Plasmid-mediated colistin-resistance genes: mcr

Colistin is regarded as a last-line drug against serious infections caused by multidrug-resistant Gram-negative bacterial pathogens. Therefore, the emergence of mobile colistin resistance (mcr) genes has attracted global concern and led to policy changes for the use of colistin in food animals across many countries. Currently, the distribution, function, mechanism of action, transmission vehicles, origin of mcr, and new treatment strategies against MCR-producing pathogens have been extensively studied. Here we review the prevalence, structure and function of mcr, the fitness cost and persistence of mcr-carrying plasmids, the impact of MCR on host immune response, as well as the control strategies to combat mcr-mediated colistin resistance.

Dihydroartemisinin inhibits plasmid transfer in drug-resistant Escherichia coli via limiting energy supply

Conjugative transfer of antibiotic resistance genes (ARGs) by plasmids is an important route for ARG dissemination. An increasing number of antibiotic and nonantibiotic compounds have been reported to aid the spread of ARGs, highlighting potential challenges for controlling this type of horizontal transfer. Development of conjugation inhibitors that block or delay the transfer of ARG-bearing plasmids is a promising strategy to control the propagation of antibiotic resistance. Although such inhibitors are rare, they typically exhibit relatively high toxicity and low efficacy in vivo and their mechanisms of action are inadequately understood. Here, we studied the effects of dihydroartemisinin (DHA), an artemisinin derivative used to treat malaria, on conjugation. DHA inhibited the conjugation of the IncI2 and IncX4 plasmids carrying the mobile colistin resistance gene ( mcr-1) by more than 160-fold in vitro in Escherichia coli, and more than two-fold (IncI2 plasmid) in vivo in a mouse model. It also suppressed the transfer of the IncX3 plasmid carrying the carbapenem resistance gene bla NDM-5 by more than two-fold in vitro. Detection of intracellular adenosine triphosphate (ATP) and proton motive force (PMF), in combination with transcriptomic and metabolomic analyses, revealed that DHA impaired the function of the electron transport chain (ETC) by inhibiting the tricarboxylic acid (TCA) cycle pathway, thereby disrupting PMF and limiting the availability of intracellular ATP for plasmid conjugative transfer. Furthermore, expression levels of genes related to conjugation and pilus generation were significantly down-regulated during DHA exposure, indicating that the transfer apparatus for conjugation may be inhibited. Our findings provide new insights into the control of antibiotic resistance and the potential use of DHA.

Effects of dietary supplementation of Saccharomyces cerevisiae fermentation product to sows and their offspring on growth and meat quality

This study evaluated the effects of long term dietary supplementation of Saccharomyces cerevisiae fermentation product (SCFP) in the diets for sows and offspring on growth performance, intestinal morphology, volatile fatty acid production, and carcass characteristics of offspring. Newly weaned pigs (n = 256) were allotted to 4 treatments based on a 2 × 2 factorial arrangement. Each treatment had 8 pens with 8 pigs per pen. First factor was maternal dietary effects (no SCFP, or SCFP at 12.0 and 15.0 g/d through gestation and lactation, respectively) and the second factor was dietary supplementation of SCFP to offspring (no SCFP, or SCFP at 0.2 and 0.1% for nursery and finisher, respectively). Pigs were on a 6-phase feeding program with assigned diets from nursery to slaughter. Body weights (BW) and feeder weights were measured at the end of each phase. On d 5 after weaning, 1 pig per pen was euthanized to evaluate intestinal morphology and volatile fatty acid production. At 115 kg of BW, 1 pig from each pen was slaughtered to measure carcass characteristics. Feeding diets with SCFP to sows or to their offspring had no effect on BW, overall average daily gain (ADG), average daily feed intake (ADFI), and gain-to-feed (G:F) ratio during the nursery or finisher period. Feeding SCFP to sows tended to increase (P = 0.098) cecal butyric acid production in their offspring. Pigs with SCFP tended to have a greater (P = 0.084) concentration of acetic acid but a reduced (P = 0.054) propionic acid in colon digesta than pigs without SCFP regardless of maternal feeding regimen. Loin marbling scores were greater (P = 0.043) in pigs with SCFP than those without SCFP regardless of maternal feeding regimen. Overall, supplementation of SCFP in sow diets did not affect growth performance or intestinal morphology of their offspring. Supplementation of SCFP in diets of offspring from nursery to slaughter had little effect on growth performance. However, inclusion of SCFP from nursery to slaughter improved marbling score possibly by increased acetic acid and butyric acid production in the large intestine.

Effects of feed grade L-methionine on intestinal redox status, intestinal development, and growth performance of young chickens compared with conventional DL-methionine

This study was conducted to test the effects of supplemental L-Met on redox status, gut development, and growth performance of young broiler chickens compared with DL-Met. A total of 888 (half male and half female) 1-d-old Ross 308 chickens were weighed and randomly allotted to 7 treatments in a randomized complete block design for 21 d, including a basal diet (BD), the BD + 0.095% L-Met or DL-Met, the BD + 0.190% L-Met or DL-Met, and the BD + 0.285% L-Met or DL-Met (representing 60, 70, 80, and 90% of the Met + Cys requirement). Feed disappearance and BW were recorded every 7 d. Liver and duodenum samples were collected on d 0, 7, and 21 to measure redox status and intestine morphology. On d 7, chicks fed a diet supplemented with either 0.285% L-Met or 0.285% DL-Met had increased (P < 0.05) concentrations of glutathione (GSH) and reduced (P < 0.05) protein carbonyl (PC) and malonedialdehyde contents in duodenum mucosa compared with chicks fed the BD. Chicks fed a diet supplemented with 0.285% L-Met had greater (P < 0.05) villus width compared with chicks fed a diet supplemented with 0.285% DL-Met. Chicks fed a diet supplemented with 0.285% L-Met had lower (P < 0.05) crypt depth and greater (P < 0.05) villus height:crypt depth ratio compared with chicks fed a diet supplemented with 0.285% DL-Met or the BD. On d 21, chicks fed a diet supplemented with 0.285% L-Met had increased (P < 0.01) concentrations of GSH and total antioxidant capacity (TAC) but reduced (P < 0.05) PC content in duodenum mucosa compared with chicks fed a diet supplemented with 0.285% DL-Met and the BD. Chicks fed a diet supplemented with 0.285% L-Met had greater (P < 0.05) villus height compared with chicks fed the BD. During the entire 21-d supplementation of either L-Met or DL-Met, ADG and G:F were enhanced (P < 0.01) compared with chicks fed the BD. Chicks fed diets supplemented with L-Met had greater (P < 0.05) ADG and G:F than chicks fed diets supplemented with DL-Met. The relative bioavailability of L-Met to DL-Met for ADG and G:F was 138.2 and 140.7%, respectively. Overall, supplementation of either L-Met or DL-Met has beneficial effects on villus development in association with increased GSH production and levels of TAC and reduced protein oxidation in duodenum. Supplementation of L-Met served a better function on redox status and development of the gut of chicks compared with DL-Met. Chicks fed diets with L-Met had better growth response than chicks fed diets with DL-Met.

Effect of feed grade L-methionine on growth performance and gut health in nursery pigs compared with conventional DL-methionine

Two experiments were conducted to test if supplementation of LMET has beneficial effects on growth performance and gut health in nursery pigs compared with DL-Met. In Exp. 1, 168 pigs in 56 pens were randomly allotted to 7 dietary treatments for 20 d, including a basal diet (BD; 55% of the NRC requirement for Met), the BD+0.048% L-Met or DL-Met (70% of the NRC requirement), the BD+0.096% L-Met or DL-Met (85% of the NRC requirement), and the BD+0.144% L-Met or DL-Met (100% of the NRC requirement). Body weight and feed disappearance were recorded every 5 d for computation of growth performance. In Exp. 2, 20 individually housed nursery pigs were randomly allotted to 2 dietary treatments for 20 d: DML (0.16% Met from the BD+0.145% supplemental DL-Met) or LMET (0.16% Met from the BD+0.145% supplemental L-Met). Both diets had Met meeting 95% of the NRC requirement. Duodenum samples from all pigs were collected at the end of the trial to evaluate morphology and redox status. In Exp. 1, during the entire 20 d, pigs fed diets supplemented with L-Met tended to have greater (P=0.087) ADG and reduced (P<0.01) plasma urea nitrogen (PUN) than pigs fed diets supplemented with DL-Met. The relative bioavailability (RBA) of L-Met to DL-Met for ADG and G:F was 143.8 and 122.7%, respectively. In Exp. 2, pigs fed a diet supplemented with L-Met had duodenum tissue with greater (P<0.05) concentrations of glutathione (GSH) and greater villus height and width as well as lower (P<0.05) concentrations of protein carbonyl compared with pigs fed DL-Met. Overall, compared with DL-Met, the use of L-Met as a source of supplemental Met in nursery pig diets enhanced duodenum villus development in association with reduced oxidative stress and improved GSH. The beneficial effects of supplementing L-Met compared to DL-Met in gut of nursery pigs resulted in a potential enhancement of ADG and reduction of PUN.

Novel polymorphic microsatellite markers in Odontobutis potamophila

We characterized 16 novel polymorphic loci isolated from a partial genomic DNA library of Odontobutis potamophila enriched for CA repeats. We tested the variability of these microsatellites on 51 unrelated individuals collected in China. All loci were polymorphic. The average allele number was 14.6 per locus, ranging from 2 to 27. The observed heterozygosity ranged from 0.35 to 0.90, with an average of 0.70, whereas the average expected heterozygosity was 0.76. Twelve of the 16 microsatellites conformed to Hardy-Weinberg equilibrium and were inherited independently. These developed microsatellites will be useful in studies of population genetics and other genetic studies on this important food species.

Molecular characterization, expression, and immunological response analysis of the TWEAK and APRIL genes in grass carp, Ctenopharyngodon idella

TWEAK and APRIL are important members of the TNF superfamily, which play a crucial role in several diseases. Here, we describe the identification of grass carp (Ctenopharyngodon idella) homologs of TWEAK and APRIL (designated gcTWEAK and gcAPRIL, respectively) and their response to Aeromonas hydrophila and Aquareovirus infection. The gcTWEAK cDNA sequence contains 2273 bases with an open reading frame of 753 bases encoding 250-amino acid residues. The gcTWEAK protein contains a predicted transmembrane domain, a putative furin protease cleavage site, 3 conserved cysteine residues, and a typical TNF homology domain. The gcAPRIL cDNA sequence contains 1408 bases with an open reading frame of 747 bases encoding 248-amino acid residues. The gcAPRIL protein contains a predicted transmembrane domain, a putative furin protease cleavage site, 2 conserved cysteine residues, and a typical TNF homology domain corresponding to other, known APRIL homologs. Reverse transcription-polymerase chain reaction analysis shows that both gcTWEAK and gcAPRIL transcripts are predominantly expressed in the skin, spleen, and head kidney, and they are significantly upregulated in most immune tissues by A. hydrophila and Aquareovirus infections. Our results demonstrate that liver is the most responsive tissue against bacterial infection, whereas gill is the most responsive tissue against viral infection. The association of increased gcTWEAK and gcAPRIL expression after bacterial and viral infections suggests that they play a potentially important role in the immune system of fish.

Effects of supplementing Saccharomyces cerevisiae fermentation product in sow diets on performance of sows and nursing piglets

Forty-two sows were used to determine the effects of adding a Saccharomyces cerevisiae fermentation product (SCFP) to the gestation and lactation diets on the performance of sows and their progeny. At 5 d before breeding, sows were allotted to 2 dietary treatments representing 1) sows fed a diet with 12.0 g of fermentation product/d through gestation and 15.0 g of fermentation product/d through lactation (SCFP treatment, n=22), and 2) sows fed a diet with equal amounts of a mixture of corn and soybean meal instead of the SCFP (CON treatment, n=20). Sow BW and backfat thickness were recorded. Blood was collected from sows, as well as piglets, for the measurement of cell numbers, plasma urea nitrogen (PUN), and IgG. Fecal samples from d 7 to 9 of lactation were collected to determine apparent total tract nutrient digestibility. The composition of colostrum and milk was also measured. No difference (P > 0.10) in reproductive performance was observed between treatments. However, sows in the SCFP treatment tended to have increased total litter weaning weight (P=0.068) and litter BW gain (P=0.084) compared with sows in the CON treatment. Neutrophil count was decreased (P < 0.05) by adding the fermentation product on d 110 of gestation and d 17 of lactation, whereas a decreased (P < 0.05) white blood cell count was observed only on d 110 of gestation. Concentration of PUN tended to be greater (P=0.069) for sows in the CON treatment compared with sows in the SCFP treatment on d 110 of gestation. Apparent total tract nutrient digestibility values of ash, CP, DM, and ether extract were not affected (P > 0.10) by adding the fermentation product. Protein and fat contents in colostrum and milk did not differ (P > 0.10) between treatments. Colostrum from sows in the SCFP treatment contained a greater (P < 0.05) amount of ash than colostrum from sows in the CON treatment. Immunoglobulin G measured in the colostrum, milk, and plasma of piglets did not differ (P > 0.10) between sows in the CON and SCFP treatments. This study indicates that adding the SCFP in the gestation and lactation diets has the potential to 1) improve litter BW gain during lactation, possibly by improving maternal protein utilization, as shown in a tendency to reduce PUN; 2) improve the maternal health status, as shown by the reduced neutrophil cell count; and 3) increase milk production, as shown in a tendency to improve litter BW gain without affecting nutrient composition of the colostrum and milk.

The effects of berberine on the magnitude of the acute inflammatory response induced by Escherichia coli lipopolysaccharide in broiler chickens

One hundred twenty-six 19-d-old male broiler chickens were used to determine the effects of berberine on the magnitude of the acute inflammatory response induced by Escherichia coli lipopolysaccharide (LPS). The birds were weighed and randomly allotted to 1 of 3 treatments at d 19 (3 treatments x 7 replicates x 6 birds). The treatments comprised a control group in which saline was injected at d 21, an LPS-treated group in which LPS (3 mg/kg of BW) was injected at d 21, and finally a berberine and LPS-treated group in which berberine (15 mg/kg of BW) was orally administered from d 19 to d 24 with LPS injection (3 mg/kg of BW) at d 21. Injection of LPS alone decreased (P < 0.01) weight gain, feed intake, and feed conversion compared with the control and the berberine-administered group. Relative liver weight was increased (P < 0.05) in the LPS-treated group 72 h postinjection compared with the control and the berberine-treated group. Total counts of white blood cells and lymphocytes were also increased (P < 0.05) in the LPS-treated group 72 h postinjection. The heterophil concentration of the LPS-treated group was greater (P < 0.05) than that of both the control and the berberine-administered group 24 h postinjection. Broilers in the LPS-treated group had greater (P < 0.05) total serum protein compared with birds in the control and the berberine-administered group both 24 and 72 h postinjection. In addition, the plasma interleukin-6 level of the LPS-treated group was significantly elevated (P < 0.01) at 24 h compared with that of the control and the berberine-administered group. Our results indicate that LPS injection initiated a series of physiological changes typical of an acute phase response in broiler chickens. These effects were largely mitigated by oral administration of berberine.

Effects of yeast culture supplementation on growth performance, intestinal health, and immune response of nursery pigs

A total of 216 weaning pigs were used in 2 experiments to determine the effects of dietary supplementation of yeast culture (YC) at different dose levels on the growth performance, nutrient digestibility, intestinal morphology, intestinal microflora, and immune response in weanling pigs and to determine whether YC can be a candidate to replace antibiotic growth promoters (AGP). In Exp. 1, 192 pigs (7.5 +/- 0.2 kg of BW) weaned at 28 d of age were randomly allotted to 6 treatments: 1) control (without AGP or YC); 2) AGP (chlortetracycline, 80 mg/kg); 3) 2.5 g/kg of YC (Diamond V XP Yeast Culture); 4) 5 g/kg of YC; 5) 10 g/kg of YC; and 6) 20 g/kg of YC. Each treatment had 8 replicated pens with 4 pigs per pen. Pigs were fed the experimental diets for 21 d. Average daily gain of pigs fed 5 g/kg of YC was greater (P < 0.05) than that of pigs in the control and other YC groups. However, there was no difference between the YC and AGP group. Pigs supplemented with 5 g/kg of YC, 10 g/kg of YC, and AGP had a greater (P < 0.01) ADFI than the control; however, G:F was not affected by treatment. Thus, 5 g/kg of YC supplementation level was chosen for Exp. 2. In Exp. 2, to elucidate the mode of action of YC, 24 nursery pigs (5.8 +/- 0.1 kg of BW; 21 d of age) were randomly allotted into 3 treatments for a 21-d trial. Treatments consisted of 1) control (without AGP or YC), 2) AGP, and 3) 5 g/kg of YC. Blood samples were collected weekly to measure CD4(+), CD8(+) percentage, and blood cytokine content. All pigs were harvested to determine treatment effects on gut microbiota, morphology, and immune function. Dietary supplementation of 5 g/kg of YC improved (P < 0.05) ADG of pigs compared with the control group, but performance of pigs fed YC was similar to those fed AGP. Pigs receiving 5 g/kg of YC had greater (P < 0.05) digestibility of DM, CP, GE, and jejunal villus height and villus height:crypt depth ratio (P < 0.05) compared with pigs fed the control diet. However, no differences in performance, digestibility, or gut morphology were observed between pigs fed YC and AGP. Gut interferon (IFN)-gamma concentrations were greater (P < 0.01) for pigs supplemented with YC compared with control pigs and pigs supplemented with AGP on d 21. However, plasma IFN-gamma concentrations were decreased (P < 0.01) in pigs supplemented with YC and AGP compared with control pigs on d 7, and CD4(+) was decreased (P < 0.01) in pigs supplemented with YC and AGP on d 14. Results indicate that dietary YC supplementation at 5 g/kg had a positive effect on growth performance of nursery pigs by improving jejunal villus height and villus height:crypt depth ratio and by modulating gut immune response. The comparable effect of 5 g/kg of YC supplementation and AGP on the growth performance of nursery pigs indicates that YC may be a good candidate as an antibiotic alternative.

Effects of chito-oligosaccharide supplementation on the growth performance, nutrient digestibility, intestinal morphology, and fecal shedding of Escherichia coli and Lactobacillus in weaning pigs

A total of 50 weaning pigs (16 d of age; 4.72 +/- 0.23 kg of BW) were selected to investigate the effect of dietary chito-oligosaccharide (COS) supplementation on growth performance, fecal shedding of Escherichia coli and Lactobacillus, apparent digestibility, and small intestinal morphology. Pigs housed in individual metabolic cages were assigned randomly to 5 treatments (n = 10), including 1 basal diet (control), 3 diets with COS supplementation (100, 200, and 400 mg/kg), and 1 diet with chlortetracycline (CTC) supplementation (80 mg/kg). Fresh fecal samples were collected to evaluate shedding of E. coli and Lactobacillus on d 0, 7, 14, and 21 postweaning. Fresh fecal samples collected from each cage from d 19 to 21 were stored frozen for determination of apparent total tract digestibility. On d 21, all pigs were killed to collect the middle sections of the duodenum, jejunum, and ileum for determination of mucosa morphology. Supplementation of COS at 100 and 200 mg/kg and supplementation of CTC improved (P < 0.05) overall ADG, ADFI, and G:F in comparison with the control. Supplementation of COS at 200 mg/kg as well as supplementation of CTC increased (P < 0.05) apparent total tract digestibility of DM, GE, CP, crude fat, Ca, and P, whereas COS at 100 mg/kg increased (P < 0.05) the digestibility of DM, Ca, and P in comparison with the control diet. Pigs receiving diets supplemented with COS or CTC had a decreased (P < 0.05) incidence of diarrhea and decreased diarrhea scores compared with control pigs. Fecal samples from pigs receiving diets supplemented with COS had greater (P < 0.05) Lactobacillus counts than those from control pigs and pigs receiving diets supplemented with CTC on d 14 and 21. However, supplementation of COS at 200 mg/kg and supplementation of CTC decreased (P < 0.05) E. coli counts in the feces on d 21 compared with the control diet. Dietary supplementation of COS at 200 mg/kg and of CTC increased (P < 0.05) the villus height and villus:crypt ratio at the ileum and jejunum, and COS at 100 mg/kg also increased (P < 0.05) the villus height in the ileum compared with the control diet. The current results indicated that dietary supplementation of COS at 100 and 200 mg/kg enhanced growth performance by increasing apparent digestibility, decreasing the incidence of diarrhea, and improving small intestinal morphology.

Effects of chito-oligosaccharide supplementation on performance, nutrient digestibility, and serum composition in broiler chickens

A total of 196 day-old male broiler chicks were randomly allocated to 1 of 4 treatments in a study conducted to determine the effects of dietary supplementation of chito-oligosaccharide (COS) on growth, nutrient digestibility, and serum composition. The experimental diets consisted of an unsupplemented control diet based on corn, soybean meal, and fish meal or similar diets supplemented with either chlortetracycline, 50 mg/kg of COS, or 100 mg/kg of COS. Each treatment was fed to 7 replicate pens of birds, with 7 birds per pen. Broiler performance, nutrient digestibility, cecal microbial concentrations, and serum indices were measured at the end of the starter (d 21) and grower phases (d 42). During the starter period and overall, broilers fed 50 or 100 mg/kg of COS had better (P<0.05) average daily gain, average daily feed intake, and feed conversion than the control birds. The performance of birds fed chlortetracycline was generally intermediate between that of the control and the 2 COS treatments. Compared with the birds in the control or chlortetracycline treatments, the birds receiving 100 mg/kg of COS had better nutrient digestibility of DM, energy, calcium, and phosphorus; higher (P<0.05) concentrations of cecal Lactobacillus; and lower (P<0.05) serum triglyceride and total cholesterol during the starter phase. During the grower phase, the birds fed 100 mg/kg of COS had higher (P<0.05) calcium digestibility and CP retention than those fed the chlortetracycline treatment, and lower concentrations of cecal Escherichia coli than birds in the control treatment. The serum growth hormone level in birds fed 50 mg/kg of COS was higher (P<0.05) than in the other treatments. The birds fed 100 mg/kg of COS had lower (P<0.05) serum triglyceride, higher (P<0.05) serum high-density lipoprotein cholesterol, and higher serum total protein content than birds in the other treatments. In conclusion, dietary supplementation with COS appeared to improve the average daily gain of broilers by increasing the average daily feed intake and nutrient digestibility and modulating the concentrations of cecal microbial flora. Additionally, COS increased serum protein and high-density lipoprotein cholesterol and decreased serum triglyceride.

[Effect on intratumoral T lymphocyte and its subset in oral squamous cell carcinoma following immumnochemotherapy]

The relative numbers of CD(3)(+),CD(3)(+),CD(8)(+) and HLA-RD(+) cells in the tumor tissue before and after inductive therapy was counted using immunohistochemical technique of Avidin Biotin-Peroxidase Complex(ABC),and then the effect on local immune cell following two different inductive therapies was comparatively analysed.The results showed that S-PVP therapy could result in significant increasing in numbers of CD(3)(+)and CD(4)(+) cells intratumorally as compared with pre-therapy(P<0.05),and in slignt increasing in numbers of CD(8)(+) and HLA-DR(+) cell,which is no significant difference between pre-and post-therapy.In the PVP group,there was no significant difference in numbers of CD(3)(+),CD(4)(+),CD(8)(+) and HLA-DR(+) cells between pre-and post-treatment.The results suggested that T lymphocyte in the tumor site could significantly increase in numbers following the S-PVP therapy,and PVP chemotherapy did not obviously affect the local cellular immunity.

[Observation of clinical and pathological responses in short-term following immunochemotherapy for oral squamous cell carcinoma]

24 patients with oral SCC in Stage T3 or T4 were randomly divided into two groups,and treated with two inductive therapies,13 cases of whom received an immumochemotherapy regimen(Sapylin 15 KE+CDDP 70mg/m(2)+VCR 1.4mg/m(2)+PYM 80mg,S-PVP) and 11 cases,a chemotherapy regimen(CDDP 90mg/m(2)+VCR 1.4mg/m(2)+PYM 80mg,PVP) as control.The clinical response and pathological effect after immunochemotherapy or chemotherapy were evaluated through the clinical measurement of tumor size and pathological examination of the specimen.The results showed that the rate of clinical and pathological responses in S-PVP group were 92.3% and 84.6%,respectively;and in PVP group,72.7% and 45.5%.There was a significant difference between two groups in pathological effect(P<0.05),which indicated that the S-PVP regimen in short-term was better than of inductive chemotherapy.It may be relatively objective and accurate in comparison with clinical investigation which could act as an important supplement to the evaluation of clinical response.