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 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.     

Postantibiotic effects and postantibiotic sub-MIC effects of ciprofloxacin, pefloxacin and amikacin on the biological properties ofSalmonella strains

The postantibiotic effect (PAE) and the postantibiotic sub-MIC effect (PASME) of ciprofloxacin, pefloxacin and amikacin were studied forSalmonella typhimurium andS. enteritidis strains. PAE was induced by 2× and 4×MIC of antibiotics studied for 0.5 h. After PAE and PASME their effect on prophage induction of a lysogenicS. typhimurium strain and on Congo red binding for both strains as a marker of their surface hydrophobicity was examined. The longest PAE was found after treatment with ciprofloxacin, higher values being observed withS. typhimurium. PAEs of pefloxacin and amikacin were much lower, except for the suprainhibitory concentration 4×MIC of amikacin withS. enteritidis (6.9 h). PASMEs of ciprofloxacin did not allow any regrowth of either strain. For other antibiotics the PASME's were different while concentrations of 2×MIC+0.2×MIC and 0.3×MIC, and of 4×MIC+0.1×MIC, 0.2×MIC and 0.3×MIC of amikacin did not allow any regrowth ofS. enteritidis. PAEs of the antibiotics tested did not affect the Congo red binding by bothSalmonella strains, but the PAEs of ciprofloxacin and pefloxacin expressively induced a prophage of lysogenicS. typhimurium strain. We noted the influence of Congo red binding after applying 4×MIC+0.1×MIC, 0.2×MIC and 0.3×MIC of amikacin forS. typhinurium and 2×MIC+0.1×MIC forS. enteritidis.     

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.     

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.     

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.     

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.     

Effect of the Inoculum Size on Carbapenem Susceptibilities of β-Lactamase-Negative,Ampicillin-Resistant <Emphasis Type="Italic">Haemophilus influenzae</Emphasis>

A higher inoculum size of β-lactamase-positive Haemophilus influenzae is reported to increase minimum inhibitory concentrations (MICs) for β-lactams. However, the effect of inoculum size of β-lactamase-negative, ampicillin-resistant H. influenzae (BLNAR) on MICs for carbapenems has not been investigated. This study evaluated the effect of inoculum size on MICs for carbapenems and other β-lactams in nine clinical isolates of BLNAR. The MICs were determined by both the standard method described by the Clinical and Laboratory Standards Institute (final inoculum size of 5 × 10⁵ colony-forming units [CFU]/ml) and a modified method (final inoculum size of 5 × 10⁶ CFU/ml) using viable cell counts. The findings showed that the higher inoculum size increased MICs for imipenem, meropenem, panipenem, biapenem, ampicillin, ceftazidime, and ceftriaxone. The inoculum effect (4 log₂ dilution or a greater increase in the MIC) with imipenem, meropenem, panipenem, and biapenem was found in three, five, two, and two isolates, respectively. The magnitude of the inoculum effect for panipenem significantly increased with the levels of MICs, but correlation between them for the others was not statistically significant. The mutations of penicillin-binding protein genes had little relevance to the reduced susceptibility to carbapenems or to the magnitude of the inoculum effect. These results suggest that MIC determination using turbidity can produce interpretive errors in the antimicrobial susceptibility testing of BLNAR for carbapenems because of their inoculum effect. Thus, accurate adjustment of inoculum size, such as viable cell count, is helpful for confirming the true MICs when the isolates are interpreted as “resistant” by turbidity-based MIC determination.     

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.     

The presence of blaIMP genes on plasmids DNA isolated from multidrug-resistant Pseudomonas aeruginosa strains at University Hospital in Bialystok (Poland)--first report

Resistance to carbapenems is emerging, and it is a great problem to therapeutics. Seven multidrug-resistant (MDR) of Pseudomonas aeruginosa strains were isolated from urine and bronchial specimens. All isolates showed resistance to imipenem and meropenem (MIC; > or =16 mg/L). The resistance to carbapenems in two of seven strains was associated with the production of a metallo-beta-lactamases. Plasmids DNA probes were used to investigate the presence of genes coding for IMP-type enzymes. PCR experiments revealed that bla(IMP) genes were present in two isolates of Pseudomonas aeruginosa (MIC >32 microg/mL for both carbapenems).     

Inhibitory effect of a lipopeptide biosurfactant produced by Bacillus subtilis on planktonic and sessile cells of Trichosporon spp.

The present study aimed to investigate the inhibitory effect of a bacterial biosurfactant (TIM96) on clinical strains of Trichosporon. Additionally, the effect of TIM96 on the ergosterol content, cell membrane integrity, and the hydrophobicity of planktonic cells was assessed. The inhibitory activity of TIM96 against Trichosporon biofilms was evaluated by analyzing metabolic activity, biomass and morphology. MIC values ranged from 78.125 to 312.5 μg ml^?1 for TIM96; time-kill curves revealed that the decline in the number of fungal cells started after incubation for 6 h with TIM96 at both MIC and 2×MIC. The biosurfactant reduced the cellular ergosterol content and altered the membrane permeability and the surface hydrophobicity of planktonic cells. Incubation at 10×MIC TIM96 reduced cell adhesion by up to 96.89%, thus interfering with biofilm formation. This concentration also caused up to a 99.2% reduction in the metabolic activity of mature biofilms. The results indicate potential perspectives for the development of new antifungal strategies.     

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).     

Alterations in surface hydrophobicity ofAcinetobacter baumannii induced by meropenem

Six strains ofAcinetobacter baumannii out of eleven strains tested revealed a strong hydrophobic character. This was demonstrated by adherence of bacteria to xylene in the range of 90–94%. Changes in surface hydrophobicity of these strains were studied after treatment with meropenem at subinhibitory concentrations (sub-MICs) (1/4, 1/8, 1/16 or 1/32 of the MICs). All strains showed a reduced adherence to xylene after the action of meropenem at 1/4 or 1/16 of the MICs. Hydrophobicity of the treated bacteria was decreased to 1.3–70% (1/16 of the MICs) or to 12–86% (1/4 of the MICs), depending on the strain. A decrease in surface hydrophobicity of three strains was also observed after their exposure to meropenem at 1/8 of the MICs (to 18–71% of the control values). Meropenem at 1/32 of the MICs practically did not affect bacterial hydrophobic properties, with the exception of one strain.     

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.     

Interaction of meropenem with ‘N’ and ‘B’ isoforms of human serum albumin: a spectroscopic and molecular docking study

Carbapenems are used to control the outbreak of β-lactamases expressing bacteria. The effectiveness of drugs is influenced by its interaction with human serum albumin (HSA). Strong binding of carbapenems to HSA may lead to decreased bioavailability of the drug. The non-optimal drug dosage will provide a positive selection pressure on bacteria to develop resistance. Here, we investigated the interaction between meropenem and HSA at physiological pH 7.5 (N-isoform HSA) and non-physiological pH 9.2 (B-isoform HSA). Results showed that meropenem quenches the fluorescence of both ‘N’ and ‘B’ isoforms of HSA (ΔG < 0 and binding constant ~10⁴ M^?1). Electrostatic interactions and van der Waal interactions along with H-bonds stabilized the complex of meropenem with ‘N’ and ‘B’ isoforms of HSA, respectively. Molecular docking results revealed that meropenem binds to HSA near Sudlow’s site II (subdomain IIIA) close to Trp-214 with a contribution of a few residues of subdomain IIA. CD spectroscopy showed a change in the conformation of both the isoforms of HSA upon meropenem binding. The catalytic efficiency of HSA (only N-isoform) on p-nitrophenyl acetate was increased primarily due to a decrease in K_m and an increase in k_cat values. This study provides an insight into the molecular basis of interaction between meropenem and HSA.     

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.     

Control of the growth of Alicyclobacillus acidoterrestris in industrialized orange juice using rosemary essential oil and nisin

The use of rosemary essential oil (RO) and its combination with nisin (RO+N) in preventing the multiplication of Alicyclobacillus acidoterrestris in orange juice was evaluated. The minimum inhibitory and bactericidal concentrations (MIC and MBC) for RO were both 125 μg ml⁻¹ while RO+N displayed a synergistic effect. The use of RO and RO+N at concentrations of 1, 4 and 8× MIC in orange juice for 96 h was evaluated in terms of their sporicidal effectiveness. With regard to the action against A. acidoterrestris spores, RO at 8× MIC was sporostatic, whereas RO+N at 1× MIC was sporicidal. Morphological changes in the structure of the micro-organism after treatment were also observed by microscopy. Furthermore, flow cytometric analysis showed that most cells were damaged or killed after treatment. In general, the antioxidant activity after addition of RO+N decreased with time. The results demonstrate that using the combination of RO and nisin can prevent the A. acidoterrestris growth in orange juice.     

Antibacterial activity and carbapenem re-sensitizing ability of 1,10-phenanthroline-5,6-dione and its metal complexes against KPC-producing Klebsiella pneumoniae clinical strains

Infections caused by KPC-producing Klebsiella pneumoniae (Kp-KPC) are associated with high mortality rates due to the increased number of resistant isolates and the scarcity of therapeutic options. This scenario reinforces the urgent need for new chemotherapeutics. Herein, we investigated the effects of 1,10-phenanthroline-5,6-dione (phendione) and its metal-based complexes, [Cu(phendione)₃](ClO₄)₂.4H₂O (Cu–phendione) and [Ag(phendione)₂]ClO₄ (Ag–phendione), both alone and also combined with carbapenems (meropenem (MEM), and imipenem), against 46 clonally distinct clinical strains of Kp-KPC. All isolates were found to be multidrug resistant in accordance with their susceptibility patterns by disk diffusion method. Compounds geometric mean (GM)-MIC and GM-MBC values (μmol l⁻¹), respectively, were: phendione, 42·06 and 71·27; Cu–phendione, 9·88 and 13·75; and Ag–phendione, 10·10 and 13·06. Higher synergism rates of MEM-containing combinations were observed by the checkerboard assay, particularly with the two metal complexes. Moreover, drug combinations were able to re-sensitize 87% of the phenotypically non-susceptible strains. Time-kill studies, with MEM plus Cu–phendione or Ag–phendione, indicated that combinations with 0·5× MIC of each agent produce synergistic effects after 9–12 h. The MEM plus Ag–phendione eradicated about 10⁶ CFU per ml of bacteria. These findings support the effectiveness of the re-sensitizing combinatorial approach and provide evidence that phendione-based compounds offer real promise in the fight against Kp-KPC infections.     

Effect of essential oils on pathogenic and biofilm-forming Vibrio parahaemolyticus strains

Abstract

In this study, the effect of three essential oils (EOs) – clove oil (CO), thyme oil (TO), and garlic oil (GO), which are generally recognized as safe – on the planktonic growth, minimum inhibitory concentration (MIC), minimum bactericidal concentration (MBC), motility, biofilm formation, and quorum sensing (QS) of Vibrio parahaemolyticus was investigated. All three EOs showed bacteriostatic activity, with MICs in the range 0.02%–0.09% (v/v). CO and TO completely controlled planktonic growth at 0.28% and 0.08% (v/v), which is four times their MIC (4?×?MIC), after 10?min, whereas GO completely controlled growth at 0.36% (v/v) (4?×?MIC) after treatment for 20?min. V. parahaemolyticus motility was significantly reduced by all three EOs at 4?×?MIC (0.28% for CO, 0.08% for TO, and 0.36% for GO), whereas QS was controlled and biofilm formation reduced by all three EOs at 8?×?MIC (0.56% for CO, 0.16% for TO, and 0.72% for GO) after 30?min of treatment. These results suggest that CO, TO, and GO have a significant inhibitory effect on V. parahaemolyticus cells in biofilm sand thus represent a promising strategy for improving food safety. These results provide the evidence required to encourage further research into the practical use of the proposed EOs in food preparation processes.     

Parsimony analysis of endemicity as a panbiogeographical tool: an analysis of Caribbean plant taxa

To demonstrate that parsimony analysis of endemicity (PAE) can be a method implementing the panbiogeographic approach, we analyzed two data matrices of 40/38 biogeographic provinces × 148 plant species from the Caribbean subregion of the Neotropical region, one where taxa are represented by individual tracks and the other where taxa are represented by single sample localities. We obtained six generalized tracks resulted from the PAE of the areas × individual tracks matrix, and one generalized track from the PAE of the areas × single sample localities matrix, with the latter nested within the former tracks. The results obtained show that PAE works as a panbiogeographical tool if it is based on an areas × individual tracks matrix. When performed in this way, PAE retrieves spatial information that is lost when it is based on an areas × single sample localities matrix, raising doubts regarding the conclusions derived from this latter type of analysis. © 2010 The Linnean Society of London, Biological Journal of the Linnean Society, 2010, 101 , 961–976.