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Journal of Clinical Microbiology, May 2003, p. 2147-2152, Vol. 41, No. 5
0095-1137/03/$08.00+0 DOI: 10.1128/JCM.41.5.2147-2152.2003
Copyright © 2003, American Society for Microbiology. All Rights Reserved.
Characterization of Mycobacterium montefiorense sp. nov., a Novel Pathogenic Mycobacterium from Moray Eels That Is Related to Mycobacterium triplex
Michael H. Levi,1* John Bartell,2 Leanne Gandolfo,2 Sandra C. Smole,3,4 Sylvia F. Costa,5 Louis M. Weiss,1,5 Linda K. Johnson,1,6 Gerard Osterhout,2 and Lawrence H. Herbst1,6
Department of Pathology,1
Institute for Animal Studies,6
Department of Medicine, Montefiore Medical Center The Albert Einstein College of Medicine, Bronx, New York 10461,5
MIDI, Inc., and MIDI Labs, Inc., Newark, Delaware 19713,2
Infectious Disease Section, Department of Medicine, Boston University School of Medicine,3
Medical Service, VA Boston Healthcare System, Boston, Massachusetts 021304
Received 27 August 2002/
Returned for modification 10 January 2003/
Accepted 29 January 2003

ABSTRACT
The characterization of a novel
Mycobacterium sp. isolated from
granulomatous skin lesions of moray eels is reported. Analysis
of the
hsp65 gene, small-subunit rRNA gene, rRNA spacer region,
and phenotypic characteristics demonstrate that this organism
is distinct from its closest genetic match,
Mycobacterium triplex,
and it has been named
M.
montefiorense sp. nov.

TEXT
Granulomatous skin disease has occurred sporadically and persistently
within captive exhibit populations of moray eels, including
green moray (
Gymnothorax funebris) and spotted moray (
G.
moringa)
eels (
5), where it has led to eel death, reducing sizable aquarium
collections of these fish. We have identified a mycobacterium
as the etiologic agent of granulomatous skin disease in moray
eels (
5). On sequence analysis, the 16S rRNA gene of the eel
Mycobacterium sp. was most closely related to that of
Mycobacterium triplex, an opportunistic pathogen of humans (
3,
4). The present
report describes the phenotypic and genotypic characterization
of this novel, slow-growing, acid-fast bacterium and clarifies
the taxonomy of this isolate in the genus
Mycobacterium. On
the basis of previous recommendations for the description of
new mycobacteria (
10) and the data presented here, we propose
this as a new mycobacterium species called
M.
montefiorense.
M. triplex (ATCC 700071) was obtained from the American Type Culture Collection (ATCC; Manassas, Va.). The Mycobacterium sp. previously described by Herbst et al. was stored at -70oC (5). All phenotypic and genetic analyses were performed with biomass obtained from growth of this isolate on either Trypticase soy agar with 5% sheep blood or Middlebrook 7H10 agar. Type strains have been deposited at the American Type Culture Collection (ATCC BAA-256) and the Deutsche Sammlung von Mikroorganismen und Zellkulturen, Braunschweig, Germany (DSM-44602).
As 16S ribosomal typing indicated that the organism isolated from moray eels was a Mycobacterium sp., acid-fast stains and biochemical tests were performed. Both the coccus form from blood agar and the rod form from Middlebrook medium were acid fast when stained with Kinyoun stain. The coccobacillary morphology of M. montefiorense on blood agar was consistent with the "streptococcus-like" organisms observed in previous studies of the pathology of eel skin lesions (5). Mycobacterial biochemical tests were performed by using standard methods as previously described (7). M. triplex has previously been demonstrated to be similar to M. simiae and M. avium complex (3) by conventional biochemical tests. Several differences in biochemical reactions were demonstrated for M. triplex and M. montefiorense (Table 1); e.g., M. triplex was urease positive and M. montefiorense was urease negative. There was a clear difference in temperature requirements and colony morphology. M. montefiorense would not grow at temperatures of >30°C. Growth from Middlebrook-based medium at 25°C demonstrated beaded acid-fast rods that were slow growing and nonchromogenic. The colonies were small and transparent. M. triplex grew poorly at temperatures of <30°C but grew well at 37°C, producing a mucoid opaque colony.
Fatty acid methyl esters were obtained from
M.
montefiorense and
M.
triplex by saponification, methylation, and extraction.
These were then separated by gas-liquid chromatography and identified
by using the Sherlock Microbial Identification System (MIDI,
Inc.), which identifies bacteria on the basis of their unique
fatty acid profiles (
15,
18). The profiles of
M.
triplex and
M.
montefiorense were qualitatively similar, but three fatty
acid peaks had significant quantitative differences (18:2 w6,9c/18:0
ANTE, 4.36% [
M.
montefiorense] and 2.0% [
M.
triplex]; 18:0,
4.73% [
M.
montefiorense] and 1.48% [
M.
triplex]; 18:0 10-methyl,
1.14% [
M.
montefiorense] and 5.23% [
M.
triplex]). This data
are consistent with the idea that these are closely related
but distinct organisms as the presence or absence of peaks or
a >2% difference in similar peaks constitutes a significant
difference between species (
15,
18).
Mycolic acids were extracted from M. montefiorense and M. triplex by using the following modifications of the previously published procedure (6): saponification for 30 min, derivatization for 10 min at 60°C in an uncapped vial precoated with potassium bicarbonate, and no clarification step. Dried extracts were resuspended in isopropanol (IPA) and transferred to a vial containing fluorescently derivatized mycolic acids (Corixa Corporation), which were used as reference standards. High-performance liquid chromatography (HPLC) analysis was performed on an Agilent 1100 HPLC system (Agilent, Wilmington, Del.) with a column heater (70°C) and a fluorescence detector. Separation of the mycolic acids was achieved with a Zorbax SB-C18 column (4.6 by 75 mm), a mobile phase of methanol-IPA, and a linear gradient of 25 to 95% IPA over a 10-min period with a flow rate of 1.5 ml/min. Raw chromatographic data were acquired with ChemStation software and processed by using Sherlock software for calculation of relative percentages. Chromatograms were aligned, and adjusted retention times were calculated by ChemStation on the basis of the retention times of the two internal standards. Each peak may be a pure compound (mycolic acid) or a mixture of several mycolic acid classes (methoxy, keto, etc.). When analyzed under standard conditions, the compounds elute in a reproducible pattern. The mycolic acid profile of M. montefiorense was visually compared to that of M. triplex, and the peaks were aligned (Fig. 1). For convenience, only those peaks with heights of >2% of the total peak height are labeled. M. triplex produced a triple-cluster HPLC profile consistent with previously published results (3, 4). There were significant qualitative (peaks 2 and 5) and quantitative (peaks 3 and 4) differences between M. triplex and M. montefiorense, indicating that these are distinct organisms.
Sequencing of the 16S rRNA gene and subsequent phylogenetic
analysis had previously revealed the eel isolate to be a
Mycobacterium sp., with its closest match being
M. triplex (
5,
12). Bootstrap
analysis was therefore performed with a 50% majority rule consensus
tree by using PAUP 4.0 (D. Swofford, Sinauer Associates, Inc.,
Sunderland, Mass.) with additional
Mycobacterium sp. sequences.
The 16S rRNA gene analysis indicates that
M.
montefiorense (AF330038)
formed a subclade in the phylogenetic tree together with
M.
triplex, as supported by the high bootstrap value of this subclade
(Fig.
2). A neighbor-joining tree constructed by using the MicroSeq
Microbial Identification and analysis software and database
(Applied Biosystems) yielded similar results (data not shown)
(
5).
M. montefiorense differs from
M.
triplex at nine positions
in its 16S rRNA gene sequence (0.59%). For slow-growing mycobacteria,
differences such as these within the 16S rRNA gene have been
considered significant for the identification of a genetically
unique and distinct taxon (
8,
9).
Sequencing of
M.
montefiorense internal transcribed spacer (ITS)
rRNA, amplified by using the Sp1(5'ACCTCCTTTCTAAGGAGCACC3')-Sp2
(5'GATGCTCGCAACCACTATCCA3') primer pair (
16), demonstrated that
it is distinct from that of
M.
triplex (Fig.
3), and BLASTN
analysis demonstrated that it does not correspond to any known
ITS rRNA in the GenBank database (
1). Roth (
16) has proposed
a method for the identification of
Mycobacterium spp. that is
based on the restriction patterns generated from the ITS region
amplified with primers Sp1 and Sp2. Restriction sites of the
ITS rRNAs were examined and compared by using MapDraw (Lasergene;
DNASTAR, Inc., Madison, Wis.). Under Roth's system,
M.
montefiorense would cluster with
M.
genavense,
M.
lentiflavum, and
M.
triplex in that it would not be resolved from these organisms by restriction
cleavage with
AvaII,
TaqI, or
DdeI.
M. montefiorense can, however,
be distinguished from
M.
triplex by using
MspI, which produces
three fragments from the ITS of
M.
triplex and only two fragments
from the ITS of
M.
montefiorense.
To further support the characterization of this new species,
an

400-bp PCR fragment was obtained from the 65-kDa heat shock
protein gene (
hsp65) sequences of
M.
montefiorense,
M.
triplex,
and
M.
genavense by using TB11 (5'-ACCAACGATGGTGTGTCCAT-3')
and TB12 (5'-CTTGTCGAACCGCATACCCT-3') (
14). Sequences of the
hsp65 amplicon demonstrated that
M.
montefiorense differs from
M.
triplex by 10 of 441 nucleotides and
M.
genavense by 14 of
441 nucleotides of the
hsp65 gene sequence (Table
2). Comparison
of the
hsp65 sequence from 385 bp of
M.
montefiorense with those
of 385 bp of
M.
triplex and 360 bp of
M.
genavense by BLASTN
demonstrated sequence similarities of 97.4 and 96.1%, respectively
(Table
3) (
1). The
hsp65 phylogenetic data are consistent with
the idea that
M.
montefiorense is a unique species.
This polyphasic taxonomic study was carried out to demonstrate
that this moray eel isolate is a new species of mycobacterium,
M.
montefiorense. Three different genetic approaches demonstrated
that the isolate belongs to the slow-growing clade of mycobacteria.
Although analysis of the 16S rRNA gene has become a standard
technique in bacterial taxonomy (
13), a second method is often
necessary to confirm a new species because of limited variation
in the 16S rRNA gene in many mycobacterial species (
3,
11,
14,
17,
19). The
hsp65 gene is a housekeeping gene that has been
used extensively both for species identification and for species
differentiation based on species-specific variation (
2,
11).
Both the 16S rRNA gene and
hsp65 data support the conclusions
that this isolate is distinct from
M.
triplex and that it is
a new
Mycobacterium species. The variability in the ITS region
is also very useful for the separation of closely related species.
For example, the ITS region has been used to characterize a
new
M.
triplex-like organism that caused a human infection (
4).
Analysis of the ITS sequences of
M.
triplex, an
M.
triplex-like
human isolate (
4), and
M.
montefiorense demonstrated that each
is unique. While moles percent G+C content has been recommended
as another descriptive factor for slow-growing mycobacteria,
this value was not determined for
M.
montefiorense (
10). Phenotypic
methods were consistent with the genotypic data. Fatty acid
analysis, mycolic acid analysis, and biochemical testing supported
the idea that
M.
montefiorense is distinct from
M.
triplex.
It should be noted, however, that the biochemical tests are
designed for organisms that grow at temperatures of >30°C.
Analysis of
M.
montefiorense and
M.
triplex at their optimal
growth temperatures demonstrated clear biochemical differences.
All of the data presented in this paper, therefore, demonstrate
that the
Mycobacterium sp. isolated from moray eels is unique,
and we believe that they are sufficient to justify the designation
of this eel isolate as a new species within the genus
Mycobacterium named
M. montefiorense.
Our original description of this organism was the first isolation of an M. triplex-related species from fish (5). M. triplex is a member of a group of slowly growing mycobacteria classified by the Centers for Disease Control and Prevention as SAV organisms on the basis of their relatedness to M. simiae and M. avium (3, 4). We are, however, aware of other groups finding similar organisms in other marine fish (20), suggesting that these slow-growing organisms are more common in the marine environment than previously suspected. It is possible that many SAV organisms are pathogens of fish and other organisms in the marine ecosystem. Further study of the epizootiology and pathogenesis of M. montefiorense and other SAV organisms in fish, aquatic mammals, and humans will be critical in the elucidation of the impact of these mycobacteria on ecosystems, as well as human health.
Taxonomic description of M. montefiorense sp. nov.
Mycobacterium montefiorense (mon.te.fi.or.en'se. N. L. adj. montefiorense, of Montefiore, referring to the Montefiore Medical Center). M. montefiorense was named after the Montefiore Medical Center, Bronx, N.Y., the medical institution where it was isolated that has provided medical care to the Bronx, N.Y., community for >100 years. These bacteria grow at 25°C but not at 30 or 37°C. Growth from Middlebrook-based medium at 25°C demonstrates beaded acid-fast rods that are slow growing and nonchromogenic. The bacteria are biochemically inactive (negative urease, arylsulfatase, niacin, nitrate reduction, Tween 80 hydrolysis, 5% NaCl tolerance, and catalase). This organism can be isolated on sheep blood agar if the cultures are kept for up to 20 weeks at 25°C. Growth on blood agar demonstrates coccobacillary forms when stained with methylene blue, but these bacteria resist Gram stain. M. montefiorense has been demonstrated to be an etiologic agent of a granulomatous skin disease of moray eels.
Nucleotide sequence accession numbers.
The 16S ribosomal gene and the ITS region sequence (AF330038) and a partial hsp65 gene sequence (AY027785) have been deposited in the GenBank database.

ACKNOWLEDGMENTS
We thank Hitesh Patel and Ervin Melton for valuable help in
the mycobacteriology laboratory, Michael Alexander for help
with HPLC, and Aidan C. Parte for advice on nomenclature. We
thank Neal Steigbigel for his inspired teaching of infectious
diseases at Montefiore Medical Center.
L.M.W. is supported by National Institutes of Health grants AI31788 and AI39454.

FOOTNOTES
* Corresponding author. Mailing address: Microbiology Laboratory, Montefiore Medical Center, 111 E. 210th St., Bronx, NY 10467. Phone: (718) 920-4189. Fax: (718) 654-7402. E-mail:
Mlevi{at}Montefiore.org.


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Journal of Clinical Microbiology, May 2003, p. 2147-2152, Vol. 41, No. 5
0095-1137/03/$08.00+0 DOI: 10.1128/JCM.41.5.2147-2152.2003
Copyright © 2003, American Society for Microbiology. All Rights Reserved.
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