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Characteristics of R931 and other Pseudomonas aeruginosa R factors
Abstract:
R factors were detected in 3.3% of 233 hospital isolates of Pseudomonas aeruginosa using P. aeruginosa recipients in conjugations. Transferred markers included streptomycin, tetracycline, and sulfonamide resistance. Gentamicin resistance was transferred from two strains previously shown to acetylate gentamicin. A group of R factors exemplified by R931 were characterized by failure to transfer to Escherichia coli recipients. Such R factors formed a single compatibility group when examined in a P. aeruginosa recipient. Other P. aeruginosa R factors, including RP4, showed stable coexistence with the R931 group. It is proposed that RP4 and similar R factors be members of the P-1 compatibility group and that R931, R3108, R209, and R130 be members of a group termed P-2. The buoyant densities of all R factors examined were similar, about 1.716 to 1.719 g/cm(3). The content of R-factor deoxyribonucleic acid (DNA) relative to the total DNA varied among the different R factors, ranging from about 18 +/- 2% in log-phase cells of 931 (R931) to undetectable for 679 (R679). However, R679, which transferred from strain 679 at extremely low and irregular frequencies to an E. coli host, was shown to represent about 4% R-factor DNA in that host. The relative DNA content of R931 appeared to decline in the stationary growth phase of 931 (R931) or 280 (R931). R931 covalently closed circular DNA was isolated by ethidium bromide-CsCl gradient centrifugation and examined by electron microscopy. Two major molecular distributions existed, having contour lengths of 0.5 and 12.4 mum. The molecular weights were estimated to be 10(6) and 25 x 10(6). Both molecules were under relaxed replication control. R factor R931 exists as a naturally occurring high-frequency transfer system in P. aeruginosa strains 931 and 1310. However, in strain 280 it acts as if subject to fertility repression. Other members of the P-2 compatibility group also are high-frequency transfer systems in the natural host and in strain 1310. RP4 is restricted from recipient strain 1310. Some additional recipient effects were noted in that strains 1310 or 280 sometimes differed in recipient effectiveness with a given donor. Agglutination reactions with absorbed antiserum were able to distinguish between two members of the same R-factor compatibility group, R931 and R3108.
Insights
R factors, genetic elements conferring antibiotic resistance, were found in Pseudomonas aeruginosa hospital isolates. Two new compatibility groups, P-1 and P-2, were proposed for these R factors based on transferability and coexistence studies.
Area of Science:
- Microbiology
- Genetics
- Molecular Biology
Background:
- R factors are plasmids that confer antibiotic resistance.
- Prevalence and characteristics of R factors in Pseudomonas aeruginosa are important for understanding antibiotic resistance.
- Previous studies have identified various R factors in P. aeruginosa, but their classification and transfer properties require further investigation.
Purpose of the Study:
- To detect and characterize R factors in hospital isolates of Pseudomonas aeruginosa.
- To determine the transferability of R factors to different recipients.
- To classify R factors into compatibility groups and analyze their DNA content and molecular properties.
Main Methods:
- Conjugation experiments using P. aeruginosa recipients to detect R factor transfer.
- Characterization of transferred markers including antibiotic resistance.
- Electron microscopy and buoyant density centrifugation to analyze R factor DNA.
- Compatibility tests to group R factors.
Main Results:
- R factors were detected in 3.3% of 233 P. aeruginosa isolates, carrying resistance to streptomycin, tetracycline, and sulfonamide.
- Gentamicin resistance was transferred from strains known to acetylate gentamicin.
- Two distinct R factor compatibility groups, P-1 (e.g., RP4) and P-2 (e.g., R931), were proposed based on transferability to E. coli and coexistence studies.
- R931 DNA showed two major molecular distributions (0.5 and 12.4 µm contour length) under relaxed replication control.
- Relative DNA content varied among R factors and was influenced by growth phase.
Conclusions:
- The study identified and classified R factors in P. aeruginosa into two novel compatibility groups, P-1 and P-2.
- R factor R931 represents a high-frequency transfer system in certain P. aeruginosa strains but can be subject to fertility repression.
- The findings contribute to the understanding of R factor diversity and antibiotic resistance mechanisms in P. aeruginosa.