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Biomedical subjects

N Craven

Publications and source records attributed to N Craven.

10 recordsLinked to original sources
PubMed1989

Regulation of phagolysosome pH in bovine and human neutrophils: the role of NADPH oxidase activity and an Na+/H+ antiporter.

Fluorescein-labelled Staphylococcus aureus were used to follow changes in phagolysosome (PL) pH of bovine and human neutrophils following phagocytosis. Under aerobic conditions there was an alkalinisation of the PL followed by a slow decline. Under anaerobic conditions no alkalinisation of the PL was seen, and pharmacological inhibition of the NADPH oxidase with diphenyleneiodonium (DPI) resulted in a rapid acidification of the PL following phagocytosis. The inclusion of amiloride, an inhibitor of Na+/H+ antiporter activity, produced a more rapid alkalinisation phase following phagocytosis under aerobic conditions and reduced, but did not abolish, the acidification phases seen under anaerobic conditions or following treatment of neutrophils with DPI. The results suggest that PL pH is influenced by NADPH oxidase activity and to a lesser extent by a Na+/H+ antiporter. The antibacterial effectiveness of neutrophil granule proteins may be affected under conditions that influence the functioning of these two systems.

Amiloride↗
PubMed1989

Pathological changes following implantation of intramammary devices (IMD) and immunological mediator release by cells on recovered IMDs.

Implantation of abraded polyethylene intramammary devices (IMD) for six months in the mammary glands of cows resulted in macroscopic and microscopic pathological changes in udder tissue. These changes were characterised by hyperplasia and metaplasia of the epithelial cells and hypertrophy of the subepithelial connective tissue examined by light and electron microscopy (EM). Quarters containing IMDs also had increased numbers of neutrophils and macrophages in the subepithelial stroma compared with control quarters. IMDs recovered six months after implantation were shown by transmission and scanning EM to be covered with plaque and cells. These cells were mainly macrophages, although other leucocytes were also present. In vitro culture of recovered IMDs in the presence of lipopolysaccharide resulted in the release of neutrophil chemotactic factor, or factors, and interleukin-1. Some quarters with IMDs also had concurrent infections at the time of slaughter. In these cases both the pathological changes seen in the tissues and the release of soluble mediators following in vitro culture of the IMDs were significantly increased compared with sterile quarters containing IMD.

Animals↗
PubMed1988

Oxygen concentration in milk of healthy and mastitic cows and implications of low oxygen tension for the killing of Staphylococcus aureus by bovine neutrophils.

The partial pressure of O2 in milk from normal cows and from cows with mastitis was measured and the concentrations of O2 calculated. Oxygen levels of milk from normal cows were similar to those in venous plasma, but inflammation of the mammary gland led to a dramatic drop in O2 concentration to less than 10% of control values. Intracellular survival of Staphylococcus aureus strain M60 in bovine neutrophils was greater under anaerobic than aerobic conditions. The implications of low O2 concentrations in milk from infected mammary glands for the bactericidal activity of bovine neutrophils is discussed.

Animals↗
PubMed1988

Effect of pH changes on the killing of Staphylococcus aureus and other mastitis pathogens by bovine neutrophil granule extracts.

A partly purified extract of granules from bovine neutrophils was used to investigate killing of mastitis pathogens by the non-oxidative killing system of the neutrophil. Eight strains of Staphylococcus aureus, two of Escherichia coli and two of Streptococcus uberis were used. Different strains of bacteria had different sensitivities to killing by the extract, three strains of staphylococci being particularly resistant. Whereas E coli were killed most effectively at pH 6.0, little or no killing of S aureus took place below pH 6.5 and, although S uberis were also killed better above neutral pH, significant killing also took place at acidic pH levels. Resistance to killing by the extract was not significantly correlated with that by intact neutrophils.

Animals↗
PubMed1986

Antimicrobial drug susceptibility of Staphylococcus aureus isolated from bovine mastitis.

Isolates of Staphylococcus aureus (106) from bovine mastitis were tested for susceptibility to antimicrobial agents. beta-lactamase was produced by 69.8 per cent of isolates and 7.5 per cent were resistant to streptomycin (minimum inhibitory concentration more than 32 micrograms/ml). Resistance to other agents was rare. Intrinsic resistance or tolerance to beta-lactam antibiotics was not found.

Animals↗
PubMed1979

The location of Staphylococcus aureus in experimental chronic mastitis in the mouse and the effect on the action of sodium cloxacillin.

Chronic staphylococcal mastitis was established in the mouse and electron miscroscopic examination of mammary tissue showed that the staphylococci were within epithelial cells, neutrophils and macrophages. Suspensions of cells containing staphylococci were prepared from chronically infected glands and incubated with sodium cloxacillin in vitro. This procedure resulted in a reduction in bacterial numbers, but a significantly greater reduction was obtained if the somatic cells were disrupted by sonication before the addition of cloxacillin. The results imply that the intracellular location of the staphylococci protects them against the action of the antibiotic.

Animals↗
PubMed1976

Computer analysis of the single-breath nitrogen washout curve.

A computerized system has been developed to analyze the parameters that can be derived from the nitrogen washout curve. Analog signals for air flow, volume, and nitrogen concentration are entered either on-line or off-line into a 24,000 mini-computer. The program calculates vital capacity, total lung capacity, and residual volume, as well as the slope of phase III, closing volume in liters, total lung capacity, residual volume, closing capacity, closing volume/vital capacity ratio, and closing capacity/total lung capacity ratio. Validation tests showed excellent correlation between hand- and computer-calculated values of closing volume(r=0.864), vital capacity (r=0.997), total lung capacity (r=0.991), and slope of phase III (R=0.926). We concluded that the computerized system for analysis of the expired nitrogen washout curve is as reliable as hand calculations and is immeasurably faster.

Diagnosis, Computer-Assisted↗
PubMed1975

Learning pulmonary function interpretation: deductive versus inductive methods.

Volunteer undergraduate medical students were randomly divided into 2 groups. One group were given pulmonary function data and the correct diagnoses from 18 patients. They were told to try to derive the rules by which the diagnoses were made. The other group were given the data from the same 18 patients, but were required to use a computer-assisted instructional program to arrive at the diagnoses in a deductive fashion. Both groups were pre- and post-tested. The deductive method provided higher post-test results. The inductive method took longer and produced more dropouts from the study.

Analysis of Variance↗