Modified resazurin microtiter assay for in vitro and in vivo assessment of sulfamonomethoxine activity against the fish pathogen <Emphasis Type="Italic">Nocardia seriolae</Emphasis>

Resazurin microtiter assay (REMA) was carried out using four sulfonamides, three culture media, and four inoculum sizes as a first screening step to establish an easy-to-interpret sulfonamides susceptibility testing method for Nocardia seriolae. The in vitro activity of sulfamonomethoxine (SMM) against 190 clinical N. seriolae isolates was then examined, and in vivo experimental treatment was performed. When the culture medium and the inoculum size were considered in tandem, a 0.5× the original concentration of cation-adjusted Mueller–Hinton broth and an inoculum size of 10² CFU/well showed the clearest endpoint reading for all tested drugs, and the REMA-generated data were in excellent agreement with those generated by the reference Etest method. SMM activity showed minimum inhibitory concentration (MIC) values of 4–32 μg/ml against all tested N. seriolae isolates. Treatment of amberjack groups experimentally infected with N. seriolae isolates having SMM MICs of 4 and 32 μg/ml, resulted in survival rates of 100% and 87.5% in the two groups, respectively. In this study, we developed a simple visual method to test SMM activity against N. seriolae.     

A new host record of Sphaerospora epinepheli (Myxosporea: Bivalvulida) occurring on orange-spotted grouper Epinephelus coioides from Thailand: epidemiology, histopathology and phylogenetic position

In 1991, the first record of Sphaerospora epinepheli was described as a kidney parasite of wild and cultured malabar grouper, Epinephelus malabaricus, along coastlines of Thailand, the Gulf of Thailand and the Andaman Sea. However, the present study detected high infection of this parasite in kidney renal tubes of orange spotted grouper, Epinephelus coioides, collected from Andaman Sea. The highest infection rate of 36.82% was observed during the rainy season in 2009 in Phang-Nga Bay, in the north of Andaman Sea, which is an important grouper production site in Thailand. The biological and histopathological data of the parasite in this new host record are presented. Species classification is described based on morphological data of mature spore and molecular analysis of myxosporean 18S rDNA phylogeny including that of S. epinepheli which infected E. malabaricus. The genetic position of this parasite found in two host species was also studied. The phylogenetic tree analysis of small-subunit rDNA sequences of S. epinepheli from both infected hosts was constructed using two algorithms, maximum likelihood (ML) and Bayesian inference (BI). They were placed in the clustered basal sphaerosporid clade that contain four long SSU rDNA sphaerosporid species including Sphaerospora truttae, Sphaerospora elegans, Sphaerospora ranae, Sphaerospora fugu and Bipteria formosa with strong bootstrap supports. Histopathologically, renal intratubular myxosporean spores were associated with tubulonephosis, tubular necrosis, chronic interstitial nephritis and mimic membranoproliferative glomerulonephritis. This myxosporean parasite appears to be a significant pathogen on the basis of pathological changes in the renal tubules and is highly distributed in orange-spotted grouper.     

Spatiotemporal distribution of barley and wheat plants naturally infected with bacterial black node in fields in western Japan

Bacterial black node caused by Pseudomonas syringae pv. syringae is the most serious bacterial disease of barley and wheat in Japan. The spatiotemporal distribution of barley and wheat plants infected with bacterial black node in fields in 2016–2017 was analyzed using Taylor’s model and Iwao’s model. In Taylor’s model, the sample variance (s ²) of the total and the newly diseased plants at each observation increased with mean plant density (m). In Iwao’s model, although the mean crowding (m*) of total and newly recognized diseased plants increased with m, Taylor’s model fit the data better than did Iwao’s model. Thus, bacterial black node could be explained as a colony expansion model.     

Morphological Studies on Zoospores of Aphanomyces cochlioides and Changes during Interaction with Host Materials

The behavioral and morphological diversity of intact zoospores of Aphanomyces cochlioides and their dynamic morphological changes when interacting with the host or a host-specific zoospore attractant were studied by light and electron microscopy. The reniform-ovate zoospore has two heterokont flagella, both inserted in a ventral groove. The anterior flagellum possesses two rows of tripartite tubular hairs (TTHs) distributed throughout its length, whereas the posterior flagellum was ornamented with two rows of highly dense fine tubular hairs, except on its tapered terminal part. The tip of the posterior flagellum has a bunch of similar fine hairs like those on the flagellum shaft. The biflagellated zoospores quickly aggregated on the host (spinach) root, adhered to the root surface, encysted by shedding or retracting the flagella, germinated at a fixed point to form germ tubes, and finally invaded the root tissues via the appressoria within 50–60 min. This precise homing response of A. cochlioides zoospores reflects guidance by a host-specific signal(s) for locating potential infection sites, differentiation of zoospores to cystospores, formation of infection structures and/or germ-tube tropism for completing pre-infection events in haste. Prior to the encystment, the posterior flagellum may be involved in successful docking on the root surface by tip contact followed by shedding or retraction. Received 22 January 2001/ Accepted in revised form 28 May 2001     

Reovirus isolation from healthy dogs in Japan

Twenty-two strains of viruses isolated from apparently healthy dogs were identified as reoviruses on the basis of their biological, physico-chemical and morphological properties. The cross hemagglutination-inhibition test revealed that all of them were of type 1, except one which was of type 3. The significance of reovirus isolation from healthy animals is discussed.     

Protective effect of Clostridium septicum alpha-toxoid vaccine against challenge with spores in guinea pigs

The protective effect of an alpha-toxoid vaccine of Clostridium septicum purified alpha-toxin was investigated in guinea pigs. Purified alpha-toxin was treated with formalin to make toxoid, and alpha-toxoid vaccine was prepared by mixing alpha-toxoid (4 to 64 microg/dose) with an aluminum phosphate gel as adjuvant. Guinea pigs were immunized twice with different doses of alpha-toxoid vaccine, and challenged with spores of C. septicum. The guinea pigs surviving after challenge had been immunized with 8 microg/dose or more of alpha-toxoid. All these animals produced titers of 20 units or higher of antitoxin at the challenge. The results suggest that C. septicum alpha-toxin plays an important role in protection against challenge with spores in guinea pigs.     

Effect of farm household income levels and rice-based diet or water hyacinth (Eichhornia crassipes) supplementation on growth/cost performances and meat indexes of growing and finishing pigs in the Mekong Delta of Vietnam

An on‐farm trial was carried out to improve the current low‐income farmers’ diet and to assess farm conditions that could accept the new ingredients using locally available feed resources in the Mekong Delta region. A total of 42 local Large White‐type pigs, comprising 20 barrows and 22 gilts with initial‐to‐final mean live weight of 34.2–93.0 kg, were used. The trial was designed as a 3 × 3 factorial with three agricultural gross income levels of seven farm households and three dietary treatments. The annual income levels were high income (HI; $US2355 on average), medium income (MI; $US1439) and low income (LI; $US1116). The three types of diets were farmers’ common diet (FCD), rice‐based diet (RBD) and water‐hyacinth (Eichhornia crassipes)‐supplemented diet (WHD). A total of 12 pigs, consisting of two barrow–gilt couples in each diet treatment, were slaughtered at the end of the trial. The daily weight gain (DG) was higher and the feed conversion ratio (FCR) was lower in the MI and LI pigs than in the HI pigs over the entire fattening period (P < 0.01). No significant effect of the diet treatments was observed on the aforementioned two parameters, but the backfat thickness was least in WHD (16.8 mm) and next least in RBD (17.1 mm), compared with that of FCD pigs (19.4 mm; P < 0.05). The iodine values of RBD and WHD backfat were lower (P < 0.001) than those of FCD backfat. The cost performance, defined as feed cost per kg weight gain, was lowest for MI, intermediate for LI and highest for HI levels (P < 0.05). Therefore, the benefit was highest at the MI level and lowest at the HI level (P < 0.05). In contrast, cost performance of the diet treatments tended to be higher in FCD, and lower in RBD and WHD (P < 0.1). Then, the benefit tended to be higher in RBD and WHD than in the FCD diet (P < 0.1). Overall, these results suggest that the RBD and WHD diets be recommended especially to households with medium and low agricultural incomes.     

Resistance of Venturia nashicola to thiophanate-methyl and benomyl: build-up and decline of resistance in the field

Changes in the proportion of benzimidazole-resistant strains in populations of Venturia nashicola were monitored in pear orchards. Successive applications of thiophanate-methyl increased the level of resistance in the populations. When the application of benzimidazoles was stopped and other fungicides were applied, the proportion of highly resistant strains gradually decreased and the proportion of intermediately resistant, weakly resistant and sensitive strains increased. It is suggested that this phenomenon is an example of genetic homeostasis within microbial populations.