Effects Of Subminimal Inhibitory Concentrations Research Articles

Effects of sub-minimal inhibitory concentrations of EDTA on growth of Escherichia coli and the release of lipopolysaccharide

Release of lipopolysaccharide from E. coli was studied in the presence of sub-minimal inhibitory concentrations of ethylenediaminetetraacetic acid (EDTA). In untreated cells no release was detected with 50 mM Mg2+ in the medium, but a steady release of over 50% of the synthesized lipopolysaccharide was observed with 0.1 mM Mg2+. EDTA at MIC/8 led to a 2- to 3-fold higher release, presumably by an adjustment of the concentration of unchelated Mg2+ to a value still sustaining normal growth but giving rise to a highly unstable outer membrane. No structural difference was observed between cell-bound and released lipopolysaccharide.

The effect of subminimal inhibitory concentrations of penicillin on growth rate and haemolysin activity of group G Streptococcus.

The influence of the subminimal inhibitory concentrations (1/3 and 1/4 of the MIC) of penicillin on growth rate and on haemolysin production of a strain of group G Streptococcus was studied. It was shown that 1/3 of the MIC almost completely inhibited the bacterial growth, but it was not able to inhibit haemolysin activity in the culture supernate. The generation time of bacteria grown in 1/4 of the MIC was approximately twice longer than that of the control culture. In all cultures, the haemolysin, after being produced (or liberated), reached a peak and decreased to low levels, which could suggest that group G Streptococcus produces some end products of metabolism that are able to inhibit haemolysin activity.

Modification of Pseudomonas aeruginosa virulence factors by sub-inhibitory concentrations of antibiotics.

This study's objectives were to evaluate the effects of subminimum inhibitory concentrations (MICs) of tobramycin, gentamicin, netilmicin, streptomycin, ciprofloxacin, cefotaxime and piperacillin on proteinase production, alginate and siderophore synthesis by two strains of Pseudomonas aeruginosa. One of these strains, of recent clinical isolation, was mucoid. In fact it is well known that mucoid strains are more resistant than non-mucoid; there is, moreover, evidence that in cystic fibrotic lungs the non-mucoid P. aeruginosa are invariably replaced by mucoid variants. Our results show that subinhibitory concentrations of beta-lactams and quinolones significantly reduced the amount of alginate. Protease production was affected by all antibiotics tested.

Effects of subminimal inhibitory concentrations of minocycline on neutrophil chemotactic factor production in comedonal bacteria, neutrophil phagocytosis and oxygen metabolism

Comedonal bacteria, Propionibacterium acnes, P. granulosum and coagulase-negative staphylococci (CNS) seem to play an important initiating role in the inflammatory process by producing neutrophil chemotactic factors. The attracted neutrophils, after phagocytosis, release inflammatory factors such as reactive oxygen species (ROS). We investigated the effects of minocycline at subminimal inhibitory concentrations (sub-MIC), i.e. one-tenth MIC, on the production of human neutrophil chemotactic factors in comedonal bacteria, and on several inflammatory parameters of neutrophils, including neutrophil phagocytosis and generation of ROS (O2-, H2O2, OH.). ROS generation in a cell-free, xanthine-xanthine oxidase system was also assessed. Production of neutrophil chemotactic factors in all strains of P. acnes, P. granulosum and CNS were significantly suppressed by sub-MIC minocycline. Sub-MIC minocycline effectively reduced three kinds of neutrophil-generated ROS (O2-, H2O2, OH.). However, neutrophil phagocytosis and the ROS generated in a cell-free system were not markedly changed in the presence of sub-MIC minocycline. The results suggest that sub-MIC minocycline has an anti-inflammatory effect by inhibiting the production of neutrophil chemotactic factors in comedonal bacteria as well as ROS generated by neutrophils in the inflammatory process of acne.

Effects of antibiotics on the growth and morphology of Pasteurella multocida

The effects of subminimal inhibitory concentrations (subMICs) of certain antibiotics, namely penicillin G, tetracycline and trimethoprim/sulphamethoxazole, on the growth and morphology of Pasteurella multocida were evaluated. SubMICs of penicillin markedly reduced the growth of P. multocida. Tetracycline and trimethoprim/sulphamethoxazole had no effect on its growth. SubMICs of penicillin greatly affected the morphology of P. multocida. At the highest concentrations tested (1/2 and 1/4 MIC) cells were acapsulate, and long filamentous cells (4-6 microns) were observed with some isolates. There was no correlation between the observed differences in the penicillin-binding proteins of the P. multocida isolates, and the extent of cell filamentation induced by penicillin G. SubMICs of tetracycline and trimethoprim/sulphamethoxazole did not seem to affect capsule production although filamentation was observed. Our results indicate that subMICs of penicillin can reduce growth of P. multocida. Furthermore, results also indicate that subMICs of antibiotics can affect the production of capsular material and the morphology of P. multocida.

Effect of Sub-Minimal Inhibitory Concentrations of Ciprofloxacin and Fleroxacin on the Bacterial Capsular Antigen and Opsonophagocytosis by Human Polymorphonuclear Leukocytes

We have studied the effect of sub-minimal inhibitory concentrations (sub-MIC) of ciprofloxacin and fleroxacin on capsulated (K+) and non-capsulated (K-) Gram-negative bacilli (Escherichia coli O1:K1, O7:K1, O1:K-, O7:K-, and Klebsiella oxytoca) as well as on Staphylococcus aureus and we investigated the interaction of antibiotic pretreated bacteria with human serum and polymorphonuclear leukocytes (PMN). Following overnight growth in the presence of 1/2 MIC of the antibiotics, bacteria were opsonized in human serum and incubated with PMN. Opsonophagocytosis was quantified as the ratio of uptake by PMN of radioactively labeled bacteria. Ciprofloxacin and fleroxacin enhanced the phagocytosis rate of E. coli K+ strains (control 5-10%; 1/2 MIC of ciprofloxacin and fleroxacin 70-80%) of K. oxytoca (control O-2%; 1/2 MIC of ciprofloxacin and fleroxacin 35-40%) as well as of Staph. aureus (control 5-10%; 1/2 MIC of the antibiotics 35-40%). Opsonophagocytosis of K- strains was not altered. The enhancement of opsonophagocytosis was a complement dependent process. Exposure of capsulated E. coli to ciprofloxacin as well as to fleroxacin resulted in decreased amounts of the capsular antigen.

Effect of ampicillin, cefmetazole and minocycline on the adherence of Branhamella catarrhalis to pharyngeal epithelial cells.

Using pharyngeal epithelial cells from a healthy adult and eight strains of Branhamella catarrhalis (B. catarrhalis) isolated from eight patients with respiratory infection the effect of subminimal inhibitory concentrations of cefmetazole, ampicillin and minocycline on adherence was examined. Cefmetazole-treated bacterial attachment (44 +/- 28; mean +/- S.D.) decreased significantly (p less than 0.05) compared to the control (84 +/- 27). Statistically no significant difference in adherence was found between ampicillin-treated bacteria (63 +/- 36) and the control (95 +/- 40) or minocycline-treated bacteria (91 +/- 39) and the control (109 +/- 40). Large bacteria was observed after cefmetazole and ampicillin treatment. In addition to diplococci, tetrads were observed after cefmetazole treatment. Significant correlation between the MICs and adherence ability was not found. The results suggests that these three antibiotics were not responsible for the increase in B. catarrhalis infection by increasing adherence ability.

The effect of subminimal inhibitory concentrations of antimicrobial agents on three bacterial mixtures.

A test tube technique was developed to screen bacterial mixtures to detect interbacterial interactions that play a role in determining sensitivity to antimicrobial agents. We found 3 mixtures where these bacterial interactions change the sensitivity to antimicrobials or change the proportions of each bacterial species in the mixture. The mixtures were: Fusobacterium nucleatum 102.3 and Bacteroides endodontalis ATCC 35406; F. nucleatum 102.3 and B. endodontalis BN11 a-f; and Capnocytophaga ochracea 1956c and Eubacterium saburreum 162.4. The antimicrobials used were metronidazole for the first 2 mixtures and tetracycline for the last. F. nucleatum seems to protect B. endodontalis from the action of metronidazole. Conversely, the growth inhibition of C. ochracea by E. saburreum was lifted when tetracycline was present. We also found that the growth of C. ochracea can then permit the subsequent growth of E. saburreum. The test tube method permits the evaluation both of interbacterial interactions and the detection of any protective mechanism against antimicrobial agents in a bacterial mixture. We found that F. nucleatum 102.3 can decrease the metronidazole level in the culture medium, and by the use of 14C-metronidazole we demonstrated that acetamide is produced from metronidazole.

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.

Effects of sub-minimum inhibitory concentrations of cephalosporins on Bacteroides species.

Effects of sub-minimum inhibitory concentrations of cephalosporins on Bacteroides species.

Effect of subminimal inhibitory concentrations of antimicrobial agents on the piliation and adherence of Neisseria meningitidis

Neisseria meningitidis is known to be highly resistant to lincomycin (minimum inhibitory concentration greater than 32 micrograms/ml). However, during studies on meningococcal piliation, we noticed a significant reduction in the number of pili after cultivation on lincomycin-containing selective media. This observation was followed up by in vitro and in vivo studies on the relation between lincomycin and meningococcal adherence to human epithelial cells. We found a remarkable decrease in in vitro piliation and adherence after exposure to lincomycin at concentrations as low as 0.05 micrograms/ml. By giving four healthy meningococcal carriers lincomycin orally for 3 to 6 days, the possible in vivo effect of lincomycin was studied. A marked decrease in the meningococcal counts of the pharyngeal secretion was observed. One person completely lost his meningococcal strain during the observation period.

Effects of subminimal inhibitory concentrations of aminoglycosides on the penicillinase production of Staphylococcus aureus.

The effects of subminimal inhibitory concentrations of kanamycin, amikacin and gentamicin on the production of penicillinase by Staphylococcus aureus were tested on 12 penicillin-resistant strains. Of the 36 experiments performed, 16 (44%) displayed an increase and 9 (25%) produced a decrease in the penicillinase activity of the strains. These effects were observed at concentrations ranging from 1:2 to 1:2,048 of the respective minimal inhibitory concentration, irrespective of the susceptibility of the strain to the aminoglycoside drug.

Effects of subminimal inhibitory concentrations of chloramphenicol, erythromycin and penicillin on group A streptococci.

Group A streptococci strains were grown in broth containing subminimal inhibitory concentrations of chloramphenicol, erythromycin and penicillin, and tested for possible changes in colonial morphology, activity and amount of cellular and extracellular components. The following components were tested: T protein, M protein, opacity factor, lipoteichoic acid, hyaluronic acid, streptolysin S, streptolysin O, DNase, hyaluronidase and NADase. Sub-MICs of these drugs produced variable changes in the bacteria. They increased the amount of hyaluronic acid and hyaluronidase, decreased the amount of M protein, and enhanced phagocytosis and the release of lipoteichoic acid. The results indicate that sub-MICs of chloramphenicol, erythromycin and penicillin may affect the pathogenicity and toxinogenicity of group A streptococci.

Effect of subminimal inhibitory concentrations of penicillin on hyaluronidase production by group a streptococci

A sensitive dye-binding assay was employed to study the extracellular hyaluronidase produced by three penicillin-sensitive strains of group A streptococci belonging to M types 4, 24 and 28. Enzyme was produced by all strains at appreciable levels. Subminimal inhibitory concentrations of penicillin in growing cultures increased enzyme production by M types 4 and 24 strains. Growth of the M type 28 R strain with added antibiotic was accompanied by a reduced production of hyaluronidase.

Anomalous cellular morphology and growth characteristics of Neisseria meningitidis in subminimal inhibitory concentrations of penicillin G.

The effects of subminimal inhibitory concentrations of penicillin G on Neisseria meningitidis in the presence and absence of selected stabilizers were examined. Subminimal inhibitory concentrations of penicillin G decreased cell numbers and altered both colonial and ultrastructural morphologies of this meningococcus. Although these levels of penicillin did not have immediate adverse effects on cell mass increase, deoxyribonucleic acid synthesis, or the incorporation of [3H]leucine into protein, they did significantly alter the division rate and the integrity of the cell envelope. The inability of many of the abnormal membranous cell types produced in subminimal inhibitory concentrations of penicillin to form either complete or properly oriented division septa and the overproduction of cell wall material at such sites was indicative of the disruptive effects of this antibiotic on functions necessary for maintaining the normal division process. The addition of the stabilizers polyvinylpyrrolidone-40 and horse serum to the test medium diminished the effects of penicillin G as evidenced by a fourfold increase in the minimal inhibitory concentration. Moreover, such stabilizers maintained the association of the outer membrane with the peptidoglycan and inner membrane.

Effects of Subminimal Inhibitory Concentrations of Antibiotics in Experimental Infections

The antibacterial effects of subminimal inhibitory concentrations (sub-MICs) of antibiotics were studied in two animal models. In mice, the oral cephalosporin CGP 9000 was effective in 11 of 20 different gram-negative infections and cephalexin was effective in one of these infections, both at 50% effective doses (ED(50)) that produced peak concentrations of drug in plasms equal to one-half to one-sixteenth the minimal inhibitory concentration (MIC) for the infecting organism. In gram-positive infections, both antibiotics were effective only at concentrations above the MIC. In rabbits, sub-MICs of cephaloridine, ampicillin, and gantamicin were maintained for 6-10 hr by intravenous infusion. At steady-state concentrations equal to one half to one-eighth the MIC, the beta-lactam antibiotics caused elongation and filamentation, and gentamicin caused enlargement, of Proteus mirabilis, Escherichia coli, and Salmonella typhimurium in peritoneal exudate; the number of viable cells of each of these bacteria was temporarily reduced. In infections with E. coli and P. mirabilis, sub-MIC's of beta-lactam antibiotics and of gentamicin prolonged the survival rates for infected animals beyond those for control animals. Rabbits infected with S. typhimurium and treated with ampicillin at a concentration of one-third the MIC Tended to die sooner than did control animals.

Effect of subminimal inhibitory concentrations of mecillinam on the synthesis of DNA, RNA, and protein of Salmonella typhimurium: a proposed mechanism of action.

Salmonellae alter their rod-like morphology to become large ovals within 3-5 hr after being exposed to concentrations of mecillinam below the minimal inhibitory concentration. Before this overt morphologic change occurs, synthesis of DNA increases, with a concomitant decrease in total protein synthesis. Incorporation of [3H]leucine into cell wall protein is markedly inhibited by mecillinam, whereas incorporation of leucine into soluble intracellular proteins is enchanced by the drug. Electrophoretic separation of stained, soluble intracellular proteins of salmonellae exposed to mecillinam indicates that as many as 15-20 individual groups of protein occur at higher concentrations in mecillinam-exposed salmonellae than in unexposed control organisms. These results suggest that, at low concentrations, mecillinam binds selectively to cell wall components, thereby interfering with the assembly of the cell wall during growth. This interference causes a buildup of newly synthesized soluble proteins that are normally involved in cell wall assembly. The weakening of the cell wall, combined with this buildup, causes the cell to assume a three-dimensional oval structure that is the result of equal hydrostatic pressure exerted by the medium.

Effects of Subminimal Inhibitory Concentrations of Antibiotics on Adhesiveness of Escherichia coli in Vitro*

The adhesion of radiolabeled Escherichia coli (strain SS142) to monolayers of Intestine 407, a human epithelioid tissue culture cell line, was investigated. In this assay the adhesion of bacteria grown in the presence of subminimal inhibitory concentrations of tetracycline, clindamycin,, or trimethoprim-sulfametrole was reduced in a manner that was dose dependent. In contrast, at such concentrations nalidixic acid enhanced the adhesion of this bacterial strain, and other antibiotics-e.g., penicillin G, ampicillin, mecillinam, cephacetrile, cephalexin, cefotaxime, chloramphenicol, and streptomycin-did not affect its adhesiveness.

Effects of subminimal inhibitory concentrations of ampicillin, chloramphenicol, and nitrofurantoin on the attachment of Escherichia coli to human uroepithelial cells in vitro.

An in vitro system with epithelial cells of the human urinary tract and Escherichia coli isolated from the urine of pateints with acute pyelonephritis was used for tests of the effect of antibacterial agents on bacterial adhesion. E. coli treated with subminimal inhibitory amounts of ampicillin attached less than untreated control bacteria. Subminimal inhibitory amounts of chloramphenicol and nitrofurantoin had no effect on adhesion of the 15 strains of E. coli tested. The combination of bacterial pretreatment with ampicillin and addition of antibodies to the adhesion test tube decreased adhesion more than did either treatment separately.