Evidence for dynamic exchange of qac gene cassettes between class 1 integrons and other integrons in freshwater biofilms

Class 1 integrons carried by pathogens have acquired over 100 different gene cassettes encoding resistance to antimicrobial compounds, helping to generate a crisis in the management of infectious disease. It is presumed that these cassettes originated from environmental bacteria, but exchange of gene cassettes has surprisingly never been demonstrated outside laboratory or clinical contexts. We aimed to identify a natural environment where such exchanges might occur, and determine the phylogenetic range of participating integrons. Here we examine freshwater biofilms and show that families of cassettes conferring resistance to quaternary ammonium compounds ( qac ) are found on class 1 integrons identical to those from clinical contexts, on sequence variants of class 1 integrons only known from natural environments, and on other diverse classes of integrons only known from the chromosomes of soil and freshwater Proteobacteria . We conclude that gene cassettes might be readily shared between different integron classes found in environmental, commensal and pathogenic bacteria. This suggests that class 1 integrons in pathogens have access to a vast pool of gene cassettes, any of which could confer a phenotype of clinical relevance. Exploration of this resource might allow identification of resistance or virulence genes before they become part of multi-drug-resistant human pathogens.     

Four neural circuit models and their role in the organization of voluntary movement

Four neural circuit models and their role in the organization of voluntary movement are presented here. These circuits collectively control a ballistic type biped voluntary movement. The structure of each circuit, and its function is discussed. Three of the circuits are central and contribute to the construction of two classes of inputs, analogous to the α signals and γ signals in biological systems. The fourth circuit plays a role in stabilization of the movement, and in compensation for the receptors. Digital computer simulations are undertaken to demonstrate the construction of all the intermediate signals and the response of a two link biped to these efferent signals.     

Histochemical demonstration of enzymatic heterogeneity within the mesocoxal and metacoxal muscles of Periplaneta americana

Enzymatic activity in the mesocoxal and metacoxal muscles of the cockroach, Periplaneta americana, has been characterized using histochemical techniques. Our interpretation of the histochemical stains for myosin-ATPase (pre-incubated at pH 9.4, 10.4 and 4.3). NADH reductase, succinic dehydrogenase (SDH), and lactic dehydrogenase (LDH) has enabled us to classify fibres within these muscles according to established fibre typing strategies. The results reaffirm the biochemical heterogeneity reported for the mesocoxal muscles and allow us to confirm the expected heterogenity in the homologous metacoxal muscles. These techniques have proven to be an effective tool for assessing the biochemical properties of muscle fibres.     

Isolation of psychrophilic species of Bacillus

Larkin, J. M. (Washington State University, Pullman), and J. L. Stokes. Isolation of psychrophilic species of Bacillus. J. Bacteriol. 91:1667-1671. 1966.-Ninety psychrophilic isolates of Bacillus were obtained from soil, mud, and water by selective enrichment at 0 C. They grew well at 0 C, optimally at 20 to 25 C, and failed to grow at 30 or 35 C. Their minimal and maximal growth temperatures were lower than those for mesophilic species of Bacillus by 10 C or more. Growth of psychrophilic isolates also occurred at -2 and -4.5 C, and both spore formation and spore germination occurred at 0 C.     

Effects of corticosteroids on postnatal lung and airway growth in the ferret

To investigate the influence of corticosteroids on postnatal lung and airway growth, young male ferrets were given cortisone acetate (20 mg/kg im daily) beginning at 8 wk of age. At 19 wk of age pulmonary function was measured. The lungs were excised for measurements of recoil pressures and wet and dry weights. The dimensions of central and peripheral airways were estimated from analysis of bronchial casts. Corticosteroid-treated animals were shorter and tended to be lighter than control animals but were heavier in relation to length. Total lung capacity was reduced in proportion to the reduction in body size. Lung recoil and wet-to-dry weight ratios were nearly identical. Maximal expiratory flows were reduced in proportion to the reduction in body size. Size-corrected airway conductance was reduced, suggesting a sensitivity of central airways to growth suppression by corticosteroids. Peripheral airways, on the other hand, were not smaller in treated animals and were larger in proportion to body size. In the ferret corticosteroid administration is associated with a suppression of lung parenchymal growth similar to that of overall body growth. The peripheral airways may be less sensitive and the central airways more sensitive to the effect of corticosteroids on growth.