An emerging Panton-Valentine leukocidin-positive CC5-meticillin-resistant Staphylococcus aureus-IVc clone recovered from hospital and community settings over a 17-year period from 12 countries investigated by whole-genome sequencing

BACKGROUND

A novel Panton-Valentine leukocidin (PVL)-positive meticillin-resistant Staphylococcus aureus (MRSA) clonal complex (CC)5-MRSA-IVc ('Sri Lankan' clone) was recently described from Sri Lanka. Similar isolates caused a recent Irish hospital outbreak.

AIM

To investigate the international dissemination and diversity of PVL-positive CC5-MRSA-IVc isolates from hospital and community settings using whole-genome sequencing (WGS).

METHODS

Core-genome single nucleotide polymorphism (cgSNP) analysis, core-genome multi-locus sequence typing (cgMLST) and microarray-based detection of antimicrobial-resistance and virulence genes were used to investigate PVL-positive CC5-MRSA-IVc (N = 214 including 46 'Sri Lankan' clone) from hospital and community settings in 12 countries over 17 years. Comparators included 29 PVL-positive and 23 PVL-negative CC5/ST5-MRSA-I/II/IVa/IVc/IVg/V.

RESULTS

Maximum-likelihood cgSNP analysis grouped 209/214 (97.7%) CC5-MRSA-IVc into Clade I; average of 110 cgSNPs between isolates. Clade III contained the five remaining CC5-MRSA-IVc; average of 92 cgSNPs between isolates. Clade II contained seven PVL-positive CC5-MRSA-IVa comparators, whereas the remaining 45 comparators formed an outlier group. Minimum-spanning cgMLST analysis revealed a comparably low average of 57 allelic differences between all CC5/ST5-MRSA-IVc. All 214 CC5/ST5-MRSA-IVc were identified as 'Sri Lankan' clone, predominantly spa type t002 (186/214) with low population diversity and harboured a similar range of virulence genes and variable antimicrobial-resistance genes. All 214 Sri Lankan clone isolates and Clade II comparators harboured a 9616-bp chromosomal PVL-encoding phage remnant, suggesting both arose from a PVL-positive meticillin-susceptible ancestor. Over half of Sri Lankan clone isolates were from infections (142/214), and where detailed metadata were available (168/214), most were community associated (85/168).

CONCLUSIONS

Stable chromosomal retention of pvl may facilitate Sri-Lankan clone dissemination.

Dogs as carriers of virulent and resistant genotypes of Clostridioides difficile

While previous research on zoonotic transmission of community-acquired Clostridioides difficile infection (CA-CDI) focused on food-producing animals, the present study aimed to investigate whether dogs are carriers of resistant and/or virulent C. difficile strains. Rectal swabs were collected from 323 dogs and 38 C. difficile isolates (11.8%) were obtained. Isolates were characterized by antimicrobial susceptibility testing, whole-genome sequencing (WGS) and a DNA hybridization assay. Multilocus sequence typing (MLST), core genome MLST (cgMLST) and screening for virulence and antimicrobial resistance genes were performed based on WGS. Minimum inhibitory concentrations for erythromycin, clindamycin, tetracycline, vancomycin and metronidazole were determined by E-test. Out of 38 C. difficile isolates, 28 (73.7%) carried genes for toxins. The majority of isolates belonged to MLST sequence types (STs) of clade I and one to clade V. Several isolates belonged to STs previously associated with human CA-CDI. However, cgMLST showed low genetic relatedness between the isolates of this study and C. difficile strains isolated from humans in Austria for which genome sequences were publicly available. Four isolates (10.5%) displayed resistance to three of the tested antimicrobial agents. Isolates exhibited resistance to erythromycin, clindamycin, tetracycline and metronidazole. These phenotypic resistances were supported by the presence of the resistance genes erm(B), cfr(C) and tet(M). All isolates were susceptible to vancomycin. Our results indicate that dogs may carry virulent and antimicrobial-resistant C. difficile strains.

Diversity of methicillin-resistant coagulase-negative Staphylococcus spp. and methicillin-resistant Mammaliicoccus spp. isolated from ruminants and New World camelids

Information about livestock carrying methicillin-resistant coagulase-negative staphylococci and mammaliicocci (MRCoNS/MRM) is scarce. The study was designed to gain knowledge of the prevalence, the phenotypic and genotypic antimicrobial resistance and the genetic diversity of MRCoNS/MRM originating from ruminants and New World camelids. In addition, a multi-locus sequence typing scheme for the characterization of Mammaliicoccus (formerly Staphylococcus) sciuri was developed. The study was conducted from April 2014 to January 2017 at the University Clinic for Ruminants and the Institute of Microbiology at the University of Veterinary Medicine Vienna. Seven hundred twenty-three nasal swabs originating from ruminants and New World camelids with and without clinical signs were examined. After isolation, MRCoNS/MRM were identified by MALDI-TOF, rpoB sequencing and typed by DNA microarray-based analysis and PCR. Antimicrobial susceptibility testing was conducted by agar disk diffusion. From all 723 nasal swabs, 189 MRCoNS/MRM were obtained. Members of the Mammaliicoccus (M.) sciuri group were predominant (M. sciuri (n = 130), followed by M. lentus (n = 43), M. fleurettii (n = 11)). In total, 158 out of 189 isolates showed phenotypically a multi-resistance profile. A seven-loci multi-locus sequence typing scheme for M. sciuri was developed. The scheme includes the analysis of internal segments of the house-keeping genes ack, aroE, ftsZ, glpK, gmk, pta1 and tpiA. In total, 28 different sequence types (STs) were identified among 92 selected M. sciuri isolates. ST1 was the most prevalent ST (n = 35), followed by ST 2 (n = 15), ST3 and ST5 (each n = 5), ST4 (n = 3), ST6, ST7, ST8, ST9, ST10 and ST11 (each n = 2).

Women temporarily synchronize their menstrual cycles with the luminance and gravimetric cycles of the Moon

Many species synchronize reproductive behavior with a particular phase of the lunar cycle to increase reproductive success. In humans, a lunar influence on reproductive behavior remains controversial, although the human menstrual cycle has a period close to that of the lunar cycle. Here, we analyzed long-term menstrual recordings of individual women with distinct methods for biological rhythm analysis. We show that women's menstrual cycles with a period longer than 27 days were intermittently synchronous with the Moon's luminance and/or gravimetric cycles. With age and upon exposure to artificial nocturnal light, menstrual cycles shortened and lost this synchrony. We hypothesize that in ancient times, human reproductive behavior was synchronous with the Moon but that our modern lifestyles have changed reproductive physiology and behavior.

Multiple distinct outbreaks of Panton-Valentine leucocidin-positive community-associated meticillin-resistant Staphylococcus aureus in Ireland investigated by whole-genome sequencing

BACKGROUND

Panton-Valentine leucocidin (PVL)-positive community-associated meticillin-resistant Staphylococcus aureus (CA-MRSA) is increasingly associated with infection outbreaks.

AIM

To investigate multiple suspected PVL-positive CA-MRSA outbreaks using whole-genome sequencing (WGS).

METHODS

Forty-six suspected outbreak-associated isolates from 36 individuals at three separate Irish hospitals (H1-H3) and from separate incidents involving separate families associated with H2 were investigated by whole-genome multi-locus sequence typing (wgMLST).

FINDINGS

Two clusters (CH1 and CH2) consisting of 8/10 and 6/6 PVL-positive t008 ST8-MRSA-IVa isolates from H1 and H2, respectively, were identified. Within each cluster, neighbouring isolates were separated by ≤5 allelic differences; however, ≥73 allelic differences were identified between the clusters, indicating two independent outbreaks. Isolates from the H3 maternity unit formed two clusters (CH3-SCI and CH3-SCII) composed of four PVL-negative t4667 ST5-MRSA-V and 14 PVL-positive t002 ST5-MRSA-IVc isolates, respectively. Within clusters, neighbouring isolates were separated by ≤24 allelic differences, whereas both clusters were separated by 1822 allelic differences, indicating two distinct H3 outbreaks. Eight PVL-positive t127 ST1-MRSA-V+fus and three PVL-negative t267 ST97-MRSA-V+fus isolates from two distinct H2-associated families FC1 (N = 4) and FC2 (N = 7) formed three separate clusters (FC1 (t127), FC2 (t127) and FC2 (t267)). Neighbouring isolates within clusters were closely related and exhibited ≤7 allelic differences. Intrafamilial transmission was apparent, but the detection of ≥48 allelic differences between clusters indicated no interfamilial transmission.

CONCLUSION

The frequent importation of PVL-positive CA-MRSA into healthcare settings, transmission and association with outbreaks is a serious ongoing concern. WGS is a highly discriminatory, informative method for deciphering such outbreaks conclusively.

Molecular characterization of methicillin-resistant Staphylococcus aureus in nosocomial infections in a tertiary-care facility: emergence of new clonal complexes in Saudi Arabia

Changes in the molecular epidemiology of methicillin-resistant Staphylococcus aureus (MRSA) continue to be reported. This study was carried out to characterize MRSA isolates in Saudi Arabia. MRSA isolates causing nosocomial infections (n = 117) obtained from 2009–2015 at a tertiary-care facility in Riyadh, Saudi Arabia, were studied. Molecular characterization of isolates was carried out using the StaphyType DNA microarray (Alere Technologies, Jena, Germany). Fourteen clonal complexes (CC) were identified, with the most common being CC80 (n = 35), CC6 (n = 15), CC5 (n = 13) and CC22 (n = 12). With the exception of nine ST239 MRSA-III isolates, all others were of community-associated MRSA lineages. The following strains are identified for the first time in Saudi Arabia: ST8-MRSA-IV [PVL⁺/ACME⁺], USA300 (n = 1); ST72-MRSA-IV USA700 (n = 1); CC5-MRSA-IV, [PVL⁺/edinA⁺], WA MRSA-121 (n = 1); CC5-MRSA-V+SCCfus, WA MRSA-14/109 (n = 2), CC97-MRSA-IV, WA MRSA-54/63; CC2250/2277-MRSA-IV and WA MRSA-114. CC15-MRSA (n = 3) was identified for the first time in clinical infection in Saudi Arabia. None of the isolates harboured vancomycin resistance genes, while genes for resistance to mupirocin and quaternary ammonium compounds were found in one and nine isolates respectively. Fifty-seven isolates (48.7%) were positive for Panton-Valentine leukocidin genes. While the staphylokinase (sak) and staphylococcal complement inhibitor (scn) genes were present in over 95% of the isolates, only 37.6% had the chemotaxis-inhibiting protein (chp) gene. Increasing occurrence of community-acquired MRSA lineages plus emergence of pandemic and rare MRSA strains is occurring in our setting. Strict infection control practices are important to limit the dissemination of these MRSA strains.

Molecular characterization of Staphylococcus aureus isolates causing skin and soft tissue infections in patients from Malakand, Pakistan

Comparatively few studies have been published describing Staphylococcus aureus/MRSA epidemiology in Central Asia including Pakistan. Here, we report the genotyping of Staphylococcus aureus strains (that include both methicillin-susceptible and methicillin-resistant Staphylococcus aureus) from community- and hospital-acquired skin and soft-tissue infections in a tertiary care hospital in the Malakand district of the Khyber Pakhtunkhwa Province of Pakistan. Forty-five isolates of Staphylococcus aureus were characterized by microarray hybridization. Twenty isolates (44 %) were MRSA, whereas 22 (49 %) were PVL-positive. Fourteen isolates (31 %) harboured both mecA and PVL genes. The dominant clones were CC121-MSSA (n = 15, 33 %) and the PVL-positive "Bengal Bay Clone" (ST772-MRSA-V; n = 13, 29 %). The PVL-positive CC8-MRSA-IV strain "USA300" was found once. The pandemic ST239-MRSA-III strain was absent, although it has previously been observed in Pakistan. These observations require a re-assessment of schemes for initial antibiotic therapy to cover MRSA and they emphasise the need for a rapid and non-molecular test for PVL.

ST2249-MRSA-III: a second major recombinant methicillin-resistant Staphylococcus aureus clone causing healthcare infection in the 1970s

Typing of healthcare-associated methicillin-resistant Staphylococcus aureus (MRSA) from Australia in the 1970s revealed a novel clone, ST2249-MRSA-III (CC45), present from 1973 to 1979. This clone was present before the Australian epidemic caused by the recombinant clone, ST239-MRSA-III. This study aimed to characterize the genome of ST2249-MRSA-III to establish its relationship to other MRSA clones. DNA microarray analysis was conducted and a draft genome sequence of ST2249 was obtained. The recombinant structure of the ST2249 genome was revealed by comparisons to publicly available ST239 and ST45 genomes. Microarray analysis of genomic DNA of 13 ST2249 isolates showed gross similarities with the ST239 chromosome in a segment around the origin of replication and with ST45 for the remainder of the chromosome. Recombination breakpoints were precisely determined by the changing pattern of nucleotide polymorphisms in the genome sequence of ST2249 isolate SK1585 compared with ST239 and ST45. One breakpoint was identified to the right of oriC, between sites 1014 and 1065 of the gene D484_00045. Another was identified to the left of oriC, between sites 1185 and 1248 of D484_01632. These results indicate that ST2249 inherited approximately 35.3% of its chromosome from an ST239-like parent and 64.7% from an ST45-like parent. ST2249-MRSA-III resulted from a major recombination between parents that resemble ST239 and ST45. Although only limited Australian archival material is available, the oldest extant isolate of ST2249 predates the oldest Australian isolate of ST239 by 3 years. It is therefore plausible that these two recombinant clones were introduced into Australia separately.

Staphylococcus aureus plasmids without mobilization genes are mobilized by a novel conjugative plasmid from community isolates

OBJECTIVES

To describe a family of conjugative plasmids isolated from colonizing community Staphylococcus aureus and determine their ability to mobilize unrelated antimicrobial resistance/virulence plasmids, not encoding mobilization functions.

METHODS

Plasmid pWBG749 was labelled with Tn551 (pWBG749e) to enable laboratory manipulation. Plasmid pWBG749e was conjugated into S. aureus of seven different lineages that harboured unrelated plasmids and mobilization experiments were performed. Plasmids were screened by EcoRI restriction and hybridization with probes prepared from unique pWBG749 conjugation genes.

RESULTS

Conjugative plasmids pWBG745, pWBG748 and pWBG749 belong to the same conjugative-plasmid family as the vancomycin resistance plasmid pBRZ01. Plasmid pWBG749e mobilized five unrelated plasmids. Mobilized plasmid pWBG744 is a pIB485-family plasmid that was also found in international S. aureus.

CONCLUSIONS

Plasmid pWBG749e can mobilize unrelated S. aureus plasmids whose means of dissemination have not previously been understood.

Multiple cases of methicillin-resistant CC130 Staphylococcus aureus harboring mecC in milk and swab samples from a Bavarian dairy herd

The discovery of a new mecA homolog, mecC, necessitates a modification of diagnostic procedures for the identification of methicillin-resistant Staphylococcus aureus (MRSA), as most assays used for the genotypic and phenotypic mecA detection cannot currently recognize mecC. Although the prevalence, distribution, and importance of mecC are not yet completely understood, an exchange of mecC-MRSA between humans and animals seems possible. All previously reported observations of mecC-positive strains have been sporadic. To the best of our knowledge, this is the first report about multiple cases of mecC-positive Staph. aureus in 1 dairy herd. Clonal complex 130 Staph. aureus harboring mecC were found in milk samples from 16 of 56 lactating cows kept in a herd in Bavaria, Germany. Almost all quarter milk samples positive for mecC-MRSA had the lowest possible California Mastitis Test score; composite somatic cell counts obtained from monthly milk recordings showed a mean of 51,600 cells/mL in mecC-MRSA affected cows. Additionally, mecC-positive clonal complex 130 Staph. aureus were detected in swab samples from the mammary skin and a teat lesion of 1 cow from this herd. This report suggests that mecC-carrying strains are able to spread among livestock, and that they have the ability to cause multiple cases in single herds. Therefore, future studies targeting MRSA in dairy cows need to consider mecC.

Molecular fingerprinting of Staphylococcus aureus from bone and joint infections

The objective of the study was to determine if a clonal complex (CC) of Staphylococcus aureus or certain virulence and adhesion factors were associated with infections of bones and prosthetic implants. One hundred and nineteen isolates were characterised using microarrays. There was no evidence for a single virulence factor or CC being causative for bone and implant infections. Isolates belonged to 20 different CCs, with CC8 (19.33%), CC45 (17.65%) and CC30 (12.61%) being dominant. Population structure and the relative abundances of virulence genes was similar to previously described isolates from healthy carriers. Differences to carrier isolates included a higher proportion of CC45, a lower proportion of CC15, as well as a higher abundance of sak (staphylokinase) among patient isolates. For 23 patients with infections of total knee or hip prosthetics, it was possible to simultaneously obtain nasal swabs. Fifteen (65.2%) carried S. aureus in their anterior nares. In nine of them (39.1%), isolates from the infection site were identical to carriage isolates. This suggests an elevated risk of infection for S. aureus carriers and the possibility of endogenous infection in a high proportion of them. Therefore, the pre-operative screening and eradication of S. aureus in patients receiving total joint prosthetics should be considered.

Characterisation of MRSA from Malta and the description of a Maltese epidemic MRSA strain

Malta has one of the highest prevalence rates of methicillin-resistant Staphylococcus aureus (MRSA) in Europe. However, only limited typing data are currently available. In order to address this situation, 45 MRSA isolates from the Mater Dei Hospital in Msida, Malta, were characterised using DNA microarrays. The most common strain was ST22-MRSA-IV (UK-EMRSA-15, 30 isolates). Sporadic strains included ST36-MRSA-II (UK-EMRSA-16, two isolates), PVL-positive ST80-MRSA-IV (European Clone, one isolate), ST228-MRSA-I (Italian Clone/South German Epidemic Strain, one isolate) and ST239-MRSA-III (Vienna/Hungarian/Brazilian Epidemic Strain, one isolate). Ten MRSA isolates belonged to a clonal complex (CC) 5/ST149, spa type t002 strain. This strain harboured an SCCmec IV element (mecA, delta mecR, ugpQ, dcs, ccrA2 and ccrB2), as well as novel alleles of ccrA/B and the fusidic acid resistance element Q6GD50 (previously described in the sequenced strain MSSA476, BX571857.1:SAS0043). It also carried the gene for enterotoxin A (sea) and the egc enterotoxin locus, as well as (in nine out of ten isolates) genes encoding the toxic shock syndrome toxin (tst1) and enterotoxins C and L (sec, sel). While the presence of the other MRSA strains suggests foreign importation due to travel between Malta and other European countries, the CC5/t002 strain appears, so far, to be restricted to Malta.

DNA microarray-based genotyping of methicillin-resistant Staphylococcus aureus strains from Eastern Saxony

A diagnostic microarray was used to characterise a collection of methicillin-resistant Staphylococcus aureus (MRSA) isolates from hospitals in the German region of Eastern Saxony. The most abundant epidemic MRSA (EMRSA) strains were ST5-MRSA II (Rhine-Hesse EMRSA, EMRSA-3), CC5/ST228-MRSA I (South German EMRSA), ST22-MRSA IV (Barnim EMRSA, EMRSA-15) and ST45-MRSA IV (Berlin EMRSA). Other strains were found only as sporadic isolates or in minor outbreaks. These strains included ST1-MRSA IV, ST8-MRSA IV (Hannover EMRSA and others), clonal group 5 strains carrying SCCmec type IV elements (Paediatric clone), ST45-MRSA V, CC8/ST239-MRSA III and ST398-MRSA V. Panton-Valentine leukocidin-positive MRSA isolates were still very rare. The predominant strain was ST80-MRSA IV, although increasing numbers of different strains have recently been detected (ST8-MRSA IV, ST30-MRSA IV and ST59-MRSA V). For more common MRSA strains, it was possible to detect variants that differed mainly in the carriage of additional resistance determinants and certain virulence-associated genes. Detection of such variants can sometimes allow epidemic strains to be resolved beyond spa types to a hospital-specific level, which is of significant value for epidemiological purposes.

High diversity of Panton-Valentine leukocidin-positive, methicillin-susceptible isolates of Staphylococcus aureus and implications for the evolution of community-associated methicillin-resistant S. aureus

In total, 100 Staphylococcus aureus isolates from diverse cases of skin and soft-tissue infection at a university hospital in Saxony, Germany, were characterised using diagnostic microarrays. Virulence factors, including Panton-Valentine leukocidin (PVL), were detected and the isolates were assigned to clonal groups. Thirty isolates were positive for the genes encoding PVL. Only three PVL-positive methicillin-resistant S. aureus (MRSA) isolates were found, two of which belonged to European clone ST80-MRSA IV and one to USA300 strain ST8-MRSA IV. The remaining methicillin-susceptible PVL-positive isolates belonged to a variety of different multilocus sequence types. The predominant strains were agrI/ST22, agrII/CC5, agrIII/CC30 and agrIV/ST121. In order to check for possible bias caused by regional or local outbreak strains, an additional 18 methicillin-susceptible, PVL-positive isolates from the UK were tested. Approximately two-thirds of the UK isolates belonged to types that also comprised approximately two-thirds of the isolates from Saxony. Some methicillin-susceptible PVL-positive isolates (agrI/ST152, agrIII/ST80 and agrIII/ST96) closely resembled known epidemic community-acquired MRSA (CaMRSA) strains. These findings indicate that the current rise in PVL-positive CaMRSA could be caused by the dissemination of novel SCCmec elements among pre-existing PVL-positive strains, rather than by the spread of PVL phages among MRSA strains.

Development and evaluation of a real-time PCR assay for detection of Pneumocystis jiroveci

Pneumocystis jiroveci is an important agent of pneumonia in immunocompromised hosts. Usually, this pathogen is detected by Giemsa or direct fluorescence stains of bronchoalveolar lavage (BAL) fluids. Microscopic methods, however, have 2 disadvantages. P. jiroveci is not stable outside the human body, which means that slow sample transport might result in false-negative results. Additionally, exact quantification, which is needed for therapy monitoring, is not possible. In this study, we developed a real-time polymerase chain reaction assay for the LightCycler. Two Pneumocystis-specific TaqMan systems, one based on the sequence of the 5.8S ribosomal gene and another one targeting the dihydrofolate reductase gene were evaluated. Additionally, the amount of human DNA in the sample was measured by a TaqMan assay based on the human albumin gene, allowing assessment of sample quality and quantification normalized on sample concentration. For clinical evaluation, 69 BAL specimens from 26 positive patients as well as 60 negative controls were tested. Both systems were able to detect all proven cases of Pneumocystis pneumonia. Differentiation of carriage, asymptomatic reactivation, and clinical infection as well as normalized quantification by calculating the ratio of Pneumocystis DNA to human DNA are discussed.

Comparative genomics and DNA array-based genotyping of pandemic Staphylococcus aureus strains encoding Panton-Valentine leukocidin

Within the last few years, methicillin-resistant Staphylococcus aureus (MRSA) strains encoding Panton-Valentine leukocidin (PVL) have emerged and spread worldwide. This epidemic can be attributed to a small number of distinct clones. The present study used a novel assay, based on multiplex linear DNA amplification and subsequent microarray hybridisation, to simultaneously detect all relevant exotoxins, antimicrobial resistance determinants and the allelic variants of agr. The genes of the staphylococcal exotoxin-like (set) locus were also included for typing purposes. This assay, together with multilocus sequence typing (MLST) and spa typing, was applied to 56 clinical isolates and reference strains representing all major pandemic PVL-MRSA lineages, as well as to phylogenetically-related strains and putative ancestors. Array hybridisation results allowed the assignment of isolates to clonal groups, which were in accordance with MLST and spa typing data. Ten distinct clonal groups of PVL-MRSA (ST1, ST5, ST8, ST22, ST30, ST59/359, ST80/583, ST88, ST93 and ST152), including 12 MLST types, were identified and analysed with regard to resistance determinants and genes coding for exotoxins. The array hybridisation data confirmed that pandemic PVL-positive strains originate from very diverse genetic backgrounds, and provided insights into the evolution of some lineages. The DNA microarray technique provides a valuable epidemiological tool for the detailed characterisation of clinical isolates and comparison of strains at a global level.

Microarray-based characterisation of a Panton-Valentine leukocidin-positive community-acquired strain of methicillin-resistant Staphylococcus aureus

Recent years have witnessed the emergence of novel methicillin-resistant Staphylococcus aureus (MRSA) strains that produce the potent toxin Panton-Valentine leukocidin (PVL). PVL-positive strains can cause complicated skin infections or necrotising pneumonia with high mortality, and these strains have the potential for epidemic spread in the community. In 2004-2005, two case clusters and two isolated cases were observed in eastern Saxony and southern Brandenburg. These were the first known infections with PVL-positive community-acquired MRSA (caMRSA) in this part of Germany. The isolates belonged to agr type III, spa type 44 or spa type 131, and showed a SmaI macrorestriction pattern that corresponded to caMRSA of clonal group ST80. The isolates were susceptible to levofloxacin, macrolides, clindamycin, gentamicin and vancomycin. Most isolates showed resistance to tetracycline and fusidic acid because of the presence of the tetK and far1 genes. A novel plasmid (designated pUB102) harbouring far1, tetK and blaZ was characterised and partially sequenced. Microarray analysis revealed that the caMRSA isolates harboured genes encoding several bi-component toxins (lukF/S-PVL, lukD/E, lukS/F plus hlgA, and another putative leukocidin homologue). Neither tst1 nor genes for enterotoxins A-Y were detected, but the isolates harboured several staphylococcal enterotoxin-like toxin genes (set genes), as well as genes encoding an epidermal cell differentiation inhibitor (edinB) and exfoliative toxin D (etD). Comparative analysis of other isolates from Australia, Germany, Switzerland and the UK showed that these isolates were representative of a widespread clone of caMRSA.

Rapid genotyping of methicillin-resistant Staphylococcus aureus (MRSA) isolates using miniaturised oligonucleotide arrays

This study evaluated a DNA oligonucleotide array that recognised 38 different Staphylococcus aureus targets, including all relevant resistance determinants and some toxins and species-specific controls. A new method for labelling sample DNA, based on a linear multiplex amplification that incorporated biotin-labelled dUTP into the amplicon, was established, and allowed detection of hybridisation of the amplicons to the array with an enzymic precipitation reaction. The whole assay was validated by hybridisations with a panel of reference strains and cloned specific PCR products of all targets. To evaluate performance under routine conditions, the assay was used to test 100 methicillin-resistant S. aureus (MRSA) isolates collected from a university hospital in Saxony, Germany. The results showed a high correlation with conventional susceptibility data. The ermA and ermC macrolide resistance genes were found in 40% and 32% of the isolates, respectively. The most prevalent aminoglycoside resistance gene was aphA3 (57% of the isolates), followed by aacA-aphD (29%) and aadD (29%); tet genes, mupR and dfrA were rare. There were no isolates with van genes or genes involved in resistance to quinupristin-dalfopristin. Enterotoxins were detected in 27% of the isolates. Genes encoding Panton-Valentine leukocidin, toxic shock syndrome toxin and exfoliative toxins were not found. The DNA array facilitated rapid and reliable detection of resistance determinants and toxins under conditions used in a routine laboratory and has the potential to be used for array-based high-throughput screening.

Comparative morphologic and immunohistochemical investigation of spontaneously occurring thymomas in a colony of European hamsters

This study documents the characteristics of a large series of spontaneously occurring thymomas in a laboratory colony of European hamsters (Cricetus cricetus). Thymomas are rare organotypic neoplasms originating from the thymic epithelial compartment. Because the hamster thymomas largely resembled their human counterparts, the recent World Health Organization (WHO) classification of human thymic epithelial tumors was used. Forty hamsters of both sexes aged 3-29 months were examined macroscopically and histologically. In 22 (55%) of the 40 animals, necropsy revealed enormous whitish masses in the anterior mediastinum, with a diameter ranging from 0.5 to 4.5 cm and a lobulated structure. The anatomy of the thymus region was normal in the remaining 18 hamsters. Histologically, the tumors presented as thymuslike organoid structures with areas of medullary and cortical differentiation and a predominance of lymphoid cells. A network of epithelial cells in the cortical areas, demonstrated immunohistochemically with a cross-reactive antibody against pancytokeratin, supported the diagnosis of thymoma. Cortical lymphocytes showed positive staining with cross-reacting antibodies against CD3 and terminal deoxynucleotidyl transferase, characteristic of immature T cells. On the basis of these findings, the tumors were classified as B1 thymomas, in some cases with AB or B2 components, according to the new WHO classification for human thymic epithelial tumors.