Review Questions:

Why do new strains of the fluusually come from China?

How is the genome of the flu virus different from the genome of most other organisms?

What kind of pathogen causesShistosomaisis?

Bacterial Diseases, Antibiotics and Antibiotic Resistance

The Magic Bullet

INFECTIOUS DISEASES KILL OVER 17 MILLION PEOPLE A YEAR:

Up to half the world's population of 5.72 billion are at risk of many endemic diseases. In addition, millions of people are developing cancers as a direct result of preventable infections by bacteria and viruses

Some major diseases, such as cholera, malaria and tuberculosis are making a deadly comeback in many parts of the world, despite being preventable or treatable.

At the same time, many new and highly infectious diseases such as HIV/AIDS and the notorious Ebola haemorrhagic fever - both of which are incurable - are emerging to pose additional threats.

Fears are growing over a possible food-chain link between bovine spongiform encephalopathy ("mad cow disease") and a variant of the incurable Creutzfeldt-Jakob disease, due to an infectious agent that attacks the human brain.

How Antibiotics Work

Paul Erlich:

The ideal antibiotic kills only the pathogen with no harmful effects on the host cells.

Some Examples:

Sulfa drugs are anti-infectives which are used to treat stomach and urinary infections.

Some commonly used sulfa drugs: co-trimoxazole/Bactrim, Septa sulfisoxazole/Gantrisin

INTERACTION-Avoid alcohol, as the combination may cause nausea.

Penicillin kills bacteria by interfering with the ability tosynthesize cell wall.

Penicillins are antibiotics used for treatment of a wide variety of infections.

Some commonly used penicillins: amoxicillin, ampicillin, bacampicillin, penicillin G and penicillin V

Some Examples:

Tetracyclines are antibiotics that are used to treat a wide variety of infections. Some commonly used brand names:tetracycline hydrochloride/Achromycin, Sumycin, Panmycin

INTERACTION-These drugs should not be taken within two hours of eating dairy products such as milk, yogurt or cheese, or taking calcium or iron supplements.

Tetracyclines work by inhibiting bacterial ribosomes.

Robert Koch was the first to demonstrate a causual link between a specific microorganism and an infectious disease.

He worked with anthrax around 1877 and tuberculosis around 1894.

Bacillus anthracis

Koch's postulates

1. The microbe must be present in every case of the disease and not present in healthy animals

2. It must be isolated and grown in a pure culture

3. The same disease must result when the isolated microbe is inoculated into a healthy host

4. The same microbe must be isolated again from the diseased host

The methods developed by Koch were so successful that by the early 20th century, the etiologic agent for nearly every important bacterial disease had been isolated and identified.

Antibiotics and other life-saving drugs used against many diseases are rapidly losing their effectiveness as bacteria and other microbes develop resistance to them.

For example, doctors worldwide are losing some of the most useful and affordable antibiotics against the two principal bacteria which cause pneumonia, the major cause of death in children.

Antibiotic Resistance Genes

Antibiotic use selects for populations of antibiotic-resistant pathogens. Some bacteria avoid theeffect of penicillin by the production of penicillinase, an enzyme that destroys penicillin.

“A strain of the bacterium Streptococcus pneumoniae, resistant to the six most frequently used antibiotics and spread worldwide including U.S. day care centers and hospitals, appears to disguise itself from the immune system by changing its coat, report scientists from The Rockefeller University.”

“S. pneumoniae is a common source of bacterial infections in children, the elderly and AIDS patients, says Tomasz.

Worldwide, the number of deaths from infections with this bacteria each year are similar to that of tuberculosis--3 to 4 million.”

Antibiotic Resistance Genes