In a comparison of the Bactec system and the lysis concentration procedure in the isolation of Brucella species in 54 patients the recovery rate was similar (60% and 55%, respectively). However, the recovery time was significantly shorter with the lysis concentration method than with the Bactec system (3.5 days versus 14 days). The lysis concentration procedure for the culture of Brucella is simple, inexpensive and reliable, and produces results for the clinician relatively quickly.

BackgroundMethicillin-resistant Staphylococcus aureus (MRSA) is a human pathogen, representing an infection control challenge. Conventional MRSA screening takes up to three days, therefore development of rapid detection is essential. Real time-PCR (rt-PCR) is the fastest method fulfilling this task. All currently published or commercially available rt-PCR MRSA assays relay on single or double-locus detection. Double-locus assays are based on simultaneous detection of mecA gene and a S. aureus-specific gene. Such assays cannot be applied on clinical samples, which often contain both coagulase-negative staphylococci (CoNS) and S. aureus, either of which can carry mecA. Single-locus assays are based on detection of the staphylococcal cassette chromosome mec (SCCmec) element and the S. aureus-specific orfX gene, assuming that it is equivalent to mecA detection.FindingsParallel evaluation of several published single and double-locus rt-PCR MRSA assays of 150 pure culture strains, followed by analysis of 460 swab-derived clinical samples which included standard identification, susceptibility testing, followed by PCR detection of staphylococcal suspected isolates and in-PCR mixed bacterial populations analysis indicated the following findings.Pure cultures analysis indicated that one of the single-locus assay had very high prevalence of false positives (Positive predictive value = 77.8%) and was excluded from further analysis. Analysis of 460 swab-derived samples indicated that the second single-locus assay misidentified 16 out of 219 MRSA's and 13 out of 90 methicillin-sensitive S. aureus's (MSSA) were misidentified as MRSA's. The double-locus detection assay misidentified 55 out of 90 MSSA's. 46 MSSA containing samples were misidentified as MRSA and 9 as other than S. aureus ending with low positive predicted value (<85%) and very low specificity (<62%).ConclusionThe results indicate that high prevalence of false-positive and false-negative reactions occurs in such assays.