Action of selected antibiotics on four common bacteria associated with diseases of fish

Abstract. Four bacteria commonly associated with diseases of fish ( Aeromonas hydrophila complex, Aeromonas salmonicida, Flexibacter columnaris -like organisms and Pseudomonas fluorescens ) were evaluated in a serial dilution system for susceptibility to four antibiotics commonly used in the treatment of bacterial fish diseases (chloramphenicol, erythromycin, furpyrinol and oxytetracycline). Findings were expressed as minimum inhibitory concentration (MIC) and minimum bactericidal concentration (MBC). Furpyrinol was found to have the lowest MIC and MBC against A. hydrophila complex, A. salmonicida and F. columnaris-like organisms. MIC and MBC's for oxytetracycline were complicated by the presenceof R-plasmids, but were less than 4.0 mcg/ml for those without plasmids. Pseudomonas fluorescens was susceptible only to oxytetracycline. MIC for all groups of organisms using chloramphenicol was generally less than 16.0 mcg/ml. Susceptibility to erythromycin by these groups of organisms was greater than 16 mcg/ml.     

Comparative sensitivity of five fish cell lines to wild type infectious haematopoietic necrosis virus from two Oregon sources

Abstract. Five fish cell lines (CHSE-214, STE-137, RTG-2, EPC and FHM) were compared for sensitivity to infectious haematopoietic necrosis virus (IHNV) from samples obtained from naturally-infected fish. Infectious ovarian fluids were obtained from steelhead trout, Salmo gairdneri Richardson, at the Round Butte Hatchery in central Oregon and tissue homogenates were prepared from chinook salmon, Oncorhynchus tshawytscha (Walbaum), alevins during an IHN virus epizootic at the Elk River Hatchery in coastal Oregon. The only lines to show characteristic viral cytopathology by plaque or end-point dilution assay for the steelhead trout virus isolate were the EPC and FHM cell lines. The chinook salmon isolates produced CPE in CHSE-214, STE-137, FHM and EPC cells. The titre of the salmon virus isolate was 10-50-fold higher on FHM and EPC cells by both assay methods. Neither by end-point nor plaque assay did the Round Butte or Elk River isolates produce CPE on RTG-2 cells. With both virus isolants both cell lines showed that greater sensitivity was obtained with plaque assay than with end-point titration. Pre-treatment of the cells with the polycation, polybrene, did not increase the virus titre in either assay. However, a transient enhancement in virus titre was observed in polybrene-treated STE-137 and CHSE-214 cells.     

Enteric redmouth bacterium: comparison of isolates from different geographic areas

Abstract. Characteristics of 18 strains of Yersinia ruckeri the causative agent of enteric redmouth disease, from a variety of hosts and a wide geographic range were compared. Except for variations in colonial morphology and in citrate, sorbitol, and trehalose reactions, the strains were morphologically and biochemically homogeneous. Sixteen strains reacted with antiserum against the first serotype reported, and one strain reacted with antiserum against a more recently reported serotype. One strain represented a third serotype. Evidence presented indicated that extension of the geographic range may not be entirely a result of the transport of carrier fish.     

Duration of Mycoplasma hyopneumoniae Infection in Gnotobiotic Pigs

Sixteen gnotobiotic pigs raised in flexible plastic isolators (four pigs per isolator) were inoculated with a culture of Mycoplasma hyopneumoniae. One pig was killed and underwent necropsy at weekly intervals for the following 16 weeks. Macroscopic lesions were observed in the lungs of 13 of 16 pigs and microscopic lesions were found in 14 of 16 pigs. Mycoplasma hyopneumoniae was cultured from the trachea or lungs from 10 of the 16 pigs. Scanning electron microscope studies showed areas of damage to the cilia, collections, of leucocytes and mucus, and mycoplasma in the trachea as well as the bronchi. These conditions were found in all the pigs seen at necropsy from nine to 16 weeks postinoculation and there was no evidence of noticeable regression or recovery during this 16 week period.     

Failure of hyperimmune plasma to prevent pneumonia caused by Rhodococcus equi in foals

SUMMARY A trial was conducted on a Thoroughbred stud to determine whether or not the administration of anti-Rhodococcus equi hyperimmune plasma would reduce the prevalence of R equi pneumonia (rattles) in foals born in the 1992 horse breeding season. Hyperimmune plasma was administered to 34 foals; another 57 foals were untreated. There was no significant difference in the number of transfused foals developing R equi pneumonia compared with the untreated foals. The time required for recovery from pneumonia between the 2 groups was not significantly different.     

Serological responses to two serovar‐independent ELISA antigens of Actinobacillus pleuropneumoniae in Australian commercial pig herds

Objective To compare serological responses in pig herds classified as low or high risk for disease caused by Actinobacillus pleuropneumoniae, using two ELISA tests based on serovar‐independent antigens. Procedure Cross‐sectional sampling was undertaken in 13 commercial herds, the clinical and slaughter histories of which indicated either freedom from (n = 5) or prior confirmed cases of A. pleuropneumoniae (n = 8). In nine herds, approximately 40 pigs each were sampled at 4, 8, 12, 16 and 20 weeks. Three of the remaining four herds were sampled between 6 and 30 weeks of age, and the last was sampled only prior to slaughter, at approximately 24 weeks. Sera were tested in ELISA based on two antigens common among A. pleuropneumoniae serovars: a 39‐kDa outer membrane protein and a recombinant ApxIVA‐N terminus protein. Results Sampling of 1 and 5 to 6‐month‐old pigs provided the most useful information on herd status. The 39‐kDa ELISA was sensitive in detecting infected herds, but had evidence of cross‐reactivity with high seroreactivity rates in older pigs in some low‐risk herds. The ApxIVA‐N ELISA was less seroreactive in high‐risk herds and had higher specificity in low‐risk herds. Conclusion ELISA based on the 39‐kDa subunit are of limited use, because of possible cross‐reactivity, but a high negative predictive value may be useful for risk assessment in suspect herds. Maternal antibody to ApxIVA‐N may be of value in detecting high‐risk herds, but 5% of 4‐week‐old pigs in low‐risk herds were also seropositive in this assay.     

Gradual Occlusion of Extrahepatic Portosystemic Shunts in Dogs and Cats Using the Ameroid Constrictor

Gradual occlusion of the splenic vein, using a specialized device (ameroid constrictor), was evaluated experimentally in three normal beagle dogs. Splenoportograms were used to verify that total occlusion of the splenic vein had occurred in all dogs within 4 to 5 weeks after application of the device. The ameroid constrictor (AC) was also evaluated as a method of gradual vascular occlusion in 12 dogs and two cats with single, extrahepatic, portosystemic shunts (PSS). Serum bile acid (SBA) concentrations were measured and portal scintigraphy (PS) was performed on all 14 animals preoperatively and 10, 20, 30, and 60 days postoperatively. Two dogs (14%) died from portal hypertension in the early postoperative period. One dog and one cat developed multiple acquired PSS, confirmed by mesenteric portography 90 days after the operation. Portal scintigraphy confirmed total occlusion of the primary shunt in the other 10 animals. Shunt fractions (SF), as measured by PS on postoperative days 30 and 60, declined significantly from preoperative values. Significant decreases were noted between preoperative and postoperative values for preprandial SBA on postoperative day 60 and for postprandial SBA on postoperative day 30. SBA concentrations did not correlate with SF. Based on this study, gradual vascular occlusion using the AC is recommended as a method for treatment of single, extrahepatic, PSS.     

Immunological detection of cardiac glycosides in plants

Summary Australian native and introduced plants were examined, using digoxin immunoassays, to detect the presence of cross-reacting cardiac glycosides. These compounds were found in 27 species from 20 genera. The assay technique can also be used on serum samples to confirm cardiac glycoside ingestion.     

CRETINISM IN A NORTH AMERICAN BLACK BEAR(URSUS AMERICANUS)

Congenital hyperplastic goiter and cretinism were documented in a 16 month-old male North American black bear (Ursus americanus). The cub was captured at approximately 8 months of age and maintained for an additional 8 months in captivity. Clinical signs included growth retardation, clumsiness, and facial dysmorphism. Hypothyroidism was documented by determining serum triiodothyronine (T3) and thyroxine (T4) levels. Lysosomal storage disease was ruled out by measuring various lysosomal enzyme activities. Serologic, radiographic, computed tomographic, necropsy, and histopathologic findings were consistent with congenital hypothyroidism and cretinism.