RESUMO
The type III arginine catabolic mobile element (ACME) was detected in three Staphylococcus epidermidis oral isolates recovered from separate patients (one healthy, one healthy with dental implants, and one with periodontal disease) based on ACME-arc-operon- and ACME-opp3-operon-directed PCR. These isolates were subjected to whole-genome sequencing to characterize the precise structural organization of ACME III for the first time, which also revealed that all three isolates were the same sequence type, ST329.
Assuntos
Elementos de DNA Transponíveis/genética , Genoma Bacteriano/genética , Staphylococcus epidermidis/genética , Arginina/metabolismo , Proteínas da Membrana Bacteriana Externa/genética , Proteínas de Bactérias/genética , Sequência de Bases , Variação Genética , Sequenciamento de Nucleotídeos em Larga Escala , Humanos , Proteínas de Membrana Transportadoras/genética , Boca/microbiologia , Análise de Sequência de DNA , Infecções Estafilocócicas/microbiologia , Staphylococcus epidermidis/isolamento & purificaçãoRESUMO
BACKGROUND: Linezolid is often the drug of last resort to treat infections caused by Gram-positive cocci. Linezolid resistance can be mutational (23S rRNA or L-protein) or, less commonly, acquired [predominantly cfr, conferring resistance to phenicols, lincosamides, oxazolidinones, pleuromutilins and streptogramin A compounds (PhLOPSA) or optrA, encoding oxazolidinone and phenicol resistance]. OBJECTIVES: To investigate the clonality and genetic basis of linezolid resistance in 13 linezolid-resistant (LZDR) methicillin-resistant Staphylococcus epidermidis (MRSE) isolates recovered during a 2013/14 outbreak in an ICU in an Irish hospital and an LZDR vancomycin-resistant Enterococcus faecium (VRE) isolate from an LZDR-MRSE-positive patient. METHODS: All isolates underwent PhLOPSA susceptibility testing, 23S rRNA sequencing, DNA microarray profiling and WGS. RESULTS: All isolates exhibited the PhLOPSA phenotype. The VRE harboured cfr and optrA on a novel 73 kb plasmid (pEF12-0805) also encoding erm(A), erm(B), lnu(B), lnu(E), aphA3 and aadE. One MRSE (M13/0451, from the same patient as the VRE) harboured cfr on a novel 8.5 kb plasmid (pSEM13-0451). The remaining 12 MRSE lacked cfr but exhibited linezolid resistance-associated mutations and were closely related to (1-52 SNPs) but distinct from M13/0451 (202-223 SNPs). CONCLUSIONS: Using WGS, novel and distinct cfr and cfr/optrA plasmids were identified in an MRSE and VRE isolate, respectively, as well as a cfr-negative LZDR-MRSE ICU outbreak and a distinct cfr-positive LZDR-MRSE from the same ICU. To our knowledge, this is the first report of cfr and optrA on a single VRE plasmid. Ongoing surveillance of linezolid resistance is essential to maintain its therapeutic efficacy.
Assuntos
Antibacterianos/farmacologia , Infecção Hospitalar/epidemiologia , Farmacorresistência Bacteriana , Enterococcus faecium/efeitos dos fármacos , Linezolida/farmacologia , Plasmídeos/análise , Staphylococcus epidermidis/efeitos dos fármacos , Surtos de Doenças , Enterococcus faecium/genética , Enterococcus faecium/isolamento & purificação , Genes Bacterianos , Hospitais , Humanos , Irlanda/epidemiologia , Análise em Microsséries , Testes de Sensibilidade Microbiana , RNA Ribossômico 23S/genética , Análise de Sequência de DNA , Staphylococcus epidermidis/genética , Staphylococcus epidermidis/isolamento & purificação , Enterococos Resistentes à Vancomicina/efeitos dos fármacos , Enterococos Resistentes à Vancomicina/genética , Enterococos Resistentes à Vancomicina/isolamento & purificação , Sequenciamento Completo do GenomaRESUMO
Linezolid is often the drug of last resort for serious methicillin-resistant Staphylococcus aureus (MRSA) infections. Linezolid resistance is mediated by mutations in 23S rRNA and genes for ribosomal proteins; cfr, encoding phenicol, lincosamide, oxazolidinone, pleuromutilin, and streptogramin A (PhLOPSA) resistance; its homologue cfr(B); or optrA, conferring oxazolidinone and phenicol resistance. Linezolid resistance is rare in S. aureus, and cfr is even rarer. This study investigated the clonality and linezolid resistance mechanisms of two MRSA isolates from patients in separate Irish hospitals. Isolates were subjected to cfr PCR, PhLOPSA susceptibility testing, 23S rRNA PCR and sequencing, DNA microarray profiling, spa typing, pulsed-field gel electrophoresis (PFGE), plasmid curing, and conjugative transfer. Whole-genome sequencing was used for single-nucleotide variant (SNV) analysis, multilocus sequence typing, L protein mutation identification, cfr plasmid sequence analysis, and optrA and cfr(B) detection. Isolates M12/0145 and M13/0401 exhibited linezolid MICs of 64 and 16 mg/liter, respectively, and harbored identical 23S rRNA and L22 mutations, but M12/0145 exhibited the mutation in 2/6 23S rRNA alleles, compared to 1/5 in M13/0401. Both isolates were sequence type 22 MRSA staphylococcal cassette chromosome mec type IV (ST22-MRSA-IV)/spa type t032 isolates, harbored cfr, exhibited the PhLOPSA phenotype, and lacked optrA and cfr(B). They differed by five PFGE bands and 603 SNVs. Isolate M12/0145 harbored cfr and fexA on a 41-kb conjugative pSCFS3-type plasmid, whereas M13/0401 harbored cfr and lsa(B) on a novel 27-kb plasmid. This is the first report of cfr in the pandemic ST22-MRSA-IV clone. Different cfr plasmids and mutations associated with linezolid resistance in genotypically distinct ST22-MRSA-IV isolates highlight that prudent management of linezolid use is essential.
Assuntos
Staphylococcus aureus Resistente à Meticilina/genética , Staphylococcus aureus/genética , Antibacterianos/farmacologia , Cromossomos Bacterianos/genética , Farmacorresistência Bacteriana Múltipla/genética , Staphylococcus aureus Resistente à Meticilina/efeitos dos fármacos , Plasmídeos/genética , RNA Ribossômico 23S/genética , Infecções Estafilocócicas/genética , Staphylococcus aureus/efeitos dos fármacosRESUMO
Whole-genome sequencing (WGS) of 41 patient and environmental sequence type 22 methicillin-resistant Staphylococcus aureus staphylococcal cassette chromosome mec type IV (ST22-MRSA-IV) isolates recovered over 6 weeks in one acute hospital ward in Dublin, Ireland, where ST22-MRSA IV is endemic, revealed 228 pairwise combinations differing by <40 single nucleotide variants corresponding to potential cross-transmission events (CTEs). In contrast, 15 pairwise combinations of isolates representing five CTEs were previously identified by conventional molecular epidemiological typing. WGS enhanced ST22-MRSA-IV tracking and highlighted potential transmission of MRSA via the hospital environment.
Assuntos
Infecção Hospitalar , Microbiologia Ambiental , Genoma Bacteriano , Sequenciamento de Nucleotídeos em Larga Escala , Staphylococcus aureus Resistente à Meticilina/genética , Infecções Estafilocócicas/microbiologia , Humanos , Staphylococcus aureus Resistente à Meticilina/classificação , Staphylococcus aureus Resistente à Meticilina/isolamento & purificação , Epidemiologia Molecular , Tipagem Molecular , Infecções Estafilocócicas/epidemiologia , Infecções Estafilocócicas/transmissãoRESUMO
Clonal replacement of predominant nosocomial methicillin-resistant Staphylococcus aureus (MRSA) strains has occurred several times in Ireland during the last 4 decades. However, little is known about sporadically occurring MRSA in Irish hospitals or in other countries. Eighty-eight representative pvl-negative sporadic MRSA isolates recovered in Irish hospitals between 2000 and 2012 were investigated. These yielded unusual pulsed-field gel electrophoresis and antibiogram-resistogram typing patterns distinct from those of the predominant nosocomial MRSA clone, ST22-MRSA-IV, during the study period. Isolates were characterized by spa typing and DNA microarray profiling for multilocus sequence type (MLST) clonal complex (CC) and/or sequence type (ST) and SCCmec type assignment, as well as for detection of virulence and antimicrobial resistance genes. Conventional PCR-based SCCmec subtyping was undertaken when necessary. Extensive diversity was detected, including 38 spa types, 13 MLST-CCs (including 18 STs among 62 isolates assigned to STs), and 25 SCCmec types (including 2 possible novel SCCmec elements and 7 possible novel SCCmec subtypes). Fifty-four MLST-spa-SCCmec type combinations were identified. Overall, 68.5% of isolates were assigned to nosocomial lineages, with ST8-t190-MRSA-IID/IIE±SCCM1 predominating (17.4%), followed by CC779/ST779-t878-MRSA-ψSCCmec-SCC-SCCCRISPR (7.6%) and CC22/ST22-t032-MRSA-IVh (5.4%). Community-associated clones, including CC1-t127/t386/t2279-MRSA-IV, CC59-t216-MRSA-V, CC8-t008-MRSA-IVa, and CC5-t002/t242-MRSA-IV/V, and putative animal-associated clones, including CC130-t12399-MRSA-XI, ST8-t064-MRSA-IVa, ST398-t011-MRSA-IVa, and CC6-t701-MRSA-V, were also identified. In total, 53.3% and 47.8% of isolates harbored genes for resistance to two or more classes of antimicrobial agents and two or more mobile genetic element-encoded virulence-associated factors, respectively. Effective ongoing surveillance of sporadic nosocomial MRSA is warranted for early detection of emerging clones and reservoirs of virulence, resistance, and SCCmec genes.
Assuntos
Variação Genética/genética , Staphylococcus aureus Resistente à Meticilina/genética , Proteínas de Bactérias/genética , DNA Bacteriano/genética , Eletroforese em Gel de Campo Pulsado , Irlanda , Staphylococcus aureus Resistente à Meticilina/classificação , Análise de Sequência com Séries de OligonucleotídeosRESUMO
Methicillin-resistant Staphylococcus aureus (MRSA) has been a major cause of nosocomial infection in Irish hospitals for 4 decades, and replacement of predominant MRSA clones has occurred several times. An MRSA isolate recovered in 2006 as part of a larger study of sporadic MRSA exhibited a rare spa (t878) and multilocus sequence (ST779) type and was nontypeable by PCR- and DNA microarray-based staphylococcal cassette chromosome mec (SCCmec) element typing. Whole-genome sequencing revealed the presence of a novel 51-kb composite island (CI) element with three distinct domains, each flanked by direct repeat and inverted repeat sequences, including (i) a pseudo SCCmec element (16.3 kb) carrying mecA with a novel mec class region, a fusidic acid resistance gene (fusC), and two copper resistance genes (copB and copC) but lacking ccr genes; (ii) an SCC element (17.5 kb) carrying a novel ccrAB4 allele; and (iii) an SCC element (17.4 kb) carrying a novel ccrC allele and a clustered regularly interspaced short palindromic repeat (CRISPR) region. The novel CI was subsequently identified by PCR in an additional 13 t878/ST779 MRSA isolates, six from bloodstream infections, recovered between 2006 and 2011 in 11 hospitals. Analysis of open reading frames (ORFs) carried by the CI showed amino acid sequence similarity of 44 to 100% to ORFs from S. aureus and coagulase-negative staphylococci (CoNS). These findings provide further evidence of genetic transfer between S. aureus and CoNS and show how this contributes to the emergence of novel SCCmec elements and MRSA strains. Ongoing surveillance of this MRSA strain is warranted and will require updating of currently used SCCmec typing methods.
Assuntos
Antibacterianos/farmacologia , Proteínas de Bactérias/genética , Cromossomos Bacterianos , Infecção Hospitalar/tratamento farmacológico , Farmacorresistência Bacteriana Múltipla/genética , Staphylococcus aureus Resistente à Meticilina/genética , Infecções Estafilocócicas/tratamento farmacológico , Adolescente , Adulto , Alelos , Sequência de Bases , Pré-Escolar , Mapeamento Cromossômico , Coagulase/deficiência , Coagulase/genética , Infecção Hospitalar/microbiologia , Feminino , Hospitais , Humanos , Recém-Nascido , Sequências Repetidas Invertidas , Irlanda , Masculino , Staphylococcus aureus Resistente à Meticilina/efeitos dos fármacos , Staphylococcus aureus Resistente à Meticilina/isolamento & purificação , Pessoa de Meia-Idade , Dados de Sequência Molecular , Análise de Sequência com Séries de Oligonucleotídeos , Reação em Cadeia da Polimerase , Análise de Sequência de DNA , Infecções Estafilocócicas/microbiologiaRESUMO
One hundred seventy-five isolates representative of methicillin-resistant Staphylococcus aureus (MRSA) clones that predominated in Irish hospitals between 1971 and 2004 and that previously underwent multilocus sequence typing (MLST) and staphylococcal cassette chromosome mec (SCCmec) typing were characterized by spa typing (175 isolates) and DNA microarray profiling (107 isolates). The isolates belonged to 26 sequence type (ST)-SCCmec types and subtypes and 35 spa types. The array assigned all isolates to the correct MLST clonal complex (CC), and 94% (100/107) were assigned an ST, with 98% (98/100) correlating with MLST. The array assigned all isolates to the correct SCCmec type, but subtyping of only some SCCmec elements was possible. Additional SCCmec/SCC genes or DNA sequence variation not detected by SCCmec typing was detected by array profiling, including the SCC-fusidic acid resistance determinant Q6GD50/fusC. Novel SCCmec/SCC composite islands (CIs) were detected among CC8 isolates and comprised SCCmec IIA-IIE, IVE, IVF, or IVg and a ccrAB4-SCC element with 99% DNA sequence identity to SCC(M1) from ST8/t024-MRSA, SCCmec VIII, and SCC-CI in Staphylococcus epidermidis. The array showed that the majority of isolates harbored one or more superantigen (94%; 100/107) and immune evasion cluster (91%; 97/107) genes. Apart from fusidic acid and trimethoprim resistance, the correlation between isolate antimicrobial resistance phenotype and the presence of specific resistance genes was ≥97%. Array profiling allowed high-throughput, accurate assignment of MRSA to CCs/STs and SCCmec types and provided further evidence of the diversity of SCCmec/SCC. In most cases, array profiling can accurately predict the resistance phenotype of an isolate.
Assuntos
Proteínas de Bactérias/genética , Staphylococcus aureus Resistente à Meticilina/efeitos dos fármacos , Staphylococcus aureus Resistente à Meticilina/genética , Análise de Sequência com Séries de Oligonucleotídeos/métodos , Ácido Fusídico/farmacologia , Tipagem de Sequências Multilocus , Trimetoprima/farmacologiaRESUMO
The arginine catabolic mobile element (ACME) is prevalent among methicillin-resistant Staphylococcus aureus (MRSA) isolates of sequence type 8 (ST8) and staphylococcal chromosomal cassette mec (SCCmec) type IVa (USA300) (ST8-MRSA-IVa isolates), and evidence suggests that ACME enhances the ability of ST8-MRSA-IVa to grow and survive on its host. ACME has been identified in a small number of isolates belonging to other MRSA clones but is widespread among coagulase-negative staphylococci (CoNS). This study reports the first description of ACME in two distinct strains of the pandemic ST22-MRSA-IV clone. A total of 238 MRSA isolates recovered in Ireland between 1971 and 2008 were investigated for ACME using a DNA microarray. Twenty-three isolates (9.7%) were ACME positive, and all were either MRSA genotype ST8-MRSA-IVa (7/23, 30%) or MRSA genotype ST22-MRSA-IV (16/23, 70%). Whole-genome sequencing and comprehensive molecular characterization revealed the presence of a novel 46-kb ACME and staphylococcal chromosomal cassette mec (SCCmec) composite island (ACME/SCCmec-CI) in ST22-MRSA-IVh isolates (n=15). This ACME/SCCmec-CI consists of a 12-kb DNA region previously identified in ACME type II in S. epidermidis ATCC 12228, a truncated copy of the J1 region of SCCmec type I, and a complete SCCmec type IVh element. The composite island has a novel genetic organization, with ACME located within orfX and SCCmec located downstream of ACME. One PVL locus-positive ST22-MRSA-IVa isolate carried ACME located downstream of SCCmec type IVa, as previously described in ST8-MRSA-IVa. These results suggest that ACME has been acquired by ST22-MRSA-IV on two independent occasions. At least one of these instances may have involved horizontal transfer and recombination events between MRSA and CoNS. The presence of ACME may enhance dissemination of ST22-MRSA-IV, an already successful MRSA clone.
Assuntos
Staphylococcus aureus Resistente à Meticilina/genética , Staphylococcus epidermidis/genética , Genótipo , Dados de Sequência Molecular , Análise de Sequência com Séries de Oligonucleotídeos , Reação em Cadeia da PolimeraseRESUMO
ST22-methicillin-resistant Staphylococcus aureus type IV (ST22-MRSA-IV) is endemic in Irish hospitals and is designated antibiogram-resistogram type-pulsed-field group (AR-PFG) 06-01. Isolates of this highly clonal strain exhibit limited numbers of pulsed-field gel electrophoresis (PFGE) patterns and spa types. This study investigated whether combining PFGE and spa typing with DNA sequencing of the staphylococcal cassette chromosome mec element (SCCmec)-associated direct repeat unit (dru typing) would improve isolate discrimination. A total of 173 MRSA isolates recovered in one Irish hospital during periods in 2007 and 2008 were investigated using antibiogram-resistogram (AR), PFGE, spa, dru, and SCCmec typing. Isolates representative of each of the 17 pulsed-field group 01 (PFG-01) spa types identified underwent multilocus sequence typing, and all isolates were ST22. Ninety-seven percent of isolates (168 of 173) exhibited AR-PFG 06-01 or closely related AR patterns, and 163 of these isolates harbored SCCmec type IVh. The combination of PFGE, spa, and dru typing methods significantly improved discrimination of the 168 PFG-01 isolates, yielding 65 type combinations with a Simpson's index of diversity (SID) of 96.53, compared to (i) pairwise combinations of spa and dru typing, spa and PFGE typing, and dru and PFGE typing, which yielded 37, 44, and 43 type combinations with SIDs of 90.84, 91.00, and 93.57, respectively, or (ii) individual spa, dru, and PFGE typing methods, which yielded 17, 17, and 21 types with SIDs of 66.9, 77.83, and 81.34, respectively. Analysis of epidemiological information for a subset of PFG-01 isolates validated the relationships inferred using combined PFGE, spa, and dru typing data. This approach significantly enhances discrimination of ST22-MRSA-IV isolates and could be applied to epidemiological investigations of other highly clonal MRSA strains.
Assuntos
Técnicas de Tipagem Bacteriana/métodos , Impressões Digitais de DNA/métodos , Staphylococcus aureus Resistente à Meticilina/classificação , Staphylococcus aureus Resistente à Meticilina/genética , Análise por Conglomerados , DNA Bacteriano/química , DNA Bacteriano/genética , Eletroforese em Gel de Campo Pulsado , Genótipo , Humanos , Irlanda , Testes de Sensibilidade Microbiana , Sensibilidade e Especificidade , Análise de Sequência de DNA , Infecções Estafilocócicas/microbiologia , Proteína Estafilocócica A/genéticaRESUMO
OBJECTIVE: The aim of this study was to investigate co-located nasal Staphylococcus aureus and coagulase-negative staphylococci (CoNS) (mainly Staphylococcus epidermidis), recovered from healthy medical students in their preclinical year, prior to exposure to the healthcare environment, for the carriage of genes and genetic elements common to both species and that may contribute to S. aureus and methicillin-resistant S. aureus (MRSA) evolution. DESIGN: Prospective observational cross-sectional study. Carriage of antimicrobial resistance and virulence-associated genes in the absence of significant antibiotic selective pressure was investigated among healthy medical students from geographically diverse origins who were nasally co-colonised with S. aureus and CoNS. Clonal lineages of S. aureus isolates were determined. SETTING/PARTICIPANTS: Dublin-based international undergraduate medical students. RESULTS: Nasal S. aureus carriage was identified in 137/444 (30.8%) students of whom nine (6.6%) carried MRSA (ST59-MRSA-IV (6/9), CC1-MRSA-V-SCCfus (3/9)). The genes mecA, fusB, ileS2, qacA/qacC and the arginine catabolic mobile element-arc were detected among colonising nasal staphylococci and had a significantly greater association with CoNS than S. aureus. The rate of co-carriage of any of these genes in S. aureus/CoNS pairs recovered from the same individual was <1%. CONCLUSIONS: The relatively high prevalence of these genes among CoNS of the healthy human flora in the absence of significant antibiotic selective pressure is of interest. Further research is required to determine what factors are involved and whether these are modifiable to help prevent the emergence and spread of antibiotic resistance among staphylococci.
Assuntos
Proteínas de Bactérias/genética , Farmacorresistência Bacteriana/genética , Nariz/microbiologia , Staphylococcus/genética , Staphylococcus/isolamento & purificação , Estudantes de Medicina , Antibacterianos/farmacologia , Proteínas de Bactérias/efeitos dos fármacos , Portador Sadio/microbiologia , Estudos Transversais , Farmacorresistência Bacteriana/efeitos dos fármacos , Feminino , Humanos , Irlanda , Masculino , Prevalência , Estudos Prospectivos , Infecções Estafilocócicas , Staphylococcus aureus/genética , Staphylococcus aureus/isolamento & purificação , Staphylococcus epidermidis/genética , Staphylococcus epidermidis/isolamento & purificaçãoRESUMO
Staphylococcus aureus and Staphylococcus epidermidis are frequent commensals of the nares and skin and are considered transient oral residents. Reports on their prevalence in the oral cavity, periodontal pockets and subgingivally around infected oral implants are conflicting, largely due to methodological limitations. The prevalence of these species in the oral cavities, periodontal pockets and subgingival sites of orally healthy individuals with/without implants and in patients with periodontal disease or infected implants (peri-implantitis) was investigated using selective chromogenic agar and matrix-assisted laser desorption/ionization time-of-flight mass spectrometry. Staphylococcus epidermidis was predominant in all participant groups investigated. Its prevalence was significantly higher (P = 0.0189) in periodontal pockets (30%) than subgingival sites of healthy individuals (7.8%), and in subgingival peri-implantitis sites (51.7%) versus subgingival sites around non-infected implants (16.1%) (P = 0.0057). In contrast, S. aureus was recovered from subgingival sites of 0-12.9% of the participant groups, but not from periodontal pockets. The arginine catabolic mobile element (ACME), thought to enhance colonization and survival of S. aureus, was detected in 100/179 S. epidermidis and 0/83 S. aureus isolates screened using multiplex PCR and DNA microarray profiling. Five distinct ACME types, including the recently described types IV and V (I; 14, II; 60, III; 10, IV; 15, V; 1) were identified. ACME-positive S. epidermidis were significantly (P = 0.0369) more prevalent in subgingival peri-implantitis sites (37.9%) than subgingival sites around non-infected implants (12.9%) and also in periodontal pockets (25%) compared to subgingival sites of healthy individuals (4.7%) (P = 0.0167). To investigate the genetic diversity of ACME, 35 isolates, representative of patient groups, sample sites and ACME types underwent whole genome sequencing from which multilocus sequence types (STs) were identified. Sequencing data permitted ACME types II and IV to be subdivided into subtypes IIa-c and IVa-b, respectively, based on distinct flanking direct repeat sequences. Distinct ACME types were commonly associated with specific STs, rather than health/disease states or recovery sites, suggesting that ACME types/subtypes originated amongst specific S. epidermidis lineages. Ninety of the ACME-positive isolates encoded the ACME-arc operon, which likely contributes to oral S. epidermidis survival in the nutrient poor, semi-anaerobic, acidic and inflammatory conditions present in periodontal disease and peri-implantitis.
RESUMO
Community-associated spa type t127/t922 methicillin-resistant Staphylococcus aureus (MRSA) prevalence increased from 1%-7% in Ireland between 2010-2015. This study tracked the spread of 89 such isolates from June 2013-June 2016. These included 78 healthcare-associated and 11 community associated-MRSA isolates from a prolonged hospital outbreak (H1) (n = 46), 16 other hospitals (n = 28), four other healthcare facilities (n = 4) and community-associated sources (n = 11). Isolates underwent antimicrobial susceptibility testing, DNA microarray profiling and whole-genome sequencing. Minimum spanning trees were generated following core-genome multilocus sequence typing and pairwise single nucleotide variation (SNV) analysis was performed. All isolates were sequence type 1 MRSA staphylococcal cassette chromosome mec type IV (ST1-MRSA-IV) and 76/89 were multidrug-resistant. Fifty isolates, including 40/46 from H1, were high-level mupirocin-resistant, carrying a conjugative 39 kb iles2-encoding plasmid. Two closely related ST1-MRSA-IV strains (I and II) and multiple sporadic strains were identified. Strain I isolates (57/89), including 43/46 H1 and all high-level mupirocin-resistant isolates, exhibited ≤80 SNVs. Two strain I isolates from separate H1 healthcare workers differed from other H1/strain I isolates by 7-47 and 12-53 SNVs, respectively, indicating healthcare worker involvement in this outbreak. Strain II isolates (19/89), including the remaining H1 isolates, exhibited ≤127 SNVs. For each strain, the pairwise SNVs exhibited by healthcare-associated and community-associated isolates indicated recent transmission of ST1-MRSA-IV within and between multiple hospitals, healthcare facilities and communities in Ireland. Given the interchange between healthcare-associated and community-associated isolates in hospitals, the risk factors that inform screening for MRSA require revision.