Concomitant antibiotic and mercury resistance among gastrointestinal microflora of feral brook trout, Salvelinus fontinalis.

Twenty-nine bacterial isolates representing eight genera from the gastrointestinal tracts of feral brook trout Salvelinus fontinalis (Mitchell) demonstrated multiple maximal antibiotic resistances and concomitant broad-spectrum mercury (Hg) resistance. Equivalent viable plate counts on tryptic soy agar supplemented with either 0 or 25 µM HgCl(2) verified the ubiquity of mercury resistance in this microbial environment. Mercury levels in lake water samples measured 1.5 ng L(-1); mercury concentrations in fish filets ranged from 81.8 to 1,080 ng g(-1) and correlated with fish length. The presence of similar antibiotic and Hg resistance patterns in multiple genera of gastrointestinal microflora supports a growing body of research that multiple selective genes can be transferred horizontally in the presence of an unrelated individual selective pressure. We present data that bioaccumulation of non-point source Hg pollution could be a selective pressure to accumulate both antibiotic and Hg resistant bacteria.

Identification of a multidrug efflux pump in Flavobacterium johnsoniae.

In this study, the mechanism conferring multiple drug resistance in several strains of flavobacteria isolated from the ovarian fluids of hatchery reared 3-year old brook trout Salvelinus fontinalis was investigated. Metabolic fingerprinting and 16S rRNA gene sequences identified the isolates as Flavobacterium johnsoniae. The isolates exhibited multiple resistances to a wide range of antimicrobial classes including penicillin, cephem, monobactam, aminoglycoside, and phenicol. Although plasmids and other transposable elements containing antimicrobial resistance genes were not detected, the isolates did contain a genomic sequence for a chloramphenicol-inducible resistance-nodulation-division family multidrug efflux pump system. Efflux pumps are non-specific multidrug efflux systems. They are also a component of cell-cell communication systems, and respond specifically to cell membrane stressors such as oxidative or nitrosative stress. Understanding of efflux pump mediated antibiotic resistances will affect efficacy of clinical treatments of fishes associated with F. johnsoniae epizootics.

Transferable, multiple antibiotic and mercury resistance in Atlantic Canadian isolates of Aeromonas salmonicida subsp. salmonicida is associated with carriage of an IncA/C plasmid similar to the Salmonella enterica plasmid pSN254.

OBJECTIVES: The aim of this study was to examine the molecular basis for multiple antibiotic and mercury resistance in Canadian isolates of Aeromonas salmonicida subsp. salmonicida. METHODS: Phenotypic and genotypic methods were employed to identify plasmid-associated antibiotic and mercury resistance genes and to determine the organization of those genes in multidrug-resistant (MDR) A. salmonicida isolates. RESULTS: The MDR phenotype was transferable via conjugation using Escherichia coli, Aeromonas hydrophila and Edwardseilla tarda as recipients. Antibiotic and mercury resistance genes were carried by a conjugative IncA/C plasmid. Three distinct antibiotic resistance cassettes were characterized; first a class I integron containing an aadA7 gene encoding for an aminoglycoside-3'-adenyltransferase, the second cassette showed 99.9% nucleotide sequence homology to a cassette previously identified in the Salmonella enterica IncA/C plasmid pSN254, containing floR, tetA, sulII and strA/strB sequences. The third cassette showed 100% nucleotide sequence similarity to a transposon-like element, containing a bla(CMY-2) beta-lactamase in association with sugE and blc sequences. This element is known to be widely distributed among clinical and food-borne Salmonella and other Enterobacteriaceae throughout Asia and the United States. Mercury resistance was linked to the presence of a mer operon that showed 100% nucleotide sequence homology to the mer operon carried by plasmid pSN254. CONCLUSIONS: Each MDR A. salmonicida isolate carried the same plasmid, which was related to plasmid pSN254. This is the first report of plasmid-mediated florfenicol-resistant A. salmonicida in North America. In addition, it is the first report of a plasmid-associated AmpC beta-lactamase sequence in a member of the Aeromonadaceae.

Liquid-crystal-solid interface structure at the antiferroelectric-ferroelectric phase transition.

Total internal reflection is used to probe the molecular organization at the surface of a tilted chiral smectic liquid crystal at temperatures in the vicinity of the bulk antiferroelectric-ferroelectric phase transition. Data are interpreted using an exact analytical solution of a real model for ferroelectric order at the surface. In the mixture T3, ferroelectric surface order is expelled with the bulk ferroelectric-antiferroelectric transition. The conditions for ferroelectric order at the surface of an antiferroelectric bulk are presented.

Energy loss of fast quarks in nuclei.

We report an analysis of the nuclear dependence of the yield of Drell-Yan dimuons from the 800 GeV/c proton bombardment of 2H, C, Ca, Fe, and W targets. Employing a new formulation of the Drell-Yan process in the rest frame of the nucleus, this analysis examines the effect of initial-state energy loss and shadowing on the nuclear-dependence ratios versus the incident proton's momentum fraction and dimuon effective mass. The resulting energy loss per unit path length is -dE/dz = 2.32+/-0.52+/-0.5 GeV/fm. This is the first observation of a nonzero energy loss of partons traveling in a nuclear environment.

[The discovery of Dermacentor reticulatus (Ixodida, Ixodidae) in the East German districts of Leipzig and Halle]. / Funde von Dermacentor reticulatus (Ixodida, Ixodidae) in den DDR-Berzirken Leipzig und Halle).

A report on findings of Dermacentor reticulatus, a very rare tick species in the GDR, in 3 localities situated in the heath region of Düben and Dahlen (GDR districts of Leipzig and Halle). Three adults of Dermacentor reticulatus ticks were caught by brushing over the vegetation with a flag in one of 235 places in May and September 1987. On the other hand, a total of 2,877 Ixodes ricinus ticks was found in all places. In the same year, from the same area, we also found 2 adults of Dermacentor reticulatus on a man's clothing and on a horse.

[Wound myiasis in cattle infested by Lucilia caesar (Diptera: Calliphoridae)]. / Wundmyiasis beim Rind durch Lucilia caesar (Diptera:Calliphoridae).

A case report on facultative wound myiasis after sectio caesarea in a cow by larvae of Lucilia caesar in May 1986.

[Experimental studies on the course and the effects of pediculosis in domestic swine]. / Experimentelle Untersuchungen über Verlauf und Auswirkungen des Läusebefalls beim Hausschwein.

Weaned piglets, aged between six and eight weeks, underwent one single experimental infection, using few imaginal stages as well as second and third larval stages of Haematopinus suis. Louse populations of various densities developed on animals of the same litter under the same keeping and feeding conditions. No unambiguous reduction in body weight increase was observed throughout the two months of the experiment. Even pigs with 2,107 or 2,135 adult lice and their larval stages were not affected. Some of the pigs developed allergic dermal inflammations in the course of pediculosis and suffered from considerable aggravation of pruritus which used to be of minor importance before. Excessive rubbing, in response to that itching, led to mechanically caused skin lesions, some of them bleeding.