Encoding graphs by words and morphisms

This thesis is related to encoding graphs by words, where we deal with so called word representation of graphs, relevant to them semi-transitive orientations, and more exotic ways to represent graphs via bijections with certain words and pattern-avoiding permutations. In Chapter 2, we introduce a way to define classes of split graphs via iterations of morphisms and present a number of general results on word-representation of such graphs. A particular result obtained by us that goes beyond the study of split graphs, is a characterization of word-representable graphs in terms of permutations of columns of the adjacency matrices. We also provide a complete classification of word-representable split graphs defined by iteration of morphisms using two 2x2 matrices. In Chapter 3, we study families of directed split graphs obtained by iterations of morphisms applied to the adjacency matrices and giving as the limit infinite directed split graphs. For each of such a family we ask the question on whether all graphs in the family are oriented semi-transitively (i.e. are semi-transitive) or a finite iteration k of the morphism produces a non-semi-transitive orientation (which will stay non-semi-transitive for all iterations > k). We fully classify semi-transitive infinite directed split graphs in question. In Chapter 4, we present encoding p-Riordan graphs by p-Riordan words, and encoding Riordan graphs by pattern-avoiding permutations. Also, we encode oriented Riordan graphs by balanced words over the alphabet {0, 1, 2}, and provide, as a bi-product, a proof of a known enumerative result about closed walks in the 3-cube.This thesis is related to encoding graphs by words, where we deal with so called word representation of graphs, relevant to them semi-transitive orientations, and more exotic ways to represent graphs via bijections with certain words and pattern-avoiding permutations. In Chapter 2, we introduce a way to define classes of split graphs via iterations of morphisms and present a number of general results on word-representation of such graphs. A particular result obtained by us that goes beyond the study of split graphs, is a characterization of word-representable graphs in terms of permutations of columns of the adjacency matrices. We also provide a complete classification of word-representable split graphs defined by iteration of morphisms using two 2x2 matrices. In Chapter 3, we study families of directed split graphs obtained by iterations of morphisms applied to the adjacency matrices and giving as the limit infinite directed split graphs. For each of such a family we ask the question on whether all graphs in the family are oriented semi-transitively (i.e. are semi-transitive) or a finite iteration k of the morphism produces a non-semi-transitive orientation (which will stay non-semi-transitive for all iterations > k). We fully classify semi-transitive infinite directed split graphs in question. In Chapter 4, we present encoding p-Riordan graphs by p-Riordan words, and encoding Riordan graphs by pattern-avoiding permutations. Also, we encode oriented Riordan graphs by balanced words over the alphabet {0, 1, 2}, and provide, as a bi-product, a proof of a known enumerative result about closed walks in the 3-cube

Word-representability of split graphs generated by morphisms

A graph G=(V,E) is word-representable if and only if there exists a word w over the alphabet V such that letters x and y, x≠y, alternate in w if and only if xy∈E. A split graph is a graph in which the vertices can be partitioned into a clique and an independent set. There is a long line of research on word-representable graphs in the literature, and recently, word-representability of split graphs has attracted interest. In this paper, we first give a characterization of word-representable split graphs in terms of permutations of columns of the adjacency matrices. Then, we focus on the study of word-representability of split graphs obtained by iterations of a morphism, the notion coming from combinatorics on words. We prove a number of general theorems and provide a complete classification in the case of morphisms defined by 2 × 2 matrices

Encoding labelled pp-Riordan graphs by words and pattern-avoiding permutations

The notion of a $p$-Riordan graph generalizes that of a Riordan graph, which, in turn, generalizes the notions of a Pascal graph and a Toeplitz graph. In this paper we introduce the notion of a $p$-Riordan word, and show how to encode $p$-Riordan graphs by $p$-Riordan words. For special important cases of Riordan graphs (the case $p=2$) and oriented Riordan graphs (the case $p=3$) we provide alternative encodings in terms of pattern-avoiding permutations and certain balanced words, respectively. As a bi-product of our studies, we provide an alternative proof of a known enumerative result on closed walks in the cube.Comment: To appear in Graphs and Combinatorics, 14 pages, 1 fiugur

Semi-transitivity of directed split graphs generated by morphisms

A directed graph is semi-transitive if and only if it is acyclic and for any directed path u1 → u2 → ··· → ut, t ≥ 2, either there is no edge from u1 to ut or all edges ui → uj exist for 1 ≤ i < j ≤ t. In this paper, we study semi-transitivity of families of directed split graphs obtained by iterations of morphisms applied to the adjacency matrices and giving in the limit infinite directed split graphs. A split graph is a graph in which the vertices can be partitioned into a clique and an independent set. We fully classify semi-transitive infinite directed split graphs when a morphism in question can involve any n×m matrices over {−1,0,1} with a single natural condition

Complete Genome Sequence of the Extensively Drug-Resistant Extended-Spectrum β-Lactamase-Producing Proteus mirabilis Isolate HK294, Obtained from Poultry Feces in Hong Kong

Here, we report the complete genome sequence of Proteus mirabilis isolate HK294, recovered from pooled poultry feces in Hong Kong in 2022. The chromosome contained 32 antimicrobial resistance genes, including the extended-spectrum β-lactamases blaCTX-M-65 and blaCTX-M-3. Almost all resistance genes were part of either an integrative conjugative element or a Tn7-like transposon

Complete Genome Sequence of the Extensively Drug-Resistant Extended-Spectrum β-Lactamase-Producing Proteus mirabilis Isolate HK294, Obtained from Poultry Feces in Hong Kong.

Here, we report the complete genome sequence of Proteus mirabilis isolate HK294, recovered from pooled poultry feces in Hong Kong in 2022. The chromosome contained 32 antimicrobial resistance genes, including the extended-spectrum β-lactamases blaCTX-M-65 and blaCTX-M-3. Almost all resistance genes were part of either an integrative conjugative element or a Tn7-like transposon

Serotypes, Antimicrobial Resistance Profiles, and Virulence Factors of Salmonella Isolates in Chinese Edible Frogs (Hoplobatrachus rugulosus) Collected from Wet Markets in Hong Kong

Salmonella is an important agent of gastrointestinal disease in humans. While livestock, such as cattle, poultry, and pigs, are well-recognised animal reservoirs of Salmonella, there is a lack of data on Salmonella in edible frogs, even though frog meat is a popular food worldwide. In this study, 103 live edible Chinese frogs (Hoplobatrachus rugulosus) were collected from wet markets throughout Hong Kong. After euthanasia, faeces or cloacal swabs were examined for Salmonella. Overall, Salmonella spp. were isolated from 67 (65%, CI: 0.554–0.736) of the samples. The serotypes included S. Saintpaul (33%), S. Newport (24%), S. Bareilly (7%), S. Braenderup (4%), S. Hvittingfoss (4%), S. Stanley (10%), and S. Wandsworth (16%). Many isolates were phylogenetically related. A high number of genes encoding for resistance to clinically relevant antimicrobials, and a high number of virulence determinants, were identified. Antimicrobial susceptibility testing (AST) identified multidrug resistance (MDR) in 21% of the isolates. Resistance to ampicillin, ciprofloxacin, nalidixic acid, and tetracycline was common. These results demonstrate that a high percentage of live frogs sold for human consumption in wet markets are carriers of multidrug-resistant Salmonella. Public health recommendations for handling edible frogs should be considered, to mitigate the risk of Salmonella transmission to humans

Effect of poly (ethylene-co-vinyl acetate) grade on water resistance and mechanical properties of particleboard

Three-layer particleboard was prepared in the laboratory using a similar composition and processing condition to those used in the plant production of particleboard. Poly(ethylene-co-vinyl acetate) (EVA) was mixed with natural rubber-wood particles in the core layer to reduce the water resistance of the particleboard. The properties of three EVA grades with vinyl acetate contents of 19%, 22%, and 28% were melt indexes of 530, 1.8, and 6.8 g/10 min, melting temperatures of 84, 86, and 75 °C, and molecular weights of 29000, 68000, and 61000 g/mol, respectively. The addition of 5% EVA significantly decreased the thickness swelling and water absorption properties of the particleboard. The mechanical properties of the particleboard that were determined were the modulus of rupture, modulus of elasticity, internal bond strength, and screw holding force. A statistical analysis of the data showed that the addition of 5% EVA did not deteriorate the mechanical properties. EVA22 seemed to be the optimal grade

Reducing the risk of transmission of critical antimicrobial resistance determinants from contaminated pork products to humans in South-East Asia

Antimicrobial resistance (AMR) is a critical challenge worldwide as it impacts public health, especially via contamination in the food chain and in healthcare-associated infections. In relation to farming, the systems used, waste management on farms, and the production line process are all determinants reflecting the risk of AMR emergence and rate of contamination of foodstuffs. This review focuses on South East Asia (SEA), which contains diverse regions covering 11 countries, each having different levels of development, customs, laws, and regulations. Routinely, here as elsewhere antimicrobials are still used for three indications: therapy, prevention, and growth promotion, and these are the fundamental drivers of AMR development and persistence. The accuracy of detection of antibiotic resistant bacteria (ARB) and antibiotic resistance genes (ARG) depends on the laboratory standards applicable in the various institutes and countries, and this affects the consistency of regional data. Enterobacteriaceae such as Escherichia coli and Klebsiella pneumoniae are the standard proxy species used for indicating AMR-associated nosocomial infections and healthcare-associated infections. Pig feces and wastewater have been suspected as one of the hotspots for spread and circulation of ARB and ARG. As part of AMR surveillance in a One Health approach, clonal typing is used to identify bacterial clonal transmission from the production process to consumers and patients – although to date there have been few published definitive studies about this in SEA. Various alternatives to antibiotics are available to reduce antibiotic use on farms. Certain of these alternatives together with improved disease prevention methods are essential tools to reduce antimicrobial usage in swine farms and to support global policy. This review highlights evidence for potential transfer of resistant bacteria from food animals to humans, and awareness and understanding of AMR through a description of the occurrence of AMR in pig farm food chains under SEA management systems. The latter includes a description of standard pig farming practices, detection of AMR and clonal analysis of bacteria, and AMR in the food chain and associated environments. Finally, the possibility of using alternatives to antibiotics and improving policies for future strategies in combating AMR in a SEA context are outlined

Isolation of community-associated methicillin-resistant Staphylococcus aureus (MRSA) sequence type (ST) 30 from house rats (Rattus tanezumi) in Hong Kong.

Methicillin-resistant Staphylococcus aureus (MRSA) is of major public health concern due to its resistance to multiple antibiotics. This resistance has been observed in various settings, including hospitals and communities, and has been detected in both animals and humans. Although peridomestic rat species (Rattus spp.) are well described reservoirs of several human pathogens and antimicrobial resistant bacteria, little is known about their role in MRSA epidemiology. In order to investigate whether Rattus spp. in Hong Kong are potential carriers of MRSA, 221 rats were caught from various ecological areas and nasopharyngeal samples were cultured on MRSA selective media. Genotypic characteristics of MRSA were confirmed by whole genome sequencing. Two clonal sequence type (ST) 30 MRSA isolates, harbouring mecA on staphylococcal chromosome cassette (SCC) mec type IVc, were cultured from two house rats (Rattus tanezumi) caught in two densely populated urban areas. To the best of the authors' knowledge, this is the first detection of community-associated (CA)-MRSA strain ST30 SCCmec IVc in peridomestic rodents in Hong Kong and globally. Our finding indicates that house rats can be carriers of MRSA strains that are widely distributed in the community