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Multi-drug Resistant Organisms and Emerging Pathogens

Methicillin Resistant Staphylococcus aureus (MRSA)

Staphylococcus aureus (commonly known as staph) are common bacteria and at least 30% of the population carry S aureus on their skin or inside their nose. Most of the time this causes no infection or illness. However, sometimes S aureus can cause invasive infection and serious illness. Some strains of staph are resistant to multiple antibiotics, including methicillin and are usually known as methicillin resistant Staphylococcus aureus or MRSA. Sometimes MRSA is referred to as "golden staph".

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Vancomycin Resistant Enterococcus (VRE)

The genus Enterococcus (species Enterococcus faecalis and Enterococcus faecium) bacteria are part of the normal flora of the gastrointestinal and the female genital tract. Enterococci may develop resistance to a variety of antibiotics, particularly when repeatedly exposed to broad spectrum antibiotics. Most of the time, they do not cause infection, but may be associated with serious infection, particularly patients who are immunocompromised.

Vancomycin-resistant Enterococci (VRE) are specific types of antimicrobial-resistant bacteria that are resistant to vancomycin; a commonly used antibiotic for bacterial infections, including Enterococci. VRE is not more pathogenic, however is more likely to colonise vulnerable patients and there are fewer treatment options if invasive infection occurs.

VRE acquisition is usually healthcare-associated. Transmission may occur between patients, related to health workers, or be from environmental contamination.

Patients at risk for VRE acquisition include those on antibiotics, particularly broad-spectrum agents for extended periods; patients who are immunocompromised, those who have undergone abdominal or chest surgery; and those with urinary catheters or central intravenous lines.

Multidrug resistant gram negative organisms

Gram-negative bacilli (GNB) are a large group of bacteria that are commonly found in the intestinal tract of humans and most animals. They are part of the normal microflora and are essential for proper digestive processes. However, these bacteria may cause 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. Patients who are immunocompromised or who have long hospital admissions are especially vulnerable to infections with resistant GNB. There is global concern about the increasing incidence of antimicrobial resistance in the group of bacteria, making serious infections with these organisms increasingly difficult to treat.

Some strains are now resistant to many, most, or all available treatments resulting in increased illness and death from bacterial infections. Examples of Gram-negative bacteria that have demonstrated significant rates of antimicrobial resistance include:

  • Escherichia coli, which causes the majority of urinary tract infections
  • Acinetobacter baumanii, which causes disease mainly in healthcare settings, particularly in intensive care units
  • Pseudomonas aeruginosa, which causes bloodstream infections and pneumonia in hospitalised 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 Gonorrhoeae.

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. C difficile is widely distributed in the environment and faecal flora of humans and animals and almost always infection and/or colonisation 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. Infection is most commonly in the lungs, but may occur in other organs, including the brain and kidney, or bones and lymph nodes. Primary infection with TB may be very mild, or even asymptomatic however, TB may reactivate as a result of immunocompromise including advanced age.

TB is transmitted mainly by inhalation of infectious droplets produced by persons with pulmonary or laryngeal tuberculosis during coughing, laughing, shouting, singing or sneezing and most commonly in the home, or other environments where there may be overcrowding and/or poor ventilation. Transmission can occur in healthcare from 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 in the gram-negative bacilli group that are resistant to most antimicrobials.

Enterobacterales are a type of bacteria (known as Gram-negative bacilli, such as E. coli and Enterobacter), which are part of the normal gastrointestinal flora. Rarely, and mainly in people with underlying serious disease, they can cause serious and life-threatening blood stream infection, pneumonia, urinary tract and wound infection.

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 specific carbapenemases, which are enzymes which destroy carbapenems and other important β-lactam antibiotics such as penicillins and cephalosporins. Antibiotic treatment options for CPE are therefore limited.

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 been shown to be transmitted between patients and has been associated with a number of healthcare-associated outbreaks internationally. Another unusual feature of the global emergence of C. auris 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.

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Mycobacterium chimaera

Some heater-cooler units used in cardiac surgery have been contaminated with a rare bacterium called Mycobacterium chimaera (or M. chimaera). There is a very small risk that exposure to these units in the operating theatre may lead to infections in exposed patients that can appear many years after 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 a small number from NSW. All isolates undergo whole genome sequencing to assess whether the identified M. chimaera is the outbreak strain.

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