An improved assay with 4-(2-thiazolylazo)-resorcinol for non-esterified fatty acids in biological fluids

A simple and rapid colorimetric assay for non-esterified fatty acids (NEFA) was developed employing extraction of samples with 0.1 mol/l glycine (pH 2.7) and methoxyethanol : butyl ether, and formation of a copper-fatty acid soap detected with 4-(2-thiazolylazo)-resorcinol. The method developed is sensitive enough to detect as little as 11 nmol/0.25 ml sample. Results are not affected by marked molar excesses of phospholipids, cholesterol, cholesterol esters, triglycerides, bilirubin, or lactate. Recovery of palmitate in the extract averages 94.2 +/- 3.2% (S.D.) and other long chain fatty acids are recovered equally. The copper-NEFA-indicator complex formed is stable. Extracted samples can be stored for as long as 2 weeks without appreciable changes in measured NEFA content. The method developed is suitable for both manual and semi-automated procedures for determining NEFA content in biological fluids.     

Evaluation of a new screening system for enteric pathogens

The two-hour Rapid SST strip (DMS Laboratories, Inc.) was compared with our standard screening system (triple sugar iron agar, lysine iron agar, and urea) for enteric pathogens. We tested 50 stock cultures of enteric pathogens and 213 stool cultures received in the Barnes Hospital Clinical Microbiology Laboratory over a two-month period. All enteric pathogens from the stock cultures and clinical specimens were identified correctly with the Rapid SST system. More false-positive reactions were observed with the Rapid SST system (34%) than with the conventional system (23%). However, the costs associated with using both systems were equivalent and the test results were available one day faster with the Rapid SST system. Thus, the Rapid SST is a rapid, accurate, and cost-effective method for screening stool specimens for enteric pathogens.     

Comparative study of the ability of four aminoglycoside assay techniques to detect the inactivation of aminoglycosides by beta-lactam antibiotics

In vitro inactivation of aminoglycosides (tobramycin, gentamicin, and amikacin) by beta-lactams (cefazolin, cefotaxime, moxalactam, carbenicillin, piperacillin, mezlocillin, and azlocillin) was measured using the enzyme-mediated immunoassay (EMIT), fluorescence polarization immunoassay ( TDX ), radioimmunoassay (RIA), and bioassay. No significant inactivation of aminoglycosides was produced by high levels of the three cephalosporins as measured by EMIT, RIA, or bioassay. Inactivation of tobramycin and gentamicin by mezlocillin and azlocillin was comparable to that seen with piperacillin but less than that with carbenicillin. In general, the bioassay detected the greatest degree of aminoglycoside inactivation and the EMIT assay detected the least for all drug combinations. The TDX and RIA techniques were equivalent in their ability to detect aminoglycoside inactivation by beta-lactam antibiotics.