Monoclonal antibodies to TEM-1 plasmid-mediated beta-lactamase

Monoclonal antibody-mediated detection of CTX-M β-lactamases in Gram-negative bacteria

Gram-negative bacteria (GNB) that express CTX-M β-lactamases have become a serious threat to the clinical management of GNB infections. While antibody-based platforms have been successfully used in research settings to study and detect other β-lactamases-including SHV, CMY, and TEM enzymes-there is currently a lack of antibody-based tools to detect the CTX-M enzymes. Here we describe the development of an anti-CTX-M sandwich ELISA based on a pair of monoclonal antibodies (mAbs)-mAb 6101-33 and mAb 6101-19-used as the capture and detection antibody, respectively. This antibody pair detected CTX-M variants from group 1 (CTX-M-15), group 2 (CTX-M-2), group 8 (CTX-M-8), and group 9 (CTX-M-14) that were expressed by a training set of clinical GNB isolates. The limit of detection for this sandwich ELISA was 30ng of recombinant CTX-M-15, and CTX-Ms expressed by 10⁶ lysed CFU of GNB. When tested against a blinded panel of 78 clinical isolates, the sandwich ELISA demonstrated a sensitivity of 96% and a specificity of 100%. The mAb pair did not cross-react with bacteria that contained other β-lactamases, including TEM, SHV, OXA, KPC, NDM, CMY, and DHA. In conclusion, we developed a highly sensitive and specific sandwich ELISA, capable of detecting CTX-M enzyme production in GNB pathogens.

Detection of β-lactamase residues in milk by sandwich ELISA

β-Lactamase residues in milk represent a public health risk. The cylinder plate detection method, which is based on bacterial growth, is laborious and time consuming. In this study, 15 monoclonal antibodies (mAbs) were selected against Temoneira (TEM) 1 β-lactamase. A sandwich enzyme-linked immunosorbent assay (ELISA) based on an optimum mAb pair was developed and validated for the detection of β-lactamase. The limit of detection and linear dynamic range of the method were 4.17 ng/mL and 5.5–100 ng/mL, respectively. β-Lactamase recovery in pure milk was 96.82–103.13%. The intra- and inter-assay coefficients of variation were 6.21–7.38% and 12.96–13.74%, respectively. Our developed sandwich ELISA can be used as a rapid detection method of β-lactamase in milk.

Development of a sensitive and specific enzyme-linked immunosorbent assay for detecting and quantifying CMY-2 and SHV beta-lactamases

Polyclonal rabbit antibodies against SHV-1 and CMY-2 beta-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 beta-lactamase tested. The anti-CMY-2 antibody detected Escherichia coli CMY-2, Enterobacter cloacae P99, Klebsiella pneumoniae ACT-1, and the AmpC beta-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 beta-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 beta-lactamases by assaying known quantities of purified enzymes in ELISAs (AmpC beta-lactamases of M. morganii, C. freundii, E. coli, and E. cloacae). As the homology to CMY-2 beta-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 beta-lactamases, and the results were confirmed with PCR amplification of bla(AmpC) and bla(SHV) genes. Overall, we found that our ELISAs were at least 95% sensitive and specific for detecting SHV and AmpC beta-lactamases. The ELISA format can facilitate the identification of AmpC and SHV beta-lactamases and can be used to quantify relative amounts of beta-lactamase enzymes in clinical and laboratory isolates.

Selection and application of antibodies modifying the function of beta-lactamase

Nine monoclonal antibodies directed against class A beta-lactamases were detected and selected by a novel screening procedure based on assaying the modifications in the catalytic and stability properties of beta-lactamase in solution. Unlike conventional screening, e.g., ELISA or immunoprecipitation, the present method does not depend on firm binding and thus favors detection of low affinity antibodies. Individual antibodies were found to affect the enzymatic activity in various ways including stimulation, neutralization, protection and stabilization. Class A beta-lactamases show only 20% among members of this class. In contrast, two of our monoclonal antibodies cross-reacted with different beta-lactamases and thus demonstrate the presence of shared structural epitopes in this class of enzymes. One of the cross-reacting antibodies was elicited by sequential immunization with two different beta-lactamases. Taken together, our findings stress the importance of the screening method in antibody selection and illustrate the use of 'functional' monoclonal antibodies in the study of the structure-function relationship in an enzyme.

Novel carbenicillin-hydrolyzing beta-lactamase (CARB-5) from Acinetobacter calcoaceticus var. anitratus

A strain of Acinetobacter calcoaceticus var. anitratus highly resistant to ticarcillin but susceptible to ticarcillin in combination with clavulanic acid (2 mg/l) was found to produce a constitutive beta-lactamase. This enzyme was periplasmic with a characteristic substrate profile of a carbenicillin-hydrolyzing enzyme. Enzyme inhibition was detected with antiserum (anti-CARB-3), pCMB, cloxacillin, clavulanic acid and sulbactam. This novel enzyme with a molecular mass of 28,000 resembles other plasmid-mediated carbenicillinases (CARB) but differs in its apparent isoelectric point estimated as 6.3 and has been designated CARB-5 on this basis.