Formation of robust bound states of interacting microwave photons.

Systems of correlated particles appear in many fields of modern science and represent some of the most intractable computational problems in nature. The computational challenge in these systems arises when interactions become comparable to other energy scales, which makes the state of each particle depend on all other particles1. The lack of general solutions for the three-body problem and acceptable theory for strongly correlated electrons shows that our understanding of correlated systems fades when the particle number or the interaction strength increases. One of the hallmarks of interacting systems is the formation of multiparticle bound states2-9. Here we develop a high-fidelity parameterizable fSim gate and implement the periodic quantum circuit of the spin-½ XXZ model in a ring of 24 superconducting qubits. We study the propagation of these excitations and observe their bound nature for up to five photons. We devise a phase-sensitive method for constructing the few-body spectrum of the bound states and extract their pseudo-charge by introducing a synthetic flux. By introducing interactions between the ring and additional qubits, we observe an unexpected resilience of the bound states to integrability breaking. This finding goes against the idea that bound states in non-integrable systems are unstable when their energies overlap with the continuum spectrum. Our work provides experimental evidence for bound states of interacting photons and discovers their stability beyond the integrability limit.

Qutrit Randomized Benchmarking.

Ternary quantum processors offer significant potential computational advantages over conventional qubit technologies, leveraging the encoding and processing of quantum information in qutrits (three-level systems). To evaluate and compare the performance of such emerging quantum hardware it is essential to have robust benchmarking methods suitable for a higher-dimensional Hilbert space. We demonstrate extensions of industry standard randomized benchmarking (RB) protocols, developed and used extensively for qubits, suitable for ternary quantum logic. Using a superconducting five-qutrit processor, we find an average single-qutrit process infidelity of 3.8×10^{-3}. Through interleaved RB, we characterize a few relevant gates, and employ simultaneous RB to fully characterize crosstalk errors. Finally, we apply cycle benchmarking to a two-qutrit CSUM gate and obtain a two-qutrit process fidelity of 0.85. Our results present and demonstrate RB-based tools to characterize the performance of a qutrit processor, and a general approach to diagnose control errors in future qudit hardware.

Effect of maturity and hybrid on ruminal and intestinal digestion of corn silage in dry cows.

The aim of this study was to evaluate the effect of stage of maturity at harvest on extent of starch, neutral detergent fiber (NDF), and protein digestion, and rumen fermentation in dry cows fed whole-plant corn silage from different hybrids. Four nonlactating Holstein cows cannulated at the rumen and proximal duodenum were fed 4 corn silages differing in hybrid (flint vs. flint-dent) and maturity stage (early vs. late) in a 4 × 4 Latin square design. From early to late maturity, starch content increased (from 234.5 to 348.5 g/kg), whereas total-tract (99.7 to 94.5%) and ruminal starch digestibility (91.3 to 86.5%) decreased significantly. The decrease in ruminal starch digestibility with increasing maturity was similar between hybrids. No effects were found of maturity, hybrid, or maturity × hybrid interaction on total-tract NDF digestibility, ruminal NDF digestibility, true digestibility of N and organic matter in the rumen, or microbial synthesis. Harvesting at later maturity led to increased ruminal ammonia, total volatile fatty acid concentrations, and acetate/propionate ratio but not pH. This study concludes that delaying date of harvest modifies the proportions of digestible starch and NDF supplied to cattle. Adjusting date of corn harvest to modulate amount of rumen-digested starch could be used as a strategy to control nutrient delivery to ruminants.

Dynamics of magnetization at infinite temperature in a Heisenberg spin chain.

Understanding universal aspects of quantum dynamics is an unresolved problem in statistical mechanics. In particular, the spin dynamics of the one-dimensional Heisenberg model were conjectured as to belong to the Kardar-Parisi-Zhang (KPZ) universality class based on the scaling of the infinite-temperature spin-spin correlation function. In a chain of 46 superconducting qubits, we studied the probability distribution of the magnetization transferred across the chain's center, [Formula: see text]. The first two moments of [Formula: see text] show superdiffusive behavior, a hallmark of KPZ universality. However, the third and fourth moments ruled out the KPZ conjecture and allow for evaluating other theories. Our results highlight the importance of studying higher moments in determining dynamic universality classes and provide insights into universal behavior in quantum systems.

Antimicrobial resistance of Listeria monocytogenes strains isolated from humans in France.

Susceptibility to antibiotics of 4,816 clinical L. monocytogenes strains isolated since 1926 was studied, and the temporal evolution of susceptibility to antibiotics was analyzed through several decades. The mechanisms of resistance in each resistant strain were studied. The prevalence of resistant strains was estimated at 1.27% among isolates from humans. Resistance to tetracyclines+ and fluoroquinolones was more common and has recently emerged. Although acquired resistance in clinical L. monocytogenes did not implicate clinically relevant antibiotics, the possibility of resistance gene transfers, the description of the first clinical isolate with high-level resistance to trimethoprim, and the recent increase in penicillin MICs up to 2 microg/ml reinforce the need for microbiological surveillance.

Distribution and characterization of Listeria monocytogenes clinical isolates in Portugal, 1994-2007.

In recent years, the number of cases of listeriosis has increased worldwide. Ninety-five isolates of Listeria monocytogenes recovered from Portuguese human cases of listeriosis have been characterized by biotyping (cadmium and arsenic sensitivity), polymerase chain reaction (PCR) grouping, and by pulsed-field gel electrophoresis (PFGE) applying the enzymes AscI and ApaI. Isolates were classified into one of three PCR groups; IVb (71.6%), IIb (17.9%), and IIa (10.5%). Four biotypes were differentiated: sensitive to arsenic/cadmium (48.4%), arsenic-sensitive and cadmium-resistant (25.3%), resistant to arsenic and sensitive to cadmium (18.9%), and resistant to both heavy metals (7.4%). Combined analyses of AscI and ApaI patterns yielded a total of 58 PFGE types with five sets (G, Jb, KKa, Me, and U) of Portuguese strains, each of which were indistinguishable by PFGE typing. In the present study, it was demonstrated that there are recurrent pulsotypes and that some were the same pulsotypes linked to outbreaks in France. In addition, there are some pulsotypes spread throughout the country, while others only appear in a restricted region. This study allowed the assembly of a first large pulsotype database of Portuguese clinical strains.

[MRI evaluation of residual breast carcinoma after neoadjuvant chemotherapy]. / Cancer du sein traité par chimiothérapie néoadjuvante: évaluation du reliquat tumoral par l'IRM mammaire.

PURPOSE: This study aims to evaluate the sensibility and specificity of MRI in the detection and size measuring of residual breast cancer in patients treated with neoadjuvant chemotherapy before surgery. PATIENTS AND METHODS: This is a retrospective study of 32 women, who underwent breast MRI before and after neoadjuvant treatment. MRI has been confronted to surgical pathology results. RESULTS: The sensibility of MRI to assess pathologic Complete Response (no invasive residual tumor) was excellent (100%) but the specificity was low (55,5%). There was no false negative case and four false positive cases (Two ductal carcinomas in situ and two scars-like fibrosis). When MRI outcomes were compared with the presence or absence of invasive or in situ residual carcinoma, only one false negative case was noticed (one "in situ" residual tumor). The correlation between tumor size measured by MRI and histopathology was low (r=0,32). Underestimations of tumor size were due to non-continuous tumor regression or invasive lobular carcinoma or association of invasive carcinoma and intra ductal breast cancer. Over estimations of tumor size were due to chemotherapy-induced changes. CONCLUSION: MRI is a sensitive but poorly specific method to assess the pathological complete response after neoadjuvant chemotherapy. Estimation of tumor size and detection of isolated residual in situ carcinoma are fare. Therefore, surgical intervention remains necessary whatever the MRI outcomes.

Hepatopulmonary Syndrome and Post-Liver Transplantation Complications: A Case-Control Study.

BACKGROUND: Although liver transplantation (LT) improves survival in cirrhotic patients with hepatopulmonary syndrome (HPS), few data exist concerning post-operative complications in these patients. OBJECTIVE: To compare complications after LT between patients with and without HPS. METHODS: In a case-control study, we retrospectively analyzed all patients who underwent LT in our center from January 2010 to July 2016. We compared cases of identified HPS to controls matched for age, MELD score, comorbidities, red blood cells transfused, and highest dosage of norepinephrine perfused during transplantation. RESULTS: Among 451 transplanted patients, we identified 71 patients with HPS who could be analyzed. We found a significantly (p<0.001) higher number of post-operative complications in patients with HPS (median 5 vs 3), with more occurrence of cardiac, infectious and surgical complications than in the controls: 39.4% vs 12.7% (p<0.001), 81.7% vs 49.3% (p<0.001), and 59.2% vs 40.1% (p<0.029), respectively. There were also more ICU readmissions at 1 month among HPS patients (10 vs 1, p=0.01). There was no significant difference concerning ventilation data, lengths of ICU or hospital stay (8.5 [range 3-232] and 32 [14-276] days, respectively on the whole cohort) and death in the ICU (4.2% on the whole cohort). The 1-year survival was higher in HPS patients (94.4% vs 81.1%, p=0.034); there was no difference in 5-year survival. CONCLUSION: HPS patients seem to have a higher number of complications in the first month following LT.

Effect of increasing the proportion of chicory in forage-based diets on intake and digestion by sheep.

There is a lot of evidence that chicory could be a highly palatable and nutritious source of forage for ruminants, well adapted to climate change and dry conditions in summer, thanks to its resistance to drought and high water content. This study aimed to describe the effect of incorporating chicory to ryegrass or to a ryegrass-white clover mixture on feeding behaviour, digestive parameters, nitrogen (N) balance and methane (CH4) emissions in sheep. In total, three swards of ryegrass, white clover and chicory were established and managed in a manner ensuring the forage use at a constant vegetative stage throughout the experiment. In all, four dietary treatments (pure ryegrass; binary mixture: 50% ryegrass-50% chicory; ternary mixture: 50% ryegrass-25% white clover-25% chicory; and pure chicory) were evaluated in a 4×4 replicated Latin square design with eight young castrated Texel sheep. Each experimental period consisted of an 8-day diet adaptation phase, followed by a 6-day measuring phase during which intake dynamics, chewing activity, digestibility, rumen liquid passage rate, fermentation end-products, N balance and CH4 emissions were determined. Data were analysed using a mixed model and orthogonal contrasts were used to detect the potential associative effects between ryegrass and chicory. The daily voluntary dry matter intake was lower for pure ryegrass than for diets containing chicory (P<0.001) and increased quadratically from 1.39 to 1.74 kg/day with increasing proportion of chicory. Huge positive quadratic effects (P<0.001) between ryegrass and chicory were detected on eating time and eating rate just after feeding indicating an increase of the motivation to eat with mixtures, whereas rumination activity decreased linearly with the proportion of chicory (P<0.001). The organic matter digestibility was similar among treatments (around 80%), but a strong positive quadratic P<0.001) effect was observed on liquid passage rate suggesting that chicory allowed fast particle breakdown in the rumen. Animals fed with the ryegrass-white clover-chicory mixture had the higher urinary N losses (P<0.001), whereas retained N per day or per g N intake was greater when the proportion of chicory was at least 50% (P<0.001) being ~40% greater than for the other treatments. The CH4 yield was lower with pure chicory than with the other treatments (P<0.001) for which emissions were similar. In conclusion, mixing ryegrass and chicory in equal proportions produces a synergy on voluntary intake and an improved N use efficiency likely due to complementarity in chemical composition, increased motivation to eat and faster ruminal particle breakdown.

Standing radiological analysis with a low-dose biplanar imaging system (EOS system) of the position of the components in total hip arthroplasty using an anterior approach: a cohort study of 102 patients.

AIMS: The primary aim of this study was to analyse the position of the acetabular and femoral components in total hip arthroplasty undertaken using an anterior surgical approach. PATIENTS AND METHODS: In a prospective, single centre study, we used the EOS imaging system to analyse the position of components following THA performed via the anterior approach in 102 patients (103 hips) with a mean age of 64.7 years (sd 12.6). Images were taken with patients in the standing position, allowing measurement of both anatomical and functional anteversion of the acetabular component. RESULTS: The mean inclination of the acetabular component was 39° (standard deviation (sd) 6), the mean anatomical anteversion was 30° (sd 10), and the mean functional anteversion was 31° (sd 8) five days after surgery. The mean anteversion of the femoral component was 20° (sd 11). Anatomical and functional anteversion of the acetabular component differed by > 10° in 23 (22%) cases. Pelvic tilt was the only pre-operative predictive factor of this difference. CONCLUSION: Our study showed that anteversion of the acetabular component following THA using the anterior approach was greater than the recommended target value, and that substantial differences were observed in some patients when measured using two different measurement planes. If these results are confirmed by further studies, and considering that the anterior approach is intended to limit the incidence of dislocation, a new correlation study for each reference plane (anatomical and functional) will be necessary to define a 'safe zone' for use with the anterior approach. TAKE HOME MESSAGE: EOS imaging system is helpful in the pre-operative and post-operative radiological analysis of total hip arthroplasty.

Frequent moving of grazing dairy cows to new paddocks increases the variability of milk fatty acid composition.

The aim of this work was to investigate the variations of milk fatty acid (FA) composition because of changing paddocks in two different rotational grazing systems. A total of nine Holstein and nine Montbéliarde cows were divided into two equivalent groups according to milk yield, fat and protein contents and calving date, and were allocated to the following two grazing systems: a long duration (LD; 17 days) of paddock utilisation on a heterogeneous pasture and a medium duration (MD) of paddock utilisation (7 to 10 days) on a more intensively managed pasture. The MD cows were supplemented with 4 kg of concentrate/cow per day. Grazing selection was characterised through direct observations and simulated bites, collected at the beginning and at the end of the utilisation of two subsequent MD paddocks, and at the same dates for the LD system. Individual milks were sampled the first 3 days and the last 2 days of grazing on each MD paddock, and simultaneously also for the LD system. Changes in milk FA composition at the beginning of each paddock utilisation were highly affected by the herbage characteristics. Abrupt changes in MD milk FA composition were observed 1 day after the cows were moved to a new paddock. The MD cows grazed by layers from the bottom layers of the previous paddock to the top layers of the subsequent new paddock, resulting in bites with high organic matter digestibility (OMD) value and CP content and a low fibre content at the beginning of each paddock utilisation. These changes could induce significant day-to-day variations of the milk FA composition. The milk fat proportions of 16:0, saturated FA and branched-chain FA decreased, whereas proportions of de novo-synthesised FA, 18:0, c9-18:1 and 18:2n-6 increased at paddock change. During LD plot utilisation, the heterogeneity of the vegetation allowed the cows to select vegetative patches with higher proportion of leaves, CP content, OMD value and the lowest fibre content. These small changes in CP, NDF and ADF contents of LD herbage and in OMD values, from the beginning to the end of the experiment, could minimally modify the ruminal ecosystem, production of precursors of de novo-synthesised FA and ruminal biohydrogenation, and could induce only small day-to-day variations in the milk FA composition.

Transient expression assays with the proximal promoter of a newly characterized actin gene from the oyster Crassostrea gigas.

We undertook the characterization of an actin gene and its proximal promoter in the oyster Crassostrea gigas. A complete actin cDNA was identified, sequenced and its amino acid sequence deduced. Comparative analysis showed a high homology with actin of other species and that this gene is closer to the cytoplasmic form of actins than to the muscle type. A probe derived from the 5'-untranslated region of the cDNA was then used to isolate the actin gene from a genomic library. The gene was sequenced and shown to contain a single 643 bp intron. A 1670 bp fragment upstream from the open reading frame was isolated and sequenced. This upstream region displays typical features of actins such as a serum response element (CarG box). This fragment was cloned into the promoterless vector pGL3-basic and the resulting construct was transfected into cells of dissociated oyster heart primary cultures. Its capacity to express the luciferase in this in vitro homologous system was monitored and showed high expression levels. This is the first complete actin sequence reported so far for the oyster C. gigas and its promoter is the first available among bivalves.

Usefulness of three probes in typing isolates of methicillin-resistant Staphylococcus aureus (MRSA).

Fifty-nine epidemiologically unrelated methicillin-resistant Staphylococcus aureus (MRSA) isolates from different geographical areas and 23 phage-type 77 MRSA isolates from France were investigated. Cellular DNA, digested with restriction endonucleases EcoRI or HindIII, was probed with plasmids carrying the gene encoding 16S rRNA (pBA2), the gene aacA-aphD (pSF815A) and the gene aacA-aphD plus part of IS256 (pIP1307). When probed with pBA2, most of the unrelated isolates displayed the same hybridisation pattern. A greater diversity in patterns was detected in gentamicin-resistant strains with the two other probes. The most accurate fingerprinting of these isolates was obtained with the probe pIP1307. Moreover, this probe appeared to be useful for tracing the phage-type 77 epidemic MRSA isolates widespread in French hospitals.

Epidemiological study of Staphylococcus aureus resistance to new quinolones in a university hospital.

During a 14-month period, from December 1984 to February 1986, 630 Staphylococcus aureus isolates were identified at Broussais Hospital. Thirty-eight isolates (6%), from 35 patients, were found to be pefloxacin-resistant S. aureus (PRSA) with minimal inhibitory concentrations greater than or equal to 8 mg l-1. PRSA isolates were tested for susceptibility to 35 antibiotics, including nine quinolones, and heavy metal ions. Phage-type was determined. Out of the 38 PRSA isolates, 35 (92%) were methicillin- and multiply-resistant; however, all PRSA isolates were sensitive to vancomycin and coumermycin. Fifteen isolates (39%) had similar phage-type and identical antibiotic susceptibility pattern with high level resistance to pefloxacin (MICs equal to 64 mg l-1); they were isolated from the same surgical unit. The 23 remaining PRSA isolates differed by their phage and susceptibility patterns. Pefloxacin MICs ranged from 8 to 512 mg l-1 with a bimodal distribution; cross-resistance was observed with the eight other quinolones tested. Only nine PRSA isolates (24%), including four 'epidemic' isolates, were obtained from patients who had been treated with quinolones. From these data there is apparently no direct relationship between quinolone administration and selection of PRSA in infected patients.

In Vitro Activity of the Limulus Antimicrobial Peptide Tachyplesin I on Marine Bivalve Pathogens

Tachyplesin 1 is an antimicrobial peptide extracted from hemocytes of the Japanese horseshoe crab Tachypleus tridentatus. We studied the in vitro activity of tachyplesin I against bivalve pathogens: the oyster parasites Bonamia ostreae, the intrahemocytic parasite of the flat oyster Ostrea edulis and Perkinsus marinus, the histozoic parasite of the Eastern oyster Crassostrea virginica, and the bacterium Vibrio P1, pathogenic for the clam Tapes philippinarum. Viability of the protozoans was assessed microscopically by the uptake of the vital dyes acridine orange and ethidium bromide. Following exposure to tachyplesin I, B. ostreae and P. marinus viabilities were reduced in a dose-dependent manner, up to, respectively, 94 and 62% within a 500 µg/ml peptide concentration. The fine structure of P. marinus was highly altered by the peptide. Tachyplesin I also displayed a potent activity against marine vibrios, with a MIC of 0.4-0.8 µg/ml against Vibrio P1. We examined the morphology of oyster hemocytes treated by tachyplesin I, together with the cell functional capabilities to produce chemiluminescence. No effect of the peptide was found on bivalve host cells. As transgenic technology is currently being applied to marine invertebrates, these results indicate that tachyplesin I may provide effective gene sequences to be manipulated in order to produce disease-resistant bivalves.

Effects of condensed tannins in wrapped silage bales of sainfoin (Onobrychis viciifolia) on in vivo and in situ digestion in sheep.

The objective of this study was to characterize the condensed tannins (CTs) in wrapped silage bales of sainfoin (Onobrychis viciifolia) and examine their potential action on in vivo and in situ digestive characteristics in sheep. Silage was made from sainfoin, cut at two phenological stages. The first phenological stage, at which silage was made, was from the first vegetation cycle at the end of flowering and the second stage silage was made from regrowth, 5 weeks after the first cut, but before flowering. The silages made from the two phenological stages were fed to 12 rumen-fistulated sheep in a crossover design. Of the 12 sheep, six received polyethylene glycol (PEG) to bind with and remove the effects of CT, whereas the other six were dosed with water. Organic matter digestibility, total-tract N digestibility and N (N) balance were measured over 6 days. Kinetic studies were performed on total N, ammonia N (NH3-N) and volatile fatty acids (VFAs) in rumen fluid before and 1.5, 3 and 6 h after feeding. The kinetics of degradation of dry matter and N from Dacron bags suspended in the rumen were also determined. Biological activity of CT (protein-binding capacity) and CT concentration were greater for the silage made from sainfoin at the early flowering stage. Total-tract N digestibility was increased by the addition of PEG (P < 0.001) to the sainfoin silage before flowering (P < 0.001). CTs decreased N excretion in urine (P < 0.05) and increased faecal N excretion (P < 0.001), but had no effect on body N retention, which is beneficial for the animal. Ruminal N degradability was smaller in the presence of active CT (P < 0.001) at both phenological stages; however, soluble N (P = 0.2060) and NH3-N (P = 0.5225) concentrations in rumen fluid remained unchanged. The results of this experiment indicate that CT in the sainfoin retain their ability to affect the nutritive value of preserved forage legumes.

Occurrence of associative effects between grasses and legumes in binary mixtures on in vitro rumen fermentation characteristics.

When animals are fed a grass and legume mixture, digestive interactions can occur in the rumen between the substrates contained in the different plants, and the response of the animal to the combination of forages can differ from the balanced median values of their components considered individually. Our objective was to assess the associative effects between temperate forages in 8 grass-legume binary combinations on in vitro rumen fermentation characteristics to highlight synergies or antagonisms in terms of nutritional and environmental impacts. Two grasses (cocksfoot, CF; ryegrass, RG) and 4 legume species (alfalfa, A; white clover, WC; red clover, RC; sainfoin, SAN) were incubated alone and in grass-legume mixture (1:1, wt/wt) in batches containing buffered rumen fluid during 3.5 and 24 h. For each substrate and each incubation time, parameters describing the degradation of the energetic and nitrogenous compounds and their partition into fermentation end products were measured. Data were subjected to ANOVA using a mixed procedure to test quadratic contrasts. At 3.5 h of incubation, many quadratic effects were observed. The presence of A, WC, or RC in mixtures quadratically increased the NH(3)-N production (up to +28% when compared with the calculated value, P < 0.001), whereas the presence of condensed tannin (CT) activity in SAN considerably decreased it (up to -67%, quadratic effect, P < 0.001) and the N disappearance. To a lesser extent, the presence of SAN reduced the proportion of methane in the gas produced (up to 7%, quadratic effect, P = 0.018). Generally, the degradation of OM and NDF was not stimulated by mixing grass and legume, except for SAN. However, the presence of SAN severely impaired the NDF digestion at the early phase of fermentation. At 24 h of incubation, few associative effects were observed in comparison with those observed at 3.5 h of incubation, but the effect of CT of SAN on N metabolism was still clearly present. This study shows that, among the grass-legume mixtures tested in vitro, only the presence of SAN can interact with the grasses to reduce the degradation of proteins and the production of methane but with a transitory negative effect on fiber digestion.

Contribution of a typing method based on IS256 probing of SmaI-digested cellular DNA to discrimination of European phage type 77 methicillin-resistant Staphylococcus aureus strains.

The incidence of infections with phage type 77 methicillin-resistant Staphylococcus aureus (MRSA) strains increased in France in 1987. These strains are widespread in numerous European hospitals. The SmaI restriction profiles of total DNA extracted from 74 phage type 77 MRSA strains isolated from 1987 to 1994 in 10 hospitals in eight European cities (in France, Belgium, and Spain) were analyzed. Hybridization with a probe containing a 468-bp DNA fragment from within the transposase gene of the insertion sequence IS256 was also examined. Forty-three SmaI profiles were detected. Twenty major genotypes were identified, and each genotype contained strains with the same profile or profiles which differed by no more than three bands. Strains isolated in different countries and at several-year intervals were often grouped within the same genotype. A larger number of genotypes could be discriminated by analysis of the patterns of hybridization with the IS256 probe. SmaI restriction fragments with the same apparent electrophoretic mobility could, in some cases, be distinguished by the presence or the absence of nucleotide sequences hybridizing with IS256. The strains that grouped within the same genotype after hybridization with IS256 were mostly those isolated in the same hospital and at less than 12-month intervals. Consequently, the IS256 probe that we used improved restriction profile analysis for discrimination between the intrahospital, outbreak-related phage type 77 MRSA strains and the endemic strains disseminated in various cities and countries.

Distribution of genes encoding resistance to streptogramin A and related compounds among staphylococci resistant to these antibiotics.

The levels of resistance to pristinamycin (Pt) and to its major constituents, pristinamycin IIA and IB (PIIA and PIB, respectively; classified as streptogramins A and B, respectively) were determined for 126 staphylococcal isolates. The results suggest tentative susceptibility breakpoints of < or = 2, < or = 8, and < or = 0.5 microgram/ml for PIIA, PIB, and Pt, respectively. Fifty-six isolates that were inhibited by > or = 4 micrograms of PIIA per ml were investigated for the presence of staphylococcal genes encoding resistance to PIIA (vga, vat, and vatB) and PIB (vgb). None of these genes was found in the 4 isolates inhibited by 4 micrograms of PIIA per ml or in 4 of the other 52 isolates tested. The remaining 48 isolates harbored plasmids carrying vatB and vga or combinations of genes (vga-vat-vgb or vga-vat). The absence of any known PIIA resistance gene from the four Staphylococcus aureus isolates inhibited by > or = 8 micrograms of PIIA per ml suggests that there is at least one PIIA resistance mechanism in staphylococci that has not yet been characterized.

The value of rRNA gene restriction site polymorphism analysis for delineating taxa in the genus Staphylococcus.

A total of 101 staphylococcal strains were ribotyped using EcoRI and HindIII as restriction enzymes and plasmid pBA2 as the rDNA probe. Isolates from 10 newly described staphylococcal taxa were among those examined. All the ribotypes were added to our database, Staph DB, which now contains the sizes of the bands of 135 EcoRI and 120 HindIII ribotypes from 408 strains belonging to 42 staphylococcal taxa. The relatedness of ribotypes was evaluated by using the Dice coefficient. The ribotypes, and thus the strains, were clustered by the unweighted pair group method with averages (UPGMA). Separation into clusters correlated well with the delineation of the staphylococcal species but not with that of the different subspecies. No discrimination was possible between Staphylococcus vitulinus and Staphylococcus pulvereri. Ecovar-specific groups were evident within Staphylococcus intermedius and Staphylococcus hyicus. The data increase the usefulness of rRNA gene restriction site polymorphism analysis for staphylococcal taxonomy.