Science Starter: How do Fossil Records show evidence for Evolution?

Bad Germs – Good evidence of Natural Selectionpneumonia Staph infection

TB-tuberculosis

Antibiotics – The Biggest Advance in Medicine of the 20th Century

or is it?

Streptococcus pneumoniaeis

Bacteria and Antibiotic Resistance

Streptococcus pneumoniaeis a leading cause of serious illness among young children worldwide and is the most frequent cause of pneumonia, bacteremia, sinusitis, and acute otitis media (AOM). Widespread overuse of antibiotics contributes to emerging drug resistance.

Bacillus anthracisMycobacterium tuberculosis

Salmonella Typhi.

Some Other Bad Germs

Methicillin-resistant Staphylococcus aureus

How is that an example of Natural Selection?

Natural Selection in Action① Microbes – bacteria, some fungi, viruses –

have a short generation time: bacteria 20 min② Mutation Rates are much higher③ 1+2 = greater genetic variation upon which

natural selection can act④ Selective pressure or survival of the fittest –

use of drugs or vaccines to kill the microbes

• Those that adapt will survive and become resistant to the drugs we use

• The adapted microbes will reproduce, the others will be dead – so adapted ones (drug-resistant ones) are the only ones left standing

Flu Virus – a special Challenge• Viruses adapt to US – to our defenses• Its genes mutate often – produce different

proteins• When two different viruses infect he same cell,

they can swap genes• Our Immune system recognizes proteins on the

surface of the virus – so viruses change these surface protein constantly to escape detection

Flu Vaccines

• Made each year differently to match a few different strains of flu virus (usually last years strains)

• How effective the vaccine is depends on how well it matches this years flu virus strains – how similar the vaccine is to the current virus

During years when it is not well matched to circulating viruses, it’s possible that no benefit from flu vaccination may be observed.

During years when there is a good match, it’s possible to measure substantial benefits from vaccination in terms of preventing flu illness.

A good match is difficult to achieve, because the virus changes so frequently

How effective is the flu vaccine?