It is imperative that we first identify the difference between bacteria and viruses. Bacteria are single-celled microorganisms which can be beneficial or detrimental to our health. Bacteria can live in hosts (such as humans) but are also found in many environments across the planet. A virus, however, has no cell structure and requires a host in order to survive. Infections can be caused by viruses or bacteria (e.g., chest infections, UTIs (urinary tract infections), etc.), but the way we treat them differs hugely. Mammalian hosts can have vaccinations against numerous viruses in order to prevent their infection, but viruses such as the common cold are not curable in this way, and usually they just need time to pass before recovery. Bacteria, however, are combated using antibiotics. Later we'll discuss how antibiotics do this but it is important to note this key point: Viruses cannot be killed by antibiotics.
The Good
'Good' bacteria are found on our skin, in our airways and digestive systems. These bacteria are the first line of defence, like frontline soldiers, preventing viruses and other potentially detrimental things (such as pathogens) from getting further into our systems and making us unwell. The bacteria found naturally in each of us differs from person to person and is called our microbiome \citep{Eckburg_2005}. The microbiome helps to enhance our immune system.
The Bad
These are the disease-causing bacteria and usually become prevalent when our microbiomes are disrupted, meaning the 'bad' bacteria has more room to grow and are no longer regulated by the 'good' bacteria. Examples of disease-causing bacteria are Staphylococcus aureus (causing infections such as pneumonia and ear infections ), Neisseria meningitidis (causing bacterial meningitis), Clostridium tetani (causing tetanus), etc.
The Ugly
The overuse of antibiotics has led to a very ugly situation. By removing good bacteria from our bodies, we've opened up an opportunity for bad bacteria to infiltrate, multiply and spread.
How antibiotics work
The first antibiotic to be discovered/developed was penicillin (1920), helping countless people since then to overcome bacterial infections.
- Beta-lactams: Beta-lactam antibiotics prevent the bacterial cell wall from forming and as a result, the bacterial cell cannot support itself and will eventually burst. Mammalian cells do not have a cell wall like bacteria, meaning that only bacterial cells are specifically targeted by this type of antibiotic. Penicillin is an example of a beta-lactam antibiotic.
- Macrolides: These antibiotics target ribosomes, which are responsible for aiding protein building within bacterial cells. Ribosomes also perform this function in mammalian cells, but there are sufficient differences between bacterial and mammalian ribosomes which allow for the bacterial ribosomes to be targeted specifically. Macrolides are able to block the process of ribosomes and thus, prevent bacterial proteins from being made, which in turn stops cellular functions. Erythromycin is an example of a macrolide antibiotic.
- Quinolones: As a bacteria begins to copy its DNA, quinolones act to break the DNA strands apart, preventing the bacterial cells from multiplying. Eventually, the remaining bacterial cells won't be able to survive in the hostile environment. Levofloxacin is an example of a quinolone antibiotic.
Pesky Bacteria: Antibiotic Resistance
It should be stated that it is the bacteria itself which becomes resistant, NOT us as individuals. For instance, gonorrhea is developing resistance to antibiotics used to treat it and is the 2nd most commonly reported infectious disease. \citet{cdc}
How do bacteria develop resistance? Unlike mammalian cells, bacterial cells divide and multiply rapidly. As a result, mutations will arise because the bacterial DNA is copied too quickly and thus, errors in the DNA sequence will occur.
Bacteria also have this ‘nifty’ way of making non-resistant cells, resistant! As if they weren’t annoying enough already. The process is called horizontal gene transfer.