Subinhibitory Concentrations Of Antibiotics Research Articles

The effects of subinhibitory concentrations of various antibiotics on phagocytosis of Streptococcus faecalis.

This study reports the effects of subinhibitory concentrations of the antibiotics, clindamycin, gentamicin, moxalactam, and penicillin G, against 6 blood isolates of Streptococcus faecalis to determine possible enhancement of phagocytosis. In addition, combinations of penicillin G plus streptomycin, penicillin G and gentamicin, and clindamycin plus gentamicin were studied to determine synergistic growth inhibition. Results suggest no observable effect in phagocytosis from subinhibitory concentrations of the studied antibiotics singly or in combination. The number of viable intracellular Str. faecalis were also not affected by pre-treatment with antibiotics.

Effects of subinhibitory antibiotics on bactericidal activity of chronic granulomatous disease granulocytes in vitro.

Experiments were performed on leukocytes from patients with chronic granulomatous disease (CGD), incubated with subinhibitory concentrations of antibiotics (clindamycin, methicillin and N-demethyl-lincomycin). Results indicate a minor enhancement of bactericidal activity. This improvement occurred in both CGD homozygotes and one heterozygote and may indicate a future role for the use of low dose antibiotics to augment immune defences such as granulocyte function.

Effects of subinhibitory concentrations of antibiotics on Staphylococcus aureus interactions with fibronectin.

Bacterial adherence to host tissues relies on interactions between tissue macromolecules and bacterial surface molecules. One of the major predisposing factors to infection with Staphylococcus aureus is trauma to tissues. A common element in traumatized tissues is fibronectin. In previous studies, we have shown that fibronectin binds to Staph. aureus. In this paper, we have investigated the effects of subinhibitory concentrations of antibiotics on fibronectin interactions with Staph. aureus. Exposure of Staph. aureus to 1/4 MIC of penicillin increases the number of binding sites and enhances adherence of Staph. aureus to a collagen-fibronectin matrix. Chloramphenicol, erythromycin, clindamycin, and U57,930E all decreased the number of binding sites. Also, U57,930E reduced Staph. aureus adherence to a collagen-fibronectin matrix. Taken together, these data suggest that penicillin may enhance Staph. aureus adherence to tissue fibronectin whereas U57,930E might reduce such binding.

Effects of low concentrations of antibiotics on Escherichia coli adhesion.

We have previously shown that subinhibitory concentrations of antibiotics may influence the adhesion of Escherichia coli SS142 to human epithelioid tissue culture cells. This report shows that these effects are not limited to E. coli SS142 or to our tissue culture system. Most of the 10 E. coli strains studied showed decreased adhesion to Intestine 407 tissue culture cells after growth in 25% of the minimum inhibitory concentration of streptomycin, tetracycline, trimethoprimsulfametrole, chloramphenicol, and clindamycin. Nalidixic acid at 25% of the minimum inhibitory concentration caused an increase of adhesion. The hemagglutinating activity of the five hemagglutinating strains and the adhesiveness of E. coli SS142 to human buccal cells were similarly affected by low concentrations of the above-mentioned antibiotics. We conclude that E. coli adhesion to human epithelioid tissue culture cells is a valid model of bacterial adhesion because of its high accuracy and reproducibility.

Effect of subinhibitory antibiotic concentrations on the phagocytosis of Staphylococcus aureus.

The effect of subinhibitory antibiotic concentrations on the phagocytosis of Staphylococcus aureus was studied by pretreating 3H-thymidine labelled bacteria with one-third the minimal inhibitory concentration of clindamycin, doxycyclin, cefotiam, vancomycin, piperacillin and penicillin G, respectively. Pretreatment with clindamycin and doxycyclin resulted in enhanced uptake of the bacteria by polymorphonuclear leukocytes compared to the untreated control. The augmented phagocytosis was still observed at 1/32 the MIC of clindamycin and 1/64 the MIC of doxycyclin, and when the serum was diluted to a concentration of 1%. Pretreatment of the bacteria with penicillin, cefotiam, piperacillin and vancomycin had no effect on phagocytosis. Inhibitors of bacterial protein synthesis induce alterations of Staphylococcus aureus leading to increased phagocytosis, whereas antibiotics acting on cell wall synthesis are without effect.

Subcutaneous staphylococcal infections in mice: the influence of antibiotics on staphylococcal extracellular products.

Using a mouse subcutaneous abscess model the effect of subinhibitory concentrations of antibiotics upon alpha-hemolysin, nuclease, lipase and esterase production was investigated. Infected mice treated with erythromycin (10 mg/kg), chloramphenicol (10 mg/kg) and fucidin (5 mg/kg) were compared with those given lincomycin (10 mg/kg) and clindamycin (5 mg/kg). In reference to the first three drugs, early blanching occurred at the inoculation site and necrosis appeared within 18 h, whereas wit the other two agents, lesion progressed more slowly with a slight induration only at the site of injection becoming apparent after 24 h. Neither alpha-hemolysin nor nuclease was elaborated in the lesion of mice treated with lincomycin and clindamycin. Histological examinations of skin of mice treated with the latter antibiotics revealed a localized abscess with little or no spreading of the bacteria as compared to untreated mice and to mice treated with the other antibiotics. Evidence is presented which suggests significant involvement of the extracellular products in the pathogenesis of staphylococcal infection.

Sublethal concentrations of antibiotics, effects on bacteria and the immune system.

Biological specimens obtained from patients with infections that are treated with antibiotics at dosages that resulted in body fluid concentrations below those that are minimally inhibitory, exhibit abnormal forms of bacteria. Identical morphological changes can be induced in vitro when the parental normal forms of the bacteria. Identical morphological changes can be induced in vitro when the parental normal forms of the bacteria are exposed to subminimal concentrations of certain antibiotics. The phenomenon of induced abnormal morphology and ultrastructure has received consideration in terms of: (1) the relationship of the induced alterations of the specific bacterial species to the given antibiotic, (2) in vitro conditions required for antibiotic induced alterations, (3) the mechanisms of action; (4) immune responses to the abnormal forms, and (5) relationship between abnormal structure and the inhibition of bacterial replication. This review provides the reader with a description and the significance of current research in the above areas which together comprise the growing field of subinhibitory concentrations of antibiotics.

Effect of subinhibitory concentrations of antibiotics on the adhesion of Streptococcus pyogenes to pharyngeal epithelial cells.

The hydrophobicity and charge of the cell surface of M protein-positive (M+) and the less virulent M protein-negative (M-) strains of type 12 Streptococcus pyogenes have been studied, respectively, by hydrophobic interaction chromatography and free zone electrophoresis. The M+ strain had a more hydrophobic and a more negatively charged surface than the M- strain. When the M+ strain was cultivated in the presence of sub-minimum inhibitory concentrations of different antibiotics, its hydrophobicity either decreased or did not change. The M+ organisms adhered to pharyngeal epithelial cells more avidly than M+; however, cultivation of both strains with sub-minimum inhibitory concentrations of penicillin and rifampin led to the decrease in adhesion. Tetracycline caused a decrease in adhesion for the M+ strain only, whereas cephalothin and polymyxin (to which the strains are resistant) did not affect adhesion or hydrophobicity of the M+ organisms. The negative surface charge of the M+ bacteria increased considerably upon exposure to rifampin and penicillin, and the M- bacteria exhibited small or no change. The contributions of these changes to suppression of infections are discussed.

Bacterial adhesion in the pathogenesis of infective endocarditis. Effect of subinhibitory antibiotic concentrations on streptococcal adhesion in vitro and the development of endocarditis in rabbits.

Bacterial adhesion to the constituents of nonbacterial thrombotic endocarditis (NBTE) is important in the pathogenesis of endocarditis. Subinhibitory concentrations (subMIC) of some antibiotics decrease bacterial adhesion to epithelial cells in vitro. We utilized an in vitro assay system to study the effect of subMIC of various antibiotics on streptococcal adhesion to a fibrin-platelet matrix (simulating NBTE). The results were (a) bacterial adhesion of Streptococcus sanguis and Streptococcus faecalis to NBTE was significantly reduced by vancomycin, penicillin, tetracycline, chloramphenicol and streptomycin (P less than 0.01 vs. controls) but not rifampin or trimethoprimsulfametrole; (b) the effect was dose-dependent and increased with duration of exposure to antibiotic; (c) reduction in bacterial adhesion did not correlate with altered retention by hydrophobic-interaction chromatography. This reduction in adhesion correlated with a diminished capacity of subMIC exposed Streptococcus sanguis (1/4 vancomycin minimum inhibitory concentration (MIC) X 4 h) to produce endocarditis in vivo. After intravenous inoculation of 10(6) colony-forming units of preincubated organisms into rabbits with traumatized aortic valves, 6 of 22 developed endocarditis vs. 17 of 22 controls (P = 0.03). These results may be relevant to prophylaxis of endocarditis since exposure of bacteria to subMIC of various antibiotics may reduce bacterial adherence both, to mucosal surfaces, and to damaged cardiac valves.

Direct microscopic observation of the effect of erythromycin on Staphylococcus aureus

SummaryA series of experiments was carried out in vitro to investigate the activity of erythromycin against Staphylococcus aureus SG 511 at various stages of growth using a method of direct microscopic examination of a microculture. The results showed that 3 μg erythromycin/ml immediately halted bacterial multiplication and only about 20% of the population went through one more division. After exposing bacteria to this concentration of erythromycin for 2 hours, only sub-inhibitory concentrations of the antibiotic were needed to control growth. These findings raise questions on the dosage and duration of treatment with erythromycin in clinical practice.

Effect of subinhibitory concentrations of antibiotics on the emergence of drug resistant bacteria in vitro

Effect of subinhibitory concentrations of antibiotics on the emergence of drug resistant bacteria <i>in vitro</i>

Effects of cerulenin on antibiotic-induced lysis of streptococcus faecalis (S. faecium).

Addition of the antibiotic cerulenin to cultures lowered the minimal effective concentration of penicillin G or methicillin required to produce bacterial lysis and killing. This effect was most pronounced at subinhibitory antibiotic concentrations. Cerulenin had no significant effects on lysis or killing induced in the presence of D-cycloserine, fosfomycin, bacitracin, or vancomycin.

Antibiotic-Associated Colitis: Effects of Antibiotics on Clostridium difficile and the Disease in Hamsters

Fifteen isolates of Clostridium difficile from hamsters and human patients were inhibited or killed by low concentrations of metronidazole, vancomycin, penicillin, and ampicillin; the isolates were often reesistant to tetracycline, cephalosporins, trimethoprim-sulfamethoxazole, clindamycin, erythromycin, and aminoglycosides. Antibiotics to which C. difficile was susceptible were able to prevent or postpone the colitis caused by clindamycin in hamsters. Colitis could be produced by treatment of hamsters with any one of these antibiotics. Production of colitis not only involved selection of resistant variants, but in some instances seemed to result from the acquisition of organisms after treatment, their persistence despite treatment, or from subinhibitory cecal concentrations of antibiotic (explainable by either pharmacologic factors or enzymatic inactivation). As in humans, no organisms other than C. difficile have been implicated conclusively as etiologic agents of colitis in hamsters. Our results suggest it may be wise to use isolation precautions for patients with colitis caused by C. difficile.

NITROBLUE TETRAZOLIUM (NBT) REDUCTION BY BACTERIA EMPLOYED FOR RAPID DETERMINATION OF ANTIBIOTIC CONCENTRATIONS IN SERUM

The ability of bacteria to reduce nitroblue tetrazolium (NBT) to formazan, and the inhibition of this process by antibiotics, have been utilized in a method to determine antibiotic concentrations in serum. Escherichia coli, growing in the presence of increasing but subinhibitory concentrations of antibiotics, produces diminished amounts of formazan. This is photometrically quantified and the optical density obtained with the sample is compared with those obtained with know concentrations. Levels of aminoglycosides below 1 microgram/ml can be measured in the presence of other antibiotics also, and the assay can be carried out in three hours. Good correlation was obtained when 49 serum samples containing varying concentrations of sisomicin were tested simultaneously by the NBT assay and a disc diffusion method.

Abnormal Forms of Bacteria Produced by Antibiotics

Subinhibitory concentrations of antibiotics can produce in vitro aberrant forms of bacteria that are similar to those observed in specimens and cultures from patients being treated with antibacterial agents. Eight species of bacteria were grown on membranes placed on agar containing subinhibitory concentrations of nine antibiotics. The resulting organisms were examined by Gram stain and electron microscopy. Gram stains showed filamentous and granular forms of enterobacteria with bipolar staining, giant staphylococci, and rodlike pneumococci. Electron micrographs showed changes in the number and distribution of ribosomes in enterobacteria and septum abnormalities in cocci. Such abnormal forms can occasionally simulate the appearance of quite different species, and they may indicate the presence of a subinhibitory antibiotic concentration at the site of infection as a result of prior antibacterial therapy.

The demonstration and significance of synergism between -lactam antibiotics.

Summary Synergism has been demonstrated between selected pairs of β-lactam antibiotics against four representative strains of β-lactamase-producing Gramnegative bacteria (Pseudomonas aeruginosa, Escherichia coli, Klebsiella aerogenes and an R-factor-bearing E. coli strain). A pour-plate double-diffusion technique with subinhibitory concentrations of antibiotics was used. Synergism has been proven by demonstrating a bactericidal effect, and by the isobologram technique. Seven out of 14 highly resistant strains of Gram-negative bacteria proved to be more sensitive to certain combinations of β-lactam antibiotics than to any of these antibiotics alone, tested at 1 mg per ml (a concentration attainable in the urine during therapy). Some aspects of the possible clinical use of combined therapy with two β-lactam antibiotics are discussed.

Effect of Mg 2+ and Ethylenediaminetetraacetate on the In Vitro Activity of Coumermycin A 1 and Novobiocin Against Gram-Negative Bacteria

The effect of Mg(2+) and ethylenediaminetetraacetic acid (EDTA) on the in vitro activity of coumermycin A(1) and novobiocin was determined against Pseudomonas aeruginosa, Escherichia coli, Klebsiella pneumoniae, and Proteus mirabilis grown in Trypticase Soy Broth or defined synthetic medium. In the presence of EDTA, the activity of coumermycin A(1) was significantly enhanced (8- to 40-fold) against all four organisms in the synthetic medium lacking Mg(2+); novobiocin activity was increased to a lesser extent (4- to 16-fold) against three strains and remained unchanged against P. mirabilis. Addition of 200 mug of Mg(2+) per ml to the synthetic medium containing EDTA completely reversed the enhancement of activity of both antibiotics by EDTA only against P. aeruginosa. The addition of Mg(2+) to the synthetic medium appreciably inhibited the activity of novobiocin (sixfold) but not coumermycin A(1) against E. coli, and had little or no effect on the activity of either antibiotic against the remaining organisms. K. pneumoniae showed the greatest susceptibility to both antibiotics, and addition of EDTA enhanced this activity from 4-fold to 20-fold in all of the media tested. Subinhibitory concentrations of both antibiotics induced filament formation by all four organisms in all media. In addition, lysis of K. pneumoniae cells was observed.