What are enterococci?
Enterococci are bacteria found in the faeces of most humans and many animals. There are two types of enterococci associated with normal healthy people and which also occasionally cause human disease. They are called Enterococcus faecalis and Enterococcus faecium.
The commonest infections caused by enterococci are urinary tract infections and wound infections. These, and a variety of other infections, including infection of the blood stream (bacteraemia), heart valves (endocarditis) and the brain (meningitis) can occur in severely ill patients in hospital.
Enterococci also frequently colonise open wounds and skin ulcers. In these circumstances the bacteria can be grown from a lesion but they are not causing the patient any illness.
Enterococci are amongst the most antibiotic resistant bacteria isolated from humans. Minor infections can usually be treated by antibiotics such as penicillins, macrolides or tetracyclines, taken by mouth.
However, only penicillins, or teicoplanin and vancomycin (two expensive and potentially toxic antibiotics which can only be given by injection) are reliably effective against serious enterococcal infections such as endocarditis or meningitis. Serious infections often need prolonged treatment, usually with several antibiotics being given together by injection.
What are VRE?
Until recently, resistance amongst enterococci to the antibiotic vancomycin was unknown. However in 1986 the first vancomycin-resistant enterococcus (VRE) was found in France and a year later the first strain was isolated in the UK. Similar strains have now been found world-wide.
The genetic material which makes enterococci resistant to vancomycin has probably been passed on from other types of bacteria that do not cause human disease but which are already vancomycin-resistant. Bacteria that are resistant to vancomycin are commonly also resistant to a similar antibiotic called teicoplanin, and vice versa.
In a number of European countries, including the UK, antibiotics related to vancomycin such as avoparcin have been included in the feed given to farm animals because they help to improve meat yields. Animals and meat from farms where this practice takes place have also been found to have VRE indistinguishable from human strains. It is suspected that humans may acquire VRE through contact with these animals or by eating their meat.
The bacteria then reside harmlessly in the patient's gut until the patient is admitted to hospital. Here, due to the influence of antibiotic therapy, VRE may spread from the gut and cause an infection in another part of the body.
What diseases do VRE cause?
At present VRE are common only in patients who have been in hospital for long periods, those who have received certain antibiotics (especially vancomycin, teicoplanin or cephalosporins) and those who have been fed by naso-gastric tube. However VRE are found in the faeces of people who have never been in hospital or recently been given antibiotics.
VRE behave like other enterococci and cause the same range of infections; they are not more or less likely to cause illness than vancomycin-sensitive enterococci. In normal healthy people illness due to VRE is very rare, hence family members and household contacts of patients with VRE are not at any risk and normal social hygiene should prevent them acquiring the organism.
VRE are becoming more common in hospitals world-wide. A number of different strains of VRE are contributing to the increase both in the UK and abroad.
Treatment of VRE infections
There are two main problems when treating VRE infections. Firstly, the range of antibiotics available for treatment is limited. Secondly, predicting the antibiotics to which the strain will be sensitive, and therefore appropriate for treatment, is difficult.
A number of new antibiotics are under development although it is too soon to know whether any of these will be safe and effective enough against VRE for widespread use. By comparison, those people found to be harmlessly colonised by VRE in their gut or elsewhere need no special treatment with antibiotics or antiseptics. Over a period of time many of these people become spontaneously clear of VRE.
How is the spread of VRE prevented?
Restricting the use of antibiotics, especially vancomycin, teicoplanin and cephalosporins to those patients who really need them will help to limit the isolation of more VRE. Limiting the use of vancomycin-like antibiotics in veterinary practice should reduce the colonisation of animals by VRE and their subsequent spread to humans.
In hospitals, scrupulous handwashing by all hospital staff between each patient contact, thorough cleaning of hospital environment and proper decontamination of equipment should all help to prevent the spread of VRE.
Most patients with VRE, whether they are suffering illness or not, will be nursed in a single room while they are in hospital. Staff will wear plastic gloves and disposable aprons while caring for these patients. Once a patient with VRE is discharged from hospital, their room will be carefully cleaned and all linen and other clinical waste disposed of in special bags.
(Source: Association of Medical Microbiologists)