Chloramphenicol acetylation in Streptomyces

Twenty-one strains of actinomycetes were screened for the presence of chloramphenicol acetyltransferase, the enzyme responsible for chloramphenicol resistance in many species of bacteria. Only five strains, belonging to three species, yielded mycelial lysates which catalysed the formation of chloramphenicol acetates in the presence of acetyl-coenzyme A: Streptomyces coelicolor Müller, S. acrimycini, and S. griseus. A mutant of S. acrimycini selected for an increase in resistance to chloramphenicol had a higher specific activity for chloramphenicol acetyltransferase than that found in the parental strain; the enzyme was not inducible in the mutant, the parental strain, or any other strain tested. Chloramphenicol was not acetylated by lysates of a strain of S. venezuelae, the organism known to produce it.     

Incidence and morphology of carotid shudders in aortic valve disease

The incidence and morphology of shudders in carotid arterial pulse tracings were examined in 73 patients with aortic valve disease documented by cardiac catheterization. Two forms of carotid shudder were recorded: coarse and fine. Shudders were present in 67 per cent of patients with aortic stenosis, 48 per cent of patients with aortic insufficiency, and 57 per cent of patients with mixed aortic stenosis and insufficiency. No significant difference existed among these three groups of patients with respect to the over-all incidence of carotid shudders or with respect to the incidence of coarse or fine shudders. In patients with aortic insufficiency, stroke volume index (Fick) and phonocardiographic systolic ejection murmur amplitude were significantly greater (p less than 0.01, p less than 0.001, respectively) in those with coarse carotid shudders compared with those manifesting fine or absent shudders. Loud, flow-related, systolic ejection murmurs of aortic insufficiency are capable of producing radial vibrations in the aortic wall which are recorded as carotid shudders. The finding of a carotid shudder in a patient with aortic valve disease does not enable the physician to distinguish between stenosis, insufficiency, or mixed stenosis and insufficiency.     

Inverse effect of chronically elevated blood flow on atherogenesis in miniature swine

The effect of chronically elevated blood flow on the development of atherosclerosis in miniature swine was studied. Fistulas connecting the right external iliac artery and vein were surgically created in four swine, while three were not fistulated. Pulsed Doppler velocity detection cuffs placed around the abdominal aorta and both iliac arteries of all pigs permitted chronic measurements of blood velocity, blood velocity distributions, and blood flow. All swine were fed an atherogenic diet consisting of 20% beef tallow, 3% cholesterol, and 5% cholic acid for 6 months. This diet elevated the serum cholesterol to values exceeding 500 mg/100 ml. Creation of the arteriovenous fistula (AVF) markedly elevated blood velocity and flow in the abdominal aorta and in the shunted iliac artery. In the shunted animals the aortic blood flow was 42.1 +/- 2.0 ml/sec compared with 17.3 +/- 1.4 ml/sec in the unshunted swine. The velocity distribution pattern across the vessel was also indicative of an elevated wall shear stress. After 6 months, the animals were killed and the arterial vessels examined macroscopically and microscopically for the presence of atherosclerotic lesions. In the shunted pigs, 17 +/- 15% of the lumenal surface was occupied by sudanophilic lesions, whereas 80 +/- 8% of the surface was covered by lesions in the unshunted (control) pigs. From these studies, it is apparent that mechanical factors related to blood flow rates can influence the development of atherosclerotic lesions in swine.