Peripheral inactivation of gentamicin

Peripheral inactivation of aminoglycosides is defined as a reversible process related to the specific physico-chemical conditions prevailing in abscesses. Conditions of reduced pH and pO2, such as are found frequently within abscesses, may reduce strongly the antibacterial effect of aminoglycosides, possibly by their interfering action on aminoglycoside transport into the bacteria. In addition, binding factors in purulent exudates, such as leukocyte chromatin exposed to any aminoglycoside after cell lysis, may bind a significant proportion of the total antibiotic, leading to an equivalent decrease of the concentration of the free, biologically active drug. In contrast, intact phagocytes, which do not bind aminoglycosides on their chromatin because of drug exclusion from the viable cells, protect ingested bacteria from being killed by large amounts of antibiotics. The role played by the different inactivating factors has yet to be defined in a clinical context, by analysis of experimental abscesses as an extension of the present in-vitro data. L'inactivation périphérique des aminosides est définie comme un processus reversible lié aux conditions physico-chimiques locales des sites infectés. L'abaissement du pH et de la pO2 fréquemment décrit au niveau des abcès, peut réduire fortement l'activité antibactérienne des aminosides, en réduisant l'accumulation intracellulaire de ces antibiotiques par les bactéries. D'autre part, on observe un effet de captation des aminosides par des constituants du matériel purulent, en particulier par la chromatine des neutrophiles lysés. Cette captation diminue la concentration d'antibiotique libre qui seule est biologiquement active. Par contraste avec les neutrophiles lysés, les neutrophiles vivants ne captent pas les aminosides au niveau de leur chromatine et protègent les bacténes qu'ils ont phagocytés de l'effet bactéricide des aminosides. Ces effets semblent être dûs à l'absence de pénétration des aminosides a l'intérieur des neutrophiles vivants. L'importance clinique de ces différents facteurs inactivant les amino-sides n'est pan encore établie, en l'absence de données expérimentales obtenues chez l'anima

Gentamicin Inactivation in Purulent Exudates: Role of Cell Lysis

Factors contributing to the binding and reversible inactivation of gentamicin by purulent exudates were studied in a simplified in vitro model consisting of purified human polymorphonuclear leukocytes (PMNLs). Whereas intact PMNLs (106-108/ml) bound almost no [14C]gentamicin, freeze-thawed PMNLs showed extensive [14C]gentamicin binding, expressed as antibiotic cosedimenting with particulate material from the lysed PMNLs. Antibiotic binding could be related to the concentration of lysed PMNLs and to the amount of [14C]gentamicin added. Binding of [14C]gentamicin by lysed PMNLs was highly sensitive to DNase I but was unaffected by RNase, Triton X-100, or protease. Purified chromatin or DNA from either purulent exudates or lysed PMNLs reproduced the [14C]gentamicin-binding pattern obtained with crude PMNL lysate. These results show that gentamicin inactivation in purulent exudates can be correlated with binding of the antibiotic to lysed PMNLs; PMNL chromatin DNA is identified as one of the major binding factor

The inhibition of neutrophil antibacterial activity by ultra-high molecular weight polyethylene particles.

Following infection, bacterial killing by polymorphonuclear leukocytes (neutrophils) is the main host defense against bacteria. Our hypothesis is that particles of ultra-high molecular weight polyethylene (UHMWP) may impair local neutrophil function and consequently reduce neutrophil bacterial killing. To determine how the in vitro phagocytic-bactericidal activity of neutrophils was affected by exposure to wear particles, tests were run comparing the effects of different particle composition, and different concentrations and sizes of UHMWP particles. There was a significant correlation between the number of particles and the decrease in neutrophil bactericidal activity (p<0.01), and the greatest effect was obtained with a concentration of 10(7) UHMWP/ml. There was a significant decrease in neutrophil bactericidal activity by incubation with particles of 0.1-5 microm (p<0.01), but not with larger size. The results suggest that neutrophil functional defects triggered by the presence of UHMWP particles may potentially contribute to the susceptibility of loose implants to bacterial infections

Concentrations of azithromycin in tonsillar and/or adenoid tissue from paediatric patients

Azithromycin levels in tonsillar and/or adenoid tissue were determined in children (1.6-7.5 years old) who were scheduled for surgical removal of their tonsils and/or adenoids. The children received azithromycin oral suspension lOmg/kg once daily for 3 days. Tissue samples were obtained during surgery 1 (n = 4), 2 (n = 5), 4 (n = 6), or 8 (n = 5) days after the last dose of azithromycin. Serum samples were also obtained from four children in each of these groups at the time of surgery. Mean tissue concentrations of azithromycin were 10.33 ± 3.01, 7.21 ± 4.04, 9.30 ± 3.74 and 1.49 ± 0.48 mg/kg, respectively, 1, 2, 4 and 8 days after the last dose. At the corresponding times, serum concentrations were markedly lower: 47.25 ± 19 19, 14.00 ± 8.45, 8.00 ± 2.16 and <4 μg/L, respectively. The mean tissue:serum concentration ratios were, 227 ± 54, 547 ± 184 and 956 ± 355, respectively, 1, 2 and 4 days after treatment. No adverse events attributable to azithromycin were observed in any of the 23 children who had received at least one dose of azithromycin. The study shows that levels of azithromycin in tonsillar and adenoid tissue were consistently higher than in serum and remained elevated up to 8 days after the end of dosing, supporting the use of a short-course (3-day), once-daily regimen of azithromycin in the treatment of upper respiratory tract infection

The discriminatory power of MALDI-TOF mass spectrometry to differentiate between isogenic teicoplanin-susceptible and teicoplanin-resistant strains of methicillin-resistant Staphylococcus aureus

To explore the discriminatory power of matrix-assisted laser desorption ionization-time of flight mass spectrometry (MALDI-TOF MS) for detecting subtle differences in isogenic isolates, we tested isogenic strains of Staphylococcus aureus differing in their expression of resistance to methicillin or teicoplanin. More important changes in MALDI-TOF MS spectra were found with strains differing in methicillin than in teicoplanin resistance. In comparison, very minor or no changes were recorded in pulsed-field gel electrophoresis profiles or peptidoglycan muropeptide digest patterns of these strains, respectively. MALDI-TOF MS might be useful to detect subtle strain-specific differences in ionizable components released from bacterial surfaces and not from their peptidoglycan networ

Pathogenesis of Foreign Body Infection: Description and Characteristics of an Animal Model

An animal model involving the subcutaneous implantation of tissue cages into guinea pigs and subsequent infection with Staphylococcus aureus was used to study factors pertinent to foreign body infection. Whereas 108 colony-forming units (cfu) of S. aureus strain Wood 46 did not produce any abscesses in the absence of foreign material, 102 cfu was sufficient to infect 95% of the tissue cages despite the presence of polymorphonuclear leukocytes (PMNLs) in sterile tissue cage fluid. Opsonization of S. aureus by tissue cage fluid was adequate during the first hour of infection, but opsonic coating of the organisms decreased at 20 hr after the induction of infection. PMNLs from sterile tissue cage fluid showed decreased phagocytic and bactericidal activities when compared with PMNLs from either blood or peritoneal exudate obtained after short- or long-term stimulation (P < 0.001

Role of Bacterial Exopolymers and Host Factors on Adherence and Phagocytosis of Staphylococcus aureus in Foreign Body Infection

Using a previously developed guinea pig model of foreign body infection, we examined ultrastructural and functional surface alterations of Staphylococcus aureus strain Wood 46 during the early phase of infection. Exopolymer-free bacteria were prepared and inoculated into subcutaneously implanted tissue cages. After three hours, the bacteria showed abundant capsular and intercellular exopolymers, which were visualized by transmission electron microscopy. Exopolymers were also produced by S. aureus exposed in vitro to fluid from the tissue cage. In contrast, human serum albumin prevented exopolymer production by S. aureus. The influence of exopolymers on the susceptibility of S. aureus to ingestion and phagocytic killing by neutrophils was tested in vitro and found to be negligible. Furthermore, adherence of S. aureus to fibronectin-coated surfaces was unaffected by the presence or absence of exopolymers. Thus, in our experimental model, exopolymers are produced early during the onset of infection, but they have little impact on adherence and phagocytosi