Kan Lam

Early healing events in a porcine model of contaminated wounds: effects of nanocrystalline silver on matrix metalloproteinases, cell apoptosis, and healing.

A porcine model of wound healing was employed to examine the impact of nanocrystalline silver–coated dressings on specific wound healing events. Full‐thickness wounds were created on the backs of pigs, contaminated with an experimental inoculum containing Pseudomonas aeruginosa, Fusobacterium sp., and coagulase‐negative staphylococci, and covered with dressing products either containing silver or not. Nanocrystalline silver‐coated dressings promoted rapid wound healing, particularly during the first several days post‐injury. Healing was characterized by rapid development of well vascularized granulation tissue that supported tissue grafting 4 days post‐injury, unlike control dressed wounds. The proteolytic environment of wounds treated with nanocrystalline silver was characterized by reduced levels of matrix metalloproteinases. Matrix metalloproteinases have been shown to be present in chronic ulcers at abnormally high levels, as compared with acute wounds, and may contribute to the nonhealing nature of these wounds. Cellular apoptosis occurred at a higher frequency in the nanocrystalline silver–treated wounds than in wounds dressed with other products. The results suggest that nanocrystalline silver may play a role in altering or compressing the inflammatory events in wounds and facilitating the early phases of wound healing. These benefits are associated with reduced local matrix metalloproteinase levels and enhanced cellular apoptosis. (WOUND REP REG 2002;10:)

Ascending infection of the biliary tract after surgical sphincterotomy and biliary stenting

It has been widely accepted that there is an ascending route of bacterial infection of the biliary tract but there is a lack of direct evidence. This hypothesis was tested in an animal experiment using the cat as an animal model. The implantation of biliary stents and surgical sphincterotomy were performed in these animals, with sham controls. Stents bypassing the sphincter of Oddi with the tip in the duodenal lumen were colonized by duodenal micro‐organisms and the biliary tract was heavily contaminated. Blockage of these stents resulted in biliary obstruction. Stents implanted within the common bile duct, proximal to the sphincter were largely unaffected by biofilm formation. After surgical sphincterotomy the biliary tract was also contaminated but, in the absence of obstruction, the animals did not develop any symptoms. It was concluded that ascending infection by duodenal biliary reflux, via the sphincter of Oddi, is an important route of infection in the biliary system.

Healing of porcine donor sites covered with silver‐coated dressings

OBJECTIVE To compare rates of healing of donor sites in pigs between those dressed with silver-coated dressings and those dressed with petrolatum-impregnated absorbent gauze. DESIGN Open study with each animal acting as its own control. SETTING University research facility, Canada. ANIMALS 6 young specific-pathogen-free domestic pigs. INTERVENTIONS A total of 72 wounds about 1 cm x 2 cm x 0.4 mm were made in rows of eight on each pig with a dermatome. They were divided into three groups of 24, and dressed with petrolatum gauze, or silver-coated dressings moistened with sterile water either once only or daily for 10 days. All dressings were secured in place with an elastic bandage. MAIN OUTCOME MEASURES Erythema, infection, epidermal migration, and healing. RESULTS Wounds dressed with moistened silver-coated dressings re-epithelialised significantly more quickly. This resulted in complete re-epithelialisation within 70% of the time taken by those wounds dressed with petrolatum gauze. CONCLUSION Silver-coated dressings provide a moist environment for the healing wound combined with an effective antimicrobial agent, and this significantly accelerates healing compared with wounds dressed with traditional petrolatum gauze dressings.

Bacterial biofilm, brown pigment stone and blockage of biliary stents

Abstract Bacterial pathogens gain access into the biliary system by descending via the portal venous circulation or ascending through the sphincter of Oddi in duodenal‐biliary reflux. Bacteria thrive as glycocalyx‐enclosed microcolonies, coalescing to form an adherent biofilm. The establishment of biofilm is a key event in the formation of biliary sludge and pigment gallstones, and the blockage of biliary stents. The biofilm mode of growth is very effective because it provides bacteria with a measure of protection from antibacterial agents and phagocytic leucocytes. Calcification of the matrix confers further protection for the micro‐organisms living inside the biofilm. To date, attempts to prevent blockage of biliary stent have employed physical methods by using large self‐expandable stents and stents without side hole. Incorporation of antibiotics within stents has not been successful presumably because bacteria once living in their biofilm are quite resistant to antimicrobial agents. Even the most toxic bile salts have no effect on the biofilm bacteria. Yet, hydrophobic bile salts reduce bacterial adhesion on biomaterial, suggesting that incorporation of such bile salts might prevent the formation of bacterial biofilm.

Is there a synergistic effect between mixed bacterial infection in biofilm formation on biliary stents

BACKGROUND Biliary sludge which forms as a result of bacterial adherence and biofilm formation in the biliary system is a recognized cause of blockage of plastic stents. Bacteriological cultures of sludge have revealed a mixed infection with gram-positive and gram-negative bacteria. Animal studies have shown that prophylactic ciprofloxacin, which selectively suppress gram-negative bacteria, results in prolonged stent patency despite colonization of the stents by gram-positive bacteria. METHODS We tested a possible synergistic effect between gram-negative and gram-positive bacteria in adherence and biofilm formation on plastic stents. Clinical isolates of Escherichia coli and Enterococcus were cultured in separate chemostats to achieve a steady growth. Adherence of the two bacteria on plastic stent surface were tested separately by perfusing infected bile with the respective bacteria through different modified Robbins devices containing 10F polyethylene stent pieces up to 4 days. In a second experiment, Enterococcus was perfused through stent pieces precolonized with E. coli for 24 hours. The stent pieces were then removed daily and analyzed by bacteriologic culture and scanning electron microscopy for bacterial adherence and biofilm formation. RESULTS Gram-negative E. coli were more adherent than gram-positive Enterococcus. Precolonization with E. coli facilitates subsequent attachment of Enterococcus. CONCLUSIONS We concluded that there is a synergistic effect between gram-positive and gram-negative bacteria in adherence and biofilm formation.

In vitro evaluation of antibiotic prophylaxis in the prevention of biliary stent blockage.

BACKGROUND Bacterial adherence and biofilm formation are important factors in the blockage of biliary stents. Clinical studies with oral antibiotic prophylaxis to prevent stent blockage have produced conflicting results. The aim of this study was to evaluate the in vitro effect of single antibiotic (ciprofloxacin, ceftazidime, or ampicillin) treatment on adherence of Escherichia coli and Enterococcus to plastic stents. METHODS Selected clinical isolates of E coli and Enterococcus were perfused through a modified Robbins device containing segments of polyethylene stents. The stents were removed daily and the number of bacteria attached was measured. The effect of antibiotic treatment on bacterial adherence was tested by the perfusion of individual antibiotics into separate modified Robbins devices using a side-arm adaptor and the results were compared with saline controls. RESULTS Compared with the saline controls, ciprofloxacin and ceftazidime caused a 10- to 100-fold reduction in the number of E coli attached to the stents, whereas ampicillin had no effect on adherence of E coli. Ampicillin caused a 5- to 10-fold reduction in Enterococcus adherence but there was no change with ceftazidime. Sustained reduction in E coli adherence was observed with prolonged ciprofloxacin perfusion. CONCLUSION Timely treatment with appropriate antibiotics reduced bacterial adherence in vitro and may be potentially beneficial in the prevention of stent blockage.

Comparative evaluation of fleroxacin, ampicillin, trimethoprimsulfamethoxazole, and gentamicin as treatments of catheter-associated urinary tract infection in a rabbit model

Fleroxacin, ampicillin, trimethoprim-sulfamethoxazole, and gentamicin were comparatively evaluated for effectiveness in treating experimentally induced catheter-associated urinary tract infection and bacteriuria in a rabbit model with a closed drainage system. Fleroxacin, ampicillin and gentamicin effectively eliminated a lactose-negative, streptomycin-resistant uropathogenic strain of Escherichia coli (WE6933) from bag urine and catheter port urine, while trimethoprim-sulfamethoxazole only marginally reduced urine bacterial counts when compared to rabbits that received no antibiotic therapy. Fleroxacin eliminated E. coli from the catheter surfaces and from tissues adjacent to the catheter. Ampicillin or gentamicin therapy also eliminated biofilm bacteria from the catheter surfaces, but did not eliminate th residual bacteria from tissue adjacent to the septic catheters despite achieving urine levels of antibiotics substantially higher than minimum bactericidal concentrations for this pathogen. Trimethoprim-sulfamethoxazole was ineffective in eliminating E. coli from the catheter surfaces and the adjacent tissues. The ability of fleroxacin to effectively eliminate biofilm bacteria from catheter surfaces and tissues adjacent to such medical devices in the urinary tract may prove useful in the treatment of catheter-associated urinary tract infection and bacteriuria in mammals and humans.

Cigarette smoke increases gastric ulcer size in part by an angiotensin II-mediated mechanism in rats

To assess the mechanism of the effect ofcigarette smoke on ulcer disease we employed a rat modelin which cigarette smoke increases the size of aceticacid-induced gastric ulcer and decreases the hyperemia at the ulcer margin. We postulate thatcigarette smoke increases angiotensin II (avasoconstrictor) in ulcer tissue. Since directmeasurement of angiotensin II in small tissue samples isproblematic, we compared the messenger ribonucleic acid (mRNA)for its precursors (angiotensinogen and renin) in ulcerand normal gastric tissue. We also evaluated the effectof enalapril, which blocks the conversion of angiotensin I to angiotensin II on ulcer size.In the ulcer tissue, cigarette smoke produced asignificant increase in mRNA for angiotensinogen but notfor renin. Enalapril decreased the size of the gastric ulcer in rats exposed to cigarette smoke. Thedata support the possibility that in ulcer tissuecigarette smoke stimulates an angiotensin II-mediatedmechanism, which may in part be responsible for the impairment of ulcer margin hyperemia andaggravation of ulcer size.