Important antimicrobial resistant organisms

• Antimicrobial resistance has emerged in bacteria due to various reasons:

  • Bacteria can be inherently resistant to certain antimicrobials
  • Bacteria can acquire resistance to other antimicrobials through mutation or genetic exchange processes
  • Factors like suboptimal antimicrobial stewardship, non-compliance, limited access to diagnostic facilities, and inappropriate use in other sectors contribute to antimicrobial resistance
• Consequences of antimicrobial resistance (AMR) include:

  • Changes in microbial fitness leading to bacteria being less susceptible
  • Empiric treatment failures
  • Delayed appropriate treatment of sepsis
  • Increased morbidity, mortality, healthcare costs, and hospital stays
  • Increased use of more expensive medications and broader spectrum antimicrobials
• Common antimicrobial resistant organisms include:

  • Gram-negatives like Enterobacterales (K. pneumoniae, E. cloacae, E. coli), Acinetobacter baumannii, Pseudomonas aeruginosa, Stenotrophomonas maltophilia
  • Gram-positives like Meticillin-resistant Staphylococcus aureus (MRSA), Vancomycin-resistant enterococci (VRE)
  • Others like Multi-drug-resistant Mycobacterium tuberculosis, Rapidly-growing mycobacteria, Mycobacterium avium complex
• Factors contributing to antimicrobial resistance include:

  • Suboptimal antimicrobial stewardship
  • Non-compliance by prescribers or patients
  • Limited access to diagnostic facilities
  • Inappropriate use in other sectors like agriculture
• Infections caused by antimicrobial resistant organisms can lead to:

  • Empiric treatment failures
  • Delayed appropriate treatment of sepsis
  • Increased morbidity, mortality, healthcare costs, and hospital stays
• Empiric antimicrobial treatment for suspected bacterial meningitis may include IV Ceftriaxone plus vancomycin to provide broad cover and additional cover for potential beta-lactam resistant Gram-positives
• If the organism causing the infection was found to be penicillin susceptible, switching the patient to IV Benzylpenicillin could be considered
• Penicillin-resistant Streptococcus pneumoniae can be prevented by measures like appropriate use of antimicrobials and vaccination with available vaccines like the 23-valent pneumococcal polysaccharide vaccine (PPV-23) and the 13-valent pneumococcal conjugate vaccine (PCV-13)
• In Europe in 2022, almost 1-in-4 (23%) of invasive S. pneumoniae infections were due to penicillin non-susceptible isolates
• Meticillin-resistant Staphylococcus aureus (MRSA) is mainly associated with hospital and healthcare environments and can cause a similar spectrum of infections as meticillin-susceptible Staphylococcus aureus (MSSA)
• MRSA is decreasing across the EU/EEA, but many countries in Southern Europe still have high levels of MRSA
• Laboratory findings like Optochin can help identify the organism causing the infection, such as Streptococcus pneumoniae
• Changing empiric antimicrobials may be considered based on laboratory findings to ensure appropriate treatment
• MRSA is intrinsically resistant to beta-lactams due to the production of an altered penicillin binding protein (PBP2a) encoded by the mecA gene, which confers resistance to most beta-lactam antibiotics
• In the treatment of MRSA infection, vancomycin would be the most appropriate antimicrobial
• A well-recognised side-effect of vancomycin is nephrotoxicity
• The most likely source of the MRSA infection in the 70-year-old woman after knee replacement surgery was the hospital
• To prevent MRSA infections, it is important to follow infection prevention measures such as standard precautions, antimicrobial stewardship, isolation of colonised patients with contact precautions, and topical decolonisation of colonised individuals
• Linezolid, used in the treatment of MRSA, requires monitoring for potential side effects like myelosuppression and interactions with certain antidepressants
• Patients taking linezolid should avoid food and beverages with high tyramine content to prevent an increase in blood pressure
• VRE (Vancomycin-resistant enterococci) are often found in the enteric tract and are inherently resistant to several antimicrobial classes
• VRE resistance can develop through different mechanisms, with some located on the enterococcal chromosome and others on plasmids that can be transferred between enterococci
• Enterobacterales, a large order of Gram-negative rods found in the enteric tract, can develop resistance to different antimicrobial classes, leading to multi-drug resistance (MDR)
• Enterobacterales can produce enzymes like extended-spectrum beta-lactamases (ESBL) and carbapenemases, which can inhibit a wide range of beta-lactam antibiotics, including carbapenems
• Members of Enterobacterales can share genes that encode for beta-lactamases, contributing to the spread of antimicrobial resistance
• Carbapenemases, produced by Enterobacterales, can destroy carbapenems, the last resort beta-lactam antibiotics with the largest spectrum of activity
• VRE carriers do not require treatment, and VRE, whether vancomycin-susceptible or resistant, does not cause diarrhea unless the patient has diarrhea for another reason, shedding VRE into their environment
• Treatment of VRE infections should be based on susceptibilities of the individual isolate
• Weekly full blood counts are recommended for patients on linezolid to monitor for myelosuppression
• Linezolid is contraindicated for patients taking SSRIs and tricyclic antidepressants due to potential interactions
• Vancomycin requires therapeutic drug monitoring due to renal and ototoxicity
• Linezolid can lead to bone marrow suppression and is not recommended for use for more than four weeks
• Infection prevention measures are crucial to prevent the emergence and transmission of MRSA in healthcare settings
• The most appropriate antimicrobial for the treatment of MRSA infection is vancomycin
• Nephrotoxicity is a well-recognised side-effect of vancomycin
• The hospital was the most likely source of the MRSA infection in the 70-year-old woman after knee replacement surgery
• Beta-lactams are crucial in treating infections caused by Enterobacterales, but the acquisition of beta-lactamase enzymes by Enterobacterales can render beta-lactams ineffective
• Enterobacterales can produce ESBLs and carbapenemases like OXA-48, KPC, NDM, VIM, and IMI carbapenemases
• ESBL E. coli can share with K. pneumoniae, making it ESBL K. pneumoniae
• CPE E. cloacae can share with E. coli, making it CPE E. coli