Introduction
The world is full of microorganisms – bacteria, fungi, parasites and viruses. Our immune system has evolved to “fight” those that can harm the body and to coexist peacefully with countless others. Every human being has a normal flora, a collection of microorganisms living in different parts of the body. In general these tiny forms of life are useful; for example, they help digest food and act as a barrier against harmful microorganisms
Most of them cause no problems unless their balance within the body is disturbed or the immune system is weakened. If this happens, there may be opportunistic overgrowth of one type of resident flora, or one or more harmful microorganisms may cause an infection
When a person’s immune system cannot fight a pathogen or restore the normal balance of the flora, antibiotics may be needed. These are medicines (antibacterial, antiviral and antifungal) developed to fight infections caused by these microorganisms; they target different physical characteristics of the microorganisms, such as their ability to reproduce, their cell wall or their metabolism. Different antibiotics are effective against different types of microorganism. Some are highly specific, used for example to eliminate one particular family of bacteria without upsetting the balance of the normal flora. Others are broad-spectrum, developed to inhibit the growth of many microorganisms. A broad-spectrum antibiotic can act both on pathogens and on the normal flora.
Some microorganisms can show varying degrees of resistance to certain antibiotics.
The antibiogram is often used to determine whether a particular antibiotic treatment is effective in inhibiting the growth of the microorganisms causing an infection.
Resistance
Bacterial resistance can be innate (natural) or acquired.
Some bacteria are naturally resistant to specific antibiotics. This resistance is part of the normal physical characteristics of the bacterium.
Because bacteria multiply very quickly, they go through many generations in a short time; resistance to antibiotics can therefore arise from a mutation in the bacterium’s genome. If the mutation gives a survival advantage, it will probably be passed on to later generations.
Acquired resistance can develop through a process of selection. When a patient is treated with an antibiotic, most of the sensitive bacteria are killed. If treatment is stopped before it can act on all the pathogenic bacteria, the survivors may develop resistance to that antibiotic. This means that later treatment with the same antibiotic may not work.
Resistance can also develop when resistant bacteria exchange or share their genetic material with sensitive bacteria. This happens more often in healthcare settings, where many patients are treated with antibiotics and many have weakened immune systems. For example, resistant strains such as MRSA (methicillin-resistant Staphylococcus aureus) have been a problem in hospitals for decades and are becoming very common in healthcare settings.
Once resistance has developed, for whatever reason, the bacterium concerned can spread throughout a community and potentially throughout the world. Once a strain of bacteria has become resistant to one or more drugs, the only options are to try to stop it spreading and to find another drug that can inhibit its growth.
Second- or third-choice drugs are often more expensive and more toxic (i.e. with more side effects). This challenge is made worse by the fact that bacteria are becoming resistant faster than new antibiotics are being developed.
Prevention
Sooner or later, every antibiotic will face one or more strains of bacteria that have become resistant to it, and its usefulness will eventually decline. What we can do is use antibiotics properly, for the length of time and at the doses prescribed by the doctor. In this respect, taking an antibiotic for too short a time can encourage the selection of resistant strains and make that antibiotic permanently ineffective.
Some useful tips for patients:
• Do not take antibiotics when they are not really needed, as often happens with viral illnesses
• When they are prescribed, complete the whole course of antibiotics, following the instructions carefully.
• Do not take antibiotics without first consulting a doctor.
• Limit the use of antibiotics.
Some useful tips for doctors:
• Limit antibiotic prescriptions to cases where the medicine is really needed.
• Report outbreaks of resistant bacteria; rapid identification and isolation can reduce their spread