Aquarium pets as a source of antibiotic-resistant salmonellae.

Thirteen serotypes of Salmonella isolated from imported ornamental aquarium frogs, snails, and their waters were shown to be multi-drug-resistant. Among the resistances exhibited were resistance to gentamicin, sulfamethoxazole-trimethoprim, cephalothin, and nalidixic acid. Frog isolates displayed eight different patterns and snails isolates had two different resistance patterns. The most common serotype, Salmonella typhimurium, was resistant to 18 antibacterials while other salmonellae were resistant to 9 to 16 antibacterials. Resistances in S. typhimurium and S. bovis-morbificans were conjugative and a number of R plasmids participated in the resistance. The plasmid-mediated resistance in S. typhimurium was stable and the levels of resistance conferred were markedly higher than in the other salmonellae tested. Resistance of other serotypes was non-conjugative and resistance to the beta-lactam antibiotics was unstable.     

Amperometric enzyme electrodes

Three different types of amperometric enzyme electrode are described. The first type uses a conducting organic-salt electrode to oxidize NADH. Results for sensors for ethanol and for bile acids are presented. In the second type of sensor, flavoenzymes are directly oxidized on the surface of the conducting organic-salt electrode. Results for five different enzymes are described. The mechanism of the enzyme oxidation is discussed and the reaction is shown to take place by heterogeneous redox catalysis and not by homogeneous mediation. The enzymes are strongly adsorbed on the electrode; microelectrodes for in vivo studies can be constructed without a membrane. Results for in vivo studies of changing glucose levels in the brain of a freely moving rat are presented. The third type of sensor is designed to measure low levels of toxic gases such as H2S and HCN. This is done by monitoring the inhibition by the toxic gas of the activity of the respiratory enzyme cytochrome oxidase.     

Effects of experimental cortical seizures on respiratory motor nerve activities in piglets.

Airway obstruction at the level of the larynx causes respiratory insufficiency during experimental seizures in spontaneously breathing, anesthetized piglets (T. E. Terndrup and W. E. Fordyce, Pediatr. Res., 38: 61-66, 1995). To investigate further the neural mechanisms of this obstruction, the activities of the phrenic nerve (PH) and the recurrent laryngeal motor branches to the thyroarytenoid (TA) and posterior cricoarytenoid (PCA) muscles were analyzed in 11 anesthetized, vagotomized, paralyzed, and ventilated piglets. After a control recording period, seizures were induced by subcortical penicillin G injections. Compared with baseline conditions, nerve activities became irregular during seizures. Extraneous TA bursts during PH activation were evident in all piglets during seizures. During ictal phases of seizures, the peak integrated activities of the PH and the expiratory component of the PCA, but not TA or inspiratory PCA activities, were significantly decreased compared with interictal phases. During seizures, a significant delay in the onset of the inspiratory component of PCA activation with respect to the onset of the PH was observed. This study helps to explain respiratory impairment during cortical seizures by providing evidence of impaired timing of activation of laryngeal dilator mechanisms and coordination with those activating the diaphragm. Cyclical PH inhibition during high-intensity cortical discharges may provide a secondary mechanism producing respiratory insufficiency during seizures.     

The donnan equilibrium

A complete solution has been obtained for the distribution of ions and for the electrostatic potential in a simple Donnan equilibrium, namely, where the membrane is permeable to two ions, but not to the third. Electrical neutrality is shown to be an extremely good approximation everywhere except close to the membrane.     

Characteristics of Australia's alien flora vary with invasion stage

Aim

Directly or indirectly, humans select the plants that they transport and introduce outside of species native ranges. Plants that have become invasive may therefore reflect which species had the chance to invade, rather than which species would become invasive given the chance. We examine characteristics of failed introductions, along with invasion successes, by investigating (a) variation in plant characteristics across invasion stages, and (b) how observed characteristics predict the likelihood of species moving through invasion stages.

Location

Australia.

Time period

1770s to present.

Major taxa studied

34,650 plant species, across 424 families.

Methods

We used a comprehensive list of 34,650 plant species that are known to have been introduced to Australia, 4,081 of which are classified as naturalized and 428 as invasive. We represent plant characteristics with categorical growth forms, three functional traits (plant height, seed mass, and specific leaf area) and three factors related to species introduction histories (native regions, purpose, and minimum residence times).

Results

(a) The types of species introduced determine the types of species that naturalize and become invasive; (b) species introduction histories predict the likelihood of species moving through invasion stages; and (c) the numbers of species naturalizing (~15%) and becoming invasive (~15%) slightly exceeds expectation from the “tens rule”, which expects that 10% of introduced species naturalize and 10% become invasive.

Main conclusions

Our findings are significant for global biosecurity, indicating that functional traits alone cannot be used to predict a species' risk of becoming invasive. Rather, evidence suggests that characteristics of species introductions—specifically, a longer time-lag since first introduction and more pathways of introduction—define the relative risks of species moving through invasion stages. This is important for assessing future invasion risks, as future introductions may differ from those of the past. Our work highlights the need to reduce the number of species introduced.     

Aminoalkylphosphonofluoridate derivatives: Rapid and potentially selective inactivators of serine peptidases

Phosphonic acid analogs of N-Cbz-alanine and N-Cbz-phenylalanine have been converted to the ester and amide fluoridates and evaluated as inactivators of elastase (EC 3.4.21.11) and chymotrypsin (EC 3.4.21.1). These inhibitors, which mimic the natural peptide substrates, are the most potent inactivators of elastase and chymotrypsin yet reported, showing a modest selectivity which correlates with the substrate specificity of the two enzymes.     

A note on Das Gupta's two-sex population model

Some critical comments are made on the two-sex deterministic population model recently put forward by P. Das Gupta in this Journal, both in its interpretation and relation to any possible stochastic version of the model, and in regard to the validity of solutions other than the asymptotic limiting case.     

Idling in Mao’s Shadow: Heroin Addiction and the Contested Therapeutic Value of Socialist Traditions of Laboring

The Chinese government has come under attack by international critics for forcing drug users to labor in the name of treatment. While joining these activists in criticizing conditions in compulsory labor centers, former detainees who congregated at a drop-in center in southern Yunnan also defended the therapeutic potential of socialist legacies of laboring. Shuttling between laboring in state compulsory centers and idling in a market economy, long-term heroin users saw their difficulties in recovering from addiction as inextricably linked to their inability to find suitable work opportunities. Certain drop-in center attendees maintained that earlier Communist laboring projects had helped wayward citizens, including drug addicts, “merge into” society as productive workers. This group evoked the stable long-term jobs and benefits once provided by local state-owned enterprises and the radical revolutionary power of “remolding through labor” they imagined to have existed in the first years of the People’s Republic as powerful alternatives to their recent crisis of idling. The nuanced ways that drop-in center regulars revisited the potential healing power of earlier traditions of socialist laboring as remedies to their contemporary struggles complicates long-standing debates about coercion in treatment and the responsibility of the postsocialist state towards marginalized workers.