How many of the following statements are correct?
1. Bacteriophages are ‘good viruses’ that naturally prey on bacteria.
2. There are believed to be 10 times as many phages as bacteria on earth.
3. Unlike an antibiotic, phages may only kill a few strains of a particular bacterium.
4. Phages have been used for burns, foot ulcers, gut infections, respiratory infections, and urinary tract infections.