Plasmids encoding

Another group of antibiotics that can be inactivated by hydrolysis are 14- and 15- membered macrolides [2]. Esterases cleave the lactone ring. The plasmid encoded ere genes are found in members of the Enter-obacteriaceae and increase the intrinsic resistance. Furthermore, these esterases can also be found in some isolates of erythromycin resistant staphylococci. 

It has been shown that an AAC enzyme variant (AAC (6 )-Ib-cr, cr for ciprofloxacin resistance) found in various Enterobacteriaceae is capable of A-acetylating fluoroquinolones with an unmodified piperazinyl substituent at the amino nitrogen. Although the increase in MIC is low, this plasmid encoded quinolone resistance determinant can augment further development of clinically relevant resistance. 

Acetyl-CoA is also utilized as a cofactor to modify chloramphenicol by O-acetyltranferases (CATs). These enzymes have been found in many different bacterial genera and are usually plasmid encoded in clinical isolates. Furthermore, streptogramin type A antibiotics are acetylatedby Vat enzymes that occur on plasmids in staphylococci and enterococci. 

Nucleotidylation - the addition of adenylate-residues by Lnu enzymes - can also be the cause of resistance to lincosamide antibiotics in staphylococci and enterococci. A plasmid encoded ADP-ribosylating transferase (Arr-2) that leads to rifampicin resistance has been detected in various Enterobacteriaceae as well as in Pseudomonas aeruginosa. 

Resistance to trimethoprim can be due to the acquisition of plasmid encoded non-allelic variants of the chromosomal DHFR enzyme that are antibiotic unsusceptible. The genes may be part of transposons that then insert into the chromosome. For instance, in gram-negative bacteria the most widespread gene is dhfrl on transposon Tn7. 

Acquired, non-plasmid-encoded resistance to biocides can result when bacteria are exposed to gradually increasing concentrations of a biocide. Examples are provided by highly QAC-resistant Serratia marcescens, and chlorhexidine-resistant Ps. mirabilis, Ps. aeruginosa md Ser. marcescens. 

Impaired uptake Gram-negative Plasmid-encoded porin modification QACs... 

Efflux Gram-positive Plasmid-encoded expulsion from cells QACs Chlorhexidine ... 

There is enzymahc reduction of mercury to Hg metal and its vaporization in 1, and enzymatic hydrolysis followed by vaporization in 2. Plasmid-encoded resistance to other metallic ions has also been described but, apart from silver, is probably of little clinical relevance. 

Tan H-M, JR Mason (1990) Cloning and expression of the plasmid-encoded benzene 2,3,4,6-tetrachlorobiphe-nyl dioxygenase genes from Pseudomonas putida ML2. FEMS Microbiol Lett 72 259-264. 

Van der Meer JR, ARW van Neerven, EJ de Vries, WM de Vos, AJB Zehnder (1991) Cloning and characterization of plasmid-encoding genes for the degradation of 1,2-dichloro-, 1,4-dichloro-, and 1,2,4-trichlo-robenzene of Pseudomonas sp. strain P51. J Bacterial 173 6-15. 

Haak B, S Fetzner, F Lingens (1995) Cloning, nucleotide sequence, and expression of the plasmid-encoded genes for the two-component 2-halobenzoate 1,2-dioxygenase from Pseudomonas cepacia 2CBS. J Bacterial Yll 667-675. 

Chauhan A, RK Jain (2000) Degradation of o-nitrobenzoate via anthranilic acid (o-aminobenzoate) hyArthro-acterprotophormiae a plasmid-encoded new pathway. Biochem Biophys Res Commun 267 236-244. 

Schenk S, A Hoelz, B Krauss, K Decker (1998) Gene structures and properties of enzymes of the plasmid-encoded nicotine catabolism of Arthrobacter nicotinovorans. J Mol Biol 284 1323-1339. 

Denis-Larose, C. Labbe, D. Nergeron, H., et al., Conservation of plasmid-encoded dibenzothiophene desulfurization genes in several Rhodococci. Applied and Environmental Microbiology, 1997. 63 pp. 2915-2919. 

The first step in creating a specific mRNA species is to construct a plasmid encoding the mRNA behind a T7, T3, or SP6 RNA polymerase promoter sequence. The S boundary of the mRNA is defined by the position of the promoter transcription start site and the S end is defined by restriction digest of the plasmid prior to in vitro transcription. 

Navarro-Garcia F, Canizalez-Roman A, Luna J, Sears C, Nataro JP Plasmid-encoded toxin of enteroaggregative Escherichia coli is internalized by epithelial cells. Infect Immun 2001 69 1053-1060. 

Nataro JP, Seriwatana J, Fasano A, Maneval DR, Guers LD, Noriega F, Dubovsky F, Levine MM, Morris JG Jr Identification and cloning of a novel plasmid-encoded enterotoxin of enteroinvasive Escherichia coli and Shigella strains. Infect Immun 1995,63 4721-4728. 

The mechanism of tellurium resistance has been investigated using genetic manipulation similar to that of Se (see above) and cellular oxidant capacity apparently plays an important role.144,206 A few tellurite determinants - both chromosomal and plasmid encoded - have been identified in bacte-ria.113,147 192 207 208 Recent studies have focused on the role of methyltransf-erases in Te resistance. Liu et a/.111 determined that the E. coli gene tehB uses S-adenosyl methionine and a methyltransferase in tellurite detoxification, but while no methylated tellurium compounds (see below) were observed, a loss of tellurite was observed in tellurite-amended cultures and Te complexation was inferred.191... 

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