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PubMed1984

Comparative activity of imipenem (N-formimidoyl thienamycin) on enterococci and its interactions with aminoglycosides.

Activity of imipenem (N-formimidoyl thienamycin, ampicillin and vancomycin against 27 Streptococcus faecalis and 5 Str. faecium was determined. Also evaluated were the interactions of imipenem, ampicillin and vancomycin with streptomycin or amikacin or sissomicin. Imipenem showed the most inhibitory activity against Str. faecalis with MIC50 and MIC90 values 0.5 and 2 mg/l respectively, Str. faecium strains were less susceptible to imipenem with MIC50/MIC90 values of 2/16 mg/l. Imipenem showed good bactericidal activity against both groups of strains with MBC50/MBC90 values of 1/4 and 4/16 mg/l respectively. The most favourable interactions (synergy and addition) of imipenem were with streptomycin (72.2%) and sissomicin (53.2%). Combinations containing amikacin were the least favourable. Similar results were obtained with these combinations against Str. faecium.

Amikacin↗
PubMed1987

Dynamics of ceftazidime-pefloxacin interaction shown by a new killing curve-chequerboard method.

Since in-vitro methods for studying drug interactions are difficult to evaluate and different results occur with the chequerboard (isobolograms-FIC index) and killing curve methods, a new approach associating these two methods was used to study the ceftazidime-pefloxacin interaction. In 64 tubes in a chequerboard pattern, viable bacteria were counted at 0, 2.5, 5 and 24 h, by a microdilution method and a multiple inoculator replicating method. The bacterial inoculum consisted of 5 X 10(6)-10(7) cfu/ml. Twelve strains belonging to six genera were tested: Acinetobacter, Citrobacter, Enterobacter, Klebsiella, Serratia and Pseudomonas. During the first 5 h no antagonism was noted, but few differences in viable count equal to or greater than 2 log10 were observed. The results of the drug interaction were equivalent to those of the more rapid bactericidal antibiotic concentrations (ceftazidime or pefloxacin). At 24 h, synergy was observed: ceftazidime prevented the late regrowth noted with pefloxacin, but with Citrobacter spp. regrowth was also observed with ceftazidime and none of the combinations were bactericidal.

Acinetobacter↗
PubMed1995

Assessment of therapeutic potential by means of a probability model of antimicrobial action.

The probability model of antimicrobial action is based on the definition of bactericidal activity as the probability, q, that any cell in the population will be killed during a division interval. Bacteriostatic activity is defined as a change in the division intervals (generation times) of the cells. A simplified, homogeneous model is used which assumes that, at a constant concentration of the drug, all cells have the same kill probability and the same generation times. Birth-death analysis techniques require that the combined bacteriostatic and bactericidal effects of the drug (they are not mutually exclusive) are accounted for. Moreover, to suitably reflect the combined effect, the rate of change of the viable population, i.e. the slope of a kill curve (activity), needs to be expressed not in terms of exposure time, but in units of drug-free generations (DFGs), obtained by dividing exposure time by a measured DFG time interval (growth rate). A Discrete MIC (DMIC) is defined as the zero slope kill curve, coinciding with the horizontal axis and dividing population change into a restrained (subinhibitory) growth region, below the DMIC, and population reduction above it. At the DMIC, the probability of a cell being killed is 0.5, resulting in no change from the initial inoculum concentration, since half the cells are killed but the remaining cells double. The DMIC is found to be a measure of bactericidal activity only, even though bacteriostatic activity may also be present. An antibiotic-organism activity profile includes measurement of the DMIC, rate of change of activity at the DMIC and normalized activity at a number of clinically relevant drug concentrations. An overall, quantitative efficacy value over a dosing interval can be obtained from the activity profile and expressed as the number of DFGs which are needed to achieve a 99.9% reduction of the viable population at the site of infection. These reference efficacy values can be used to derive interpretive standards (break-points) based upon a quantitative relationship between laboratory measurements and population reduction at the site of infection. Model-derived measures of efficacy also provide a basis for assessing drug combination activity, including quantitative criteria of synergy and antagonism.

Anti-Bacterial Agents↗
PubMed1998

In-vitro activity and killing effect of quinupristin/dalfopristin (RP59500) on nosocomial Staphylococcus aureus and interactions with rifampicin and ciprofloxacin against methicillin-resistant isolates.

Quinupristin/dalfopristin (RP59500) is a novel streptogramin and a semisynthetic derivative of pristinamycins IA and IIB. The following properties of RP59500 were investigated: (i) its in-vitro activity against 164 hospital isolates of Staphylococcus aureus, 101 of which were methicillin-resistant (MRSA); (ii) its killing effect against 24 MRSA and seven methicillin-susceptible (MSSA) isolates; (iii) its interactions with rifampicin and ciprofloxacin against 18 MRSA isolates, six susceptible to both rifampicin and ciprofloxacin and 12 resistant to both, at 1 x MIC, 2 x MIC and 4 x MIC. Rifampicin and ciprofloxacin were applied at a concentration equal to their mean serum levels in order to establish the clinical relevance of the results. The MIC50, MIC90, MBC50 and MBC90 of quinupristin/dalfopristin were, respectively, < or = 0.015, 2, 0.12 and 2 mg/L for MRSA isolates and < or = 0.015, 0.06, < or = 0.015 and 0.25 mg/L for MSSA isolates. All isolates were inhibited by quinupristin/dalfopristin. Its killing effect varied with concentration and time, being optimal at 4 x MIC and after 24 h growth. Strains surviving 24 h exposure to this agent had much higher MICs than the parent strain, but only a limited number of them became resistant. Quinupristin/dalfopristin at 2 x MIC and 4 x MIC showed in-vitro synergy with rifampicin against highly resistant isolates mainly at 6 h and 24 h of growth involving 50-83% of MRSA isolates, and showed synergy with ciprofloxacin at 24 h involving 42-75% of isolates. The MIC increase in colonies surviving at 24 h was restricted by the presence of rifampicin or ciprofloxacin. In contrast, the above combinations acted synergically over the total number of MRSA strains susceptible to both rifampicin and ciprofloxacin. The above findings show that quinupristin/dalfopristin is a very potent antistaphylococcal agent, and that its activity against MRSA isolates is enhanced when it is combined with rifampicin or ciprofloxacin.

Anti-Bacterial Agents↗
PubMed1998

The effect of antifungal drugs in combination on the growth of Candida glabrata in solid and liquid media.

The effect of drugs in combination on the growth of Candida glabrata was studied in solid medium by demonstration of reduced or enhanced growth, and in liquid medium by determination of interaction indices. Amphotericin B and 5-fluorocytosine showed a synergic effect, while combinations of amphotericin B and miconazole, and miconazole and 5-fluorocytosine exhibited antagonistic effects. In addition, concentration-dependent antagonism was observed amongst combinations of metabolic inhibitors, between inhibitors of sterol biosynthesis (terbinafine, miconazole, ketoconazole, clotrimazole, econazole, fluconazole, itraconazole and amorolfine) and inhibitors of nucleic acid or protein biosynthesis (5-fluorocytosine, 5-fluorouracil, rifampicin and chlortetracycline). This antagonism was strain-specific, occurring with C. glabrata strain 4, Saccharomyces cerevisiae strain 237 and Candida albicans strain 72R, but not with C. albicans strain 6406 or Candida parapsilosis strain 3104.

Agar↗
PubMed2005

In vitro activity and killing effect of temporin A on nosocomial isolates of Enterococcus faecalis and interactions with clinically used antibiotics.

OBJECTIVE: To study the in vitro activity of temporin A, a basic, highly hydrophobic, antimicrobial peptide amide derived from the skin of the European red frog Rana temporaria, alone and in combination with co-amoxiclav, imipenem, ciprofloxacin, linezolid and vancomycin, against 42 nosocomial isolates of Enterococcus faecalis. Fourteen of these were resistant to vancomycin. METHODS: Antimicrobial activity of temporin A was measured by MIC, MBC and time-kill studies and by the chequerboard titration method. RESULTS: All isolates were inhibited at concentrations of 1 to 16 mg/L. Combination studies carried out with E. faecalis ATCC 29212 and ATCC 51299 demonstrated synergy only when the peptide was combined with co-amoxiclav and imipenem. CONCLUSIONS: Our findings show that temporin A is active against E. faecalis and that its activity could be enhanced when it is combined with other antimicrobial agents.

Anti-Bacterial Agents↗
PubMed2005

mef(A), mef(E) and a new mef allele in macrolide-resistant Streptococcus spp. isolates from Norway.

OBJECTIVES: To type mef genes in a nationwide collection of clinical isolates of Streptococcus pneumoniae and Streptococcus pyogenes as well as pharyngeal carrier strains of viridans streptococci in Norway. METHODS: Erythromycin-resistant mef-positive multilocus sequence-typed (MLST) clinical isolates of S. pneumoniae (n = 36) and S. pyogenes (n = 12) from the National Surveillance Program for Antimicrobial Resistance (NORM) as well as viridans streptococci (n = 20) from healthy adults were included. PCR-amplified mef genes were initially discriminated by BamHI digestion. Selected mef genes from representatives of different sequence types (STs) of S. pneumoniae (n = 11) and S. pyogenes (n = 4), and viridans group streptococcal species (n = 8) were typed by sequencing and their strains examined for co-resistances. Hydropathy plots of different mef-encoded proteins were performed. RESULTS: A predominance of mef(A) was detected in S. pneumoniae (23/36) and S. pyogenes (9/12) due to the clonal spread of ST9 and ST39, respectively. mef(E) was the most widely distributed mef determinant occurring in nine different STs of S. pneumoniae and in four different viridans species. A new mef allele was identified in two STs of S. pyogenes. CONCLUSIONS: mef(E) is the most widely distributed mef determinant in Norwegian clinical strains of S. pneumoniae and pharyngeal carrier strains of various viridans streptococci. However, mef(A) is more prevalent in S. pneumoniae and S. pyogenes due to clonal spread. A new mef allele was found in two different STs of S. pyogenes.

Amino Acid Sequence↗
PubMed2006

Reversing methicillin resistance in MRSA using a bacterial transforming agent.

BACKGROUND: Antimicrobial resistance in staphylococci remains a significant problem in the clinical management of infections. New therapeutic entities are required for the prophylaxis and treatment of staphylococcal infection including those caused by methicillin-resistant Staphylococcus aureus (MRSA). Potential candidates include bacterial transforming agents (BTAs), compounds that can potentiate the activity of cell-wall-active antimicrobials by hypersensitizing the bacterial cell wall to the bactericidal effects of these drugs. BTAs have been found to inhibit MRSA in vitro when administered in combination with established antibiotics. OBJECTIVES: To examine the antimicrobial potential of a known BTA (BTA 19976a) on strains of MRSA in vitro. METHODS: Etest and time-kill methodologies were employed to assess the inhibitory potential of BTA at 10% w/v on strains of E-MRSA-3, E-MRSA-15 and E-MRSA-16. RESULTS: Etests demonstrated a reduction in the oxacillin MIC for E-MRSA-3, E-MRSA-15 and the NCTC 12493 reference strain of MRSA when exposed to BTA at 10% w/v. Time-kill assays similarly demonstrated a reduction in viable counts for organisms exposed to methicillin at 40 mg/L+BTA at 10% w/v, compared with methicillin alone, an effect which varied in cidality, pattern of killing and regrowth between strains. CONCLUSIONS: The antimicrobial effects of this BTA on MRSA are encouraging and warrant further investigation with large numbers of different epidemic strains and a comprehensive PK/PD evaluation. This could lead to new therapeutic entities for the prophylaxis and treatment of staphylococcal infections.

Anti-Bacterial Agents↗
PubMed2003

Cytoprotective properties of carboxymethyl cellulose (CMC) when used prior to wearing contact lenses treated with cationic disinfecting agents.

PURPOSE: Disinfecting agents found in current multipurpose solutions (MPS) may produce low-grade ocular surface insults. This study investigates the potential for carboxymethylcellulose (CMC) to chemically complex residual disinfectants in situ. METHODS: The chemical availability of the MPS disinfectant polyhexamethylene biguanide (PHMB) was examined using a spectrophotometric assay. PHMB bioactivity was assessed by survival of bacteria in the presence of MPS with varying amounts of added CMC. RESULTS: Chemical availability of PHMB in water or MPS was reduced within 10 minutes of adding CMC. With the addition of CMC to MPS, survival rates for bacteria improved substantially, depending on the bacterial species, concentration, and exposure time. CONCLUSIONS: Carboxymethylcellulose rapidly binds PHMB and reduces its chemical availability and bioactivity. These results suggest a potential cytoprotective effect of CMC on the ocular surface when used before lens insertion.

Biguanides↗
PubMed1989

The effect of cilofungin (LY 121019) in combination with amphotericin B or flucytosine against Candida species.

Cilofungin was combined with amphotericin B or flucytosine to determine if synergistic inhibition or killing occurred against 50 strains of various Candida species. Synergistic inhibition of growth occurred only once with amphotericin B and cilofungin and only 2 times with flucytosine and cilofungin. Synergistic killing occurred in 5 strains with the amphotericin B-cilofungin combination and in 7 strains with the flucytosine-cilofungin combination. Antagonism occurred frequently with both the amphotericin B-cilofungin and the flucytosine-cilofungin combinations.

Amphotericin B↗
PubMed2006

daime, a novel image analysis program for microbial ecology and biofilm research.

Combinations of microscopy and molecular techniques to detect, identify and characterize microorganisms in environmental and medical samples are widely used in microbial ecology and biofilm research. The scope of these methods, which include fluorescence in situ hybridization (FISH) with rRNA-targeted probes, is extended by digital image analysis routines that extract from micrographs important quantitative data. Here we introduce daime (digital image analysis in microbial ecology), a new computer program integrating 2-D and 3-D image analysis and visualization functionality, which has previously not been available in a single open-source software package. For example, daime automatically finds 2-D and 3-D objects in images and confocal image stacks, and offers special functions for quantifying microbial populations and evaluating new FISH probes. A novel feature is the quantification of spatial localization patterns of microorganisms in complex samples like biofilms. In combination with '3D-FISH', which preserves the 3-D structure of samples, this stereological technique was applied in a proof of principle experiment on activated sludge and provided quantitative evidence that functionally linked ammonia and nitrite oxidizers cluster together in their habitat. This image analysis method complements recent molecular techniques for analysing structure-function relationships in microbial communities and will help to characterize symbiotic interactions among microorganisms.

Biofilms↗
PubMed2004

In-vitro activity of nikkomycin Z alone and in combination with polyenes, triazoles or echinocandins against Aspergillus fumigatus.

The in-vitro activity of nikkomycin Z was investigated in combination with polyenes, triazoles or echinocandins against 20 clinical isolates of Aspergillus fumigatus with the fractional inhibitory concentration index (FICI) method. The drug interactions were classified as synergic (FICI < or = 0.5), no interaction (FICI > 0.5, but FICI < or = 4) or antagonistic (FICI > 4). The fungicidal activity of nikkomycin Z alone and in combination with a representative echinocandin (caspofungin) or triazole (voriconazole) was also examined with time-kill experiments and fungal cell viability assays. Two-drug combinations of nikkomycin Z with amphotericin B (FICI 3.59 +/- 0.57), amphotericin B lipid complex (FICI 3.95 +/- 0.74), liposomal amphotericin B (FICI 3.62 +/- 0.98), itraconazole (FICI 2.0 +/- 0.0), voriconazole (FICI 1.07 +/- 0.37), posaconazole (FICI 2.20 +/- 0.44) or ravuconazole (FICI 1.76 +/- 0.44) showed no interactions, but the pairwise combination of nikkomycin Z with caspofungin (FICI 0.22 +/- 0.19) or micafungin (FICI 0.35 +/- 0.27) showed synergic activity against A. fumigatus. Time-kill studies and fungal cell viability assays showed that neither nikkomycin Z nor caspofungin alone possessed fungicidal activity against A. fumigatus, whereas a combination of these two drugs at concentrations > or = 2 mg/L (> or = 0.031 x the concentration of drug that produced no visible growth) killed germinated conidia within 24 h in a concentration-dependent manner. These data suggest that two-drug combinations of nikkomycin Z with echinocandins, but not with polyenes and triazoles, have a synergic effect against A. fumigatus.

Aminoglycosides↗
PubMed2005

Rhizosphere geometry and heterogeneity arising from root-mediated physical and chemical processes.

The rhizosphere differs from the bulk soil in a range of biochemical, chemical and physical processes that occur as a consequence of root growth, water and nutrient uptake, respiration and rhizodeposition. These processes also affect microbial ecology and plant physiology to a considerable extent. This review concentrates on two features of this unique environment: rhizosphere geometry and heterogeneity in both space and time. Although it is often depicted as a soil cylinder of a given radius around the root, drawing a boundary between the rhizosphere and bulk soil is an impossible task because rhizosphere processes result in gradients of different sizes. For instance, because of diffusional constraints, root uptake can result in a depletion zone extending <1 mm for phosphate to several centimetres for nitrate, while respiration may affect the bulk of the soil. Rhizosphere processes are responsible for spatial and temporal heterogeneities in the soil, although these are sometimes difficult to distinguish from intrinsic soil heterogeneity. A further complexity is that these processes are regulated by plants, microbial communities and soil constituents, and their many interactions. Novel in situ techniques and modelling will help in providing a holistic view of rhizosphere functioning, which is a prerequisite for its management and manipulation.

Ecosystem↗