Microbiology Flashcards
H Pylori is often acquired at age ——
Around ——–% of world population infected.
Acquired at young age (consequences later in life)
50% of world population infected.
H Pylori - routes of contraction
Direct contact, oral-oral, feacal-oral
H Pylori infection increases risk of:
Duodenal ulcer, gastritis.
Gastric ulcer.
Gastric carcinoma.
Gastric lymphoma.
Why does H Pylori produce ammonia?
To increase the pH and protect itself from highly acidic environments.
How does H Pylori produce ammonia?
By producing UREASE
H2O + H+ »_space;» ammonium bicarbonate
Gastroenteritis
illness caused by eating foods contaminated with microorganisms, toxins and poisons
Dysentery
Inflammation of intestine, causing diarrhoea associated with blood and mucus
(associated with tenesmus - cramping in rectal area)
Dysentery is commonly caused by ——-
shigella and campylobacter
Diarrhoea
> 3 unformed stools in a day when the subject has taken no laxatives
Bacillus cereus (key points)
REHEATING STARCHY FOOD (e.g. rice)
Short incubation (1-6hrs)
Vomiting
Lasts 24hrs
Staph aureus (key points)
FOOD LEFT AT ROOM TEMP (milk, meat, fish)
short incubation (1-6hrs)
Lasts 1-2 days
Both bacillus cereus and staph aureus usually cause {upper/lower} GI symptoms.
upper (e.g. vomiting)
Staph aureus has a preformed toxin called ———— causing ———–
enterotoxin B causes rapid absorption
Most common cause of food poisoning is ————
campylobacter
Campylobacter
key points
RAW POULTRY/RAW MILK (unpasteurised)
D&V (may be bloody), abdo pain, fever.
Lasts 2-10 days
**risk of Guillain Barre syndrome.
You are more likely to get ——– from raw chicken than salmonella
campylobacter
———— is the most common strain of campylobacter
Campylobacter jejuni
Salmonella is serotyped according to ———
O-antigen
Salmonella
key points
OUTBREAKS RAW MEAT, RAW EGG, RAW MILK. (can be transmitted from reptiles) D&V (unlikely to be bloody), abdo pain, fever. Lasts 2-7 days
Shigella
key points
CONTAMINATED food/water with lots of HAND CONTACT (salad/sandwiches/raw veg)
BLOODY DIARRHOEA/mucous, vomiting, abdo cramps, fever…
Lasts 2-7 days
Shigella toxin =
shiga toxin - type 1 and type 2
TYPE 2 IS WORSE
Shigella toxin - method of action
Toxin binds to receptors on renal cells, RBC’s and other cells»_space; inhibits protein synthesis»_space; cell death
E.coli (0157)
CATTLE/BEEF, RAW MILK - usually undercooked beef
Rare - outbreaks
BLOODY DIARRHOEA (may have vomiting, abdo pain)
Lasts 5-10 days
**risk of HUS
E.coli toxin =
verotoxin
Why do you not give antibodies for E. coli infection?
Increases risk of HUS
Verotoxin - method of action
binds to enterocytes»_space; inhibition of protein synthesis»_space; cell death»_space; provides verotoxin route to bloodstream»_space; cause death of vascular endothelial cells»_space; clots form within small vessels»_space; clots + verotoxin carried to kidneys»_space; renal cell death»_space; renal failure»_space; HUS
What is HUS?
Haemolytic-uremic syndrome
group of blood disorders characterized by low RBCs, acute kidney failure, and low platelets - caused by E. coli infection.
Most < 16 yrs old.
HUS - symptoms
Abdo pain, fever, pallor, petechiae (purple spots on the skin due to damaged blood vessels), oliguria.
Bloody diarrhoea but it may have stopped.
Why should antibiotics be avoided in the treatment of food poisoning?
Possibly E. coli - risk of HUS
Risk of antibiotic resistance
Illness is usually self-limiting
HUS may be precipitated by ———-
Antibiotics, antimotility, and NSAIDS.
Gastroenteritis + urinary symptoms suggesting kidney involvement =
HUS
HUS - investigations/management
Any patient with bloody stools gets tested
FBC, U&E’s, LFT, urine samples
Lactate dehydrogenase – chemical released from damaged cells
Must notify relevant health boards of any HUS cases.
Treatment is supportive
Must notify health protection unit of any —— infections
E. coli (0157)
———– and ———- infection both result in bloody diarrhoea
shigella and E. coli (0157)
*campylobacter may also cause bloody diarrhoea
Listeria
key points
THE FRIDGE ORGANISM - soft cheeses, deli meats, unpasteurised milk.
Fever, stiff neck, confusion, vomiting - pregnant women and immunocompromised at risk.
Incubation 3-70 days, lasts WEEKS.
C. Diff most commonly occurs when ——
the patient has been given hospital antibiotics
antibiotics kill normal competitive bowel flora, allowing C. diff overgrowth
C. diff can progress to ——-
pseudomembranous colitis or bowel perforation
Risk of C. diff is increased by ———
As well as hospital antibiotics, anything that reduces the acidity of the stomach can increase risk
e.g. PPI’s carry a risk
C. diff toxin =
Toxin A (enterotoxin) and Toxin B (cytotoxin)
What antibiotics increase the risk of C. Diff?
4Cs Cephalosporin Ciprofloxacin Co-amoxiclav Clindamycin
C. diff - symptoms
Watery diarrhoea.
Abdo pain and fever.
C. diff - treatment
Non-severe = Metronidazole oral (10 days).
Severe: Vancomycin oral + Metronidazole IV (10 days).
Rotavirus
key points
Usually children in nurseries (most common cause of diarrhoea in kids under 3)
Mild, watery profuse diarrhoea (bloody = RED FLAG) - rehydrate
Incubation 48hrs, lasts a week
Norovirus
key points
CRUISE SHIPS, WARDS, NURSING HOMES (can be contracted from shellfish)
Highly infectious.
Explosive D&V (no blood) - rehydrate
Incubation 48hrs, lasts 1-3 days
In gastroenteritis, all stool samples get tested for ————
salmonella, shigella, campylobacter, E.coli 0157 and cryptosporidium
Gastroenteritis - investigations
stool culture, stool microscopy, stool toxin and stool PCR
In gastroenteritis,
if suspected bacteria - investigation =
if suspected virus - investigation =
if suspected protozoa - investigation =
bacteria = stool culture
( or stool toxin for c. diff or E. coli)
virus = stool PCR
protozoa = stool microscopy (for cysts)
In gastroenteritis, do a stool culture if ——– are suspected, and do a stool toxin if —- are suspected.
Stool culture = salmonella, campylobacter
Stool toxin = c. diff, E. coli
Gastroenteritis - treatment
No antibiotics - except to treat c. diff.
Rehydration = key
Someone who has been at a BBQ and thought the burgers looked funny
E.coli
Someone who had been at a Chinese buffet/had reheated a takeaway with rice
Bacillus cereus
Someone remembers eating a cream cake that had been left out
Staph aureus
Care home where many of its residents have diarrhoea and some aren’t urinating
HUS - E.coli
Tropical gastroenteritis - causes
Someone travelling + doing one of the following:
Swimming in lakes
Drinking water from local taps
Sexual activity
Insect bites
Did they get vaccinations before they left
Acute travellers diarrhoea
3 loose stools in 24hrs on the back of travelling (1/3rd have fever also)
Acute travellers diarrhoea - causative organism
Usually enterotoxigenic e. coli
If returned from cruise ship = noro/rotavirus
Acute travellers diarrhoea - management
Stool culture
Rehydration
Current travellers = single dose of ciprofloxacin
Cholera
Drinking water contaminated with faeces
Profuse watery diarrhoea (RICE-WATER STOOLS)
Massive fluid loss
Toxin mediated
Enteric fever
Common Fever, headache, abdo pain (also GI bleeding and perforation) Either TYPHOID (salmonella typhi - most severe) or PARATYPHOID (s. paratyphi)
Enteric fever usually occurs in what scenario?
patients who are returning from SE Asia and the Indian subcontinent
Enteric fever - clinical findings
Abdominal tenderness
Hepatosplenomegaly
Enteric fever - management
Patients need isolated immediately
If unstable (septic) = IV ceftriaxone
Otherwise use oral ciprofloxacin
Resistant cases = azithromycin in fluoroquinolone
Amoebiasis
Protozoa - POOR SANITATION
Protozoa lives in cysts»_space; once ingested. emerge. multiply.
Can often cause liver abscesses
Intermittent diarrhoea, upper abdo pain/discomfort, fever, sweats, nausea, headaches
Amoebiasis - investigations
Stool MICROSCOPY
Abdominal x-ray (for toxin mega colon)
CXR (may show raised right hemi-diaphragm)
May need endoscopy, biopsy
Amoebiasis - management
Metronoidazole
Paramomycin (used to clear gut lumen of parasites)
Giardiasis
Protozoa
Affects duodenum/proximal jejunum
Watery, malodourous diarrhoea, bloating, flatulence, abdo cramps, weight loss
Giardiasis - investigation
Stool microscopy for cysts
PCR in developed countries
Giardiasis - treatment
Metronidazole/Tinidazole
Helminth Infections
Parasitic infection
Associated with eosinophilia
Parasite contracted from swimming in lake Malawi
Schistosomiasis (Flukes)
Parasite contracted from eating undercooked meat
Tape worms (Cestode)
Helminth Infections - diagnosis
Usually diagnosed by the passage of adult worm or eggs in the stool
