The possibility that the strains included within the Mycobacterium avium complex (MAC), but not belonging either to M. avium or to Mycobacterium intracellulare, may be members of undescribed taxa, has already been questioned by several taxonomists. A very homogeneous cluster of 12 strains characterized by identical nucleotide sequences both in the 16S rDNA and in the 16S–23S internal transcribed spacer was investigated. Similar strains, previously reported in the literature, had been assigned either to the species M. intracellulare on the basis of the 16S rDNA similarity or to the group of MAC intermediates. However, several phenotypical and epidemiological characteristics seem to distinguish these strains from all other MAC organisms. The unique mycolic acid pattern obtained by HPLC is striking as it is characterized by two clusters of peaks, instead of the three presented by all other MAC organisms. All of the strains have been isolated from humans and all but one came from the respiratory tract of elderly people. The clinical significance of these strains, ascertained for seven patients, seems to suggest an unusually high virulence. The characteristics of all the strains reported in the literature, genotypically identical to the ones described here, seem to confirm our data, without reports of isolations from animals or the environment or, among humans, from AIDS patients. Therefore, an elevation of the MAC variant was proposed and characterized here, with the name Mycobacterium chimaera sp. nov.; this increases the number of species included in the M. avium complex. The type strain is FI-01069T (=CIP 107892T=DSM 44623T).
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.
The present report describes a fatal case of imported AIDS-related disseminated histoplasmosis capsulati infection associated with multiple coexisting infections, diagnosed with cultural recovery of Histoplasma capsulatum var. capsulatum with a commercial radiometric Mycobacterium medium. The epidemiological and clinical features of histoplasmosis capsulati and duboisii in Europe are reviewed by examining also 69 documented cases of Histoplasma capsulatum var. capsulatum infection (25 in AIDS patients) and 17 cases of Histoplasma capsulatum var. duboisii infection (3 in HIV-infected patients), described since 1980. This draws special attention to the role played during recent years by the emergence of the HIV pandemic and the progressive intensification of travel and immigration as risk factors for this disease in our continent. AIDS patients, who are prone to multiple concurrent opportunistic infections which may share clinical and laboratory features with each other and with other HIV-associated diseases, represent the most relevant current group at risk for severe disseminated histoplasmosis, which may come to medical attention far from their place of origin.
Seven cases of Alcaligenes xylosoxidans bacteremia and/or respiratory disease in patients infected with the human immunodeficiency virus (HIV) are described. Reported only thrice previously in this setting, these bacterial complications occurred during different phases of HIV infection and were associated with leukopenia-neutropenia in four patients and a central vascular catheter in two. Although the majority of cases were diagnosed after day 3 of hospitalization, a distinct source of infection was never identified. In four patients with advanced underlying disease, a polymicrobial infection was present. In vitro resistance to aminoglycosides, first-generation cephalosporins, and aztreonam was identified, but treatment with fluoroquinolones, piperacillin, or an aminoglycoside in combination with either ceftazidime or pefloxacin was successful in all cases. The relevance of Alcaligenes xylosoxidans and related species of gram-negative non-glucose fermenting bacilli as opportunistic pathogens in the immunocompromised host and in the setting of HIV infection is briefly reviewed.
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