Dept of Natural Sciences and Mathematics

For 2 ≤ k < n, we define the k-averaging dynamic process in which solutions to k-player bankruptcy problems are used iteratively and averaged to arrive at an n-player allocation. For consistent bankruptcy rules, we prove that the n-player solution is the unique attractive fixed point of this dynamic process by adapting results from Dagan and Volij . We provide alternate proofs that the fixed point is attractive for the Proportional rule (based on Markov chains) and the TAL rules (for k = 2). For the latter, we consider when the convergence is finite or asymptotic. For comparison, we demonstrate that an n-player solution for an inconsistent rule is not necessarily a fixed point of the dynamic process. We discuss generalizations of the dynamic process in which the averaging occurs over alternate network topologies.

Seasonal shifts in host use by mosquitoes from birds to mammals drive the timing and intensity of annual epidemics of mosquito-borne viruses, such as West Nile virus, in North America. The biological mechanism underlying these shifts has been a matter of debate, with hypotheses falling into two camps: (1) the shift is driven by changes in host abundance, or (2) the shift is driven by seasonal changes in the foraging behavior of mosquitoes. Here we explored the idea that seasonal changes in host use by mosquitoes are driven by temporal patterns of host reproduction. We investigated the relationship between seasonal patterns of host use by mosquitoes and host reproductive phenology by examining a seven-year dataset of blood meal identifications from a site in Tuskegee National Forest, Alabama USA and data on reproduction from the most commonly utilized endothermic (white-tailed deer, great blue heron, yellow-crowned night heron) and ectothermic (frogs) hosts. Our analysis revealed that feeding on each host peaked during periods of reproductive activity. Specifically, mosquitoes utilized herons in the spring and early summer, during periods of peak nest occupancy, whereas deer were fed upon most during the late summer and fall, the period corresponding to the peak in births for deer. For frogs, however, feeding on early-and lateseason breeders paralleled peaks in male vocalization. We demonstrate for the first time that seasonal patterns of host use by mosquitoes track the reproductive phenology of the hosts. Peaks in relative mosquito feeding on each host during reproductive phases are likely the result of increased tolerance and decreased vigilance to attacking mosquitoes by nestlings and brooding adults (avian hosts), quiescent young (avian and mammalian hosts), and mate-seeking males (frogs).

Speeding up sequential programs on multicores is a challenging problem that is in urgent need of a solution. Automatic parallelization of irregular pointer-intensive codes, exemplified by the SPECint codes, is a very hard problem. This paper shows that, with a helping hand, such auto-parallelization is possible and fruitful.

Understanding the data structures in a program is crucial to understanding how the program works, or why it doesn't work. Inspecting the code that implements the data structures, however, is an arduous task and often fails to yield insights into the global organization of a program's data. Inspecting the actual contents of the heap solves these problems but presents a significant challenge of its own: finding an effective way to present the enormous number of objects it contains.

Squamates (lizards and snakes) have independently evolved viviparity over 100 times, and exhibit a wide range of maternal investment in developing embryos from the extremes of lecithotrophic oviparity to matrotrophic viviparity. This group therefore provides excellent comparative opportunities for studying endocrine and immune involvement during pregnancy, and their possible interactions. We studied the cottonmouth (Agkistrodon piscivorus), since they exhibit limited placentation (e.g., ovoviviparity), allowing comparison with squamate species hypothesized to require considerable maternal immune modulation due to the presence of a more extensive placental connection. Furthermore, the cottonmouth's biennial reproductive cycle provides an opportunity for simultaneously comparing pregnant and nonpregnant females in the wild. We document significantly elevated concentrations of progesterone (P4) and significantly lower concentrations of estradiol (E2) in pregnant females relative to non-pregnant females. Pregnant females had lower plasma bacteria lysis capacity relative to non-pregnant females. This functional measure of innate immunity is a proxy for complement performance, and we also determined significant correlations between P4 and decreased complement performance in pregnant females. These findings are consistent with studies that have determined P4's role in complement modulation during pregnancy in mammals, and thus this study joins a growing number of studies that have demonstrated convergent and/or conserved physiological mechanisms regulating viviparous reproduction in vertebrates.

In recent years several new staphylococcal enterotoxins (SEs) have been described, which currently have largely unknown frequencies of occurrence and roles in human or animal disease. One hundred and ninety-one Staphylococcus aureus isolates from cows (99), goats (39), sheep (23), rabbits (15), chickens (15) and a cat (1) were screened for SE genes sea–see, seg–seo and seq and for the tst gene encoding staphylococcal toxic shock syndrome toxin-1 using multiplex PCRs and individual PCRs for the seb and sek genes. One hundred and ten isolates tested positive for at least one of these 16 superantigen (SAg)-encoding genes. There were statistically significant differences in the frequencies of some of these SAg genes between isolates from different animals. No strain possessed either the sea or see gene. The sec gene was present in 51 isolates, the sed gene in eight and the seb gene in one. The seh gene was found in four strains and the sek and seq genes together in one isolate. The most...

In a recent landmark trial of bacteremia caused by methicillin-resistant Staphylococcus aureus (MRSA) isolates, vancomycin MICs were ≥1 μg/ml for only 16% of the isolates, and accessory gene regulator ( agr ) function as measured by delta-hemolysin activity was absent or reduced in only 28.1% of the isolates. This clinical study did not capture a population of MRSA isolates predictive of vancomycin treatment failure.

Since the year 2000, linezolid has been used in the United States to treat infections caused by antimicrobial-resistant Gram-positive cocci. At present, linezolid-resistant (Lin r ) Staphylococcus aureus and Staphylococcus epidermidis strains are rare and the diversity of their genetic backgrounds is unknown. We performed sequence-based strain typing and resistance gene characterization of 46 Lin r isolates that were collected from local and national sources between the years 2004 and 2007. Resistance was found to occur in at least three clonal complexes (CCs; lineages) of S. aureus and in at least four subclusters of a predominant, phylogenetically unstable CC of S. epidermidis . New candidate resistance mutations in 23S rRNA and the L4 riboprotein were identified among the S. epidermidis isolates. These findings suggest that linezolid resistance has emerged independently in multiple clones of S. aureus and with a variety of ribosomal mutations in multiple clones of S. epidermidis .

A novel composite transposon (Tn 6072 ) resembling staphylococcal cassette chromosome mercury (SCC Hg ) was identified in a collection of sequence type (ST) 239 methicillin (meticillin)-resistant Staphylococcus aureus (MRSA) isolates from Romanian hospitals. Tn 6072 is homologous to the 5′ region of SCC Hg found in staphylococcal cassette chromosome mec (SCC mec ) type III prototype strain 85/2082 but lacks the characteristic mer operon. SCC Hg has previously been reported to integrate downstream of orfX , at the same chromosomal location as SCC mec . Tn 6072 , by contrast, is demarcated by two IS 431 elements, flanked by 8-bp direct repeats, and inserted upstream of the origin of replication, within an open reading frame homologous to SAR2700 of S. aureus strain MRSA252. Analysis of a geographically and temporally diverse collection of 111 strains from the ST239 clonal group uncovered 11 additional strains harboring Tn 6072 , demonstrating a lineage-specific insertion pattern. Comp...

Phenotypic biotyping has traditionally been used to differentiate bacteria occupying distinct ecological niches such as host species. For example, the capacity of Staphylococcus aureus from sheep to coagulate ruminant plasma, reported over 60 years ago, led to the description of small ruminant and bovine S. aureus ecovars. The great majority of small ruminant isolates are represented by a single, widespread clonal complex (CC133) of S. aureus, but its evolutionary origin and the molecular basis for its host tropism remain unknown. Here, we provide evidence that the CC133 clone evolved as the result of a human to ruminant host jump followed by adaptive genome diversification. Comparative whole-genome sequencing revealed molecular evidence for host adaptation including gene decay and diversification of proteins involved in hostpathogen interactions. Importantly, several novel mobile genetic elements encoding virulence proteins with attenuated or enhanced activity in ruminants were widely distributed in CC133 isolates, suggesting a key role in its host-specific interactions. To investigate this further, we examined the activity of a novel staphylococcal pathogenicity island (SaPIov2) found in the great majority of CC133 isolates which encodes a variant of the chromosomally encoded von Willebrandbinding protein (vWbp Sov2), previously demonstrated to have coagulase activity for human plasma. Remarkably, we discovered that SaPIov2 confers the ability to coagulate ruminant plasma suggesting an important role in ruminant disease pathogenesis and revealing the origin of a defining phenotype of the classical S. aureus biotyping scheme. Taken together, these data provide broad new insights into the origin and molecular basis of S. aureus ruminant host specificity.

Staphylococcal chromosomal cassette mec (SCCmec) is a mobile genetic element that carries resistance genes for beta-lactam antibiotics. Coagulase-negative staphylococci, such as S. epidermidis, are thought to be a reservoir of diverse SCCmec elements that can spread to the most virulent staphylococcal species, S. aureus, but very little is known about the extent of crossspecies spread of these elements in natural populations or their dynamics in different species. We addressed these questions by using a sample of 86 S. aureus and S. epidermidis isolates with SCCmec type IV that were collected from a single hospital over a period of six months. To subtype SCCmec IV, we used multiplex PCR to detect structural variations and we used sequences from a fragment of the ccrB gene and from the dru repeats to detect additional variations. Multiplex PCR had significantly lower typeability than ccrB:dru sequencing, due to more nontypeable isolates among S. epidermidis. No statistically significant differences in diversity were detected by subtyping method or species. Interestingly, while only 4 of 24 subtypes (17%) were shared between species, these so-called shared subtypes represented 58 of 86 isolates (67%). The shared subtypes differed significantly between species in their frequencies. The shared subtypes were also significantly more concordant with genetic backgrounds in S. aureus than in S. epidermidis. Moreover, the shared subtypes had significantly higher minimum inhibitory concentrations to oxacillin in S. aureus than in S. epidermidis. This study has identified particular SCCmec IV subtypes with an important role in spreading beta-lactam resistance between species, and has further revealed some species differences in their abundance, linkage to genetic background, and antibiotic resistance level.

Background: At a time when the molecular epidemiology of methicillin-resistant Staphylococcus aureus (MRSA) was changing, we sought to characterize several genotypic markers and glycopeptide susceptibility features of clinical isolates from patients with bacteraemia. Methods: One hundred and sixty-eight MRSA bloodstream isolates obtained from three multicentre clinical trials were microbiologically and genotypically characterized. Results: All isolates were susceptible to vancomycin (MIC 2 mg/L); 38% belonged to accessory gene regulator (agr) group I, 52% belonged to group II and 10% belonged to group III. Typing of the staphylococcal cassette chromosome mec (SCCmec) showed that 67% were type II and 33% were type IV. The agr group II polymorphism was associated with SCCmec II (P < 0.001). Fifty-three percent of SCCmec II and 27% of SCCmec IV isolates had vancomycin MICs 1 mg/L (P 50.001). One hundred percent of agr II strains were predicted to be members of clonal complex 5. SCCmec II was the genetic marker most predictive of vancomycin MICs of 1 mg/L. SCCmec IV isolates were more likely to have vancomycin MICs 0.5 mg/L. Conclusions: Given that SCCmec IV is a marker for a community-based organism for which less prior vancomycin exposure is predicted, we conclude that prior antibiotic exposure in agr group II organisms may account for their increased vancomycin MICs.

Production of icaADBC -encoded polysaccharide intercellular adhesin, or poly- N -acetylglucosamine (PIA/PNAG), represents an important biofilm mechanism in staphylococci. We previously described a glucose-induced, ica -independent biofilm mechanism in four methicillin-resistant Staphylococcus aureus (MRSA) isolates. Here, biofilm regulation by NaCl and glucose was characterized in 114 MRSA and 98 methicillin-sensitive S. aureus (MSSA) isolates from diagnosed device-related infections. NaCl-induced biofilm development was significantly more prevalent among MSSA than MRSA isolates, and this association was independent of the isolate&#39;s genetic background as assessed by spa sequence typing. Among MSSA isolates, PIA/PNAG production correlated with biofilm development in NaCl, whereas in MRSA isolates grown in NaCl or glucose, PIA/PNAG production was not detected even though icaADBC was transcribed and regulated. Glucose-induced biofilm in MRSA was ica independent and apparently media...