Ten outbreaks of a new serogroup C meningococcal disease emerged during 2003-2005 in China. The multilocus sequence typing results indicated that unique sequence type 4821 clone meningococci were responsible for these outbreaks. Herein, we determined the entire genomic DNA sequence of serogroup C isolate 053442, which belongs to ST-4821. Comparison of 053442 gene contents with other meningococcal genomes shows that they have similar characteristics, including thousands of repetitive elements and simple sequence repeats, numerous phase-variable genes, and similar virulence-related factors. However, many strain-specific regions were found in each genome. We also present the results of a genomic comparison of 28 ST-4821 complex isolates that were isolated from different serogroups using comparative genomic hybridization analysis. Genome comparison between the newly emerged hyperinvasive isolates belonging to different serogroups will further our understanding of their respective pathogenetic mechanisms.

Let X be an arbitrary continuous random variable and Z be an independent Gaussian random variable with zero mean and unit variance. For t > 0, Costa proved that e 2h(X+ √ tZ) is concave in t, where the proof hinged on the first and second order derivatives of h(X + √ tZ). Specifically, these two derivatives are signed, i.e., ∂ ∂t h(X +

The pH response of Shigella flexneri 2a 301 was identified by gene expression profiling. Gene expression profiles of cells grown in pH 4.5 or 8.6 were compared with the profiles of cells grown at pH 7.0. Differential expression was observed for 307 genes: 97 were acid up-regulated, 102 were acid down-regulated, 91 were base up-regulated, and 86 were base down-regulated. Twenty-seven genes were found to be both acid and base up-regulated, and 29 genes were both acid and base down-regulated. This study showed that (1) the most pH-dependent genes regulate energy metabolism; (2) the RpoS-dependent acid-resistance system is induced, while the glutamate-dependent acid resistance system is not; (3) high pH up-regulates some virulence genes, while low pH down-regulates them, consistent with Shigella infection of the low gut; and (4) several cross-stress response genes are induced by pH changes. These results also illustrate that many unknown genes are significantly regulated under acid or basic conditions, providing researchers with important information to characterize their function.

Consider a communication network represented by a directed graph G = (V, E), where V is the set of nodes and E is the set of point-to-point channels in the network. On the network a secure message M is transmitted, and there may exist wiretappers who want to obtain information about the message. In secure network coding, we aim to find a network code which can protect the message against the wiretapper whose power is constrained. Cai and Yeung [5] studied the model in which the wiretapper can access any one but not more than one set of channels, called a wiretap set, out of a collection A of all possible wiretap sets. In order to protect the message, the message needs to be mixed with a random key K. They proved tight fundamental performance bounds when A consists of all subsets of E of a fixed size r. However, beyond this special case, obtaining such bounds is much more difficult. In this paper, we investigate the problem when A consists of arbitrary subsets of E and obtain the following results: 1) an upper bound on H(M ); 2) a lower bound on H(K) in terms of H(M ). The upper bound on H(M ) is explicit, while the lower bound on H(K) can be computed in polynomial time when |A| is fixed. The tightness of the lower bound for the pointto-point communication system is also proved. through a number of point-to-point channels. It is assumed that the wiretapper can access any one but not more than one set of channels, called a wiretap set, out of a collection A of all possible wiretap sets, where A is specified by the problem under consideration. For example, A could be the collection of all wiretap sets each containing a single channel. In this case, the wiretapper can access any one but not more than one channel. The strategy to protect the private message is the same as that in classical information-theoretic cryptography. Specifically, the private message and the random key are combined by means of a coding scheme, so that a wiretapper observes some mixtures of the message and the key, where these mixtures are statistically independent of the message. On the other hand, the receiver node can decode the message from the information received on all the channels. Note that in secret sharing and its subsequent generalizations, it is assumed that the key is available only to the transmitter and transmission in all the channels is noiseless.Cai and Yeung [5] generalized secret sharing to secure network coding, in which a private message is sent to possibly more than one receiver through a network of point-to-point channels. The model they studied, which we refer to as the wiretap network (see also El Rouayheb and Soljanin [6]), is described as follows. In this model, the assumptions about the wiretapper and the strategy to protect the private message are the same as in the wiretap channel II. The significant difference is that there exist intermediate nodes in the network that can encode, and there may be more than one receiver node. The solution is that we send both the private message and the key via a network coding s...