Characterization of Campylobacter jejuni in large-billed crows (Corvus macrorhynchos) in Tochigi prefecture, Japan.

As free-living crows are a potential source of Campylobacter infections in broilers and cattle, we characterized Campylobacter spp. isolated from crows using multilocus sequence typing and antimicrobial susceptibility testing. We obtained 82 samples from 27 birds captured at seven different times using a trap set in Tochigi prefecture, Japan. Campylobacter jejuni was isolated from 55 (67.1%) of the 82 samples and classified into 29 sequence types, of which 21 were novel. Tetracycline and streptomycin resistance rates were 18.2% and 3.6%, respectively. These results show that most types of C. jejuni infecting crows differ from those isolated from humans, broilers, and cattle. Thus, the importance of free-living crows as reservoirs of Campylobacter infections in broilers and cattle may be limited.

Pathogenic characterization of Erysipelothrix rhusiopathiae Met-203 type SpaA strains from chronic and subacute swine erysipelas in Japan.

To characterize the Erysipelothrix rhusiopathiae Met-203 type surface protective antigen (Spa) A strains causing swine erysipelas in Japan, the nucleotide sequence of the hypervariable region of the spaA gene was determined in 80 E. rhusiopathiae (serotype 1a) isolates collected from pigs with chronic and subacute swine erysipelas in 14 prefectures in 2008-2014. In this study, 14 (17.5%) isolates were Met-203 type SpaA strains. We confirmed the pathogenicity of a Met-203 type SpaA strain in specific-pathogen-free pigs. In this experiment, the two challenged pigs displayed arthritis, urticaria and other clinical signs, but recovered within 10 days. Our results reveal the existence of the E. rhusiopathiae Met-203 type strains that have been causing chronic erysipelas in Japan.

Establishment of an equine tetanus antitoxin reference standard for veterinary use in Japan.

To establish the first National Veterinary Assay Laboratory (NVAL) equine tetanus antitoxin reference standard for veterinary use, we manufactured vials of a candidate antitoxin. These were quality tested for moisture content, vacuum, colour, clarity, and the presence of foreign objects. Ultimately, 115 quality-controlled vials were prepared. To estimate the antitoxin potency of the candidate standard, three different laboratories conducted parallel line assays alongside the existing antitoxin standard. These potency estimates ranged from 38 to 42 IU. This activity was maintained for two years after manufacture, as compared with a fresh vial. No statistically significant non-linearity or non-parallelism of the regression lines was observed (p > 0.05). Statistical assessment of inter- and intra-laboratory variability revealed acceptable coefficients of variation of 3.2% and 2.4-3.1%, respectively. Based on these results, the potency of the potential reference standard was calculated at 40 units of antitoxin activity per 1-mL vial. Vials of this preparation were distributed for use as the first equine tetanus antitoxin reference standard for veterinary use in September 2015.

Development of a serology-based assay for efficacy evaluation of a lactococcicosis vaccine in Seriola fish.

Lactococcicosis is an infection caused by the bacterium Lactococcus garvieae and creates serious economic damage to cultured marine and fresh water fish industries. The use of the assay currently applied to evaluate the potency of the lactococcicosis vaccine is contingent upon meeting specific parameters after statistical analysis of the percent survival of the vaccinated yellowtail or greater amberjack fish after challenge with a virulent strain of L. garvieae. We found that measuring the serological response with a quantitative agglutinating antibody against the L. garvieae antigen (phenotype KG+) was an effective method of monitoring the potency of lactococcicosis vaccines. Vaccinated fish had significantly higher antibody titers than control fish when the L. garvieae Lg2-S strain was used as an antigen. Furthermore, the titer of the KG + agglutinating antibody was correlated with vaccine potency, and the cut-off titer was determined by comparing the data with those from the challenge test. An advantage of the proposed serology-based potency assay is that it will contribute to reduced numbers of animal deaths during vaccine potency evaluations.

Prevalence of Met-203 type spaA variant in Erysipelothrix rhusiopathiae isolates and the efficacy of swine erysipelas vaccines in Japan.

Since 2009, erysipelas infection among pigs in Japan has been increasing. This study investigated the prevalence, and characteristics of Erysipelothrix rhusiopathiae isolates in Japan from 2008 to 2010 and assessed the efficacy of current commercial erysipelas vaccines. Based on polymorphisms in a 432-bp hypervariable region in the surface protective antigen A (spaA) gene, 34 isolates were classified into three groups: (i) Group 1 with methionine at position 203 (Met-203) and isoleucine at position 257 (Ile-257) (18 isolates of serotype 1a and one untypable isolate). (ii) Group 2 with Ile-257 (12 isolates of serotypes 1a, 1b, 2, 10 and 11), and (iii) Group 3 with alanine at position 195 (Ala-195) and Ile-257 (three isolates of serotype 1a). Isolates with Met-203 were highly pathogenic in mice and pigs, causing death in the pig and LD50 values of 0.45-1.45 CFU per mouse. One live and three inactivated commercial E. rhusiopathiae vaccines were evaluated for efficacy against a Met-203 isolate. Almost all mice and pigs that received vaccine survived, while non-vaccinated controls all died within 5 days of the challenge. This indicates that swine erysipelas vaccines might be still effective in protecting animals against the recently prevalent Met-203 isolates in Japan.

Development of an in vitro assay based on humoral immunity for quality control of oil-adjuvant Pseudotuberculosis vaccine in Yellowtail Seriola quinqueradiata.

Photobacterium damselae subsp. piscicida is an infectious pathogen that causes Pseudotuberculosis in Yellowtail fish. In Japan, several oil-adjuvant vaccines for Pseudotuberculosis have been approved for control of infectious diseases in aquaculture. Before distribution of an approved fish vaccine, an artificial challenge test for quality control is performed by the manufacturer and National Veterinary Assay Laboratory under Pharmaceutical Law of Japan to confirm potency. In this study, artificial challenge tests with a range of five diluted or undiluted approved vaccines was performed to determine the relationship between antigen levels and vaccine efficacy. Immunization of fish with the undiluted vaccine prevented Pseudotuberculosis. Results of artificial challenge tests demonstrated vaccine efficiency was dose dependent. Agglutination assays using immune sera were performed to determine agglutination titers, which were also dose dependent. These results suggest a link between survival rate in the artificial challenge tests and agglutination titers. Western blotting analysis identified a specific protein approximately 37 kDa in size in vaccinated fish. We confirmed antibodies were produced in vaccinated fish by immunoreactions with the approved vaccine. An agglutination assay based on humoral immunoreactions would be a useful alternative to the artificial challenge test for quality control of vaccines for aquaculture.

Effect of Antimicrobial Exposure on AcrAB Expression in Salmonella enterica Subspecies enterica Serovar Choleraesuis.

Understanding the impact of antimicrobial use on the emergence of resistant bacteria is imperative to prevent its emergence. For instance, activation of the AcrAB efflux pumps is responsible for the emergence of antimicrobial-resistant Salmonella strains. Here, we examined the expression levels of acrB and its multiple regulator genes (RamA, SoxS, MarA, and Rob) in 17 field isolates of S. Choleraesuis by using quantitative PCR methods. The expression of acrB increased in eight of the field isolates (P < 0.05). The expression of acrB was associated with that of ramA in one isolate, soxS in one isolate, and both these genes in six isolates. Thereafter, to examine the effect of selected antimicrobials (enrofloxacin, ampicillin, oxytetracycline, kanamycin, and spectinomycin) on the expression of acrB and its regulator genes, mutants derived from five isolates of S. Choleraesuis were selected by culture on antimicrobial-containing plates. The expression of acrB and ramA was higher in the mutants selected using enrofloxacin (3.3-6.3- and 24.5-37.7-fold, respectively), ampicillin (1.8-7.7- and 16.1-55.9-fold, respectively), oxytetracycline (1.7-3.3- and 3.2-31.1-fold, respectively), and kanamycin (1.6-2.2- and 5.6-26.4-fold, respectively), which are AcrAB substrates, than in each of the parental strains (P < 0.05). In contrast, in AcrAB substrate-selected mutants, the expression of soxS, marA, and rob remained similar to that in parental strains. Of the four antimicrobials, the level of ramA expression was significantly higher in the enrofloxacin- and ampicillin-selected mutants than in the oxytetracycline- and kanamycin-selected mutants (P < 0.05), whereas the expression levels of acrB and multiple regulator genes in spectinomycin-selected mutants were similar to those in each parental strain. These data suggest that exposure to antimicrobials that are AcrAB substrates enhance the activation of the AcrAB efflux pump via RamA, but not via SoxS, MarA, or Rob in S. Choleraesuis.

An in vitro method for evaluating endotoxic activity using prostaglandin E(2) induction in bovine peripheral blood.

Severe side effects of veterinary vaccines, in particular Histophilus somni-containing vaccines for cows, have frequently been reported in Japan. These side effects are probably caused by endotoxins. Contamination levels of endotoxins could be monitored using the Limulus amebocyte lysate (LAL) test; however, the LAL test is not completely adequate for evaluation of in vivo endotoxic activities. In this study, we established a method for evaluating endotoxic activities using prostaglandin E2 (PGE2) induction in bovine peripheral blood. Blood and standard endotoxin, derived from Escherichia coli, were mixed and incubated. The concentration of induced PGE2 in the culture supernatant reached a maximum after 24-h incubation. A linear dose-response curve was observed for PGE2 concentration and the logarithmic transformed standard endotoxin concentration (5-5000 ng/ml). The endotoxic activity of H. somni in cows was the highest among those of several tested endotoxins. However, the LAL activities of H. somni were not as high as those of the other tested endotoxins. These results may provide a reason for the many report of side effects of H. somni-containing vaccines. The PGE2 detection assay described here could be a valuable method for evaluating the endotoxic activities of vaccines in cows.

Bovine whole-blood culture as a tool for the measurement of endotoxin activities in Gram-negative bacterial vaccines.

In order to analyze bovine immune reactions against the Gram-negative bacterial vaccine, bovine whole-blood culture was used to investigate the pro-inflammatory cytokine responses stimulated with lipopolysaccharides (LPS) extracted from Escherichia coli, Salmonella enterica, Pseudomonas aeruginosa, and Klebsiella pneumoniae. We also examined the interaction between LPS and aluminum hydroxide gel for endotoxin activity and pro-inflammatory cytokine responses of whole bovine blood. Alteration in the mRNA concentrations of tumor necrosis factor (TNF)-α, interleukin (IL)-1ß, and IL-10 in whole-blood culture at 4h after stimulation with different doses of LPS was observed and determined by quantitative reverse-transcription polymerase chain reaction (qRT-PCR). The mRNA concentrations of TNF-α and IL-1ß changed in a dose-dependent manner and differed depending on the type of LPS. Limulus test revealed that endotoxin activity was remarkably reduced when aluminum hydroxide gel was added to LPS. In contrast, the mRNA concentration of TNF-α in whole bovine blood was enhanced by LPS mixed with aluminum hydroxide gel. These results suggest that bovine whole-blood culture can be utilized to detect endotoxin activity of Gram-negative bacterial vaccines. In addition, whole-blood culture offers several advantages, such as ease of performance, few preparation artifacts, and a physiological cell environment, for investigating bovine immune response compared with the Limulus test.

Clostridium difficile isolated from the fecal contents of swine in Japan.

A total of 250 fecal content samples were collected from 25 farrow-to-finish pig farms and examined for the prevalence of Clostridium difficile by using ethanol treatment followed by plating onto selective media--cycloserine-cefoxitin-mannitol agar--for the isolation of Clostridium difficile. Two specimens (0.8%, 95% confidential interval: 0-2.9%) were positive for C. difficile. One isolate was only positive for toxin B, and the other isolate was negative for both toxins A and B. Thus, prevalence of Clostridium difficile was found to be low among finishing pigs in Japan.

Evaluation of transferability of R-plasmid in bacteriocin-producing donors to bacteriocin-resistant recipients.

Bacteriocin-producing Escherichia coli (donors) rapidly kill conventional recipient E. coli DH5α in conjugation experiments. To evaluate plasmid transferability of bacteriocin-producing donors, we established 2 different bacteriocin-resistant mutants derived from E. coli DH5α and used them as recipients. When the bacteriocin-resistant mutants were used in conjugation experiments, the transconjugant recovery from 20 bacteriocin-producing donors increased from 5% (1/20) to 65% (13/20), and the transfer frequencies increased. These results showed that bacteriocins inhibited the transfer of the R-plasmid from bacteriocin-producing donors. Thus, application of bacteriocin-resistant recipients might aid the evaluation of the potential transferability of plasmids from bacteriocin-producing donors.

Establishment of evaluation method to determine effects of veterinary medicinal products on manure fermentation using small-scale composting apparatus.

To evaluate on a laboratory scale the influence of veterinary medicinal products (VMPs) excreted into feces on manure fermentation, we have developed an evaluation method that uses a small-scale composting apparatus. Each run is of approximately 3 kg scale and the operation can be conducted in an environmentally controlled laboratory. The main evaluation parameter is calorific value generated by aerobic fermentation. At the sulfadimethoxine (SDM) trial, the volume of CO(2) generated during fermentation and the disappearance of the inhibitory effect of immature manure on sprouting (using Komatsuna (Brassica rapa var. perviridis)) were measured. In addition, DNA of 16S rRNA was extracted from a manure sample and subjected to denaturing gradient gel electrophoresis (DGGE). The results suggest that the presence of such VMPs in feces affected the microbial community in manure fermentation, and indicate that the evaluation method may be used as a standard method to evaluate the effect of VMPs on the microbial community. Using the method, we obtained data of the influence of five VMPs approved for stockbreeding in Japan on swine manure fermentation. Erythromycin (EM) affected the calorific value even at a relatively low concentration (105 mg/3 kg manure). In contrast, oxytetracycline hydrochloride (OTC), norfloxacin (NFLX), and tylosin tartrate (TS) had no effect at that concentration. These VMPs also affected the increase of fermentation temperature when added at high concentrations.

Contribution of enhanced efflux to reduced susceptibility of Salmonella enterica serovar Choleraesuis to fluoroquinolone and other antimicrobials.

We examined antimicrobial susceptibility and efflux systems in laboratory-derived mutants of Salmonella enterica serovar Choleraesuis selected by culture on fluoroquinolone-containing plates. The mutants exhibited decreased susceptibilities to quinolones and several other antimicrobials. Mutations in the gyrA gene were not always found in the mutants. Accumulation assays revealed that intracellular enrofloxacin concentrations were significantly lower in the mutants compared with parent isolates. Increased expression of acrB mRNA can explain the decreased susceptibilities to several antimicrobials but not in the case of carbonyl cyanide m-chlorophenylhydrazone (CCCP). Decreased susceptibility to CCCP may result from the increased expression of emrA mRNA. These results suggest that the enhancement of multiple efflux pumps is responsible for decreased susceptibilities to several antimicrobials in the laboratory-derived mutants.

Intracellular concentrations of enrofloxacin in quinolone-resistant Salmonella enterica subspecies enterica serovar Choleraesuis.

The emergence of fluoroquinolone-resistant strains of Salmonella enterica subspecies enterica serovar Choleraesuis is an important concern in several countries, including Japan. We examined the intracellular concentration of enrofloxacin in S. Choleraesuis to determine the existence of a relationship with the emergence of quinolone resistance. The intracellular concentration of enrofloxacin was significantly lower in nalidixic acid-resistant isolates compared with nalidixic acid-susceptible isolates. In the presence of carbonyl cyanide m-chlorophenylhydrazone, the intracellular concentration of enrofloxacin increased in all isolates, with no significant difference in the intracellular concentration between nalidixic acid-susceptible and -resistant isolates. The frequency of emergence of fluoroquinolone-resistant mutants was higher in susceptible isolates with a low intracellular concentration of enrofloxacin. The results presented suggest that a decrease in the intracellular concentration of enrofloxacin is related to active efflux pumps and contributes to the emergence of fluoroquinolone resistance.