Emergence of carbapenem-resistant Escherichia coli producing CMY-2-type AmpC {beta}-lactamase in Brazil

This study reports the first emergence of carbapenem-resistant Escherichia coli producing CMY-2-type AmpC β-lactamase in Brazil, expanding the geographic distribution of this resistance mechanism in South America. Four multidrug-resistant E. coli strains (EC1-EC4) were isolated sequentially from blood and wound cultures of a 46-year-old liver transplant patient hospitalized in São Paulo between June and August 2007. All isolates were resistant to carbapenems, extended-spectrum cephalosporins, cefoxitin, and fluoroquinolones, remaining susceptible only to aminoglycosides. Molecular analysis confirmed the presence of blaCMY-2 genes with 99% identity to previously described plasmid-encoded variants. Importantly, all four isolates demonstrated loss of a 36 kDa outer membrane porin, a key mechanism contributing to carbapenem resistance alongside AmpC production. The combination of CMY-2 AmpC β-lactamase expression and porin deficiency conferred high-level resistance to multiple β-lactam antibiotics. Despite treatment with polymyxin B, the patient died from sepsis-related multiple organ failure. This case confirms that CMY-2-producing strains have become established in Latin America, representing an emerging public health concern requiring continued surveillance.

Key findings

• First documented emergence of carbapenem-resistant E. coli producing CMY-2-type AmpC β-lactamase in Brazil, with isolates showing 99% sequence identity to previously described plasmid-encoded CMY-2 genes
• Carbapenem resistance resulted from combined mechanisms: CMY-2 AmpC β-lactamase production plus loss of a 36 kDa outer membrane porin
• All four E. coli isolates recovered from a single patient were clonally related and exhibited multidrug resistance, remaining susceptible only to aminoglycosides
• CMY-2-producing enterobacteria have become established in South America, representing an emerging public health threat distinct from previously reported IMP-1 and KPC-2 mechanisms in the region