Microbiology - Handbook

Question 1

Bacteriology - Diagnostic techniques

Answer 1

Direct examination
Culture
Antibody detection
Others

Question 2

Direct examination

Answer 2

Macroscopic - minutes. Appearance, colour, smell
Microscopic - hours. Gram stain - Positive stain (Purple), Negative stain (Pink)
Other stains - Acid fast, wet film, KOH (fungi), india ink (cryptococcus), dark ground (syphillis)

Question 3

Culture

Answer 3

Can take days or weeks due to fastidious organisms
Pus may be present
Swab - transport medium
Fluid - Urine, CSF, joint aspirate
Faeces
In laboratory there are 2 media - Solid and liquid
Solid media - blood agar and anaerobic
Liquid media - bacteria dilutes
Blood culture - aerobic and anaerobic broths

Question 4

Serology

Answer 4

IgM

Question 5

Others

Answer 5

Antigen detection
PCR
Gas liquid chromatography
Toxin detection

Question 6

Once bacteria have been stained they can immediately be detected by

Answer 6

Light microscopy

Question 7

Organism that is both gram-positive and coagulase-positive

Answer 7

Staphylococcus Aureus

Question 8

Sterile sites in the body where there should be no colonising organisms so any bacteria isolated from samples taken in these places will be either important pathogens or contaminants

Answer 8

Blood
CSF - Cerebrospinal fluid
Pleural fluid
Peritoneal cavity 
Joints
Urinary tract
Lower resp tract

Question 9

Other areas in the body are colonised with bacteria already (Flora)

Answer 9

Mouth 
Skin 
Genital tract
Urethra
Faecal

Question 10

Pathogens often have different growth requirements comapred to normal flora, thus conditions can be manipulated to promote growth of pathogens but restrict growth of flora

Answer 10

Atmosphere - air, CO2, anaerobic
Temp - 30, 37, 43C
Media - nutrients

Question 11

Media types

Answer 11

Blood agar - Sheep/horse blood. Good medium for growing many different types of bacteria
Chocolate agar - Blood agar heated to 80C for 5 minutes to release some nutrients into the agar to make it easier to grow certain organisms that do not grow as easily
MacConkey agar - Grows gram-neg bacilli and differentiates them into lactose-fermenters (pink) and non-lactose fermenters (white)
CLED - Differentiates organisms in urine
Gonococcus agar - Neisseria gonorrhoea
Sabouraud’s agar - Cultures fungi
XLD agar - Differentiates shigella and salmonella

Question 12

Most likely microbiological causes of dysenteric illness

Answer 12

Shigella

Salmonella