Role of horn flies (Haematobia irritans) in Staphylococcus aureus-induced mastitis in dairy heifers

OBJECTIVE: To determine whether Staphylococcus aureus can colonize in horn flies and whether colonization is sufficiently persistent for transmission of the organism to cows by flies. ANIMALS: 2 Jersey heifers exposed to infected horn flies. PROCEDURE: Staphylococcus aureus was allowed to colonize in horn flies, and duration of colonization was determined. Flies with colonized S aureus were allowed to feed on teats of uninfected heifers to determine whether intramammary infection could be transmitted from fly to heifer. Scab material from naturally infected heifers was submitted for bacteriologic culture to determine whether S aureus was present and whether scabs could serve as a possible source of S aureus for flies. RESULTS: Staphylococcus aureus colonized in horn flies and remained for up to 96 hours after exposure. Exposure of teats of uninfected heifers to horn flies colonized with S aureus resulted in intramammary infection in 3 of 4 exposed teats. Culture of scab material from teats of naturally infected heifers revealed high concentration of S aureus (> 107 colony-forming units/mg), and flies without previously colonized S aureus were allowed to feed on scabs; S aureus colonized in them just as readily as it did in flies that had fed on experimentally infected blood. CONCLUSIONS: Horn flies are capable of transmitting S aureus-induced intramammary infection to heifers, and scabs on teats are a potential source of S aureus. Fly control on dairy cows in herds with known S aureus problems is recommended as a method to help prevent these infections.     

Detection of bacteriocins of lactic acid bacteria isolated from foods and comparison with pediocin and nisin

A total of 663,533 colonies from 72 dairy and meat sources showed a detection rate of 0.2% for bacteriocin producers using direct plating techniques. A further 83,000 colonies from 40 fish and vegetable sources showed a detection rate of 3.4% for bacteriocin producers using selective enrichment procedures. A collection of seven purified isolates showing a different host spectrum of bacteriocin activity and with the ability to produce bacteriocins in broth culture were compared with nisin and pediocin (with respect to their inhibitory activity, determined by the critical dilution method), against various indicator bacteria in agar and broth. The sensitivity of Listeria species to various bacteriocins was influenced by the agar and broth test systems used. A Lactobacillus curvatus strain was found to be the most suitable indicator for quantitating antimicrobial effects of all the bacteriocins investigated in both agar and broth test systems. The bacteriocin-producing isolates were characterized by biochemical reactions and DNA restriction enzyme profiles and taxonomic identification revealed species of Lactobacillus, Carnobacterium and Lactococcus assigned on the basis of 16S rDNA sequences.     

Posttranslational modifications of the 5'-AMP-activated protein kinase beta1 subunit

The AMP-activated protein kinase (AMPK) consists of catalytic alpha and noncatalytic beta and gamma subunits and is responsible for acting as a metabolic sensor for AMP levels. There are multiple genes for each subunit and the rat liver AMPK alpha1 and alpha2 catalytic subunits are associated with beta1 and gamma1 noncatalytic subunits. We find that the isolated gamma1 subunit is N-terminally acetylated with no other posttranslational modification. The isolated beta1 subunit is N-terminally myristoylated. Transfection of COS cells with AMPK subunit cDNAs containing a nonmyristoylatable beta1 reduces, but does not eliminate, membrane binding of AMPK heterotrimer. The isolated beta1 subunit is partially phosphorylated at three sites, Ser24/25, Ser182, and Ser108. The Ser24/25 and Ser108 sites are substoichiometrically phosphorylated and can be autophosphorylated in vitro. The Ser-Pro site in the sequence LSSS182PPGP is stoichiometrically phosphorylated, and no additional phosphate is incorporated into this site with autophosphorylation. Based on labeling studies in transfected cells, we conclude that alpha1 Thr172 is a major, although not exclusive, site of both basal and stimulated alpha1 phosphorylation by an upstream AMPK kinase.     

Incidence and pathophysiological changes in chronic two-kidney hypertension in the dog

Unilateral renal artery plication in dogs reduced renal blood flow by 80% and produced a sustained elevation in arterial pressure whereas plasma renin activity increased for only 4 days. Sodium was retained for 3 days after plication, but this response is similar to that after a sham operation. Of seven dogs studied chronically, elevated arterial pressure was sustained for 27 days or longer in six animals. In three dogs hypertension continued for 2 mo before collateral vessels developed and arterial pressure fell; ligation of these collaterals restored hypertension. Arterial pressure was unaffected by an infusion of [1-sarcosine, 8-alanine] angiotensin II in chronic hypertensive dogs on a normal sodium intake. This angiotensin antagonist lowered arterial pressure after sodium depletion, but became ineffective following rapid sodium repletion. Chronic hypertensive dogs showed normal responses to deoxycorticosterone acetate. These findings suggest that the renin-angiotensin system is not critically involved in maintenace of chronic two-kidney renovascular hypertension in the dog. The data also show that the homeostatic role played by the renin-angiotensin system in the maintenance of arterial pressure remained intact in chronic hypertension.     

Conversion of cortisol to cortisone by the human uterus and its reversal in pregnancy

Inter-conversion of cortisol (F) and cortisone (E) was investigated by incubating minced tissue with tritiated cortisol or cortisone and then separating the products by Sephadex LH-20 column chromatography. In non-pregnant subjects conversion of F to E predominated (43.4+/-3.4% vs 0.1+/-0.4% for E to F). In early pregnancy F leads to E decreased and E leads to F rose while at term E leads to F (46.3+/-9.1%) exceeded F leads to E (15.1+/-6.8%). These results were in accord with those obtained by assaying the endogenous concentrations. In non-pregnant subjects the F/E ratio (1.1+/-0.6) was lower than that found in serum (6.3+/-2.2) while at term the uterine F/E (9.0+/-1.8) was similar to that of serum (8.8+/-2.0). These changes resulted in an 8-fold increase in uterine F compared with a 3-fold increase in serum F, while uterine E fell to 1/2 and serum E doubled. Thus, during pregnancy there is a dramatic reversal of the reaction in the uterus in favour of the active hormone. It seems possible that the increase in cortisol thus brought about may play an anti-immune role in uterine wall, the single tissue apart from blood in direct contact with fetal tissue.     

Thermonuclear Fusion Power

The present state and future possibilities of controlled-nuclear-fusion research are reviewed, including basic concepts and problems, as well as various approaches based on magnetic- and nonmagnetic-confinement schemes. Considerable progress has so far been made in both plasma physics and fusion-reactor technology, and a closer relationship has been established between theory and experiments. Still, none of the present approaches will, for certain, lead to the final solution of a full-scale reactor. Intensified work along broad lines, with emphasis also on basic research and new ideas, is necessary for future success.     

TCM/SSMA communication systems with cascaded sequences and PAM/QAMsignal sets

An expression in matrix form for the multiple-access interference (MAI) in an asynchronous direct-sequence spread-spectrum multiple-access (DS/SSMA) communication system with cascaded sequences (CVs), arbitrary chip waveforms, and trellis-coded modulation (TCM) with a pulse amplitude modulation (PAM) or quadrature amplitude modulation (QAM) signal set is obtained. TCM provides significant coding gain while the CVs decrease the correlation between the MAI of adjacent data intervals. The expression is used to calculate arbitrarily accurate probability density functions (PDFs) of the MAI in the TCM system and to derive an accurate approximation of the MAI variance. It also helps illustrate some properties of the MAI by separating contributing parameters into different matrices. We derive an approximation of the upper union bound on the bit-error probability and investigate its applicability. The results show that CV schemes can greatly reduce the pairwise error probabilities (PEPs) until the length of the CV becomes greater than that of the error weight sequence (EWS) under consideration