Pathogenic and Nonpathogenic Microorganisms an idea Nilansu Das

Pathogenic and Non-pathogenic Microorganisms : an idea Nilansu Das Dept. of Molecular Biology Surendranath College

The Syllabus

Microorganisms Associated with Humans

Important Terminologies

Non-Pathogenic Microorganisms

Pathogenic Microorganisms

Factors that Determine Pathogenicity of Bacteria

The Syllabus

Origin of drug resistance has genetic basis. g u r D f e c n s e R a t is o n i g i r O Drug resistance can be genetically encoded by the microbial pathogen and the genes responsible for it are present on both the chromosome and plasmids.

Chromosome-Mediated Drug Resistance Spontaneous mutations in the chromosome, although they do not occur very often, will make bacteria drug resistant. (e. g. , the streptomycin receptor protein on bacterial ribosomes). Transposons are a type of transposable elements in bacterial chromosome that, in addition to genes involved in transposition, carries other genes; often genes conferring antibiotic resistance. Many composite transposons contain genes for antibiotic resistance, and some bear more than one resistance gene. They are found in both gram-negative and gram-positive bacteria.

Transposon-Mediated Drug Resistance Some examples and their resistance markers are : Tn 5 (kanamycin, bleomycin, streptomycin) Tn 9 (chloramphenicol) Tn 10 (tetracycline) Tn 21 (streptomycin, spectinomycin, sulfonamide) Tn 551 (erythromycin) Tn 4001 (gentamicin, tobranycin, kanamycin).

Plasmid-Mediated Drug Resistance Plasmid is an extra-chromosomal genetic element that replicates independently of the host chromosome, is not essential for growth, and has no extracellular form. Large number of different plasmids occur naturally in bacterial cells. Among the most widespread and well-studied groups of plasmids are the R plasmids (resistance plasmids), which confer resistance to antibiotics. R plasmid resistance is usually due to the presence of genes in it encoding enzymes that inactivate the antibiotic or genes that encode enzymes that either prevent antibiotic update or actively pump it out of the bacterial cell.

Drug Resistance encoded by genes of R plasmid genes encode penicillinase enzyme (βlactamase) that splits the β-lactam ring in penicillins, and inactivate the antibiotic. Chloramphenicol resistance is due to an R plasmid gene-encoded enzyme that acetylates the antibiotic (Chloramphenicol acetyl transferase). Several R plasmids confer multiple antibiotic resistance because a single R plasmid may possess different genes, each encoding a different antibioticinactivating enzyme.

Site at which Penicillin is attacked by enzymes encoded by R plasmid genes

Site at which Penicillin is attacked by enzymes encoded by R plasmid genes

Site at which Aminoglycoside antibiotics (eg. Streptomycin) are attacked by enzymes encoded by R plasmid genes

k n a h T u o Y Stay safe…. observe Extreme Precautions