Rapid identification and antimicrobial susceptibility testing of positive blood cultures using MALDI-TOF MS and a modification of the standardised disc diffusion test: a pilot study.

AIMS: In an era when clinical microbiology laboratories are under increasing financial pressure, there is a need for inexpensive, yet effective, rapid microbiology tests. The aim of this study was to evaluate a novel modification of standard methodology for the identification and antimicrobial susceptibility testing (AST) of pathogens in positive blood cultures, reducing the turnaround time of laboratory results by 24 h. METHODS: 277 positive blood cultures had a Gram stain performed and were subcultured and incubated at 37°C in a CO2 atmosphere for 4-6 h. Identification of the visible growth was performed using matrix-assisted laser desorption time of flight mass spectrometry (MALDI-TOF MS). Taking a modified approach to the Clinical and Laboratory Standards Institute-standardised AST methodology, an inoculum density of 0.5 McFarland was prepared from the early growth for disc diffusion testing. The standard AST method was also performed on the 18-24 h culture. RESULTS: 96% (n=73/76) of gram-negative organisms were correctly identified by MALDI-TOF MS. Comparative analysis of the rapid and standard AST results showed an overall interpretive category error rate of 7.7% (6.7% minor errors, 0.6% major errors and 0.4% very major errors). 100% of Staphylococcus aureus (n=41) and enterococcus isolates (n=9) were correctly identified after 4-6 h incubation. The overall AST categorical agreement was also 100% for these isolates. CONCLUSIONS: An incubation of 4-6 h directly from positive blood cultures allowed for both a rapid species identification and an antimicrobial susceptibility result approximately 24 h earlier than is possible using standard methodology.

Mandatory use of confirmation stage with Chlamydiazyme during urinary sediment analysis.

AIMS: To assess whether false positive results found when the first stage Chlamydiazyme test is performed on urinary sediment could be reduced by using the more specific second stage blocking assay. METHODS: Sediment from 173 urine samples from patients with suspected urinary tract infection caused by Gram negative bacteria and 23 control urine samples were tested using the Chlamydiazyme assay system, which included a blocking assay. RESULTS: A reaction result with the first stage Chlamydiazyme assay test was seen in 102 (58.9%) of the test urine samples. First stage reactivity was not blocked by the Chlamydiazyme confirmatory assay performed on repeat testing. All were correctly identified as true negative (first test false positive) results. CONCLUSIONS: Use of a second (specific) blocking assay for the analysis of urinary sediment using Chlamydiazyme eliminates false positive results in Gram negative urinary tract infections.

A case of acquired factor X deficiency with in vivo and in vitro evidence of inhibitor activity directed against factor X.

A 67-year-old woman had symptoms of an upper respiratory tract infection for which she received a five-day course of erythromycin. Epistaxis and gross hematuria subsequently developed, and the patient was found to have a selective Factor X deficiency. She received supportive therapy and prothrombin complex concentrates (Factors II, VII, IX, and X), with subsequent resolution of her transient Factor X deficiency. Her hospital course, however, was complicated by the development of multiple cerebral infarctions. This is the tenth reported case of transient Factor X deficiency not associated with amyloidosis. In seven of the previous cases, as in this patient, the deficiency was associated with a preceding upper respiratory infection. This is the only case, however, with evidence of inhibitory activity in the plasma that was directed toward Factor X.

An unusual case using DNA polymorphisms to determine parentage of human remains.

The 2-year-old daughter of two farm laborers was reported missing while the farm owner was harvesting corn. Unidentifiable tissues and body parts were subsequently found admixed with silage. Samples of blood collected from the parents of the missing child as well as portions of the tissue recovered from the silage were subjected to analysis of DNA polymorphisms with probes usually used to identify paternity. In addition, allele-specific oligonucleotides were used to detect DNA polymorphism at the DQ alpha locus following DNA amplification using the polymerase chain reaction. In this case, the DNA results established that the tissue recovered from the silage was of human origin and confirmed the probable parentage of the two farm laborers.