Bacteria and antibiotics Page refs for this section = Textbook p

BACTERIA

Good ref = Textbook p66 labels, p65 functions of the structures. Unit 2 Handbook (part 3) p22-24.

Name the features A to I below A H C G D I E B F

Bacterial DNA One large circular chromosome May also contain a small circle of DNA called a plasmid Not associated with histones (attached proteins)

Variation in bacterial DNA Occurs by mutation Change in the organic base sequence in the DNA. Leads to an alteration in the protein produced and changes a characteristic/or a reaction by the bacterial cell This may allow the bacterial cell to become resistant to an antibiotic.

Antibiotics Are Substances produced by living organisms that can destroy or inhibit the growth of microorganisms

Osmotic lysis The antibiotic prevents the formation of bacterial cell walls. Water can then enter the cell, causing it to swell and burst. This is osmotic lysis. The bacterium dies. Read section on top of HB p23 about MRSA (Methicillin Resistant Staphylococcus aureus)

CNHCH C O OCN CH 3 COOH S The mutation allows the bacterium to make a new protein enzyme called penicillinase which breaks down the β lactam ring structure of the penicillin. This inactivates the penicillin antibiotic. THE RESULT OF A CHANCE DNA MUTATION LEAD TO SOME POPULATIONS OF BACTERIA BECOMING RESISTANT TO THE ANTIBIOTIC PENICILLIN The Structure of Penicillin Antibiotic:

HOW ANTIBIOTIC RESISTANCE CAN BE PASSED ON TO MORE BACTERIA

Vertical Gene Transmission – by Bacterial Cell Division ie Asexual reproduction/binary fission

Vertical Transmission

Bacterial reproduction Bacteria reproduce by a method called binary fission, which is asexual. The first stage involves DNA replication. Then the cell splits into 2, so that each new daughter cell produced contains a genetically identical copy of the main circular chromosome and the plasmids.

Horizontal Gene Transmission – by Bacterial Conjugation Second bacterium receives a copy of the plasmid from the other bacterium.

Conjugation A sex pilus forms a temporary link between the donor and recipient bacterial cells. A plasmid with a resistance gene(s) is transferred directly to the recipient cell. Both bacterial cells now contain a copy of the plasmid and will both now be resistant to a certain antibiotic.

Conjugation in Bacteria with a Plasmid bacterial DNAplasmid The plasmid with a resistance gene (R) is in the donor cell initially R R R The plasmid begins to replicate R R The plasmid is sent through to the recipient bacterial cell RR The cells separate – both species now contain a copy of the plasmid with a gene on it for antibiotic resistance. A pilus links the 2 bacterial cells R Species A Species B

1. In a large enough population of microorganisms a small number are naturally resistant through random genetic variation i.e. via a spontaneous mutation 2. Exposure to antibiotic eliminates the susceptible majority. 3. The small number of survivors multiply rapidly in the absence of competition Evolution of Antibiotic Resistance in Bacteria 4. The population is now more or less 100% antibiotic-resistant

Some bacteria will be resistant to a particular antibiotic Resistant bacteria have a selective advantage in the presence of the antibiotic In the presence of the antibiotic Non-resistant bacteria are inhibited or destroyed by the antibiotic Resistant bacteria flourish in the presence of the antibiotic, because there is little competition for nutrients. (selected population) How does resistance develop in a population of bacteria? There will be variation in the population as a result of: Mutation or Conjugation

TASK: Check your missing words task top of HB p24 ANSWER WORDS in the correct order for the answers: Allele Killed Advantage Reproduce

Development of antibiotic resistance to TB

Why is TB so difficult to treat: 1Treatment for TB involves taking antibiotics for 6-9 months non-stop. 2As patients start to feel better they tend to stop taking their antibiotics. However, at this point even though the most susceptible TB bacteria have been killed, a few TB bacteria that are more resistant will remain alive in the body. 3Resistant strains of TB Mycobacterium survive, multiply and can even pass on their alleles for resistance to other strains/species of bacteria by conjugation.

Multiple-antibiotic resistant strains of TB have developed.

Superbugs! Bacteria which are resistant to one antibiotic may pass the plasmid containing the resistance gene to another bacterium which is already resistant to a second antibiotic. This then multiplies leading to resistance to both antibiotics etc.

How bacteria can become resistant to more than one antibiotic Bacteria treated with antibiotic ABacteria treated with antibiotic B resistant bacterium most bacteria are killed during conjugation the plasmid with the gene for resistance to antibiotic A is copied into the bacterium already resistant to antibiotic B bacterium resistant to antibiotics A and B resistant bacterium multiplies to form a new strain resistant to antibiotics A and B

MRSA MRSA (methicillin-resistant Staphylococcus aureus) infections are more difficult to treat due to the antibiotic-resistance of the bacteria Some strains are resistant to nearly all antibiotics It causes a range of illnesses from skin infections to life-threatening meningitis or septicaemia It can take time to determine which drugs to use to treat it, so patients can become very ill

MRSA (cont) People in hospitals tend to be weaker and more vulnerable to infection Careful attention has to be paid to not transfer infection between patients

A few pictures of MRSA sufferers

Do the application exercise from p222 NT textbook on

If you have a Biology AS revision guide, there is a REALLY EXCELLENT double page spread ON P84-85 to study about the use of antibiotics, the ethical considerations connected with this and antibiotic resistance by bacteria on p It would be valuable for you to read this!