ABSTRACT
USA500 isolates are clonal complex 8 (CC8) Staphylococcus aureus strains closely related to the prominent community- and hospital-associated USA300 group. Despite being relatively understudied, USA500 strains cause a significant burden of disease and are the third most common methicillin-resistant S. aureus (MRSA) strains identified in the U.S. Emerging Infections Program (EIP) invasive S. aureus surveillance. To better understand the genetic relationships of the strains, we sequenced the genomes of 539 USA500 MRSA isolates from sterile site infections collected through the EIP between 2005 and 2013 in the United States. USA500 isolates fell into three major clades principally separated by their distribution across different U.S. regions. Clade C1 strains, found principally in the Northeast, were associated with multiple IS256 insertion elements in their genomes and higher levels of antibiotic resistance. C2 was associated with Southern states, and E1 was associated with Western states. C1 and C2 strains all shared a frameshift in the gene encoding AdsA surface-attached surface protein. We propose that the term "USA500" should be used for CC8 strains sharing a recent common ancestor with the C1, C2, and E1 strains but not in the USA300 group.IMPORTANCE In this work, we have removed some of the confusion surrounding the use of the name "USA500," placed USA500 strains in the context of the CC8 group, and developed a strategy for assignment to subclades based on genome sequence. Our new phylogeny of USA300/USA500 will be a reference point for understanding the genetic adaptations that have allowed multiple highly virulent clonal strains to emerge from within CC8 over the past 50 years.
Subject(s)
Methicillin-Resistant Staphylococcus aureus/classification , Methicillin-Resistant Staphylococcus aureus/genetics , Molecular Typing , Phylogeography , Staphylococcal Infections/epidemiology , Staphylococcal Infections/microbiology , Epidemiological Monitoring , Methicillin-Resistant Staphylococcus aureus/isolation & purification , Molecular Epidemiology , United States/epidemiology , Whole Genome SequencingABSTRACT
We describe two cases of donor-derived methicillin-resistant Staphylococcus aureus (MRSA) bacteremia that developed after transplantation of organs from a common donor who died from acute MRSA endocarditis. Both recipients developed recurrent MRSA infection despite appropriate antibiotic therapy, and required prolonged hospitalization and hospital readmission. Comparison of S. aureus whole genome sequence of DNA extracted from fixed donor tissue and recipients' isolates confirmed donor-derived transmission. Current guidelines emphasize the risk posed by donors with bacteremia from multidrug-resistant organisms. This investigation suggests that, particularly in the setting of donor endocarditis, even a standard course of prophylactic antibiotics may not be sufficient to prevent donor-derived infection.
Subject(s)
Genome, Bacterial , Methicillin-Resistant Staphylococcus aureus/isolation & purification , Organ Transplantation/adverse effects , Sequence Analysis, DNA , Staphylococcal Infections/transmission , Tissue Donors , DNA, Bacterial/genetics , Humans , Male , Methicillin-Resistant Staphylococcus aureus/genetics , Polymorphism, Single Nucleotide , Staphylococcal Infections/microbiologyABSTRACT
We describe a real-time PCR assay for the detection of methicillin-resistant Staphylococcus aureus and genes encoding toxic shock syndrome toxin 1 and Panton-Valentine leukocidin. Rapid screening and detection of toxins is a useful tool for surveillance studies and outbreak investigations involving large numbers of isolates.
Subject(s)
Bacterial Toxins/analysis , Bacteriological Techniques/methods , Enterotoxins/analysis , Exotoxins/analysis , Leukocidins/analysis , Methicillin-Resistant Staphylococcus aureus/isolation & purification , Multiplex Polymerase Chain Reaction/methods , Real-Time Polymerase Chain Reaction/methods , Staphylococcal Infections/microbiology , Superantigens/analysis , Bacterial Toxins/genetics , DNA, Bacterial/genetics , Enterotoxins/genetics , Exotoxins/genetics , Genes, Bacterial , Humans , Leukocidins/genetics , Mass Screening/methods , Methicillin-Resistant Staphylococcus aureus/genetics , Superantigens/geneticsABSTRACT
AdvanDx VRE EVIGENE, a commercial vanA/vanB DNA hybridization assay to identify vancomycin-resistant enterococci (VRE), was evaluated for the detection of vanA in Staphylococcus aureus. Performance was assessed using S. aureus, VRE, and vancomycin-intermediate and -susceptible isolates. The assay demonstrated 100% sensitivity and specificity when analyzed visually and by optical density.
