Communicable disease factsheets
Antibiotic Resistance
Fact sheet on antibiotic resistance: background; Vancomycin resistant Enterococcus (VRE) - the disease and its agent, transmission, possible links to antibiotic use in animals; Methicillin resistant Staphylococcus aureus - the disease and its agent; control of the spread of VRE and MRSA; surveillance and reporting.
Background
The emergence of antibiotic resistant bacteria (in particular, bacteria resistant to multiple antibiotics) is a worldwide concern. Antibiotics are often used indiscriminately and this has contributed to the rise of antibiotic resistance in a variety of bacteria, including species of Enterococcus, Staphylococcus, Mycobacterium and Pneumococcus. The emergence of vancomycin resistant Enterococcus (VRE), methicillin resistant Staphylococcus aureus (MRSA) and more recently vancomycin resistant Staphylococcus aureus (VRSA) are of particular concern in hospital settings. These bacteria may infect seriously ill patients, causing life-threatening infections that respond poorly to most commonly used antibiotics.The emergence of antibiotic resistant organisms has been attributed to over-use of broad spectrum antibiotics in humans. There is also some concern that inappropriate veterinary use of antibiotics may lead to development of antibiotic resistant bacteria, which could in turn infect humans.
When antibiotics are administered for an infection, bacteria that are highly susceptible to the drug will be destroyed. However, bacteria that have some resistance from the start, or that acquire it later (through mutation or gene exchange), may survive, especially if too little drug is given to overwhelm the bacteria that are present. Those organisms, facing reduced competition from susceptible bacteria, will go on to proliferate. When exposed to an antibiotic, the most resistant bacteria in a group will inevitably outgrow all others.
Vancomycin resistant Enterococcus (VRE)
The disease and its agent
Enterococcus is a gram positive coccus that normally colonises the lower gastrointestinal tract and genital tract of healthy individuals. This organism may, however, be pathogenic in certain circumstances, causing urinary tract infections, wound infections, septicaemia and endocarditis. Vancomycin resistant Enterococcus (VRE) is a strain that has developed resistance to many commonly used antibiotics. VRE threatens to compromise effective treatment of infections caused by these multi-resistant gram-positive bacteria, particularly in seriously ill, hospitalised patients who may need treatment with vancomycin where other antibiotics have failed.VRE was first found in the USA in the 1980s. It has since been isolated in Europe, Britain, Japan and many other countries including Australia. The first Australian isolate occurred in a Melbourne hospital in 1994.
Enterococci are naturally resistant to many antibiotics including cephalosporins, aminoglycosides and clindamycin, and may also be resistant to tetracyclines and erythromycin. Three types of vancomycin resistance are found in enterococci; Van A, Van B and Van C. Van A and B type resistance accounts for most significant infections in clinical settings involving E. faecium and E. faecalis. Van C resistance is a low-level intrinsic resistance found naturally in rarer species of enterococcus (NHMRC, Vancomycin resistant enterococcus in Australia, 1996).
Transmission
Someone who is colonised with VRE can pass on these bacteria through inadequate hand washing, eg a bedridden patient can contaminate their environment after using bedpans, by contact with other people or inanimate objects such as door knobs and telephones.Methicillin resistant Staphylococcus aureus
The disease and its agent
Staphylococcus aureus is a common bacterium found on the skin, but it may be the cause of a number of diseases and conditions ranging from minor to life threatening. In hospital situations, S. aureus is a common cause of impetigo and purulent skin infections in newborns. An emerging problem is the increasing association of resistant S. aureus with post-surgical infections, which threatens the recovery of hospitalised surgical patients. The degree of infection varies from stitch abscesses, to septic phlebitis, chronic osteomyelitis, pneumonia, meningitis, endocarditis and sepsis. Approximately 85% to 90% of isolates will be antibiotic resistant S. aureus, which may have developed resistance to penicillin, methicillin and aminoglycosides such as gentamicin. Usually referred to as "MRSA," methicillin resistant S. aureus is a growing problem that threatens the integrity of hospital care.Control of the spread of VRE and MRSA
Control of the spread of VRE and MRSA hospital infections is primarily addressed through stringent infection control procedures and careful use of antibiotics. The NHMRC publication, "Infection Control in the Health Care Setting" provides guidelines on infection control, and is updated regularly to address new infection control issues. Health care establishments are encouraged to maintain programs of ongoing improvement in infection control practice and to strictly adhere to the highest infection control measures.In hospitals, patients with VRE should be kept in isolation, and normal isolation procedures implemented. Isolation is to prevent spread of the organism to other patients. As the bacterium can survive for long periods in the environment, cleaning of surfaces is important.
Guidelines for appropriate use of antibiotics in humans are provided in Therapeutic Guidelines: Antibiotic, Version 11, 2000, published by Therapeutic Guidelines Limited, Level 2, 55 Flemington Rd, North Melbourne Victoria 3051 - www.tg.com.au
Information correct at the time of writing, March 2002