What other organisms are classified as Carbapenem-Resistant Enterobacteriaceae (CRE)?

Organisms Classified as Carbapenem-Resistant Enterobacteriaceae (CRE)

Klebsiella pneumoniae and Escherichia coli are the predominant organisms classified as CRE, with K. pneumoniae accounting for 53-77% of all CRE isolates and representing the most frequently recovered CRE species in U.S. healthcare settings. 1

Primary CRE Species

Klebsiella pneumoniae is the dominant CRE organism:

• Represents approximately 53-77% of all CRE isolates in surveillance studies 1
• Carbapenem-resistant K. pneumoniae (CRKP) is the most commonly encountered CRE species in the United States 2
• Prevalence increased dramatically from <1% of all Klebsiella isolates in 2000 to 8% by 2007 1

Escherichia coli is the second major CRE organism:

• CDC and HICPAC guidelines specifically target both Klebsiella species and E. coli for active surveillance cultures because these two organisms represent the majority of CRE encountered in the United States 1
• These organisms can be detected without molecular methods, making them practical surveillance targets 3

Other Enterobacteriaceae Species

While the guidelines emphasize K. pneumoniae and E. coli, CRE encompasses all members of the Enterobacteriaceae family that demonstrate resistance to carbapenems (doripenem, imipenem, or meropenem) 2. This broader family includes:

• Other Klebsiella species beyond K. pneumoniae 3
• Additional Enterobacteriaceae genera that can acquire carbapenem resistance through carbapenemase production or other mechanisms 3

Clinical Surveillance Rationale

The focused surveillance on Klebsiella spp. and E. coli is strategically justified because:

• These two species constitute the vast majority of clinically significant CRE infections 3, 1
• Detection methods for these organisms are more readily available in standard microbiology laboratories 1
• Carbapenemase genes are carried on mobile genetic elements (plasmids and transposons), allowing rapid dissemination between bacterial species 2

Resistance Mechanism Classification

All CRE organisms share carbapenem resistance but differ in mechanisms:

• Carbapenemase-producing Enterobacteriaceae (CPE) produce enzymes (KPC, NDM, VIM, IMP, OXA-48-like) that hydrolyze carbapenems 3
• Non-CPE CRE achieve resistance through other mechanisms such as porin loss 3, 2
• The term "CPE" is more precise than "CRE" when carbapenemase production is confirmed 2