Performance assessment of new multiplex probe assay for identification of mycobacteria

A new DNA probe assay (INNO LiPA Mycobacteria; Innogenetics, Ghent, Belgium) for the simultaneous identification, by means of reverse hybridization and line-probe technology, of Mycobacterium tuberculosis complex, Mycobacterium kansasii, Mycobacterium xenopi, Mycobacterium gordonae, the species of the Mycobacterium avium complex (MAC), Mycobacterium scrofulaceum, and Mycobacterium chelonae was evaluated on a panel of 238 strains including, besides representatives of all the taxa identifiable by the system, a number of other mycobacteria, some of which are known to be problematic with the only other commercial DNA probe system (AccuProbe; Gen-Probe, San Diego, Calif.), and two nocardiae. The new kit, which includes a control probe reacting with the whole genus Mycobacterium, correctly identified 99.6% of the strains tested; the one discrepancy, which remained unresolved, concerned an isolate identified as MAC intermediate by INNO LiPA Mycobacteria and as Mycobacterium intracellulare by AccuProbe. In five cases, because of an imperfect checking of hybridization temperature, a very slight, nonspecific, line was visible which was no longer evident when the test was repeated. Two strains whose DNA failed amplification at the first attempt were regularly identified when the test was repeated. Interestingly, the novel kit dodged all the pitfalls presented by the strains giving anomalous reactions with AccuProbe. A unique feature of INNO LiPA Mycobacteria is its ability to recognize different subgroups within the species M. kansasii and M. chelonae, while the declared overlapping reactivity of probe 4 with some M. kansasii and Mycobacterium gastri organisms and of probe 9 with MAC, Mycobacterium haemophilum, and Mycobacterium malmoense, may furnish a useful aid for their identification. The turnaround time of the method is approximately 6 h, including a preliminary PCR amplification.

Preliminary evaluation of sensititre system for identifying gram-negative bacilli

The automated microdilution Sensititre System (Sensititre, LtD.) was evaluated for the identification of 120 clinically isolated fermenter and non-fermenter Gram negative bacilli and of 12 ATCC reference strains (American Type Culture Collection). Daily and overnight (5 and 18 hours) identifications were performed according to the manufacturer. In both cases, the results were compared with those obtained with the overnight API 20E (API System, La Balme les Grottes, Montalieu Vercieu) used as reference method. Concordance between the results obtained after 5 hrs of incubation and those obtained with API 20E was found in 65% of cases (acceptable identification criteria with probability over 80%). When results were determined after 18 hrs of incubation (identification criteria with probably over 80%) concordance was found in 82.5%. Reproducibility obtained by repeated (10 times) identification with four different strains was 100% both at 5 hrs and 18 hrs. Identification accuracy of the 12 ATCC strains was 8/12 (66.6%) after 5 hrs and 12/12 (100%) after 18 hrs.

Ofloxacin: in vitro activity against recently isolated gram-negative bacterial strains

The activity of ofloxacin was determined against 117 Enterobacteriaceae, 13 Acinetobacter var, anitratus, 124 Pseudomonas aeruginosa in comparison with other antibiotics. Its activity was very high: against Enterobacteriaceae the minimum inhibitory concentration (MIC)50 was 0.125 micrograms/ml, the MIC90 1 micrograms/ml, and the geometric mean (GM) was 0.4 micrograms/ml against Acinetobacter var. anitratus the MIC50 1 micrograms/ml, MIC90 4 micrograms/ml, GM 1.7 micrograms/ml. Unlike other authors we found that the activity of ofloxacin was influenced by the selection of P. aeruginosa resistant to carbenicillin and gentamicin.

Patterns of haemagglutinating activity of Escherichia coli

MR and MS adhesins on 169 strains of Escherichia coli subjected to different cultural conditions were detected. Haemagglutination Test (static settling test in plastic microtiter trays) was used and several species of red blood cells were employed. The results confirm that different media can influence the expression of the adhesins and that using as many species of red blood cells as possible one can detect different adhesins.

[Detection of bacteremia by biphasic and radiometric methods]

During one year period our laboratory carried out 859 hemocultures. These have been evaluated with two methods: a conventional biphasic method (Castaneda bottles), and the automated radiometric method (Bactec System). 185 cultures were obtained with one or both methods. Of these 3.5% were considered contaminated, therefore the clinically significant isolation rate was 16.2%. Of these 86.4% was recovered by biphasic system and 79.8% by Bactec System. The recovery time to positivity and spectrum of isolates were similar for the two methods. Although there were substantially more contaminants isolated in the Vacutainer-Bactec System.

Opsonophagocytosis of group B streptococci: the role of sialic acid

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