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The third biovariant of Mycobacterium fortuitum
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Tubercle and Lung Disease
In reply We are honored to have the opportunity to respond to Dr Grange. The numerical taxonomy done by Dr Grange and his colleagues’ was the major determinant in the early classification of the various groups and subgroups of rapidly growing mycobacteria. At issue is whether Mycobacterium fort&urn should be maintained as a species with 3 subgroups, or whether we should follow the major species determinant at present, which is based not on phenotypic differences but on overall chromosomal DNA relatedness (homology). The issue seems relatively clear-cut for 2 of these groups. The study referenced by Dr Grange* and two additional studies3.4 clearly define that biotype A of M. fort&urn (also known as M. fortuitum biovariant fortuitum) and M. fort&urn biotype B (also known as M. fortuitum biovariant peregrinum) lack sufficient DNA homology to be included in the same species. We agree with the recent suggestion by Kusunoki and E&i5 that these 2 groups go back to their original names of M. fortuitum and M. peregrinum. These 2 groups (species, in our minds) are readily separated in the laboratory by the ability of M. peregrinum but not M. fortuitum to grow on mannitol as a sole carbon source.‘.6 The problem with the taxonomic status of the third biovariant complex remains unanswered. As noted by Dr Grange, it is complicated by the absence of a named type strain in national culture collections, its several features in common with M. peregrinum and the absence of DNA or RNA relatedness studies. It is further complicated by the fact that several phenotypic features allow for the separation of this group into several subgroups. This includes susceptibility to kanamycin, utilization of sorbitol, beta lactamase patterns and ammonia production from thymidine (the latter test of which we have no experience). There is hope on the horizon, however. Recently, Telenti et a1,7 using restriction endonuclease analysis of polymerase chain amplified gene sequences for the 65 KDa heat shock protein, showed M. fortuitum, M. peregrinum and third biovariant isolates to be distinctly different at the genomic level. Interestingly, at this level of analysis the third biovariant appeared more closely related to M. fortuitum than to M. peregrinum. In another study by Kirschner et al,’ a 1.5 Kb segment of DNA encoding for 16s rRNA from multiple nonpigmented rapidly growing mycobacterial taxonomic groups was amplified by polymerase chain reaction and the resultant fragment sequenced. The recently provided ATCC strains of sorbitol positive (ATCC 49403) and sorbitol negative (ATCC 49404) third biovariant complex strains were genetically distinct from one another, and were more distinct from one another than from M. fortuitum and M. peregrinum. The latter 2 species were also readily distinguishable by this technique. Given these rapidly evolving genetic relatedness studies, I am reluctant to group the third biovariant complex anywhere than where it currently is. In addition,
evaluation of overrall chromosomal DNA relatedness to M. fortuitum and M. peregrinum is ongoing, as are studies of the relatedness of the 1.5 Kb fragment of 16s rRNA sequences for additional isolates of the third biovariant compelx. Believing in our hearts that the genetically based taxonomic status of these organisms is relatively near, we would like to leave their status in limbo where it is at present until these studies are completed. Richard J. Wallace, Jr, MD Vincent A. Steingrube Department of Microbiology University of Texas Health Center P.O. Box 2003 Tyler, TX 75710 USA
References 1. Pattyn S R, Magnusson M, Stanford J L, Grange J M. A study of Mycobacterium fort&urn (ranae). .I Med Microbial 1974; 7: 67-76. 2. Levy-Frebault V, Grimont F, Grimont P A D, David H L. Deoxyribonucleic acid relatedness study of the Mycobacterium fortuitum-Mycobacter-ium chelonae complex. Int J Syst Bacterial 1986; 36: 458460. 3. Baess I. Deoxyribonucleic acid relatedness among species of rapidly growing mycobacteria. Acta Path Microbial Stand B. 1982; 90: 371-375. 4. Baess I, Bentzon M W. Deoxyribonucleic acid hybridization between different species of mycobacteria. Acta Path Microbial Acand B. 1978; 86: 71-76. 5. Kusunoki S, Ezaki T. Proposal of Mycobacterium peregrinum sp. nov., nom. rev., and elevation of Mycobacterium chelonae subsp. abscessus (Kubica et al) to species status: Mycobucterium abscessus comb. nov. Int J Svst Bacterial 1992: 43: 240-245. 6. Silcox V A, Good R C, Floyd M M. Identification of clinically significant Mycobacterium fortuitum complex isolates. J Clin Microbial 1981; 14: 686-691. 7. Telenti A, Marchesi F, Balz M, Bally F, Bottger E C, Bodmer T. Rapid identification of mycobacteria to the species level by polymerase chain reaction and restriction enzyme analysis. J Clin Microbial 1993; 31: 175-178. 8. Kirschner P, Kiekenbeck M, Meissner D, Wolters J, Bottger E C. Genetic heterogeneity within Mycobacter-ium fortuitum complex species: genotypic criteria for identification. J Clin Microbial 1992; 30: 2772-2775.
Tuberculosis is increasing in England and Wales With the exception of the War years, most developed countries experienced a steady decline in cases of tuberculosis until the mid 1980s. Cases in developing countries, where accurate records are available, were also apparently declining or remaining constant. However, from about 1985, cases in some developed countries such as the USA,’ and in many developing countries, particularly those in Sub-Saharan Africa,2 have been increasing, in some instances dramatically. Analysis of the age and sex structure of those diagnosed with disease has shown occurrence to be predominantly among younger males in the USA,’ therefore implicating HIV as a cause. However, other evidence suggests that social deprivation may be a factor.3 Notification has been compulsory in England and Wales since 1912, and
Tubercle and Lung Disease
In reply We are honored to have the opportunity to respond to Dr Grange. The numerical taxonomy done by Dr Grange and his colleagues’ was the major determinant in the early classification of the various groups and subgroups of rapidly growing mycobacteria. At issue is whether Mycobacterium fort&urn should be maintained as a species with 3 subgroups, or whether we should follow the major species determinant at present, which is based not on phenotypic differences but on overall chromosomal DNA relatedness (homology). The issue seems relatively clear-cut for 2 of these groups. The study referenced by Dr Grange* and two additional studies3.4 clearly define that biotype A of M. fort&urn (also known as M. fortuitum biovariant fortuitum) and M. fort&urn biotype B (also known as M. fortuitum biovariant peregrinum) lack sufficient DNA homology to be included in the same species. We agree with the recent suggestion by Kusunoki and E&i5 that these 2 groups go back to their original names of M. fortuitum and M. peregrinum. These 2 groups (species, in our minds) are readily separated in the laboratory by the ability of M. peregrinum but not M. fortuitum to grow on mannitol as a sole carbon source.‘.6 The problem with the taxonomic status of the third biovariant complex remains unanswered. As noted by Dr Grange, it is complicated by the absence of a named type strain in national culture collections, its several features in common with M. peregrinum and the absence of DNA or RNA relatedness studies. It is further complicated by the fact that several phenotypic features allow for the separation of this group into several subgroups. This includes susceptibility to kanamycin, utilization of sorbitol, beta lactamase patterns and ammonia production from thymidine (the latter test of which we have no experience). There is hope on the horizon, however. Recently, Telenti et a1,7 using restriction endonuclease analysis of polymerase chain amplified gene sequences for the 65 KDa heat shock protein, showed M. fortuitum, M. peregrinum and third biovariant isolates to be distinctly different at the genomic level. Interestingly, at this level of analysis the third biovariant appeared more closely related to M. fortuitum than to M. peregrinum. In another study by Kirschner et al,’ a 1.5 Kb segment of DNA encoding for 16s rRNA from multiple nonpigmented rapidly growing mycobacterial taxonomic groups was amplified by polymerase chain reaction and the resultant fragment sequenced. The recently provided ATCC strains of sorbitol positive (ATCC 49403) and sorbitol negative (ATCC 49404) third biovariant complex strains were genetically distinct from one another, and were more distinct from one another than from M. fortuitum and M. peregrinum. The latter 2 species were also readily distinguishable by this technique. Given these rapidly evolving genetic relatedness studies, I am reluctant to group the third biovariant complex anywhere than where it currently is. In addition,
evaluation of overrall chromosomal DNA relatedness to M. fortuitum and M. peregrinum is ongoing, as are studies of the relatedness of the 1.5 Kb fragment of 16s rRNA sequences for additional isolates of the third biovariant compelx. Believing in our hearts that the genetically based taxonomic status of these organisms is relatively near, we would like to leave their status in limbo where it is at present until these studies are completed. Richard J. Wallace, Jr, MD Vincent A. Steingrube Department of Microbiology University of Texas Health Center P.O. Box 2003 Tyler, TX 75710 USA
References 1. Pattyn S R, Magnusson M, Stanford J L, Grange J M. A study of Mycobacterium fort&urn (ranae). .I Med Microbial 1974; 7: 67-76. 2. Levy-Frebault V, Grimont F, Grimont P A D, David H L. Deoxyribonucleic acid relatedness study of the Mycobacterium fortuitum-Mycobacter-ium chelonae complex. Int J Syst Bacterial 1986; 36: 458460. 3. Baess I. Deoxyribonucleic acid relatedness among species of rapidly growing mycobacteria. Acta Path Microbial Stand B. 1982; 90: 371-375. 4. Baess I, Bentzon M W. Deoxyribonucleic acid hybridization between different species of mycobacteria. Acta Path Microbial Acand B. 1978; 86: 71-76. 5. Kusunoki S, Ezaki T. Proposal of Mycobacterium peregrinum sp. nov., nom. rev., and elevation of Mycobacterium chelonae subsp. abscessus (Kubica et al) to species status: Mycobucterium abscessus comb. nov. Int J Svst Bacterial 1992: 43: 240-245. 6. Silcox V A, Good R C, Floyd M M. Identification of clinically significant Mycobacterium fortuitum complex isolates. J Clin Microbial 1981; 14: 686-691. 7. Telenti A, Marchesi F, Balz M, Bally F, Bottger E C, Bodmer T. Rapid identification of mycobacteria to the species level by polymerase chain reaction and restriction enzyme analysis. J Clin Microbial 1993; 31: 175-178. 8. Kirschner P, Kiekenbeck M, Meissner D, Wolters J, Bottger E C. Genetic heterogeneity within Mycobacter-ium fortuitum complex species: genotypic criteria for identification. J Clin Microbial 1992; 30: 2772-2775.
Tuberculosis is increasing in England and Wales With the exception of the War years, most developed countries experienced a steady decline in cases of tuberculosis until the mid 1980s. Cases in developing countries, where accurate records are available, were also apparently declining or remaining constant. However, from about 1985, cases in some developed countries such as the USA,’ and in many developing countries, particularly those in Sub-Saharan Africa,2 have been increasing, in some instances dramatically. Analysis of the age and sex structure of those diagnosed with disease has shown occurrence to be predominantly among younger males in the USA,’ therefore implicating HIV as a cause. However, other evidence suggests that social deprivation may be a factor.3 Notification has been compulsory in England and Wales since 1912, and