Guideline for Diagnosis and Management of Carbapenemase‑Producing Enterobacterales

Epidemiology

• Carbapenem resistance in Europe has risen more than seven‑fold since 2006, with Italy and Greece reporting > 50 % resistance among Klebsiella pneumoniae isolates. 1

Molecular Classification of Major Carbapenemases

• KPC (Class A, serine‑based) accounts for ≈ 47 % of meropenem‑resistant Enterobacterales worldwide. 1
• NDM (Class B, metallo‑β‑lactamase) represents ≈ 21 % of carbapenem‑resistant isolates. 1
• OXA‑48‑like (Class D, oxacillinase) comprises ≈ 19 % of carbapenem resistance. 1
• Mechanistic distinction: NDM and other MBLs hydrolyze all β‑lactams except aztreonam, whereas KPC and OXA‑48 have different hydrolytic spectra. 2
• Inhibitor susceptibility: MBLs cannot be inhibited by classic serine β‑lactamase inhibitors (e.g., avibactam, vaborbactam), while KPC and OXA‑48 are inhibited by newer β‑lactam/β‑lactamase inhibitor combinations. 2

Rapid Detection Strategies

Genotypic Testing (Preferred)

• Real‑time PCR delivers 98 % sensitivity, 100 % specificity, and a ≤ 3‑hour turnaround. 3
• Loop‑mediated isothermal amplification (LAMP) provides a 2–3‑hour result with sensitivity and specificity comparable to PCR. 3

Phenotypic Testing (Resource‑Limited Settings)

• Combined Disc Test (CDT) with appropriate inhibitors yields 100 % sensitivity for isolated KPC or MBL producers, 96.8 % for co‑producers, and 98.8 % specificity. 3
• Modified carbapenem inactivation method (mCIM) / EDTA‑modified CIM (eCIM) shows ≈ 95 % concordance with molecular results. 3
• Limitations of CDT: sensitivity ≈ 88 % and specificity ≈ 79 % for MBL detection; poor performance for IMP‑type enzymes. 3
• Modified Hodge test identified 47/48 carbapenemase producers in validation studies. 3

Treatment Recommendations by Carbapenemase Type

KPC‑Producing Isolates

• First‑line: Ceftazidime/avibactam or meropenem/vaborbactam – strong recommendation, moderate‑quality evidence. 2
• Alternative: Imipenem/relebactam or cefiderocol – conditional recommendation, low‑quality evidence. 2
• Rationale: These β‑lactam/β‑lactamase inhibitor combos effectively inhibit class A serine enzymes. 2

NDM / Other MBL‑Producing Isolates

• First‑line: Ceftazidime/avibactam plus aztreonam – strong recommendation (evidence level not specified). 2
• Rationale: Aztreonam remains stable against MBLs, while avibactam protects aztreonam from co‑produced ESBLs. 2

OXA‑48‑Like Producing Isolates

• First‑line: Ceftazidime/avibactam – conditional recommendation, very low‑quality evidence (citation not provided; omitted).

Clinical Implementation Algorithm

• Immediate rapid carbapenemase testing should be performed when carbapenem resistance is suspected or confirmed. 1
• Identify the specific carbapenemase family (KPC vs. NDM/MBL vs. OXA‑48) before selecting therapy. 1
• Select antimicrobial regimen based on the enzyme class as outlined above. 1
• Prompt initiation of active therapy after a positive blood culture markedly reduces mortality in critically ill patients with carbapenemase‑producing infections. 2

Key Pitfalls to Avoid

• Do not assume all carbapenem‑resistant organisms harbor the same carbapenemase; treatment must be tailored to the identified enzyme. 1
• Do not delay rapid carbapenemase testing; phenotypic susceptibility alone is insufficient for optimal therapy selection. 1
• Avoid using ceftazidime/avibactam or meropenem/vaborbactam alone for MBL‑producing infections, as these agents do not inhibit metallo‑β‑lactamases. 1
• Do not rely on CDT for detecting IMP‑type MBLs due to its poor accuracy for this variant. 3

Carbapenemase-Producing Enterobacterales

Classification and Mechanism

• KPC (Class A) is a serine-based carbapenemase that remains the most common type globally, accounting for 47.4% of meropenem-resistant Enterobacterales 4
• MBL (Class B) includes metallo-beta-lactamases such as NDM, VIM, and IMP enzymes that require zinc ions for activity, representing 20.6% of carbapenem-resistant isolates 4
• OXA-48 (Class D) is an oxacillinase-type carbapenemase accounting for approximately 19% of carbapenem resistance 4

Critical Clinical Differences

• The most important distinction is that MBLs hydrolyze all beta-lactam antibiotics except aztreonam, while KPC and OXA-48 have different hydrolytic profiles that directly impact treatment selection 4
• MBLs hydrolyze all beta-lactam classes except monobactams (aztreonam) 4
• MBLs cannot be inhibited by classic serine beta-lactamase inhibitors (avibactam, vaborbactam) 4

Treatment Implications by Carbapenemase Type

• For KPC producers, first-line treatment is ceftazidime/avibactam or meropenem/vaborbactam (STRONG recommendation, MODERATE evidence) 4
• For OXA-48 producers, first-line treatment is ceftazidime/avibactam (CONDITIONAL recommendation, VERY LOW evidence) 5
• For MBL producers, first-line treatment is ceftazidime/avibactam PLUS aztreonam (STRONG recommendation) 5
• Alternative treatment for MBL producers is cefiderocol 5
• Aztreonam remains stable against MBLs since they cannot hydrolyze monobactams 4

Geographic Distribution and Epidemiology

• Carbapenem resistance has increased more than seven-fold since 2006 in Europe 4

Common Pitfalls to Avoid

• Do not assume all carbapenem-resistant bacteria have the same carbapenemase - treatment efficacy depends entirely on the specific enzyme class 4
• Do not delay rapid carbapenemase testing - phenotypic susceptibility testing alone is insufficient for optimal treatment selection 4

Genotypic Carbapenemase Detection and Implications for Therapy

Diagnostic Accuracy of Molecular Testing

• Real‑time PCR for carbapenemase genes provides ≈ 98 % sensitivity and 100 % specificity with a turnaround time of ≤ 3 hours, making it the preferred method over phenotypic assays for rapid identification of the carbapenemase class. 6, 7

Clinical Significance of Carbapenemase Co‑Production

• Documented co‑production of KPC with metallo‑β‑lactamases (e.g., NDM, VIM, IMP) requires combination antimicrobial regimens—such as a β‑lactam/β‑lactamase inhibitor plus aztreonam or polymyxin‑based therapy—to ensure activity against both enzyme families. 6