A 38-year-old woman from Delhi presents with a urinary tract infection caused by an ESBL-producing Escherichia coli. Which is the most common ESBL type encountered in clinical practice worldwide and in India?

Explanation

## ESBL Classification and Epidemiology **Key Point:** CTX-M ESBLs are the most prevalent ESBL type globally and in India, accounting for >80% of ESBL-producing Enterobacteriaceae in recent surveillance data. ### Historical Context of ESBL Types | ESBL Type | Origin | Prevalence | Geographic Pattern | |-----------|--------|-----------|--------------------| | **CTX-M** | Chromosomal (Kluyvera) | >80% globally | Dominant worldwide, especially India | | **TEM** | Plasmid-derived | ~10–15% | Declining; historically common | | **SHV** | Chromosomal (K. pneumoniae) | ~5–10% | Sporadic; declining | | **OXA** | Chromosomal (Acinetobacter) | <5% | Rare as ESBL; more common as carbapenemase | ### Why CTX-M Dominates 1. **Horizontal gene transfer:** CTX-M genes are located on mobile genetic elements (plasmids, integrons) that spread efficiently across species and continents. 2. **Selective advantage:** CTX-M enzymes have high catalytic efficiency against third-generation cephalosporins (especially cefotaxime), driving selection in antibiotic-heavy environments. 3. **Indian epidemiology:** CTX-M-15 and CTX-M-1 variants are the most common in Indian hospitals and community settings [cite:Chopra et al., Indian J Med Microbiol]. **Clinical Pearl:** The rise of CTX-M ESBLs parallels the increased use of third-generation cephalosporins in developing countries, making it the hallmark of modern ESBL resistance. **High-Yield:** In any NEET PG question about "most common ESBL," the answer is CTX-M unless the stem specifies a particular geographic region or historical period (pre-2000). ### Why Other Types Are Less Common - **TEM:** First ESBL discovered (1983), but plasmid-borne TEM variants are now outcompeted by CTX-M due to lower catalytic efficiency. - **SHV:** Primarily chromosomal in K. pneumoniae; plasmid-borne SHV ESBLs are rare and declining. - **OXA:** OXA-type β-lactamases are predominantly carbapenemases (OXA-48, OXA-181), not classical ESBLs.