Bactericidal Concentrations Of Antibiotics Research Articles

An approach for the evaluation of synergy between antimicrobials

Synergy can be assessed by a variety of microbiological techniques. Mathematical modelling of synergy data can accomplish similar results and may provide more information than currently available techniques. In this study a combination of 1/4 MIC of aztreonam (AZTR) and 1 MIC of ciprofloxacin (CIPX) showed synergy against Pseudomonas aeruginosa in killing curve studies (based on the two log different criteria) at the end of 24 h. However, re-growth was always observed even when bactericidal concentrations of antibiotics were present. The surviving organisms showed a two-fold increase of MIC to CIPX after the studies and this resistance was not reversible. A mathematical model to quantitatively describe this observation is proposed.

Listeria monocytogenes infections--therapeutic possibilities and problems.

Listeriosis in humans is a rare disease, which, however, is known to be epidemic and endemic. The prognosis has remained unsatisfactory up to today, the fatality being at least 10% and often considerably higher depending on the clinical features of the disease and the patient's age. Three population groups are at risk: pregnant women, fetuses and newborn infants. Furthermore, immunosuppression in older patients due to disease, therapy, or age also plays a role. The incidence of Listeria infections in patients over 45 is clearly increasing. Due to the nature of the pathogen (in vivo bactericidal concentrations of antibiotics are often not attainable; intracellular growth) a high dosage of ampicillin is recommended. Although the present therapeutic possibilities are not satisfactory, a combination of ampicillin and an aminoglycoside appears to be the best therapy at present. Other combinations such as rifampicin and beta-lactam antibiotics have exhibited in vitro antagonism. The preferred therapy, ampicillin, can only be recommended with reservations because it is not optimally effective.

Effects of subminimal inhibitory concentrations of antibiotics on the adherence of Pseudomonas aeruginosa to tracheobronchial mucin.

Bacterial adherence to mucins may be important in tracheobronchial infections in cystic fibrosis. Sublethal concentrations of antibiotics reduce bacterial adherence to epithelial cells and mucins. This reduction in adherence may be a component of antimicrobial effects in infections at anatomical sites where bactericidal concentrations of antibiotics are difficult to achieve. We therefore tested the effects of sublethal concentrations of an aminoglycoside, tobramycin, and a beta-lactam antibiotic, ceftazidime, on the adherence of Pseudomonas aeruginosa to tracheobronchial mucin, since mucus secretions are often colonized by P. aeruginosa in cystic fibrosis. Adherence of the mucoid strains tested was inhibited by ceftazidime, but not by tobramycin. This effect of ceftazidime may partially explain its efficacy in patients with cystic fibrosis despite variables achieved in sputum.

The minimum inhibitory and bactericidal concentrations of antibiotics and anti-ulcer agents against Campylobacter pyloridis.

The minimum inhibitory and bactericidal concentrations of twenty-two antibiotics, in liquid and solid media, and three anti-peptic ulcer drugs in liquid media were determined against twenty isolates of Campylobacter pyloridis. Camp. pyloridis was very susceptible to most antibiotics, more so than Camp. jejuni and Camp. fetus, but was resistant to nalidixic acid. The MIC90 of cimetidine against Camp. pyloridis was 512 mg/l, and of ranitidine was 6400 mg/l. The difference in susceptibility patterns between Camp. pyloridis and other campylobacters may indicate that Camp. pyloridis is not a member of the Campylobacter genus.

Method of reliable determination of minimal lethal antibiotic concentrations.

The lack of a standardized, statistically reliable method for in vitro determinations of the minimal lethal or bactericidal concentrations of antibiotics has complicated analyses of isolates of Staphylococcus aureus which appear to be inhibited but not killed by the usual concentrations of cell wall-active antibiotics. We describe a method which identifies some of the covariants involved in determinations of minimal lethal concentrations. Lethality was defined as a 99.9% reduction in the initial inoculum of bacteria after 24 h of incubation. We limited the sample volume to 0.01 ml to minimize the inhibitory effect of antibiotic and corresponding rejection values, which detected lethality with a high degree of sensitivity and specificity. When the number of colonies on subculture was equal to or less than the rejection value, the antibiotic was considered lethal for the test organism. Rejection values encompassed initial inocula from 10(5) to 10(7) colony-forming units per ml for single and duplicate samples and allowed for 1 or 5% variability in pipette volumes and errors in initial inoculum determinations. This method was used to determine the minimal lethal concentrations of semi-synthetic penicillins for S. aureau isolates, one of which was tolerant to the killing action of penicillin.

Intracellular multiplication of Legionella pneumophila in cultured human embryonic lung fibroblasts.

Cell cultures of normal human embryonic lung fibroblasts were inoculated with two strains of Legionella pneumophila, the etiological agent of Legionnaires disease. Large numbers of intact organisms, including many dividing forms, were seen within fibroblasts by light and electron microscopy. Intracellular multiplication of organisms was demonstrated by the progressive increase in bacterial colony counts from plated extracts of infected fibroblast cultures in which extracellular multiplication had been eliminated by bactericidal concentrations of antibiotics. It is evident that L. pneumophila can thrive in an intracellular environment, and this property may be significant in the pathogenesis of Legionnaires disease.