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WorksheetsLesson 7: ANTIMICROBIAL SUSCEPTIBILITY TESTING
Total questions: 27
Worksheet time: 57mins
ANTIMICROBIAL SUSCEPTIBILITY TESTING matchy
It measures the ability of an antibiotic or other microbial agent to inhibit the bacterial growth.
Principle
To determine whether the bacterial isolate is capable of expressing resistance to the antimicrobial agents for selected for treatment.
Primary Goal
a circular area around the spot of the antibiotic in which the bacteria colonies do not grow.
Zone of Inhibition
DISK DIFFUSION METHOD (KIRBY-BAUER Test)
The most common method for Antimicrobial Susceptibility Testing (AST)
Medium
Mueller-Hinton Agar (MHA)
ph level
7.2-7.4
temperature
35-37
depth of medium
4
FACTORS AFFECTING DISK DIFFUSION; wherein it should medium should be MHA
depth of the agar
pH of the media
Growth rate of the microbe
Amount of inoculum
Sustainability of the medium used
Standard: 0.5 McFarland/Barium Sulfate Suspension
99.5ml of 2% H2SO4 & 0.5ml of 1.175% BaCl2)
99.5ml of 1% H2SO4 & 0.5ml of 1.175% BaCl2)
99.0ml of 0.5% H2SO4 & 0.5ml of 1.175% BaCl2)
99.5ml of 1% H2SO4 & 0.7ml of 1.175% BaCl2)
not all antibiotics class are effective to all of your bacterial infections.
true
false
To maintain reproducibility and consistency in the resistance profile.
(a)
crucial in terms of the growth of the bacteria
PH
zone of inhibition
AST
Thickness of the agar
DISK DIFFUSION METHOD also known as
(a)
KIRBY-BAUER Test is:
aerobic, need co2
anaerobic, need co2
aerobic, no co2 needed
anaerobic, no co2 needed
Before performing AST, we have already pre-identified what specific bacteria is causing the infection of your patient.
t
f
15mm
Disk distance
150mm
12 discs
100mm
5-6 discs
avoid false resistance thru these except
Increase moisture
decrease ZOI
Increased drying
4mm thick agar
avoid false sensitivity thru these except
Increase moisture
increase ZOI
Increased drying
below 4mm - thin agar
(a) microorganism respond to therapy with that antimicrobial agent
microorganism falls into a range of susceptibility in which the MIC approaches or exceed the level of antimicrobial agent that can be achieved
(a)
bacteria is (a) since no zone or small zone of inhibition
Appearance of individual colonies is
unacceptable
acceptable
After planting your bacterial suspension in MHA, we should wait for at least 15 mins before application of antibiotics. this is applicable for avoiding
false sensitivity
false resistance
error in ZOI
false resistance
after 15 mins
(delay of disc application)
Increased moisture
That’s why we need to turn/invert our culture media
thickness of medium
4mm
Increased organism
decrease ZOI
Too turbid bacterial suspension which is not same with the turbidity of the McFarland solution
cause decrease zone of inhibition
false sensitivity
after 15 mins
(delay of disc application)
Increased drying
Temperature of the environment/incubator is increased too much
Thickness is below 4mm
Thin medium
Decreased organisms
Increase ZOI
DISK DIFFUSION METHOD
Pure inocula are obtained by selecting 4-5 colonies of the same morphology
false resistanceColonies are suspended into 0.85% NSS to achieve a turbid suspension.
Bacterial suspension and McFarland solution are compared by matching the turbidity of the tubes against a dark background.
Turn the plate 60 degrees between each streaking (Overlaping streaking)
Within 15 minutes of inoculation, antimicrobial agents are applied onto MHA. Within 15 minutes of disk placement, plates are inverted and incubated at 35°C for 16-18 hrs.
Diameter of each inhibition zone is measured by using
(a)
used for microbiology being used for microbial susceptibility testing.
(a)
caused by a strain of Staphylococcus bacteria that’s become resistant to oxacillin and methicillin.
(a)
HA-MRSA stands for
(a)
CA-MRSA stands for
(a)
Community – associated MRSA
Often begins as a painful skin boil. Spread by skin to-skin contact.
HEALTH CARE-ASSOCIATED MRSA (HA-MRSA)
Are associated with invasive procedures or devices, such as surgeries, intravenous tubing or artific
gold standard
To detect the mecA gene, is the most common gene that mediates oxacillin resistance in Staphylococci
Nucleic acid amplification test; example Polymerase chain reaction (PCR)
