Characterisation of haemolytic RTX toxins produced by Australian isolates of Actinobacillus pleuropneumoniae

The haemolytic RTX toxins of 27 isolates of A. pleuropneumoniae , representing all serovars which have been isolated from pigs in Australia, were characterized. The quantity of protein secreted by these isolates into the media was not significantly different between serovars, but haemolytic activity was only detected in the unconcentrated supernatants from cultures of serovar 1 and 5 isolates. Haemolytic activity in supernatants of serovar 2, 3 and 7 isolates was detected only after the supernatants were concentrated. On Southern hybridization blots, genomic DNA of serovar 1 and 5 isolates contained regions which were similar to the cloned structural genes for ApxI (apxIA ) and for ApxII (apxIIA ). In contrast, genomic DNA of serovar 2, 3 and 7 isolates only contained regions similar to, if not identical with, the cloned apxIIA gene. The haemolytic activity of the culture supernatant depended on the type or composition of media and adaptability of the bacteria to in vitro cultivation. Low passage cultures of A. pleuropneumoniae , which were characterized by waxy colonies, produced significantly weaker haemolytic activity than A. pleuropneumoniae after several passages in vitro

Characterisation of haemolytic RTX toxins produced by Australian isolates of Actinobacillus pleuropneumoniae

The haemolytic RTX toxins of 27 isolates of A. pleuropneumoniae , representing all serovars which have been isolated from pigs in Australia, were characterized. The quantity of protein secreted by these isolates into the media was not significantly different between serovars, but haemolytic activity was only detected in the unconcentrated supernatants from cultures of serovar 1 and 5 isolates. Haemolytic activity in supernatants of serovar 2, 3 and 7 isolates was detected only after the supernatants were concentrated. On Southern hybridization blots, genomic DNA of serovar 1 and 5 isolates contained regions which were similar to the cloned structural genes for ApxI (apxIA ) and for ApxII (apxIIA ). In contrast, genomic DNA of serovar 2, 3 and 7 isolates only contained regions similar to, if not identical with, the cloned apxIIA gene. The haemolytic activity of the culture supernatant depended on the type or composition of media and adaptability of the bacteria to in vitro cultivation. Low passage cultures of A. pleuropneumoniae , which were characterized by waxy colonies, produced significantly weaker haemolytic activity than A. pleuropneumoniae after several passages in vitro

Regulation of Bronchomotor Tone in Conscious Calves

peer reviewedaudience: researcher, professional, studentThe purpose of this study was to investigate the effects of some alpha and beta sympathomimetic and sympatholytic drugs on respiratory impedance in healthy conscious calves. Ten Friesian calves were investigated in this study. The forced oscillation technique was used to measure the resistance (Rrs) and the reactance (Xrs) of the respiratory system at frequencies ranging from 4 to 26 Hz. Isoprenaline (1 microgram/kg i.v.), propranolol (3 micrograms/kg i.v.), noradrenaline (2 micrograms/kg i.v.), xylazine (20 micrograms/kg i.v.) and yohimbine (0.25 mg/kg i.v.) were were administered. Isoprenaline induced a significant decrease of Rrs. An increase of Rrs after administration of propranolol was observed but without any change of the frequency dependence of Rrs. A small increase in the resonant frequency was also recorded. A decrease of Rrs was recorded after yohimbine injection. Noradrenaline and xylazine administration increased the resistances and the resonant frequency and induced a negative frequency dependence of Rrs. These results suggest that (1) the major effects of beta adrenergic drugs are on the central airways, (2) the alpha adrenergic system may play a role on the regulation of bronchomotor tone in calves, (3) the effects of alpha adrenergic drugs are on both central and peripheral airways and (4) the forced oscillation technique allows the differentiation of calibre changes occurring in small and large airways

Investigation of the effects of histamine inhalation on the tracheobronchial tree of calves by the forced oscillation technique.

Effects of histamine inhalation were investigated with two different techniques in nine conscious, healthy calves. The oesophageal balloon technique was used to measure the dynamic respiratory compliance (Cdyn) and the pulmonary resistance (RL). The reactance (Xrs) and the resistance (Rrs) of the respiratory system were measured at high frequencies by the forced oscillation technique. These parameters were recorded before and after histamine inhalation. Three histamine dihydrochloride solution concentrations were used (16 mg/ml; 32 mg/ml; 64 mg/ml). Histamine inhalation induced a decrease in Cdyn and Xrs an increase in Rrs, RL and of the resonant frequency and a negative frequency dependence of Rrs. Some of these changes were satisfactorily correlated with the histamine solution concentrations. The resonant frequency was well correlated with Cdyn. It was concluded that histamine inhalation induces a decrease of the calibre of small and large airways and a non-homogeneous behaviour of the pulmonary ventilation in awake calves. The forced oscillation technique can be used to perform an inhalation provocation test in unsedated animals