# Klebsiella and Carbapenem-Resistant Enterobacterales

> Klebsiella and carbapenem-resistant Enterobacterales for NEET-PG Microbiology, covering capsule, ESBL, KPC and NDM enzymes and enzyme-guided treatment.

- Canonical URL: https://prepelephant.com/topics/neet-pg/microbiology/klebsiella-and-carbapenem-resistant-enterobacterales
- Exam / course: NEET-PG · Subject: Microbiology
- Publisher: PrepElephant (https://prepelephant.com) — Prepared and reviewed by the PrepElephant Academic Review Team
- First published: 2026-10-14
- Last updated: 2026-10-14
- Reference basis: Mandell, Douglas and Bennett's Principles and Practice of Infectious Diseases; Ananthanarayan and Paniker's Textbook of Microbiology; Harrison's Principles of Internal Medicine
- How to cite: "Klebsiella and Carbapenem-Resistant Enterobacterales", PrepElephant, https://prepelephant.com/topics/neet-pg/microbiology/klebsiella-and-carbapenem-resistant-enterobacterales

## Direct answer

Klebsiella and carbapenem-resistant Enterobacterales describe Enterobacterales, mainly Klebsiella pneumoniae, that resist carbapenems, most often through carbapenemase enzymes such as KPC and NDM. Carbapenemases hydrolyse the reserve beta-lactams, so these infections need agents chosen by enzyme type, such as ceftazidime-avibactam for KPC or cefiderocol for metallo-beta-lactamases. Rapid detection and strict infection control limit their spread in hospitals.

## What you must remember

- **Capsule:** a thick polysaccharide capsule protects Klebsiella pneumoniae from phagocytosis, and hypermucoviscous strains give a positive string test.
- **Lobar pneumonia:** Klebsiella pneumoniae causes necrotising lobar pneumonia, often in alcoholics and diabetics, with thick, currant jelly sputum.
- **ESBL:** extended-spectrum beta-lactamases such as CTX-M hydrolyse third-generation cephalosporins and are detected by clavulanate synergy.
- **KPC:** Klebsiella pneumoniae carbapenemase, a class A serine enzyme that is widely disseminated and inhibited by avibactam.
- **NDM:** New Delhi metallo-beta-lactamase, a class B zinc-dependent enzyme that is not inhibited by clavulanate or avibactam.
- **Biochemistry:** Klebsiella is lactose-fermenting, urease-positive, indole-negative and Voges-Proskauer-positive, with mucoid colonies.
- **Infection control:** carbapenemase genes travel on plasmids, so contact precautions, hand hygiene and screening of contacts limit hospital spread.

## An enzyme-guided pathway for a carbapenem-resistant isolate

An intensive care patient with ventilator-associated pneumonia grows Klebsiella pneumoniae that is resistant to all carbapenems. The steps show how the laboratory and clinician identify the enzyme class before choosing a drug.

1. **Confirm the resistance:** minimum inhibitory concentration or disc testing confirms reduced susceptibility to imipenem, meropenem and ertapenem.
2. **Screen for carbapenemase:** a modified carbapenem inactivation method or a rapid immunochromatographic assay identifies enzymes such as KPC, NDM, OXA-48 and VIM.
3. **Identify the enzyme class:** an EDTA-imipenem synergy test shows an enlarged zone of inhibition when a metallo-beta-lactamase is present, separating these from serine carbapenemases.
4. **Select a targeted regimen:** ceftazidime-avibactam or meropenem-vaborbactam is considered for KPC, while cefiderocol or aztreonam combined with avibactam is used for NDM, with colistin as a fallback.
5. **Apply infection control:** contact precautions and dedicated equipment are started at once, since carbapenemase genes spread between organisms on plasmids.
6. **Report the result:** the isolate is reported to the antimicrobial stewardship and infection control committees, so that the local antibiogram and ward practice are updated.

## Where the exam tries to catch you

Carbapenem-resistant Enterobacterales questions test enzyme classes and which inhibitor works against which enzyme.

- **Trap:** treating a carbapenem-resistant isolate like an ESBL producer — **Correct:** carbapenemases escape standard beta-lactamase inhibitors, so enzyme-specific agents are needed.
- **Trap:** expecting clavulanate to inhibit NDM — **Correct:** metallo-beta-lactamases such as NDM are not inhibited by clavulanate or avibactam, so the choice of agent depends on the enzyme class.
- **Trap:** assuming carbapenem resistance always means carbapenemase production — **Correct:** resistance can also arise from porin loss combined with AmpC or ESBL production, so phenotypic and genotypic testing are both used.

## Frequently asked questions

### What is the main mechanism of carbapenem resistance in Klebsiella pneumoniae?
The main mechanism is carbapenemase production, with KPC, NDM, OXA-48 and VIM being the important enzymes. These enzymes hydrolyse carbapenems, and their genes often sit on plasmids that spread between bacteria.

### Why is Klebsiella pneumoniae pneumonia described as producing currant jelly sputum?
Klebsiella pneumoniae causes necrotising lobar pneumonia with thick, blood-tinged, mucoid sputum that resembles currant jelly. The sputum reflects the heavy capsule and the mucoid nature of the infection in susceptible patients.

### Which enzymes does ceftazidime-avibactam cover?
Ceftazidime-avibactam combines a cephalosporin with avibactam, a beta-lactamase inhibitor that blocks KPC, many ESBL enzymes and AmpC. It is inactive against metallo-beta-lactamases such as NDM, so the enzyme class must be known before it is chosen.

### Which test distinguishes metallo-beta-lactamase producers from serine carbapenemases?
The EDTA-imipenem synergy test distinguishes metallo-beta-lactamase producers from serine carbapenemases. EDTA chelates zinc, so an enlarged inhibition zone around the EDTA-containing disc suggests metallo-beta-lactamase production.

### Why do carbapenem-resistant Enterobacterales need strict infection control?
Carbapenem-resistant Enterobacterales spread readily in intensive care units, on contaminated hands and on equipment, and carbapenemase genes travel on plasmids. Contact precautions, hand hygiene and screening of contacts limit spread in hospitals.