The Molecular Characterization of Extended-Spectrum Beta-Lactamase (ESBL) and Carbapenem- Resistant Enterobacteriaceae (CRE) in Chicago Children, a two center study
Background: The study objectives were to 1) determine the genetic basis of ESBL and CRE phenotypes in Enterobacteriaceae isolates from children in two medical centers; 2) determine genetic relatedness of dominant ESBL and CRE strains.
Methods: We conducted a retrospective cohort study of clinical gram-negative isolates obtained from children ages 0-17 years hospitalized between 2011-12 at Rush and Lurie Children's Hospitals. PCR amplification of b-lactamase (blaTEM, blaSHV, blaCTX-M, blaKPC) genes was performed using established primers and amplified under thermocycling conditions. Repetitive-sequence-based PCR (rep-PCR) was used to assess the similarity of strains. Multilocus sequence typing (MLST) and DNA sequencing was performed on representative isolates from rep-PCR strain types for bacterial nomenclature and characterization. Plasmid DNA was extracted from select isolates and transformed into electrocompetent E. coli.
Results: Ninety-two isolates exhibited ESBL and/or CRE phenotypes. The predominant organism was E. coli 55/92 (59.8%) and predominant genotype was blaCTX-M 37/92 (40.2%). Some isolates contained >1 bla gene. Rep-PCR performed on the 55 E. coli revealed a diverse group with the most predominant strain accounting for 8/55 (14.5%) isolates (Figure 1). MLST was performed on select E. coli (LC5, LC34, LC54) and K. pneumoniae (LC8 & LC77). LC34 represents the predominant E. coli strain by rep-PCR and LC54 was selected as an unrelated strain type. LC34 was ST43 (ST131 in Achtman's MLST scheme). DNA sequencing confirmed the bla as CTX-M-15. LC54 carrying blaTEM was identified as ST3. LC5 and LC77 carried blaKPC. ST types for LC5 and LC77 were ST29 and ST105 respectively and DNA sequencing confirmed presence of KPC-2 carbapenemase. DNA containing antibiotic resistance genes from LC5 (KPC-2) and LC34 (CTX-M-15) E. coli strains were successfully transferred suggesting plasmid-based origin.
Conclusion: ESBL and CRE in children are diverse in origin. E. coli carrying the bla CTX-M gene are thought to be primarily community-acquired , whereas dissemination of blaKPC is traditionally in the healthcare setting. Like in adults, CTX-M is spread in E.coli ST131. In contrast, K.pneumoniae KPC bearing strains were non ST258, suggesting a different dissemination pattern than in adults.
Figure 1. Relatedness of E. coli
L. K. Logan,
A. M. Hujer, None
X. Zheng, None
R. Bonomo, None