Molecular evolution, species distribution, and clinical consequences of an endemic aminoglycoside resistance plasmid

Abstract

During the first 6 years after appearing in one hospital, a 92-kilobase conjugative plasmid, pBWHl, 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 pBWHl 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.The percentages of clinical isolates of different bacterial species resistant to specific antibiotics are frequently calculated to delineate the usefulness of these drugs. Such tabulations will reflect in large part the distribution of resistance plasmids among strains of the species being surveyed, since a majority of resistance genes are carried by plasmids (4). The distribution of the plasmids may be determined by properties of the plasmids themselves such as their transferability, host range, or stability or the selective advantages conferred by their resistance genes or other cryptic genes (4,5). Also, properties of the host strains such as their fitness to occupy niches in which they come in contact with antibiotics might contribute to the observed distribution of plasmids.The surveillance of antibiotic resistance plasmids has been aided by plasmid fingerprinting, using restriction endonucleases (6,9,10,15,24,27)

Molecular epidemiology of TEM-3 (CTX-1) beta-lactamase

“…A similar organization in plasmids of types II and IV could account for the differences observed by hybridization and the fact that resistance determinants are clustered on the DNA molecule. Our study confirms the relative stability of plasmids of incompatibility group 7 or M (11,15) and their capacity to be responsible for plasmid epidemics (20,26). Cefotaxime is commonly used in France, often in combination with amikacin.…”

Effects of Silver-based Wound Dressings on the Bacterial Flora in Chronic Leg Ulcers and Its Susceptibility In Vitro to Silver

“…Silver has been shown to induce resistance in arange of bacterial species (1,5,6). Several of the silver-resistant strains have been collected from silver-treated patients at bum centres, where these strains have sometimes caused outbreaks (7,8).…”

In vitro activity, extraction, separation and structure elucidation of antibiotic produced by Streptomyces anulatus NEAE-94 active against multidrug-resistant Staphylococcus aureus

“…There has been a steady increase in antibiotic resistance during the past several decades, accounting for the long list of currently available antimicrobial agents that are now insufficient for the control of microbial infections [1,2]. Staphylococcus aureus is a bacterial pathogen responsible for serious infections in humans and is becoming increasingly resistant to many commonly used antibiotic treatments [3].…”