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Background: Bacteriophage has been renewed attention as a new antibacterial agent due to the limitations of antibiotic treatment. Bacteriophages are generally thought to be highly host specific and even strain specific, but a small number of polyvalent bacteriophages have been found to infect bacteria of different genera. Results: In this study, a virulent lytic bacteriophage (named Salmonella phage PSH-1) of Salmonella Enteritidis was isolated from the sewage samples of a large-scale pig farm, PSH-1 demonstrated lytic activity against four multidrug-resistant Salmonella Enteritidis isolates and Escherichia coli, and then its biological characteristics, genome and bacteriostatic ability were investigated. The results showed that the initial titer of PSH-1 was 1.15 × 1010 PFU/mL and the optimal multiplicity of infection (MOI) was 0.01, PSH-1 has stable activity in the range of pH 3.0–11.0. One-step growth curve showed that its latent period was 20 min, burst time was 80 min, and the burst was 495 particles. The whole-genome sequencing results revealed phage PSH-1 had a linear dsDNA with 48,466 bp length. The G/C content was 45.33%. Non-coding RNA genes and virulence factors were not found. Eighty- five open reading frames (ORFs) were identified after online annotation. By tests, the use of phage could succeed in controlling the artificial Salmonella contamination in milk at a range of temperatures. Conclusions: This study reports a novel Salmonella Enteritidis phage PSH-1, which has a robust lytic ability, no virulence factors, and good stability. The characterization and genomic analysis of PSH-1 will develop our understanding of phage biology and diversity and provide a potential arsenal for controlling of salmonellosis. [ABSTRACT FROM AUTHOR]

Background: Fosfomycin is an important broad-spectrum bactericidal antibiotic to treat multidrug-resistant bacteria infections. It is generally accepted that heteroresistant bacteria are an intermediate stage in the formation of drug resistance, but there are few studies on the formation mechanism underlying fosfomycin heteroresistance (FHR).Objectives: To reveal the characteristics and formation mechanisms of FHR in Escherichia coli isolates obtained from chickens.Methods: We identified the FHR according to the population analysis profile (PAP) test and in vitro time-kill assay. Growth curves for FHR E. coli and their subpopulations were measured. Also, the subpopulations were repeatedly cultured in fosfomycin-free medium for 5-20 overnight incubation periods. The formation mechanisms of FHR in E. coli isolates were identified through accumulation assay, carbohydrate utilization testing, real-time relative quantitative PCR analysis, DNA sequencing, transcriptomic analysis, intracellular ATP and cAMP-level assessment.Results: Four of six E. coli strains were confirmed to show FHR, with a total of six subpopulations. The subpopulations restored phenotypic susceptibilities to fosfomycin within 5-20 overnight incubation sessions, but four of six subpopulations still maintained FHR characteristics. Differing from their parental isolates, the uptake of fosfomycin in the subpopulations through GlpT was reduced remarkably. Further studies identified that the low expression of glpT was due to the decrease of intracellular cAMP levels in the subpopulations, which was caused by the decreased ATP levels in cells.Conclusions: Our findings revealed the formation mechanism of E. coli isolates showing FHR obtained from chicken in China and characterized the dynamic change traits in vitro of the subpopulations. [ABSTRACT FROM AUTHOR]

Background: The increasing use of colistin causes a serious breach in our last line of defence against MDR Gram-negative pathogens. Our previous study showed that CpxR overexpression increases the susceptibility of acrB and cpxR double-deleted Salmonella enterica serovar Typhimurium to colistin.Objectives: To identify the mechanism of CpxAR and efflux pumps that synergistically enhance the susceptibility of S. Typhimurium to colistin.Methods: A series of cpxR- and tolC-deleted mutants and a cpxR-complemented strain from a multidrug-susceptible standard strain of S. Typhimurium (JS) were generated in our previous study. Herein, we investigated the susceptibility of these strains to colistin through the broth microdilution method, time-kill curves and survival assays. Growth curves were measured by OD600 in LB broth, tryptone-soy broth (TSB) and M9-glucose (0.2%) minimal media. Finally, molecular mechanisms underlying the mode of action were elucidated by transcriptomic analysis.Results: We found that in contrast to JS (0.8 mg/L), the MIC of colistin for JSΔtolC::kan showed a 16-fold decrease (0.05 mg/L). Notably, JSΔcpxRΔtolC and JSΔcpxRΔtolC/pcpxR were associated with a 256-fold decrease (0.0031 mg/L) compared with JS. Growth curves identified that JSΔcpxRΔtolC and JSΔcpxRΔtolC/pcpxR displayed a markedly lower growth rate and poorer adaptability. In addition, time-kill curves and survival assays showed that JSΔcpxRΔtolC and JSΔcpxRΔtolC/pcpxR were more susceptible to colistin. Lastly, double deletion of cpxR and tolC enhanced oxidative damage through promoting oxidative phosphorylation, the tricarboxylic acid (TCA) cycle and trimethylamine N-oxide (TMAO) respiration.Conclusions: Our findings revealed that double deletion of cpxR and tolC significantly increases the susceptibility of S. Typhimurium to colistin. [ABSTRACT FROM AUTHOR]

To characterize the formation mechanism and characteristics of two cointegrate plasmids in Salmonella enterica serotype Enteritidis strain S13, plasmids from strain S13 and three corresponding transconjugants were subjected to whole genome sequencing and analyzed using bioinformatics tools. The traits of two fusion plasmids in transconjugants were characterized by stability and conjugation experiments. Sequence analysis indicated that strain S13 contained four plasmids, including mcr-1 -bearing pS13-1, bla CTX–M–55-carrying pS13-2, tet (M)-bearing pS13-3, and floR -carrying pS13-4. IncN1-F33:A–:B– plasmid pS13-2, respectively, fused with IncFI:A–:B– plasmid pS13-3 and IncX1 plasmid pS13-4, which generated two cointegrate plasmids, designated pS13D and pS13F, which involved in two intermolecular replicative mechanisms mediated by IS 26 and the novel transposon Tn 6952 (Δ Tn AS3 -IS 26 - Δ IS Ecp1 - ramA - Δ IS 26 - Δ Tn AS1), respectively. This is the first report of the fusion of the IncN1-F33:A–:B– plasmid and IncFI:A–:B– plasmid mediated by IS 26 , and with IncX1 plasmid mediated by Tn 6952. The formation and evolution of cointegrate plasmids could expand the resistance and host spectrum of fusion plasmids. [ABSTRACT FROM AUTHOR]

Background: The two-component signalling systems PmrAB and PhoPQ of Salmonella have been extensively studied with regard to colistin resistance. We previously showed that overexpressed CpxR could significantly increase the colistin susceptibility (16-fold compared with the WT strain) of Salmonella enterica serovar Typhimurium (Salmonella Typhimurium) through PmrAB and PhoPQ.Objectives: To identify the potential target genes of CpxR in PmrAB- and PhoPQ-related signalling pathways.Methods: His6-CpxR was prokaryotically expressed and purified by Ni-NTA resin affinity chromatography. β-Galactosidase activity assays were conducted to investigate whether CpxR could regulate the promoters of colistin resistance-related genes (CRRGs). Electrophoretic mobility shift assays (EMSAs) were used to further detect His6-CpxR complexes with promoters of CRRGs.Results: We demonstrated for the first time (to the best of our knowledge) that CpxR and the AcrAB-TolC efflux pump have reciprocal effects on CRRG transcription. Additionally, CpxR could regulate the colistin susceptibility of Salmonella Typhimurium by binding directly to the promoters of phoPQ, pmrC, pmrH and pmrD at the CpxR box-like sequences or indirectly through other regulators including pmrAB and mgrB.Conclusions: CpxR could regulate the colistin susceptibility of Salmonella Typhimurium by a multitarget mechanism. [ABSTRACT FROM AUTHOR]

ICE Hpa1 was identified in the genome of a serovar 8 Haemophilus parasuis ST288 isolate YHP170504 from a case of swine lower respiratory tract infection. The aim of the present study was to characterize the integrative conjugative element ICE Hpa1 and its multiresistance region. Susceptibility testing was determined by broth microdilution and the complete ICE Hpa1 was identified by WGS analysis. The full sequence of ICE Hpa1 was analyzed with bioinformatic tools. The presence of ICE Hpa1 , its circular intermediate and integration site were confirmed by PCR and sequence analysis. Transfer of ICE Hpa1 was confirmed by conjugation. ICE Hpa1 has a size of 68,922 bp with 37.42% GC content and harbors 81 genes responsible for replication and stabilization, transfer, integration, and accessory functions, as well as seven different resistance genes [ bla Rob–3, tet (B), aphA1 , strA , strB , aac(6)′-Ie-aph(2′)-Ia , and sul2 ]. Conjugation experiments showed that ICE Hpa1 could be transferred to H. parasuis V43 with frequencies of 6.1 × 10–6. This is the first time a multidrug-resistance ICE has been reported in H. parasuis. Seven different resistance genes were located on a novel integrative conjugative element ICE Hpa1 , which suggests that the ICE Hpa1 is capable of acquiring foreign genes and serving as a carrier for various resistance genes. [ABSTRACT FROM AUTHOR]

The objective of this study was to explore the genetic and biological features of the tet (M)-harboring plasmid pTS14 in Salmonella enterica strain S14 isolated from a chicken fecal sample. Plasmid pTS14 was identified by conjugation, S1-pulsed-field gel electrophoresis (PFGE), Southern hybridization, and plasmid sequencing. The biological characteristics of pTS14 were assessed via stability, growth kinetics, and starvation survival experiments. Strain S14, belonging to ST3007, harbored a 119-kb tet (M)-bearing IncF2:A1:B1 conjugative plasmid pTS14. The plasmid pTS14 contained a novel transposon Tn 6709 with the genetic structure IS 26 - tnpA1 - tnpA2 -Δ orf13 - LP - tet (M)- tnpX -Δ tnpR -IS 26 , and the resistance genes tet (B), tet (D), strAB , sul2 , and bla TEM–1b. In addition, pTS14 was found to be highly stable in the recipient strain E. coli J53. The transconjugant TS14 exhibited a higher survival ratio than E. coli J53 under permanent starvation-induced stress. The tet (M)-bearing IncF2 epidemic plasmid lineage may accelerate the dissemination of tet (M) and other genes by coselection, which could constitute a potentially serious threat to clinical treatment regimens. [ABSTRACT FROM AUTHOR]

Background: IS26-flanked transposons played an increasingly important part in the mobilization and development of resistance determinants. Heterogeneous resistance-encoding plasmid clusters with polymorphic MDR regions (MRRs) conferred by IS26 in an individual Escherichia coli isolate have not yet been detected.Objectives: To characterize the complete sequence of a novel blaCTX-M-65- and fosA3-carrying IncZ-7 plasmid with dynamic MRRs from an E. coli isolate, and to depict the mechanism underlying the spread of resistance determinants and genetic polymorphisms.Methods: The molecular characterization of a strain carrying blaCTX-M-65 and fosA3 was analysed by antimicrobial susceptibility testing and MLST. The transferability of a plasmid bearing blaCTX-M-65 and fosA3 was determined by conjugation assays, and the complete structure of the plasmid was obtained by Illumina, PacBio and conventional PCR mapping, respectively. The circular forms derived from IS26-flanked transposons were detected by reverse PCR and sequencing.Results: A novel IncZ-7 plasmid pEC013 (∼118kb) harbouring the blaCTX-M-65 and fosA3 genes was recovered from E. coli isolate EC013 belonging to D-ST117. The plasmid was found to have heterogeneous and dynamic MRRs in an individual strain and the IS26-flanked composite transposon-derived circular intermediates were identified and characterized in pEC013.Conclusions: The heterogeneous MRRs suggested that a single plasmid may actually be a cluster of plasmids with the same backbone but varied MRRs, reflecting the plasmid's heterogeneity and the survival benefits of having a response to antimicrobial-related threatening conditions in an individual strain. [ABSTRACT FROM AUTHOR]

Tet(M)-type proteins confer resistance to tetracycline and related antibiotics by interacting with the ribosome. Genes encoding Tet(M) have been found in a range of bacteria, including Escherichia coli. In the current study, conjugation experiments were performed between seven different tetracycline-resistant, azide-susceptible E. coli strains isolated from ducks and tetracycline-sensitive, azide-resistant E.coli J53. Transconjugants were obtained from two of the strains at a frequency of 1.2 × 10−8. PCR, southern blotting and sequencing demonstrated that tet (M) in the transconjugants was located on a ~50 kb IncHI2-type plasmid and was part of a composite transposon, designated Tn6539. This transposon is flanked by two IS26 elements in opposite orientation and contains the Tn3Δ tnpA +Δ orf13 - lp - tet (M)+gamma delta+ tnpX +Δ tnpR sequences. The Δ orf13 - lp - tet (M) sequence was a highly conserved genetic fragment in E. coli harboring tet (M) and mainly located in the composite transposons flanked by IS6-family elements. In summary, Tn6539 is a new composite transposon capable of horizontal transfer of tet (M) among E. coli isolates. [ABSTRACT FROM AUTHOR]

A multi-drug resistant Escherichia coli C21 was isolated from a chicken in China. It was shown to be positive for the presence of the blaTEM-1, blaCTX-M-55 and rmtB genes by PCR. This strain was examined by phylogenetic grouping, conjugation experiments, plasmid analysis, PCR-based replicon typing and multi-locus sequence typed (MLST). The genetic environment of blaCTX-M-55 was investigated by PCR mapping. The strain belonged to phylogroup A, ST156. The blaCTX-M-55 and rmtB genes were found to be present in separate plasmids that belonged to the IncI1 and IncN families, respectively. These antibiotic-resistant plasmids could be transferred to the recipient strain alone or together. A new arrangement of IS Ecp1Δ-IS 1294-ΔIS Ecp1-blaCTX-M-55-ORF 477, in which the IS Ecp1 element was disrupted by another IS 1294 element, was identified initially. Conjugative transfer and IS elements found in this study could lead to the rapid dissemination of blaCTX-M-55 and rmtB among strains of Enterobacteriaceae, which could pose a threat to animal husbandry and public health. [ABSTRACT FROM AUTHOR]

The article presents a study which examines the presence of pleuromutilin lincosamide streptogramin A (PLSa) resistance gene Isa(E) in enterococci from human and swine. It is stated that 41 Enterococcus faecalis, 45 Enterococcus faecium, 9 Enterococcus casseliflavus and 7 Enterococcus gallinarum were isolated from 232 faecal samples, 33 from humans and 69 from swine. Results show that Isa(E) gene in enterococcal strains from both human and pigs are present.

The article discusses a study which examined the location of Tn3-associated rmtB together with qnrS1, aac(6')-Ib-cr and blaCTX-M-15 on an F49:A-:B- plasmid in an Escherichia coli ST10 strain isolated from cows in China. Study authors found that Tn3-associated rmtB together with qnrS1, aac(6')-Ib-cr and blaCTX-M-15 are co-located on an Escherichia coli plasmid from cows. It also described the presence of rmtB gene in food-producing animal.

The article discusses a study which determined the co-location of Tn1548-associated armA with qnrB2, aac(6')-Ib-cr and blaCTX-M-3 on an IncFII plasmid in a Salmonella enterica subspecies enterica serovar Paratyphi B strain from chickens in China. Study authors found that the plasmid present in the transformant SC-01T belonged to the incompatibility group IncFII. They also discovered that the armA gene in human and animal isolates mainly belong to IncL/M,IncN and IncF replicon groups.

The Archangel pigeon mitochondrial DNA has 17,235 bp and its structural organization is conserved compared to those of other birds. In this study, we report the basic characteristics of the Archangel mitochondrial genome, including structural organization and base composition of the rRNAs, tRNAs and protein-coding genes, as well as characteristics of tRNAs. These features are applicable for the study of phylogenetic relationships in pigeons. [ABSTRACT FROM AUTHOR]