[Classification of R-factors. Possible errors and their elimination]

Area of Science:

• Microbiology
• Molecular Biology
• Genetics

Background:

• Plasmid classification is crucial for understanding bacterial genetics and epidemiology.
• Nosocomial infectious outbreaks require accurate characterization of causative agents, including plasmids.
• Existing methods for plasmid classification have limitations that can lead to errors.

Purpose of the Study:

• To emphasize the necessity of classifying plasmids for accurate epidemiological studies.
• To describe a method for classifying plasmids using sex-phages and incompatibility grouping.
• To identify R-factors as key indicators of nosocomial outbreak uniformity.

Main Methods:

• Utilized the HFRT-system for determining pilus groups by sex-phages.
• Identified plasmid incompatibility to subdivide pilus groups into incompatibility groups.
• Employed recombination-deficient rec A- strains of E. coli K12 to prevent plasmid recombination.
• Added trypsin to inhibit plasmid-coded colicin production.
• Carefully selected indicator plasmids and considered their spontaneous loss and transposon activity.

Main Results:

• The uniformity of nosocomial infectious outbreaks is determined by R-factors, not the infectious agent itself.
• Established a system for classifying plasmids based on pilus groups and incompatibility.
• Differentiated between incoming and resident incompatibility.
• Minimized potential errors in plasmid classification through rigorous testing.

Conclusions:

• R-factors are more indicative of nosocomial outbreak uniformity than the infectious agent.
• The described method provides a robust approach to plasmid classification.
• Accurate plasmid classification is essential for controlling infectious diseases and understanding bacterial evolution.