Methicillin-resistant Staphylococcus Aureus Clusters Research Articles

Exploring the virulence potential of immune evasion cluster genes in methicillin-resistant Staphylococcus aureus from cancer patients

Methicillin-resistant Staphylococcus aureus (MRSA) is accountable for a plethora of infections, ranging from minor cutaneous manifestations to grave metastatic conditions. The dissemination of MRSA among cancer patients poses a substantial public health hazard on a global scale. This study explores the association between MRSA and bacteriophage-encoded immune evasion cluster (IEC) genes. This investigation employed a total of 168 pathogenic MRSA collected from 38 cancer and 130 non-cancer patients. A cefoxitin disc diffusion method followed by PCR analysis was used to identify the mecA gene. In this study, we employed singleplex and multiplexed PCR techniques to detect specific IEC genes. No association (p = 0.98) was observed between the sex and age of patients and MRSA isolates. However, MRSA isolates demonstrated a notable association (p = 0.01) with pus samples in non-cancer patients and skin swabs in cancer patients. The resistance profiles of MRSA strains from cancer and non-cancer patients did not show significant differences (p > 0.05). Notably, the sea gene was found to be more prevalent in MRSA isolates from cancer patients, displaying a significant association (p = 0.03). Additionally, this study identified two novel and distinct combinations of IEC types, namely V1 (sea, chp, scn) and V2 (sea, scn). Cancer patients had higher multidrug resistance and toxin gene abundance than non-cancer patients. The identification of two novel IEC patterns underscores the urgent need to control MRSA dissemination in hospitals and monitor emerging clones.

Prospective Genomic Surveillance Reveals Cryptic MRSA Outbreaks with Local to International Origins among NICU Patients.

Methicillin-resistant Staphylococcus aureus (MRSA) infections cause substantive morbidity and mortality in neonates. Using publicly available resources from the National Center of Biotechnology Information (NCBI) and Food and Drug Administration's (FDA) GalaxyTrakr pipeline, we illustrate the dynamics of MRSA colonization and infection in neonates. Over 217 days of prospective surveillance, analyses revealed concurrent MRSA transmission chains affecting 11 of 17 MRSA-colonized patients (65%), with two clusters that demonstrated intervals of more than a month among the appearance of isolates. All MRSA infected neonates (n = 3) showed previous colonization with the infecting strain. GalaxyTrakr clustering of the NICU strains, in the context of 21,521 international isolates deposited in NCBI's Pathogen Detection Resource, revealed NICU isolates to be distinct from adult MRSA strains seen locally and internationally. Clustering of the NICU strains within an international context enhanced the resolution of strain clusters and supported the rule-out of suspected, local transmission events within the NICU. Analyses also identified sequence type 1535 isolates, emergent in the Middle East, carrying a unique SCCmec with fusC and aac(6')-Ie/aph(2'')-1a that provided a multidrug-resistant phenotype. NICU genomic pathogen surveillance, leveraging public repositories and outbreak detection tools, supports rapid identification of cryptic MRSA clusters, and can inform infection prevention interventions for this vulnerable patient population. Results demonstrate that sporadic infections in the NICU may be indicative of hidden chains of asymptomatic transmission best identified with sequenced-based approaches.

Dehydration Tolerance in Epidemic versus Nonepidemic MRSA Demonstrated by Isothermal Microcalorimetry.

ABSTRACTMethicillin-resistant Staphylococcus aureus (MRSA) clusters are considered epidemic or nonepidemic based on their ability to spread effectively. Successful transmission could be influenced by dehydration tolerance. Current methods for determination of dehydration tolerance lack accuracy. Here, a climate-controlled in vitro dehydration assay using isothermal microcalorimetry (IMC) was developed and linked with mathematical modeling to determine survival of 44 epidemic versus 54 nonepidemic MRSA strains from France, the United Kingdom, and the Netherlands after 1 week of dehydration. For each MRSA strain, the growth parameters time to end of first growth phase (tmax [h]) and maximal exponential growth rate (μm) were deduced from IMC data for 3 experimental replicates, 3 different starting inocula, and before and after dehydration. If the maximal exponential growth rate was within predefined margins (±36% of the mean), a linear relationship between tmax and starting inoculum could be utilized to predict log reduction after dehydration for individual strains. With these criteria, 1,330 of 1,764 heat flow curves (data sets) (75%) could be analyzed to calculate the post-dehydration inoculum size, and thus the log reduction due to dehydration, for 90 of 98 strains (92%). Overall reduction was ~1 log after 1 week. No difference in dehydration tolerance was found between the epidemic and nonepidemic strains. Log reduction was negatively correlated with starting inoculum, indicating better survival of higher inocula. This study presents a framework to quantify bacterial survival. MRSA strains showed great capacity to persist in the environment, irrespective of epidemiological success. This finding strengthens the need for effective surface cleaning to contain MRSA transmission.IMPORTANCE Methicillin-resistant Staphylococcus aureus (MRSA) is a major cause of infections globally. While some MRSA clusters have spread worldwide, others are not able to disseminate successfully beyond certain regions despite frequent introduction. Dehydration tolerance facilitates transmission in hospital environments through enhanced survival on surfaces and fomites, potentially explaining differences in transmission success between MRSA clusters. Unfortunately, the currently available techniques to determine dehydration tolerance of cluster-forming bacteria like S. aureus are labor-intensive and unreliable due to their dependence on quantitative culturing. In this study, bacterial survival was assessed in a newly developed assay using isothermal microcalorimetry. With this technique, the effect of drying can be determined without the disadvantages of quantitative culturing. In combination with a newly developed mathematical algorithm, we determined dehydration tolerance of a large number of MRSA strains in a systematic, unbiased, and robust manner.

Outbreak of MRSA in a Gynecology/Obstetrics Department during the COVID-19 Pandemic: A Cautionary Tale.

Since March 2020, the COVID-19 pandemic forced hospitals worldwide to intensify their infection control measures to prevent health care-associated transmission of SARS-CoV-2. The correct use of personal protective equipment, especially the application of masks, was quickly identified as priority to reduce transmission with this pathogen. Here, we report a nosocomial cluster of methicillin-resistant Staphylococcus aureus (MRSA) that occurred during the COVID-19 pandemic in a gynecology/obstetrics department, despite these intensified contact precautions. Five MRSA originating from clinical samples after surgical intervention led to an outbreak investigation. Firstly, this included environmental sampling of the operation theatre (OT) and, secondly, a point prevalence screening of patients and health care workers (HCW). All detected MRSA were subjected to whole genome sequencing (WGS) and isolate relatedness was determined using core genome multilocus sequence typing (cgMLST). WGS revealed one MRSA cluster with genetically closely related five patient and two HCW isolates differing in a single cgMLST allele at maximum. The outbreak was terminated after implementation of infection control bundle strategies. Although contact precaution measures, which are also part of MRSA prevention bundle strategies, were intensified during the COVID-19 pandemic, this MRSA outbreak could take place. This illustrates the importance of adherence to classical infection prevention strategies.

806. Uncluttering Case Clusters: Use of Rapid Sequencing to Exclude Transmission Events

Abstract Background Newly identified multi-drug resistant organisms (MDRO) isolated from hospitalized patients with shared epidemiological characteristics can either represent transmission events or independent, unrelated acquisitions. Whole genome sequencing (WGS) can improve the efficiency of investigations triggered by MDRO cases with apparent epidemiological linkages by early exclusion of clonality. We report an implementation of WGS to investigate a cluster of methicillin-resistant Staphylococcus aureus (MRSA) and a cluster of carbapenem-resistant Enterobacterales (CRE) inpatient nosocomial infections. Methods Study participants included five Neonatal ICU (NICU) patients with nosocomial MRSA isolates recovered between June and August 2020, and two Respiratory Acute Care Unit (RACU) patients with nosocomial CRE infections in October 2020. Routine unit surveillance activities and characterization using standard epidemiologic criteria identified the isolates as nosocomial to their respective unit. The isolates then underwent WGS and single nucleotide polymorphism (SNP)-based relatedness analysis. Results The MRSA cluster included five neonates with either clinical or surveillance isolates. WGS identified one of the five isolates as methicillin susceptible S. aureus due to the absence of the mecA or mecC resistance gene, despite growth on chromogenic MRSA screening agar. WGS revealed each of the five isolates as belonging to a distinct multi locus sequence type (MLST) group with thousands of SNP differences between samples. The CRE cluster included two patients with Klebsiella pneumoniae isolated from clinical cultures within five days of each other with identical antimicrobial susceptibility profiles. WGS of the two isolates revealed that they belonged to different MLSTs and had tens of thousands of differing SNPs. WGS results suggest that a nosocomial transmission linking these infections was highly unlikely. For both investigations, WGS returned results within thirty-six hours of sample receipt. Figure 1. Corynebacterium striatum Respiratory Cultures January 2020-February 2021 Panel showing single nucleotide polymorphism (SNP) differences between isolates for respective clusters. Conclusion Apparent transmission events can be resource intensive to investigate and manage. The application of rapid WGS allowed for early discontinuation of cluster investigations and conservation of resources. Disclosures Virginia M. Pierce, MD, UpToDate, Inc. (Other Financial or Material Support, Author) Mohamad Sater, PhD, Day Zero Diagnostics (Employee, Shareholder) Miriam Huntley, PhD, Day Zero Diagnostics (Employee, Shareholder) Ian Herriott, BS, Day Zero Diagnostics (Employee, Shareholder) Tim Farrell, MS, Day Zero Diagnostics, Inc. (Employee, Shareholder) David C. Rosenberg, MD, Cepheid Diagnostics (Consultant)Day Zero Diagnostics (Consultant)SeLux Diagnostics (Consultant) Erica S. Shenoy, MD, PhD, Vertex Pharmaceuticals (Individual(s) Involved: Self): I gave a single lecture in 3/2020 for which I received financial compensation, Other Financial or Material Support

Evaluation of the bioMérieux EPISEQ-CS Software for wgMLST-Based Bacterial Strain Typing

Background: Whole-genome sequencing (WGS) is becoming the method of choice for outbreak analysis of microbial pathogens. However, the main challenge with WGS for microbial strain typing is the conversion of raw sequencing data to actionable results for epidemiology and surveillance analysis. We evaluated the bioMrieux EPISEQ-CS, a cloud-based WGS data analysis software for outbreak detection to compare the results for 4 groups of different species previously characterized by strain typing and commonly isolated in hospital-acquired infections. Methods: In total, 30 methicillin-resistant Staphylococcus aureus (MRSA), 15 Clostridioides difficile (CDIFF), 17 Pseudomonas aeruginosa (PSA), and 10 Acinetobacter baumannii (ACB) isolates were included in this study. All isolates had been previously characterized by rep-PCR using the DiversiLab system (bioMrieux, France) and saved at 70C. Before testing, samples were thawed and plated, and DNA extraction was performed on the QIAcube (Qiagen, Hilden, Germany) using the DNEasy Ultra Clean Microbial kit extraction protocol. DNA libraries were prepared using the Nextera DNA Flex Kit and sequenced on the Illumina iSeq100 platform according to manufacturer’s recommendations (Illumina, San Diego, CA). Generated sequences were uploaded into EPISEQ-CS, and wgMLST-based analysis was performed. We compared clusters generated by the DiversiLab system and EPISEQ-CS. Results: DiversiLab identified 9 MRSA clusters among 30 isolates. EPISEQ-CS reclassified 14 of 30 isolates into 5 MRSA clusters and the remaining 16 isolates were unrelated. DiversiLab identified 2 CDIFF clusters among 15 isolates. EPISEQ-CS reclassified 3 isolates into 1 CDIFF cluster and determined the remaining 12 to be unrelated. DiversiLab identified 5 PSA clusters among 17 isolates, whereas EPISEQ-CS reclassified all 17 isolates as unrelated. DiversiLab identified 2 ACB clusters among 10 isolates, whereas EPISEQ-CS reclassified 2 ACB isolates into 1 cluster and determined 8 to be unrelated. Analysis using Simpson’s diversity index (D) suggested that the EPISEQ-CS showed increased diversity when compared to DiversiLab clustering across all bacterial species analyzed in this study. Conclusions: EPISEQ-CS enabled a comprehensive wgMLST analysis, including quality control and comparative epidemiological analysis, thereby providing a more reliable method for bacterial strain typing. As WGS becomes more affordable and applicable to routine epidemiological surveillance, EPISEQ-CS provides an informative tool in the monitoring of hospital-acquired infections.Funding: NoneDisclosures: None

Low methicillin-resistant Staphylococcus aureus carriage rate among Italian dental students

We assessed methicillin-resistant Staphylococcus aureus (MRSA) carriage rate among dental students from an Italian university. A total of 157 subjects participated (67 preclinical students and 90 clinical students); samples were collected from the nose, mouth, and skin. Five preclinical students and 0 clinical students were MRSA-positive. Carriage rates were 3.2% (95% confidence interval [CI], 0.4%-6.0%) overall, 7.5% (95% CI, 1.2%-13.8%) in preclinical students and 0% in clinical students. There were 2 MRSA clusters among the preclinical students: 3 second-year and 2 first-year students, who sat close to one another in the classroom the day of the sample. MRSA carriage was not associated with dental health care. The pooled carriage rate among dental students was assessed to obtain a reliable figure of carriage rate unaffected by local conditions. The 4 published surveys were pooled, and the fixed-effects method was used. Among the 484 dental students, the pooled carriage rate was 4.1% (95% CI, 2.4%-5.8%).

The use of the temporal scan statistic to detect methicillin-resistant Staphylococcus aureus clusters in a community hospital.

BackgroundIn healthcare facilities, conventional surveillance techniques using rule-based guidelines may result in under- or over-reporting of methicillin-resistant Staphylococcus aureus (MRSA) outbreaks, as these guidelines are generally unvalidated. The objectives of this study were to investigate the utility of the temporal scan statistic for detecting MRSA clusters, validate clusters using molecular techniques and hospital records, and determine significant differences in the rate of MRSA cases using regression models.MethodsPatients admitted to a community hospital between August 2006 and February 2011, and identified with MRSA > 48 hours following hospital admission, were included in this study. Between March 2010 and February 2011, MRSA specimens were obtained for spa typing. MRSA clusters were investigated using a retrospective temporal scan statistic. Tests were conducted on a monthly scale and significant clusters were compared to MRSA outbreaks identified by hospital personnel. Associations between the rate of MRSA cases and the variables year, month, and season were investigated using a negative binomial regression model.ResultsDuring the study period, 735 MRSA cases were identified and 167 MRSA isolates were spa typed. Nine different spa types were identified with spa type 2/t002 (88.6%) the most prevalent. The temporal scan statistic identified significant MRSA clusters at the hospital (n = 2), service (n = 16), and ward (n = 10) levels (P ≤ 0.05). Seven clusters were concordant with nine MRSA outbreaks identified by hospital staff. For the remaining clusters, seven events may have been equivalent to true outbreaks and six clusters demonstrated possible transmission events. The regression analysis indicated years 2009–2011, compared to 2006, and months March and April, compared to January, were associated with an increase in the rate of MRSA cases (P ≤ 0.05).ConclusionsThe application of the temporal scan statistic identified several MRSA clusters that were not detected by hospital personnel. The identification of specific years and months with increased MRSA rates may be attributable to several hospital level factors including the presence of other pathogens. Within hospitals, the incorporation of the temporal scan statistic to standard surveillance techniques is a valuable tool for healthcare workers to evaluate surveillance strategies and aid in the identification of MRSA clusters.

Bacterial whole-genome sequencing revisited: portable, scalable, and standardized analysis for typing and detection of virulence and antibiotic resistance genes.

Multidrug-resistant nosocomial pathogens present a major burden for hospitals. Rapid cluster identification and pathogen profiling, i.e., of antibiotic resistance and virulence genes, are crucial for effective infection control. Methicillin-resistant Staphylococcus aureus (MRSA), in particular, is now one of the leading causes of nosocomial infections. In this study, whole-genome sequencing (WGS) was applied retrospectively to an unusual spike in MRSA cases in two intensive care units (ICUs) over the course of 4 weeks. While the epidemiological investigation concluded that there were two separate clusters, each associated with one ICU, S. aureus protein A gene (spa) typing data suggested that they belonged to single clonal cluster (all cases shared spa type t001). Standardized gene sets were used to extract an allele-based profile for typing and an antibiotic resistance and toxin gene profile. The WGS results produced high-resolution allelic profiles, which were used to discriminate the MRSA clusters, corroborating the epidemiological investigation and identifying previously unsuspected transmission events. The antibiotic resistance profile was in agreement with the original clinical laboratory susceptibility profile, and the toxin profile provided additional, previously unknown information. WGS coupled with allelic profiling provided a high-resolution method that can be implemented as regular screening for effective infection control.

Healthcare worker-related MRSA cluster in a German neonatology level III ICU: A true European story

Here we investigated a cluster of eight newly Methicillin-resistant Staphylococcus aureus (MRSA)-colonized neonates at an ICU, and present data on molecular strain characterization as well as the source identification process in which we analyze the impact of MRSA-colonized HCWs. Molecular strain characterization revealed a unique pattern which was identified as spa-type t 127--an extremely rare strain type in Germany. Environmental sampling and screening of parents of colonized neonates proved negative. However, staff screening identified one healthcare worker (HCW; 1/134) belonging to a group of recently employed Romanian HCWs who was colonized with the spa 127 strain. Subsequent screening also detected MRSA in 9/51 Romanian HCWs (18%) and 7/9 (14% of all) isolates showed the same molecular pattern as the index case (spa/PFGE type). All carriers were successfully decolonized, after which no new patient cases occurred. As a result, we have now implemented a universal screening programme of all new employees as part of our infection control management strategy. MRSA-colonized HCWs can act as a source for in hospital transmission. Since HCWs from high endemic countries are particular prone to being colonized, they may pose a risk to patients.

A pilot study of rapid benchtop sequencing of Staphylococcus aureus and Clostridium difficile for outbreak detection and surveillance

ObjectivesTo investigate the prospects of newly available benchtop sequencers to provide rapid whole-genome data in routine clinical practice. Next-generation sequencing has the potential to resolve uncertainties surrounding the route and...

Automated Detection of Infectious Disease Outbreaks in Hospitals: A Retrospective Cohort Study

Detection of outbreaks of hospital-acquired infections is often based on simple rules, such as the occurrence of three new cases of a single pathogen in two weeks on the same ward. These rules typically focus on only a few pathogens, and they do not account for the pathogens' underlying prevalence, the normal random variation in rates, and clusters that may occur beyond a single ward, such as those associated with specialty services. Ideally, outbreak detection programs should evaluate many pathogens, using a wide array of data sources. We applied a space-time permutation scan statistic to microbiology data from patients admitted to a 750-bed academic medical center in 2002-2006, using WHONET-SaTScan laboratory information software from the World Health Organization (WHO) Collaborating Centre for Surveillance of Antimicrobial Resistance. We evaluated patients' first isolates for each potential pathogenic species. In order to evaluate hospital-associated infections, only pathogens first isolated >2 d after admission were included. Clusters were sought daily across the entire hospital, as well as in hospital wards, specialty services, and using similar antimicrobial susceptibility profiles. We assessed clusters that had a likelihood of occurring by chance less than once per year. For methicillin-resistant Staphylococcus aureus (MRSA) or vancomycin-resistant enterococci (VRE), WHONET-SaTScan-generated clusters were compared to those previously identified by the Infection Control program, which were based on a rule-based criterion of three occurrences in two weeks in the same ward. Two hospital epidemiologists independently classified each cluster's importance. From 2002 to 2006, WHONET-SaTScan found 59 clusters involving 2-27 patients (median 4). Clusters were identified by antimicrobial resistance profile (41%), wards (29%), service (13%), and hospital-wide assessments (17%). WHONET-SaTScan rapidly detected the two previously known gram-negative pathogen clusters. Compared to rule-based thresholds, WHONET-SaTScan considered only one of 73 previously designated MRSA clusters and 0 of 87 VRE clusters as episodes statistically unlikely to have occurred by chance. WHONET-SaTScan identified six MRSA and four VRE clusters that were previously unknown. Epidemiologists considered more than 95% of the 59 detected clusters to merit consideration, with 27% warranting active investigation or intervention. Automated statistical software identified hospital clusters that had escaped routine detection. It also classified many previously identified clusters as events likely to occur because of normal random fluctuations. This automated method has the potential to provide valuable real-time guidance both by identifying otherwise unrecognized outbreaks and by preventing the unnecessary implementation of resource-intensive infection control measures that interfere with regular patient care. Please see later in the article for the Editors' Summary.

LINEZOLID-RESISTANT STAPHYLOCOCCUS AUREUS IN TWO PEDIATRIC PATIENTS RECEIVING LOW-DOSE LINEZOLID THERAPY

We report 2 sisters with hyper-IgE syndrome treated with daily suppressive dosages of linezolid (LZD) who developed LZD-resistant Staphylococcus aureus carrying the G2576T mutation in the 23S rRNA gene. Molecular typing suggested transmission of the resistant strain from one sister to the other. LZD-susceptible S. aureus was isolated 2 months after LZD discontinuation. LZD-resistant S. aureus remains rare but may occur while receiving suppressive therapy.

Geographic information system localization of community-acquired MRSA soft tissue abscesses

Background Soft tissue infections with methicillin-resistant Staphylococcus aureus (MRSA) pose an ever-increasing risk to children in the community. Although historically these infections were limited to children with prolonged hospitalization, the authors have seen an increase in community-acquired infections in children without identifiable risk factors. The goal of this study is to determine the incidence of truly community-acquired MRSA soft tissue infections in our community and geographically map regions of increased risk. Methods After obtaining the institutional review board's approval, a retrospective chart review was conducted on 195 patients records who underwent an incision and drainage of soft tissue infections from January 1, 2000, to December 31, 2003. Thirteen patients were excluded from the study because no cultures were taken at the time of incision and drainage. Results The most common organism isolated from wound culture was S aureus, 40% (73/182), of which 45% (33/73) were MRSA. Eighty-one percent (27/33) of MRSA infections were in Springfield, 1 of 18 towns represented in the patient population. Geographic information system analysis identified a significant MRSA cluster 1.96 km in diameter within the city of Springfield. Conclusions Geography proved to be a significant risk factor for presenting with MRSA infection. Geographic maps of antibiotic resistance can be used to guide physician antibiotic selection before culture results are available. This has significant implications for the health care provider in proper antibiotic selection within the community.

Methicillin-resistant staphylococci isolated from animals

Staphylococci isolated from animals ( n = 311) were screened for methicillin resistance by oxacillin agar screening. Oxacillin-resistant strains were tested for the presence of the mecA gene by PCR. Isolates were identified by standard techniques and 16S rDNA analysis, and their antimicrobial susceptibilities were tested using an agar diffusion method. MecA-positive strains were further analyzed using pulsed-field gel electrophoresis (PFGE). From 11 multidrug-resistant staphylococci, 6 were mecA-positive: 2 methicillin-resistant Staphylococcus aureus (MRSA) and 4 Staphylococcus haemolyticus. Screening of 300 staphylococci (100 S. aureus, 100 S. intermedius and 100 coagulase-negative staphylococci (CNS)) randomly chosen from the strain collection of the Veterinary Microbiological Diagnostic Center yielded five oxacillin-resistant coagulase-negative staphylococci, four of which were mecA-positive. PFGE showed that all mecA-positive staphylococci isolated from animals had distinct patterns. However, one MRSA isolated from a flank fistula of a dog showed homology to a human epidemic MRSA cluster, suggesting that transfer of MRSA between humans and dogs might occur.

Integration of molecular characterization of microorganisms in a global antimicrobial resistance surveillance program.

The SENTRY Antimicrobial Surveillance Program has incorporated molecular strain typing and resistance genotyping as a means of providing additional information that may be useful for understanding pathogenic microorganisms worldwide. Resistance phenotypes of interest include multidrug-resistant pathogens, extended-spectrum beta-lactamase (ESBL)-producing Enterobacteriaceae, methicillin-resistant Staphylococcus aureus (MRSA), vancomycin-resistant enterococci, and fluoroquinolone-resistant (FQR) strains of gram-negative bacilli and Streptococcus pneumoniae. Clusters of > or =2 isolates within a given resistance profile that are linked temporally and by hospital location are flagged for DNA fingerprinting. Further characterization of organisms with respect to resistance genotype is accomplished with use of polymerase chain reaction and DNA sequencing. This process has been highly successful in identifying clonal spread within clusters of multiresistant pathogens. Between 50% and 90% of MRSA clusters identified by phenotypic screening contained evidence of clonal spread. Among the Enterobacteriaceae, ESBL-producing strains of Escherichia coli and Klebsiella pneumoniae are the most common pathogens causing clusters of infection, and approximately 50% of recognized clusters demonstrate clonal spread. Clusters of Pseudomonas aeruginosa, Acinetobacter species, and Stenotrophomonas maltophilia have been noted with clonal spread among patients with urinary tract, respiratory, and bloodstream infections. Characterization of mutations in the FQR-determining region of phenotypically susceptible isolates of E. coli and S. pneumoniae has identified first-stage mutants among as many as 40% of isolates. The ability to characterize organisms phenotypically and genotypically is extremely powerful and provides unique information that is important in a global antimicrobial surveillance program.

Molecular epidemiology of methicillin-resistant Staphylococcus aureus in 12 New York hospitals. MRSA Collaborative Study Group.

Consecutive single-patient methicillin-resistant Staphylococcus aureus (MRSA) isolates (270) from 12 hospitals (8217 beds) in metropolitan New York City were collected during May 1996. In 11 of 12 hospitals, MRSA was most frequent in the general medical services. DNA typing ("fingerprinting") revealed that mecA:Tn554:PFGE (pulsed-field gel electrophoresis) type I:A:A accounted for 113 (42%) of 270 isolates, was detected in all hospitals, and was the predominant clone in 9. Thirteen of 15 I:E:F isolates were from 1 hospital, and the remaining 2 were from another hospital of the same health system. Type V:NH:E was isolated from 22 (79%) of the 28 patients with AIDS, including 8 of 9 patients from an additional hospital. Subtype V:NH:E2 was recovered from 11 patients, 9 of whom had AIDS, including all 5 AIDS patients from one floor of a nursing home affiliated with a third hospital. By using both mecA:Tn554 probes and PFGE, MRSA clusters and outbreaks may be detected and provide a rationale for appropriate infection control intervention.

Tracing the spread of methicillin-resistant Staphylococcus aureus by Southern blot hybridization using gene-specific probes of mec and Tn554.

In a community hospital in Brooklyn, New York, over a 3-year period, 79 methicillin-resistant Staphylococcus aureus (MRSA) isolates from five different case clusters were subtyped by Southern blot hybridization with two previously characterized gene probes, mec and Tn554. Together, the genotyping enabled the hospital infection control team to differentiate simultaneous MRSA clusters in the surgical intensive care unit (type I:A) and the open heart unit (type II:J), document the spread of one strain (type I:A) between roommates, identify an endemic strain (type II:J) from cardiac monitors and medical personnel, and identify an unrelated outbreak strain (type II:NH) in the labor and delivery unit. On the basis of this investigation it is clear that the routine DNA fingerprinting of MRSA in health care facilities, to monitor their spread and identify cases of nosocomial infections, is an important infection control measure.