Early detection of extended-spectrum β-lactamase from blood culture positive for an Enterobacteriaceae using βLACTA test

Bacterial pellets from Enterobacteriaceae positive blood cultures prepared using ammonium chloride were tested for rapid detection of β-lactamase using the commercial βLACTA test and read after 30 minutes. During 7 months, 137 bacterial pellets were tested prospectively. βLACTA test exhibited a sensitivity of 75% and a specificity of 100% for the detection of third-generation cephalosporin resistance. False negative tests were mainly observed with hyperproduced chromosomal or plasmid-borne AmpC

AST agreement, per antibiotics.

<p>Counts of concordant pairs of AST results are in green, minor discrepancies (sensitive versus intermediate or intermediate versus resistant) are in yellow and major discrepancies (sensitive versus resistant) are in red. Only antibiotics tested more than 10 times are represented. Complete results are available in <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0187263#pone.0187263.s002" target="_blank">S2 Table</a>. AMC = amoxicillin-clavulanic acid; AMK = amikacin; AMP = ampicillin; AMX = amoxicillin; CAZ = ceftazidime; CIP = ciprofloxacin; CLI = clindamycin; CLR = clarithromycin; CRO = ceftriaxone; CXM = cefuroxime; ERY = erythromycin; ETP = ertapenem; FEP = cefepime; FOF = fosfomycin; GEN = gentamicin; IPM = imipenem; LVX = levofloxacin; MEM = meropenem; NIT = nitrofurantoin; PEN = penicillin; SXT = trimethoprim-sulfamethoxazole; TEC = teicoplanin; TET = tetracycline; TOB = tobramycin; TZP = piperacillin-tazobactam; VAN = vancomycin.</p

AST panels without panels for the same bacteria in the results of the corresponding sample.

<p>AST panels without panels for the same bacteria in the results of the corresponding sample.</p

Matrix-Assisted Laser Desorption Ionization-Time of Flight Mass Spectrometry for Direct Bacterial Identification from Positive Blood Culture Pellets ▿

An ammonium chloride erythrocyte-lysing procedure was used to prepare a bacterial pellet from positive blood cultures for direct matrix-assisted laser desorption-ionization time of flight (MALDI-TOF) mass spectrometry analysis. Identification was obtained for 78.7% of the pellets tested. Moreover, 99% of the MALDI-TOF identifications were congruent at the species level when considering valid scores. This fast and accurate method is promising

Repartition of Gram staining discrepancies.

<p>Repartition of Gram staining discrepancies.</p

Culture results: Agreement and description of discrepant cases.

<p>Culture results: Agreement and description of discrepant cases.</p

Molecular biology results pairs reparation.

<p>Straight line represents the line of identity, expressing perfect match. Pointed lines delaminate a ± 3.3 Ct tolerance margin. Represented are low positive versus negative results (n = 5, diamonds); moderate positive versus negative results (n = 1, square), quantitative discrepancies with over one log₁₀ difference in copies/ml (straight triangles, n = 3), quantitative discrepancy with difference over 3.3Ct but less than one log10 (reversed triangle, n = 1); agreeing positive results (rounds, n = 20). 92 negative agreeing results are not represented on this figure. Note that these results here include two negative pairs and one positive pair of tests that were not quantitatively reported in copies/ml but only reported in Ct number by the laboratory.</p

Interlaboratory Comparison of Results of Susceptibility Testing with Caspofungin against Candida and Aspergillus Species

Seventeen laboratories participated in a study of interlaboratory reproducibility with caspofungin microdilution susceptibility testing against panels comprising 30 isolates of Candida spp. and 20 isolates of Aspergillus spp. The laboratories used materials supplied from a single source to determine the influence of growth medium (RPMI 1640 with or without glucose additions and antibiotic medium 3 [AM3]), the same incubation times (24 h and 48 h), and the same end point definition (partial or complete inhibition of growth) for the MIC of caspofungin. All tests were run in duplicate, and end points were determined both spectrophotometrically and visually. The results from almost all of the laboratories for quality control and reference Candida and Aspergillus isolates tested with fluconazole and itraconazole matched the NCCLS published values. However, considerable interlaboratory variability was seen in the results of the caspofungin tests. For Candida spp. the most consistent MIC data were generated with visual “prominent growth reduction” (MIC(2)) end points measured at 24 h in RPMI 1640, where 73.3% of results for the 30 isolates tested fell within a mode ± one dilution range across all 17 laboratories. MIC(2) at 24 h in RPMI 1640 or AM3 also gave the best interlaboratory separation of Candida isolates of known high and low susceptibility to caspofungin. Reproducibility of MIC data was problematic for caspofungin tests with Aspergillus spp. under all conditions, but the minimal effective concentration end point, defined as the lowest caspofungin concentration yielding conspicuously aberrant hyphal growth, gave excellent reproducibility for data from 14 of the 17 participating laboratories