Esculin hydrolysis by Enterobacteriaceae.

Literature reports disagree concerning esculin hydrolysis in the family Enterobacteriaceae. A total of 2,490 strains of the family were investigated for esculin hydrolysis by two methods, the esculin spot test and the PathoTec incubation strip, which measures constitutive enzyme, and five growth-supporting methods, which determine both constitutive and inducible enzymes. The five growth-supporting media studied were: Vaughn-Levine, the standard esculin hydrolysis medium (P. R. Edwards and W. H. Ewing, Identification of Enterobacteriaceae, 3rd ed., 1972); Vaughn-Levine without iron; Vaughn-Levine without Andrade's indicator; and bile-esculin medium. Growth media were incubated at 35 degrees C and checked every 24 h for 120 h. On growth media, 0.3% of Escherichia coli were positive in 24 h, 34% in 48 h, and 61% in 120 h. No strains were positive on the "nongrowth" tests. It appeared that the esculin hydrolysis enzyme(s) of E. coli was inducible rather than constitutive. All esculin hydrolyzers, which yielded positive tests on "constitutive tests" and 24-h tests, were limited to the genera Klebsiella, Enterobacter, and Serratia and species of Proteus vulgaris, Proteus rettgeri, and Citrobacter diversus. When used with standardized inoculum size and incubation time, the esculin hydrolysis test is very useful for differentiation within the family Enterobacteriaceae.     

Coordinated multivesicular release at a mammalian ribbon synapse

Traditional models of synaptic transmission hold that release sites within an active zone operate independently. Although the release of multiple vesicles (multivesicular release; MVR) from single active zones occurs at some central synapses, MVR is not thought to require coordination among release sites. Ribbon synapses seem to be optimized to release many vesicles over an extended period, but the dynamics of MVR at ribbon synapses is unknown. We examined MVR at a ribbon synapse in a retinal slice preparation using paired recordings from presynaptic rod bipolar and postsynaptic AII amacrine cells. When evoked release was highly desynchronized, discrete postsynaptic events were larger than quantal miniature excitatory postsynaptic currents (mEPSCs) but had the same time course. The amplitude of these multiquantal mEPSCs, which seem to arise from the essentially simultaneous release of multiple vesicles, was reduced by lowering release probability. The release synchrony reflected in these multivesicular events suggests that release within an active zone is coordinated during MVR.     

Central control of developmental plasticity in the mammalian visual cortex

Visual experience influences the development of visual cortex functions. By manipulating retinal activity the efficacy of excitatory connections between the eyes and cortical neurones can be modified dramatically. A criterion for the enhancement or impairment of transmission is the temporal contiguity of pre- and postsynaptic activation. For a change to occur it is necessary that the cortical cells respond to retinal activity but this condition is not sufficient. Further permissive gating signals of nonretinal origin are required. It is proposed that these "now print" signals act by controlling the Ca2+-conductance of cortical dendrites. The possible role of these activity dependent modifications is discussed in the context of the development of cooperatively coupled cell assemblies.     

Characteristics of employment and job satisfaction in nontraditional dental hygiene practice settings

Little is known concerning the employment characteristics of hygienists practicing in nontraditional settings. Respondents were identified through screening (n = 38,380) a listing of the entire population of hygienists licensed in the United States. The screening identified 1,301 hygienists practicing in nontraditional settings. These hygienists were mailed comprehensive questionnaires; completed questionnaires were returned by 84.3 percent of the hygienists. Data were collected describing hygienists' reasons for seeking employment in nontraditional settings, their sources of information concerning job opportunities in nontraditional settings, benefits, and job satisfaction. The main source of information concerning employment opportunities in nontraditional settings was "word of mouth." Hygienists were motivated to seek employment in nontraditional settings primarily by a desire for a more challenging position and personal satisfaction. The hygienists were overwhelmingly satisfied with all aspects of nontraditional employment except opportunities for advancement. Respondents were found to receive standard benefits similar to those of employees in other industries.     

Erythrocyte homeostasis: antibody-mediated recognition of the senescent state by macrophages.

We tested the hypothesis that the accumulation of bound autologous antibody on a "senescent epitope" identifies aged erythrocytes for phagocytic removal by macrophages. Erythrocytes were collected from mice maintained on a hypertransfusion protocol designed to yield cells of defined age. The mouse erythrocytes were assayed for the presence of bound antibody by measuring their susceptibility to ingestion by macrophages from mouse peritoneal exudates and by flow cytofluorometry. Both assays disclosed that only the oldest mouse erythrocytes bore detectable levels of antibody. Flow cytofluorometric analysis revealed that the frequency distribution of IgG isotypes bound to the cells reflected their levels in normal serum. Finally, treatment with trypsin abolished the ability of the macrophages to ingest erythrocytes aged in vivo. These findings support the hypothesis that antibody mediates the clearance of senescent mouse erythrocytes from the circulation and demonstrate that the presence of a trypsin-sensitive recognition structure on macrophages is an essential requirement in this homeostatic process.     

A new musculoskeletal assessment in a student population

A common finding in repetition activities (typing, running, swimming . . .), are overuse syndromes arising from a mechanical imbalance affecting overstressed soft tissues and joints. A more subtle corollary, occasioned by a sedentary life-style, is an imbalance between postural and phasic muscle groups leading to joint dysfunction. Postural and phasic muscles as defined by V Janda (New Zealand Manip Ther Assoc Tech Newsletter 2: 1-3, 1977) interplay in complex patterns which determine strength and coordination for normal function. Joint pathology, and central or peripheral nervous system impairment, all lead to compensatory changes in the muscle function, namely the tendency for postural muscles to become tight and for phasic muscles to weaken. Faulty posture through muscle imbalance compromises joint mechanics predisposing to dysfunction. Appropriate management of musculoskeletal disorders should recognize the role of imbalance between postural and phasic muscles in both the etiology and sequelae of the disorder. A musculoskeletal examination of 35 students was undertaken to develop assessment skills, devise a recording form, and refine a test sequence to assist data collection. The principal finding of tightness in postural muscles is consistent with the theory that these muscles undergo adaptive shortening. This survey provided the opportunity to examine the incidence of muscle imbalance in a young adult population and to prepare guidelines for future study. J Orthop Sports Phys Ther 1986;8(1):34-41.