Properties of Silver Sulfadiazine-Resistant Enterobacter cloacae

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)

Section: Resultsmentioning

confidence: 99%

Section: Resultsmentioning

confidence: 99%

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

Mayer¹,

Hopkins²,

Gilleece³

et al. 1986

“…Although the clinical applicability of SN cannot be determined from this study, SN has several features which make it clinically attractive. Silver is not associated with significant side effects, is not an allergen, and is only rarely associated with the induction of resistant strains of bacteria (5,7). In addition, the silver ions delivered by the SN are not accompanied by a carrier molecule or anion which may be associated with systemic side effects, such as occurs with both silver nitrate and silver sulfadiazine.…”

Section: Resultsmentioning

confidence: 99%

Silver-nylon: a new antimicrobial agent

Deitch¹,

Marino²,

T³

et al. 1983

The potential effectiveness of a silver nylon (SN) fabric as an antimicrobial agent was evaluated in a series of in vitro experiments. The results indicated that silver ions from the SN fabric penetrated 2 mm of agar and killed a challenge of 6.9 X 10(7) Pseudomonas aeruginosa, 4.1 X 10(7) Staphylococcus aureus, and 1.4 X 10(7) Candida albicans organisms per cm2 of SN fabric after 24 h of incubation at 37 degrees C. To determine some of the microbicidal limits of the SN, the distance between the SN fabric and the microbial challenge was increased. Increasing the height of the agar column overlying the SN fabric diminished the inhibitory effect of SN on microbial growth. For each increase in agar height of 2 mm, up to a total height of 8 mm, the effectiveness of SN to inhibit microbial growth decreased by a factor of 10. This distance-related decrease in the microbicidal ability of SN could be overcome by placing the SN fabric in contact with the agar column for 24 to 72 h before microbial challenge. On the basis of these experiments, it appears that SN is an effective antimicrobial agent, although further work must be performed before it is applied clinically.

“…The use of topical AgNO3 and, occasionally, preparations containing mercury has been widespread in the management of burns. Transferable silver resistance has been demonstrated in Salmonella typhimurium (8), and there is evidence for its plasmid location in Enterobacter cloacae (1,12). Transmissible plasmids in a variety of gramnegative bacilli, including E. coli, S. typhimurium, and Pseudomonas sp., have been shown to mediate mercury resistance (13,15).…”

mentioning

confidence: 99%

Susceptibility of Bacteroides spp. to heavy metals

Riley¹,

Mee²

1982

The susceptibility of 105 strains of Bacteroides to arsenate, silver, nickel, cobalt, lead, cadmium, chromium, and mercuric ions was tested by using an agar dilution technique. All strains of Bacteroides were multiply resistant. Bacteroides fragilis was significantly more resistant to silver ions than other Bacteroides species and slightly more resistant to several other ions. Arsenate was the most active ion tested, with 75% of strains being susceptible. All 25 strains of B. fragilis tested against silver sulfadiazine were susceptible.