Lecture 7 - Bacterial diarrhoea Flashcards
what are the symptoms of acute gastrointestinal illness?
- vomiting
- diarrhoea
- abdominal pain
- fever
what is dysentery?
bloody diarrhoea
what bacteria causes can lead to AGI?
- campylobacter
- cholera
- clostridioides difficile
- salmonella
- E coli
- etc
what causes lead to AGI in total?
- bacteria (common)
- viral
- protozoal
- toxin (staph aureus, non-microbial)
what are the sources or routes of transmission?
contaminated food, water or direct or indirect contact with feces
what is the most common microbial cause of diarrhoeal disease in NZ?
campylobacteriosis (~6000 cases per year)
how many children get diarrhoea disease each year?
1.7 billion, and 500,000 die
how many cases are there of cholera worldwide each year?
between 1.7-4 million, and 20,000 to 143,000 deaths
what is cholera rice water stool?
when profuse diarrhoea is so watery it looks like water rice had been boiled in
is cholera prevalent in new zealand?
no, there is hardly any cholera cases in NZ
what does vomiting and diarrhoea due to cholera lead to?
dehydration, often severe
where is cholera’s resevior?
in shellfish in waters and human carriers
how does transmission of cholera occur?
human carriers (feces into water - contamination)
- can be asymptomatic
or eat the shellfish of course
describe the colonisation of cholera
- survives passage through stomach
- colonises intestine, aided by a pilus for attachment
- produces toxin AB5
- stimulates Cl- secretion: secretory diarrhoea
what is the incubation period of cholera?
anywhere between 12h and 5 days
what is an infectious dose of cholera?
an infectious dose is between 10^5 and 10^8 CFU, but may be lower if stomach acid is not produced (food scarcity)
symptoms of cholera?
- vomiting
- rice water stools
- dehydration
how do we diagnose cholera?
- rice water stools very telltale symptom
- selective agar
- PCR tests (quicker)
- rapid diagnostic tests (quickest)
how does the selective agar select for cholera?
- high concentrations of thiosulphate and citrate inhibit enteric bacteria
- bile salts inhibit gram +ve bacteria
- TCBs select for vibrios such as cholera
how does the selective agar differentiate cholera?
- the agar plate contains sucrose and an indicator. when cholera ferments the sucrose, the pH drops and the green turns to yellow
- results overnight
how can a gram stain be used to diagnose cholera?
gram staining the rice water stools shows red curved rods
- gram negative bacilli
what are rapid diagnostic tests for vibrio cholerae and why are they not very reliable?
- dipstick which changes colour in presence of cholera
- high rate of false negatives
what are the treatment aims?
- oral rehydration therapy (or IV drip if severe)
- prevent the spread with good hygiene and sanitation
role of antibiotics in cholera?
recommended in severe cases
also in moderate cases if an epidemic
(cheap and bacteriocidic, but must be used after vomiting phase to retain)
which antibiotic is commonly used against cholera and why?
doxycycline
- it is cheap and bacteriocidal
how to prevent cholera?
- safe water
- good sanitation
- good personal hygiene
not essential but good: - nutrition
- vaccine?
what effect does doxycyline have on a patient with cholera?
- reduction in duration of symptoms (reduces the need for ORT/clean water)
- reduces shedding (reduces transmission routes)
gastroenteritis is often ____ _________
self limiting
- GP will say come back if your symptoms worsen or dont improve
how long does it take to get over gastroenteritis?
approx 10 days
why aren’t anti diarrhoeal drugs recommended when there is blood in the feces?
- stop the ‘flow’
- bacteria become more concentrated have more time in contact with the intestinal mucosa
when are anti diarrhoeal drugs okay to use?
when the diarrhea is only watery
why don’t we use antibiotics for campylobacter infections?
- they reduce the severity and duration of the diarrhoea, but it also damages the good gut flora/bacteria
- only recommended if severe or prolonged or spread infection
if antibiotics are administered for campylobacter, what antibiotics will be used?
macrolides
- but campylobacter resistance levels are increasing
what does stool microscopy of campylobacter show?
- not highly definitive due to many other bacteria in stool
- can see campylobacter (thin gram negative bacteria, looks like a skinny crinkle cut chip)
what other tests can we do for campylobacter?
- PCR tests
- cultures
what cultures can we use to test for campylobacter
- blood agar containing ABs that reduce emergence of other enteric bacteria
- microaerophilic
- other pathogens come back negative
sources of campylobacter?
- chicken
- heavy rainfall causes animal feces into water supply
transmission of campylobacter?
via the fecal oral route, and ingestion of contaminated food/water
- microorganism is ingested.
what is the course and symptoms of campylobacter?
incubation is 2-11 days
- vomiting
- diarrhoea
- fever
- sometimes bacteremia
duration is 3 days to 3 weeks
how often do people die from campylobacter?
not often, only about 1 in 8,000 cases
- infants or immunocompromised
- cross reactions
colonisation of campylobacter?
- has a flagella
- adhesins
- pili
- lipopolysaccharide for immune evasion (difficult to recognise - camouflage effect)
how does campylobacter cause damage?
toxins CLT (cholera like toxin - increases water secretion) and CDT (cytolethal distending toxin - leads to cell death)
what is a nosocomical diarrhoea?
hospital acquired
source of clostridioides difficile?
- part of the normal flora of the GI tract
- 5% carriers
- 20% in hospital (contamination from diarrhoea of another infected person)
who is most at risk with clostridioides difficile?
hospital patients receiving antibiotics (beta lactams and clindamycin and fluroquinolones)
- longer than 1 week in hospital
- other treatments that disrupt the colonic flora (removes competition)
colonisation of clostridioides difficile?
- other broad spectrum ABs reduce numbers of other competing colonic flora
- clostridioides difficile grows to high numbers
- may be sensitive to antibiotics but forms an endospore and survives them
what is an endospore?
- dormant survival structure, not used by many bacterium
- allows it to survive in hospital
how are endospores/clostridioides difficile killed?
heated to 121 degrees
sporicidal chemicals
what kind of aerobes are clostridioides difficile?
obligate anaerobes, which means they can’t survive in oxygen.
however the endospores can survive in oxygen
what are the bacterial virulence factors of clostridioides difficile?
- toxin A and toxin B of clostridioides difficile.
how does clostridioides difficile move into the cell?
- attachment
- RME
- pH increases and clostridioides difficile is released
- causes collapse of the actin cytoskeleton
how does clostridioides difficile effect the epithelia of the gut?
- rounding of epithelial cells cause loss of protection, allows toxin B and other bacteria to enter into the submucosa
- leads to epithelial cell death which forms a pseudomembrane (ulceration), and the submucosa underneath becomes inflamed.
- as this worsens, we get toxic megacolon
what diagnostic tests can we use for clostridioides difficile?
- early diagnosis is important for effective treatment
- antibody based assays
what antibody based assays do we use to diagnose clostridioides difficile?
for toxins and for GDH, a cell associated antigen
what diagnostic tests do we do if the antibody based assays come back negative?
- PCR for toxin genes
- gram stain for a gram positive bacilli
- patients will very likely have a raised WBC count
why don’t we use microscopy or cultures very often for clostridioides difficile diagnosis?
because many people carry this bacterium, so it could come back as present but not be what is causing the issue
how do we treat clostridioides difficile?
- discontinue implicated AB
- kill with an AB (metronidazole or vancomycin if resistant)
- support fluid loss and pain
- restoration of microflora/probiotics (fecal transplants to outcompete CD)
what must the ward do if there is a clostridioides difficile case?
- attention to hygiene and cleanliness, there is potential for an outbreak
- limit use of predisposing AB
- there is a 20% relapse rate
if clostridioides difficile became more serious e.g toxic megacolon, how would we treat it?
stronger antibiotic such as vancomycin
support fluid loss and pain
if clostridioides difficile looks to be getting better what do we do?
restoration of gut flora via fecal transplant or probiotics
