Mercury Resistance and R Plasmids in Escherichia coli Isolated from Clinical Lesions in Japan

Abstract

The mercury and antibiotic resistance of 338 strains of Escherichia coli isolated from hospital patients was determined. Resistance to mercury was found in 58.6% of the isolates. The frequencies of resistance to streptomycin (Sm), tetracycline (Tc), chloramphenicol (Cm), kanamycin (Kan), cephaloridine (Cer), and gentamicin (Gm) were 66.3,60.3, 56.5, 42.9, 32.1, and 1.5%, respectively. Among the above, 198 mercury-and antibiotic-resistant isolates were selected and tested for their ability to transfer the resistance to susceptible strains of E. coli K-12 and Klebsiella pneumoniae JK5. R plasmids carrying mercury resistance were demonstrated in 89.9% of the mercury-resistant strains of E. coli. Furthermore, R(Hg,Sm,Tc,Cm) plasmids were demonstrated most frequently, followed by R(Hg,Sm,Tc,Cm,Kan), R(Hg,Cm,Kan), and R(Hg,Sm,-Tc,Cm,Kan,Cer) plasmids.Resistance of bacteria to mercury has been described by several authors from the viewpoints of morphology (23), genetics, and biochemistry. In many bacteria, resistance to mercury is associated with a plasmid (7,8,13,14,16,17,19). Generally, microorganisms have been shown to detoxify mercurial compounds metabolically by forming either volatile mercury derivatives (1,12,16,19,22) or mercury mercaptides (5,15,18,25). There are also many bacteria that are resistant to other metallic ions such as cadmium, arsenate, lead, zinc, cobalt, and nickel (8-10, 13, 17).It is of interest that resistance to these metals is mediated by the same plasmid that determines resistance to antibiotics. Also, most of these metals have recently been listed as established or possible causes of environmental pollution. For example, methyl mercury is known to cause Minamata disease (6,20), and cadmium is the causative agent of Itai-Itai disease in Japan.The role of R plasmids in drug resistance has been widely studied (2-4, 11, 21, 24), and extrachromosomal determinants are a main cause of the increase in numbers of drug-resistant bacteria. However, the factors selecting for these metal-resistant bacteria have not yet been identified. We believe that metal-resistant microorganisms do not arise by chance, but that there must be selection factors beyond mere drug resistance. One of these selection factors may be environmental contamination by these heavy metals.We previously investigated the distribution of the resistance to several metallic ions such as Hg, Cd, As, and Pb among 415 strains ofStaphylococcus aureus (S. aureus) isolated from hospital patients (9). Recently, we also demonstrated 198 R plasmids with Hg resistance in Escherichia coli isolated from clinical specimens. This paper deals with the genetic properties of these R plasmids carrying Hg resistance. MATERIALS AND METHODSBacterial strains. A total of 338 strains of E. coli were isolated from the Clinical Laboratory of The Jikei University Hospital and tested for their resistance to mercury and six antibiotics. Mating experiments were carried out with a total of 198 Hg-and antibiotic-resistant strains as donors to examine the presence of...

Potential Impact of Increased Use of Biocides in Consumer Products on Prevalence of Antibiotic Resistance

“…Similar results (196) showed that 12.8% of 148 clinical E. coli isolates selected for their elevated chlorhexidine MICs were no less susceptible to use concentrations. Such changes, in the case of the Providencia isolates, were thought to affect binding of the biguanides to the cell surface and therefore reflected envelope modification (74).…”

Characterization of mercury-resistant clinical Aeromonas species

“…This was confirmed by the lack of amplification of mer A or mer R genes using plasmid DNA as a template. Our results contrast with reports in literature where mer operons reside frequently in plasmids (Nakahara et al , 1977). Previous work in our laboratory searching for Class 1 integrons revealed also a preferential chromosomal vs. plasmid localization of these elements in Aeromonas spp.…”

Formation of Mercury Sulfide from Hg(II)–Thiolate Complexes in Natural Organic Matter

“…48 In the first 5 days of reacting divalent Hg with L-cysteine ethyl ester (L-CysOEt) at a ratio of 1:2 in water equilibrated with air or purged with argon at RT, a whitish suspension progressively formed ( Figure 3D). Between 5 and 19 days, the suspensions darkened in color to black.…”