Postantibiotic effects of imipenem and enoxacin againstS. typhimurium andS. enteritidis and the influence on their surface hydrophobicity

The influence of the postantibiotic effect (PAE) and the postantibiotic sub-MICs effect (PA SME) of imipenem and enoxacin on the surface hydrophobicity ofS. typhimurium andS. enteritidis strains were studied by evaluating Congo red binding and the aggregation in molar solutions of ammonium sulfate (SAT). A PAE was induced by 2× and 4× MIC of antibiotics tested for 0.5 h. Suprainhibitory concentrations of imipenem againstS. typhimurium induced a short PAE (0.3–0.6 h) compared toS. enteritidis (6.0–9.7 h). Suprasubinhibitory concentrations of imipenem did not allow a regrowth ofS. enteritidis. Similar results were also found for enoxacin. Evaluation of surface hydrophobic properties of the salmonellas after affecting both PAEs and PA SMEs has shown that imipenem at concentrations 4×MIC and 4×MIC+0.3×MIC partially influenced the hydrophobicity ofS. typhimurium. S. enteritidis was more susceptible toward both antibiotics tested.     

Influence of the postantibiotic effect and postantibiotic Sub-MICs effect of netilmicin,tobramycin, ciprofloxacin and pefloxacin on alginate production byPseudomonas aeruginosa

The postantibiotic effect (PAE) (postantibiotic phase induced by 2× or 4×MIC) as well as the postantibiotic effect of subinhibitory concentrations (0.1×, 0.2× and 0.3× MIC) (PA SME) of netilmicin, tobramycin, ciprofloxacin and pefloxacin affected the production of the virulence factor alginate by aP. aeruginosa strain. Aminoglycosides and ciprofloxacin at a concentration of 4× MIC inhibited the alginate production more significantly than 2× MIC. Suprainhibitory concentrations of aminoglycosides were more effective than pefloxacin (2× or 4× MIC) and ciprofloxacin (2× MIC). PA SME demonstrated by the above antibiotics (with the exception of ciprofloxacin 2× MIC +00.1× MIC) suppressed alginate production more efficiently.     

Postantibiotic effects of gentamicin and netilmicin onSerratia marcescens: Effects on hydrophobicity and motility

The impact of postantibiotic effect (PAE) of aminoglycosides (gentamicin, netilmicin) on cell-surface hydrophobicity and motility of a clinical isolateSerratia marcescens was evaluated. For the induction of PAE 2× and 4×MIC concentrations of both antibiotics were used. Gentamicin and netilmicin induced a PAE of similar duration after 2×MIC concentration (2.7 and 2.8 h, respectively). Both aminoglycosides demonstrated concentration-dependent PAE. At a concentration of 4×MIC they produced PAEs of 5.9 and 8.2h, respectively. The evaluation of hydrophobic properties ofS. marcescens after affecting PAE showed that both aminoglycosides inhibited adherence to xylene. This inhibition was also concentration-dependent. More expressive, was netilmicin which inhibited the adhesion by 70.5% at 2×MIC and by 85.2% at 4×MIC. Netilmicin inhibited also the adhesion to nitrocellulose filter by 34.7% at 4×MIC. Exposure of the bacterial cells to suprainhibitory concentrations of both aminoglycosides resulted only in moderate inhibition of motility of strain tested compared to the unexposed cells.     

Postantibiotic effect of various antibiotics on Legionella pneumophila strains isolated from water systems

The postantibiotic effects (PAE) of azithromycin, clarithromycin, ciprofloxacin, and levofloxacin were investigated against Legionella pneumophila (L. pneumophila) strains isolated from several hot water systems of different buildings in Istanbul. Each strain in logarithmic phase of growth was exposed to concentrations of antibiotics equal to minimum inhibitory concentration (MIC) and 4× MIC for 1?h. Recovery periods of test cultures were evaluated after centrifugation using the viable counting method. The mean values of PAEs for the strains of L. pneumophila, azithromycin at a concentration equal to and 4 times of MIC values were found 1.75?±?0.28 h and 4.06?±?0.44?h, for clarithromycin 2.98?±?0.70?h and 4.18?±?0.95?h, for ciprofloxacin 2.97?±?0.63?h and 4.70?±?0.63?h, for levofloxacin 2.05?±?0.33?h and 3.78?±?0.46?h, respectively. All of the antibiotics showed increased PAE values in a concentration-dependent manner. The findings of our study may play useful role in selecting the appropriate timing of doses during therapy with antimicrobials to treat patients infected with L. pneumophila.     

Influence onEnterobacter cloacae metabolism, cell-surface hydrophobicity and motility of suprainhibitory concentrations of carbapenems

The impact of postantibiotic effect (PAE) of carbapenems (imipenem, meropenem) on the metabolism (biosynthesis of macromolecules, respiration), cell-surface hydrophobicity and motility of a clinical isolate ofEnterobacter cloacae was examined. The metabolism was evaluated after 16 h and after 1 d of cultivation using 2× and 4× minimum inhibitory concentrations (MIC) of both antibiotics for the induction of PAE. Imipenem at 4×MIC did not induce PAE. After a 16-h cultivation (in the postantibiotic phase of both carbapenems), inhibition of nucleosynthesis and protein synthesis was found; after a 1-d cultivation, during regrowth stimulation of mainly¹⁴C-leucine incorporation was found. The presence of the exogeneous intermediates of citrate cycle,viz. 2-oxoglutarate, increased the respiratory activity of the cells. The cell-surface hydrophobicity (evaluated by three methods—bacterial adhesion to hydrocarbon, nitrocellulose-filter test and salt-aggregation test) decreased after PAE of both carbapenems; meropenem was more effective. Motility (an important virulence factor) was inhibited in the postantibiotic phase of both carbapenems; the 4×MIC caused a higher inhibition.     

Norfloxacin and ursolic acid: in vitro association and postantibiotic effect against Staphylococcus aureus

Aims: We investigated the effectiveness in vitro of the association between norfloxacin (NOR) and ursolic acid (UA) against Staphylococcus aureus. Methods and Results: The minimal inhibitory concentrations (MICs), the minimal bactericidal concentrations, the bacterial killing and the postantibiotic effect (PAE) of NOR and UA were determined both singly and in combination. A synergistic interaction was observed against Staph. aureus ATCC 29213: the mean PAEs were 3 h for NOR, ?1·2 h for UA (1 × MIC) and 2·0 h for UA (2 × MIC). Synergism was observed with longer PAEs and postantibiotic sub‐MIC effects after NOR/UA exposure. UA was also active against clinical isolates and methicillin‐resistant Staph. aureus. Conclusions: The application of antimicrobial combinations may address the rising resistance to established classes of both systemic and topical agents. Significance and Impact of the Study: In vitro interactions between NOR and UA may contribute to the development of novel topical agents for the treatment of skin infections as well as for topical formulations.     

Postantibiotic effects of rifampin, amikacin, clarithromycin and ethambutol used alone or in various two-, three- and four-drug combinations against Mycobacterium avium

The postantibiotic effects (PAEs) of rifampin, amikacin, clarithromycin, and ethambutol were determined radiometrically against five AIDS-associated isolates of Mycobacterium avium. and were found to be 20.8+/-3.4. 18.4+/-2.5, 11.8+/-1.7. and 2.4+/-0.9 h, respectively. Various two-, three- or four-drug combinations were also screened: the PAEs for a two-drug combination were generally longer than individual drugs (mean PAE of 13.8+/-1.5 to 29.2+/-7.4 h instead of 2.4+/-0.9 to 18.4+/-2.5 h for single drugs). The addition of a third drug further increased the mean PAE to a range of 21.0+/-2.6 to 32.4+/-6.1 h. Both rifampin+clarithromycin and rifampin+amikacin were the most potent two-drug combinations resulting in longer PAEs than individual drugs, whereas rifampin+amikacin+clarithromycin was the most potent three-drug combination. Parallel viable count determinations showed a good correlation between the PAE results obtained by the radiometric method or by bacterial viability assessment. These results are useful in planning future clinical investigations to clarify the possible implication of PAE in drug schedule and dosage, a line of information that is urgently needed to guide the drug administration in M. avium-infected AIDS patients, who are presently over-burdened with the administration of too many drugs for HIV-treatment and opportunistic infections.     

Effects of subinhibitory concentrations of antibiotics on biological properties ofSalmonella typhimurium

We followed the effects of subinhibitory concentrations (sub-MICs) of 7 antibiotics (ticarcilin, cefotaxim, streptomycin, gentamicin, ciprofloxacin, pefloxacin, mitomycin C) on the sensitivity of aSalmonella typhimurium strain to standard bacteriophages, on the phage DNA as well as on the factors of virulence (permeability and cytotoxic activity). The phage type was not changed by the sub-MICs of the tested antibiotics. However, differences were found in culture filtrates prepared from the bacterial suspensions of the strain cultivated with the sub-MICs. Marked inducing effects on phage DNA were exhibited by mitomycin C (1/2, 1/4, 1/8 of the MIC), pefloxacin (1/2, 1/4, 1/8 of the MIC) and ciprofloxacin (1/2, 1/4, weakly also 1/8 of the MIC). Ticarcilin (1/2 of the MIC), like the aminoglycosides streptomycin and gentamicin (1/2, 1/4, 1/8 of the MIC), had a weak effect. Sub-MICs of the studied antibiotics (with the exception of 1/8 of the MIC of ciprofloxacin and 1/4 of the MIC of ticarcilin) decreased the permeability reaction in rabbit skin. Most effective was streptomycin (1/2 of the MIC). Sub-MICs of the tested antibiotics (with the exception of 1/4 and 1/8 of the MIC of ciprofloxacin and 1/4 of the MIC of pefloxacin) caused also an inhibition of the factor responsible for morphological changes on Vero cells. Gentamicin and streptomycin were effective at all the sub-MICs tested.     

Quinolone effects in the SOS chromotest and in the synthesis of biomacromolecules

The genotoxicity of quinolone antibiotics (ciprofloxacin, enoxacin, nalidixic acid, norfloxacin, ofloxacin, pefloxacin) was studied on the selected mutantE. coli strain PQ37 (SOS chromotest). The genotoxicity was expressed by SOS-inducing potential (SOSIP) values. The highest SOSIP values were found with ciprofloxacin (SOSIP=1967 δIF/nmol), the lowest value was observed with nalidixic acid (SOSIP=0.3 ΔIF/nmol). Similar results were also found with the biosynthesis of nucleic acids, as indicated by incorporation of¹⁴C-adenine into TCA-insoluble fractions ofS. typhimurium cells (ciprofloxacin IC₅₀=0.39, nalidixic acid IC₅₀=400). DNA-damaging effects were tested in the absence of an exogenous metabolizing system.     

Effect of suprainhibitory concentrations of quinolones on hydrophobicity and motility of Serratia marcescens

The effect of suprainhibitory concentrations of quinolones (ciprofloxacin, enoxacin and norfloxacin) on the growth, hydrophobicity and motility of a nosocomial pathogen Serratia marcescens was studied. A postantibiotic effect (PAE) was induced by 2x of 4x MIC concentrations for 0.5 h. By using the 2x MIC concentrations all three quinolones induced equally long PAE approximately 1 h. The longest PAE of 5.4 h at 4x MIC concentration was induced by enoxacin. The results obtained showed that suprainhibitory concentrations of quinolones significantly stimulated the adhesion of S. marcescens to xylene, with the exception of enoxacin, which inhibited the adhesion to 61.2% at 4x MIC concentration. These results correlated with those in the salt aggregation test. The adhesion of strains to nitrocellulose filters did not influence the aftereffect of suprainhibitory concentrations of quinolones. Exposure of bacterial cells to suprainhibitory concentrations of ciprofloxacin and norfloxacin caused a reduction in motility, while this effect was more distinct at 4x MIC concentration. The results suggest that any consideration of postantibiotic effects should include the residual antibiotic effects on virulence factors, in addition to the defined suppression of bacterial regrowth.     

Inhibition ofPseudomonas aeruginosa alginate expression by subinhibitory concentrations of antibiotics

The effects of subinhibitory concentrations (1/4, 1/8, 1/16 of the MIC) of quinolones (ciprofloxacin, enoxacin, nalidixic acid, norfloxacin, ofloxacin, pefloxacin), aminoglycosides (amikacin, gentamicin, netilmicin, streptomycin, tobramycin), β-lactams (aztreonam, ceftazidime, imipenem, ticarcilin) and macrolides (erythromycin, roxitromycin) on the excretion of alginate by aP. aeruginosa strain were studied. Both β-lactam and macrolide antibiotics were found ineffective at the concentrations tested, except erythromycin and imipenem at 1/4 MIC. Aminoglycosides at a concentration of 1/4 MIC reduced most effectively the excretion of alginate. Quinolones were also effective at this sub-MIC; 1/16 MIC was ineffective with all antibiotics or stimulated the production of alginate.     

Postantibiotic effects of subinhibitory concentrations of some antibiotics and their influence onPseudomonas aeruginosa enzymic activity

The postantibiotic effects of subinhibitory concentrations (PA SMEs) and virulence factor alterations induced by ciprofloxacin, tobramycin and netilmicin inPseudomonas aeruginosa were studied. After induction of the postantibiotic phase (PA) (2x or 4x MIC) the cultures were exposed to subinhibitory concentrations (0.1, 0.2 and 0.3x MIC) of the same antibiotic PA SME). The regrowth of treated as well as control cultures was followed for 24 or 45 h. In the sterile culture filtrates obtained from these bacterial cultures, elastase and proteinase were determined. Ciprofloxacin and aminoglycosides exhibited PA SMEs of 3.5–35 h for certain combinations of supra-subinhibitory antibiotic concentrations. Longer PA SMEs were observed after treatment with higher sub-MICs. Tobramycin at 0.2 and 0.3x MIC (postantibiotic phase induced by 2x MIC) and at all sub-MICs added to the bacteria previously exposed to 4x MIC do not allow any regrowth of bacterial culture. PA SMEs of tested antibiotics affected virulence factors ofP. aeruginosa. Elastase compared to proteinase was suppressed more effectively. Ciprofloxacin at 0.3x MIC reduced elastase and proteinase activity most significantly (to 14.2 and 60 % of the control values).     

Occurrence of variants with temperature-dependent susceptibility (TDS) to antibiotics among Stenotrophomonas maltophilia clinical strains

Susceptibility to 20 antibiotics was tested in 104Stenotrophomonas maltophilia strains at 37 and 30°C by means of a dilution micromethod to verity the phenomenon of temperature-dependent susceptibility (TDS). Trimethoprim-sulfamethoxazole, pefloxacin and ofloxacin were the most active preparations at 37°C (93, 90, and 86% of susceptible strains, respectively), whilst trimethoprim-sulfamethoxazole, cefoperazone-sulbactam and pefloxacin performed best at 30°C (94, 94, and 76% of susceptible strains, respectively). Variants 37TDS (minimum inhibitory concentration, MIC, of tested antibiotics at least 4-times lower at 37 than at 30°C) occurred in 60%. Variants 30TDS (at least 4-times lower value of MIC at 30 than at 37°C) were found in 7.7%. Both variants in susceptibility to tested antibiotics appeared in 23.1%, whilst neither of them was observed in 9.6%. The 37TDS phenomenon was recorded most of all with gentamicin (51% of strains), amikacin (47), colistin (44) and tetracycline (34). The 30TDS phenomenon was found particularly with cefoperazone-sulbactam (16.0% of strains) and colistin (10.0%). The above phenomena may be due to changes in membrane permeability, temperature-dependent ribosomal changes, and insufficient adaptation to higher temperatures of some strains of the originally environmental speciesS. maltophilia. Presented at the10th European Congress of Clinical Microbiology and Infectious Diseases, Stockholm (Sweden), 28–31 May 2000.     

Influence of subinhibitory concentrations of amikacin and ciprofloxacin on morphology and adherence ability of uropathogenic strains

The influence of subinhibitory concentrations (1/2, 1/4, 1/8, 1/16 and 1/32 MIC) of amikacin and ciprofloxacin on the morphology and adherence of uropathogenic strains was studied. Intensity of morphological changes was proportional to the concentrations of these antibiotics. Morphological changes were the most prominent after bacterial exposure to sub-MICs of ciprofloxacin. These concentrations, especially 1/2 MIC of ciprofloxacin, induced the formation of filaments of E. coli, K. pneumoniae, K. oxytoca, E. cloacae and A. calcoaceticus biotype anitratus. No morphological changes were observed in P. aeruginosa, S. epidermidis and S. aureus cells after exposure to subinhibitory concentrations of both antibiotics. Sub-MICs of amikacin affected the changes in cell shape only slightly. The exposure of bacterial strains to 1/2 MIC of ciprofloxacin induced increased vacuolation of the cells. We observed shrinkage of the protoplasm and the pleated cell walls in comparison with control cells. The greatest loss of adherence ability occurred at 1/2 MIC of ciprofloxacin after a 1-d incubation.     

A multi-type branching model with varying environment for bacterial dynamics with postantibiotic effect

A multi-type branching process with varying environment was used to construct a pharmacokinetic/pharmacodynamic (PK/PD) model that captures the postantibiotic effect (PAE) seen in bacterial populations after exposure of antibiotics. This phenomenon of continued inhibition of bacterial growth even after removal of the antibiotic from the growth medium is of high relevance in the context of optimizing dosing regimens. The clinical implication of long PAEs lies in the interesting possibility of increasing the intervals between drug administrations.The model structure is generalizable to most types of antibiotics and is useful both as a theoretical framework for understanding the time properties of PAE and to explore optimal antibiotic dosing regimens. Data from an in vitro study with Escherichia coli exposed to different dosing regimens of cefotaxime were used to evaluate the model.     

Antibacterial and mutagenic activities of new isothiocyanate derivatives

Nine newly synthetized isothiocyanate derivatives were demonstrated to posses antibacterial and genotoxic activitiesin vitro. 4-Hydroxybutyl isothiocyanate exhibited a broad antibacterial effect, with MIC values of 762 μmol/L forStaphylococcus aureus andEscherichia coli. Ethyl 4-methylsulfoxidobutanoate had the highest antibacterial activity in Gram-positive bacteria, the MIC value being 425 μmol/L forS. aureus. The highest tested concentrations of ethyl 4-isothiocyanatobutanoate and 4-hydroxybutyl isothiocyanate produced a bacteriocidal effect in Gram-positive bacteria. The compounds showed no mutagenic effects onSalmonella typhimurium tester strains TA 98 and TA 100, either in the absence or in the presence of a metabolically active microsomal S9 fraction from rat liver using standard Ames test.     

Pharmacodynamic parameters of aminoglycosides and their effect on exoenzymes ofPseudomonas aeruginosa

Aminoglycosides at 2× or 4× minimum inhibitory concentration induced postantibiotic effects againstPseudomonas aeruginosa lasting 3.5–4.9 h (gentamicin) and 0.5–3.7 h (selemycin). Postantibiotic effects of subinhibitory concentrations of the aminoglycosides tested were substantially longer. Some combinations of supra- and subinhibitory concentrations of antibiotics did not even allow any regrowth of the bacterial strain. The postantibiotic effects and postantibiotic effects of subinhibitory concentrations of gentamicin and selemycin were associated with changes ofP. aeruginosa elastase and proteinase. Combinations of supra- and subinhibitory concentrations more pronouncedly suppressed enzymic activities than did suprainhibitory concentrations alone.     

Salmonella typhimurium A1-R targeting of a chemotherapy-resistant BRAF-V600E melanoma in a patient-derived orthotopic xenograft (PDOX) model is enhanced in combination with either vemurafenib or temozolomide

A metastatic melanoma obtained from the right chest wall of a patient was previously established orthotopically in the right chest wall of nude mice as a patient-derived orthotopic xenograft (PDOX) model. We previously showed that the combination of tumor-targeting Salmonella typhimurium A1-R (S. typhimurium A1-R) and chemotherapy was highly effective against the melanoma PDOX. In the present study, we investigated the mechanism of the high efficacy of this combination. Two weeks after implantation, 40 PDOX mouse models were randomized into 4 groups of 10 mice each: untreated control (n = 10); treated with S. typhimurium A1-R (5 × 10⁷ CFU/100 μl, i.v., once a week for 2 weeks, n = 10); treated with temozolomide (TEM) (25 mg/kg, p.o. for 14 consecutive days) combined with S. typhimurium A1-R (5 × 10⁷ CFU/100 μl, i.v., once a week for 2 weeks, n = 10); treated with vemurafenib (VEM) (30 mg/kg, p.o., for 14 consecutive days) combined with S. typhimurium A1-R (5 × 10⁷ CFU/100 μl, i.v., once a week for 2 weeks) (n = 10). On day 14 from initiation, all treatments significantly inhibited tumor growth compared with untreated control (S. typhimurium A1-R: p < 0.01; TEM combined with S. typhimurium A1-R: p < 0.01; VEM combined with S. typhimurium A1-R: p < 0.01). Combination therapy with S. typhimurium A1-R was significantly more effective on tumor growth than S. typhimurium A1-R alone (with TEM: p < 0.01; with VEM: p < 0.01). Combination therapy significantly increased S. typhimurium A1-R tumor targeting alone (S. typhimurium A1-R + TEM: p < 0.01, S. typhimurium A1-R + VEM: p < 0.01), relative to S. typhimurium A1-R alone, respectively. In conclusion, chemotherapy drugs promoted targeting of S. typhimurium A1-R of melanoma, thereby enhancing efficacy against the melanoma PDOX.     

Optimization of Sterilization of Salmonella enteritidis in Meat by Surfactin and Iturin Using a Response Surface Method

In this paper, the sterilization of surfactin and iturin to Salmonella enteritidis was observed, and the optimization of the inactivation of surfactin and iturin to S. enteritidis in meat by a response surface methodology was studied. Results showed that surfactin and iturin had high sterilization to S. enteritidis, whose minimal inhibitory concentration was 6.25 and 12.50 μM respectively. The optimization result indicated that S. enteritidis could be inactivated by five orders of magnitude when the temperature was 4.83°C, the action time was 17.20 h, and the concentration (surfactin/iturin molar ratio 1:2) was 0.69 MIC.     

Pharmacodynamic parameters and hydrophobicity changes induced by meropenem in Acinetobacter baumannii.

The suppression of bacterial growth of four Acinetobacter baumannii strains after 60 min exposure to meropenem at supra-inhibitory concentrations (postantibiotic effect; PAE) or at supra-subinhibitory concentrations (postantibiotic-sub-MIC effect; PA SME) was studied. The duration of the PAE was dependent on antibiotic concentration and on the strain. Meropenem at 2x or 4x the minimum inhibitory concentration (MIC), with the exception of one strain treated with 4x MIC, did not provoke suppression of bacterial growth compared with untreated controls. The highest concentration of meropenem (8x MIC) induced PAE for the strains tested in the range of 0.6-6.9 h. The effect of supra-subinhibitory concentrations of meropenem (2x, 4x or 8x MIC + 0.2x MIC) on bacterial growth was more efficient compared with supra-inhibitory concentrations alone. Two out of the four strains treated did not renew their growth. Bacterial suspensions exposed to meropenem showed reduced surface hydrophobicity. Decreases in hydrophobicity were associated with longer PAE and PA SME depending on the strain.