357 research outputs found
Recommendations for approaches to meticillin-resistant staphylococcal infections of small animals: diagnosis, therapeutic considerations and preventative measures
Comparative host specificity of human- and pig- associated Staphylococcus aureus clonal lineages.
Bacterial adhesion is a crucial step in colonization of the skin. In this study, we investigated the differential adherence to human and pig corneocytes of six Staphylococcus aureus strains belonging to three human-associated [ST8 (CC8), ST22 (CC22) and ST36(CC30)] and two pig-associated [ST398 (CC398) and ST433(CC30)] clonal lineages, and their colonization potential in the pig host was assessed by in vivo competition experiments. Corneocytes were collected from 11 humans and 21 pigs using D-squame® adhesive discs, and bacterial adherence to corneocytes was quantified by a standardized light microscopy assay. A previously described porcine colonization model was used to assess the potential of the six strains to colonize the pig host. Three pregnant, S. aureus-free sows were inoculated intravaginally shortly before farrowing with different strain mixes [mix 1) human and porcine ST398; mix 2) human ST36 and porcine ST433; and mix 3) human ST8, ST22, ST36 and porcine ST398] and the ability of individual strains to colonize the nasal cavity of newborn piglets was evaluated for 28 days after birth by strain-specific antibiotic selective culture. In the corneocyte assay, the pig-associated ST433 strain and the human-associated ST22 and ST36 strains showed significantly greater adhesion to porcine and human corneocytes, respectively (p<0.0001). In contrast, ST8 and ST398 did not display preferential host binding patterns. In the in vivo competition experiment, ST8 was a better colonizer compared to ST22, ST36, and ST433 prevailed over ST36 in colonizing the newborn piglets. These results are partly in agreement with previous genetic and epidemiological studies indicating the host specificity of ST22, ST36 and ST433 and the broad-host range of ST398. However, our in vitro and in vivo experiments revealed an unexpected ability of ST8 to adhere to porcine corneocytes and persist in the nasal cavity of pigs
Susceptibility in vitro of canine methicillin-resistant and -susceptible staphylococcal isolates to fusidic acid, chlorhexidine and miconazole: opportunities for topical therapy of canine superficial pyoderma
OBJECTIVES: Increasing multidrug resistance amongst canine pathogenic staphylococci has renewed interest in topical antibacterial therapy for skin infections in the context of responsible veterinary prescribing. We therefore determined the activity in vitro of three clinically relevant topical agents and synergism between two of them against Staphylococcus pseudintermedius and Staphylococcus aureus. METHODS: The MICs of fusidic acid (n = 199), chlorhexidine (n = 198), miconazole (n = 198) and a 1:1 combination of miconazole/chlorhexidine (n = 198) were determined for canine isolates [50 MRSA and 49 methicillin-resistant S. pseudintermedius (MRSP), 50 MSSA and 50 methicillin-susceptible S. pseudintermedius (MSSP)] collected from the UK and Germany using an agar dilution method (CLSI VET01-A4). Fractional inhibitory concentration (FIC) indices were calculated to assess the interaction of miconazole with chlorhexidine. RESULTS: MICs of each drug/combination were significantly (P < 0.0005) higher for S. aureus when compared with S. pseudintermedius. Most strains (n = 172) had an MIC of fusidic acid of ≤0.03 mg/L (MIC ≥64 mg/L, n = 5 MRSA). All strains had MICs of chlorhexidine of 0.5–4 mg/L, except for one MRSA (MIC = 8 mg/L). All but four strains had MICs of miconazole of 1–4 mg/L (MIC = 16 mg/L, n = 3; MIC = 256 mg/L, n = 1). Miconazole/chlorhexidine (1:1 ratio) had a synergistic effect against 49/50 MRSA, 31/50 MSSA, 12/49 MRSP and 23/49 MSSP. CONCLUSIONS: Since the majority of these staphylococci, including methicillin-resistant isolates, had MICs that should be readily exceeded by topical skin application of these agents, their therapeutic efficacy for canine superficial pyoderma should be assessed. The synergistic interaction shown in vitro supports further clinical evaluation of miconazole/chlorhexidine combination therapy for staphylococcal infection
Inhibition of C. difficile and C. perfringens by commercial and potential probiotic strains and their in-vitro growth characteristics
A new routing protocol for ad hoc wireless networks design, implementation and performance evaluation
A collection of mobile nodes can form a multi-hop radio network with a dynamic topology and without the need for any infrastructure such as base stations or wired network. Such a Mobile Ad Hoc Networks (MANETs) maintain their structure and connectivity in a decentralised and distributed fashion. Each mobile node acts as both a router for other nodes traffic, as well as a source of traffic of its own
In this thesis we develop and present a new hybrid routing protocol called Multipath Distance Vector Zone Routing Protocol, which is referred to as MDVZRP. In MDVZRP we assume that all the routes in the routing table are active and usable at any time, unless the node received or discovered a broken link. There is no need to periodically update the routing tables, therefore reducing the periodic update messages and hence reducing the control traffic in the entire network.
The protocol guarantees loop freedom and alternative disjoint paths. Routes are immediately available within each routing zone. For destinations outside the zone, MDVZRP employs a route discovery technique known as routing information on demand. Once the node is informed by either the MAC layer or itself that it should discover the non- reachable nodes, MDVZRP adopts a new technique.
First, we discuss the Ad Hoc networks and routing in general, then the motivation of MDVZRP regarding the nodes‟ flat view, and the selection and acquisition of multipath getting and selection. Furthermore, we describe the stages of MDVZRP and the protocol routing process with examples. The performance of MDVZRP is then evaluated to determine its operating parameters, and also to investigate its performance in a range of different scenarios.
Finally, MDVZRP is compared with DSDV and AODV ordinary routing protocols (standard) delivering CBR traffic. Simulation results show that MDVZRP gives a better performance than DSDV in all circumstances, it is also better than AODV in most of the scenarios, especially at low mobility
MRSA carrying <i>mecC</i> in captive mara
This is the final published version. It first appeared at http://jac.oxfordjournals.org/content/early/2015/02/24/jac.dkv024.full.Objectives: To characterize the staphylococcal cassette chromosome mec (SCCmec), virulence and antimicrobial\ud
susceptibility of Staphylococcus aureus ST130 isolated from mara (Dolichotis patagonum), a large rodent species\ud
native to South America and kept in captivity at Copenhagen Zoo.\ud
Methods: The presence of mecCwas confirmed by PCR in 15 S. aureus ST130 isolated from mara during a previous\ud
study. WGS was performed on two randomly selected isolates to characterize their genomes with respect to\ud
SCCmec, virulence and resistance gene content. Antimicrobial susceptibility was tested using commercial\ud
broth microdilution tests.\ud
Results: All the isolates belonged to spa type t528 ST130 and carried mecC. Based on WGS, mecC was 100%\ud
identical to the prototype sequence of S. aureus strain LGA251. The sequence of SCCmec type XI in the mara\ud
isolates had 23 SNPs compared with the one described in LGA251. The two sequenced strains harboured a set\ud
of virulence factors and other genomic features previously observed in ST130. Both strains carried norA as the\ud
only putative antimicrobial resistance gene in addition to mecC.\ud
Conclusions: Our findings support the notion that a genetically conserved mecC-carryingMRSA ST130 clone iswidespread\ud
in a variety of unrelated hosts in Denmark. Since the mara at Copenhagen Zoo have limited contact with\ud
humans and other animal species, it remains unclear whether mara are natural hosts of ST130 or acquired this lineage\ud
from unknown sources. The broad host range of MRSA ST130 supports its designation as a generalist lineage.This study was supported by internal funding (C. E.-G., A. M. and L. G.) and by the Medical Research Council (E. M. H. and M. A. H.; G1001787/1)
High prevalence of USA300 among clinical isolates of methicillin-resistant Staphylococcus aureus on St. Kitts and Nevis, West Indies
Limited information is available on antimicrobial susceptibility and clonal distribution of Staphylococcus aureus in the Caribbean region. The aims of this study were to determine the prevalence of antimicrobial resistance among S. aureus isolates and to reveal the frequency and population structure of methicillin-resistant S. aureus (MRSA) in St. Kitts and Nevis, a small island country in the West Indies. A total of 152 S. aureus isolates were collected from consecutive samples submitted to the clinical microbiology laboratory of the main referral hospital from March 2017 to January 2018. Samples came from all units in the hospital and a small number came from external submissions, and comprised a total of 119 clinical specimens and 33 nasal swabs collected from staff and patients. All S. aureus isolates were confirmed by matrix-assisted laser desorption/ionization time-of-flight mass spectrometry. Minimal Inhibitory Concentrations (MICs) of clinically relevant antimicrobials were determined by broth microdilution, and diversity of MRSA isolates was assessed by whole genome sequencing (WGS) analysis. MRSA accounted for 45% (69/152) of the isolates. The highest rates of resistance to non-β-lactam agents were observed for erythromycin (55%), moxifloxacin (41%), and levofloxacin (40%), whereas resistance to the other drugs tested was ≤6%. All isolates were susceptible to ceftaroline, linezolid, teicoplanin, telavancin, and vancomycin. WGS-based multilocus sequence typing (MLST) showed that approximately 88% of the MRSA isolates belonged to ST8. Phylogenetic analysis on 801 single-nucleotide polymorphisms (SNPs) identified among the MRSA ST8 isolates indicates a large degree of genetic diversity. However, all ST8 strains clustered within the distinct clade that defines the USA300 North American Epidemic lineage (Panton-Valentine Leukocidin (PVL) +, arginine catabolic mobile element (ACME) +, Staphylococcal cassettes chromosome mec IVa (SCCmec IVa)). Our data show high levels of methicillin, macrolide, and fluoroquinolone resistance among S. aureus on St. Kitts and Nevis. The USA300 North American epidemic lineage is responsible for the vast majority of MRSA infections on this Caribbean island
The Early Elementary School Abbreviated Math Anxiety Scale (the EES-AMAS): A New Adapted Version of the AMAS to Measure Math Anxiety in Young Children
In the past decade, there has been increasing interest in understanding how and when math anxiety (MA) develops. The incidence and effects of MA in primary school children, and its relations with math achievement, have been investigated. Nevertheless, only a few studies have focused on the first years of primary school, highlighting that initial signs of MA may emerge as early as 6 years of age. Nevertheless, there are some issues with measuring MA in young children. One of these is that, although several scales have been recently developed for this age group, the psychometric properties of most of these instruments have not been adequately tested. There is also no agreement in the number and identity of the factors that underlie MA at this young age. Some scales also consist of several items, which make them impractical to use in multivariate studies, which aim at the simultaneous measurement of several constructs. Finally, most scales have been developed and validated in US populations, and it is unclear if they are appropriate to be used in other countries. In order to address these issues, the current studies aimed at developing a short, new instrument to assess MA in early elementary school students, the Early Elementary School Abbreviated Math Anxiety Scale (the EES-AMAS). This scale is an adapted version of the Abbreviated Math Anxiety Scale (AMAS; Hopko et al., 2003), which is one of the most commonly used scales to measure MA and has been shown to be a valid and reliable measure across a number of countries and age groups. The psychometric properties of the new scale have been investigated by taking into account its dimensionality, reliability, and validity. Moreover, the gender invariance of the scale has been verified by showing the measurement equivalence of the scale when administered to male and female pupils. We have also demonstrated the equivalence of the scale across languages (Italian and English). Overall, the findings confirmed the validity and reliability of the new scale in assessing the early signs of math anxiety and in measuring differences between genders and educational contexts. We have also shown that MA was already related to math performance, and teacher’s ratings of children’s math ability at this young age. Additionally, we have found no gender differences in MA in our samples of 6- and 7-year-old children, an important finding, given the strong evidence for gender differences in MA in older age groups
Evidence for the evolutionary steps leading to mecA-mediated ß-lactam resistance in staphylococci
The epidemiologically most important mechanism of antibiotic resistance in Staphylococcus aureus is associated with mecA–an acquired gene encoding an extra penicillin-binding protein (PBP2a) with low affinity to virtually all β-lactams. The introduction of mecA into the S. aureus chromosome has led to the emergence of methicillin-resistant S. aureus (MRSA) pandemics, responsible for high rates of mortality worldwide. Nonetheless, little is known regarding the origin and evolution of mecA. Different mecA homologues have been identified in species belonging to the Staphylococcus sciuri group representing the most primitive staphylococci. In this study we aimed to identify evolutionary steps linking these mecA precursors to the β-lactam resistance gene mecA and the resistance phenotype. We sequenced genomes of 106 S. sciuri, S. vitulinus and S. fleurettii strains and determined their oxacillin susceptibility profiles. Single-nucleotide polymorphism (SNP) analysis of the core genome was performed to assess the genetic relatedness of the isolates. Phylogenetic analysis of the mecA gene homologues and promoters was achieved through nucleotide/amino acid sequence alignments and mutation rates were estimated using a Bayesian analysis. Furthermore, the predicted structure of mecA homologue-encoded PBPs of oxacillin-susceptible and -resistant strains were compared. We showed for the first time that oxacillin resistance in the S. sciuri group has emerged multiple times and by a variety of different mechanisms. Development of resistance occurred through several steps including structural diversification of the non-binding domain of native PBPs; changes in the promoters of mecA homologues; acquisition of SCCmec and adaptation of the bacterial genetic background. Moreover, our results suggest that it was exposure to β-lactams in human-created environments that has driven evolution of native PBPs towards a resistance determinant. The evolution of β-lactam resistance in staphylococci highlights the numerous resources available to bacteria to adapt to the selective pressure of antibiotics
Characterization, mechanism of action and optimization of activity of a novel peptide-peptoid hybrid against bacterial pathogens involved in canine skin infections
Integumentary infections like pyoderma represent the main reason for antimicrobial prescription in dogs. Staphylococcus pseudintermedius and Pseudomonas aeruginosa are frequently identified in these infections, and both bacteria are challenging to combat due to resistance. To avoid use of important human antibiotics for treatment of animal infections there is a pressing need for novel narrow-spectrum antimicrobial agents in veterinary medicine. Herein, we characterize the in vitro activity of the novel peptide-peptoid hybrid B1 against canine isolates of S. pseudintermedius and P. aeruginosa. B1 showed potent minimum inhibitory concentrations (MICs) against canine S. pseudintermedius and P. aeruginosa isolates as well rapid killing kinetics. B1 was found to disrupt the membrane integrity and affect cell-wall synthesis in methicillin-resistant S. pseudintermedius (MRSP). We generated 28 analogues of B1, showing comparable haemolysis and MICs against MRSP and P. aeruginosa. The most active analogues (23, 26) and B1 were tested against a collection of clinical isolates from canine, of which only B1 showed potent activity. Our best compound 26, displayed activity against P. aeruginosa and S. pseudintermedius, but not the closely related S. aureus. This work shows that design of target-specific veterinary antimicrobial agents is possible, even species within a genus, and deserves further exploration
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