3. Cisterna R, Cabezas V, Gomez E, Busto C,
Multiple rpoB demonstrated in vitro for M. smegma-
tis, a surrogate model for M. tubercu-
Atutxa I, Ezpeleta C. Community-acquired
losis, as an increase in reversion
bacteremia. Rev Esp Quimioter.
2001;14:369–82. (mutant to wild-type) rate in rpoB526
4. Calvet HM, Yoshikawa TT. Infections in
diabetes. Infect Dis Clin North Am.
tuberculosis and or rpsL43 under counterselection by
streptomycin or rifampin, respectively
(4). A correlation between high muta-
5. Bobrow BJ. Incision and drainage of cuta-
neous abscesses is not associated with bac- tion rate and antimicrobial resistance
teremia in afebrile adults. Ann Emerg Med. was reported for Pseudomonas aerug-
1997;29:404–8. To the Editor: Rad and colleagues inosa isolates from lungs of cystic
6. Lee NY. Hickman catheter–associated bac- recently described variation in some fibrosis patients (5). The mutator P.
teremia by Leclercia adecarboxylata and genes involved in DNA repair (mutT2,
Escherichia hermannii—a case report. aeruginosa strains resulted from a
Korean J Infect Dis. 1999;31:167–70. mutT4, ogt) in Mycobacterium tuber- defective mismatch-repair system (5).
7. de Baere T, Wauters G, Huylenbrock A, culosis strains of different genotypes In M. tuberculosis, mismatch-repair
Claeys G, Peleman R, Verschraeger G, et (1). This approach can also be used to genes (mutH, mutL, mutS, and recJ)
al.Isolations of Leclercia adecarboxylata investigate developing rifampin
from a patient with a chronically inflamed were not found in its genome (6).
gallblader and from a patient with sepsis resistance in the context of emerging However, the nucleotide pool in this
without focus. J Clin Microbiol. mutator alleles. Resistance to species is exceptionally clean because
2001;39:1674–5. rifampin in M. tuberculosis strains is of the presence of several copies of
8. Ginsberg HG, Daum RS. Escherichia her- usually caused by the point mutations
mannii sepsis with duodenal perforation in the mutT gene (1,6); the MutT protein
neonate. Pediatr Infect Dis J. 1987;6:300–2. in the rpoB gene encoding the β-sub- removes oxidized guanines (8-Oxo-
9. Dahl KM, Barry J, De Biasi RL. unit of the DNA-dependent RNA dGTP), thus counteracting replication
Escherichia hermanii infection of a polymerase, which is a target of the or transcription errors. Consequently,
cephalohematoma: case report, review of drug. Although a single point muta-
literature and description of a novel inva- the MutHLS mismatch-repair system
sive pathogen. Clin Infect Dis. tion is sufficient for developing simply may be not required in M.
2002;35:e96–98. rifampin resistance, a number of arti- tuberculosis (6). Therefore, hyper-
10. Cunha BA. Strategies to control antibiotic cles (2,3) describe multiple rpoB mutability in some strains of this
resistance Semin Respir Infect. mutants for M. tuberculosis, i.e.,
2002;17:250–8. species resulting in multiple rpoB
11. Jimenez-Mejias ME, Colmenero JD, rifampin-resistant strains harboring mutants might develop under certain
Sanchez-Lora FJ, Palomino-Nicas J, mutations in different codons of rpoB. special (in vivo) circumstances
Reguera JM, Garcia de la Heras J, et al. Double, triple, and quadruple muta- through inactivation or down-regula-
Postoperative spondilodiskitis: etiology, tions in M. tuberculosis clinical iso-
clinical findings, prognosis and comparison tion of some mutT genes. Further, the
with nonoperative pyogenic spondylodiski- lates were reported in studies con- two most frequently described rpoB
tis. Clin Infect Dis.1999;29: 339–45. ducted throughout the world (2,3). mutations are 531TCG→TTG and
12. Javaloyas de Morlius M, Monreal Portella Such emergence, albeit infrequent, of 526CAC→TAC. Both are cytosine-
M. Oral antibiotic therapy in the adult bac- M. tuberculosis rpoB multiple
terial osteomyelitis: results after two years to-tymine transitions, which easily
of follow-up. Med Clin (Barc). mutants raises questions about their occur by spontaneous cytosine deam-
1999;113:488–9. biologic importance and underlying ination to uracil. Indeed, M. tubercu-
mechanisms; answers to both remain losis is a G+C rich organism, there-
Address for correspondence: Gabriel Adrian elusive. fore, it is naturally at high risk for
Popescu, "Matei Bals" Infectious Diseases I propose an explanation of these cytosine deamination. Furthermore,
Institute, Str. Grozovici, nr. 1, Bucuresti, sector observations in terms of second-order pathogenic mycobacteria are at
2, Romania; fax: 40 21 2101497; email: selection of hypermutable (mutator) increased risk for deamination
email@example.com alleles based on alterations in DNA because of the production of reactive
repair genes. Unlike that of other anti- oxygen and nitrogen intermediates
tuberculosis drugs, resistance to inside host macrophages. This deami-
rifampin is acquired in most M. tuber- nation process is normally counteract-
culosis isolates by altering a single ed by uracil-N-glycosylase, the prod-
target molecule and offers the most uct of the ung gene, and organisms
appropriate and straightforward defective in the removal of uracil
model to demonstrate possible hyper- from DNA have an increased sponta-
mutability in this species. In neous mutation rate and more
mycobacteria, hypermutability was G:C→A:T base-pair transitions (7).
Emerging Infectious Diseases • www.cdc.gov/eid • Vol. 10, No. 7, July 2004 1337
Merchant et al., by using ung+ and and for rpoB mutations in E. coli K12 in mouse macrophages. J Biol Chem.
ung– Escherichia coli strains, demon- strain (11). In the last instance, the 2003;278:24350–8.
8. Merchant K, Chen H, Gonzalez TC, Keefer
strated that total nitric oxide expo- rpoB multiple mutants were selected LK, Shaw BR. Deamination of single-
sures in the µmol/L range can lead to in vitro in a stepwise fashion, and one stranded DNA cytosine residues in aerobic
C→T mutations by a mechanism double mutant, L511Q+D516G (also nitric oxide solution at micromolar total
probably involving cytosine deamina- described in M. tuberculosis strain NO exposures. Chem Res Toxicol.
tion (8). On the other hand, in M. ), exhibited a relative fitness either 9. Billington OJ, McHugh TD, Gillespie SH.
smegmatis, the abrogation of the Ung greater than or equal to either single Physiological cost of rifampin resistance
activity leads not only to increased mutant or the wild type. Reynolds induced in vitro in Mycobacterium tubercu-
mutator phenotype but also to growth (11) suggested that this allele is losis. Antimicrob Agents Chemother.
inhibition by reactive nitrogen inter- favored not merely as a combination 10. Wagner J, Nohmi T. Escherichia coli DNA
mediates (7). In summary, I speculate of two low-level resistance mutations Polymerase IV mutator activity: genetic
that mutations in ung that do not com- but also because these mutations requirements and mutational specificity. J
pletely impair function, but do together boost resistance and preserve Bacteriol. 2000;182:4587–95.
11. Reynolds MG. Compensatory evolution in
decrease synthesis of its product, fitness. Whether the same is true for rifampin-resistant Escherichia coli.
might tolerably increase the sponta- other multiple mutant alleles in M. Genetics. 2000;156:1471–81.
neous C→T mutations, including tuberculosis rpoB remains to be seen.
those in the respective positions in the Studying the costs of resistance of Address for correspondence: Igor Mokrousov,
rpoB codons 531 and 526. This multiple rpoB mutations in a more Laboratory of Molecular Microbiology, St.
assumption seems likely because both realistic environment of animal mod- Petersburg Pasteur Institute,14, Mira Street, St.
of the aforementioned particular els of TB infection seems promising. Petersburg, 197101, Russia; fax: + 7 812 232
mutations were described in sponta- 92 17; email:firstname.lastname@example.org
neous mutants of H37Rv obtained in Igor Mokrousov*
vitro and had a Darwinian fitness *St. Petersburg Pasteur Institute, St.
slightly less than or equal to that of Petersburg, Russia
the rpoB wild-type-susceptible
parental strain (9). In contrast, the References
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tuberculosis strains of the W-Beijing fami-
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sis genes (dinP) is present in the
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moted more important frameshift Thoresen OF, Ricci ML, et al. rpoB muta- To the Editor: We read with inter-
mutations (single-base deletions) in tions in multi-drug resistant strains of
Mycobacterium tuberculosis isolated in
est an article, Human Meta-
two thirds of the spontaneous mutants Italy. J Clin Microbiol. 1999;37:1197–9. pneumovirus Detection in Patients
(10). 4. Karunkaran P, Davies J. Genetic antagonism with Severe Acute Respiratory
From an evolutionary point of and hypermutability in Mycobacterium Syndrome, in your journal (1). In the
view, the multiple rpoB mutations in smegmatis. J Bacteriol. 2000;182: 3331–5.
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report, Chan et al., did not question
M. tuberculosis have been hypothe- Blazquez J. High frequency of hyper- that SARS-CoV is the etiologic agent
sized to arise as a compensatory mutable Pseudomonas aeruginosa in cystic of severe acute respiratory syndrome
mechanism to ameliorate the fitness fibrosis lung infection. Science. (SARS); however, human metapneu-
costs of the original resistance muta- 2000;288:1251–3.
6. Cole ST. Comparative mycobacterial
movirus (HMPV) was found in 25
tion by a secondary mutation (11). genomics. Curr Opin Microbiol. (52%) of 48 probable SARS cases that
The process of adaptation to the fit- 1998;1:567–71. were investigated, and SARS-CoV
ness costs of chromosomally encoded 7. Venkatesh J, Kumar P, Krishna PSM, was detected in 11 (22.9%) of them.
resistance has been studied in E. coli Manjunath R, Varshnay U. Importance of
uracil DNA glycosylase in Pseudomonas
Another recent article reported
and Salmonella enterica serovar aeruginosa and Mycobacterium smegmatis, HMPV in five of six patients in whom
Typhi for mutations that affect trans- G+C rich bacteria, in mutation prevention, SARS was diagnosed in Canada (2);
lation in the rpsL and fusR genes (11) tolerance to acidified nitrite, and endurance four of the six were coinfected with
1338 Emerging Infectious Diseases • www.cdc.gov/eid • Vol. 10, No. 7, July 2004