The effect of tissue docosahexaenoic and arachidonic acids levels on hypersaline tolerance and leucocyte composition in striped bass (Morone saxatilis) larvae

Larval striped bass (M. saxatilis), tissue docosahexaenoic (DHA) and arachidonic (AA) acids levels were modulated through dietary enrichments and the effect on growth and survivorship examined. Mean growth was significantly greater in larvae enriched with AA than in larvae enriched with DHA (F-value for AA treatment was 20.5 versus only 5.1 for the DHA treatment). Dietary treatment did not have a significant effect on larval survivorship (56.0±2.4%, p>0.05). When challenged with hypersaline (25 psu) immersion, DHA enriched larvae survived better than AA enriched larvae, but larvae with body tissue levels of 15.4 mg AA g^–1 and 7.2–15.4 mg DHA g^–1 dry weight provided maximal survivorship to the challenge. Elevated levels of body tissue AA was generally associated with elevated levels of whole body cortisol. On the other hand, increasing levels of DHA mainly affected the kinetics of cortisol increase to hypersaline exposure. Larvae injected intraperitoneally with formalin fixed Staphylococcus aureus responded by altering the proportion of lymphocytes, monocytes and neutrophils in perpherial blood. Lymphocytes, which accounted for the largest percentage of white blood cells (over 70%), decreased in all challenged larvae during the first 6 hours post injection then returned to pre-challenge levels after 44 hours. Conversely, the relative proportion of monocytes and neutrophils rose from 14% and 2% up to 28% and 6% of the total circulating leucocytes, respectively. The largest increase occurred in larvae fed a moderate level of both DHA and AA.     

Arachidonic acid requirements in larval summer flounder, Paralichthys dentatus

The arachidonic acid (20:4n-6,AA) requirements of larval summer flounder weredetermined for the rotifer- and Artemia-feeding stages. Experimental emulsionscontained adequate n-3 highly unsaturated fattyacid (HUFA) ratios and emulsion levels of AAwere set at 0, 3, 6, 9, and 12% (AA0, AA3,AA6, AA9, and AA12). Examination of fatty acidlevels in live feeds and larval tissuesconfirmed the physiological incorporation offatty acids relative to dietary levels. In thefirst experiment, survival, growth, andsalinity tolerance (2-h in 70) were measuredat 18 days after hatch (dah) after feeding thelarvae the various levels of AA. Larvae fedAA6-enriched rotifers were better able tosurvive the salinity tolerance test. AAenrichment up to 12% had no effect on growthand survival. In the second experiment, larvaewere fed AA0- or AA6-enriched rotifers until 23dah, followed by unenriched 24- and 48-h Artemia nauplii until 32 dah. These larvaethen were subdivided and fed AA-enriched Artemia from 33-45 dah. At the end of thisexperiment, larvae fed AA6-enriched rotifershad higher survival, increased growth, andsurvived better in the salinity tolerance test(2-h in 80). The enrichment of Artemiadid not have any effect on these variables.Thus, the provision of AA6-enriched rotifers(10 mg AA g^–1 DW) early in larvaldevelopment may serve to enhance larval stresstolerance at the rotifer stage while alsoincreasing larval survival, growth, and stresstolerance later in the Artemia stage.     

Specific detection by PCR of Streptococcus agalactiae in milk.

The aim of this study was to develop a simple and specific method for direct detection of Streptococcus agalactiae from cow's milk. The method was based on polymerase chain reaction (PCR) using species-specific and universal primers derived from the 16S rRNA gene. The amplification product was verified by restriction endonuclease digest and sequencing. Specific identification was proven on a collection of 147 S. agalactiae isolates of bovine and human origin. In addition, 17 strains belonging to different bacterial species that potentially can be found in milk samples also tested negative. The PCR developed was used for direct detection of S. agalactiae in milk, using for the first time with gram-positive bacteria the nucleic acid-binding properties of diatomaceous earth. The test, which has high specificity, high sensitivity (100 cfu/mL), and can be carried out in less than 24 h, represents an innovative diagnostic tool for the detection of S. agalactiae in milk.     

Zooming in on microscopic flow by remotely detected MRI

Magnetic resonance imaging (MRI) can elucidate the interior structure of an optically opaque object in unparalleled detail but is ultimately limited by the need to enclose the object within a detection coil; acquiring the image with increasingly smaller pixels reduces the sensitivity, because each pixel occupies a proportionately smaller fraction of the detector's volume. We developed a technique that overcomes this limitation by means of remotely detected MRI. Images of fluids flowing in channel assemblies are encoded into the phase and intensity of the constituent molecules' nuclear magnetic resonance signals and then decoded by a volume-matched detector after the fluids flow out of the sample. In combination with compressive sampling, we thus obtain microscopic images of flow and velocity distributions ~10(6) times faster than is possible with conventional MRI on this hardware. Our results illustrate the facile integration of MRI with microfluidic assays and suggest generalizations to other systems involving microscopic flow.     

Genomic relatedness among reference strains of different Streptococcus suis serotypes.

Hybridization studies using genomic DNA and a rDNA probe revealed genetic relatedness among reference strains of different Streptococcus suis serotypes. Although most serotype 22 isolates are biochemically atypical, the reference strain of capsular type 22 is genetically related to other S. suis serotypes, but not to Streptococcus pneumoniae. Using DNA digested with BamHI and BglII for ribotyping, some S. suis reference strains had common patterns, but this analysis mainly revealed variations in patterns of S. suis strains of different serotypes.