Gram staining, Culture , Antimicrobial sensitivity test

Gram stain

• Technique used to differentiate two large groups of bacteria based on their different cell wall constituents. ( peptidoglycan )

• Are they Gram positive or negative? • What is the morphology (rod, coccus, spiral,

pleomorphic [variable form] etc)? • Do cells occur singly or in chains, pairs etc? • How large are the cells?

N. Meningitidis

N. Meningitidis

H.influenzae

Streptococcus agalactae

Microbiological Culture

• Multiplying microbial organisms by letting them reproduce in predetermined culture media under controlled laboratory conditions.

Culture media

Solid vs broth Reducing

Non-synthetic vs chemically defined Selective

Differential

S.pneumoniae

H.Influenzae in chocolate agar

N.Meningitidis

Antibiotic sensitivity test

• Laboratory test determines how effective antibiotic therapy is against bacterial infections.

- Kirby-Bauer method - - Muller –Hinton agar

References

• http://serc.carleton.edu/microbelife/research_methods/microscopy/gramstain.html

• http://pathmicro.med.sc.edu/fox/culture.htm