Assessment of Omitting MacConkey Agar as a Primary Inoculating Medium for MALDI-TOF MS-Based Bacterial Identification from Urine, Blood, and Respiratory Samples.

OBJECTIVE: MacConkey agar (MAC) is commonly used as a primary medium for conventional bacterial identification in clinical microbiology laboratories. Matrix-assisted laser desorption ionization time-of-flight mass spectrometry (MALDI-TOF MS) has revolutionized microbial identification and is considered a reliable identification tool. While conventional identification methods rely on colony characteristics, MALDI-TOF MS requires a pure isolate on a solid medium. METHODS: This study investigated whether MAC can be omitted as a routine inoculation medium for urine, lower respiratory tract (LRT), and positive blood culture samples. The study included 462 clinical samples. Among these, 221 were urine samples, 141 were positive blood cultures, and the remaining 100 were LRT samples. The samples were inoculated on blood agar (BA) and MAC for the control group and on BA only for the experimental group, followed by incubation and identification with MALDI-TOF MS. RESULTS: The BA only group showed the same microbial identification using MALDI-TOF MS as the control BA and MAC groups for blood and LRT specimens. For urine samples, 99.1% (219/221) of the samples produced the same identification results for the two groups. The cause of discrepant results for two urine specimens was due to Proteus species overgrowth on BA, which hindered non-Proteus spp. identification for the BA-only group. CONCLUSION: Our results may indicate that omitting MAC has little or no impact on the recovery of organisms present in culture. However, due to possible Proteus spp. overgrowth, caution should be exercised in the decision to omit MAC from the primary inoculating medium, which necessitates further studies in other centers with a larger sample size.

Economic and workflow analysis of a blood bank automated system.

BACKGROUND: This study compared the estimated costs and times required for ABO/Rh(D) typing and unexpected antibody screening using an automated system and manual methods. METHODS: The total cost included direct and labor costs. Labor costs were calculated on the basis of the average operator salaries and unit values (minutes), which was the hands-on time required to test one sample. To estimate unit values, workflows were recorded on video, and the time required for each process was analyzed separately. RESULTS: The unit values of ABO/Rh(D) typing using the manual method were 5.65 and 8.1 min during regular and unsocial working hours, respectively. The unit value was less than 3.5 min when several samples were tested simultaneously. The unit value for unexpected antibody screening was 2.6 min. The unit values using the automated method for ABO/Rh(D) typing, unexpected antibody screening, and both simultaneously were all 1.5 min. The total cost of ABO/Rh(D) typing of only one sample using the automated analyzer was lower than that of testing only one sample using the manual technique but higher than that of testing several samples simultaneously. The total cost of unexpected antibody screening using an automated analyzer was less than that using the manual method. CONCLUSIONS: ABO/Rh(D) typing using an automated analyzer incurs a lower unit value and cost than that using the manual technique when only one sample is tested at a time. Unexpected antibody screening using an automated analyzer always incurs a lower unit value and cost than that using the manual technique.

High-resolution melting curve analysis for rapid detection of rifampin and isoniazid resistance in Mycobacterium tuberculosis clinical isolates.

We evaluated high-resolution melting (HRM) curve analysis as a tool for detecting rifampin (RIF) and isoniazid (INH) resistance in Mycobacterium tuberculosis in an accurate, affordable, and rapid manner. Two hundred seventeen M. tuberculosis clinical isolates of known resistance phenotype were used. Twenty-nine known rpoB mutant DNAs, including rare mutations, were also included. Four pairs of primers were designed: rpoB-F/R (for codons 516 to 539 of rpoB), rpoB-516F/R (for codons 508 to 536 of rpoB), katG-F/R (for the codon 315 region of katG), and inhA-F/R (for the nucleotide substitution of C to T at position -15 of inhA). An HRM curve was generated for each isolate after real-time PCR differentiated the mutant from the wild-type strains. DNA sequencing of the target regions was performed to confirm the results of the HRM curve analysis. All but one of the 73 RIF-resistant (RIF-R) strains and all 124 RIF-susceptible (RIF-S) isolates were correctly identified by HRM curve analysis of rpoB. Twenty-seven of 29 known rpoB mutants were detected. In HRM curve analysis of katG and inhA, 90 INH-R strains that harbored katG or inhA mutations, or both, and all INH-S strains were correctly identified. Ten phenotypically INH-R strains not harboring katG or inhA mutations were not detected. The HRM curve analysis will be a useful method for detection of RIF and INH resistance in M. tuberculosis in a rapid, accurate, simple, and cost-effective manner.