A 42-year-old woman from Mumbai is admitted with severe pneumonia and sepsis. Sputum culture grows a gram-negative rod identified as *Klebsiella pneumoniae*. Antibiotic susceptibility testing shows resistance to all beta-lactams including carbapenems (meropenem MIC 16 µg/mL), but susceptibility to colistin and tigecycline. The organism produces a Hodge test-positive result. Which carbapenemase enzyme is most likely responsible for this resistance pattern in this Indian hospital setting?

Explanation

## Carbapenemase-Mediated Resistance: NDM in Indian Context ### Clinical Presentation and Key Findings **Key Point:** The combination of pan-beta-lactam resistance (including carbapenems), Hodge test positivity, and Indian geographic origin strongly suggests NDM (New Delhi Metallo-Beta-Lactamase) production. ### Why NDM? 1. **Geographic epidemiology**: NDM was first identified in India (2008) and remains endemic in Indian hospitals. It is the most common carbapenemase in India and South Asia. 2. **Pan-carbapenem resistance**: The organism is resistant to meropenem with elevated MIC (16 µg/mL), indicating true carbapenemase activity. 3. **Hodge test positive**: This phenotypic test detects carbapenemase production by demonstrating inactivation of carbapenem in the test medium. 4. **Colistin and tigecycline susceptibility**: Typical pattern for NDM-producing organisms; these are last-line agents for pan-resistant gram-negatives. 5. **Organism**: *Klebsiella pneumoniae* is a common NDM producer in India. ### Carbapenemase Classification and Comparison | Feature | NDM (Class B) | KPC (Class A) | OXA-48 (Class D) | |---------|---------------|--------------|------------------| | **Mechanism** | Metallo-enzyme (Zn²⁺-dependent) | Serine beta-lactamase | Oxacillinase | | **Carbapenem Resistance** | Strong (MIC ≥16) | Strong (MIC ≥16) | Moderate (MIC 2–8) | | **Cephamycin Resistance** | Yes | Yes | No (susceptible) | | **Hodge Test** | Positive | Positive | Negative/Weak | | **Beta-lactamase Inhibitor** | NOT inhibited by clavulanic acid | Inhibited by clavulanic acid | NOT inhibited | | **Geographic Origin** | India, South Asia (endemic) | USA, Europe, Middle East | Europe, Middle East | | **Colistin Susceptibility** | Usually susceptible | Usually susceptible | Usually susceptible | **High-Yield:** NDM is the most common carbapenemase in India. It is a metallo-beta-lactamase (Class B) that requires zinc for catalytic activity and is NOT inhibited by standard beta-lactamase inhibitors. ### NDM Epidemiology in India **Clinical Pearl:** NDM-producing organisms are increasingly prevalent in Indian healthcare settings, community environments, and even drinking water sources. Patients with recent hospitalization, healthcare exposure, or travel to India are at high risk of NDM-producing gram-negative infections. **Mnemonic: NDM-India-Hodge** — New Delhi Metallo-Beta-Lactamase is endemic in India, produces Hodge test positivity, and causes pan-carbapenem resistance. ### Diagnostic Algorithm for Carbapenem Resistance ```mermaid flowchart TD A[Carbapenem-Resistant Gram-Negative]:::outcome --> B{Hodge Test}:::decision B -->|Positive| C[Carbapenemase Producer]:::action B -->|Negative| D[Non-enzymatic Resistance]:::action C --> E{Beta-lactamase Inhibitor Response?}:::decision E -->|Inhibited by Clavulanic Acid| F[KPC or Serine Carbapenemase]:::outcome E -->|NOT Inhibited| G[NDM or Metallo-Carbapenemase]:::outcome D --> H[Altered PBPs or Efflux Pumps]:::outcome G --> I[Consider Geographic Origin]:::action I -->|India/South Asia| J[NDM Most Likely]:::action I -->|USA/Europe| K[IMP or VIM]:::action ``` **Tip for Exam:** When you see "India" + "carbapenem resistance" + "Hodge positive," think NDM first. KPC is more common in the USA and Europe.