RESUMO
Bacteria of different genera isolated at nine medical centers in different parts of the United States and at one center in Venezuela during the first decade of gentamicin usage carried the gentamicin resistance gene 2"-aminoglycoside nucleotidyltransferase on the same transferable plasmid. Such widespread dissemination of a newly observed resistance gene on one plasmid suggests that a new resistance gene may emerge once on a single plasmid, which then carries it to other centers and other plasmids. The resistance gene might, therefore, be contained if detected early.
Assuntos
Bactérias/genética , Genes Bacterianos , Gentamicinas/uso terapêutico , Plasmídeos , Bactérias/efeitos dos fármacos , Conjugação Genética , Resistência Microbiana a Medicamentos , Eletroforese em Gel de Ágar , Escherichia coli , Humanos , Intestinos/microbiologia , Nucleotidiltransferases/genéticaRESUMO
We present a genetic and physical characterization of the IncM plasmid pBWH1. A physical map was constructed for the enzymes EcoRI, BamHI, SalI, BglII, HindIII, MstII, and XhoI. A series of deletions and a series of subclones of pBWH1 were constructed and used to determine the locations on this map of the transfer region; the replication region; and the genes determining resistance to beta-lactams, chloramphenicol, the sulfonamides, and gentamicin. We compared 51 different isolates, including isolates which had lost individual antibiotic resistances or the transfer phenotype, and showed that variations occurred in all regions of the plasmid genome. Frequently, correlations could be made between phenotypic variation and variation of the EcoRI fragments which contained the gene determining that phenotype.
Assuntos
Enterobacteriaceae/genética , Fatores R , Mapeamento Cromossômico , FenótipoRESUMO
During the first 6 years after appearing in one hospital, a 92-kilobase conjugative plasmid, pBWH1, which encoded resistance to chloramphenicol and sulfonamides and determined TEM-1 beta-lactamase and 2''-aminoglycoside nucleotidyltransferase, underwent a variety of molecular changes. It was most prevalent initially in isolates of Klebsiella pneumoniae, then in isolates of Serratia marcescens, and finally, after nearly disappearing, in isolates of Enterobacter cloacae. Evolutionary changes in the plasmid did not account for its shifts in species distribution, since the original molecule was found in isolates of each species. The late resurgence of pBWH1 occurred after a copy of its original molecule entered a distinctive ornithine decarboxylase-negative strain of E. cloacae, new to the hospital. The resulting transconjugant strain, chromosomally resistant to topical silver salts and to cephalosporins, and with the addition of pBWH1-encoded aminoglycoside resistance, spread in the hospital by causing an outbreak of sepsis in the burn unit, where these were commonly used antibacterial agents. Thus, an endemic plasmid became prevalent in a new host species because one of its genes supplemented the fitness of an uncommon strain of the species for a particular clinical niche.
Assuntos
Aminoglicosídeos/farmacologia , Enterobacter/genética , Enterobacteriaceae/genética , Klebsiella pneumoniae/genética , Fatores R , Serratia marcescens/genética , Evolução Biológica , Infecção Hospitalar , Enzimas de Restrição do DNA , DNA Bacteriano/genética , Enterobacter/efeitos dos fármacos , Klebsiella pneumoniae/efeitos dos fármacos , Serratia marcescens/efeitos dos fármacos , Especificidade da Espécie , Fatores de TempoRESUMO
We collected serotyped isolates of salmonella from reference laboratories in the United States, tested their susceptibility to antibiotics, and extracted plasmids from isolates that were resistant to a different combination of antibiotics from each of three serotypes. Restriction-endonuclease digestion showed that within each of the three groups, plasmid molecules from animal and human isolates were often identical or nearly identical. One serotype-plasmid combination appeared to be endemic in cattle in 20 states and infected 26 persons in two states. The human cases, which were not recognizably related except for their common plasmids, appeared to be clustered in time but geographically dispersed, like cases in previous outbreaks spread by food products. These findings suggest that resistance plasmids may be extensively shared between animal and human bacteria, and that spread of multiresistant strains of salmonella among animals and human beings, as observed in Britain, may have been undetected in the United States for lack of comparable surveillance.