Question: You said that "Staph" have a bad side, when they resist to antibiotics. Where does this usually happen and can we see any symptoms beforehand?

Jim Caryl answered on 17 Jun 2011:

Staph can have a bad side when they find themselves in an environment where a person’s immune system is not fighting them off. The thing about S. aureus is that it can live in your nose without causing you any problems whatsoever, and one of the reasons for this is that the high-salt environment of your nose actually suppressed the ‘weapons’ that Staph has.

However, it sometimes gets into open cuts, say on your hand. When in this environment, the low-salt environment triggers the bacteria to unleash its weapons, and it has many. Each weapon allows it to move through the tissues of your skin to eat more and try and prevent your immune system from killing it. Sometimes with early treatment, salt washes, disinfectant and a good immune system, such cuts will heal. Sometimes they don’t, and even healthy people may need antibiotics to help suppress the bacteria long enough for your immune system to sort them out.

In very ill people, their immune systems may be so poor that we need the antibiotics to be even more effective, and kill as much of the infection as possible. This is very difficult, so the treatment can take a long time, and put the body under a lot of stess.

Many S. aureus also encode genes that make highly toxic compounds, which make you skin look like you’ve been scalded with hot water, or make you sick or have diarrhoea in the case of Staphylococcal food poisoning. Some attack parts of your blood and can be especially dangerous.

S. aureus can have all of the above weapons whether they are resistant to antibiotics or not. Being resistant does not automatically mean that they are better at starting an infection – it just means they are better at persisting in an infection when you try to treat with antibiotics.

So in any infection is it worth trying to figure out what antibiotics the bacteria causing it are resistant to, or more specially, what antibiotics actually work on them – and then using that antibiotic. When people go into hospitals for operations, they are often screened for resistant Staph such as MRSA, and those people have to be isolated and treated with special anti-MRSA antibiotics before they can be operated on, in case their operation wound gets infected.