A previously uncommon strain of C. difficile with variations in toxin genes has become more resistant to fluoroquinolones and has emerged as a cause of geographically dispersed outbreaks of C. difficile-associated disease.

Oxacillin-resistant Staphylococcus aureus (ORSA) is a virulent pathogen responsible for both health careassociated and community onset disease. We used SmaI-digested genomic DNA separated by pulsed-field gel electrophoresis (PFGE) to characterize 957 S. aureus isolates and establish a database of PFGE patterns. In addition to PFGE patterns of U.S. strains, the database contains patterns of representative epidemic-type strains from the United Kingdom, Canada, and Australia; previously described ORSA clonal-type isolates; 13 vancomycin-intermediate S. aureus (VISA) isolates, and two high-level vancomycin-resistant, vanA-positive strains (VRSA). Among the isolates from the United States, we identified eight lineages, designated as pulsed-field types (PFTs) USA100 through USA800, seven of which included both ORSA and oxacillinsusceptible S. aureus isolates. With the exception of the PFT pairs USA100 and USA800, and USA300 and USA500, each of the PFTs had a unique multilocus sequence type and spa type motif. The USA100 PFT, previously designated as the New York/Tokyo clone, was the most common PFT in the database, representing 44% of the ORSA isolates. USA100 isolates were typically multiresistant and included all but one of the U.S. VISA strains and both VRSA isolates. Multiresistant ORSA isolates from the USA200, -500, and -600 PFTs have PFGE patterns similar to those of previously described epidemic strains from Europe and Australia. The USA300 and -400 PFTs contained community isolates resistant only to ␤-lactam drugs and erythromycin. Noticeably absent from the U.S. database were isolates with the previously described Brazilian and EMRSA15 PFGE patterns. These data suggest that there are a limited number of ORSA genotypes present in the United States.Oxacillin-resistant Staphylococcus aureus (ORSA), more commonly referred to as methicillin-resistant S. aureus (MRSA) (even though methicillin is rarely tested in U.S. laboratories), is a frequent cause of infections both in health care and community settings and is endemic in many U.S. hospitals (12,26,27,32,48,56). While a variety of strain typing methods have been used over the years to track the spread of ORSA (64), most outbreaks of ORSA have been characterized by bacteriophage typing or pulsed-field gel electrophoresis (PFGE). Although public health institutions in several countries, such as Australia (68) (8,9,11), and of ORSA causing severe disease and death in children (6,27,42) all argued that better tracking of ORSA strains nationwide was needed to monitor the spread of such organisms. Thus, the Centers for Disease Control and Prevention (CDC), in collaboration with state health departments, has undertaken the goal of assembling a national database of S. aureus PFGE profiles similar to the PulseNet program for Escherichia coli O157:H7 (62).The overall goal of this study was to assemble a database of ORSA PFGE profiles and to identify major lineages of ORSA present in the United States. PFGE was chosen over other typing methods, such as multilocus sequence...

No abstract

Nasal colonization with MRSA has increased in the United States, despite an overall decrease in nasal colonization with S. aureus. PFGE types associated with community transmission only partially account for the increase in MRSA colonization.

Vancomycin is usually reserved for treatment of serious infections, including those caused by multidrug-resistant Staphylococcus aureus. A clinical isolate of S. aureus with high-level resistance to vancomycin (minimal inhibitory concentration = 1024 microg/ml) was isolated in June 2002. This isolate harbored a 57.9-kilobase multiresistance conjugative plasmid within which Tn1546 (vanA) was integrated. Additional elements on the plasmid encoded resistance to trimethoprim (dfrA), beta-lactams (blaZ), aminoglycosides (aacA-aphD), and disinfectants (qacC). Genetic analyses suggest that the long-anticipated transfer of vancomycin resistance to a methicillin-resistant S. aureus occurred in vivo by interspecies transfer of Tn1546 from a co-isolate of Enterococcus faecalis.