A simple and reliable method using a polymerase chain reaction (PCR) was devised to identify methicillinresistant staphylococci. By using lysates of the strain to be tested as templates and 22-mer oligonucleotides as primers, a 533-bp region of mecA, the structural gene of a low-affinity penicillin-binding protein (PBP 2'), was amplified by PCR and detected by agarose gel electrophoresis. Results obtained by this method were compared with those obtained by broth microdilution MIC determination for 210 and 100 clinical isolates of Staphylococcus aureus and coagulase-negative staphylococci, respectively. Of 99 mecA-negative S. aureus isolates, 100% of the strains were methicillin susceptible and 98% of the strains were oxacillin susceptible. Three strains (3%) of 111 mecA-positive S. aureus isolates exhibited almost the same susceptibility to ,(-lactams as the mecA-negative ones and did not produce detectable amounts of PBP 2' despite the presence of the mecA gene. One of them yielded typically methicillin-resistant variants at a low frequency with concomitant recovery of PBP 2' production. The mecA gene was also found in coagulase-negative Staphylococcus epidermidis, Staphylococcus haemolyticus, Staphylococcus sciuri, Staphylococcus saprophyticus, and Staphylococcus caprae and conferred resistance on most of the bacteria. * Corresponding author. species were identified by Staphyogram (Terumo, Tokyo, Japan), an identification kit, and the coagulase test. S. aureus SR3626, SR3633, SR3636, SR3639, SR3665, SR3681, and SR3716 were used as mecA-positive control organisms (12), and S. aureus ATCC 25923, 209P JC-1, and Smith were used as mecA-negative control organisms.

The structure of silicene fabricated on a Ag(111) surface was determined using reflection high-energy positron diffraction with a linac-based brightness-enhanced intense positron beam. From the rocking curve analysis, the silicene was verified to have a buckled structure with a spacing of 0.83Å between the top and the bottom Si layers. The distance between the bottom Si layer in the silicene and the first Ag layer was determined to be 2.14Å. These results agree with the theoretically predicted values from a previous study [Phys. Rev. Lett. 108, 155501 (2012)] within an error of ±0.05Å.

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Photodetachment of the positronium negative ion, a bound state of one positron and two electrons, has been observed. Development of a method to produce the ions efficiently using a Na coated tungsten surface has enabled the first observation of the photodetachment. The obtained lower limit of the photodetachment cross section for the wavelength of 1064 nm is consistent with the theoretical calculations reported so far. The experimental field developed in the present work gives new opportunities to explore the quantum mechanical three-body problem and to develop energy-tunable positronium beams.

The atomic configuration and electronic band structure of Pt-induced nanowires on a Ge(001) surface are investigated using scanning tunneling microscopy, reflection high-energy positron diffraction, and angle-resolved photoemission spectroscopy. A previously proposed theoretical model, composed of Ge dimers on the top layer and buried Pt arrays in the second and fourth layers [Vanpoucke et al., Phys. Rev. B 77, 241308(R) (2008)], is found to be the fundamental structure of the observed nanowires. At low temperatures (T < 80 K), each Ge dimer is alternately tilted in the surface normal direction (asymmetric), causing a p(4 × 4) periodicity. At high temperatures (T > 110 K), each Ge dimer is flat with respect to the horizontal axis (symmetric), giving rise to p(4 × 2) periodicity. Upon the above phase transition, the electronic band dispersion related to the Ge dimers in the deeper energy region shifts to the Fermi level.