diagnosis of infection

Question 1

specimen types

Answer 1

urine 
swab
blood
tissue
sputum
feaces

Question 2

1)direct detection

Answer 2

detection of whole organism by microscopy

detection of component e.g antigen, nucleic acid

Question 3

microscopic

Answer 3

CSF in meningitis

gram negative diploccoci = neisseria

Question 4

antigen

Answer 4

clostridium difficile glutamata dehydrogenase antigen toxin detected using lateral flow

Question 5

nucleic acid

Answer 5

Neisseria meningitidis uses direct sequence specific target

streptoccocus pneumoniae amplify unknown sequence using 16s rRNA match with sequence in database

Question 6

uses of direct detection

Answer 6

establishes present of organism at one site
tests for non cultivable organisms
directs empirical therapy 
fast
epidemiological info

Question 7

limitations of direct detection

Answer 7

no info on susceptibility testing

Question 8

2) culture

Answer 8

isolation of the pathogen allows
identification
typing
susceptibility testing

Question 9

different culture media

Answer 9

clostridium perfringens requires anaerobic
mycobacterium obligate aerobe
bordetella pertussis is fastideous - fresh blood and potato starch

Question 10

fresh blood agar

Answer 10

non selective

nutricious

Question 11

mannitol salt agar

Answer 11

selects for halophile growth and pH indicator for fermenters

Question 12

MacConkey agar

Answer 12

bile salts select for enteric organisms
pH indicator detects lactose fermenter - turns red - E. coli
VPAT - selective for neisseria gonorrhea and campylobacter jejuni

Question 13

gram stain

Answer 13

gram positive = purple = peptidoglycan

negative = counter stain

Question 14

haemolysins

Answer 14

streptococcis
a haemolysins - strep pneumonia (resistant to optochin), strep viridans (oral)
B haemolysis - strep pyogenes

Question 15

oxidase test

Answer 15

test for cytochromes
pseudemonas positive = purple
fermenter = no cytochromes = negative = clear = e coli

Question 16

catalase test

Answer 16

differentiates streptococci with staphylococci

staph = positive = bubbles

Question 17

coagulase

Answer 17

staph aureus is positive

Question 18

biochemical tests

Answer 18

AI strips mini biochemical reactions

octal score looked up in a database

Question 19

maldi tof

Answer 19

time of flight analysis
mass spectrometer produces spectrum of bacterial proteins
compared to database of known spectra to produce ID

Question 20

culture uses

Answer 20

targeted antimicrobial therapy

Question 21

limitations of culture

Answer 21

cultivable organisms only

Question 22

succeptibility testing

Answer 22

viable organism
measure zone of inhibition
E- test gives MIC
BSAC

Question 23

3) immunological tests

Answer 23

detection of an immune response to infection

Question 24

antibody detection

Answer 24

ELIZA

IgM permits timing from initial infection

Question 25

seroconversion

Answer 25

requires a fourfold rise in antibody titre ie present at both 1/2 and 1/64

Question 26

IFN-y release assay

Answer 26

Tuberculosis

Question 27

antibody detection uses and limitations

Answer 27

confirms exposure to antigen
epidemiological info
restricted to patients with detectable antigen response - not in immunocomprimised
retrospective - usually too late to treat if immune response high