Genetic transfer and genome evolution in MRSA

Gürtler, Volker; Mayall, Barrie C.

doi:10.1099/00221287-147-12-3195

Cited by 8 publications

(6 citation statements)

References 5 publications

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“…On the other hand, most of the isolates that have identical ccrAB alleles show differences in the mec complex, hence disfavoring the suggestion of horizontal transfer of SCCmec. In contrast to the recombinase genes, mecA is very well conserved, with only 1 to 2 bp differences out of 2,007 bp among S. aureus, S. epidermidis, and S. sciuri (14,21). This might imply that there is a difference in selective pressure on the ccrAB and mecA gene products or that these genes have different evolutionary histories.…”

Section: Discussionmentioning

confidence: 99%

Local Variants of Staphylococcal Cassette Chromosome mec in Sporadic Methicillin-Resistant Staphylococcus aureus and Methicillin-Resistant Coagulase-Negative Staphylococci: Evidence of Horizontal Gene Transfer?

Hanssen

Kjeldsen

Sollid

2004

Antimicrob Agents Chemother

216

206

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The mecA gene in Staphylococcus aureus is located on the genetic element staphylococcal cassette chromosome (SCC). Different SCCmecs have been classified according to their putative recombinase genes (ccrA and ccrB) and overall genetic composition. Clinical isolates of coagulase-negative staphylococci (CoNS; n ‫؍‬ 39) and S. aureus (n ‫؍‬ 20) from Norway, India, Italy, Finland, the United States, and the United Kingdom were analyzed by pulsed-field gel electrophoresis, which showed that most isolates were genetically unrelated. Cluster analyses of 16S rRNA gene and pta sequences confirmed the traditional biochemical species identification. The mecI, mecR1, mecA, and ccrAB genes were detected by PCRs, identifying 19 out of 20 S. aureus and 17 out of 39 CoNS isolates as carriers of one of the three published ccrAB pairs. New variants of SCCmec were identified, as well as CoNS isolates containing ccrAB genes without the mec locus. ccrAB and mec PCRs were verified by hybridization. Sequence alignments of ccrAB genes showed a high level of diversity between the ccrAB alleles from different isolates, i.e., 94 to 100% and 95 to 100% homology for ccrAB1 and ccrAB2, respectively. All of the ccrAB3 genes identified were identical. Genetically unique and sporadic methicillin-resistant S. aureus (MRSA) contained local variants of ccrAB gene pairs identical to those found in MR-CoNS but different from those in MRSA from other regions. Allelic variants of ccrAB in isolates from the same geographic region showed sequence conservation independent of species. The species-independent sequence conservation found suggests that there is a closer genetic relationship between ccrAB2 in Norwegian staphylococci than between ccrAB2 sequences in international MRSA and Norwegian MRSA. This might indicate that different staphylococcal species acquire these genes locally by horizontal gene transfer.

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Section: Discussionmentioning

confidence: 99%

Local Variants of Staphylococcal Cassette Chromosome mec in Sporadic Methicillin-Resistant Staphylococcus aureus and Methicillin-Resistant Coagulase-Negative Staphylococci: Evidence of Horizontal Gene Transfer?

Hanssen

Kjeldsen

Sollid

2004

Antimicrob Agents Chemother

216

206

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“…Similarly, rrn copy numbers of 7, 8, and 9 occur within different Vibrio cholerae strains (17,36). Recombination events between rrn operons may be the reason for rrn operon copy number variations among strains of the same species (1,25,28,36). It is still not clear what benefit there might be to an organism in having multiple rrn copies.…”

Section: Discussionmentioning

confidence: 99%

“…Sequence differences between ISRs of the same size most likely arise from nucleotide substitution events (4,5,25,30). Also, some ISRs were of similar length (e.g., rrnE and rrnF of S. aureus) but had sequence blocks with different nucleotide sequences, probably because of recombination events (25,27,28). Some of the ISRs were identical in length, and any differences in their sequences were due to single nucleotide deletions, insertions, or substitutions (4,5,25,30).…”

Section: Discussionmentioning

confidence: 99%

The Mosaic Nature of Intergenic 16S-23S rRNA Spacer Regions Suggests rRNA Operon Copy Number Variation in Clostridium difficile Strains

Sadeghifard

Gürtler

Beer

et al. 2006

Appl Environ Microbiol

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Clostridium difficile is a major spore-forming environmental pathogen that causes serious health problems in patients undergoing antibiotic therapy. Consequently, reliable and sensitive methods for typing individual strains are required for epidemiological and environmental studies. Ribotyping is generally considered the best method, but it fails to account for sequence diversity which might exist in intergenic 16S-23S rRNA spacer regions (ISRs) within and among strains of this organism. Therefore, this study was undertaken to compare the sequence of each individual ISR in five strains of C. difficile to explore the extent of this diversity and see whether such information might provide the basis for more sensitive and discriminatory strain typing methods. After targeted PCR amplification, cloning, and sequencing, the diversity of the ISRs was used as a measure of rRNA operon copy number. In C. difficile strains 630, ATCC 43593, A, and B, 11, 11, 7, and 8 ISR length variants, respectively, were found (containing different combinations of sequence groups [i to xiii]), suggesting 11, 11, 7, and 8 rrn copies in the respective strains. Many ISRs of the same length differed markedly in their sequences, and some of these were restricted in occurrence to a single strain. Most of these ISRs did not contain any tRNA genes, and only single copies of the tRNA Ala gene were found in those that did. The presence of ISR sequence groups (i to xiii) varied between strains, with some found in one, two, three, four, or all five strains. We conclude that the intergenic 16S-23S rRNA spacer regions showed a high degree of diversity, not only among the rrn operons in different strains and different rrn copies in a single strain but also among ISRs of the same length. It appears that C. difficile ISRs vary more at the inter-and intragenic levels than those of other species as determined by empirical comparison of sequences. The precise characterization of these sequences has demonstrated a high level of mosaic sequence block rearrangements that are present or absent in multiple strain-variable rrn copies within and between five different strains of C. difficile.

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“…For example, the ccrAB genes found in SCCmec types II and IV can vary up to 5% at the nucleotide level (18). This is in contrast to mecA, which is known to be highly conserved (99 to 100% nucleotide identity) (17). It is possible that some of the mutations in CcrAB cause a loss of recombinase function, thereby stabilizing SCCmec in the chromosome.…”

mentioning

confidence: 99%

A Subset of Staphylococcus aureus Strains Harboring Staphylococcal Cassette Chromosome mec (SCC mec ) Type IV Is Deficient in CcrAB-Mediated SCC mec Excision

Noto¹,

Archer

2006

Antimicrob Agents Chemother

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The gene encoding resistance to ␤-lactam antibiotics in the staphylococci is found on the chromosome in a genomic island designated staphylococcal cassette chromosome mec, or SCCmec. In addition to the resistance gene mecA, SCCmec also contains site-specific recombinase genes that are capable of catalyzing the chromosomal excision and reintegration of SCCmec. SCCmec is found in five major isotypes partially defined by the recombinase genes present, either ccrAB or ccrC. Of these, SCCmec type IV is presumed to be mobile in the environment, and this mobility may be partially responsible for the rise in community-associated methicillinresistant staphylococcal infections. In this study, we investigate the presumptive first step in type IV SCCmec mobility: chromosomal excision of the element. CcrAB from a panel of six Staphylococcus aureus and four Staphylococcus epidermidis strains were able to catalyze chromosomal excision of SCCmec types I and II, indicating that these proteins maintain recombinase activity despite varying by up to 3.7% at the amino acid level. Excision of type IV SCCmec was not universally seen, as a subset of S. aureus strains with type IV SCCmec did not excise their element. These strains are all highly related and represent a lineage of successful community-associated pathogens. In addition, the inability to excise SCCmec in these strains is associated with the insertion of a presumptive mobile element containing the gene for staphylococcal enterotoxin H (seh) immediately downstream of SCCmec on the chromosome. Acquisition of this mobile element, containing a known virulence gene, appears to have stabilized the chromosomal integration of the methicillin resistance gene in these strains.

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Genetic transfer and genome evolution in MRSA

Abstract: Microbiology Comment provides a platform for readers of Microbiology to communicate their personal observations and opinions in a more informal way than through the submission of papers.

Cited by 8 publications

References 5 publications

Local Variants of Staphylococcal Cassette Chromosome mec in Sporadic Methicillin-Resistant Staphylococcus aureus and Methicillin-Resistant Coagulase-Negative Staphylococci: Evidence of Horizontal Gene Transfer?

Local Variants of Staphylococcal Cassette Chromosome mec in Sporadic Methicillin-Resistant Staphylococcus aureus and Methicillin-Resistant Coagulase-Negative Staphylococci: Evidence of Horizontal Gene Transfer?

The Mosaic Nature of Intergenic 16S-23S rRNA Spacer Regions Suggests rRNA Operon Copy Number Variation in Clostridium difficile Strains

A Subset of Staphylococcus aureus Strains Harboring Staphylococcal Cassette Chromosome mec (SCC mec ) Type IV Is Deficient in CcrAB-Mediated SCC mec Excision

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