Saran's Learn Microbiology

  ANTIBIOTIC SENSITIVITY TEST Aim             To determine the sensitivity (sensitive or resistant) of Antibiotics against bacterial pathogens. Principle             An antibiotic sensitivity (or susceptibility) test is done to help choose the antibiotic that will be most effective against the specific types of bacteria infecting an individual person. One method that is used to determine antibiotic susceptibility is the sensitivity disk method of Kirby - Bauer (named after W. Kirby and A. W. Bauer in 1966). In this method, antibiotics are impregnated onto paper disks and then placed on a seeded Mueller-Hinton agar plate using a mechanical dispenser or sterile forceps. The plate is then incubated for 16 to 18 hours, and the diameter of the zone of inhibition around the disk is measured. The inhibition zone diameter that is produced will indicate the susceptibility ...

  ANTIMICROBIAL RESISTANCE ·     Antimicrobial resistance happens when microorganisms change when they are exposed to antimicrobial drugs. Microorganisms that develop antimicrobial resistance are sometimes referred to as “Superbugs”. ·       Antimicrobial resistance happens when microorganisms develop the ability to defeat the drugs designed to kill them. That means the germs are not killed and continue to grow. ·     Among the major challenges facing microbiologists today are the problems presented by pathogens that are resistant to antimicrobial agents. ·        As a result of Antimicrobial resistance, the medicines become ineffective and infections persist in the body, increasing the risk of spread to others. ·        New resistance mechanisms are emerging and spreading globally, threatening our ability to treat common infectious diseases, resulting in prolonged ill...

  ANTIBIOTICS ·     Antibiotics are the Secondary metabolites produced by the microorganisms which have the capacity to inhibit or kill the growth of another microorganisms particularly bacteria. ·        Antibiotics are low molecular weight non – protein molecules. ·        The term Antibiotic was first coined by Selman A. Waksman. ·        Penicillin was the first discovered Antibiotic. It was discovered by Alexander Fleming from the fungal Mold Penicillium notatum . ·       Streptomycin was the second discovered Antibiotic. It was discovered by Selman A. Waksman from the soil Actinobacteria Streptomyces griseus . ·      Antibiotics are used for treating Bacteria diseases only. They are not used for treating other microbial diseases. ·        Based on its spectrum of activity, Antibiotics are classi...

REQUIRED CONCENTRATIONS AND TIMES FOR CHEMICAL DESTRUCTION OF MICROORGANISMS Disinfectants Microorganisms Disinfectant concentration Time Chlorine Mycobacterium tuberculosis 50 ppm 50 sec Entamoeba cyst 0.1 ppm 150 min Hepatitis A Virus 3 ppm 30 min Ethyl alcohol Staphylococcus aureus 70 % 10 min Escherichia coli 70 % 2 min Poliovirus 70 % 10 min Hydrogen peroxide Staphylococcus aureus 3 % 12.5 sec Neisseria gonorrhoea 3 % 0.3 sec Herpes simplex virus 3 % 12.8 sec Quaternary Ammonium compounds Staphylococcus aureus 450 ppm 10 min Salmonella typhi 300 ppm 10 min ...