Microbiology Flashcards
What is the causative organism in TB? and how do you test for it?
Mycobacterium tuberculosis (acid alcohol fast bacilli). Test: Ziehl-neelson stain (turns blue to red)
What investigations are relevant to TB?
CXR - showing caseous necrosis.
PCR - gives specific info on organism (amplifies single copy of DNA)
What group of people are commonly affected by TB?
The middle-eastern population and the immunocompromised
What are the symptoms of infective endocarditis?
presence of new murmur. fever. embolic event/ sepsis of unknown origin. heart failure.
What investigations are done for endocarditis?
3 sets of blood culture. Echo
What are the signs of endocarditis?
Janeway lesions. Roth spots. Splinter haemorrhages. clubbing.
What is the most common cause of infective endocarditis? describe.
Staph. aureus. Gram positive cocci in clusters. Differentiated by coagulase test (positive).
What is the most common coagulase negative staphylococcus and what does it commonly infect?
Staph. epidermidis. Common skin comensal which infects prosthetic valves, IV catheter lines
What organism usually affects IV drug users in endocarditis and what valve is affected?
Staph. aureus. Tricuspid valve. (normally, endocarditis affects mitral or aortic valve)
What is a (alpha) partial haemolytic organism that causes endocarditis?
Strep. Viridans.
Strep. pneumonia also partial haemolytic, not related to endocarditis though
What is a non-haemolytic (gamma) organism that causes endocarditis?
Enterococcus spp.
Why do you give low dose gentamicin in endocarditis?
to prevent renal failure
What is the empirical treatment for endocarditis?
Amoxicillin IV + Gentamicin IV (low dose)
What is the treatment for endocarditis caused by Staph. aureus?
Flucloxacillin IV
What is the treatment for endocarditis caused by Strep. Viridans?
Benzylpenicillin IV + Gentamicin IV
What is the treatment for endocarditis caused by Staph. epidermidis?
Vancomycin IV + Gentamicin IV + Rifampicin (PO)
What is the treatment for endocarditis caused by Enterococcus spp.?
Amoxicillin/vancomycin IV + Gentamicin IV
What is the treatment for endocarditis caused by MRSA?
Vancomycin IV + Rifampicin PO
What is the treatment of right sided endocarditis?
Flucloxacillin IV
What are the two typical causes of pneumonia?
Strep. pneumonia + Haemophilus influenza
Give the symptoms of Strep. pneumonia.
rusty sputum. herpes labialis (cold sore)
gram positive cocci in chains
Describe pneumonia due to Haemophilus influenza.
Small gram negative bacilli. Common in COPD patients. Treat with amoxicillin, if allergic, doxycycline.
Describe pneumonia due to Mycoplasma pneumonia.
Common in children/ young bludz. Erythema multiforme. Dry cough. flu like symptoms.
Describe pneumonia due to Legionella pneumophila.
Suspect in patients who have travelled (colonises water tanks). DIARRHOEA. Test urine for antigens.
Describe pneumonia due to Staph. aureus.
Suspect in IV drug users. common complication of influenza virus.
What kind of pneumonia is due to goats/sheep?
Coxiella brunetti.
What kind of pneumonia is due to pet birds? what are its symptoms?
Chlamydia psittaci. mucoid sputum.
What is the treatment for severe CAP?
Clarithromycin IV + Co-amoxiclav IV
What is the treatment of moderate CAP?
Amoxicillin IV
What is the treatment of mild CAP?
Amoxicillin (po)
How do you determine the severity of CAP pneumonia?
Using CURB65 score.
Confusion. Urea > 7. Resp rate >= 30. BP systolic = 65. each criteria = 1 point.
0 - 1 = mild, 2 = moderate, 3+ = severe
What is the treatment of severe HAP?
(MAG) Metronidazole IV + Amoxicillin IV + Gentamicin IV
What is the treatment of non-severe HAP?
Metronidazole (po) + Amoxicillin (po)
Name two possible causative organisms of HAP.
E. coli
Klebsiella spp.
What organism should you suspect in an alcoholic patient with pneumonia? give symptoms.
Klebsiella spp. Red jelly sputum (due to aspiration pneumonia)
Which antibiotics act on the cell wall?
Cephalosporins (eg. ceftriaxone). penicillins. glycopeptides (eg. Vancomycin)
Which antibiotic acts on bacterial DNA?
Metronidazole
Name 2 macrolide antibiotics and its mode of action.
Clarithromycin. Erythromycin (safe for pregnancy). Acts on bacterial ribosomes.
What kind of antibiotic is Co-amoxiclav?
Beta-lactamase inhibitor
Which parts of the lung can compress the heart?
Right middle lobe. Left upper lobe.
What is the most common cause of GI infection in the UK.
Campylobacter jejuni
What is meant by the “source” and “vehicle” of infection?
source = where bacteria comes from eg. farm animal vehicle = how infection occurred eg. undercooked poultry
What is the source and vehicle of infection in Campylobacter?
source = farm animals vehicle = undercooked poultry, unpasturised milk
What is the incubation period of Campylobacter?
3 - 10 days
What are the symptoms of Campylobacter jejuni infection?
Abdominal pain. Diarrhoea ± blood. fever
Where does Campylobacter jejuni cause inflammation?
Colon and (rectum)—>hence the blood
How do you treat Campylobacter jejuni?
Usually self-limiting. However, if evidence of systemic illness - erythromycin (or ciprofloxacin)
What is the source and vehicle of infection of Salmonella enterica?
Source = farm animals vehicle = undercooked poultry
What are the symptoms of Salmonella enterica infection?
Diarrhoea. VOMITTING. fever. Abd cramps.
What is the incubation period of Salmonella enterica?
12 - 48 hours
How do you treat Salmonella enterica infection?
Usually self-limiting. If evidence of systemic ilness, give Ciprofloxacin.
Where does Salmonella enterica cause inflammation?
Ileum + colon
Which group does Shigella spp. often infect?
occur in vulnerable children
What is the source/ vehicle of infection in Shigella?
HUMAN only infection. Person-to-person spread.
How does Shigella go about its thaaang?
Causes severe inflammation of intestinal mucosa but does not invade any further (ie. blood stream, therefore no fever)
What is the incubation period of Shigella?
1 - 9 days
What are the symptoms of Shigella infection?
Acute watery, bloody diarrhoea.
How do you treat Shigella infection?
You don’t. Self-limiting. No antibiotics.
What is the “genus” name and “species” name of Escherichia coli
genus = Escheichia species = coli
In E. coli O157:H7, what do the O and H stand for?
O = surface antigen H = flagellar antigen
In infective endocarditis, if patient allergic to penicillins (eg. amoxicillin), what would you give instead?
VanCOmycin. (glyCOpeptides)
do not confuse with COPD = doxycycline
Name 2 other antibiotic groups (other than macrolides) and examples of each which act on bacterial ribosomes
tetracyclines (Doxycycline)
aminoglycosides (gentamicin)
How does E. coli O157 achieve its effects? what does this do?
by producing verotoxins, damaging RBC and the kidney, leading to Haemolytic-Uraemic Syndrome (HUS).
In HUS, what occurs?
Increase in RBC haemolysis. increase in blood urea levels.
Give me three facts about E. Coli O157
Commonest cause of renal failure in children (also affects elderly).
carried as part of the normal gut flora in cattle.
Beef is contaminated only on the outside surface.
What symptoms are caused by E. Coli O157 infection?
water, BLOODY diarrhoea. Abdo pain.
How do you treat E. Coli O157 infection?
You dinnay. Antibiotics are contraindicated as they may increase the release of verotoxins.
What is the incubation period of E. Coli O157?
1 - 9 days
What category does Campylobacter, Salmonella, Shigella and E. coli all fall under?
Gram negative bacilli
What is the incubation period of cholera and where is it commonly found?
1-9 days. Commonly found in disaster/war-zones.
How does cholera produce i’s effects? where and what does this do?
releases exotoxins which affect the cells of the small intestine, causing an outpouring of fluid
What are the symptoms of cholera?
severe watery diarrhoea - “rice-water stools”
causing severe dehydration
How do you treat cholera infection?
With fluid and electrolyte replacement. No antibiotics.
What is the source/ vehicle of cholera?
human only infection. Person-to-person spread.
What causes typhoid fever?
Salmonella tyhphi/paratyphi A + B
Describe typhoid fever.
It is a febrile illness to begin with (fever, flu-like symptoms), followed by diarrhoea 3 weeks later.
What is the incubation period of typhoid and the source/vehicle?
2-3 weeks. Human only infection, person-to-person spread.
What are the signs/symptoms of typhoid fever?
fever. followed by diarrhoea 3 weeks later. “rose spots” on abdomen (rash).
how do you treat typhoid fever?
with antibiotics eg. ciprofloxacin
What organisms are detected in stool microscopy?
(parasites)
Giardia lamblia
cryptosporidium
Enterobius vermicularis
Which organisms would you use toxin detection in stool for?
C. diff
E. coli O157
Which organisms would you use stool for culture?
campylobacter salmonella shigella vibrio cholera salmonella typhi
What do you use PCR for?
(viruses)
norovirus (most common cause of viral gastroenteritis in adults)
rotavirus (most common cause of viral gastroenteritis in kids)
Rhinovirus (most common cause of viral infection in adults causing common cold)
RespSynticalVirus (most common cause of bronchiolitis in kids)
Influenze A/B : A - worldwide pandemics (local epidemics)
B - localised endemics (expected)
What are the symptoms of Giardia lamblia infection?
(protozoal infection) diarrhoea, malabsorption syndrome, anorexia, abdo pain, flatulance
what antibiotic is used for Giardia lamblia infection?
oral Metronidazole
What is seen in the Enterobius vermicularis infection? who is usually infected? and what is a symptom?
tiny white thread like looking worms seen in stool. affects school children. peri-anal itch
what is a symptom of enterobious vermicularis infection and what antibiotic is used?
peri-anal itch. oral mebendazole.
What 3 GI infections are related to pre-formed toxins?
Staph. aureus
Clostridium perfringens
Bacilus cereus
How does staph. aureus cause its effects?
some strains produce an exotoxin called Enterotoxin. this enterotoxin is absorbed within 1-2hours of ingestion, causing vomitting.
How does Clostridium perfringens do its thing?
spores survive cooking which then release enterotoxins. vomitting, diarrhoea, abdo cramping within 12-48hrs.
What foods are clostridium perfringens, staph aureus and bacillus cereus associated with
clostridium perfringens: meaty gravy (part of normal gut flora in humans and animals)
staph aureus: cream cake
bacillus cerus: rice
How do you test for staph aureus (GI), clostridium perfringens and bacillus cerus?
test food for presence of toxins.