Elzu's micro notes

Aim To prepare antibiotic discs economically and to determine   the resistance pattern of   antibiotics against common pathogens. Principle Antibiotics are   defined as   antimicrobial substances which inhibit the growth of pathogenic bacteria. It is widely used in treatment of many diseases. Penicillin was the first antibiotic, discovered by Alexander Fleming in1928. Antimicrobial susceptibility testing can be studied   by different methods such as disk diffusion method, dilution method, E test   method. The  disk -diffusion agar methods assess the effectiveness of  antibiotics  on a specific microorganism. Each disc is a standard size and is impregnated with a standard volume and concentration of the antibiotic. Impregnated   disc with a known concentration of an antimicrobial compound is placed on Mueller-Hinton (MH) agar which is swabbed with test organism .After incubation, t he absence of growth around the antibiotic disks in...

Aim To determine the antibiotic sensitivity of the given organism by Kirby – Bauer disc diffusion method. Principle Kirby – Bauer disc diffusion method is commonly employed for antibiotic sensitivity test. The test is based on the fact that for a given antibiotic, the size of zone of inhibition is related to MIC                  {Minimum   Inhibitory Concentration }. MIC is referred as the lowest concentration of the antibiotic that exhibits the zone of inhibition on the assay plate. Kirby – Bauer Agar disk diffusion method provides qualitative interpretive category results of susceptible, intermediate, and resistant bacterial isolate Materials required ·          Sterile forceps ·          Sterile swabs ·          Broth culture of the organism ·    ...

Hyperchromic shift on DNA melting Aim To   demonstrate   hyperchromic   shift   on   DNA   melting. Principle Hyperchromicity is the an   increase   in the absorbtion of ultraviolet light by a solution of DNA when subjected to heat, alkaline conditions, etc. Hyperchromicity of DNA occurs when the DNA duplex is denatured .The UV absorbance   is increased when the DNA strands are being separated, either by heat or by addition of   denaturant or by increasing   pH level. Heat denaturation of DNA is also called melting when DNA in solution is heated above its melting temperature [usually more than 80 o C ], the double stranded DNA unwinds to form single stranded DNA. The bases becomes unstacked and can thus absorb more light. The G + C content often determined from the melting temperature [Tm] of DNA . In double stranded DNA ,three hydrogen bonds joins G C base pairs, and 2 hydrogen bonds connect AT bases pairs. DNA with a...

ESR determination by Westergren’s method Aim To determine the erythrocyte sedimentation rate of the given sample. Principle The erythrocyte sedimentation test is a nonspecific test. It is raised in a wide range of infections, inflammatory, degenerative and malignant conditions associated with changes in plasma proteins particularly increases with fibrinogen, immunoglobulins and C reactive proteins. The ESR is also affected   by many other factors including anaemia, pregnancy, haemoglobinopathies and treatment with anti-inflammatory drugs. Moderately raised sedimentation rates can sometimes be found in healthy people, particularly those living in tropical countries and a normal ESR cannot exclude disease. When performed, test results must be interrupted in conjugation with clinical findings and the results of other laboratory tests. When anticoagulated   blood in a vertically positioned Westergren’s pipette is left undisturbed, red cells aggregate ,stack together to...