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Multi-drug Resistant Organisms and Emerging Pathogens

Methicillin Resistant Staphylococcus aureus (MRSA)

Staphylococcus aureus (commonly known as staph) is a type of bacteria frequently found on the skin or in the nose, with around 30% of people carrying it without any signs of illness. While it usually causes no harm, it can sometimes lead to invasive infections and serious health issues. Certain strains of staph have developed resistance to multiple antibiotics, including methicillin. These are known as methicillin-resistant Staphylococcus aureus (MRSA), and are sometimes referred to as "golden staph."

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Vancomycin Resistant Enterococcus (VRE)

Bacteria of the Enterococcus genus, particularly Enterococcus faecalis and Enterococcus faecium, are normally found in the gastrointestinal tract and female genital tract. While they usually do not cause illness, they can lead to serious infections, especially in immunocompromised individuals. Enterococci can develop resistance to multiple antibiotics, particularly after repeated exposure to broad-spectrum agents.

Vancomycin-resistant Enterococci (VRE) are strains that have become resistant to vancomycin, an antibiotic commonly used to treat serious bacterial infections, including those caused by Enterococci. Although VRE is not inherently more virulent, it more readily colonises vulnerable patients and limits treatment options if infection occurs.

VRE is typically acquired in healthcare settings. Transmission can happen between patients—via health workers hands or contaminated environments. Those at higher risk of acquiring VRE include patients receiving prolonged courses of broad-spectrum antibiotics, immunocompromised individuals, those who have had abdominal or chest surgery, and patients with urinary catheters or central intravenous lines.

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Multidrug resistant gram negative organisms

Gram-negative bacilli (GNB) are a diverse group of bacteria commonly found in the intestinal tracts of humans and animals. As part of the normal gut flora, they play an important role in digestion. However, when introduced into normally sterile areas of the body—such as the bladder or internal tissues, often through surgical procedures or medical devices—they can cause infections. Immunocompromised patients and those with prolonged hospital stays are particularly susceptible to infections caused by resistant GNB.

There is growing global concern over rising antimicrobial resistance in this group, as some strains have become resistant to many—or even all—available antibiotics. These drug-resistant infections are increasingly difficult to treat and are associated with higher rates of illness and death.

Examples of Gram-negative bacteria that have demonstrated significant rates of antimicrobial resistance include:

  • Escherichia coli, which causes the majority of urinary tract infections
  • 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 anaerobic bacterium. It was first identified as the causative agent of pseudomembranous colitis in 1978, a condition strongly associated with the use of certain antibiotics, particularly clindamycin, which was newly introduced at the time.

C. difficile is ubiquitously distributed in the environment, and it is commonly found in the faecal flora of both humans and animals. Its ability to form resilient spores allows it to persist in various environmental reservoirs for extended periods.

Infection or colonisation by C. difficile is almost exclusively limited to the gastrointestinal tract. Disease typically arises following antibiotic-induced disruption of the normal gut microbiota, which allows C. difficile to proliferate and produce toxins, leading to symptoms ranging from mild diarrhea to severe colitis.

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Mycobacterium Tuberculosis

Tuberculosis (TB) is caused by bacteria of the Mycobacterium tuberculosis complex. Humans are the primary reservoir for this pathogen, although it can infect other animals, particularly non-human primates.

TB infection most commonly affects the lungs (pulmonary TB) but can also involve extrapulmonary sites such as the brain, kidneys, bones, and lymph nodes. Primary infection is often mild or asymptomatic, but the disease may reactivate, especially in individuals who are immunocompromised, such as the elderly or those with weakened immune systems due to other conditions or treatments.

Transmission of TB occurs primarily through the inhalation of infectious respiratory droplets. These droplets are expelled by individuals with pulmonary or laryngeal TB during activities such as coughing, sneezing, laughing, shouting, or singing. The risk of transmission is highest in close-contact settings, particularly in the home or environments with overcrowding and poor ventilation.

In healthcare settings, TB transmission may occur during high risk procedures, including:

  • Sputum induction
  • Nebuliser treatments
  • Bronchoscopy
  • Drainage of open abscesses
  • Autopsy
  • Any procedure that generates aerosols containing M. tuberculosis

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Carbapenemase-Producing Enterobacterales (CPE)

Carbapenemase producing organisms (CPO) are bacteria that are resistant to many antibiotics, including carbapenems. These organisms have genes which encode carbapenemases which are enzymes that can degrade or hydrolyse carbapenems and other beta-lactam antibiotics.

A common group of these bacteria is Enterobacterales, which includes E. coli, Klebsiella, Enterobacter, Citrobacter, Proteus, and Serratia. When these bacteria produce carbapenemases, they are called carbapenemase-producing Enterobacterales (CPE).

CPE are part of a larger group of organisms, called carbapenemase-producing organisms or CPOs, which also include species such as Pseudomonas and Acinetobacter. As the clinical management, including infection prevention and control strategies are very similar, the guidance in this document is applicable for CPOs and both terms will be used (CPE and CPO).

Preventing or reducing the risk of acquiring, infecting, and transmitting CPOs requires a combination of targeted surveillance to identify potentially colonised patients, antimicrobial stewardship, and effective infection prevention and control measures, including attention to environmental sources like sinks and wastewater. CEC resources are available here.

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Candida auris

Candida auris (C. auris) is a rare species of Candida that has been isolated in various body sites, including the skin, gastrointestinal tract, urogenital tract and respiratory tract  It has been identified as the cause of a range of invasive fungal infections similar to those caused by other Candida species. C. auris is often resistant to multiple antifungal agents typically used to treat Candida infections.

Unlike other fungal pathogens, C. auris is capable of spreading between patients and has been linked to numerous healthcare-associated outbreaks worldwide A particularly unusual aspect of its global emergence of C. auris is that, unlike many pathogens that originate from a single regional source and spread outward, whole genome sequencing of C. auris isolates from different parts of the world suggests independent clonal emergence and subsequent local transmission within each region.

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Mycobacterium chimaera

Some heater-cooler units (HCUs) used during cardiac surgery have been found to be contaminated with Mycobacterium chimaera, a rare, slow-growing environmental mycobacterium. Although the risk of infection is very low, patients exposed to these units in the operating theatre may develop infections that can manifest months or even years after surgery.

Infections associated with M. chimaera were first identified in Switzerland, where a cluster of cases was linked to a specific type of heater-cooler unit manufactured by LivaNova (formerly Sorin). These devices, used globally including in Australia, are believed to have been contaminated during the manufacturing process.

To date, over 120 cases of M. chimaera infection have been reported worldwide in patients following cardiac surgery, including a small number of confirmed cases in New South Wales (NSW). For all suspected cases, whole genome sequencing is performed to determine whether the strain matches the outbreak-associated M. chimaera.

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