Do Indeterminate Cells Represent the Precursors of Langerhans Cells?

Abstract

The increasing prevalence of infections caused by derepressed AmpC mutants that constitutively produce high levels of the AmpC enzyme is an emerging therapeutic challenge. This study aimed to evaluate the sensitivity and specificity of a novel rapid and practical phenotypic screening method for derepressed AmpC έ-lactamase production. We studied 110 gram-negative bacilli that exhibited a range of resistance mechanisms to β-lactam antibiotics: 98 Enterobacteriaceae, 8 Acinetobacter baumannii complex, and 4 Pseudomonas aeruginosa. Of the bacilli, 61 exhibited wild-type AmpC and 49 were derepressed AmpC producers. Bacterial colonies from blood, chocolate, Mueller-Hinton, and MacConkey agar were tested. By using a sterile wooden stick, the bacterial colonies were touched/pressed onto a BD BBL DrySlide Nitrocefin (Becton Dickinson, Franklin Lakes, NJ) slide 3 times. The stopwatch was started simultaneously with the first addition of the bacteria to the slide. The results were considered positive when the chromogenic indicator turned pink, and the stopwatch was stopped. The testing was performed blindly. The timed touch method with a cutoff of 8 seconds detected 98% of derepressed producers of AmpC; 5 wild-type organisms had a time of 8 seconds or less. Using colonies grown on chocolate agar, the results are as follows: sensitivity, 98%; specificity, 92%; positive predictive value, 91%; negative predictive value, 98%; and accuracy, 95%. Mutation of the AmpD gene can result in hyperproduction of AmpC β-lactamase, resulting in resistance to all cephalosporins except cefepime. Through plasmid transfer, derepressed AmpC genes have been found in many gram-negative bacteria. A method that could predict the presence of derepressed AmpC genes from primary growth days before identification and susceptibility testing could provide valuable clinical guidance. The timed touch method using a BD BBL DrySlide Nitrocefin slide could provide critical information to clinicians at least a day earlier than conventional testing. Category:Medical Microbiology