Killing Zone Research Articles

Synthesis and antibacterial action of cecropin and proline-arginine-rich peptides from pig intestine.

Two antimicrobial peptides, cecropin P1 (CP1), with a C-terminal carboxyl group, and PR-39, with an amidated, C-terminus, are found in the small intestine of the pig. Each is active against both Gram-positive and Gram-negative bacteria. We have synthesized these peptides and several analogs, including the D-enantiomers and the retro sequences, each with a free or acetylated amino terminus. The CP1 amide was also prepared. The retro CP1 peptides were much less active than the parent CP1 peptide, confirming the importance of sequence or the amide bond and helix dipole direction, and the N alpha-acetyl peptides were also less active, indicating that a free amino terminus is essential for high activity. The ratio of the lethal concentration of L/D isomers of CP1 is less than 1 for Gram-negative, but greater than 1 for Gram-positive bacteria. PR-39 showed no significant chiral selectivity toward Escherichia coli, Bacillus subtilis and Streptococcus pyogenes, but the L/D ratio was high for Pseudomonas aeruginosa (66), and very high for Staphylococcus aureus (> 1000). In the latter case the lethal concentration for the D-isomer was 0.57 microM, whereas this organism was quite resistant to the L-isomer (> 600 microM). Thus the enantiomers of CP1 and PR-39 are not equally active for all species. In a plate assay with a very small log-phase inoculum of Staph aureus, D-PR-39 produced a clear zone of killing surrounded by a zone of stimulated growth. After prolonged incubation the two zones became one clear zone. Addition of D-PR-39 to the wells of a dense turbid plate of growing cells showed a cleared zone for each of the test organisms, indicating that PR-39 lyses the bacteria rather than simply inhibiting their multiplication.

Regulation of bacterial gene expression in response to oxidative stress

Publisher Summary This chapter presents the approaches used to study the regulation of oxidative defense genes in Escherichia coli and Salmonella typhimurium . These general approaches should be useful in examining the response to oxidative stress in other organisms and in further elucidating the response in E. coli and S. typhimurium . The sensitivity of strains to oxidants has been assessed using several different approaches. The first evidence that E. coli cells possess a regulated defense response against oxidative stress came from growth curves of E. coli . AB11157 cultures grown in K medium to a density of 5 × 10 7 cells/ml were treated with 0, 10, and 30 μM hydrogen peroxide for 30 min. The cells were then challenged with a lethal dose of 5 mM hydrogen peroxide, and aliquots of cells were removed after 20, 40 and 60 rain, diluted, and spread on LB plates to determine the number of colony-forming units. The sensitivity or resistance of wild-type or mutant strains has also been determined by zone of inhibition assays. For these simple assays, 0.1 ml of an overnight culture is plated on an agar plate in 2 to 3 ml of soft agar and a disk impregnated with an oxidant is placed in the center of the agar. The zone of killing or inhibition surrounding the disk is then measured after 12 to 24 hr of growth. For this assay to be consistent the volume of the agar medium must be uniform.

The effects of excitotoxin lesions of the lateral hypothalamus on self-stimulation reward

Unilateral microinjection into rat lateral hypothalamus (LH) of the excitotoxins ibotenic acid (IBO) and N-methyl- d-aspartatic acid (NM produced a local zone of neuronal death but also produced a zone of demyelination. The size of this demyelination zone was related to excitotoxin dose and was smaller than the zone of neuron killing. In behavioral testing. MFB self-stimulation reward and performance were measured with a rate-frequency curve-shift method before and after IBO or NMDA lesions of the LH. Excitotoxin lesions were made anterior or posterior to the LH electrode so that the zone of neuronal death, but not demyelination, extended to the electrode tip. These lesions produced small, temporary LH stimulation reward deficits, leading to the conclusion that intrinsic LH neurons are not a major substrate of MFR stimulation reward.

Proportional navigation and the game of two cars: The case of a pursuer with variable speed

A stochastic version of the “game of two cars” is considered. In this version the pursuer has a variable speed owing to thrust and drag forces, whereas the evader's speed is constant. Also, the pursuer can maneuver as long as his speed is bounded by some lower and upper bounds. The motion of the players is confined to the pursuer's “effective operation zone”, D P, and the cost function of the game is the probability of the event: {before the evader enters his “safe zone”, the evader enters the pursuer's “killing zone”, K P, at some t, 0 ⩽ t ⩽ T, or the evader stays at the domain D P- K P for all t ϵ [0, t 0], for some t 0 > T}. By numerically solving a nonlinear parabolic boundary value problem on a generalized torus in R 4, it is shown that (for a range of values of some parameters) a proportional navigation guidance law is a suboptimal feedback pursuit strategy.