Frequency of heavy-metal resistance in bacteria from inpatients in Japan

• Published in: Nature (London) 1977-01, Vol.266 (5598), p.165-167
• Main Authors: NAKAHARA, HIDEOMI, ISHIKAWA, TOMOAKI, SARAI, YASUNAGA, KONDO, ISAMU, MITSUHASHI, SUSUMU
• Format: Article
• Language: English
• Subjects: Humanities and Social Sciences; letter; multidisciplinary; Science; Science (multidisciplinary)
• ISSN: 0028-0836; 1476-4687
• DOI: 10.1038/266165a0

IN many bacteria, resistance to heavy metals is associated with a plasmid 1–4 . R plasmids in Escherichia coli can determine resistance to several metallic ions such as mercury, cobalt and nickel 3 , and a penicillinase plasmid mediating resistance to mercury, cadmium, arsenate, arsenite, lead and zinc has been observed in Staphylococcus aureus 1,2 . Mechanisms controlling bacterial resistances to mercury and cadmium are quite different although both are mediated by the same penicillinase plasmid 4 . Furthermore, microorganisms generally detoxify mercurial compounds metabolically by the formation of volatile mercury 5–9 or mercury mercaptides 10–12 . It is of interest that resistance to these heavy metals is mediated by the plasmids which determine resistance to antibiotics. Most of these heavy metals are established or possible causes of environmental pollution; methyl mercury causes ‘Minamata disease’ 13,14 and cadmium causes ‘Itai-Itai disease’ 15,16 in Japan. The role of R plasmids in drug resistance has been widely studied 17–21 , and extrachromosomal determinants are a main cause of the increase in numbers of drug-resistant bacteria. Studies of heavy metal resistance have attempted to establish a relationship between resistance to heavy metals and to drugs in the hospital environment 22,23 . The factors selecting for these heavy-metal-resistant bacteria have not yet been identified. We believe that heavy-metal-resistant microorganisms do not arise by chance, but, that there must be selectional factors beyond mere drug resistance. One of these selectional factors may be environmental contamination by heavy metals. To investigate this possibility, we studied the frequency of drug and heavy-metal resistance in clinical isolates of E. coli , Klebsiella pneumoniae , Pseudomonas aeruginosa and S. aureus . We report here that the frequency of heavy-metal resistance in these strains was the same as, or higher than that of antibiotic resistance. Some R plasmids in E. coli and K. pneumoniae also carried a resistance to Hg.