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pHH502, a plasmid with IncP and IncI alpha characters, loses the latter by a specific recA-independent deletion event
Abstract:
Plasmid pHH502, of molecular weight 70 X 10(6), determined resistance to tetracycline, chloramphenicol, trimethoprim, sulphonamides and mercuric chloride and was incompatible with members of IncP and IncI alpha. It resembled other plasmids of IncI alpha in the following properties: it determined pili that were morphologically and serologically I alpha pili, whose production was repressed in established plasmid-carrying (R+) cultures; its transfer was equally efficient in liquid or on solid medium; it exerted surface exclusion against other IncI alpha plasmids; it was non-transferable to Proteus. In a reproducible, recA-independent event, pHH502 gave rise to pHH502-1, a plasmid of molecular weight 40 X 10(6), lacking determinants for resistance to tetracycline and chloramphenicol and all detectable IncI alpha characteristics. pHH502-1 was incompatible only with IncP plasmids and resembled other IncP plasmids in determining constitutive production of rigid pili, in its surface exclusion, in transferring at greater frequency on solid than in liquid medium and in being transmissible to Proteus mirabilis. It differed from other IncP plasmids in the morphology and serological type of its pili and in failing to transfer to Pseudomonas aeruginosa or Acinetobacter calcoaceticus. Small numbers of pHH502-1 rigid pili were present on bacteria carrying pHH502. Possible mechanisms for the generation of pHH502 and pHH502-1 are discussed.
Insights
Plasmid pHH502, a 70 MDa molecule, conferred multiple drug resistance and IncI alpha incompatibility. It transformed into pHH502-1 (40 MDa), losing some resistance and IncI alpha traits, gaining IncP plasmid characteristics.
Area of Science:
- Molecular Biology
- Microbiology
- Genetics
Background:
- Plasmids are extrachromosomal DNA elements crucial for bacterial adaptation and evolution.
- Understanding plasmid biology, including their transfer, incompatibility, and resistance determinants, is vital for combating antimicrobial resistance.
- IncI alpha and IncP plasmids represent distinct groups with unique characteristics influencing their behavior in bacterial populations.
Purpose of the Study:
- To characterize the properties of plasmid pHH502 and its derivative pHH502-1.
- To investigate the genetic and phenotypic changes associated with the transformation of pHH502 into pHH502-1.
- To elucidate the mechanisms underlying plasmid evolution and the acquisition of new traits.
Main Methods:
- Plasmid characterization through molecular weight determination.
- Antibiotic resistance profiling.
- Incompatibility assays with known plasmid groups (IncP, IncI alpha).
- Pili analysis (morphological and serological typing).
- Bacterial conjugation experiments to assess transfer efficiency and host range.
- RecA-independent event analysis.
Main Results:
- Plasmid pHH502 (70 MDa) conferred resistance to tetracycline, chloramphenicol, trimethoprim, sulphonamides, and mercuric chloride, exhibiting IncI alpha incompatibility.
- pHH502 produced IncI alpha pili, showed repressed production in R+ cultures, had equal liquid/solid transfer efficiency, exerted surface exclusion, and was non-transferable to Proteus.
- pHH502 spontaneously generated pHH502-1 (40 MDa), lacking tetracycline/chloramphenicol resistance and IncI alpha traits, but exhibiting IncP plasmid characteristics like constitutive rigid pili production and altered transfer efficiency.
Conclusions:
- Plasmid pHH502 possesses characteristics of IncI alpha plasmids, including specific pili and incompatibility.
- The spontaneous generation of pHH502-1 demonstrates a significant genetic rearrangement, leading to a shift in plasmid group affiliation from IncI alpha to IncP.
- pHH502-1 represents a novel IncP plasmid variant with distinct pili morphology and host range limitations, highlighting plasmid plasticity and evolution.