Bacterial Genetics. Vocabulary Binary fission Exponential growth Gram positive Gram negative Pathogen Antibiotic Selection pressure Adaptation Mutation.

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Presentation transcript:

Bacterial Genetics

Vocabulary Binary fission Exponential growth Gram positive Gram negative Pathogen Antibiotic Selection pressure Adaptation Mutation Conjugation Transduction Transformation Antibiotic resistance

Ideal conditions: Population doubles every 20 minutes

Bacteria reproduce exponentially: Population may double every 20 minutes during optimal growth! Why don’t they take over the world?!

How do bacteria reproduce? Single circular chromosome replicates Cell divides by binary fission book/growth/bactdivision.swf

Replication of DNA

Gram Stains & Bacteria Gram Negative Thin wall stains pink Outer capsule More pathogenic Gram Positive Thick cell wall of peptidoglycan stains purple Less severe infections Susceptible to penicillin

How do antibiotics work? Selective poison; Targets specific bacterial enzymes, proteins, ribosomes (that we don’t have) Penicillin – interferes with bacteria’s ability to build a cell wall (Gram +)

Bacteria fight back! Bacteria can become resistant to antibiotics Bacteria survive and pass trait to offspring Can also transfer trait to other bacteria Result: population of resistant bacteria Methicillin resistant staph. aureus

Selection Pressure & Resistance

How do bacteria become drug resistant? 1.Change the target 2.Destroys antibiotic 3.Acquire drug resistant genes from other bacteria (phone a friend)

Mutation Target in bacteria for antibiotic changes so bacteria is no longer affected by antibiotic.

Destruction Bacteria with adaptation that allows them to destroy antibiotic will survive and pass this adaptation to all offspring

Genetic Transfer Bacteria can (randomly) acquire genes from other bacteria which may allow them to become resistant to antibiotic.

Mechanisms of Genetic Exchange DNA containing resistant gene is passed from one host to another DNA can insert into new host chromosome or remain separate as a circular piece of DNA (plasmid ) 3 processes transfer genetic material (including resistance to antibiotics)

Conjugation Conjugation from HHMI biointeractiveConjugation from HHMI biointeractive

Conjugation “Mating” Donor bacterium has a plasmid with gene for drug resistance; forms pillus to connect to recipient Recipient bacterium is not drug resistant (yet) Contact required Plasmid transferred Recipient now resistant

Transduction

Phage picks up resistant gene in one bacterial host and transfers that gene to another host cell when it infects the new host.

Transformation

Griffith showed that DNA in a broth could be picked up by bacteria who then acquired new traits

Summary Conjugation – Circular Plasmid (DNA) transferred to recipient cell through sex pillus Transduction – DNA from one bacteria picked up by phage and transferred to another bacteria Transformation – naked DNA in the environment is taken up by bacterial cells

Advantage* of Drug Resistance Drug resistant bacteria quickly become dominant population – but now they are more dangerous What doesn’t kill us makes us stronger! * Advantage to bacteria, that is. You are sicker than ever. 

 The development of bacterial resistance to antibiotics provides direct evidence for evolution.

Rise of the “Super Bugs”

Gene transfer increases the spread of antibiotic resistance

“ Normal” vs. Drug Resistant Bacteria