Flashcards in Microbiology Deck (101):
Host risk factors for GI infections (5)
Age - young and elderly
Reduced acid secretion
Reduced gut motility
What is the definition of diarrhoea?
three or more looses stools in a 24 hour period
What is the source or reservoir for an infection?
This is the original source of the infection e.g. animal gut
What is the vehicle of the infection?
The means by which the infection is transmitted from one person to another
Curved gram negative bacillus
What is the incubation period of campylobacter?
What is the mechanism of action of campylobacter?
Causes inflammation of the colon and rectum (presents as blood diarrhoea) and can invade and get into the blood stream
what is the source of campylobacter?
What is the vehicle of campylobacter?
uncooked poultry, water and unpasteurised milk
What are the symptoms of campylobacter?
abdominal pain and diarrhoea with or without blood
What is the treatment for campylobacter?
Erythromycin or Ciprofloxacin for 5 days if they develop systemic illness
What is the species name for food poisoning?
What is the incubation period for salmonella?
12 - 48 hours
What is the mechanism of action for salmonella?
Causes inflammation of ileum and colon, it multiplies in the gut and causes mucosal damage, decreasing fluid absorption and increasing fluid excretion. Can also invade and reach blood stream
What is the source of salmonella?
What is the vehicle of salmonella?
what are the symptoms of salmonella?
Abdominal pain, diarrhoea, sometimes bloody and vomiting
what is the treatment for salmonella?
Ciprofloxacin for 5 days if at risk of systemic illness
What is the incubation period of shigella spp?
1 - 9 days
what is the mechanism of action of shigella spp?
Invades intestinal mucosa causing severe inflammation, does not invade any further i.e. not in blood. Pus and blood seen in stool
what is the source of shigella spp?
What is the vehicle for shigella spp?
person to person
what are the symptoms of shigella spp?
Abdominal Pain, diarrhoea and occasionally blood
what is the management for shigella spp?
Symptomatic treatment – other species, caught abroad, cause a more sever infection, treat with ciprofloxacin
What is the source of action of Escherichia coli (E. Coli)?
Produces a toxin that damages red cells and the kidneys causing haemolytic-uraemic syndrome which increases blood urea, red cell haemolysis and thrombocytopenia
what is the source of E. Coli?
normal gut flora of cattle
What is the vehicle of E. Coli?
beef - mainly burgers and mince
What are the symptoms of E. Coli?
Abdominal pain and bloody diarrhoea
What is the management of E. Coli?
What are verotoxins?
Bind to receptors found on renal cells, RBC and others in the body. They inhibit protein synthesis and cause cell death
How does haemolytic ureamic syndrome present?
abdominal pain, fever, pallor, petechiae (haemorrhages in the skin) and decreased urine production (oliguria)
What indications show on a blood test fro HUS?
High white cells
Red cell Fragments
Lactate dehydrogenase increased
What is typhoid caused by?
salmonella typhi/Salmonella paratyphi A & B
How does typhoid initially present?
Initially present as headaches, flu-like symptoms and then diarrhoea three weeks later
When does salmonella typhi become typhoid fever?
when it reaches the blood stream
what is the incubation period for typhoid fever?
14 - 21 days
what is the mechanism of action of typhoid?
Organism invades from the gut lumen, to the lymphatic system and blood stream. It is then in the reticuloendothelial system and call bladder and back to the gut lumen
what is the source of typhoid?
What is the vehicle for typhoid fever?
person-person and contaminated water
what are the symptoms of typhoid fever?
Fever, rash on abdomen (rose spots) and Diarrhoea
what is the management of typhoid fever?
Antibiotics as required – resistance to ciprofloxacin is common
what is cholera caused by?
Vibrio Cholerae – a small curved gram negative bacillus
what is the incubation period of cholera?
1 - 9 days
what is the mechanism of action of cholera?
The organism produces an exotoxin which cause an outpouring of fluid from the small intestine creating sever watery diarrhoea
what is the source of cholera?
what is the vehicle for cholera?
what are the symptoms of cholera?
water diarrhoea (rice water) causing rapid dehydration
what is the management of cholera?
Fluid and electrolyte replacement – no antibiotics
Which GI infections are associated with the ingestion of pre-formed toxins?
What do the toxins of staph aureus act on?
vagus nerve and vomiting centre
what is cryptosporidium?
what is the mechanism of action of cryptosporidium?
Occurs when the cysts are ingested which hatch into the trophozoites in the small intestine and invade cells
what is the source of cryptosporidium?
what is the vehicle for cryptosporidium?
water supply and swimming pools
what are the symptoms of cryptosporidium?
diarrhoea - sever in HIV patients
what is the management of cryptosporidium?
What is Giardia lamblia?
A protozoal infection - a single celled parasite
what is the mechanism of action of Giardia lamblia?
Infection occurs when cysts are ingested which “hatch” into trophozoites that invade the cells of the upper small intestine
what is the source of Giardia lamblia?
what is the vehicle for Giardia lamblia?
what are the symptoms of Giardia lamblia?
diarrhea, malabsorption syndrome, anorexia, abdominal pain and flatulance
what is the management of Giardia lamblia?
What is Enterobius vermicularis?
white threadworm which passes in stool
what is the mechanism of action of the tapeworm?
ova eggs are ingested and hatch in the intestine. They live in the caecum and colon, adult females come out on the perianal skin at night and lay the ova which cause and itch
what is the source of a tapeworm?
what is the vehicle for a tapeworm?
what are the symptoms of having a tapeworm?
Perianal itch and worms in stool
what is the management of a tapeworm?
Oral mebendazole. Often have to treat all members of family at once
What is required when sending a stool sample to microbiology?
one pea sized specimen for each for microscopy, toxin test and culture
do not fill the container to the top
Give a separate specimen for virology
What is the commonest cause of healthcare-associated diarrhoea?
Clostridium difficile - C. Diff
What is the source of C. Diff?
Part of the normal gut flora in the elderly and infants
What is C. Diff's mechanism of action?
organsim produces 2 toxins - an enterotoxin and a cytotoxin
How does infection occur in C. diff?
when antibiotics prescribed kill off normal gut flora allowing c. diff to overgrow and produce spores which are more resistant
what are the symptoms of C. Diff?
Diarrhoea, sometimes bloody, abdominal pain. Severe cases may progress to pseudomembranous colitis or bowel perforation
what is the management for c. diff?
less severe = oral metronidazole
more severe = oral vancomycin
describe c. diff in terms of on a gram stain?
gram positive spore bearing bacilli
what is present on the surface of the colon in c. diff?
what tests can be done which would suggest c. diff?
Screening for GDH
If GDH positive then test for toxin A&B
Culture can be done - not routine
if the screening test and toxin test for c. diff is positive what does this suggest?
If the screening test for c. diff is positive but the toxin test is negative, what does this suggest?
indeterminate result - repeat specimen
what are the two main viruses which cause diarrhoea?
when will most children contract the rotavirus?
By aged 5
How is the rotavirus spread?
person-person either direct or indirect
What are the symptoms of the rotavirus?
diarrhoea without blood
how is dehydration caused in the rotavirus?
decreased absorption of fluids and an increased secretion in the bowel
what complications can occur in children post-infection of rotavirus?
malabsorption causing diarrhoea
how is the rotavirus diagnosed?
PCR test on faeces
What is the management of the rotavirus?
when is the rotavirus vaccination given and how often?
Twice - once at 2 months old and once at 3 months old
why is the rotavirus not given to children older than 24 weeks?
There is an increased risk of intussusception
what is intussusception?
One bit of bowel pushes into the other and cuts off the blood supply
How is the norovirus spread?
faecal oral/droplet routes person to person
what is the norovirus more commonly known as?
winter vomiting bug
what are the symptoms of the norovirus?
sudden onset of explosive diarrhoea and vomiting which lasts 2-4 days
How is norovirus diagnosed?
faeces specimen or vomit swab for PCR
What is the treatment for norovirus?
rehydration - especially in the elderly or very young
when are patients at their most infectious?
when vomiting or have diarrhoea
other than diarrhoea organisms, which other ones are spread the faecal-oral route?
Resistant bacteria in the GI tract
what are the standard infection controls for diarrhoea in hospitals?
patients placed in a single room
cohort nursing in bays
Increased ward cleaning
what contact precautions are used for the control of diarrhoea in hospital?
hand washing - not alcohol gel
gloves and apron
single use of equipment
disinfecting items with hypochlorite
report exposure of contamination