1.   As drugs kill off the virus most susceptible to them, they leave behind the more resistant strains.

2.   Long-term use has led to the growth of resistant strains.

3.   More to the point, as resistant strains emerge, the greater becomes our need for new antibiotics to cure sick people.

4.   The first resistant strain was found within a year of its use and soon spread.

5.   The most effective destroyers of drugs are ordinary enzymes made in huge amounts by resistant strains.

6.   The risk of resistant strains of bacteria developing through complacent use of medicated feeds is high.

7.   Whenever possible, patients who do not respond to antibiotics should be screened for resistant strains.

8.   Although a handful of drugs still work against resistant strains, the failure of initial treatment allows infected individuals to continue transmitting the disease to their sexual partners.

9.   And because doctors here have yet to adopt modern methods of treating the disease, thousands of South Africans have tuberculosis strains resistant to all known drugs.

10.   Another concern is whether widespread post-exposure drug treatments will give rise to resistant strains of the AIDS virus.