VLD 421: Veterinary Clinical Biochemistry and Laboratory Diagnosis-II (0+1)

INTRODUCTION

• Antibiotic sensitivity test (ABST) is a method for measuring invitro susceptability of microorganisms to antimicrobial agent.
• A physician cannot predict the susceptibility of a pathogen to an antibiotic agent just by identifying the etiological agent alone, owing to many factors.
• We have been using antibiotics from the day Alexander Fleming coming out with a drug called Penicillin, while he was working with staphylococci in 1929. 
• Using different antibiotics against microbes made them to defend by unleashing a tirade of genetic mechanisms to resist the drug action. Hence, it is mandatory for physician to go for an antibiogram before starting their therapeutic regime.
• There are several laboratory methods are available for measuring the in vitro susceptibility of bacteria to antibiotics.
• This includes disc diffusion, broth and agar dilution techniques.
• Both broth and agar technique may be used to measure the activity of an antibiotic, quantitatively against a given bacterial culture .
• After incorporating several standardized steps, the agar in vitro disc diffusion method developed by Bauer-Kirby (1966) has been proposed by the National Committee for Clinical Laboratory standards, is most convenient and widely used.
• In brief, this method involves preparing a uniform lawn of test bacterium on agar plate and placing paper disc, each impregnated with defined and known concentration of antibiotic.
• Then the plates are incubated and after 18 hrs, the zone of bacterial growth inhibition around the disc is measured and compared with standards to find out the sensitivity the bacteria to given antibiotic.