Membrane interactions and antimicrobial effects of layered double hydroxide nanoparticles

Membrane interactions are critical for the successful use of inorganic nanoparticles as antimicrobial agents and as carriers of, or co-actives with, antimicrobial peptides (AMPs). In order to contribute to an increased understanding of these, we here investigate effects of particle size (42-208 nm) on layered double hydroxide (LDH) interactions with both bacteria-mimicking and mammalian-mimicking lipid membranes. LDH binding to bacteria-mimicking membranes, extraction of anionic lipids, as well as resulting membrane destabilization, was found to increase with decreasing particle size, also translating into size-dependent synergistic effects with the antimicrobial peptide LL-37. Due to strong interactions with anionic lipopolysaccharide and peptidoglycan layers, direct membrane disruption of both Gram-negative and Gram-positive bacteria is suppressed. However, LDH nanoparticles cause size-dependent charge reversal and resulting flocculation of both liposomes and bacteria, which may provide a mechanism for bacterial confinement or clearance. Taken together, these findings demonstrate a set of previously unknown behaviors, including synergistic membrane destabilization and dual confinement/killing of bacteria through combined LDH/AMP exposure, of potential therapeutic interest.

Effect of insulin on Blattela germanica Linnacus

OBJECTIVE

To determine the sensitivity of Blattela germanica L (B. germanica L) to differenct doses of insulin.

METHODS

B. germanica were reared in laboratory conditions at (25±2) °C and (50±5)% relative humidity (RH), and exposure period of 12:12 L/D. Different concentrations, viz. 5, 10, 15, 20 and 25 µ of insulin N, R, (N+R) were prepared and injected to 10 treated cockroaches with another 10 cockroaches which were injected with normal saline as control group.

RESULTS

Insulin N with a dose of 20 µ caused more than 70% mortality of B. germanica in this study. There was a significant difference between 20 µ of insulin N with other doses of 5, 10, 15 and 25 µ, and its comparison with other forms of medication also showed obvious difference (P<0.05).

CONCLUSIONS

It can be concluded that effective drug doses of insulin which can be used as posion bait or gel against German cockroaches could be utilized in the control of B. germanica in the future field studies.

Pseudomonas aeruginosa-induced infection and degradation of human wound fluid and skin proteins ex vivo are eradicated by a synthetic cationic polymer

OBJECTIVES

Antimicrobial peptides are important effectors of innate immunity. Bacteria display multiple defence mechanisms against these peptides. For example, Pseudomonas aeruginosa releases potent proteinases that inactivate the human cathelicidin LL-37. Hence, in conditions characterized by persistent bacterial colonization, such as in P. aeruginosa-infected skin wounds, there is a need for efficient means of reducing bacterial load. Here, the effect of the cationic molecule polyhexamethylenebiguanide (PHMB) was evaluated.

METHODS

Infection models in human wound fluid and human skin were established. Radial diffusion methods, bacterial growth and bactericidal assays were used for determination of effects of PHMB on bacteria in the presence of plasma, wound fluid or human skin. At the protein and tissue levels, SDS-PAGE, light microscopy and scanning electron microscopy were used to study the effects of P. aeruginosa infection before and after addition of PHMB.

RESULTS

PHMB killed common ulcer-derived bacteria in the presence of human wound fluid. Furthermore, elastase-expressing P. aeruginosa completely degraded wound fluid proteins as well as human skin during infection ex vivo. The infection, and consequent protein degradation, was reversed by PHMB.

CONCLUSIONS

The ex vivo infection models presented here should be helpful in the screening of novel antimicrobials and constitute a prerequisite for future clinical studies.

Management of choledocholithiasis encountered during laparoscopic cholecystectomy

To evaluate the prevailing methods of management and assess the safety of laparoscopic treatment of choledocholithiasis, a retrospective review of all common bile duct explorations (CBDE) initiated during laparoscopic cholecystectomy at the Medical College of Georgia was performed. From December 1990 until December 1994, 604 laparoscopic cholecystectomies were performed. In 28 of these patients (26 female, 2 male) with an age range of 17 to 60 years, CBDE was initiated; 21 were performed laparoscopically, and 7 were converted to open CBDE. The procedure was successful in completely clearing the duct of stones in 24 of 28 cases (17 laparoscopic, 7 open). Postoperative endoscopic retrograde cholangiopancreatography was successfully employed in three of the cases of retained stones, and in the fourth, the stone was felt to be small enough to pass without further intervention. Biliary balloon catheters were successfully used to clear the duct in 8 of 17 laparoscopic CBDEs, and a laparoscopic choledochoscope introduced through the cystic duct was used in 7 cases; both were used in 2 cases. The open CBDEs were performed in standard fashion utilizing balloon catheters and choledochoscopy. The only operative complications were the four above-mentioned cases of retained stones. In summary, choledocholithiasis encountered during the course of laparoscopic cholecystectomy can frequently be managed with a laparoscopic CBDE.