Pseudomonas aeruginosa R Factors Determining Gentamicin Plus Carbenicillin Resistance from Patients with Urinary Tract Colonizations

Abstract

R factors determining multiple resistance including both gentamicin and carbenicillin have been identified in high incidence among hospital isolates of Pseudomonas aeruginosa. The factors are readily transmitted to other P. aeruginosa but not to Escherichia coli strains K-12 or C, or to Proteus mirabilis. R factor-containing isolates are predominantly immunotype 7 isolated from urinary sources.Pseudomonas aeruginosa, although resistant to many antibiotics, has been generally susceptible to gentamicin and carbenicillin. Recently, descriptions have appeared of R factors in this organism, including reports of factors determining resistance to one or the other of these antibiotics (3,4,8,9,11,12,14,15, 17 with L-amino acids at 20 ,ug/ml as required. Antibiotics were used in selection plates at the following concentrations (;g/ml): gentamicin, 1 to 20; carbenicillin, 50, 500, or 750; streptomycin, 100; tetracycline, 100; kanamycin, 50; and rifampin, 100.Antibiotic resistance. Antibiotic disk susceptibilities were determined by the Bauer-Kirby method (2) with Mueller-Hinton agar (Difco). For determination of minimal inhibitory concentrations, single drops with 101 organisms from ovemight culture were spotted on similar agar media containing serial twofold supplements of antibiotic. In cases where strain interactions were likely, single samples per culture dish were examined with 35 by 10 mm dishes.Bacterial strains. All clinical strains studied were isolated and identified at Veterans Administration Hospital, Cincinnati. These and other locally derived strains are designated with the PL prefix of this laboratory. The origins and pertinent characteristics of the major mating strains are presented in Table 1. Strain PL1 is a leu mutant of strain 280 met rit. 'Ihe mutant was isolated from a stock of the parental strain which had been exposed to diethylsulfate and subjected to carbenicillin selection (1.3 mg/ml). All strains were maintained at room temperature on complex medium solidified with agar (0.75%) in sealed, screw-capped glass vials.Bacterial matings and selection of transcipients.

Virulence in Rats of Gentamicin-Carbenicillin-Resistant Pseudomonas

“…Organisms with a similar resistance pattern have been isolated with increasing frequency from 1971 through 1974 at the Cincinnati Veterans Administration Hospital. Simultaneously, resistance transfer factors (R) responsible for the development of resistance in a majority of these strains were demonstrated (6). Our clinical observations suggested that the resistant Pseudomonas were less virulent than we anticipated.…”

Plasmid-mediated resistance to antibiotic synergism in enterococci.

“…Although transfer frequencies approaching 100% have been reported among gramnegative bacteria (24), the upper end ofthe range found here (3 x 10-2) may be the highest described to date among gram-positive organisms. Because the recipient strain, JH2-7, which is sensitive to antibiotic synergism, acquired resistance to penicillin-streptomycin and penicillin-kanamycin synergism after acquisition of a plasmid from a resistant clinical isolate, these results suggest that gene(s) involved in resistance to penicillin-aminoglycoside synergism are present on that plasmid, and that they may be the same gene(s) responsible for high-level resistance to strept6mycin and kanamycin.…”

“…Therefore, we have been especially interested in the 25-50% of clinical isolates of enterococci with high-level resistance (minimal inhibitory concentration >2,000 ,ug/ml) to streptomycin and kanamycin which have now been reported from several cities, including Denver (7), Seattle (8), Boston (9), and London (10). The resistance observed in these strains is f'ar above levels that are achievable in serum without producing unacceptable toxicity (20)(21)(22)(23)(24)(25) ,ug/ml f'or streptomycin and kanamycin). However, it is clinically relevant because strains with high-level aminoglycoside resistance are also resistant to antibiotic synergism with penicillin and that aminoglycoside (11).…”

Family of Class 1 Integrons Related to In4 from Tn 1696

“…In28 is found within the transposon Tn1403 (28,53), which was recovered from a clinical strain of Pseudomonas aeruginosa which was isolated in the United States in 1973-1974 (26) and contains the IncP-2 plasmid RPL11. RPL11 transfers resistance to gentamicin, carbenicillin, streptomycin, tetracycline, sulfonamides, chloramphenicol, and mercury (26), while Tn1403 confers resistance to only carbenicillin, streptomycin, spectinomycin, and chloramphenicol (28,53). In1 is found in the multidrug resistance plasmid R46, originally from a Salmonella enterica var.…”