Multi-resistant Gram-negative bacilli (MRGN)

What are Gram-negative bacilli?

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.

Antibiotic resistant strains

Over the past few decades the incidence of resistance in this group of bacteria has increased, sometimes making it more difficult to treat serious infections with these organisms. 

Types of resistance

Resistance in Gram-negative bacilli occurs by several mechanisms and have different resistance determinants. Those that pose particular problems for hospital patients can be broadly grouped into:

• transferable beta-lactam resistance, for example AMP-C, mostly found in E.coli and Salmonella species
• extended-spectrum beta-lactamases (ESBL) (PDF 73KB) – transferable resistance to 3^rd and 4^th generation cephalosporins, mostly found in E.coli, Klebsiella and Enterobacter species
• metallo-beta-lactamases (MBL) – similar to ESBL, but can also include resistance to carbapenems, mostly found in Pseudomonas aeruginosa
• carbapenemase, for example Carbapenum-producing resistant Enterobacteriales (CPE), an emerging resistance of concern.

Returned travellers are becoming a significant source of asymptomatic carriage, therefore a recent travel history on admission is important to detect potential risk.

Mode of transmission

These organisms are mainly found in the intestine, therefore any environmental surfaces that come into contact with faecal material can become contaminated and serve as a reservoir for cross-infection. Also, these organisms generally prefer a moist environment, and can quickly colonise sink drains and taps. They have also been known to contaminate diluted disinfectants and detergent solutions used for cleaning. The primary mode of cross-transmission is via the unwashed hands of clinical staff. Patients may also spread infection by touching their own urinary catheter or wound drainage tube. The duration of asymptomatic carriage of MRGN in the bowel varies considerably, but may be months to years in low numbers.

Prevention

The prevention of infection with MRGN involves the simultaneous application of a number of strategies:

• standard and transmission-based precautions 
• identification of carriage (screening of high risk patient groups) and appropriate inpatient placement for example single room for patients that pose a high risk of transmission
  
• diligent hand hygiene practices, including alcohol-based hand rubs at point of care
• application of personal protective equipment when performing patient care activities
• appropriate cleaning and disinfection of patient surroundings and medical equipment
• antimicrobial stewardship – making sure that antibiotics are prescribed appropriately.

Management

Hospitals should have a strategy for management of MRGN colonisation and infection with practices adapted to suit the clinical setting. For example, management of patients identified with MRGN in an intensive care unit may be different to management of a patient attending an outpatient department, where the risk of transmission and infection are lower.

Further information

For further information see the MRGN guideline or contact SA Health’s Infection Control Service.