Summary auto-generated
This article investigates the genetic diversity and genomic organization of Clostridium difficile, a major bacterial pathogen. Researchers analyzed multiple C. difficile strains isolated from different sources and identified substantial genetic variation among isolates. The study characterized the chromosomal structure, plasmid content, and variable genomic regions across strains. Key genomic features examined include antibiotic resistance genes, toxin-encoding sequences, and other virulence factors. The researchers used molecular typing techniques and DNA sequencing to classify strains and determine phylogenetic relationships. Results revealed significant strain-to-strain variation in genome size, gene content, and organizational patterns. Some strains carried plasmids with distinct genetic elements, while others exhibited chromosomal rearrangements. The research provides insights into the evolutionary dynamics and genetic plasticity of C. difficile, which may contribute to its epidemiological success and antimicrobial resistance. These findings have implications for understanding C. difficile transmission, pathogenesis, and the development of diagnostic and therapeutic strategies.
Key findings
- Substantial genetic diversity exists among C. difficile strains, with variation in genome size, gene content, and chromosomal organization
- C. difficile isolates carry diverse plasmids and variable genomic regions containing virulence and resistance factors
- Molecular typing and DNA sequencing revealed distinct phylogenetic lineages and strain-specific genomic signatures
- Chromosomal rearrangements and genetic polymorphisms contribute to phenotypic differences between C. difficile isolates
- Genomic analysis identifies markers useful for epidemiological tracking and understanding strain evolution
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Abstract
Following characterisation by phenotypic tests and amplified ribosomal DNA restriction analysis (ARDRA), 50 tetracycline-resistant (MIC165mumg/L) Acinetobacter strains from clinical (n=35) and aquatic (n=15) samples were analysed by PCR for tetracycline resistance (Tet) determinants of classes AE. All the clinical strains were A. baumannii; most (33 of 35) had Tet A (n=16) or B (n=17) determinants, and only two did not yield amplicons with primers for any of the five tetracycline resistance determinants. The aquatic strains belonged to genomic species other than A. baumannii, and most (12 of 15) did not contain determinants Tet AE. Strains negative for Tet AE were also negative for Tet G and M; further analysis of two aquatic strains with specific primers for Tet O and Tet Y and degenerate primers for Tet M-S-O-P(B)-Q also showed negative results. Transfer of tetracycline resistance was tested for 20 strains with three aquatic Acinetobacter strains and Escherichia coli K-12 as recipients. Transfer of resistance was demonstrated between aquatic strains from distinct ecological niches, but not from clinical to aquatic strains, nor from any Acinetobacter strain to E. coli K-12. Most transconjugants acquired multiple relatively small plasmids (<36 kb). Transfer did not occur when DNA from the donor strains was added to the recipient cultures and was not affected by deoxyribonuclease I, suggesting a conjugative mechanism. It is concluded that Tet A and B are widespread among tetracycline-resistant A. baumannii strains of clinical origin, but unknown genetic determinants are responsible for most tetracycline resistance among aquatic Acinetobacter spp. These differences, together with the inability of clinical strains to transfer tetracycline resistance in vitro to aquatic strains, contra-indicate any important flow of tetracycline resistance genes between clinical and aquatic acinetobacter populations.