Subtle genetic changes enhance virulence of methicillin resistant and sensitive Staphylococcus aureus

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Abstract

Background

Community acquired (CA) methicillin-resistant Staphylococcus aureus (MRSA) increasingly causes disease worldwide. USA300 has emerged as the predominant clone causing superficial and invasive infections in children and adults in the USA. Epidemiological studies suggest that USA300 is more virulent than other CA-MRSA. The genetic determinants that render virulence and dominance to USA300 remain unclear.

Results

We sequenced the genomes of two pediatric USA300 isolates: one CA-MRSA and one CA-methicillin susceptible (MSSA), isolated at Texas Children's Hospital in Houston. DNA sequencing was performed by Sanger dideoxy whole genome shotgun (WGS) and 454 Life Sciences pyrosequencing strategies. The sequence of the USA300 MRSA strain was rigorously annotated. In USA300-MRSA 2658 chromosomal open reading frames were predicted and 3.1 and 27 kilobase (kb) plasmids were identified. USA300-MSSA contained a 20 kb plasmid with some homology to the 27 kb plasmid found in USA300-MRSA. Two regions found in US300-MRSA were absent in USA300-MSSA. One of these carried the arginine deiminase operon that appears to have been acquired from S. epidermidis. The USA300 sequence was aligned with other sequenced S. aureus genomes and regions unique to USA300 MRSA were identified.

Conclusion

USA300-MRSA is highly similar to other MRSA strains based on whole genome alignments and gene content, indicating that the differences in pathogenesis are due to subtle changes rather than to large-scale acquisition of virulence factor genes. The USA300 Houston isolate differs from another sequenced USA300 strain isolate, derived from a patient in San Francisco, in plasmid content and a number of sequence polymorphisms. Such differences will provide new insights into the evolution of pathogens.

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Most cited references 43

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Molecular Cloning : A Laboratory Manual

Joseph Sambrook, David William Russell (2001)

The first two editions of this manual have been mainstays of molecular biology for nearly twenty years, with an unrivalled reputation for reliability, accuracy, and clarity. In this new edition, authors Joseph Sambrook and David Russell have completely updated the book, revising every protocol and adding a mass of new material, to broaden its scope and maintain its unbeatable value for studies in genetics, molecular cell biology, developmental biology, microbiology, neuroscience, and immunology. Handsomely redesigned and presented in new bindings of proven durability, this three–volume work is essential for everyone using today’s biomolecular techniques. The opening chapters describe essential techniques, some well–established, some new, that are used every day in the best laboratories for isolating, analyzing and cloning DNA molecules, both large and small. These are followed by chapters on cDNA cloning and exon trapping, amplification of DNA, generation and use of nucleic acid probes, mutagenesis, and DNA sequencing. The concluding chapters deal with methods to screen expression libraries, express cloned genes in both prokaryotes and eukaryotic cells, analyze transcripts and proteins, and detect protein–protein interactions. The Appendix is a compendium of reagents, vectors, media, technical suppliers, kits, electronic resources and other essential information. As in earlier editions, this is the only manual that explains how to achieve success in cloning and provides a wealth of information about why techniques work, how they were first developed, and how they have evolved.

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GeneMark.hmm: new solutions for gene finding.

A. Lukashin (1998)

The number of completely sequenced bacterial genomes has been growing fast. There are computer methods available for finding genes but yet there is a need for more accurate algorithms. The GeneMark. hmm algorithm presented here was designed to improve the gene prediction quality in terms of finding exact gene boundaries. The idea was to embed the GeneMark models into naturally derived hidden Markov model framework with gene boundaries modeled as transitions between hidden states. We also used the specially derived ribosome binding site pattern to refine predictions of translation initiation codons. The algorithm was evaluated on several test sets including 10 complete bacterial genomes. It was shown that the new algorithm is significantly more accurate than GeneMark in exact gene prediction. Interestingly, the high gene finding accuracy was observed even in the case when Markov models of order zero, one and two were used. We present the analysis of false positive and false negative predictions with the caution that these categories are not precisely defined if the public database annotation is used as a control.

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Methicillin-resistant S. aureus infections among patients in the emergency department.

Gregory J Moran, Anusha Krishnadasan, Rachel Gorwitz … (2006)

Methicillin-resistant Staphylococcus aureus (MRSA) is increasingly recognized in infections among persons in the community without established risk factors for MRSA. We enrolled adult patients with acute, purulent skin and soft-tissue infections presenting to 11 university-affiliated emergency departments during the month of August 2004. Cultures were obtained, and clinical information was collected. Available S. aureus isolates were characterized by antimicrobial-susceptibility testing, pulsed-field gel electrophoresis, and detection of toxin genes. On MRSA isolates, we performed typing of the staphylococcal cassette chromosome mec (SCCmec), the genetic element that carries the mecA gene encoding methicillin resistance. S. aureus was isolated from 320 of 422 patients with skin and soft-tissue infections (76 percent). The prevalence of MRSA was 59 percent overall and ranged from 15 to 74 percent. Pulsed-field type USA300 isolates accounted for 97 percent of MRSA isolates; 74 percent of these were a single strain (USA300-0114). SCCmec type IV and the Panton-Valentine leukocidin toxin gene were detected in 98 percent of MRSA isolates. Other toxin genes were detected rarely. Among the MRSA isolates, 95 percent were susceptible to clindamycin, 6 percent to erythromycin, 60 percent to fluoroquinolones, 100 percent to rifampin and trimethoprim-sulfamethoxazole, and 92 percent to tetracycline. Antibiotic therapy was not concordant with the results of susceptibility testing in 100 of 175 patients with MRSA infection who received antibiotics (57 percent). Among methicillin-susceptible S. aureus isolates, 31 percent were USA300 and 42 percent contained pvl genes. MRSA is the most common identifiable cause of skin and soft-tissue infections among patients presenting to emergency departments in 11 U.S. cities. When antimicrobial therapy is indicated for the treatment of skin and soft-tissue infections, clinicians should consider obtaining cultures and modifying empirical therapy to provide MRSA coverage. Copyright 2006 Massachusetts Medical Society.

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Author and article information

Journal

Journal ID (nlm-ta): BMC Microbiol

Title: BMC Microbiology

Publisher: BioMed Central

ISSN (Electronic): 1471-2180

Publication date Collection: 2007

Publication date (Electronic): 6 November 2007

Volume: 7

Page: 99

Affiliations

[1 ]Department of Molecular Virology and Microbiology, Baylor College of Medicine, Houston, TX, USA

[2 ]Department of Pediatrics, Baylor College of Medicine, Texas Children's Hospital, Houston, TX, USA

[3 ]Human Genome Sequencing Center, Baylor College of Medicine, Houston, TX, USA

[4 ]Department of Molecular and Human Genetics, Baylor College of Medicine, Houston, TX, USA

[5 ]University of Houston-Downtown, Houston, TX, USA

[6 ]University of Houston, Houston, TX, USA

Article

Publisher ID: 1471-2180-7-99

DOI: 10.1186/1471-2180-7-99

PMC ID: 2222628

PubMed ID: 17986343

SO-VID: 62e4acfb-52e4-4707-941d-382e495cdf20

License:

This is an Open Access article distributed under the terms of the Creative Commons Attribution License ( http://creativecommons.org/licenses/by/2.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

Subtle genetic changes enhance virulence of methicillin resistant and sensitive Staphylococcus aureus

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Role of Microbes in Soil Fertility and Human Health

Most cited references 43

Molecular Cloning : A Laboratory Manual

GeneMark.hmm: new solutions for gene finding.

Methicillin-resistant S. aureus infections among patients in the emergency department.

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