Antimicrobial resistance

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ANTIMICROBIAL RESISTANCE By Dr. Lavanya Gudapuri 1 st year, PG, Dept. of Microbiology

Definition :

Definition Antimicrobial resistance is the ability of microbes, such as bacteria, viruses, parasites, or fungi, to grow in the presence of a chemical (drug) that would normally kill it or limit its growth. Ref: CDC, Antimicrobial drug resistance.

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Resistance of a microorganism to an antimicrobial medicine to which it was previously sensitive Withstand attack of antimicrobials so that standard treatment procedures become ineffective Infection may persist or spread


Causes Extensive availability of antibiotics Evolution Colonization


Pathways 4 main mechanisms 1 or more in same organism 1) Drug Inactivation or Modification E.g Production of Beta-lactamases by Staphylococci 2) Alteration of target site E.g Altered Pencillin binding protein in MRSA

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3) Alteration of metabolic pathway E.g Aminoglycoside resistance in Gram negative bacteria 4) Reduced drug accumulation a) Decreased uptake : Imipenem resistance in Pseudomonas b) Efflux : Erythromycin resistance in Streptococci & Staphylococci

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Molecular basis:

Molecular basis 1) Chromosomal mediated E.g PBP mutation in penicillin resistance in MRSA 2) Plasmid mediated E.g. ESBL production in Enterobacteriaceae 3) Phage mediated E.g. Resistance to beta lactam drugs in Enterobacteriaceae

Transfer :

Transfer Resistance coded by 1 or more genes Transferred between strains of species or genera Two methods of transfer. 1) Vertical by Mutation 2) Horizontal by Gene transfer


Mutations Mutations can be 1) One step mutation as in Streptomycin resistance 2 ) Stepwise mutation as in Penicillin resistance May show low resistance or High resistance

Horizontal gene transfer:

Horizontal gene transfer By various methods of gene transfer Responsible for widespread resistance Methods: 1) Transformation 2) Transduction 3) Lysogenic conversion 4) Conjugation

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Transduction: Transfer of genetic material from a donor to recipient via a bacteriophage E.g Transfer of Plasmid mediated Penicillin resistance in Staphylococci

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Conjugation: Process by which a donor bacterium transfers genetic material to a recipient bacterium Chromosome, part of chromosome or plasmid transferred Most common method of antimicrobial resistance transfer Multidrug resistance as in MRSA, ESBL, NDM ( Super bug )


RTF Plasmid consists of two components A transfer factor RT, helps conjugational transfer and resistant determinants ( r ) to each of the several drugs RTF + r determinants are known as R factor

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First discovered in Japan Infections caused due to Shigella spread resistance to following Antibiotics Sulphonamides Streptomycin Choramphenicol, Tetracycline Transferred to E. coli

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