Masashi Tanaka, Jian-Sheng Gong, Jin Zhang, Makoto Kunio Yagi

Mutations of mitochondrial DNA (mtDNA) have been reported in mitochondrial encephalomyopathies, cardiomyopathies, and diabetes mellitus. It has been proposed that accumulation of mtDNA mutations in somatic cells contributes to ageing and to degenerative diseases.1 Sequence diversity of mtDNA is marked between individuals, because the evolutionary rate of mtDNA is 5–10 times higher than that of nuclear DNA. An epidemiological study on coronary heart disease has indicated that longevity is more strongly associated with age of maternal than age of paternal death.2 It may be that maternally transmitted mitochondrial genotypes influence oxidative damage to mtDNA, the accumulation rate of mtDNA mutations, and susceptibility to degenerative

L1 TEM-1 1 2 1 1 1 2 1 1 1 2 1 1 RI- RI- L M- RI- RI- L M- RI- RI- L M- A A TE A A TE A A TE Edetic acid Clavulanate None Rn MN NReOKNReSOBKNRROUOHOONeONOOUKROOQONORK

Cann et al reported, in their study on human evolution,5 that among 147 samples from the world, only five Asians and one European carried Mt5178A. This observation indicates that Mt5178A is relatively rare among the global population. The high frequency of Mt5178A among the Japanese population (45%) may be relevant to the fact that the life expectancy at birth in Japan is among the highest on Earth. Life expectancy for females is 83·59 years, while for males it is 77·01 years.

Our findings support the concept that to carry an mtDNA genotype predisposing resistance to adult-onset diseases is one of the genetic factors for longevity. Further studies are needed to clarify the functional differences between these mtDNA variations. It will also be interesting to identify those adult-onset diseases to which individuals with Mt5178C are susceptible.

Supported in part by the programme Grants-in-Aid for Priority Areas of the Ministry of Education and Science and Culture of Japan, and a grant from Ministry of Health and Welfare to MT. We thank Ko Sahashi, Hiroaki Miyajima, Tadashi Kamiya, and Kazunobu Yamauchi.

Linnane AW, Marzuki S, Ozawa T, Tanaka M. Mitochondrial mutations as an important contributor to ageing and degenerative diseases. Lancet

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Brand F, Kiely D, Kannel W, Myers R. Family patterns of coronary heart disease mortality: the Framingham longevity study. J Clin Epidemiol

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Tanaka M, Hayakawa M, Ozawa T. Automated sequencing of mitochondrial DNA. Methods Enzymol

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Tanaka M, Ozawa T. Strand asymmetry in human mitochondrial DNA mutations. Genomics

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Cann RL, Stoneking M, Wilson AC. Mitochondrial DNA and human evolution. Nature

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Edetic acid 10(cid:6)2 mol/L, clavulanate 10(cid:6)3 mol/L, 1=metallo-enzyme from Stenotrophomonas maltophilia, TEM-1=class A enzyme.

experiments with ethidium bromide were used to determine if imipenem resistance was plasmid-mediated. Susceptibility tests and IEF were carried out on cured colonies.

Department of Gene Therapy (M Tanaka), Gifu International Institute of Biotechnology, Yagi Memorial Park, Mitake, Gifu 505-0116, Japan

Strain 1622 was resistant to all antibiotics tested, including imipenem (MIC 16 mg/L). The addition of enzyme inhibitors, including sulbactam which is usually intrinsically active against Acinetobacter spp did not reduce carbapenem MIC values. IEF detected the presence of a novel (cid:2)-lactamase designated ARI-2 (main band of pI 6.5). Enzyme activity was inhibited by clavulanate and BRL 42715 but not edetic acid (shown by IEF inhibitor overlays), indicating that ARI-2 was a class A (cid:2)-lactamase rather than a metallo-enzyme (figure). Strain 1622 inactivated imipenem as decteted by the microbiological assay. Slow imipenem hydrolysis was calculated by the modified microbiological assay (0·75 nmol min(cid:6)1 mL(cid:6)1). After plasmid curing, the ARI-2 enzyme was lost from strain 1622, detected by IEF. There was also more than a tenfold decrease in the rate of imipenem hydrolysis (0·067 nmol min(cid:6)1 mL(cid:6)1), as well as a reduction in carbapenem MIC values to susceptible levels, which strongly linked ARI-2 with plasmid-encoded carbapenemase activity.

Limitation of Acinetobacter baumannii treatment by plasmid- mediated carbapenemase ARI-2

Susan Brown, Carlos Bantar, Hilary-Kay Young, Sebastian G B Amyes

Acinetobacter species now account for 10% of nosocomial infections in intensive therapy units (ITU) in Europe. They are invariably multiresistant, and one major concern is the increasing incidence of carbapenem-resistant isolates, since these antibiotics are frequently the therapeutic choice for these infections. Carbapenem resistance in South America has already reached levels that significantly influence therapeutic choices (Carlos Bantar, unpublished data), and this looks set to be a problem in some European countries.1 ARI-1, a plasmid-mediated enzyme capable of hydrolysing imipenem, was the first carbapenemase to be isolated from this genus.2 We report a novel plasmid-mediated carbapenemase (ARI-2) from a multiresistant clinical isolate of A baumannii from Argentina (first described in 1996).3

These results, and the increasing incidence of carbapenem-resistant Acinetobacter spp, highlight how the role of these antibiotics in the treatment of ITU infections is severely threatened. Our preliminary investigations have also demonstrated the presence of ARI-2 in a number of clinical isolates of Acinetobacter (including A junii) (unpublished), from Europe and south-east Asia. This carbapenemase looks set to become a major worldwide resistance problem which, along with the recent report of a meticillin-resistant Staphylococcus aureus (MRSA) isolate with reduced susceptibility to vancomycin,5 is an indication of the alarming ability of modern pathogens to become totally resistant in response to the introduction of therapeutic strategies. The emphasis must now be on finding alternative antibiotic therapies.