Epidemic Infection by a Gentamicin-Resistant Staphylococcus Aureus in Three Hospitals

Homologous genes encoding resistance to gentamicin, tobramycin, and kanamycin through the bifunctional acetylating [AAC(6')] and phosphorylating [APH(2")] aminoglycoside-modifying enzyme were identified in staphylococci isolated from patients in the United States. The mobility of gentamicin resistance (Gmr) genes found on a prototype conjugative plasmid (pGO1) was compared with that of genes cloned from chromosomal sites. Plasmid-encoded Gmr genes and flanking sequences were introduced onto a temperature-sensitive plasmid (pRN3208) from pGO1 by homologous recombination between insertion sequence-like elements present on both replicons. Growth of Staphylococcus aureus strains containing the temperature-sensitive recombinant (pGO161) at the nonpermissive temperature for plasmid replication (42°C) revealed no translocation of Gm' from its plasmid location. A transposon (TnS51) resident on the same replicon did translocate. Chromosomal Gmr determinants were cloned, together with the gene for trimethoprim resistance (dfrA), from three geographically distinct S. epidermidis isolates; two were subcloned onto temperature-sensitive Escherichia coli-S. aureus shuttle plasmids as 7.2-kilobase BglIH fragments. Growth of both recombination-deficient and -proficient S. aureus strains containing the cloned genes at 42°C allowed detection of transposition of Gm' sequences and identification of insertion into random chromosomal sites. We have designated this 5-kilobase transposon from S. epidermidis as Tn4031.

mentioning

confidence: 99%

Mobility of gentamicin resistance genes from staphylococci isolated in the United States: identification of Tn4031, a gentamicin resistance transposon from Staphylococcus epidermidis

Thomas

Archer

1989

“…Most clinical isolates of S. aureus resistant to particular aminoglycosides have normal colonial morphology and possess plasmids directing the production of specific aminoglycoside-inactivating enzymes (4,15,20,25,26,33). The aminoglycoside-resistant strain described in this study is not of this type.…”

mentioning

confidence: 90%

Single and Combination Antibiotic Therapy of Staphylococcus aureus Experimental Endocarditis: Emergence of Gentamicin-Resistant Mutants

Miller

Wexler

Steigbigel

1978

The efficacy of nafcillin and gentamicin used alone and in combination at doses giving serum concentrations comparable to those achieved in patients was studied in rabbits with experimental Staphylococcus aureus endocarditis. The organism used was a penicillinase-producing, methicillin-susceptible, clinical isolate. The addition of gentamicin to nafcillin significantly increased the rate of killing of organisms in valvular vegetations, compared to the effect of nafcillin alone. Gentamicin alone delayed mortality but was not effective in reducing the bacterial populations of the vegetations. Bacteremia persisted in the animals treated with gentamicin alone, in contrast to the groups treated with nafcillin or the combination. Selection of a subpopulation of aminoglycoside-resistant small-colony variants occurred in animals treated with gentamicin alone. This variant was subsequently employed in the rabbit model and produced endocarditis, metastatic infection, and bacteremia comparable to those caused by the parent strain. Animals with infection produced by the variant died later than animals infected by the parent strain. Nafcillin was equally effective in reducing the population of both parent and variant strains in vitro and in therapy of the infected animals. Population studies showed the variant to be a mutant emerging at a rate of 1.9 X 10-7. It was shown to differ from the parent strain in coagulase and hemolysin production, colonial morphology, and aminoglycoside susceptibility, but was similar by light and electron microscopy and in phage type, pigmentation of colonies, deoxyribonuclease production, mannitol fermentation, and growth rate.In vitro time-kill studies with blood culture isolates of penicillinase-producing, methicillinsusceptible S. aureus have demonstrated that gentamicin at a concentration of 5 ,ug/ml is rapidly bactericidal and reduces the bacterial population at a rate greater than that achieved by nafcillin at 20 jig/ml (N. H. Steigbigel, J. I.Casey, and B. J. Heeter, Clin. Res. 21:976, 1973). The initial rate of killing at a lower concentration of gentamicin (0.5 ,ug/ml) was similar to that obtained with 5 ,ug/ml but was associated with the later overgrowth, in each of 24 strains tested, of a small-colony variant which showed increased resistance when rechallenged with aminoglycosides. The combination of nafcillin and gentamicin (0.5 yg/ml) demonstrated the initial rapid killing without the subsequent emergence of the variant strain. Studies using a high inoculum of organisms, 109 colony-forming units (CFU) per ml, demonstrated that gentamicin alone or in combination with nafcillin was significantly active, whereas nafcillin alone did not decrease the population. The relevance of these in vitro observations was studied in a model of S. aureus endocarditis in rabbits.This study was presented in part at the 16th Interscience Conference on Antimicrobial Agents and Chemotherapy, October, 1976

“…Gentamicin resistance in clinical isolates of Staphylococcus aureus has been reported in Europe (4,7,9,10) and the United States (11). Recent studies in this laboratory identified a 50S plasmid in two strains as the genetic element responsible for this resistance (11).…”

mentioning

confidence: 97%

“…The organisms studied were recovered from an outbreak of infections in our neonatal intensive care unit (Talmadge Memorial Hospital, Augusta, Ga.) and were of different phage types. Speller et al (10) reported an outbreak in three hospitals by a single strain of gentamicin-resistant S. aureus. In France, Le Goffic et al (7) have studied a gentamicin-resistant strain isolated from a blood culture.…”

mentioning

confidence: 99%

Aminoglycoside Modification by Gentamicin-Resistant Isolates of Staphylococcus aureus

Scott

Wood²,

Brownell

et al. 1978

Three clinical isolates of Staphylococcus aureus, which were previously shown to contain a 50S plasmid conferring resistance to several aminoglycosides, were examined for modifying enzymes. Both the wild-type and heat-cured derivatives of the isolates were screened for acetyl-, adenylyl-, and phosphotransferase activities. The substrates were ntamicin, amikacin and ilniieir the results indicated that even though all three activites were present, the phosphotransferase reaction was most respo i otice-es_eantibiotics. The absence of any of the modifying activites in cured derivatives of the three isolates supports the conclusion that aminoglycoside resistance in these strains is conferred by a plasmid.Gentamicin resistance in clinical isolates of Staphylococcus aureus has been reported in Europe (4, 7, 9, 10) and the United States (11). Recent studies in this laboratory identified a 50S plasmid in two strains as the genetic element responsible for this resistance (11). The organisms studied were recovered from an outbreak of infections in our neonatal intensive care unit (Talmadge Memorial Hospital, Augusta, Ga.) and were of different phage types. Speller et al. (10) reported an outbreak in three hospitals by a single strain of gentamicin-resistant S. aureus. In France, Le Goffic et al. (7) have studied a gentamicin-resistant strain isolated from a blood culture.Since gentamicin resistance in S. aureus has only recently been noted in clinical isolates, we undertook the biochemical characterization of our strains in an effort to determine which of several possible modifying enzymes could be involved in this resistance. We now describe the relative susceptibility of gentamicin, amikacin, and netilmicin to acetyltransferase (AAC) adenylyltransferase (ANT), and phosphotransferase (APT) modification by crude cell-free extracts of our S. aureus strains.