The document describes procedures for identifying gram positive bacteria and testing antibiotic sensitivity. Gram positive bacteria can be identified using colony morphology, gram stain, and confirming a gram positive result. To test antibiotic sensitivity, broth is incubated and subcultured onto agar plates. Antibiotic discs are placed on the plates, which are then incubated. Sensitivity is determined by measuring zones of inhibition, with no growth indicating sensitivity and growth within the zone indicating resistance.

1. Microbiology practical 3
( Gram +ve & Antibiotic sensitivity assay )
By : Osama Al-Zahrani
@OSAMA_Z96

2. Identification of gram positive bacteria & Antibiotic sensitivity testing
Identification of gram positive bacteria :-
Gram +ve bacteria can be identified in the lab by using different tests.
Here we well identify the bacteria by :
1- Colony morphology.
2- Gram stain.
( You can review this from first practical in hand out )
- The result of Identification must be ( Gram Positive Bacteria )

3. - Antibiotic sensitivity assay (testing) :
1- Incubation of broth.
2- Subculturing broth culture in (Mueller-Hinton) agar by sterile swab.
After these steps, put the antibiotic disc on the cultured agar, and put the agar
plate in the incubator for 24h.
- After incubation for 24h :
- If the zone of inhibition around antibiotic disc has no growth, means :
The organism is sensitive to this antibiotic.
- If the zone of inhibition around antibiotic disc has grown, means :
The organism is resistant to this antibiotic.

4. No growth around the
zone of inhibition
Antibiotic disc
Zone of inhibition After incubation for 24h :
- If the zone around the antibiotic disc has grown by
organism , means :
The organism is resistant to this antibiotic.
- If there are no growth of organism , means :
The organism is sensitive to this antibiotic.
- For example :
- The organism is sensitive to :
TS : Cotrimoxazole
KF : Cehpalothin
- The organism is resistant to the other antibiotic :
( CD & AP & PG & E )