Lee-Jene Teng

Sequence type 59 (ST59) is the dominant type of community-associated methicillin-resistant Staphylococcus aureus (MRSA) in Taiwan. Previously, we reported that ST59 MRSA harbors enterococcal IS1216V-mediated multidrug-resistant composite transposons MES_PM1 or MES_6272-2. The MES were found to have a mosaic structure, largely originating in enterococci and partly native to S. aureus. The current study aimed to track the origin of the MES and how they disseminated from enterococci to ST59 S. aureus. A total of 270 enterococcal isolates were analyzed, showing that two ST64 Enterococcus faecalis isolated in 1992 and 11 clonal complex 17 Enterococcus faecium harbored MES_PM1-like and MES_6272-2-like structures, respectively. Sequence analysis revealed that ST64 E. faecalis strain N48 acquired the MES_PM1-like structure on the plasmid pEflis48. The pEflis48 harbored the enterococci-originated region (erythromycin, kanamycin, and streptomycin resistances) and the S.aureus-originated region (chloramphenicol resistance) of MES_PM1 but was separated by the replication region of the plasmid. Homologous recombination between the two direct repeats of IS1216V resulted in excision of the replication region of the plasmid to regenerate MES_PM1. The p4780-1 and pV19 of E. faecium carried MES_6272-2-like structures with IS1216V, albeit with multiple insertions by other insertion sequences. The findings show that IS1216V plays important roles in bidirectional gene transfer of multidrug resistance between enterococci and S. aureus.

Staphylococcus argenteus is an emerging pathogen that is recognized as non-pigmented Staphylococcus aureus. However, the molecular characteristics of S. argenteus and its virulence factors have not been well studied. The present study analyzed 96 isolates of S. argenteus recovered from blood. Identification of S. argenteus was based on results of MALDI-TOF MS and lacking crtM gene. All 96 isolates were methicillin-susceptible. Multilocus sequence typing (MLST) revealed four sequence types: ST2250 (n = 72), ST2793 (n = 12), ST1223 (n = 10), and ST2198 (n = 2). All 72 ST2250 isolates harbored CRISPR loci with polymorphism of direct repeats and spacers, but no other STs carried CRISPR loci. To date, ST2793 isolates have rarely been reported in other countries. Collagen-binding adhesin gene (cna) and staphylococcal enterotoxin type C (sec) were detected in 12 (100%) and 8 (67%) ST2793 isolates, respectively. ST1223 has been reported as food poisoning pathogens, and enterotoxin gene clusters (egc) were detected in all 10 isolates, while seb gene was detected in three isolates. Two ST2198 isolates carried bone sialoprotein-binding protein gene (bbp), belonging to agr type IV. Our focus on the heterogeneity of molecular characterization in four ST types of S. argenteus revealed that S. argenteus had been isolated as early as 2000. Each ST type of S. argenteus harbors particular genetic markers that may contribute to their virulence.

We investigated antibiotic resistance of staphylococci isolated from 1128 samples of high-circulating RTE foods in Taiwan. A total of 111 Staphylococcus aureus and 709 coagulase-negative staphylococci (CoNS) comprising 23 species were isolated. The prevalence of S. aureus differed in various category of RTE foods, highest in fresh-cut fruits/vegetables (20.5%) and lowest in low-water activity (LWA) foods (0.7%). The overall staphylococcal contamination was highest in fresh-cut fruits/vegetables (62.2%), in which multiple isolates (up to 10) or species (up to 6) in single sample were frequently found. Distinct distribution of species contributed to unique feature in each category. Prevalence of antibiotic-resistant S. aureus was higher in fresh-cut fruits/vegetables samples (14.2% in 127) compared to other food categories (0-7.1%). A total of 4 MRSA carrying SCCmec type IV or VT were identified (3.6% in 111), in which 3 belonged to sequence type ST59 and one was ST5. Among CoNS, S. epidermidis and S. warneri exhibited higher non-intrinsic antibiotic resistance than other species. Of 41 methicillin-resistant CoNS (5.8% in 709) isolates, SCCmec type IV (n = 16) and type VT (n = 6) were most frequent. Isolates of S. saprophyticus, S. xylosus and S. sciuri displayed high rates of resistance to fusidic acid. Novel fusB-family determinants were identified in S. xylosus, S. sciuri and S. kloosii, which may contribute to their intrinsic resistance to fusidic acid. Compared to other food categories, fresh-cut fruits/vegetables were more contaminated by staphylococci carrying non-intrinsic resistance determinants including methicillin resistance. This nation-wide study demonstrated that some categories may have potential risk for transmitting antibiotic resistance, in which S. epidermidis and S. warneri should be gotten more attention.

The cell wall‐anchored protein‐encoding spj gene on staphylococcal cassette chromosome mec IVl (SCCmecIVl) was found to vary in size because of its 22‐ and 86‐aa repeat domains. The 22‐aa repeats are the more flexible of the two repeats, comprising three 11‐aa units, and were classified into three groups with eleven types. The 11/22‐aa repeats are longer in individuals with bullous impetigo, shorter in those with invasive disease and were absent in a fatal case, this last one having been rapidly diagnosed by PCR. IS431‐flanking pUB110 (bleO, aadD) is present on SCCmecIVl at 90%. The bacterial surface has the spj product and a unique surface layer.

Objectives: This study investigated molecular characteristics of rifampin (RIF)-resistant (RIF-R) Staphylococcus aureus isolates recovered from patients receiving RIF-containing regimens for tuberculosis (TB). Patients and methods: Patients with TB who received RIF-containing regimens from November 2009 to May 2011 at a medical center were enrolled. Nasal swabs for S. aureus culture were obtained at the time of enrollment, and then every two months until two months after RIF treatment had been completed. Genetic relatedness of the isolates was determined using pulsed-field gel electrophoresis, multilocus sequence typing, and gene typing of spa and SCCmec. The presence of RIF resistance-associated mutations in rpoB, and fusidic acid resistance genes fusB and fusC in the S. aureus isolates were analyzed. Results: Among the 200 patients enrolled in this study, 152 completed follow-ups during treatment, and 114 completed two months of follow-up after discontinuing use of RIF. At enrollment, ten patients (5%) had nasal colonization with S. aureus, namely eight with methicillin-susceptible S. aureus (MSSA), and two with methicillin-resistant S. aureus (MRSA, ST59-SCCmecIV-RIF-susceptible). All these patients were decolonized after RIF usage. Two patients with MSSA colonization at enrollment showed recolonization with genetically unrelated MSSA strains two months after completion of RIF treatment. There were five ST45-SCCmecV_T-RIF-R strains from two patients isolated during RIF exposure. Sequencing of rpoB in the RIF-R S. aureus isolates revealed different mutation sites between the MSSA and MRSA isolates. Conclusion: RIF-R S. aureus strains are more likely to result in persistent nasal carriage in TB patients receiving RIF treatment. Monitoring of emergence and possible dissemination of the MRSA ST45 strains among TB patients treated with RIF in Taiwan is warranted.