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Biomedical subjects

K Lam

Publications and source records attributed to K Lam.

At least 73 records · Page 4Linked to original sources
PubMed1992

Evaluation of strategies for central venous catheter replacement.

OBJECTIVES: To assess the consequences of leaving a bacterially colonized central venous catheter in place and to compare the effects of three catheter replacement strategies for catheter repair control in an animal model. DESIGN: Prospective study. SETTING: Laboratory and animal facility of a large university. SUBJECTS: Eighteen healthy, female, adult sheep. INTERVENTIONS: Radiopaque-siliconized elastomer central venous catheters were inserted into the jugular veins and colonized with either Escherichia coli or Staphylococcus epidermidis. After 7 days of infection, the catheters were either: a) exchanged using a guidewire; b) removed and replaced with a new catheter in a new jugular vein site after a 48-hr interval; or c) exchanged using a guidewire and antibiotics (tobramycin, cephaloridine) injected into the catheter. Animals were euthanized 7 days after insertion of the new catheter. Quantitative microbiology was performed on blood samples collected daily from the catheters and a peripheral vein, as well as from catheters and tissue recovered from the sheep at the time of autopsy. MEASUREMENTS AND MAIN RESULT: When catheters were changed using a guidewire, they became colonized by bacteria within 48 hrs, and the sheep had embolic pneumonia and vegetative endocarditis at autopsy. Similar consequences were observed when antibiotics were administered into the catheter lumen. If colonized catheters were removed and a new catheter was inserted after a 48-hr interval, recolonization, pneumonia, and endocarditis were not observed. CONCLUSIONS: Replacement of a biofilm-colonized central venous catheter over a guidewire is associated with rapid colonization of the replacement catheter and production of detached, slime-enclosed, antibiotic-resistant aggregates that colonize other catheters or initiate endocarditis or pneumonia by dissemination in the bloodstream.

Animals↗
PubMed1992

Mechanism of persistent infection associated with peritoneal implants.

The ability of rabbits to clear an intraperitoneal injection of Pseudomonas aeruginosa in the presence or absence of a surgically implanted peritoneal device was investigated. Sham-operated rabbits without an implant eliminated a P. aeruginosa challenge of 5 x 10(6) cfu/ml; lavage fluid and peritoneal tissues became culture-negative within 96 h. However, peritonitis developed in rabbits that were given the same number of bacteria in the presence of an implant; high bacterial counts were recovered from the lavage fluid and the device itself. Scanning and transmission electronmicroscopy revealed bacterial biofilms on the surface of the device. Insertion of pre-colonised devices demonstrated a rapid multiplication of sessile organisms within the resulting bacterial biofilm. Counts reached a plateau of about 1 x 10(7) cfu/cm2 of Silastic by day 16 and fluctuated around this level until the end of the study. Pre-immunisation with formalin-killed whole cells of P. aeruginosa did not reduce this bacterial growth despite high levels of specific IgG. The results confirm the failure of peritoneal defences to clear an infection in the presence of an implant following either challenge with planktonic bacteria or insertion of a pre-colonised device, and demonstrate the rapid development of bacterial biofilms on the surface of the implant which appear to protect the bacteria from host defences, even when primed by pre-immunisation.

Animals↗
PubMed1991

Bacteriologically stressed animal model of new closed catheter drainage system with microbicidal outlet tube.

We have used a catheterized rabbit model to test a newly developed catheter drainage system that incorporates a microbicidal outlet tube. In these tests, this new system was compared with a currently marketed closed drainage system, with daily challenge at the outlet tube using an auxotrophically marked uropathogenic strain of Escherichia coli. In the control series (silicone catheter connected to a standard drainage bag via a tamper-evidence seal) the challenge organism developed upstream biofilm colonization of the luminal surfaces of the catheter and drainage system that was complete in 4.6 +/- 2.1 days in 11 animals, while in 1 animal a rapid overgrowth of the system with Streptococcus faecalis developed. The presence of organisms other than the marked E. coli strain on the luminal surfaces of these control catheters showed that down stream colonization was also operative. In the test catheter drainage series, the microbicidal outlet tube insert precluded upstream colonization by the challenge organism in 12 of 16 catheters and significantly delayed (7.2 +/- 1.0 days) this colonization in the remaining 4 animals. When upstream colonization by exogenous bacteria was precluded by this effective device, downstream colonization of the drainage system by mixed populations of bacteria that probably migrated into the bladder via the extraluminal urethral route developed in some animals (6 of 16).

Animals↗
PubMed1991

Guidewire catheter change in central venous catheter biofilm formation in a burn population.

This study was designed to assess the risk of colonization and biofilm formation of central venous catheters left in situ for seven days vs those changed over a guidewire at three days and removed at seven days. Colonization was determined using scanning and transmission electron microscopy and compared to a special scraping/sonication culture method. Thirty-one catheters were examined, and no difference was found between catheters left in situ (9 of 16 colonized) and those changed over a guidewire (11 of 15 colonized). Colonization rates rose significantly from 4 of 15 catheters at the time of guidewire change to 11 of 15 at 7 days (p less than 0.001). Of the catheters defined as colonized by SEM, the special culture technique showed bacterial growth in only 35 percent, making a negative culture result of dubious value in ruling out catheter colonization. No beneficial effect of guidewire changes in reducing colonization could be demonstrated.

Bacterial Adhesion↗
PubMed1991

Bacterial invasion of the biliary system by way of the portal-venous system.

It has been suggested that bacteria in the intestine gain access into the biliary tract by entering the portal-venous blood. We have tested the hypothesis of hematogenous infection of the biliary system in cats. The animals were treated in three different groups: group A (no biliary obstruction), group B (acute biliary obstruction) and group C (chronic biliary obstruction). A mutant strain of Escherichia coli was infused into the splenic vein of cats at three different dosages (10(7), 10(5) and 10(3) with sham controls. In the unobstructed biliary system, the mutant E. coli was isolated from the bile 30 min and 90 min after the infusion of 10(7) and 10(5) E. coli, respectively. No bacteria were found in the bile with the infusion of 10(3) E. coli and in the control animals. Bile flow was significantly reduced with the infusion of bacteria. The biliary excretion of E. coli in group B was similar to that in group A. In group C, the bile output in the first hour was very high but declined rapidly. E. coli was excreted into the bile at all three dosages of infusion after 30 min. Histological sections of the liver showed that the infused bacteria entered the sinusoidal blood and that some were phagocytosed by Kupffer cells. The portal-venous blood was considered an important route of bacterial invasion into the biliary system, and the penetration of bacteria was facilitated in biliary obstruction.

Acute Disease↗
PubMed1991

Use of a grooming and foraging substrate to reduce cage stereotypies in macaques.

We examined the effects of a synthetic fleece pad on cage stereotypies in individually housed cynomolgus monkeys. Animals which received the fleece alone engaged in grooming which was associated with an increase in time spent resting. Monkeys given fleece pads sprinkled with morsels of food did not groom the fleece, but rather foraged for long periods (up to 27 min/h). Stereotyped behaviours were reduced by up to 73% by use of the fleece pad both alone and with foraging crumbles.

Animals↗
PubMed1990

Idiotypic variation in a human B lymphoma cell line.

The Ig Id of a B cell lymphoma serves as a distinct marker of the malignant clone and thus as a tumor-specific target for antibody therapy. Somatic variation of the Ig genes expressed by B cell tumors can lead to loss of reactivity with anti-Id antibodies and escape of tumors from the therapeutic effects of such antibodies. In our study, we have used anti-Id antibodies to screen for variants within a cell line derived from a patient with a large cell lymphoma of the B cell type. Cells were simultaneously stained on their surface for idiotypic and for isotypic Ig determinants using reagents labeled with different fluorochromes. Tumor cells expressing intact Ig molecules with alteration of their idiotypic determinants were isolated with the fluorescence activated cell sorter. Idiotypic variation was an ongoing process in vitro with Id- variants being generated at a rate of 2.7 x 10(-4)/cell per generation and Ig- cells being produced at a rate of 1.31 x 10(-5)/cell per generation. Subcloned variants expressed subtle differences in reactivity with a panel of three non-cross-blocking anti-Id antibodies. Analysis of Ig gene rearrangements by the Southern blotting technique using a JH probe established that the variants and the original tumor cells were all clonally related. Immunoprecipitation of surface labeled Ig molecules from the variant subclones disclosed major alterations of the lambda-L chains with no gross alterations of the mu-H chains. Related studies have established that the tumor cells undergo rearrangement and expression of new lambda-L chain genes.

Antibodies, Anti-Idiotypic↗
PubMed1990

Addisonian crisis as presenting feature in malignancies.

Metastases to the adrenal glands are common in patients with malignancy but malignant disease presenting as Addisonian crisis is rare. The authors presented two patients with acute Addisonian crises due to metastatic infiltration of the adrenal glands. They were otherwise asymptomatic from the primary tumor. Computed tomographic scan showed bilateral adrenal enlargement and transcutaneous biopsy confirmed metastatic adenocarcinoma in the adrenals. Adequate glucocorticoid replacement improves quality of life and prolongs survival.

Acute Disease↗
PubMed1990

Human polymorphonuclear leukocyte response to Pseudomonas aeruginosa grown in biofilms.

The interaction of human neutrophils with Pseudomonas aeruginosa biofilms was examined by using a chemiluminescence assay. The biofilms induced an oxidative burst response by polymorphonuclear leukocytes which was slow and only 25% of the response to planktonic bacteria. The reduced response to P. aeruginosa biofilms could play a role in the persistence of bacteria in chronic infections.

Alginates↗
PubMed1990

Growth of bacterial biofilms on Tenckhoff catheter discs in vitro after simulated touch contamination of the Y-connecting set in continuous ambulatory peritoneal dialysis.

We simulated touch contamination of peritoneal dialysis fluids perfused through an in vitro system with a modified Robbins' device (MRD) and Y-connecting tubings, to study the pathogenesis of bacterial biofilm (BB) growth on Tenckhoff catheter (TC) discs. The spike ends of Y-connecting sets were dipped in a suspension of freshly cultured cells of Staphylococcus epidermidis (3 X 10(8) cfu/ml), and connected to 2 litres of 0.5% dianeal solution which was perfused through the MRD with plugs containing TC discs. Four simulated clinical exchanges were performed with or without prior flushing and/or bleach treatment of the Y sets. Control experiments were done with fresh Dianeal solution with no contamination, flushing, or bleach treatment. BB growth on the TC discs was examined by scanning electron microscopy (SEM) and transmission electron microscopy and quantitated by routine culture of scrapings from the discs. We noted that touch contamination of dialysis fluids via the spike ends of the connecting sets can generate dense BB growth on TC discs in this experimental system (62 +/- 8% by SEM and 10.2 +/- 8.3 X 10(3) cfu/ml by culture). This growth of BB was significantly reduced by flushing the Y set with sterile Dianeal solution (24.3 +/- 3% by SEM and 5.7 +/- 3.5 X 10(1) cfu/ml by culture) and was absent by bleach treatment. We conclude that although bleach treatment of Y sets can prevent BB growth, the 'flushing' procedure alone can significantly reduce BB growth on TC from touch contamination of dialysate fluid.

Bacterial Adhesion↗
PubMed1989

Peritonitis in peritoneal dialysis: bacterial colonization by biofilm spread along the catheter surface.

We have used modern techniques of direct microscopic examination and quantitative bacterial recovery to show the existence of a route of bacterial colonization along the external and internal surfaces of Tenckhoff catheters implanted in experimental animals. The external route of progressive bacterial colonization extends from the cutaneous exit site through the dacron cuff and into the peritoneum. Bacterial growth along this route consists primarily of glycocalyx enclosed bacterial biofilms adherent to catheter and tissue surfaces, and this surface colonization may or may not give rise to peritoneal infection in which free-living bacteria are found in the peritoneal fluid. The rate of this progressive bacterial colonization depends on the degree of bacterial contamination of the exit site at the time of implantation. Exit site sterilization (hibitane) delays the process while inoculation with rabbit skin strains of Staphylococcus epidermidis accelerates it. Even with optimal implantation techniques, bacterial colonization proceeds via this subcutaneous route so that most Tenckhoff catheter surfaces are covered with a bacterial biofilm, consisting predominantly of gram positive cocci, within three weeks after the implantation of these devices. The rate of bacterial biofilm development on both surfaces of these Tenckhoff catheters, the bacterial colonization of peritoneal tissues, and the dissemination of bacteria into the peritoneal fluid are all significantly accelerated by dialysis in this experimental animal model of continuous ambulatory peritoneal dialysis (CAPD).

Animals↗
PubMed1989

Tobramycin resistance of mucoid Pseudomonas aeruginosa biofilm grown under iron limitation.

Mucoid Pseudomonas aeruginosa isolated from a patient with cystic fibrosis was cultivated at a slow growth rate (D = 0.05 h) under iron limitation in a chemostat. Biofilm was allowed to form on acrylic tiles. The kinetics of the biofilm formation was then investigated. The population of sessile bacteria reached 1.5 x 10(9) cells/cm2 on day 5 and remained relatively constant throughout the study (day 7). The population of planktonic cells in the chemostat reached 4 x 10(9) on day 1 and stayed fairly constant throughout. Planktonic cells were very sensitive to tobramycin. They were killed by exposure to 10 mg/l tobramycin within 2 h. Young biofilm cells of P. aeruginosa (day 2 of colonization) were found to be more resistant. Approximately 40% of the adherent cells remained viable after exposure to 10 micrograms tobramycin/ml for 5 h. An increase in the concentration of tobramycin to 20 mg/l resulted in an enhancement of the killing of young biofilm bacteria and approximately 1.5% of them remained viable after exposure to this concentration of antibiotic for 5 h. Old biofilm bacteria, examined at day 7, were the most resistant and 15% of the cells were found to be viable after they were exposed to 200 mg/l of tobramycin for 5 h. When either young or old biofilm cells of mucoid P. aeruginosa were scraped from the tiles to produce a planktonic cell suspension they were sensitive to 5 mg/l tobramycin.

Culture Media↗
PubMed1989

Interstitial microwave hyperthermia combined with iridium-192 radiotherapy for recurrent tumors.

From 1985 through 1987, 44 tumors in 39 patients with recurrent cancer were treated with interstitial microwave hyperthermia (HT) combined with interstitial 192Ir radiotherapy (RT). All patients had unresectable and previously treated tumors (mean RT dose 57.6 Gy). Diagnoses were squamous cell carcinoma in 27 (62%), adenocarcinoma in 11 (25%), melanoma in 5 (11%), and soft tissue sarcoma in 1 (2%) site. Interstitial RT dose was from 25 to 50 Gy (mean 38.3 Gy). The first HT session was scheduled immediately before the loading of 192Ir, and the second was scheduled following its removal. Each session lasted 45-60 min at therapeutic temperature (42.5 degrees C). Complete response (CR) was obtained in 28 (64%) sites and partial response (PR) in 15 (34%) sites. None of the CR patients had local recurrence. Tumor volume was the most important factor influencing CR (p less than 0.001). The treated site, radiation dose, and thermal dose were not significant factors for CR (p = 0.03). The overall median survival was 39 weeks, with a 2-year survival of 22%. The treatment was well tolerated, with two patients developing focal skin necrosis.

Actuarial Analysis↗
PubMed1989

Evaluation of the retrograde contamination guard in a bacteriologically challenged rabbit model.

We compared a newly developed closed urinary drainage system incorporating a retrograde contamination guard (RCG) with the conventional closed drainage system. The new system contains a solid bactericide (povidone iodine) pellet enclosed in a porous cartridge at the drain port of the urine collection bag. A catheterised rabbit model was used. The urine drainage bags were challenged daily for 8 days with an auxotrophically marked uropathogenic strain of Escherichia coli at the outlet tube. The bag urine was infected with the marked organism in 10 of the 11 rabbits in the control group (conventional collection bags) in 3.8 +/- 1.03 days and in only 1 of the 13 rabbits fitted with the RCG. The RCG effectively prevents contamination of the urine drainage bag and thus may play an important role in reducing the incidence of nosocomial urinary tract infections.

Animals↗
PubMed1989

Interaction of biofilm bacteria with antibiotics in a novel in vitro chemostat system.

Pseudomonas aeruginosa was cultivated at low growth rates under iron-limiting conditions on acrylic tiles. Biofilm cells exhibited increased tobramycin resistance compared with that of planktonic cells, and in old biofilms were more resistant than were cells in young biofilms. However, on suspension of the biofilm bacteria, glycocalyx-mediated resistance was lost.

Anti-Bacterial Agents↗
PubMed1989

Surgical therapy and radiotherapy for carcinoma of the esophagus. Treatment results in 195 patients.

Between 1963 and 1986, 195 patients with carcinoma of the esophagus were seen in the Department of Radiation Oncology at the University of Southern California School of Medicine. Of these 195 patients, 137 had unresectable or inoperable tumors and received radiotherapy. A combination of radiotherapy and surgical therapy was used in 46 patients, 9 patients were treated with surgery alone, and three with chemotherapy alone. Among the nonsurgical patients, 13 scored less than 50 on the Karnofsky scale, 25 had distant metastases, and 69 lost more than 10% of their body weight. The majority (94%) had squamous cell carcinoma and a few (6%) had adenocarcinoma. Fifty percent had middle esophageal lesions, 30% had lower lesions, and 20% had upper esophageal lesions. Stage I was diagnosed in 13%, II in 27%, III in 29%, and IV in 27%; the disease was not staged in 5%. The 5-year actuarial survival rate for all patients was 4% (median 32 weeks). The 5-year survival rate of the 46 patients with combination therapy was 18%, and it was 2% for the remaining 149 patients (p less than 0.001). These figures are independent of stage of disease. The 2-year survival rate by stage was as follows: I, 25%; II, 21%; III, 5%; and IV, 0% (p less than 0.001). Complete response was obtained in 18% and partial response in 41%. Complete response was dependent on the tumor stage. It was 40% for stage I disease, 23% for stage II, 11% for stage III, and 6% for stage IV disease. Similarly, a larger percentage (39%) of the 46 patients with combination surgical/radiation therapy had a complete response than of patients treated by either radiotherapy alone (n = 137, 12%) or surgery alone (n = 9, 11%). Complete response and initial performance status were important factors influencing survival (p less than 0.001). Surgery with adjuvant irradiation offered a better survival rate than radiotherapy or surgery used as single modalities. Treatment results for patients with advanced carcinoma of the esophagus remain poor.

Adult↗