Mrgn

KRINKO 2012 (Commission for Hospital Hygiene and Infection Prevention)

MRGN is the acronym for "multidrug-resistant gram-negative bacteria". In recent decades, multi-resistant gram-positive bacteria, which are now an important cause of nosocomial infections, have spread worldwide. For some years now, gram-negative germs, such as Pseudomonas aeruginosa, have also joined the ranks. Due to the generally poorer starting position of available antibiotics against Gram-negative germs, such multi-resistant infections are characterized by a high mortality.

In contrast to MRSA, MRGN is not defined by resistance mechanisms, but by the clinically relevant antibiotic groups to which bacteria develop resistance. The multi-resistance of MRSA is caused by various different resistance genes or enzymes (e.g. keywords such as ESBL = acronym for "extended-spectrum-ß-lactamase", which stands for a specific form of extended resistance to antibiotics in bacteria).

In the initial definition, 4 groups of antibiotics were defined, which are clinically used in cases of severe infection with Gram-negative bacteria (both members of the enterobacteria and so-called nonfermenters). The acronym MRGN is usually preceded by a number from 2-4 (2MRGN/3MRGN/4MRGN). The number presented defines the number of antibiotic classes to which the respective bacterium is resistant.

MRGN bacteria colonize about 5 out of 100 healthy people in the general population. Carbapenem-resistant enterobacteria currently already cause more infections (e.g. pneumonia, sepsis) than MRSA and VRE (vancomycin-resistant pathogens) combined.

In everyday clinical practice, 3MRGN and 4MRGN cause problems, especially in the treatment of nosocomial infections. In 2013, the Robert Koch Institute (FG14) produced a sample presentation for the definition of multiresistance in Gram-negative bacteria:

Acinetobacter baumannii (Nonfermenter)

• 3MRGN A. baumannii with resistance (R) to piperacillin, cefotaxime and ciprofloxacin, but sensitive (S) to imipenem and meropenem;
• 4MRGN A. baumannii with resistances (R) to piperacillin, cefotaxime, imipenem, meropenem and ciprofloxacin, but sensitive (S) to sulbactam. Sulbactam is not included in the multi-resistance definition.

Pseudomonas aeruginosa (Nonfermenter)

• 3MRGN P. aeruginosa with resistance (R) to piperacillin, imipenem, meropenem and ciprofloxacin, but sensitive (S) to ceftazidime and cefepim; as 4MRGN P. aeruginosa with resistances (R) to piperacillin, cefepim, imipenem and ciprofloxacin, but sensitive (S) to colistin and intermediate (I) to ceftazidim and meropenem. Intermediate results are

  evaluated

  as

  resistant results. For P. aeruginosa, ceftazidime instead of cefotaxime is also relevant for evaluation (cefotaxime is not very effective against Pseudomonas).

Klebsiella pneumoniae (enterobacteria)

• 3MRGN K. pneumoniae with ciprofloxacin (R) and ESBL#
• 4MRGN K. pneumoniae with piperacillin (R), cefotaxime (R), imipenem (R), meropenem (R) and ciprofloxacin (R), but sensitive (S) to ceftazidime

Enterobacter cloacae (or another Enterobacteriaceae species with chromosomal AmpC, such as Enterobacter aergogenes (the current name is Klebsiella aergogenes), Citrobacter freundii).

• 3MRGN E. cloacae with piperacillin (R), cefotaxime (R), ceftazidime (R) and ciprofloxacin (R), but imipenem (S) and meropenem (S). Resistance to the two cepaholsporines may be caused by overexpression of AmpC-beta-lactamase encoded in the bacterial chromosome.

Healthy people who are colonised with MRGN bacteria are called MRGN carriers. For MRG carriers, however, the germs are harmless with normal immunity. Therefore, no treatment is necessary when colonised with MRGN bacteria without signs of disease.

Therapy is only indicated if MRGN bacteria cause a clinically relevant MRGN infection. The Robert Koch-Institute recommends with the detection of the gram-negative pathogens 3MRGN and 4MRGN E.coli, Klebsiella ssp., P. aeruginosa, A. baumanii in risk areas such as neonatology, intensive care units, haemato-oncological problem units with immunologically weakened patients, accommodation in a single room with its own wet room or a cohort in patients with the same pathogen species and the same phenotype with appropriate hygienic accompanying measures. In normal areas of wards, outpatient clinics and practices, only patients with 4MRGN should be isolated. For 3MRGN basic hygiene is sufficient, as well as for 4MRGN Enterobacter spp.

S.a. ESKAPE

1. Hogardt M et al (2015) Current prevalence of multidrug-resistant organisms in long-term care facilities in the Rhine-Main district, Ge many, 2013 Euro Surveill 20. pii: 21171.
2. Huggett S et al. (2018) Antibiotics Primer 2018/2019. Asklepios, Medical Scientific Publishing Company. S.51-52
3. Leitner E et al (2018) Low prevalence of colonization with multidrug-resistant gram-negative bacteria in long-term care facilities in Graz, Austria. At J Infect Control 46:76-80.
4. Laux R et al (2013) Relevance of parents as source for contamination of neonates with multiresistant Gram-negative pathogens (MRGN)]. Z Obstetrics Neonatol 217:61-64.