Bacteria are single-cell organisms that can survive independently. You can kill them by interfering with their

metabolism (internal biological functions), which is basically what antibiotics do.

Most bacteria are neither male nor female and reproduce by simply dividing in to two.

Infections they cause include pneumonia, cystitis and food poisoning bugs like salmonella.

But not all bacteria are bad – some friendly types actually help protect us from disease.

Viruses are not cells, they have no metabolism and they cannot survive alone. A virus is a chain of DNA (genetic

material) and needs a host cell in order to stay alive.

You can, of course, pick them up on door handles and other surfaces. That’s one of the most common ways of

catching colds and flu, but that’s because they’re contained in sweat or skin cells. Once a virus gets in to cells it

persuades the cells to reproduce it! Antibiotics are useless against viruses.

Antiviral drugs either improve the immunity of the cell to the virus or interfere with the virus’s reproduction.

Virus - Bacteria Differences

Scanning electron micrograph of Escherichia coli bacilli

Viruses are the smallest and simplest life form known. They are 10 to 100 times smaller than bacteria.

The biggest difference between viruses and bacteria is that viruses must have a living host - like a plant or animal - to multiply, while most bacteria can grow on non-living surfaces.

Bacteria are intercellular organisms (i.e. they live in-between cells); whereas viruses are intracellular organisms (they infiltrate the host cell and live inside the cell). They change the host cell's genetic material from its normal function to producing the virus itself.

There are some useful bacteria but all viruses are harmful. Antibiotics cannot kill viruses, but can kill most bacteria, with the

exception of most Gram-negative bacteria. An example of a disease caused by bacteria is strep throat and an

example of an affliction caused by a virus is the flu.

Differences in ReproductionBacteria carry all the "machinery" (cell organelles) needed for their growth and multiplication. Bacteria usually reproduce asexually. In case of sexual reproduction, certain plasmids genetic material can be passed between bacteria. On the other hand, viruses mainly carry

information - for example, DNA or RNA, packaged in a protein and/or membranous coat. Viruses harness the host cell's machinery to reproduce. Their legs attach onto the surface of the cell, then the genetic material contained inside the head of the virus is injected into the cell. This genetic material can either use the cell's machinery to produce its own proteins and/or virus bits, or it can be integrated into the cell's DNA/RNA and then translated later. When enough "baby" viruses are produced the cell bursts, releasing the new viral particles. In a sense, viruses are not truly "living", but are essentially information (DNA or RNA) that float around until they encounter a suitable living host.

Structure and contents of a typical Gram positive bacterial cell