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Biomedical subjects

K Lam

Publications and source records attributed to K Lam.

At least 109 records · Page 6Linked to original sources
PubMed1985

Efficacy of vancomycin plus rifampin in experimental aortic-valve endocarditis due to methicillin-resistant Staphylococcus aureus: in vitro-in vivo correlations.

Studies of in vitro and in vivo bactericidal interactions of vancomycin plus rifampin against Staphylococcus aureus have yielded conflicting results. In this study the efficacy of this drug combination in experimental endocarditis due to a methicillin-resistant strain of S. aureus was investigated. Left-sided endocarditis was induced in 84 rabbits by an infecting strain that had been found to be synergistically killed by vancomycin plus rifampin in vitro when tested by the timed-kill curve technique; in contrast, the checkerboard technique had indicated that the two drugs were antagonistic against this strain. Infected animals received no therapy, vancomycin alone (30 mg/kg per day), rifampin alone (20 mg/kg per day), or both drugs (in the same doses). The combination was significantly more effective than the single-drug regimens in terms of (1) reduction of mean methicillin-resistant S. aureus vegetation titers (P less than .05-.0005), (2) rate and incidence of sterilization of vegetations (P less than .0005), and (3) rate of "radical" cure of endocarditis (P less than .005). Vancomycin alone and vancomycin plus rifampin were equally effective in reducing mortality and sterilizing renal abscesses. The use of vancomycin prevented the in vivo development of resistance to rifampin. No evidence that rifampin exerted an antagonistic effect on the in vivo bactericidal activity of vancomycin was found.

Animals↗
PubMed1985

The development of the optic nerve in rodents.

In mammals, normal visual function depends upon both the retinotopic organization of visual nuclei and their interconnections. We have investigated in rodents some developmental mechanisms contributing to this organization. On embryonic day 14, in the rat, retinal ganglion cells first project axons through glial channels on the retinal surface before reaching the optic stalk. We suggest that the sequence in which axons enter the stalk (central before peripheral) and their prominent fasciculation impose some retinotopic order amongst the emerging optic nerve fibres. At birth (embryonic day 21) there are over 240 000 axons in the optic nerve, all non-myelinated. However, within one week, the number falls to the adult value (100 000) and myelination, complete in the adult, commences. Axons lost include some which misproject--to the opposite eye or to inappropriate parts of central visual regions. The number of surviving retinal ganglion cells depends on the amount of appropriate target tissue available. It is well established that removal of one eye early in development increases the survival of axons in the remaining optic nerve. However, in a group of adult mice with congenital unilateral anophthalmia, we counted only 21 000 optic axons in the remaining nerve compared with the 31 000 in normal mice of the same strain. Degenerating axons were observed, suggesting that the defect is not a simple developmental failure, but is associated with active degenerative processes throughout life.

Animals↗
PubMed1985

Amikacin + ceftazidime therapy of experimental right-sided Pseudomonas aeruginosa endocarditis in rabbits.

We investigated the efficacy of a potent new antipseudomonal beta-lactam agent, ceftazidime, in a model of right-sided Pseudomonas endocarditis in 72 rabbits. Animals received either: no therapy (controls), amikacin (15 mg/kg/day), ceftazidime (100 mg/kg/day) or amikacin + ceftazidime. Amikacin + ceftazidime was significantly more effective than single-drug regimens in terms of reduction of mortality (p less than 0.01), prevention of pulmonary infarction (p less than 0.05), reduction of mean vegetation titers of Pseudomonas aeruginosa (p less than 0.05-p less than 0.0005), sterilization of vegetations (p less than 0.0005) and reduction in prevalence of bacteriologic relapses after therapy (p less than 0.005). There was no development of resistance in vivo to either amikacin or ceftazidime.

Amikacin↗
PubMed1984

Quantitative and morphological studies on developing optic axons in normal and enucleated albino rats.

In the albino rat, the number of optic axons increases from 400 on embryonic day 15 to reach a peak of 240000 at birth, before declining to adult numbers (100000) by postnatal day 5. Throughout the period of loss of axons there are few signs of degeneration in the optic nerve, which does not change its diameter: the decrease in density of axons is matched by an increase in the cross-sectional area of individual axons. Myelination of the initially non-myelinated axons starts on day 5, when axonal numbers stabilize. Following neonatal removal of one eye, fewer axons than normal are present in the contralateral optic nerve up to day 5. The axons removed by enucleation may be retino-retinal axons, representing up to 40% of the 83000 fibres lost between postnatal days 2 and 5. There is no increase in the numbers of optic axons in the remaining nerve in adult animals; this appears to be due to the small absolute numbers of ipsilateral axons saved by enucleation. After enucleation, axons remain clear and undergo a "watery" degeneration after initially swelling, and the removal of degenerative products is accomplished within four days.

Animals↗
PubMed1984

In vitro bactericidal synergy of gentamicin combined with penicillin G, vancomycin, or cefotaxime against group G streptococci.

The in vitro bactericidal interactions of penicillin G, cefotaxime, or vancomycin in combination with gentamicin were compared against 20 group G streptococci by the timed kill curve method. Synergy was noted at the following frequencies: penicillin plus gentamicin, 80%; cefotaxime plus gentamicin, 85%; vancomycin plus gentamicin, 90%. There was no bactericidal antagonism observed.

Cefotaxime↗
PubMed1984

Influence of culture conditions on expression of the mucoid mode of growth of Pseudomonas aeruginosa.

Five strains of Pseudomonas aeruginosa that are routinely distinguished by diagnostic laboratories on the basis of their colony morphology on agar media were grown in different media to assess the effects of culture conditions on mucoid growth, which we define as the copious production of exopolysaccharide. On brain heart infusion agar, only two of these strains (mucoid and gelatinous) grew as slimy mucoid colonies. None of the five strains produced a mucoid pattern of growth in Mueller-Hinton broth, in which all grew as turbid, nonmucoid, homogeneous suspensions of bacterial cells. When Mueller-Hinton broth was supplemented with Mg2+, all of the strains produced some mucoid aggregated growth, but growth in a modified version of the chemically defined medium of Vogel and Bonner, with elevated levels of Mg2+ and gluconate, produced patently mucoid growth in all strains. This mucoid growth in a liquid medium takes the form of large, coherent, slimy aggregates within the medium and of a "collar" of adherent microcolonies at the air-medium interface. Direct observations by light and electron microscopy showed the submerged aggregates and the adherent microcolonies to be composed of bacterial cells enmeshed in a copious exopolysaccharide matrix. When agar was added to the supplemented medium of Vogel and Bonner, only the mucoid and gelatinous strains produced slimy mucoid colonies on its surface. We conclude that both chemical and physical factors affect exopolysaccharide production by these clinical strains of P. aeruginosa and that the colony morphology on a single agar medium is an insufficient criterion for the designation of a given isolate as being mucoid or nonmucoid.

Agar↗
PubMed1983

Serious infections due to group G streptoccocci. Report of 15 cases with in vitro-in vivo correlations.

Serious infections due to group G streptococci have been infrequently reported. Fifteen such cases are described. Endovascular infection, particularly endocarditis, and septic arthritis were the most common clinical syndromes observed. Despite exquisite in vitro sensitivity of group G streptococci to penicillin G, the in vivo clinical response was disappointing in six of nine patients with either endocarditis or septic arthritis. The group G streptococcal isolates from the patients in this study were uniformly sensitive to the inhibitory and killing action of penicillin G, ampicillin, cefotaxime, cephalothin, cefoxitin, and vancomycin. In contrast, clindamycin, erythromycin, and chloramphenicol had relatively poor bactericidal activity against these strains, including several "tolerant" strains. Timed-kill studies with penicillin G revealed impaired killing of group G streptococci at in vitro conditions of high inocula and stationary growth phases. This may partially explain the poor clinical responses in cases of group G streptococcal endocarditis.

Anti-Bacterial Agents↗
PubMed1983

Immunogenicity of Pseudomonas aeruginosa outer membrane antigens examined by crossed immunoelectrophoresis.

By crossed immunoelectrophoresis 36 different anode-migrating antigens were demonstrated in sonicated antigen preparations of Pseudomonas aeruginosa. We numbered these antigens to establish a reference precipitin pattern. Antigen no. 31 was identified as the lipopolysaccharide (LPS) antigen, because it was found to be responsible for the O-group specificity and because it reacted with anti-LPS monoclonal antibodies and with Limulus amoebocyte lysate. Purified outer membrane proteins F (porin), H2, and I used as antigens formed precipitins with the reference antibodies, thus establishing their antigenicity. LPS that copurified with protein F and slightly contaminated protein H2 was detectable as an extra precipitin (antigen no. 31). The use of monoclonal antibodies specific for smooth LPS and rough LPS revealed different antigenic determinants in the LPS molecule and suggested that antigen no. 5 could be the core region of the LPS which is equivalent to the rough LPS. Antibodies against these outer membrane antigens were detected in patients with chronic P. aeruginosa pneumonia and in patients with acute P. aeruginosa bacteremia. Antibodies with the same specificity were also found in rats chronically infected with P. aeruginosa 7 days postinfection. This demonstrates the surface accessibility and antigenic reactivity of outer membrane antigens.

Animals↗
PubMed1983

Therapy of experimental Pseudomonas endocarditis with high-dose amikacin and ticarcillin.

Right-sided infective endocarditis due to Pseudomonas aeruginosa was induced in 130 rabbits. Animals received either: (1) no therapy (controls); (2) standard-dose amikacin (AMK) (15 mg/kg/day) plus ticarcillin (300 mg/kg/day), or (3) high-dose AMK (20 or 25 mg/kg/day) plus ticarcillin, for 20 days. Animals in each treatment group were evaluated at 10 days after therapy for bacteriologic relapse. Both standard- and high-dose AMK regimens significantly decreased mortality and Pseudomonas aeruginosa vegetation titers versus controls (p less than 0.01, p less than 0.05, respectively). Despite significantly higher serum AMK levels at 25 mg/kg/day, there was no significant difference in mean vegetation titers, percent of vegetations sterilized, or posttherapy bacteriologic relapse in the three treatment groups. AMK at 20 or 25 mg/kg/day (but not at 15 mg/kg/day) significantly reduced the incidence of pulmonary infarction versus untreated controls (p less than 0.01).

Amikacin↗
PubMed1983

In vitro immunoglobulin synthesis by lymphocytes from patients with rheumatoid arthritis. I. Effect of monocyte depletion and demonstration of an increased proportion of lymphocytes forming rosettes with mouse erythrocytes.

We have investigated B cell function in nine patients with rheumatoid arthritis (RA) compared to sex and age matched controls in a pokeweed mitogen driven system. Levels of IgG and IgM synthesized in the supernatant were measured by a competition ELISA. We have found that cultured mononuclear cells from RA patients showed a defective Ig synthesis when depleted of monocytes. In contrast RA mononuclear cells not depleted of monocytes produced substantial levels of Ig after stimulation by the mitogen. The percentages of T and B lymphocytes in the peripheral blood of RA patients were normal; however, an increased number of lymphocytes formed rosettes with mouse erythrocytes indicating an abnormality in the B cell pool. These results demonstrate defective in vitro immunoglobulin synthesis by RA lymphocytes and show the importance of monocytes in this culture system.

Adult↗
PubMed1983

In vitro susceptibility of group G streptococci to ten antimicrobial agents with broad gram-positive spectra.

Minimal inhibitory and bactericidal concentrations (MICs, MBCs) of ten antibiotics with broad spectra against grampositive cocci were determined for 25 group G streptococci (GGS). Penicillin G, cefotaxime, and ampicillin were the most active bactericidal agents, with 100% of MBCs less than or equal to 0.6 micrograms/ml. Among the nonpenicillin, noncephalosporin agents, vancomycin had the lowest MBCs, with all strains killed by less than or equal to 2.5 micrograms/ml. Despite good in vitro activity against other streptococci, erythromycin, clindamycin, and chloramphenicol had disappointing bactericidal activity against GGS. Three strains were tolerant to erythromycin, while 15 strains were tolerant to clindamycin. Chloramphenicol was the least active inhibitory agent, with an MIC90 of 13.8 micrograms/ml; this agent was also the least active bactericidal agent against GGS. with no MBCs less than 2.5 micrograms/ml and 9 strains with MBCs greater than or equal to 20 micrograms/ml. There were no GGS strains tolerant to either penicillin G or vancomycin.

Anti-Bacterial Agents↗
PubMed1982

Loss of axons from the optic nerve of the rat during early postnatal development.

The number of axons in the optic nerve of the newborn rat has been compared with the number present in the adult animal. Nerves taken from animals on the day of birth contain 242,000 +/- 29,000 (S.D.) fibres (n = 5). By the sixth postnatal day, the number of axons has fallen to the stable values of adults (99,000 +/- 3700, n = 8). Thus development of the rat's visual system during the first 5 days of life is associated with a loss of 60% of the axons present in the optic nerve at birth. Counts made on the remaining nerve after enucleation of one eye suggest that the presence of retino-retinal axons during the first 5 postnatal days cannot account for all of this reduction.

Age Factors↗
PubMed1982

Retention of catheter fragment after thoracentesis: report of two cases.

In the two cases presented here, retention of a portion of a plastic catheter in the pleural space occurred during thoracentesis. In both cases, the catheter was probably sheared off by the sharp beveled tip of the metal needle used to introduce the catheter. In one case, the retained catheter was removed during limited thoracotomy with local anesthesia. In the other case, attempts to remove the retained catheter during thoracentesis were unsuccessful, and no furather attempts were made. This complication of thoracentesis can be avoided by paying strict attention to the proper technique for insertion and withdrawal of the needle and the catheter.

Aged↗
PubMed1982

Microbial flora of the mouse ileum mucous layer and epithelial surface.

We have developed new methods to minimize fluid shear during preparation of specimens for electron microscopy and to retain the mucous blanket that covers the tissue surface of the ileum in mice. We also used general stabilization by nonspecific antibodies to minimize the collapse of the mucous layer during dehydration for electron microscopy. These methods allowed us to visualize the gradual progression of the mucous blanket from a thin diaphanous layer in newborn animals to a very thick (ca. 50 micrometers), coherent structure in older animals that contained a mixed population of bacteria and protozoa. Some bacteria, notably filamentous forms, were patently anchored to the epithelial tissue but projected into the mucous blanket, whereas others clearly existed within the mucous blanket and were unattached to the epithelial surface. Similarly, some protozoa were firmly attached to the tissue surface, whereas others were suspended in the viscous mucous blanket. In an adult animal, the mucous blanket was a very thick layer which actually occluded most of the tissue surface and contained a rich variety of bacteria and protozoa.

Animals↗