Genetic variation in bacteria Including antibiotic resistance Adaptation

Genetic variation in bacteria Including antibiotic resistance

Adaptation • Organisms adjust to suit the changing environment by natural selection – This is adaptation • This increases the reproductive success of an organism by helping members survive for longer • Adaptation and selection are important factors in the diversity of living organisms

Diversity and DNA • DNA is the genetic information passed from one generation to the next • Diversity in organisms arises from: – Mutations in DNA – Recombining DNA of two individuals – sexual reproduction

Diversity in bacteria • Namely arises via mutations and a process called conjugation • Conjugation occurs when one bacterial cell transfers DNA to another • Although conjugation recombines DNA from two individuals, it is not sexual reproduction • Allows genes for antibiotic resistance and other characteristics to be exchanged by horizontal gene transfer

F factor = plasmid Conjugation • Conjugation tube forms • The donor cells replicates the plasmid • The plasmid is cut and becomes linearised so it can move through conjugation tube • The plasmid enters the recipient cell and forms a new circular plasmid

Antibiotic resistance: two important animations!! First one focuses on conjugation Second is about antibiotic resistance • http: //www. hhmi. org/biointeractive/animatio ns/conjugation/conj_frames. htm • http: //www. sumanasinc. com/scienceinfocus/ sif_antibiotics. html

Antibiotics: What you need to know • What is an antibiotic? – A substance produced by a living organism that destroys or inhibits growth of microorganisms • How do they work? – Many ways: e. g. Penicillin can prevent bacteria from making cell walls – inhibits synthesis and assembly of cross -linkages in bacterial cell wall. • How do bacteria become resistant to antibiotics? – Mutations! – In penicillin-resistant bacteria, a new mutation arose causing the bacteria to produce an enzyme that can break down penicillin – NOTE: ANTIBIOTICS DO NOT CAUSE MUTATIONS TO ARISE! They arise randomly

Antibiotics: What you need to know • The presence of antibiotics creates a selection pressure for bacteria • In a normal population of bacteria, penicillin-resistance would not be an advantage • However, in the presence of penicillin, these bacteria have an advantage – they will survive and pass on the resistance gene – Only bacteria with the resistance gene survive – they reproduce and pass on the characteristic, increasing the numbers of resistant bacteria • Resistance can be passed vertically (from one generation to the next) or horizontally (via conjugation and exchange of plasmids) • The more we use antibiotics, the greater the chance that mutated bacteria will survive and pass on antibiotic resistance

Antibiotic links • http: //www. hhmi. org/biointeractive/Antibioti cs_Attack/frameset. html – Click on penicillin on side menu and start form there