Characterization of a Nosocomially Significant, Multiple Drug-Resistant Strain of <i>Serratia marcescen</i><i>s</i>

Abstract

A multiple drug-resistant strain of Serratia marcescens (bacteriocin type 18) was isolated from three clinical patients. The isolates were found to carry a conjugally nontransferable, nonmobilizeable resistance plasmid (R-plasmid) with resistance-(r-)determinants against ten antimicrobial drugs: ampicillin, carbenicillin, chloramphenicol, gentamicin, kanamycin, neomycin, streptomycin, tobramycin, triple sulfonamides, cotrimoxazole, and – possibly – nalidixic acid, as determined with exposure to ‘curing’agents (ethidium bromide, acridine orange, and sodium dodecyl sulfate) and by the high rate of spontaneous loss of r-determinants. Dye-buoyant density centrifugation allowed recovery of R-plasmid DNA that measured roughly 24 μm in contour length; after ‘curing’ with concomitant loss of 9 r-determinants, the contour length of the R-plasmid DNA of one isolate (No. SE 154) had decreased to roughly 15 μm, and none was detected in the sole variant of the isolate that spontaneously had lost 11 r-determinants.

Selected and Spontaneous Variants of <i>Serratia marcescens</i> with Combined Resistance against Chloramphenicol, Nalidixic Acid, and Trimethoprim

“…Variant No. 65 (SE 154) spontaneously had lost 12 r-markers on a previous occasion [18]. The confirmatory MICs of CHLOR, NA, and TMP for these spontaneously 'cured' variants are shown in table VI.…”

“…Since October, 1973, a multiple-drug-resistant strain of S. marcescens (bacteriocin type 18), which was found to be resistant against all currently available chemo therapeutic agents except amikacin, acquired nosocomial significance, in that so far (July, 1976) this particular strain had been recovered from various clinical specimens derived from 18 patients in four different uni versity hospitals at Erlangen. A recent report [18] presented evidence that the R-plasmid of this strain is nonconjugative and nonmobilizable. Furthermore, based on 'curing' data that had been obtained with ethidium bromide, acridine orange, and sodium dodecyl sulfate, and on the high rate of spontaneous loss of resistance markers (r-markers), it was tenta tively concluded that this particular R-plasmid-mediated resistance against ampicillin, carbenicillin, chloramphenicol, gentamicin, kanamycin, neomycin, streptomycin, tobramycin, triple sulfonamides, cotrimoxazole, and -possibly -nalidixic acid.…”

“…Variant No. 65 (SE 154) represented a spontaneously 'cured' clone [18] of S. marcescens isolate No. SE 154 which originally had been isolated from the exudate of a postoperatively in fected hip endoprosthesis (patient G. S.; 3/15/74).…”

“…After subculture of SE 143-b to MAC-CV plates and over night incubation at 35 °C, ten representative 'opaque' and 'gray' appearing colonies were subcultured once more (check for purity and phenotypic stability) and exam ined for disk diffusion susceptibility. The majority of colonies had lost resistance against carbenicillin and aminoglycoside antibiotics [18], but had retained resistance against CHLOR, NA, and TMP. The minority of colonies (30%), however, had lost resistance against CHLOR, NA, and TMP, but still were resistant against carbenicillin and aminoglycosides.…”

Hospital Isolates of Serratia marcescens Transferring Ampicillin, Carbenicillin, and Gentamicin Resistance to Other Gram-Negative Bacteria Including Pseudomonas aeruginosa

“…Early isolates of this species were susceptible to carbenicillin (Cb) and gentamicin (Gm) (8), the latter being considered one of the most useful antibiotics against this species (4,7). Recently, however, a number of clinical isolates of S. marcescens have been described that are resistant to one or both of these antibiotics (10,14,16). In several cases, such resistance was found to be transferable and presumably associated with R factors (11,14).…”