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.     

Antimicrobial Activity of Isepamicin (SCH21420, 1-N-HAPA Gentamicin B) Combinations with Cefotaxime,Ceftazidime, Ceftriaxone,Ciprofloxacin, Imipenem,Mezlocillin and Piperacillin Tested Against Gentamicin-Resistant and Susceptible Gram-Negative Bacilli and Enterococci

Summary

Isepamicin, formerly SCH21420 or 1-N-HAPA gentamicin B, is an aminoglycoside that was tested alone or in combination with one of seven broad spectrum drugs against 80 clinical isolates. Half of the strains were gentamicin-resistant but only one isolate (1.396) was resistant to isepamicin. The broadest spectrum comparison drugs tested alone (ciprofloxacin at 3.8% resistance and imipenem at 5.096 resistance) were associated with the lowest synergy rates when combined with isepamicin. The rank order of synergy (complete or partial) was; cefotaxime = ceftazidime = ceftriaxone = mezlocillin = piperacillin (7596 to 8096) > imipenem (66%) > ciprofloxacin (38%). Isepamicin/ampicillin combinations produced synergistic killing of those enterococci not having high-grade resistance to gentamicin or kanamycin. Enterococcus faecium strains were also refractory to isepamicin/ampicillin synergy. Isepamicin appears to be widely useable against gentamicin-resistant gram-negative bacilli cither alone or combined with most commonly used broad spectrum bcta-lactams.     

Susceptibility of 228 Non-fermenting Gram-Negative Rods to Tigecycline and Six Other Antimicrobial Drugs

Abstract

The aim of the study was to determine the in vitro activity of tigecycline and 6 other antimicrobial drugs used in clinical practice against 228 clinical isolates of nonfermenting Gram-negative rods (NFGNRs) including Acinetobacter spp. Stenotrophomonas maltophilia, and Pseudomonas aeruginosa. Minimum inhibitory concentrations (MICs) were determined according to the recommendations of the Clinical and laboratory Standards institute. For tigecycline, we used the criteria approved by the FDA. Almost 50% of the clinical isolates of Acinetobacter spp. were resistant to piperacillin/tazobactam, ciprofloxacin, gentamicin, and ceftazidime. Strains of this microorganism were more susceptible to imipenem, and even more susceptible to colistin and tigecycline; no strains were resistant to tigecycline. Stenotrophomonas maltophilia showed even greater resistance to the drugs tested. Thus, all strains were resistant to imipenem and a large percentage (82.6%) were resistant to piperacillin/tazobactam. Resistance to the other agents tested was also high, with the exception of tigecycline, with only 3 resistant strains (MIC <8 mg/ml). Tigecycline, on the other hand, was scarcely active against Pseudomonas aeruginosa, which bears efflux pump systems such as MexXY-OprM. Almost 90% of strains were resistant to ciprofloxacin; only 8% were resistant to gentamicin; over half were colistin-intermediate or -resistant, and finally, approximately half of the strains were susceptible to the 3 beta-lactams studied. In conclusion, NFGNRs present variable susceptibility patterns, although they are generally highly resistant to antimicrobial agents including those considered more specific. Tigecycline, which showed good activity against most of the strains examined, broadens the spectrum of drugs available for the treatment of infections caused by these complex microorganisms.     

Antimicrobial activity of isepamicin (SCH21420, 1-N-HAPA gentamicin B) combinations with cefotaxime, ceftazidime, ceftriaxone, ciprofloxacin, imipenem, mezlocillin and piperacillin tested against gentamicin-resistant and susceptible gram-negative bacilli and enterococci.

Isepamicin, formerly SCH21420 or 1-N-HAPA gentamicin B, is an aminoglycoside that was tested alone or in combination with one of seven broad spectrum drugs against 80 clinical isolates. Half of the strains were gentamicin-resistant but only one isolate (1.3%) was resistant to isepamicin. The broadest spectrum comparison drugs tested alone (ciprofloxacin at 3.8% resistance and imipenem at 5.0% resistance) were associated with the lowest synergy rates when combined with isepamicin. The rank order of synergy (complete or partial) was; cefotaxime = ceftazidime = ceftriaxone = mezlocillin = piperacillin (75% to 80%) greater than imipenem (66%) greater than ciprofloxacin (38%). Isepamicin/ampicillin combinations produced synergistic killing of those enterococci not having high-grade resistance to gentamicin or kanamycin. Enterococcus faecium strains were also refractory to isepamicin/ampicillin synergy. Isepamicin appears to be widely useable against gentamicin-resistant gram-negative bacilli either alone or combined with most commonly used broad spectrum beta-lactams.     

In vitro synergy of colistin combinations against extensively drug-resistant Acinetobacter baumannii producing OXA-23 carbapenemase

Fifty extensively drug-resistant Acinetobacter baumannii (XDRAB) were isolated from patients. The chequerboard microdilution method was used to determine the in vitro activities of five colistin (COL)-based combinations including COL+fosfomycin (FOS), COL+rifampicin (RIF), COL+imipenem (IMP), COL+sulbactam (SUP) and COL+levofloxacin (LVX). The synergistic activity was evaluated by the fractional inhibitory concentration index (FICI). According to our results, the combination of COL was synergistic with FOS, RIF, IMP, SUP and LVX with the ratios of 50, 72, 88, 92 and 64%, respectively. When combined with COL, the other five agents showed increased antimicrobial activities. In addition, two of the combinations, COL+RIF and COL+IMP, were more active than the combinations of COL+FOS, COL+SUP and COL+LVX. More importantly, these combination regimens could exert synergistic effects at the sub-minimum inhibitory concentration (MIC) levels against XDRAB strains.     

Determination of synergy between sulbactam,meropenem and colistin in carbapenem-resistant Klebsiella pneumoniae and Acinetobacter baumannii isolates and correlation with the molecular mechanism of resistance

Treatment of infections with carbapenem-resistant Gram negative organism is a major challenge especially among intensive care patients. Combinations of sulbactam, meropenem and colistin was studied for its synergistic activity against 100 invasive isolates of carbapenem-resistant Klebsiella pneumoniae and Acinetobacter baumannii-calcoaceticus complex by checkerboard assay and time kill assay (TKA). In addition, presence of carbapenemase production was determined by multiplex PCR. Time kill assay detected more synergy than checkerboard assay. Good bactericidal activity of 70–100% was noted with the combinations tested. Among K. pneumoniae, isolates producing NDM carbapenemase alone showed significantly more synergy than isolates producing OXA-48-like carbapenemases. In treatment of infection with carbapenem-resistant organisms, the site of infection and the type of carbapenemase produced may help to determine the most effective combination of antimicrobials.     

Gram-Negative Non-Fermenting Bacteria from Food-Producing Animals are Low Risk for Hospital-Acquired Infections

Abstract

The aim of this study was to investigate possible indications of epidemiological relationships between Pseudomonas aeruginosa and Acinetobacter baumannii isolated from food-producing animals and those of clinical origin. Screening for P. aeruginosa and A. baumannii isolates from food-producing animals was carried out on 1381 samples. usceptibility testing and PCR amplification of resistance genes were determined. Isolate clonal relatedness was established by PFGE. Forty-one P. aeruginosa and 16 A. baumannii were detected. All P. aeruginosa isolates were sensitive to ciprofloxacin, ceftazidime and piperacillin/tazobactam and seven isolates had low-level imipenem resistance. All A. baumannii isolates were sensitive to imipenem, meropenem, ciprofloxacin and piperacillin/tazobactam but were resistant to ceftazidime. The imipenem-resistant P. aeruginosa and ceftazidime-resistant A. baumannii had different PFGE patterns compared to those of human origin. Based on the findings presented here, animal isolates were not multidrug resistant and they do belong to a different pool from those of humans.     

Is Tigecycline a Good Choice in the Treatment of Multidrug-ResistantAcinetobacter baumannii Pneumonia?

Abstract

The aim of this study was to evaluate the efficacy of tigecycline in multidrug-resistant (MDR)Acinetobacter baumannii pneumonia. We retrospectively evaluated the outcome of adult patients with culture proven MDR A. baumanniipneumonia treated with tigecycline be- tween January 2009 and March 2011. The study com- prised a total of 72 MDR A. baumanniipneumonia cases (44 men, mean age 65.9±15.0). Tigecycline was used for a mean duration of 10.7±4.8 days. Microbiological eradication was observed in 47 cases (65.3%). Overall mortality was 55.5% and was lower in cases with microbiological eradication vs others (15/47 32% vs 25/25 100%, p < 0.0001). Mortality and microbiological eradication rates were not different with monotherapy vs combination therapy (p>0.05). Patients who died had lower albumin levels, higher APACHE-II scores and CRP levels. The microbiological eradication rate of tigecycline in MDR A. baumannii was considerable. However, eradication ofA. bau- mannii did not result in favorable clinical outcomes in those patients with low albumin, higher APACHE-II scores and CRP levels.     

Assessment of the combination of doripenem plus a fluoroquinolone against non-susceptible Acinetobacter baumannii isolates from nosocomial pneumonia patients

Abstract

Carbapenem- and fluoroquinolone-non-susceptible Acinetobacter baumannii were obtained from four nosocomial pneumonia patients who were clinically cured following combination therapy with doripenem/levofloxacin or ciprofloxacin. In vitro synergy of doripenem/levofloxacin or ciprofloxacin was evaluated using time-kill analysis. In vivo synergy was tested using a mouse lethal infection model. In time-kill studies, doripenem and levofloxacin were both bactericidal when tested at C_max; at ½C_max, the combination showed synergy up to 8 hours. Ciprofloxacin, alone or combined with doripenem, was not bactericidal. For mouse septicemia, doripenem (100 mg/kg) was ≧90% effective in preventing death in all four isolates. Levofloxacin (200 mg/kg) was 73% effective, and ciprofloxacin (35 mg/kg) was ineffective in preventing death. At lower drug concentrations, increased efficacy was observed for doripenem/levofloxacin, but not for doripenem/ciprofloxacin. Overall, the results suggest that a doripenem/levofloxacin combination may have clinical utility in treating some non-susceptible A. baumannii infections.     

Role of insertion sequence Aba-1 and AdeS in reduced tigecycline susceptibility in MDR-Acinetobacter baumannii clinical isolates from Cairo,Egypt

Infections caused by multidrug resistant (MDR) Acinetobacter baumannii (A. baumannii) especially in intensive care units have limited therapeutic options. Overexpression of the adeABC efflux pump may be caused either by the ISAba-1 insertion or by specific point mutations in adeR and adeS, therefore, plays a major role in conferring MDR-A. baumannii. We aimed in our study to monitor the tigecycline (TGC) susceptibility and to study the role of ISAba-1 and the adeS regulator within the AdeABC efflux pump among MDR-A. baumannii clinical isolates. MDR-A. baumannii (63) isolated from ICU patients were identified by detection of OXA-51-like gene. TGC MIC was determined by E-test and broth microdilution. PCR analysis of adeR, adeS, adeB and ISAba1 genes were done with further sequencing of adeS gene. Reduced susceptibility to TGC (MIC: 3–4 mg/L) was noticed in 6/63 (9.5%) MDR-A. baumannii isolates, ISAba-1 was detected in three isolates that two of which showed amino acid substitutions in the adeS operon. We concluded that the amino acids mutations in the adeS gene in presence of insertion ISAba-1 may play a role in conferring reduced TGC susceptibility of MDR-A. baumannii.     

Transferable Antibiotic Resistance in Multiresistant Nosocomial Acinetobacter baumannii Strains from Seven Clinics in the Slovak and Czech Republics

Abstract

Sixty-seven multiresistant nosocomial Acinetobacter baumannii isolates from patients hospitalized mostly in intensive care units of seven clinics in Slovak and Czech Republic were tested to determine their ability to transfer antibiotic resistance. All isolates were resistant to kanamycin, ticarcillin, cephalothin, cefotaxime, ceftazidime, aztreonam and susceptible to carbapen-ems, sulbactam and ampicillin/sulbactam. Sixty-five out of 67 strains transferred resistance determinants to Escherichia coli K-12 and Proteus mirabilis P-38 recipients. Analysis of selected transconjugants by an indirect selection method showed a more variable pattern of transferred resistance determinants. The clonal spread of strains transferring resistance seems to be an additional risk for occurrence of strains resistant to ceftazidime and aztreonam.     

Multidrug-Resistant Acinetobacter baumannii Outbreak in an Intensive Care Unit

Abstract

Carbapenem-resistant Acinetobacter baumannii was isolated from 15 colonized or infected patients (carriers) between April and July 2004, in a teaching hospital ICU in Rome, Italy. All isolated strains were susceptible only to gentamicin, ampicillin-sulbactam and colistin and displayed the same Random Amplified Polymorphic DNA (RAPD) 1 pattern. Twelve out of 15 strains were susceptible to tigecycline, whereas the remaining three showed intermediate susceptibility. Although infection control measures were reinforced and carriers isolated in separate rooms, A. baumannii transmission continued. Therefore, finally A. baumannii carriers were moved to another available subintensive unit, which was re-equipped, and cared for by dedicated personnel, whereas only the non infected/colonized patients remained in the ICU. This study shows that during an outbreak by multiresistant A. baumannii it may be indispensable to geographically isolate not only patients but also dedicated staff.     

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.     

In Vitro Efficacy of Levofloxacin Alone or in Combination Tested Against Multi-Resistant Pseudomonas aeruginosa Strains

Abstract

Levofloxacin, the S(-) isomer of ofloxacin, demonstrates In Vitro activity against Pseudomonas aeruginosa. To further characterize this activity, levofloxacin was tested against three populations of recent clinical isolates categorized by their resistance patterns to several other anti-pseudomonal agents. Results demonstrate the minimum inhibitory concentrations (MICs) for levofloxacin were generally two- to fourfold higher than for ciprofloxacin. Higher fluoroquinolone MICs were associated with MIC increases in other drugs. Levofloxacin demonstrated cross resistance against ciprofloxacin-resis-tant strains. Combinations of levofloxacin and several co-drugs revealed that the majority of evaluable interactions demonstrated indifferent action. Levofloxacin exhibited enhanced activity (additive or degrees of synergy) principally with piperacillin, aztreonam, or ceftazidime. The synergy and additive rate (21 to 30%) compared favorably with the enhanced interactions observed with gen-tamicin combined with piperacillin or ceftazidime (27 to 30%). Levofloxacin activity against P. aeruginosa was most comparable to that of ciprofloxacin, which was applicable against > 90% of strains found to be resistant to other classes of antimicrobial agents.     

Post-Neurosurgical Meningitis Due to Multidrug-Resistant Acinetobacter baumanii Treated with Intrathecal Colistin: Case Report and Review of the Literature

Abstract

Intrathecal colistin (Polymxin E) is becoming an important option for the treatment of post-neurosurgical meningitis caused by multidrug resistant (MDR) Acinetobacter baumannii. We report a case of 28-year-old man who developed meningitis due to MDR A. baumannii associated with an external ventricular drain. The patient was cured using a 4-week course of intrathecal colistin 3.2 mg via external ventricular drain (EVD) daily without any serious side effects.     

In Vitro Interactions of Aminoglycosides with Imipenem or Ciprofloxacin against Aminoglycoside Resistant Acinetobacter baumannii

Summary

The in vitro interactions between gentamicin, tobramycin, netilmicin and amikacin with imipenem and ciprofloxacin were evaluated by the killing curve technique against 20 clinical isolates of Acinetobacter baumannii highly resistant to aminoglycosides which were susceptible or moderately susceptible to imipenem and resistant or moderately susceptible to ciprofloxacin. Imipenem enhanced killing by gentamicin, tobramycin, netilmicin and amikacin in tests with 9, 12, 10 and 15 strains (45-75%) while ciprofloxacin with 3, 7, 5 and 6 strains (15-35%) respectively. Interaction results were influenced by the height of aminoglycoside minimum bactericidal concentrations (MBCs) but were independent of imipenem or ciprofloxacin MBCs and the presence of aminoglycoside modifying enzymes. It is concluded that enhanced killing after aminoglycoside interaction with imipenem or ciprofloxacin versus A. baumannii cannot be predicted but it should be carefully tested in vitro. The in vivo significance of the reported findings mandates clinical studies in humans.     

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.     

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.     

DR. ZECKEL'S REPLY:

Abstract

The aim of the study was to monitor the prevalence of pathogens and development of resistance in bacteria isolated from bacteremic patients.

Five University Clinics and/or Regional Hospitals in the Slovak Republic participated in the study and a total of 421 isolates were collected in the second half of the year 2002. The most prevalent organisms were coagulase-negative staphylococci (CONS) (19%) Staphylococcus aureus (18.3%), among Gram-negative bacteria Escherichia coli (13.3%) Klebsiella pneumoniae (11.4%) and Pseudomonas aeruginosa (7.8%) followed by enterococci Acinetobacter baumannii and Enterobacter sp. All CONS and S. aureus were susceptible to vancomycin; resistance to oxacillin was observed for 55% of the CONS and only for 4% of S. aureus isolates. A higher prevalence of resistance to erythromycin, clindamycin, gentamicin and ofloxacin was found in CONS in comparison to S. aureus. Enterococcus sp. isolates were fully susceptible to vancomycin and teicoplanin. Gentamicin, amoxicillin/ clavulanate, third generation cephalosporins and ciprofloxacin showed good activity against E. coli. Although 17% of K. pneumoniae isolates were resistant to ciprofloxacin, it was the most effective drug against K. pneumoniae; the prevalence of resistance to other antibiotics was rather higher. Gentamicin and ciprofloxacin were the most active against Enterobacter sp. isolates and ceftazidime and meropenem against P. aeruginosa.