Multi-drug Resistant Organisms and Emerging Pathogens

Methicillin Resistant Staphylococcus aureus (MRSA)

Staphylococcus aureus (commonly known as staph) are common bacteria. Staph are usually harmless and many healthy people carry these bacteria on their skin or in their nose. However, sometimes they can cause infection and serious illness. Some strains of staph are resistant to the antibiotic called methicillin, and to other antibiotics. These staph are known as methicillin resistant Staphylococcus aureus (MRSA). Some people call MRSA infection "golden staph".

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Vancomycin Resistant Enterococcus (VRE)

The genus Enterococcus (species Enterococcus faecalis and Enterococcus faecium) are bacteria that are generally present in the human intestines and the female genital tract, and often found in the environment. When exposed to antibiotics, resistant strains of enterococci may survive and multiply, resulting in an overgrowth of antibiotic resistant bacteria in the bowel. Vancomycin-resistant Enterococci (VRE) are specific types of antimicrobial-resistant bacteria that are resistant to vancomycin; the antibiotic often used to treat infections caused by bacterial infections, including enterococci. Although VRE is generally considered of low pathogenicity organism and can remain colonised on body surfaces, they can cause life threatening infections in immunocompromised patients.

VRE acquisition is usually health care-associated. Inter-patient transmissions, transmission related to health care workers, or environmental contamination have all been shown to contribute to acquisition. The reservoirs for VRE are colonized and infected patients; however as routine facility wide screening for VRE is not recommended, many colonised patients are not identified. Patients at risk for VRE acquisition include those on antibiotics for long periods; patients with compromised immune systems, those who have undergone abdominal or chest surgery; and those with urinary catheters or central intravenous lines. For more information refer to VRE in Healthcare Settings Centers for Disease Prevention and Control.

Multidrug resistant gram negative organisms

Gram-negative bacilli are a large group of bacteria that are commonly found in the intestinal tract of humans and most animals. They form part of the normal microflora and are essential for proper digestive processes. However, these bacteria are capable of causing infection when introduced into normally sterile body sites, such as the bladder or deep tissues, particularly via insertion of a medical device or during surgery. Serious infections require the administration of antibiotics and can be associated with a high mortality rate, particularly in vulnerable patients such as those in critical care or who are immune-suppressed. Over the past few decades concern has been expressed about the increasing incidence of resistance in this group of bacteria, making serious infections with these organisms increasingly difficult to treat. For more information refer to Gram-negative Bacteria Infections in Healthcare Settings Centers for Disease Control and Prevention.

Some strains are now resistant to many, most, or all available treatments resulting in increased illness and death from bacterial infections, and contributing to escalating healthcare costs. Examples of Gram-negative bacteria that have demonstrated drug resistance include

  • Escherichia coli, which causes the majority of urinary tract infections
  • Acinetobacter baumanii, which causes disease mainly in healthcare settings.
  • Pseudomonas aeruginosa, which causes bloodstream infections and pneumonia in hospitalized patients. It is a common cause of pneumonia in patients with cystic fibrosis.
  • Klebsiella pneumoniae, which causes many types of healthcare-associated infections, including pneumonia, urinary tract infections, and bloodstream infections
  • Neisseria gonorrhoeae, which causes the sexually transmitted disease.

Clostridioides (Clostridium) Difficile

Clostridioides (Clostridium) difficile is a Gram positive spore-forming bacterium, which was shown to be the cause of pseudomembranous colitis – a condition often associated with use of the (then) new antibiotic, clindamycin - in 1978. It is widely distributed in the environment and faecal flora of humans and animals. With rare exceptions, colonisation and infection are limited to the gastrointestinal tract.

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Mycobacterium Tuberculosis

Tuberculosis (TB) is caused by a bacterium called Mycobacterium tuberculosis complex. Humans are the primary reservoir for M. tuberculosis complex, although it is also found in other animals, predominantly primates. The bacteria usually attack the lungs, but TB bacteria can attack any part of the body such as the kidney, spine, and brain. Not everyone infected with TB bacteria becomes sick. As a result, two TB-related conditions exist: latent TB infection (LTBI) and TB disease. If not treated properly, TB disease can be fatal.

Mode of transmission: TB is transmitted mainly by inhalation of infectious droplets produced by persons with pulmonary or laryngeal tuberculosis during coughing, laughing, shouting, singing or sneezing. Transmission can occur from potentially high risk procedures including sputum induction, treatment using a nebuliser, bronchoscopy, drainage of an open abscess, autopsy or any procedure in which an aerosol containing M. tuberculosis is generated. Refer to NSW Health Tuberculosis control guidelines for more information.

Carbapenemase-Producing Enterobacterales (CPE)

Carbapenemase-producing Enterobacterales (CPE) are bacteria that are likely to be resistant to most antibiotics.

Enterobacterales are a type of bacteria (known as Gram-negative bacilli, such as E. coli and Enterobacter), which live naturally and harmlessly in people's guts, along with billions of other bacteria. Rarely, and mainly in people with underlying serious disease, they can invade the blood or tissues and cause serious infections, including in the blood, lungs, urinary tract and wounds.

Carbapenemase-producing Enterobacterales are resistant to carbapenem antibiotics, due to the presence of a carbapenemase gene usually acquired from other bacteria. This gene allows CPE to produce carbapenemase enzymes which destroy carbapenems and other important β-lactam antibiotics such as penicillins and cephalosporins. Antibiotic treatment options for CPE are therefore limited.

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Candida auris

Candida auris (C. auris) is an uncommon Candida species that has been isolated from a range of body sites, including the skin, gastrointestinal tract, urogenital tract and respiratory tract and has been identified as the cause of a range of invasive fungal infections similar to other Candida species. C. auris is frequently resistant to multiple antifungal agents commonly used to treat Candida infections.

Unlike other fungal pathogens, C. auris has shown a propensity to be transmitted between patients and been associated with a number of healthcare-associated outbreaks internationally. Another unusual feature of the emergence of C. auris globally is that, unlike most emerging pathogens which spread outward from one regional epicentre to other geographical regions, whole genome sequencing analysis of C. auris isolates from different global regions suggests that there has been independent clonal emergence and local spread within those regions. Four distinct clades that cluster geographically have been identified; South Asia (India/Pakistan), East Asia (Korea/Japan), South Africa and South America.

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Mycobacterium chimaera

Some heater-cooler units used in cardiac surgery in the past were contaminated with a rare bacterium called Mycobacterium chimaera (or M. chimaera), and there is a small risk that exposure to these units in the operating theatre may lead to infections in exposed patients that can appear months after the surgery.

Infection of cardiac surgery patients with M. chimaera associated with a particular heater-cooler unit type made by LivaNova (Sorin) was first recognised in Switzerland. These devices, which are widely used around the world including Australia, are thought to have been contaminated during manufacture. Over 100 patients worldwide have been identified with M. chimaera infections after cardiac surgery, including six people in NSW who had surgery at Prince of Wales Hospital in 2015. Genetic testing of clinical samples strongly links these six cases to the worldwide outbreak. Refer to NSW Health Mycobacterium chimaera – information for open-heart surgery patients for more information.

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