Distribution of antibiotic resistance genes among Staphylococcus species isolated from ready-to-eat foods.

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.

All-optical frequency conversion using nonlinear dynamics of semiconductor lasers.

When a semiconductor laser is subject to optical injection, it can enter the period-one dynamics through Hopf bifurcation. Under such nonlinear dynamics, equally and oppositely frequency-shifted optical signals from the injection emerge and are utilized for frequency conversion. Only a typical semiconductor laser is required as the conversion unit, where no pump or probe laser is necessary. The frequency shift can be continuously tuned by controlling the level or frequency of the injection. A bit-error ratio down to 10(-12) is observed with no or a slight power penalty for amplitude, frequency, and phase modulation at 2.5 Gbits/s, suggesting modulation format transparency of the system. Frequency down-, no-, and upconversion can be simultaneously achieved and individually selected, increasing the flexibility and reconfigurability of the system.

Improved exact confidence intervals for the odds ratio in two independent binomial samples.

For two independent binomial samples, the usual exact confidence interval for the odds ratio based on the conditional approach can be very conservative. Recently, Agresti and Min (2002) showed that the unconditional intervals are preferable to conditional intervals with small sample sizes. We use the unconditional approach to obtain a modified interval, which has shorter length, and its coverage probability is closer to and at least the nominal confidence coefficient.