In recent years, there has been a serious outbreaks of infection and increase in morbidity and mortality rate due to rise in drug-resistant bacteria. Although defining the precise public health risk and estimating the increase in costs emergent antibiotic resistance is a serious global problem.
No doubt that the antimicrobial drug has unquestionable benefit. An important job for the clinical microbiology laboratory is to perform antimicrobial susceptibility testing of significant bacterial isolates. The antibiotic susceptibility testing is important for confirming the presence of bacterial infection, identifying the responsible pathogen and directing antibiotic choices. The goals of testing are to detect possible drug resistance in common pathogens and to assure susceptibility to drugs of choice for particular infections. The test is done to help choose the antibiotic which will be the most effective against the specific types of bacteria or fungus infecting an individual person.
According to studies, the availability of microbiological and epidemiological information would help clinicians while selecting the appropriate antimicrobial agent for the treatment of a microbial infection. If predictions are to be valid, the susceptibility test must be performed by an accurate and reproducible method, the results of which should be directly applicable to the clinical situation. The ultimate criterion of the reliability of any susceptibility testing method is its correlation with the response of the patient to antimicrobial therapy.
Keeping all such parameters in mind as well as interests of professions, government and industries, TM Media offers wide range of antibiotic disc as per CLSI (Clinical Laboratory Standards Institute) standard for the end users especially belonging to clinical diagnostic and pharmaceuticals. The purpose of the Antimicrobial Susceptibility Testing (AST) is to determine the selectivity or resistance of pathogenic microbes to various antimicrobial compounds. The findings of these tests are the basis of assisting the clinical laboratories and selecting the appropriate antimicrobial agent for treatment against the infection.
TM Media play a great role in Dried Disc technique which offers a lot many advantages over the conventional wet method like easy operation and test simplicity. They are easily manipulated; they can be kept for several weeks without loss of potency, but weekly control tests must be taken care of. Dried discs are readily prepared for a standard size and impregnated with a constant amount of antibiotic so that zones of inhibition are given only by organisms whose sensitivity is within therapeutic limits. Recommended concentrations are added to each disc like Amikacin (30 mcg), Azithromycin (15 mcg), Cefepime (30 mcg), Meropenem (10mcg), etc.
TM Media’s Antibiotic test discs are majorly used for determination of susceptibility of bacteria and fungi to antimicrobial agents, applying Kirby-Bauer method*, also known as the Disk Diffusion method. There are various methods to detect the extent to which bacteria are affected by those antibiotics. Only because of convenience, efficiency and cost, the Disk Diffusion method is probably the most widely used method for determining antimicrobial resistance. The test compares the antibiotic’s ability to prevent bacterial growth to a common set of standards created by the CLSI, in order to assure its functionality at a certain concentration
Fig: Antibiotic drug susceptibility test by agar diffusion technique.
*Kirby-Bauer test or Disc diffusion method is one of the classic microbiology techniques and it is very commonly used around the world. Kirby-Bauer test or Disc diffusion method is based on the principle that Muller Hinton Agar (TM Media product code- TM 339), is first evenly seeded throughout the plate with the isolate of interest that has been diluted at a standard concentration. MHA is considered as the best medium for routine susceptibility test because it has good reproducibility, low in sulfonamide, trimethoprim, tetracycline inhibitors and gives satisfactory growth of many bacterial pathogens. Antibiotic disks, each of which are pre-impregnated with a standard concentration of a particular antibiotic, are then evenly dispensed and lightly pressed onto the agar surface. The test antibiotic picks up moisture and immediately begins to diffuse outward from the disks, creating a gradient of antibiotic concentration in the agar such that the highest concentration is found close to the disk with decreasing concentrations further away from the disk. After an overnight incubation, the bacterial growth around each disc is observed. If the test isolate is susceptible to a particular antibiotic, a clear area of “no growth” will be observed around that particular disk.
The zone around an antibiotic disk that has no growth is referred to as the zone of inhibition since this approximates the minimum antibiotic concentration sufficient to prevent growth of the test isolate. This zone is then measured in mm and compared to a standard interpretation chart used to categorize the isolate as susceptible, intermediately susceptible or resistant.
TM Media provides antibiotic in three different packaging i.e. cartridges/vial/Blister for dispensing with or without a dispenser (depending on packaging size). Antibiotic disks are packed in containers along with silica gel, designed to ensure appropriate anhydrous conditions before and during cartridges use. The diameter of the paper disk is 6mm and the antibiotic code is printed on both sides of each disk.
The range of widely used TM Media’s Antibiotic Disks:
|PRODUCT NAME||PRODUCT CODE||TECHNICAL DATA|
|CARBENICILLIN||TBD 047||CLICK HERE|
|CEFEPIME||TBD 049||CLICK HERE|
|COLISTIN (METHANE SULPHATE)||TBD 054||CLICK HERE|
|ERTAPENEM||TBD 055||CLICK HERE|
|FAROPENEM||TBD 056||CLICK HERE|
|FLUCONAZOLE (Antifungal)||TBD 057||CLICK HERE|
|GATIFLOXACIN||TBD 058||CLICK HERE|
|GENTAMICIN||TBD 060||CLICK HERE|
|LEVOFLOXACIN||TBD 062||CLICK HERE|
|LINEZOLID||TBD 063||CLICK HERE|
|MOXIFLOXACIN||TBD 065||CLICK HERE|
|OXACILLIN||TBD 066||CLICK HERE|
|PIPERACILLIN /TAZOBACTUM||TBD 068||CLICK HERE|
|STREPTOMYCIN||TBD 071||CLICK HERE|
|TEICOPLANIN||TBD 072||CLICK HERE|
|TICARCILLIN||TBD 073||CLICK HERE|
|MEROPENEM||TBD 028||CLICK HERE|
|CEFIXIME||TBD 010||CLICK HERE|
|CEFUROXIME||TBD 015||CLICK HERE|
|CIPROFLOXACIN||TBD 018||CLICK HERE|
|CO- TRIMOXAZOLE (SULPHAMETHOXAZOLE/TRIMETHOPRIM||TBD 022||CLICK HERE|
|ERYTHROMYCIN||TBD 024||CLICK HERE|
|GENTAMICIN||TBD 025||CLICK HERE|
|PENCILLIN- G||TBD 034||CLICK HERE|
|VANCOMYCIN||TBD 044||CLICK HERE|
|TETRACYCYLINE||TBD 040||CLICK HERE|
|STREPTOMYCIN||TBD 039||CLICK HERE|
Apart from this, there are a number of critical steps in this approach where it is important to take care, such as the type of medium used; depth and moisture content of the agar in the plate; incubation conditions; accurate inoculum density; storage conditions; discs must be firmly placed in contact with the agar surface otherwise the diffusion rate will not be correct.
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