Microbiology 1 (Dr Orange) Flashcards
What host factors affect your risk of gastrointestinal infection? (5)
Age (very young and elderly) Decreased gastric acid secretion Decreased gut motility Influence of colonic microflora Intestinal immunity
What bacterias seen in the UK cause Gastrointestinal infections? (8)
Campylobacter coli/ jejuni Salmonella enterica E coli O157 Shigella sonnei Staph aureus/ Clostridium perfingens/ Bacillus cereus C difficile
What viruses seen in the UK cause gastrointestinal infections? (2)
Norovirus
Rotavirus
What parasites seen in the UK cause gastrointestinal infections? (2)
Cryptosporidium sp
Giardia lamblia
What bacterias, usually imported from abroad, case gastrointestinal infections?
Vibrio cholerae/ parahaemolyticus
Salmonella typhi/ paratyphi
Aeromonas sp.
Shigella dysenteriae/ flexneri/ boydii
What parasite, usually imported from abroad, can cause GI infections?
Entamoeba histolytica
What is diarrhoea?
3 or more loose stools in 24 hours
What is the source/ reservoir of infection?
The original source of the infection e.g. animal gut, another human’s gut, etc.
What is the vehicle of infection?
The means by which the infection is transmitted from one person to another (e.g. contaminated food/ water)
What is the source and vehicle of infection of E. coli O157
Source = cattle GI tract
Vehicle of infection = undercooked hamburger
What shape is camplobacter (C. jejune, C. coli)?
Curved gram negative bacilus
What is the commonest cause bacterial GI infection in the UK?
Campylobacter
Incubation period of campylobacter?
3-10 days
How does campylobacter make you unwell?
Causes inflammation of the colon and rectum leading to bloody diarrhoea
Can invade and occasionally get into bloodstream (patients get systemically unwell with flu like symptoms)
What is the main source/ vehicle of infection of campylobacter?
Undercooked poultry + other farm animals, water and unpasteurised milk (person to person spread is rare - outbreaks usually because consumed the same chicken)
Symptoms of campylobacter?
Abdo pain
Diarrhoea =/- blood
Management of campylobacter?
Usually self limiting but give ERYTHROMYCIN or CIPROFLOXACIN for 5 days if patient develops systemic illness
What does “enteric” in Salmonella enterica mean?
It is the agreed species name for all food poisoning i.e. non-typhoidal salmonella (often still called by species name e.g. S. enteritiditis, S. typhimurium, etc.
What is the incubation period for Salmonella enterica?
12 - 48 hours
What is the mechanism of action of Salmonella enterica?
Causes inflammation of the ileum and colon - multiply in gut and cause mucosal damage, decreased mucosal damage and increased fluid excretion
Can invade and occasionally get into bloodstream
What is the source/ vehicle of infection of salmonella enterica?
Undercooked poultry + other farm animals (much less common since immunisation of poultry against Salmonella spp.)
Symptoms of salmonella enterica?
Abdo pain
Diarrhoea (occasionally bloody)
Vomiting
Management of salmonella?
Usually ciprofloxacin for 5 days if patient at risk of or develops systemic illness
What type of Shigella is seen in the UK?
Shigella sonnei (most benign type) - outbreaks occur every few years amongst cohorts of vulnerable children
Incubation period for Shigella sonnei?
1-9 days
Mechanism of action of Shigella sonnei?
Invades intestinal mucosa causing severe inflammation, but does not invade further (never seen in blood cultures)
What is seen in the stools of a patient with Shigella?
Blood and pus cells
Source/ vehicle of infection of Shigella?
Human only infection
Often spread person- person amongst young children in schools, etc.
Symptoms of shigella Sonnei?
Abdo pain
Diarrhoea (occasionally blood)
Management of Shigella sonnei?
Usually self-limiting - symptomatic treatment only
Other species of Shigella (dysenteriae, etc.) acquired abroad, usually require Ciprofloxacin due to more severe infection
What strain of E coli produces a toxin that damages red blood cells and the kidneys?
The O157:H7 strain (and a few other serotypes)
What type of toxin does E coli O157 produce and what does this do?
verotoxin (VTEC)
Damages red cells and the kidney, causing haemolytic-uraemic syndrome (HUS)
(increased blood urea, red cell haemolysis and thrombocytopenia)
Who are most at risk of developing HUS?
Children
What is the source/ vehicle of infection of E coli O157?
Carried as part of the normal gut flora in cattle
Beef becomes contained on the outside at slaughter = increased risk from minced meat and hamburgers than from a steak
Nursery/ school visits to farm
Private (untreated) water supplies = run off water from fields
Low infecting dose, so person-person spread causes 2y cases
Symptoms of E coli O157?
Abdo pain
Bloody diarrhoea is common
Management of E coli O157?
Symptomatic and supportive treatment only
Antibiotics contraindicated as may increase release of toxin
Check bloods for HUS 1 week after onset of symptoms
What does verotoxin do?
Binds to receptors found on renal cells, RBC and others
Inhibits protein synthesis
Causes cell death
Clinical presentation of HUS?
Abdo pain Fever Pallor Petechiae Oliguria (decreased urine production) Bloody diarrhoea in 90% of cases Mostly in under 16s
When is the peak presentation of HYS?
7-10 days after onset of diarrhoea
What does blood tests show which indicates HUS? (5)
High white cells Low platelets Low Hb Red cell fragments Lactate dehydrogenase (increased 1.5 times normal)
Appearance of Salmonella, Shigella and E coli O157 on gram film?
What is used to differentiate between these?
Gram negative bacilli
Biochemical tests, then serological tests
What bacteria causes typhoid and paratyphoid fever?
Salmonella typhi/ salmonella paratyphi A and B
What are the symptoms of typhoid/ paratyphoid fever?
Initially a febrile illness (bacteria circulating in bloodstream) causing headache, flu-like symptoms followed by diarrhoea 2 weeks later
When is typhoid/ paratyphoid seen in the UK?
When it has been imported from abroad
Incubation period of typhoid/ paratyphoid fever?
14 - 21 days
Mechanism of action of typhoid/ paratyphoid?
Organism invades from gut lame -> lymphatic system -> bloodstream -> reticuloendothelial system and gall bladder -> gut lumen and invades Peyer’s patches
In chronic carriers of typhoid/ parathyroid, where does the bacteria reside?
The gallbladder
What can happen during the bacteraemic phase of typhoid/ paratyphoid?
Distant sites can become infected e.g. ostemyelitis
Source of salmonella typhi/ paratyphi?
Human only infection
Spread person-person or from drinking contaminated water/ eating contaminated food/ poor sanitation (different from entericas which are associated with animals)
Symptoms of typhoid/ paratyphoid?
Fever
Rash on abdomen (“rose spots”)
Diarrhoea
Management of Typhoid/ paratyphoid?
Antibiotics are required, choice depends on sensitivities. Resistance to ciprofloxacin
What causes cholera?
Vibrio cholerae (“the comma bacillus”)
What is the appearance of Vibrio cholera?
Small curved gram negative baciluus
Where are outbreaks of cholera common?
In disaster/ war stricken situations
Incubation period of cholera?
1-9 days
Mechanism of action of cholera?
Organism produces an exotoxin that causes active outpouring of fluid from cells of small intestine resulting in severe watery diarrhoea
Source/ vehicle of infection of Vibrio cholerae
Human only infection - spread person-person or from drinking contaminated water/ poor sanitation
Symptoms of cholera?
Watery diarrhoea “rice water stools” causing rapid dehydration
Management of cholera?
Fluid and electrolyte replacement
Antibiotics NOT indicated
What causes GI infections associated with ingestion of pre-formed toxin? (3)
Staph aureus
Clostridium perfingens
Bacillus cereus
What is an enterotoxin?
A protein exotoxin released that targets the intestine
What is the typical scenario where Staph aureus is passed on through food?
Bakery worker with infected finger touches cream cake
Staph aureus multiplies producing enterotoxin (exotoxin)
Customer ingests enterotoxin
What does ingestion of staph aureus enterotoxin cause?
Acts directly on vagus nerve and vomiting centre inducing vomiting within 1 - 2 hours
What is the appearance of clostridium perfingens?
Large gram positive anaerobic bacillus
Where is clostridium profanens normally found?
Part of the normal gut flora in humans and animals
How does clostridium perfringens cause infection?
Spores survive cooking, then turn into vegetative organism some strains of which produce enterotoxin (an exotoxin)
What is clostridium perfringens infection associated with?
Inadequately refrigerated re-heated meat gravy
What is the appearance of bacillus cereus?
Large gram positive aerobic bacillus
How can a patient contract bacillus cereus?
Exotoxin can be ingested as pre-formed toxin in food
Organism can multiply in intestine, producing toxin that is absorbed from the gut
Spores survive cooking, then turn into vegetative organisms that produce toxin
What is bacillus cereus infection associated with?
Contaminated inadequately refrigerated reheated rice
What 2 bacterias have short incubation periods? (1-6 hours)
Staph aureus
What 2 bacterias have a medium incubation period? (12-48hours)?
Salmonella
Cl perfrigens
What 2 bacteria have a long incubation period? (2-14 days)
Campylobacter
E coli O157
Cryptosporidium and Giardia lamblia are both protozoal infections - true/ false?
True
Mechanism of action of cryptosporidium?
Infection occurs when cysts are ingested which “hatch” into trophozoites that invade the cells of the small intestine
Source/ vehicle of infection of cryptosporidium?
Domestic animals, especially calves
Person-person spread
Outbreaks associated with contaminated water supplies and swimming pools (cysts resistant to chlorine)
Symptoms of cryptosporidium?
Diarrhoea
Particularly severe in HIV pos patients
Management of Cryptosporidium?
Symptomatic treatment only
What type of stain can be used to identify cryptosporidium cysts?
Ziehl-Neelson stain (pink cysts against blue background)
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
Source/ vehicle of infection of Giardia lamblia?
Human only infection
?person to person spread
Outbreaks associated with contaminated water supplies
Symptoms of Giardia lamblia?
Diarrhoea Malabsorption syndrome Anorexia Abdominal pain Flatulence
Management of Giardia lamblia?
Oral metronidazole
What is the more commonly used name for Enterobius vermicularis?
Threadworms
Pathogenesis of thread worms?
Ova (egg) ingested -> hatch in intestine and live in caecum and colon -> adult females come out on to perianal skin at night and lay ova -> ova cause perianal itch -> child scratches bottom -> puts fingers in mouth
Source/ vehicle of transport of enterobius vermicularis?
Human only infection
Person-person spread (poor hygiene)
Symptoms of Enterobius vermicularis?
Perianal itch
Worms seen in stool
What is the treatment for Enterobius vermicularis?
Oral mebendazole (often have to treat all members of family at once)
What must be done if blood is seen in the patients stool?
Stool must be sent to ref lab for E coli verotoxin detection
When sending a stool sample to the lab for testing, what must you tell the lab if the patient has been abroad?
Where they were
