Heavy metal resistance plasmids

The evolution of MRSA strains is not fully understood, but the same mechanisms of mutation and gene transfer that exist in other species provide a likely reason. The emergence of gentamicin resistance plasmids illustrates the evolutionary potential of translocatable elements [186], MRSA strains which are also resistant to this aminoglycoside antibiotic are referred to as MGRSA. This evolutionary progression is also responsible for the formation of the -lactamase-heavy metal resistant plasmids [250]. Some MRSA isolates are penicillin-resistant by virtue of the enzyme /J-lactamase, which pre-dates the use of /8-lactams [251], However, the spread of the phenotype has probably arisen as a result of selection caused by the widespread usage of methicillin in hospitals. 

Moreover, the use of resistant strains is of interest. Slama et al. [21] described a heavy metal resistant BOD-sensor using Alcaligenes eufrop/jus, which contains plasmids encoding resistance to nickel, copper, cadmium, and zinc. An arsenic resistant BOD-sensor based on Pseudomonas putida was developed by Ohki et al. [35]. Another interesting possibility is the elimination of heavy metals by covering the BOD-sensor with a poly(4-vinylpyridine)-coated polycarbonate membrane [36] or polyfsodium styrene sulfonate) [62]. 

Silver, S. Misra,T. K. (1988). Plasmid-mediated heavy metal resistances. Annual Review of Microbiology, 42, 717-43. 

Resistance to heavy metals including Hg may be mediated by plasmid-borne genes. Further discussion of resistance to metal cations and metalloid anions is given in Chapter 3, Part 4. 

Eukaryotic Yeast plasmid or integration into host chromosome by homologous recombination Transient or permanent Amino acid requirement in autotrophic strain heavy metal induction of resistance gene Yeast ori sequence constitutive or inducible promoter transcription terminator... 

Heavy metals, principally mercury and silver, are now rarely used as disinfectants. Mercury is an environmental hazard, and some pathogenic bacteria have developed plasmid-mediated resistance to mercurials. Hypersensitivity to thimerosal is common, possibly in as high as 40% of the population. These compounds are absorbed from solution by rubber and plastic closures. Nevertheless, thimerosal 0.001-0.004% is still used as a preservative of vaccines, antitoxins, and immune sera. 

Resistance to heavy metals such as Hg may be mediated by plasmid-borne genes. 

Arsenic resistance is not the only toxic heavy metal ion resistance system found in bacteria. Bacteria have known plasmid and chromosomal genes for resistances to Ag+, As02, ASO4 -, Cd ", Co ", CrO/-, Cu ", Hg +, Ni +, Pb ", Sb ",... 

Bacterial resistance to arsenic ions governed by plasmids was first discovered by Novick and Roth (17) in a group of Staphylococcus aureus p-lactamase plasmids that determine resistances to antibiotics and also to heavy metals. Arsenic resistance plasmids confer tolerance to both arsenate and arsenite as well as to antimony (III) (18). Resistance to all three ions is inducible and cross-induction among them occurs (18). Arsenic resistance determinants are very common in plasmids of both gram-negative and gram-positive bacteria. 

Genetic studies have defined much of the penicillinase regulation system in S. aureus. Penicillinase production in the staphylococcus is often associated with resistance of the strain to other antibiotics and heavy metals, and these characters are carried on a plasmid (for review, see chmond [10]). These strains tend to be unstable, throwing off... 

The biological function of thioneins is, most likely, the storage and detoxification of heavy metals. Apparently, the accumulation of metals is associated with intense reduction, localization, and adhesion on the outer membrane of metal particles formed. During the adaptation period, the cells can acquire a plasmid imparting resistance to the metal. This ability is realized through the increased rate of metal ions reduction. Thus natural selection may result in the formation of metal-tolerant microbial strains. ... 

Other more or less vital functions are determined by plasmids. These small, circular DNA molecules are completely independent of the chromosome. They vary in size and number depending on the species and strain of bacteria. In Oenococcus oeni, plasmids of 2 to 40 kb are often identified and one of them has been sequenced (Fremaux et al, 1994). So far, no function of enological or physiological interest has been attributed to them. In general, the plasmids determine functions such as the fermentation of certain sugars, the hydrolysis of proteins, resistance to phages, antibiotics, heavy metals, etc. 

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