Development of a Sensitive and Specific Enzyme-Linked Immunosorbent Assay for Detecting and Quantifying CMY-2 and SHV β-Lactamases

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Abstract
Polyclonal rabbit antibodies against SHV-1 and CMY-2 β-lactamases were produced and characterized, and enzyme-linked immunosorbent assays (ELISAs) were developed. Immunoblots revealed that the anti-SHV-1 antibody recognized SHV-1 but did not recognize TEM-1, K-1, OXA-1, or any AmpC β-lactamase tested. The anti-CMY-2 antibody detected Escherichia coli CMY-2, Enterobacter cloacae P99, Klebsiella pneumoniae ACT-1, and the AmpC β-lactamases of Enterobacter aerogenes, Morganella morganii, and Citrobacter freundii. No cross-reactivity of the anti-CMY-2 antibody was seen against laboratory strains of E. coli possessing TEM-1, SHV-1, K-1, or OXA-1 β-lactamases. Operating conditions for performing ELISAs were optimized. Both anti-CMY-2 and anti-SHV-1 antibodies detected picogram quantities of purified protein in ELISAs. The reactivity of the anti-CMY-2 antibody was tested against a number of AmpC β-lactamases by assaying known quantities of purified enzymes in ELISAs (AmpC β-lactamases of M. morganii, C. freundii, E. coli, and E. cloacae). As the homology to CMY-2 β-lactamase decreased, the minimum level needed for detection increased (e.g., 94% homology recognized at 1 ng/ml and 71% homology recognized at 10 ng/ml). The ELISAs were used to assay unknown clinical isolates for AmpC and SHV β-lactamases, and the results were confirmed with PCR amplification of blaAmpC and blaSHV genes. Overall, we found that our ELISAs were at least 95% sensitive and specific for detecting SHV and AmpC β-lactamases. The ELISA format can facilitate the identification of AmpC and SHV β-lactamases and can be used to quantify relative amounts of β-lactamase enzymes in clinical and laboratory isolates.

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