In vitro interaction of colistin and rifampin on multidrug-resistant Pseudomonas aeruginosa

The administration of colistin is considered as the last alternative for infections by multidrug-resistant isolates of Pseudomonas aeruginosa; however its use is limited due to its considerable toxicity and poor pharmacokinetics. In order to define the in vitro activity of colistin combined with rifampin, 28 isolates resistant to piperacillin, ceftazidime, imipenem, meropenem, ciprofloxacin, amikacin, rifampin and colistin were tested. Seventeen of them that were found by PFGE to be genetically distinct were over time exposed to 2 microg/ml of colistin, to 2 microg/ml of rifampin and to their combination. Applied concentrations were selected to correspond to the mean serum level of the tested antimicrobials. Synergy between colistin and rifampin was found in four (23.5%), six (35.3%), seven (41.7%) and two (11.8%) isolates after 2, 4, 6 and 24 hours of growth, respectively. Bacterial re-growth was detected after 24 hours of exposure to the tested interaction. It is concluded that colistin and rifampin express a considerable in vitro synergistic effect on multidrug-resistant P. aeruginosa. The reported interaction should be tested in animal studies before introduction in clinical practice.     

Clinical and microbiological efficacy of colistin therapy alone or in combination as treatment for multidrug resistant Pseudomonas aeruginosa diabetic foot infections with or without osteomyelitis

We retrospectively evaluated the safety and effectiveness of colistin alone or in combination with other antimicrobials in eight diabetic patients with severe diabetic foot infections due to multidrug resistant (MDR) Pseudomonas aeruginosa, complicated in 4 cases by osteomyelitis. All patients received colistin after other ineffective antimicrobial treatment, when MDR P. aeruginosa strains were isolated by cultural examination and together with a multidisciplinary care approach including revascularization, surgical debridement and adequate offloading. The mean duration of therapy was 72 +/- 52.9 days. Six out of 8 patients (75%) successfully benefited from colistin therapy, while 2 patients failed and/or experienced side effects that led to discontinuation of therapy. Serious adverse events (i.e. acute renal failure and pulmonary edema) were observed in 1 patient. Our data allow us to conclude that colistin, alone or in combination with other antimicrobials, is safe and effective when administered as part of a multidisciplinary approach, to promote healing of diabetic foot infection due to MDR P. aeruginosa.     

Comparative in vitro efficacies of various antipseudomonal antibiotics based catheter lock solutions on eradication of Pseudomonas aeruginosa biofilms

Antibiotic lock technique (ALT) may be an adjunct therapy in treating catheter-related infections. The aim of this study was to determine the in vitro stability and efficacy of colistin, meropenem and levofloxacin alone or in combination with clarithromycin or heparin lock solutions against biofilm embedded Pseudomonas aeruginosa strains. The efficacy of antibiotic lock solutions was tested in an in vitro catheter biofilm model against P. aeruginosa isolated from catheter-related bacteremia. We observed that the use of meropenem, levofloxacin or colistin as a lock solution had potent bactericidal effects and could be prevented bacterial regrowth at 96 or 72 hours, respectively. When the tested antibiotics were used in combination with clarithromycin, the combinations were significantly more effective and rapid in eliminating P. aeruginosa colonization in biofilm than each of the antibiotics were used alone. Moreover, tested antibiotics in combination with heparin were not significantly different for killing effect against PA-1 and PA-27853 compared with that of each antibiotics alone. Tested catheter lock solutions may have promising adjuvants for treating infections caused by P. aeruginosa.     

Synergistic antibacterial interaction of cefotaxime and desacetylcefotaxime

Cefotaxime (CTX) is metabolized in desacetylcefotaxime (dCTX), a less potent compound which shows, however, a higher stability against selected beta-lactamases produced by Gram-negative organisms. The aim of this study was to verify if the antimicrobial activity of CTX against 260 clinical aerobic and anaerobic pathogens isolated in our institution was enhanced by its metabolic derivative dCTX. The combination of CTX and dCTX, assessed by checkerboard titration, was completely or partially synergistic towards 61% of the 220 aerobic organisms tested and against 68% of the 40 Bacteroides strains analyzed. In addition we have investigated, by the time-kill method, the in-vitro interactions against 50 aerobic strains of CTX and dCTX alone and in combination with netilmicin, a drug often employed in severe infections in combination with beta-lactam agents in order to provide effective killing of resistant nosocomial pathogens. Time-kill studies indicated that 36% of the aerobic nosocomial strains were synergistically inhibited by the combination of CTX/dCTX with netilmicin. These results indicate that dCTX makes an important contribution to the clinical efficacy of CTX.     

In vitro effects of sulbactam combinations with different antibiotic groups against clinical Acinetobacter baumannii isolates

Abstract

Treatment of multidrug resistant (MDR) Acinetobacter baumannii infections causes some problems as a result of possessing various antibacterial resistance mechanisms against available antibiotics. Combination of antibiotics, acting by different mechanisms, is used for the treatment of MDR bacterial infections. It is an important factor to determine synergy or antagonism between agents in the combination for the constitution of effective therapy. The study aimed to determine in vitro interactions interpreted according to calculated fractional inhibitory concentration (FIC) index between sulbactam and ceftazidime, ceftriaxone, cefepime, ciprofloxacin, gentamicin, meropenem, tigecycline, and colistin. Ten clinical isolates of A. baumannii were tested for determination of synergistic effects of sulbactam with different antimicrobial combinations. Minimal inhibitory concentration (MIC) values of both sulbactam and combined antibiotics decreased 2- to 128-fold. Synergy and partial synergy were determined in combination of sulbactam with ceftazidime and gentamicin (FIC index: ≤0·5 or >0·5 to <1) and MIC values of both ceftazidime and gentamicin for five isolates fell down below the susceptibility break point. Similarly, MIC value of ciprofloxacin for six ciprofloxacin resistant isolates was determined as below the susceptibility break point in combination. However, all isolates were susceptible to colistin and tigecycline, MIC values of both were decreased in combination with sulbactam. Although synergistic and partial synergistic effects were observed in the combination of sulbactam and ceftriaxone, all isolates remained resistant to ceftriaxone. The effect of cefepime–sulbactam combination was synergy in five, partial synergy in one and indifferent in four isolates. Meropenem and sulbactam showed a partial synergistic effect (FIC index: >0·5 to <1) in three, an additive effect (FIC index: 1) in one and an indifferent effect (FIC index: >1–2) in six isolates. Antagonism was not determined in any combination for clinical A. baumannii isolates in the study. In conclusion, sulbactam is a good candidate for combination treatment regimes for MDR A. baumannii infections.     

Investigation of the effects of various antibiotics against Klebsiella pneumoniae biofilms on in vitro catheter model

Klebsiella pneumoniae continues to be an important cause of community-acquired and nosocomial infection. This bacterium can cause catheter related infections by forming biofilm on the surface of catheter. The aim of our study is to determine the in vitro stability and efficacy of colistin, ciprofloxacin, tobramycin, doripenem and tigecycline alone, or in combination with clarithromycin or esomeprazole, as 24-h lock solutions against biofilm-embedded K. pneumoniae strains. The efficacy of antibiotic lock solutions was tested in an in vitro catheter biofilm model against K. pneumoniae. In our study, we observed that the use of doripenem and tobramycin as a lock solution had potent bactericidal effects. When colistin was used in combination with clarithromycin or esomeprazole, the combinations had a synergistic effect. No antagonistic effect was observed. The findings of our study have important information for effectiveness of tested antibiotic lock solution in the catheter-related infections with K. pneumoniae.     

Current and future perspectives for levofloxacin in severe Pseudomonas aeruginosa infections

The question of whether levofloxacin includes Pseudomonas aeruginosa in its spectrum of clinical activity is discussed by reviewing the major findings on this issue, mainly those published in Italy. The in vitro activity of levofloxacin against P. aeruginosa is now documented on thousands of strains worldwide. The pharmacodynamic properties of levofloxacin allow for the treatment of pseudomonal infections. The levofloxacin clinical results extrapolated from published studies document the efficacy of levofloxacin in the treatment of infections sustained by P. aeruginosa.     

In vitro activity of daptomycin alone and in combination with various antimicrobials against Gram-positive cocci

The increasing prevalence of resistant Gram-positive cocci requires the need to search for more effective agents and synergistic combinations. Forty-two vancomycin-resistant Enterococcus faecium (VREF), 30 methicillin-resistant Staphylococcus aureus (MRSA) and 36 Staphylococcus epidermidis (MRSE) strains were studied. Minimum inhibitory concentrations (MICs) were determined and synergy testing was performed by using E test for daptomycin, ampicillin-sulbactam, piperacillin-tazobactam and ticarcillin-clavulanate against staphylococci; for daptomycin, ampicillin, rifampin, and gentamicin against enterococci. Daptomycin in combination with ampicillin, rifampin, and gentamicin was tested against enterococci; daptomycin in combination with ampicillin-sulbactam, piperacillin-tazobactam, and ticarcillin-clavulanate was tested against staphylococci. Interaction categories were defined by the fractional inhibitory concentration (FIC) index. All strains of staphylococci and enterococci were susceptible to daptomycin. All three combinations showed synergy against more than 70% of the MRSA strains. Daptomycin in combination with ampicillin, rifampin, and gentamicin against enterococci showed synergies of 64.2%, 57.1% and 21.4%, respectively. This study indicates that daptomycin alone and combined with beta-lactams seems to be effective against MRSA, but further in vitro and in vivo studies on the subject are required before clinical use can be recommended.     

In vitro combined effects of cefozopran/teicoplanin and cefozopran/vancomycin on methicillin-resistant Staphylococcus aureus

We determined the in vitro effects of teicoplanin (TEIC) or vancomycin (VCM) added to cefozopran (CZOP) on 50 methicillin-resistant Staphylococcus aureus (MRSA) strains, using a modified checkerboard method with serial 1.25-fold dilutions, and assessed the time-kill curve. CZOP + TEIC was synergistic (fractional inhibitory concentration index < or = 0.5) against 98% and CZOP + VCM against 20% of strains. Both drug combinations were additive against the remaining strains. A comparison of the fractional bactericidal concentration indices for 32 strains showed synergistic bactericidal effects for CZOP + TEIC in 88%, and in 48% for CZOP +VCM, confirming that CZOP + TEIC is superior to CZOP + VCM. The time-kill curve confirms that the bactericidal potency of these drugs is increased through combined use with CZOP. These results suggest that treatment using TEIC or VCM with CZOP may be useful in treating MRSA infections, including polymicrobial infections and those involving Gram-negative rods.     

In-vitro activities of imipenem–colistin,imipenem–tigecycline,and tigecycline–colistin combinations against carbapenem-resistant Enterobacteriaceae*

The aim of the study is to determine in-vitro effects of imipenem–tigecycline, imipenem–colistin and tigecycline–colistin against carbapenem-resistant Enterobacteriaceae (CRE) isolates. A total of 25 CRE isolates were included to the study. The minimum inhibition concentrations of imipenem, colistin-sulphate and tigecycline were determined with broth dilution method. Synergistic effects of imipenem–tigecycline, imipenem–colistin and tigecycline–colistin were investigated by microdilution checkerboard technique. All of the isolates were resistant to imipenem, whereas 25% of the isolates were resistant to colistin and tigecycline. Imipenem–colistin, imipenem–tigecycline and tigecycline–colistin combinations were synergistic against 40% (10/25), 24% (6/25), and 36% (9/25) of the isolates, respectively. Antagonism was observed in 8% (2/25) of the isolates in tigecycline–colistin combination. Tigecycline–colistin was the most effective (70% synergy) combination in Klebsiella spp. strains; whereas imipenem–colistin was the most effective (75% synergy) combination in Escherichia coli strains. Synergistic effect was variable and strain-depended against CRE isolates that have been tested.     

Antibacterial and anti-biofilm activities of melittin and colistin,alone and in combination with antibiotics against Gram-negative bacteria

In vitro antibacterial and anti-biofilm activities of antimicrobial cationic peptides (AMPs) – melittin and colistin – both alone and in combination with antibiotics were evaluated against clinical isolates of Gram-negative bacteria. Minimum inhibitory concentration (MIC) and fractional inhibitory concentration (FIC) index were determined by the microbroth dilution and chequerboard techniques, respectively. The time-kill curve (TKC) method was used for determining the bactericidal activities of AMPs alone and in combination. Measurements of anti-biofilm activities were performed spectrophotometrically for both inhibition of attachment and 24-hour biofilm formation at MIC or subMIC. According to MIC₉₀ values, the most active agents against Pseudomonas aeruginosa, Escherichia coli and Klebsiella pneumoniae were colistin, imipenem and ciprofloxacin, respectively. In combination studies, synergistic effects were mostly seen with colistin–imipenem against E. coli and K. pneumoniae (50 and 54%, respectively), colistin–ciprofloxacin against P. aeruginosa (77%). In TKC studies, synergism was observed with almost all expected combinations, even more frequently than chequerboard method. All of the antimicrobial agents were able to inhibit attachment and 24-hour biofilm formation between 0–57% at 1/10?×?MIC and 7–73% at 1?×?or 1/10?×?MIC, respectively. AMPs seem to be a good candidate for antimicrobial chemotherapy with their antibacterial and anti-biofilm activities as a single agent or in combination with antibiotics.     

Emergence of tigecycline and colistin resistance in Acinetobacter species isolated from patients in Kuwait hospitals

The development of resistance is a compelling reason for reviewing administration of antibiotics. Recently, most Acinetobacter infections are caused by multidrug-resistant (MDR) strains which have necessitated the use of tigecycline or colistin. This study was undertaken to determine the susceptibility of Acinetobacter spp. to these and other drugs. A total of 250 Acinetobacter isolates were collected from the 8 government hospitals over a period of 6 months. Susceptibility to 18 antibiotics, including tigecycline and colistin, was investigated by determining their minimum inhibitory concentrations using E test. Of the 250 isolates, 13.6% and 12% were resistant to tigecycline and colistin. A total of 25.2% and 37.2% were resistant to imipenem and meropenem, respectively. Of the 250 isolates 88.4% were MDR. This relatively high prevalence of tigecycline and colistin-resistant isolates indicates an emerging therapeutic problem which may severely compromise the treatment of MDR Acinetobacter spp. infections in Kuwait.     

In vitro evaluation of the antimicrobial activity of meropenem in combination with polymyxin B and gatifloxacin against Pseudomonas aeruginosa and Acinetobacter baumannii

The antimicrobial activity of meropenem combined with either polymyxin B or gatifloxacin was evaluated by the checkerboard method against Pseudomonas aeruginosa (10 strains) and Acinetobacter baumannii (10 strains). In addition, the triple combination of polymyxin B, gatifloxacin, and meropenem was also studied as well as the polymyxin B and gatifloxacin combination. A partial synergism interaction between meropenem and polymyxin B was observed for 80% of the A. baumannii strains. In contrast, this combination showed an indifferent effect for 80% of the P. aeruginosa strains tested. The combination of meropenem and gatifloxacin showed synergism only for two strains of A. baumannii, and partial synergism and additive effect for seven strains and indifference for four strains of both species. For the strains of P. aeruginosa, the double combination of polymyxin B and gatifloxacin and the triple combination of meropenem, polymyxin B and gatifloxacin were indifferent for the majority of the strains tested, that is, 90 and 80% respectively.     

In vitro activity of beta-lactam antimicrobial agents in combination with aztreonam tested against metallo-beta-lactamase-producing Pseudomonas aeruginosa and Acinetobacter baumannii

We evaluate the antimicrobial interactions between aztreonam and selected beta-lactams when tested against metallo-beta-lactamase (MbetaL)-producing clinical strains. Ten Pseudomonsa aeruginosa strains, including nine MbetaL-producers (IMP-1, -2, -13, -16, VIM-1, -2, -7, SPM-1 and GIM-1) and five Acinetobacter baumannii strains, including three MbetaL-producers (IMP-1 and -2) were tested using time kill/bactericidal activity methods. Aztreonam at 4, 8 and 16 mg/L was combined with four other beta-lactam antimicrobials (cefepime, ceftazidime, meropenem and piperacillin/tazobactam or ampicillin/sulbactam), each tested at the recognized susceptible breakpoint concentration. Enhanced activity (synergism or additive effect) was observed with four P. aeruginosa strains (IMP-16, VIM-2, SPM-1 and GIM-1 containing strains) and four A. baumannii strains, while antagonism was observed with two P. aeruginosa (IMP-16 and SPM-1-producing strains) and one A. baumannii (non-MbetaL) strain. All other strains showed indifferent interaction (variation of +/- 1 log10 CFU/ml) with any combination evaluated.     

In Vitro Combinations of Five Intravenous Antibiotics with Dalfopristin-Quinupristin Against Staphylococcus aureus in a 3-Dimensional Model

Abstract

We compared the in vitro activity of dalfopristin and quinupristin combined with five intravenous antibiotics in a 3-dimensional model. We tested six strains of Staphylococcus aureus selected with different patterns of resistance to methicillin and eryth-romycin. Dalfopristin and quinupristin displayed a very synergistic activity against all the strains with a mean 16- or 32-fold decrease of inhibitory concentrations in combination. That synergy was even better against erythromycin-resistant strains. In combination with tigecycline or fosfomycin, the antibacterial activity could be consistently enhanced with the same decrease of inhibitory concentrations. A synergy was also observed, less regularly and at a lower level, with rifampin, gentamicin or vancomycin. Combinations of dalfopristin and quinupristin with tigecycline or fosfomycin could be very interesting in clinical practice because the inhibitory effect could be achieved with very low oncentrations of each component, even when erythromycin-resistant strains are concerned.     

Complicated urinary tract infections treated with extended-release ciprofloxacin with emphasis on Pseudomonas aeruginosa

This report focuses on the role of Pseudomonas aeruginosa in complicated urinary tract infections in a prospective, open-label, multicenter study designed to evaluate the safety and efficacy of extended-release ciprofloxacin (ciprofloxacin XR) 1000 mg once daily for 7-14 days for the treatment of complicated urinary tract infections. A total of 204 patients were valid for intention-to-treat analysis, of whom 130 were included in the clinical efficacy population. In the 56 microbiologically valid patients the bacteriological eradication rate was 82.1% and the clinical cure rate was 94.6%. Patients with P. aeruginosa infections valid for microbiological efficacy (n = 7) had 100% bacteriological eradication and clinical cure rates. In the intention-to-treat population, the bacteriological and clinical cure rates were 42.1% (51/121) and 55.9% (114/204), respectively. These rates were 58.3% and 75.0% respectively, for patients with P. aeruginosa infections. To achieve the desired 10 patients with P. aeruginosa for analysis, these data were pooled with data from a previous study. Treatment failure correlated with pre-therapy P. aeruginosa isolates being resistant to ciprofloxacin. On exploratory multivariate regression analysis, presence of neurogenic bladder, urinary retention owing to benign prostatic hypertrophy, prior urinary tract infection, and ischemic heart disease predicted P. aeruginosa infection.     

Tigecycline: a critical update

Tigecycline is the first Food and Drug Administration (FDA) approved glycylcycline antibiotic. It has shown remarkable in vitro activity against a wide variety of gram-positive, gram-negative and anaerobic bacteria including many multidrug resistant (MDR) strains. However, it has minimal activity against Pseudomonas aeruginosa and Proteus spp. To date, little resistance to tigecycline has been reported. Clinical trials studying complicated skin and skin-structure infections (cSSSIs) demonstrated that tigecycline has equivalent efficacy and safety compared with the combination of vancomycin and aztreonam. For complicated intra-abdominal infections (cIAIs), tigecycline was found to be as effective as imipenem/cilastatin. Adverse events related to tigecycline therapy, i.e. nausea and vomiting, were tolerable. Currently available data suggest that tigecycline may play an important role in the future as a monotherapy alternative to older broad-spectrum antibiotics, such as advanced generation cephalosporins, carbapenems, fluoroquinolones, piperacillin/tazobactam, and gram-positive directed agents (e.g. daptomycin, linezolid and quinupristin/dalfopristin) for which resistance is being increasingly reported from all parts of the world.     

In-vitro synergistic effect of fluconazole with nonsteroidal anti-inflammatory agents against Candida albicans strains

The in-vitro interaction and synergistic activity of the combination of fluconazole with some nonsteroidal anti-inflammatory drugs (sodium salicylate, piroxicam, tenoxicam and diclofenac sodium) were investigated in Candida albicans strains (n=7) by the microdilution checkerboard assay. The results were evaluated visually and by a spectrophotometric microplate reader at 492 nm wavelength. Fractional inhibitory index was calculated for every strain and combination according to the minimal inhibitory concentration (MICs). The combination of fluconazole with sodium salicylate, tenoxicam and diclofenac sodium showed synergy against 5, 5 and 3 of the C. albicans strains, respectively. The effect of fluconazole with piroxicam was synergistic against one strain but indifferent/additive against the others. These data suggest that combinations of sodium salicylate, tenoxicam and diclofenac sodium with fluconazole may prove to be useful as chemotherapeutic agents for the treatment of C. albicans infections caused by especially fluconazole-resistant strains. However, additional preclinical work and in vivo studies are necessary to determine their definite clinical use.     

Evaluation of aztreonam in the treatment of serious gram-negative infections in a university hospital in Saudi Arabia.

The efficacy and safety of aztreonam were evaluated in an open trial at King Khalid University Hospital, Riyadh, Saudi Arabia. A total of 45 critically-ill adult patients were enrolled in the study. All patients with documented Gram-negative infection were treated with aztreonam as monotherapy. Antibiotics active against only Gram-positive and/or anaerobic organisms were allowed. Twenty cases were clinically evaluable. Eleven had lower respiratory tract infections (pneumonia), 3 had urinary tract infections, and 6 had septicemia. Clinical signs and symptoms, cultures and other laboratory profiles were assessed prior to treatment, at 4-6 days during treatment and within 2-3 days of the end of therapy (usually 7-15 days). Nineteen out of 20 (95%) had a satisfactory clinical response. All cases with septicemia and urinary tract infections were microbiologically cured. The overall microbiological response rate was 90%. Fifty-five percent of all infections were caused by Pseudomonas aeruginosa. Two patients with Gram-negative pneumonia due to P. aeruginosa did not respond microbiologically to aztreonam therapy. No serious adverse events requiring discontinuation of aztreonam therapy were reported. No mortality occurred.     

The effect of fresh human serum on ofloxacin bactericidal activity

We have studied the possibility of an increase in ofloxacin bactericidal activity when it is combined with fresh human serum. The tested strains were 10 clinical isolates of Klebsiella pneumoniae. From among our strains 5 were susceptible to serum bactericidal activity and 5 were found to be resistant. We selected two serum concentrations (15 and 35%) to test against susceptible strains and two (55 and 75%) to test against resistant strains in combination with the minimum inhibitory concentration (MIC), 1/2MIC and 1/4MIC of ofloxacin. The results show a slight variability among the tested strains depending on microbiological characteristics of single strains, however, the serum + ofloxacin combination was advantageous. Only one exception was observed: a resistant strain that had an increased survival percentage against ofloxacin and serum in combination.