection of GI tract with wider dissemination (spread)
e. g. metastatic salmonella infection
Transmission of GI infection
- faecal-oral
3Fs:
- Food (farm to fork, cross-contamination in kitchen)
- fluids (drinking water)
- fingers (after toilet, preparing food)
- person-to-person
Transmission of GI infection
- faecal-oral
3Fs:
- Food (farm to fork, cross-contamination in kitchen)
- fluids (drinking water)
- fingers (after toilet, preparing food)
- person-to-person
Aetiological diagnosis of GI infection can be made from history alone.
True of false.
False.
Laboratory diagnosis of GI infection
There are many many normal flora.
Finding pathogen like needle in haystack.
3 approaches:
- ________ ____ (?)
- _________ ____ (?)
- ________ ____ (?)
Best known example of _________ ____ is Salmonella and Shigella on non-lactose fermenter (NLF).
Laboratory diagnosis of GI infection
There are many many normal flora.
Finding pathogen like needle in haystack.
3 approaches:
- Enrichment broth (contains nutrients for preferential growth of pathogen)
- Selective media (suppress growth of background flora)
- Differential media (distinguishes different microorgansims on the same plate using colour indicators)
Best known example of Differential media are Salmonella and Shigella on non-lactose fermenter (NLF).
Treatment of GI infections
General points:
- most/mild GI infections resolve by _________
- ______ maintenance is crucial
Antibiotics:
- only for ______/______ symptoms
- can be bad for it (can prolong/exacerbate symptoms and can be harmful e.g. in ____).
Treatment of GI infections
General points:
- most/mild GI infections resolve by themselves
- hydration maintenance is crucial
Antibiotics:
- only for severe/prolonged symptoms
- can be bad for it (can prolong/exacerbate symptoms and can be harmful e.g. in STEC).
Control of GI infections
- many pathogens have animal/environmental reservoirs that cannot be eradicated
- therefore need to ‘break chain’ of infection:
> ______ ____ (clean drinking water, proper sewage disposal)
________ __ ___ ______ (hand hygiene, avoid cross-contam, proper cooking)
___________ __ ___ ___ ____
________ ____ ___ _______ (wash it, peel it, cook it, forget it)
Control of GI infections
- many pathogens have animal/environmental reservoirs that cannot be eradicated
- therefore need to ‘break chain’ of infection:
> public health (clean drinking water, proper sewage disposal)
education in food hygiene (hand hygiene, avoid cross-contam, proper cooking)
pasteurisation of milk and dairy
sensible travel food practices (wash it, peel it, cook it, forget it)
Campylobacter
think what you know for each one.
Overview: - - - -
-
-
-
-
Clinical pres: - - - - - -
-
-
-
Campylobacter
Overview:
- gram -ve bacilli (rods)
- microaerophilic + thermophilic (42degrees)
- culture on Campylobacter selective agar
- C. jejuni most important species
Epidemiology:
- commonest foodborne bacteria in UK (70% raw chicken)
- large animal reservoir (poultry, cattle, sheep etc)
- spread with contaminated food, person-to-person transmission rare
Patho:
- inflamm, ulceration and bleeding in small+large bowel due to bacterial invasion
- bacteraemia can occur
- rarely Guillain-Barre (‘post-infectious demyelination syndrome’ characterised by ascending paralysis)
Clinical:
- incubation 2-5 days
- bloody diarrhoea
- ab cramps/pain
- fever
- lasts 2-10 days
- vomiting not usually a feature
Treatment:
- fluids
- clarithromycin for severe
- quinolone (e.g. ciprofloxacin) or aminoglycoside (gentamicin) for invasive disease
Control points:
- reduce raw poultry contam
- fully cook
Salmonella
Think what you know for each one.
Overview: - - - -
Epidemiology: - - - -
-
-
Clinical pres: - - - - -
-
Salmonella
Overview:
- gram -ve bacilli
- member of enterobacteriaceae
- culture on non-lactose fermenters (NLF)
- XLD agar
Epidemiology:
- many animal carriers
- only two not in animals are S.Typhi and S.Paratyphi (cause typhoid fever and paratyphoid fever [these make up enteric fever] )
- food-borne, in contaminated meat n dairy
- secondary person-to-person transmission
Patho:
- diarrhoea due to invasion of epithelial cells in distal small intestine, which also causes inflamm
- bacteraemia can occur
- distant organs may establish metastatic foci of infection e.g. osteomyelitis, septic arthritis, meningtis
Clinical pres:
- incubation 12-72hours
- watery diarrhoea
- vomiting common
- fever (more assoc with invasive disease)
- lasts 2-7 days
Treatment:
- fluids usually sufficient
- antibiotics for severe and bacteraemia (b-lactams, quinolones, aminoglycosides)
Control points:
- immunisation of poultry reduced S.Enteritidis (salmonella. Enteritidis) dramatically
Shigella
Think about what you know for each.
Overview: - - - -
Epidemiology: - - - - -
-
-
Clinical pres: - - - - - - -
-
-
Shigella
Overview:
- gram -ve bacilli
- member of enterobacteriaceae
- 4 species: sonnei (mild), boydii (mod), flexneri (mod), dysenteriae (severe)
- culture on non-lactosing fermenters (NLF)
- XLD agar
Epidemiology:
- diarrhoeal disease common in children
- humans only reservoir
- does not persist in environment (unlike V.cholerae)
- person-to-person spread via faecal oral route (more common and important)
- contaminated food and water less important
Patho:
- bacteria attach and colonise mucosal epithelium of terminal ileum and colon
- systemic invasion is not a feature
- S.dysenteriae produces Shiga toxin –> damages glomerular endothelium as well as intestinal epith, causes renal failure as part of haemolytic-uraemic syndrome (HUS)
Clinical pres:
- dysentery (diarrhoea with blood or mucus)
- incubation 1-3 days
- duration 2-7 days
- initially watery diarrhoea followed by bloody diarrhoea
- marked ab cramps/pain
- vomiting is uncommon
- fever
Treatment:
- fluids
- usually self-limiting though
- some S.dysenteriae infection will require renal failure treatment
Control points:
- only in humans so good hygiene
Vibrio cholerae / V.cholerae
Overview: - - - -
Epidemiology: - - - -
-
-
-
-
OTHER pathogenic Vibrio species
Vibrio parahaemolyticus is a halophilic (likes high salt) bacteria that can cause diarrhoeal disease - contaminated fish in warm coastal waters
Vibrio cholerae / V.cholerae
Overview:
- gram -ve bacilli
- comma-shaped
- serotypes defined based on ‘O’ antigens, main ones: O1 and O139
- culture on sucrose-fermenter (use thiosulphate bile sucrose as differential media)
Epidemiology:
- causes cholera (severe watery diarrhoea)
- only infects humans
- can live in fresh water
- spreads via contaminated food or water
Patho:
- flagellae and mucinase facilitate penetration of intestine
- diarrhoea due to potent protein exotoxin
Clinical pres:
- severe non-bloody diarrhoea (rice water stool)
- profound dehydration causes hypokalaemia, metabolic acidosis, hypovolaemic shock and cardiac failure
- 30-40% mortality in untreated
Treatment:
- oral or IV rehydration (reduces mortality to <1%)
- tetracycline (e.g. doxycycline) can reduce duration of shedding
Control point:
- no animal reservoir, only humans, so clean water and sanitation (clean drinking water and disposal of sewage)
OTHER pathogenic Vibrio species
Vibrio parahaemolyticus is a halophilic (likes high salt) bacteria that can cause diarrhoeal disease - contaminated fish in warm coastal waters
Escherichia coli / E.coli
Overview:
- gram __, ______
- member of _____________ family (important gut flora members in man and animal, although some strains can cause infection)
SIX DIFFERENT DIARRHOEAL GROUPS OF E.COLI:
- - - - - -
These will be discussed individually on other cards.
Memory aid:
if you take the second letter of each one (e.g. ET-EC would be T) then you can spell ‘pad thai’ (includes D and A from DA-EC)
Escherichia coli / E.coli
Overview:
- gram -ve bacilli
- member of enterobacteriaceae family (important gut flora members in man and animal, although some strains can cause infection)
SIX DIFFERENT DIARRHOEAL GROUPS OF E.COLI:
- EP-EC = enteropathogenic E.coli
- ET-EC = enterotoxigenic E.coli
- EH-EC = Enterohaemorrhagic E.coli
- EI-EC = Enteroinvasive E.coli
- EA-EC = Entero-aggregative E.coli
- DA-EC = diffuse aggregative E.coli
These will be discussed individually on other cards.
Memory aid:
if you take the second letter of each one (e.g. ET-EC would be T) then you can spell pad thai (includes D and A from DA-EC)
____ = _____________ E.coli
- diarrhoea in infants and children and traveller’s
- adherence via pili followed by “attaching and effacing” / A/E lesion which is mediated by intimin protein binding to Tir (translocated intimin receptor)
- causes disruption of intestinal microvilli
- incubation 1-2 days, lasts weeks
- watery diarrhoea with ab pain and vomiting
- fever
EPEC = Enteropathogenic E.coli
- diarrhoea in infants and children and traveller’s
- adherence via pili followed by “attaching and effacing” / A/E lesion which is mediated by intimin protein binding to Tir (translocated intimin receptor)
- causes disruption of intestinal microvilli
- incubation 1-2 days, lasts weeks
- watery diarrhoea with ab pain and vomiting
- fever
____ = ___________ E.coli
- major bacterial cause of diarrhoea in infants and children and traveller’s
- diarrhoea due to plasmid-encoded toxins:
> LT (heat-labile toxin) - analogous to cholera toxin
> ST (heat-stable toxin) - similar mode of action - incubation 1-7 days, duration 2-6 days
- watery diarrhoea with ab pain and vomiting
- no fever
ETEC = Enterotoxigenic E.coli
- major bacterial cause of diarrhoea in infants and children and traveller’s
- diarrhoea due to plasmid-encoded toxins:
> LT (heat-labile toxin) - analogous to cholera toxin
> ST (heat-stable toxin) - similar mode of action - incubation 1-7 days, duration 2-6 days
- watery diarrhoea with ab pain and vomiting
- no fever
