Search

ABSTRACTMethicillin-resistant Staphylococcus aureus(MRSA) bloodstream infections (BSI) are classified epidemiologically as health care-associated hospital onset (HAHO)-, health care-associated community onset (HACO)-, or community-associated (CA)-MRSA. Clinical and molecular differences between HAHO- and HACO-MRSA BSI are not well known. Thus, we evaluated clinical and molecular characteristics of MRSA BSI to determine if distinct features are associated with HAHO- or HACO-MRSA strains. Molecular genotyping and medical record reviews were conducted on 282 MRSA BSI isolates from January 2007 to December 2009. MRSA classifications were 38% HAHO-, 54% HACO-, and 8% CA-MRSA. Comparing patients with HAHO-MRSA to those with HACO-MRSA, HAHO-MRSA patients had significantly higher rates of malignancy, surgery, recent invasive devices, and mortality and longer hospital stays. Patients with HACO-MRSA were more likely to have a history of renal failure, hemodialysis, residence in a long-term-care facility, long-term invasive devices, and higher rate of MRSA relapse. Distinct MRSA molecular strain differences also were seen between HAHO-MRSA (60% staphylococcal cassette chromosome mectype II [SCCmecII], 30% SCCmecIII, and 9% SCCmecIV) and HACO-MRSA (47% SCCmecII, 35% SCCmecIII, and 16% SCCmecIV) (P< 0.001). In summary, our study reveals significant clinical and molecular differences between patients with HAHO- and HACO-MRSA BSI. In order to decrease rates of MRSA infection, preventive efforts need to be directed toward patients in the community with health care-associated risk factors in addition to inpatient infection control.

ABSTRACTClonal complex 30 (CC30), one of the major Staphylococcus aureuslineages, has caused extensive hospital-acquired and community-acquired infections worldwide. Recent comparative genomics studies have demonstrated that three CC30 clones—phage type 80/81, Southwest Pacific (SWP), and contemporary EMRSA-16 associated (Con) strains—shared a recent common ancestor more than 100 years ago. Panton-Valentine leukocidin (PVL), a bacteriophage encoded toxin that has been epidemiologically linked with community-associated methicillin-resistant S. aureus(CA-MRSA), has frequently been identified in CC30 clones, although the pvlgene variation and distribution of PVL-encoding phages are poorly understood. We determined here the distribution of PVL phages, PVL gene sequences, and chromosomal phage insertion sites in 52 S. aureusCC30 PVL-harboring isolates, collected from four continents over a 75-year period. Our results indicate that PVL phages with icosahedral heads, including F108PVL and FPVL, were mainly associated with phage 80/81 strains, whereas phages with elongated heads were predominantly found in SWP (FSa2958 and FTCH60) and Con (FSa2USA) strains. Nine single-nucleotide polymorphisms were identified in the lukSF-PVgene, with six isolates harboring the R variant that has been previously associated with CA-MRSA strains. Interestingly, all six R variant strains belonged to the same Con CC30 clone and carried a FSa2USA-like phage. Similar chromosomal phage insertion sites were also identified in all 52 PVL-harboring CC30 strains. These analyses provide important insights into the microepidemiology of PVL-harboring CC30 strains, while the discovery of FSa2USA-associated R variant strains sheds further light on the evolution of PVL-positive CA-MRSA.

ABSTRACTKlebsiella pneumoniaecarbapenemase (KPC)-producing Enterobacteriaceaehave emerged as major nosocomial pathogens. blaKPC, commonly located on Tn4401, is found in Gram-negative bacterial strains, with the two most common variants, blaKPC-2and blaKPC-3, identified in plasmids with diverse genetic backgrounds. In this study, we examined blaKPC-4- and blaKPC-5-bearing plasmids recovered from two K. pneumoniaestrains, which were isolated from a single New Jersey hospital in 2005 and 2006, respectively. IncN plasmid pBK31551 is 84 kb in length and harbors blaKPC-4, blaTEM-1, qnrB2, aac(3)-Ib, aph(3′)-I, qacF, qacEΔ1, sul1, and dfrA14, which confer resistance to β-lactams, quinolones, aminoglycosides, quaternary ammonium compounds, and co-trimoxazole. The conserved regions within pBK31551 are similar to those of other IncN plasmids. Surprisingly, analysis of the Tn4401sequence revealed a large IS110- and Tn6901-carrying element (8.3 kb) inserted into the istAgene, encoding glyoxalase/bleomycin resistance, alcohol dehydrogenase, and S-formylglutathione hydrolase. Plasmid pBK31567 is 47 kb in length and harbors blaKPC-5, dfrA5, qacEΔ1, and sul1. pBK31567 belongs to a novel IncX subgroup (IncX5) and possesses a highly syntenic plasmid backbone like other IncX plasmids; however, sequence similarity at the nucleotide level is divergent. The blaKPC-5gene is carried on a Tn4401element and differs from the genetic environment of blaKPC-5described in Pseudomonas aeruginosastrain P28 from Puerto Rico. This study underscores the genetic diversity of multidrug-resistant plasmids involved in the spread of blaKPCgenes and highlights the mobility and plasticity of Tn4401. Comparative genomic analysis provides new insights into the evolution and dissemination of KPC plasmids belonging to different incompatibility groups.

ABSTRACTWe describe a multiplex real-time PCR assay capable of identifying both the epidemic Klebsiella pneumoniaeST258 clone and blaKPCcarbapenemase genes in a single reaction. The assay displayed excellent sensitivity (100%) and specificity (100%) for identification of ST258 clone and blaKPCin a collection of 75 K. pneumoniaeisolates comprising 41 sequence types. Our results suggest that this assay is an effective tool for surveillance of this clone among carbapenem-resistant K. pneumoniaeclinical isolates.

We describe a novel Tn4401 variant (Tn4401d) in epidemic Klebsiella pneumoniae clone ST258, from which a partial blaKPCfragment has been excised along with ISKpn7 and a partial tnpA fragment. Nested-PCR experiments confirmed that this region can be removed from distinct Tn4401 isoforms in both K. pneumoniae and Escherichia coli. This study highlights that the region surrounding blaKPCis undergoing recombination and that Tn4401 itself is heterogeneous and highly plastic.

ABSTRACTWe describe a novel Tn4401variant (Tn4401d) in epidemic Klebsiella pneumoniaeclone ST258, from which a partial blaKPCfragment has been excised along with ISKpn7and a partial tnpAfragment. Nested-PCR experiments confirmed that this region can be removed from distinct Tn4401isoforms in both K. pneumoniaeand Escherichia coli. This study highlights that the region surrounding blaKPCis undergoing recombination and that Tn4401itself is heterogeneous and highly plastic.

ABSTRACTA total of 299 nares and 194 blood isolates of methicillin-resistant Staphylococcus aureus(MRSA), each recovered from a unique patient, were collected from 23 U.S. hospitals from May 2009 to March 2010. All isolates underwent spaand staphylococcal cassette chromosome mecelement (SCCmec) typing and antimicrobial susceptibility testing; a subset of 84 isolates was typed by pulsed-field gel electrophoresis (PFGE) using SmaI. Seventy-six spatypes were observed among the isolates. Overall, for nasal isolates, spatype t002-SCCmectype II (USA100) was the most common strain type (37% of isolates), while among blood isolates, spatype t008-SCCmectype IV (USA300) was the most common (39%). However, the proportion of all USA100 and USA300 isolates varied by United States census region. Nasal isolates were more resistant to tobramycin and clindamycin than blood isolates (55.9% and 48.8% of isolates versus 36.6% and 39.7%, respectively; for both, P< 0.05). The USA300 isolates were largely resistant to fluoroquinolones. High-level mupirocin resistance was low among all spatypes (<5%). SCCmectypes III and VIII, which are rare in the United States, were observed along with several unusual PFGE types, including CMRSA9, EMRSA15, and the PFGE profile associated with sequence type 239 (ST239) isolates. Typing data from this convenience sample suggest that in U.S. hospitalized patients, USA100 isolates of multiple spatypes, while still common in the nares, have been replaced by USA300 isolates as the predominant MRSA strain type in positive blood cultures.

Objective.To describe the epidemiology of methicillin-resistant Staphylococcus aureus(MRSA) carriage and transmission in an ambulatory hemodialysis population.Design.Prospective cohort study.Setting.Outpatient hemodialysis facility affiliated with a large academic medical center.Participants.Of the 170 facility patients, 103 (61%) participated in the study.Methods.Swab specimens of the nares, axillae, and vascular access site were collected from participants weekly for 3 weeks and then monthly for 5 months. Demographic and clinical data were collected monthly for 12 months. Molecular analysis of MRSA isolates was performed.Results.The baseline MRSA carriage prevalence was 12%. Factors associated with MRSA carriage included a history of MRSA; failed renal transplantation; hospital admission within 6 months; and receipt of a first-generation cephalosporin, cefepime, or vancomycin. Six subjects acquired MRSA after enrollment (incidence, 1.2 per 100 patient-months at-risk; overall prevalence, 18%). Molecular analysis suggested that transmission occurred within the facility. The incidence of MRSA infection among carriers was 1.76 per 100 patient-months. Community-associated strains (ie, USA300) were isolated from 28% of carriers and at least 25% of infections.Conclusions.The prevalence of MRSA carriage and the incidence of infection among carriers were high among ambulatory hemodialysis patients, and community-associated MRSA was responsible for a large portion of the MRSA burden. A relatively high rate of MRSA acquisition was observed, with indirect evidence of intrafacility transmission. Additional studies are needed to confirm these findings and to identify effective and feasible methods to prevent MRSA transmission and infection among hemodialysis patients.

ABSTRACTlukF-PVwas present in 36% of skin and soft tissue infection (SSTI)-derived methicillin-susceptible Staphylococcus aureus(MSSA) strains and comprised six distinct clones, which contained fewer enterotoxin genes than strains without lukF-PV. Clinical presentations and outcomes of lukF-PV+methicillin-resistant S. aureus(MRSA) and MSSA SSTIs were comparable. In multivariable analysis, the presence of lukF-PVremained a significant predictor for incision and drainage among MSSA strains.

ABSTRACTCarbapenem resistance mediated by plasmid-borne Klebsiella pneumoniaecarbapenemases (KPC) is an emerging problem of significant clinical importance in Gram-negative bacteria. Multiple KPC gene variants (blaKPC) have been reported, with KPC-2 (blaKPC-2) and KPC-3 (blaKPC-3) associated with epidemic outbreaks in New York City and various international settings. Here, we describe the development of a multiplex real-time PCR assay using molecular beacons (MB-PCR) for rapid and accurate identification of blaKPCvariants. The assay consists of six molecular beacons and two oligonucleotide primer pairs, allowing for detection and classification of all currently described blaKPCvariants (blaKPC-2to blaKPC-11). The MB-PCR detection limit was 5 to 40 DNA copies per reaction and 4 CFU per reaction using laboratory-prepared samples. The MB-PCR probes were highly specific for each blaKPCvariant, and cross-reactivity was not observed using DNA isolated from several bacterial species. A total of 457 clinical Gram-negative isolates were successfully characterized by our MB-PCR assay, with blaKPC-3and blaKPC-2identified as the most common types in the New York/New Jersey metropolitan region. The MB-PCR assay described herein is rapid, sensitive, and specific and should be useful for understanding the ongoing evolution of carbapenem resistance in Gram-negative bacteria. As novel blaKPCvariants continue to emerge, the MB-PCR assay can be modified in response to epidemiologic developments.

ABSTRACTA novel composite transposon (Tn6072) resembling staphylococcal cassette chromosome mercury(SCCHg) was identified in a collection of sequence type (ST) 239 methicillin (meticillin)-resistant Staphylococcus aureus(MRSA) isolates from Romanian hospitals. Tn6072is homologous to the 5′ region of SCCHgfound in staphylococcal cassette chromosome mec(SCCmec) type III prototype strain 85/2082 but lacks the characteristic meroperon. SCCHghas previously been reported to integrate downstream of orfX, at the same chromosomal location as SCCmec. Tn6072, by contrast, is demarcated by two IS431elements, flanked by 8-bp direct repeats, and inserted upstream of the origin of replication, within an open reading frame homologous to SAR2700 of S. aureusstrain MRSA252. Analysis of a geographically and temporally diverse collection of 111 strains from the ST239 clonal group uncovered 11 additional strains harboring Tn6072, demonstrating a lineage-specific insertion pattern. Complete sequence analysis of the SCCmecregions of two representative Romanian strains (BK16704, BK16691) revealed two additional novel structures derived from a type III SCCmecbackground. BK16704 possesses an SCCmec3A.1.4 structure, with an IS256insertion downstream of the right chromosomal junction. In contrast, the SCCmecelement of BK16691 is truncated downstream of the mecgene complex, with a 24-kb deletion encompassing the right chromosomal junction and an inverted downstream IS256element. This structure, tentatively named “ψSCCmec16691,” confers methicillin resistance but lacks most of the J1/J2 region, including the ccrgene complex. Taken together, these findings provide evidence for the continuing evolution of SCC elements, as well as the ST239 clonal group.

Objective.To determine the prevalence of asymptomatic carriage of Staphylococcus aureusand methicillin-resistant S. aureus(MRSA) among healthcare professionals (HCPs) who experience varying degrees of exposure to ambulatory patients and to genetically characterize isolates.Methods.This single-center, cross-sectional study enrolled 256 staff from the intensive care units, emergency department, and prehospital services of an urban tertiary care university hospital in 2008. Occupational histories and nasal samples for S. aureuscultures were obtained. S. aureusisolates were genetically characterized with the use of spatyping and screened for mecA. MRSA isolates underwent further characterization.Results.S. aureuswas isolated from 112 of 256 (43.8%) HCPs, including 30 of 52 (57.7%) paramedics, 51 of 124 (41.1%) nurses, 11 of 28 (39.3%) clerical workers, and 20 of 52 (38.5%) physicians. MRSA was isolated from 17 (6.6%) HCPs, including 1 (1.9%) paramedic, 13 (10.5%) nurses, 1 (3.6%) clerical worker, and 2 (3.8%) physicians. Among S. aureusisolates, 15.2% were MRSA. MRSA prevalence was 9.6% (12/125) in emergency department workers, 5.1% (4/79) in intensive care unit workers, and 1.9% (1/52) in emergency medical services workers. Compared with paramedics, who had the lowest prevalence of methicillin resistance among S. aureusisolates (1 of 30 [3.3%] isolates), nurses, who had the highest prevalence (13 of 51 [25.4%] isolates), had an odds ratio of 9.92 (95% confidence interval, 1.32-435.86; P= .02) for methicillin resistance. Analysis of 15 MRSA isolates revealed 7 USA100 strains, 6 USA300 strains, 1 USA800 strain, and 1 EMRSA-15 strain. All USA300 strains were isolated from emergency department personnel.Conclusions.The observed prevalence of S. aureusand MRSA colonization among HCPs exceeds previously reported prevalences in the general population. The proportion of community-associated MRSA among all MRSA in this colonized HCP cohort reflects the distribution of the USA300 community-associated strain observed increasingly among US hospitalized patients.

ABSTRACTColistin is increasingly used as an antibiotic of last resort for the treatment of carbapenem-resistant Gram-negative infections. The plasmid-borne colistin resistance gene mcr-1was initially identified in animal and clinical samples from China and subsequently reported worldwide, including in the United States. Of particular concern is the spread of mcr-1into carbapenem-resistant bacteria, thereby creating strains that approach pan-resistance. While several reports of mcr-1have involved carbapenem-resistant strains, no such isolates have been described in the United States. Here, we report the isolation and identification of an Escherichia colistrain harboring both mcr-1and carbapenemase gene blaNDM-5from a urine sample in a patient without recent travel outside the United States. The isolate exhibited resistance to both colistin and carbapenems, but was susceptible to amikacin, aztreonam, gentamicin, nitrofurantoin, tigecycline, and trimethoprim-sulfamethoxazole. The mcr-1- and blaNDM-5-harboring plasmids were completely sequenced and shown to be highly similar to plasmids previously reported from China. The strain in this report was first isolated in August 2014, highlighting an earlier presence of mcr-1within the United States than previously recognized.IMPORTANCEColistin has become the last line of defense for the treatment of infections caused by Gram-negative bacteria resistant to multiple classes of antibiotics, in particular carbapenem-resistant Enterobacteriaceae(CRE). Resistance to colistin, encoded by the plasmid-borne gene mcr-1, was first identified in animal and clinical samples from China in November 2015 and has subsequently been reported from numerous other countries. In April 2016, mcr-1was identified in a carbapenem-susceptible Escherichia colistrain from a clinical sample in the United States, followed by a second report from a carbapenem-susceptible E. colistrain originally isolated in May 2015. We report the isolation and identification of an E. colistrain harboring both colistin (mcr-1) and carbapenem (blaNDM-5) resistance genes, originally isolated in August 2014 from urine of a patient with recurrent urinary tract infections. To our knowledge, this is the first report in the United States of a clinical bacterial isolate with both colistin and carbapenem resistance, highlighting the importance of active surveillance efforts for colistin- and carbapenem-resistant organisms.