Plasmid-mediated high-level ceftriaxone resistance in a Salmonella enterica serotype typhimurium isolate

ABSTRACT

We evaluated ion exchange chromatography [IEC] on the Jeol Aminotac 500 analyzer for total homocysteine [tHcy] determination and compared it with an immunoassay method using fluorescence polarization on an Abbott IMx analyzer. IEC method validation [linearity, limit of detection, precision, interference] was made according to the French Biology Society guidelines [Societe Fran‡aise de Biologie Clinique]. Moreover, during a 2-month period, 55 plasma samples from patients scheduled for routine tHCy measurement were assayed by both methods for determining correlation. The IEC method was found linear up to at least 190 micro mol/l, and the limit of detection was 1.6 micro mol/l. Precision was studied with 3 controls at 6, 15 and 30 micro mol/l. Intra-assay coefficients of variation [n = 14] were 8.3, 3.1 and 2.3%, respectively, and inter-assay coefficients of variation [n = 15] were 9.6, 5.1 and 4.9%, respectively. No interference was found with other sulfur-containing amino acids [methionine, cysteine]. An excellent agreement was found between IEC and fluorescence polarization [Deming regression; y = 0.99x - 1.23; r = 0.97; p < 0.001]. The IEC method for tHcy measurement shows adequate precision and correlates highly with the IMx assay. The IEC method is more time-consuming but less expensive in reagent cost and allows simultaneous determination of plasma methionine concentration which may help to explain the underlying mechanism responsible for hyperhomocysteinemia