In Vitro Effects of Carbenicillin Combined with Gentamicin or Polymyxin B Against Pseudomonas aeruginosa

Disodium carbenicillin and gentamicin sulfate have both shown promise in the treatment of infections caused by Pseudomonas aeruginosa. This study was designed to explore possible synergistic relationships among the new as well as the established antimicrobial agents used to treat such infections. With an agar dilution technique, minimum inhibitory concentrations of 27 strains of P. aeruginosa were determined in two-dimensional tests. Graphs of equal biological activity (isobolograms) demonstrated moderate synergistic effects of the carbenicillin-gentamicin combination over therapeutically feasible concentration ranges. In contrast, the combination of carbenicillin and polymyxin B showed only additive or slightly antagonistic effects. Tests of bacterial killing confirmed the presence of carbenicillin-gentamicin synergy in 3 of 6 strains of P. aeruginosa, but did not show true antagonism between carbenicillin and polymyxin B. Clinical trials of both drug combinations are advisable to determine whether therapeutic results can be improved, and whether the dosages of gentamicin or polymyxin B can thereby be reduced to lessen their toxic hazards.     

In Vitro Susceptibility of Pseudomonas aeruginosa to Carbenicillin and the Combination of Carbenicillin and Gentamicin

One hundred and eleven strains of Pseudomonas aeruginosa isolated from clinical material were studied for susceptibility to carbenicillin. Of the strains, 80% were inhibited by 125 mug/ml or more. The combination of carbenicillin and gentamicin was shown to have inhibitory and bactericidal synergistic effect on 15 of 16 strains of P. aeruginosa tested. There was poor correlation between the single-disc sensitivity method and the tube dilution method.     

Influence of Serum and Calcium on the Bactericidal Activity of Gentamicin and Carbenicillin on Pseudomonas aeruginosa

Because calcium was found to be antagonistic in vitro to the activity of colistin and polymyxin B on Pseudomonas aeruginosa, the effects of calcium and serum on gentamicin and carbenicillin were also examined. Serum was antagonistic to gentamicin in antibiotic tube dilution tests on five strains of P. aeruginosa. Serum was not antagonistic to carbenicillin in tube dilution tests. Physiologic concentrations of calcium antagonized the activity of gentamicin but not carbenicillin. The antagonism observed with gentamicin was less than that previously seen with colistin. The antagonistic effect of calcium and serum was removed by a chelating agent. Gentamicin and carbenicillin may be more active in vivo against P. aeruginosa than colistin or polymyxin B.     

Effect of Carbenicillin on Pseudomonas aeruginosa

The activity of carbenicillin against 200 strains of Pseudomonas aeruginosa was measured by a quantitative agar dilution method. Minimal inhibitory concentrations (M.I.C.''s) for five graded inocula were measured in terms of complete inhibition (CI) and reduced growth (RG). The M.I.C. decreased progressively as inocula were reduced, median values for the 200 strains ranging from 100 to 37.5 μg. per ml. by the CI criterion, and from 75 to 25 μg. per ml. by the RG definition. Ratios of M.I.C. obtained for large and small inocula were usually small. Identical M.I.C.''s by both CI and RG criteria were most often obtained when the inoculum for the RG criterion was 1 or 2 logs higher than that for complete inhibition.Population analysis of 15 strains of Ps. aeruginosa showed that one specific drug concentration usually caused a sharp drop in proportion of viable cells, ranging from 3 to 5 logs. None of the populations were completely non-viable even at 150 μg. per ml. There was evidence that the viability of different-sized populations was reduced disproportionately by carbenicillin.Carbenicillin 300 μg. per ml. exerted appreciable bactericidal effect against nine of 15 strains of Ps. aeruginosa after a 24-hour contact period; after only six hours the bactericidal effect was very small.Quantitative sensitivity measurements for carbenicillin should include M.I.C. values for both CI and RG criteria, using a range of inocula for testing. Such M.I.C. values may well be useful in monitoring carbenicillin therapy of tissue infections.     

Susceptibility of Pseudomonas aeruginosa to Carbenicillin

[This corrects the article on p. 630 in vol. 20.].     

Susceptibility of Pseudomonas aeruginosa to Carbenicillin

Ninety clinical isolates of Pseudomonas aeruginosa were examined for susceptibility to carbenicillin by the broth dilution and disc diffusion methods. Inhibition zone diameters varied at given minimal inhibitory concentration levels of the antibiotic. Nevertheless, the results obtained allowed the proposal of the following tentative criteria for the interpretation of inhibition zones. Pseudomonadaceae yielding zones of inhibition measuring at least 10 and 16 mm in diameter around 25-and 100-mug discs, respectively, are sensitive to this antibiotic when examined by the standardized Bauer-Kirby method of disc susceptibility testing. Isolates characterized by zones of less than 100 mm in diameter around 25-mug discs should be tested with 100-mug discs before they are reported as sensitive or resistant to carbenicillin.     

In Vitro Action of Carbenicillin Against Bacteria Isolated from Clinical Material

More than 500 bacteria isolated from patient material were tested against carbenicillin (disodium alpha-carboxybenzylpenicillin) by diffusion and dilution modalities. The same bacteria, which included Pseudomonas aeruginosa, Escherichia coli, Klebsiella-Aerobacter-Enterobacter group, various species of Proteus, Staphylococcus aureus and epiddermidis, enterococci, pneumococci, Streptococcus pyogenes, etc., were examined for susceptibility to other antibiotics commonly used with special emphasis on ampicillin and cephalothin. The responses of pyocine-typed P. aeruginosa were the most remarkable. The majority of these bacteria displayed susceptibility to carbenicillin by both the dilution and the diffusion techniques. The concentrations of this antibiotic used in the laboratory were of the same order of magnitude as that of the other drugs. The laboratory behavior of the other bacteria, toward this new semisynthetic penicillin derivative approximated their response to ampicillin and cephalothin.     

Induction of Spheroplasts of Pseudomonas aeruginosa by Carbenicillin

Speroplasts of Pseudomonas aeruginosa were induced with carbenicillin. Morphological changes were observed as early as 1.5 hr after the initial exposure to carbenicillin.     

Carbenicillin Resistance in Pseudomonas aeruginosa from Clinical Material

Strains of Pseudomonas aeruginosa resistant to 256 μg. per ml. or more of carbenicillin (Pyopen) were isolated from 17 patients over a period of three months. The infections were not solely due to cross-infection. Low dosage and attempted eradication of the organism from inaccessible sites, such as the bronchi or skin surfaces, by using systemic treatment are two possible causes. Restraint in treating infections of doubtful importance and the use of local applications to appropriate sites with or without systemic treatment is suggested.     

Carbenicillin and gentamicin in the treatment of Pseudomonas aeruginosa infection

The administration separately and sequentially of carbenicillin and gentamicin eradicated Ps. aeruginosa infections, during the period over which they were given, in all of 25 critically ill patients. Electron microscopy revealed differences in the action of these two antibiotics against Ps. aeruginosa in vitro. Culture studies showed synergism between them and destruction by gentamicin of the carbenicillin-induced long, filamentous form of the organism.     

Susceptibility of Pseudomonas aeruginosa to Gentamicin Sulfate In Vitro: Lack of Correlation Between Disc Diffusion and Broth Dilution Sensitivity Data

Seventy-eight of 420 clinical isolates of Pseudomonas aeruginosa yielded zones of inhibition of less than 12 mm in diameter around 10-mug discs of gentamicin sulfate when tested by the standardized Bauer-Kirby disc diffusion method. Of 153 strains chosen from these isolates, one strain (0.65%) required 25 mug of gentamicin per ml for inhibition; the remainder (99.35%) were inhibited by 6 mug/ml or less of the antibiotic. It is recommended that those isolates of P. aeruginosa that yield zones of inhibition less than 12 mm in diameter be disc susceptibility-tested once more; those isolates that give zones of inhibition of less than 12 mm upon repeated examination should then be subjected to the broth dilution test before they are designated as sensitive or resistant to gentamicin.     

Inhibition of Macrophage Phagocytosis by Pseudomonas aeruginosa Rhamnolipids In Vitro and In Vivo

Patients with cystic fibrosis often have chronic and ultimately lethal pulmonary infections with Pseudomonas aeruginosa. In order to understand why these bacteria resist pulmonary clearance, we have investigated the interaction of P. aeruginosa and phagocytic cells. In an earlier study we reported that sub-lytic concentrations of two glycolipids produced by P. aeruginosa (the mono- and dirhamnolipids) caused structural changes in human monocyte-derived macrophages, and at lower concentrations inhibited the phagocytosis of Staphylococcus epidermidis by these cells. In the present study we demonstrate that rhamnolipids also inhibit the in vitro phagocytosis of both P. aeruginosa and Saccharomyces cerevisiae by thioglycollate-elicited mouse peritoneal macrophages. Using lucifer yellow to label the lysosomal compartments of macrophages, we determined that rhamnolipids interfere with the internalization of attached particles and reduce the level of phagosome-lysosome fusion of internalized targets within macrophages. We also demonstrate that physiologically relevant concentrations of rhamnolipids injected intratracheally into rat lungs inhibited the response of alveolar macrophages to a challenge of zymosan particles in vivo. These studies further demonstrate the profound inhibitory effects of P. aeruginosa rhamnolipids on macrophage function and are consistent with our hypothesis that the in situ production of these rhamnolipids directly contributes to the persistence of this pathogen in cystic fibrosis patient lungs. Received: 15 December 1995 / Accepted: 22 January 1996     

Pseudomonas aeruginosa Inhibits the Growth of Scedosporium and Lomentospora In Vitro

Mycopathologia - In vitro bacterial–fungal interaction studies in cystic fibrosis (CF) have mainly focused on interactions between bacteria and Candida. Here we investigated the effect of...     

Combined Action of Sulfamethoxazole, Trimethoprim, and Ethylenediaminetetraacetic Acid on Pseudomonas aeruginosa

Potentiation of the sulfamethoxazole-trimethoprim combination by ethylene-diaminetetraacetic acid inhibited, in vitro, four strains of Pseudomonas aeruginosa which were resistant to the sulfamethoxazole-trimethoprim combination alone.     

In Vitro Activity of Carbenicillin Against Gram-negative Bacilli

The activity of a new semisynthetic penicillin, carbenicillin, was determined against 241 strains of gram-negative bacilli with the tube-dilution technique. Of 143 strains of Pseudomonas sp., 99 had a minimal inhibitory concentration of 200 to 300 mug/ml. The majority of strains of Escherichia coli and Proteus spp. were sensitive to this antibiotic, with minimal inhibitory concentrations of 25 mug/ml or less. Strains of Klebsiella sp. were quite resistant to carbenicillin. The size of inoculum had no significant effect on the minimal inhibitory concentration for Pseudomonas sp.     

Lytic Action of B-enzyme on Pseudomonas aeruginosa

B-enzyme was produced by Bacillus subtilis YT–25 and lysed the native cells of Pseudomonas aeruginosa extensively in the presence of NLF (Native Cell-Lytic Factor). NLF was a peptide which was also produced by B. subtilis YT–25. It was found that B-enzyme hydrolyzed the peptidoglycan of P. aeruginosa eventually to disaccharide units. Because the reducing end of the enzymatic digest was muramic acid, B-enzyme seemed to be an endo-N-acetyl-muramidase. Whereas, egg white iysozyme which was an endo-N-acetylmuramidase hardly lysed the native cells of P. aeruginosa. Specific activity of B-enzyme for the murein of P. aeruginosa was higher than that of egg white Iysozyme in the buffer of low ionic strength and the surface components of P. aeruginosa did not affect the activity of B-enzyme but strongly inhibited the activity of egg white Iysozyme. These facts seemed to explain the superiority of B-enzyme to egg white Iysozyme in the lysis of the native cells of P. aeruginosa.     

The Action of Ethylenediaminetetra-acetic Acid on Pseudomonas aeruginosa

It has been shown that ethylenediaminetetra-acetic acid (EDTA) has a direct bactericidal action against strains of Pseudomonas aeruginosa and Alcaligenes faecalis . The action against Ps. aeruginosa is considered to take the form of competition for a metal essential to the integrity of the cells: some of the factors influencing this antibacterial action have been discussed. From a study of the release of solutes from cells of Ps. aeruginosa , it was concluded that the action of EDTA takes place at the cell wall of the organism: an effect by EDTA on the isolated walls of sensitive organisms has been demonstrated.