Identification and Antimicrobial Susceptibility of Alcaligenes xylosoxidans Isolated from Patients with Cystic Fibrosis

In the past decade, potential pathogens, including Alcaligenes species, have been increasingly recovered from cystic fibrosis (CF) patients. Accurate identification of multiply antibiotic-resistant gram-negative bacilli is critical to understanding the epidemiology and clinical implications of emerging pathogens in CF. We examined the frequency of correct identification of Alcaligenes spp. by microbiology laboratories affiliated with American CF patient care centers. Selective media, an exotoxin A probe for Pseudomonas aeruginosa, and a commercial identification assay, API 20 NE, were used for identification. The activity of antimicrobial agents against these clinical isolates was determined. A total of 106 strains from 78 patients from 49 CF centers in 22 states were studied. Most (89%) were correctly identified by the referring laboratories as Alcaligenes xylosoxidans. However, 12 (11%) strains were misidentified; these were found to be P. aeruginosa (n = 10), Stenotrophomonas maltophilia (n = 1), and Burkholderia cepacia (n = 1). Minocycline, imipenem, meropenem, piperacillin, and piperacillin-tazobactam were the most active since 51, 59, 51, 50, and 55% of strains, respectively, were inhibited. High concentrations of colistin (100 and 200 microg/ml) inhibited 92% of strains. Chloramphenicol paired with minocycline and ciprofloxacin paired with either imipenem or meropenem were the most active combinations and inhibited 40 and 32%, respectively, of strains. Selective media and biochemical identification proved to be useful strategies for distinguishing A. xylosoxidans from other CF pathogens. Standards for processing CF specimens should be developed, and the optimal method for antimicrobial susceptibility testing of A. xylosoxidans should be determined.     

Antimicrobial activity of doripenem and other carbapenems against gram-negative pathogens from Korea

A total of 950 gram-negative bacterial isolates from patients with bacteremia and urinary tract infections were collected from tertiary-care hospitals in Korea. In vitro antimicrobial susceptibility testing was performed using broth microdilution test according to Clinical and Laboratory Standards Institute protocol. In general, carbapenems such as doripenem, imipenem, and meropenem were very active against Enterobacteriaceae, Moraxella catarrhalis, Pseudomonas aeruginosa, and Acinetobacter sp. isolates. Doripenem was more potent than imipenem against most Enterobacteriaceae species except Proteus spp. based on minimum inhibitory concentration (MIC)(50) and MIC(90). In addition, doripenem displayed similar activity to meropenem but was superior to imipenem against ceftazidime-resistant Enterobacteriaceae isolates. For P. aeruginosa and Acinetobacter spp. isolates, MIC(50)s of doripenem were 1 and 0.5 mg/L, respectively, which were the same with those of meropenem but two- to fourfold lower than those of imipenem (both 2 mg/L). On the basis of the in vitro data, we conclude that doripenem has equivalent or more activity than other carbapenems such as imipenem and meropenem against most gram-negative pathogens from Korea. Thus, doripenem may be a promising new antimicrobial agent for the treatment of infections caused by gram-negative pathogens in Korea.     

Antimicrobial activity of doripenem (S-4661): a global surveillance report (2003)

The spectrum of activity and potency of doripenem, a broad-spectrum parenteral carbapenem currently in clinical development, was evaluated using 16 008 clinical bacterial isolates collected as part of an international surveillance project during 2003. Using reference broth microdilution methods, doripenem was found to be highly active against oxacillin-susceptible Staphylococcus aureus and coagulase-negative staphylococci (2705 and 297 isolates, respectively; MIC90s 0.06 mg/L), with a potency greater than that of other carbapenem antibiotics. Against enterococci (1474 isolates), with the exception of Enterococcus faecium, doripenem displayed modest activity (MIC50 4). Doripenem was among the most potent agents tested against Streptococcus pneumoniae, viridans group streptococci and beta-haemolytic streptococci (885, 140 and 397 isolates; MIC(90)s 0.5, 0.5 and 0.03 mg/L, respectively). For Enterobacteriaceae (> 6200 isolates), doripenem was four- to 32-fold more active than imipenem against wild-type isolates (MIC90s 0.03-0.5 mg/L). MIC90s for confirmed extended-spectrum beta-lactamase-producing Escherichia coli and Klebsiella pneumoniae (121 and 155 isolates; 0.06 and 0.12 mg/L, respectively) were two-fold higher than for wild-type isolates. Doripenem was also active against Citrobacter spp., Enterobacter spp. and Serratia spp. (MIC90s 0.06-0.25 mg/L), including ceftazidime-resistant isolates. Doripenem and meropenem were the most active agents among all beta-lactams against Pseudomonas aeruginosa (829 isolates; MIC50/90s 0.5/8 and 0.5/16 mg/L, respectively), whereas doripenem and imipenem were the most active agents against Acinetobacter spp. (155 isolates; MIC50/90s 0.5/4 and 相似文献   

In vitro activities of doripenem and other carbapenems against clinically important bacteria isolated in intensive care units: nationwide data from the SMART Programme

This nationwide surveillance of clinically important bacteria from the intensive care units (ICUs) of major teaching hospitals throughout Taiwan investigated the susceptibilities to doripenem and other comparator carbapenems from September through November 2005. Minimum inhibitory concentrations (MICs) were determined for 1,311 clinical isolates using the broth microdilution method according to Clinical and Laboratory Standards Institute (CLSI) 2005 guidelines. Doripenem showed similar (within four-fold difference of MICs) in vitro activity to meropenem for Enterobacteriaceae and probably comparable activity to meropenem against important nosocomial non-fermentative Gram-negative bacilli (NFGNBs), including Pseudomonas aeruginosa, Acinetobacter baumannii and Burkholderia cepacia. Among the four carbapenems analysed, doripenem and meropenem exhibited better in vitro activity than imipenem or ertapenem against extended-spectrum β-lactamase (ESBL)-producing Klebsiella pneumoniae and Escherichia coli isolates. However, the meropenem MIC₉₀ against ESBL-producing K. pneumoniae isolates was 2 µg/ml. Besides, doripenem with the MIC₉₀ of 0.5 µg/ml to Streptococcus pneumoniae possibly suggested its potential therapeutic effect regarding community-acquired pneumonia. Because of the heavy resistance burden in Taiwan, closely monitoring the evolutionary trend of carbapenem susceptibilities against clinically important pathogens is crucial in the future.     

In vitro activities of tigecycline, ertapenem, isepamicin, and other antimicrobial agents against clinically isolated organisms in Taiwan

This study evaluated the in vitro activities of tigecycline, ertapenem, isepamicin, and other comparators against 861 bacterial isolates recovered from patients treated in three major teaching hospitals in 2003. MICs to antimicrobial agents were determined by the agar dilution method. High rates of oxacillin resistance (58%) in Staphylococcus aureus (60 isolates), and vancomycin resistance (21%) and quinupristin-dalfopristin non-susceptibility (39%) in Enterococcus faecium (34 isolates) were found. Carbapenems had excellent in vitro activities (>or=98% susceptibility) against the 419 isolates of Enterobacteriaceae, with the MIC(50) and MIC(90) of imipenem, meropenem, and ertapenem being 0.25 and 4 mg/L, 0.03 and 0.12 mg/L, and 0.03 and 0.5 mg/L, respectively. For, Pseudomonas aeruginosa (74 isolates) and Burkholderia cepacia (21 isolates), meropenem (MIC(90), 0.25, 2, and 4 mg/L, respectively) had better in vitro activities than imipenem (MIC(90), 8, 4, and 32 mg/L, respectively) and ertapenem (MIC(90), 0.5, >32, and 32 mg/L, respectively). Isepamicin had a similar activity with amikacin against all Enterobacteriaceae, Pseudomonas aeruginosa, B. cepacia, and Acinetobacter baumannii, except for C. freundii isolates in which isepamicin had an eight-fold activity better than amikacin. Tigecycline had excellent in vitro activities against all isolates tested (MIC(90), 相似文献   

Evaluation of the VITEK 2 system for the identification and susceptibility testing of three species of nonfermenting gram-negative rods frequently isolated from clinical samples

VITEK 2 is a new automatic system for the identification and susceptibility testing of the most clinically important bacteria. In the present study 198 clinical isolates, including Pseudomonas aeruginosa (n = 146), Acinetobacter baumannii (n = 25), and Stenotrophomonas maltophilia (n = 27) were evaluated. Reference susceptibility testing of cefepime, cefotaxime, ceftazidime, ciprofloxacin, gentamicin, imipenem, meropenem, piperacillin, tobramycin, levofloxacin (only for P. aeruginosa), co-trimoxazole (only for S. maltophilia), and ampicillin-sulbactam and tetracycline (only for A. baumannii) was performed by microdilution (NCCLS guidelines). The VITEK 2 system correctly identified 91.6, 100, and 76% of P. aeruginosa, S. maltophilia, and A. baumannii isolates, respectively, within 3 h. The respective percentages of essential agreement (to within 1 twofold dilution) for P. aeruginosa and A. baumannii were 89.0 and 88.0% (cefepime), 91.1 and 100% (cefotaxime), 95.2 and 96.0% (ceftazidime), 98.6 and 100% (ciprofloxacin), 88.4 and 100% (gentamicin), 87.0 and 92.0% (imipenem), 85.0 and 88.0% (meropenem), 84.2 and 96.0% (piperacillin), and 97.3 and 80% (tobramycin). The essential agreement for levofloxacin against P. aeruginosa was 86.3%. The percentages of essential agreement for ampicillin-sulbactam and tetracycline against A. baumannii were 88.0 and 100%, respectively. Very major errors for P. aeruginosa (resistant by the reference method, susceptible with the VITEK 2 system [resistant to susceptible]) were noted for cefepime (0.7%), cefotaxime (0.7%), gentamicin (0.7%), imipenem (1.4%), levofloxacin (2.7%), and piperacillin (2.7%) and, for one strain of A. baumannii, for imipenem. Major errors (susceptible to resistant) were noted only for P. aeruginosa and cefepime (2.0%), ceftazidime (0.7%), and piperacillin (3.4%). Minor errors ranged from 0.0% for piperacillin to 22.6% for cefotaxime against P. aeruginosa and from 0.0% for piperacillin and ciprofloxacin to 20.0% for cefepime against A. baumannii. The VITEK 2 system provided co-trimoxazole MICs only for S. maltophilia; no very major or major errors were obtained for co-trimoxazole against this species. It is concluded that the VITEK 2 system allows the rapid identification of S. maltophilia and most P. aeruginosa and A. baumannii isolates. The VITEK 2 system can perform reliable susceptibility testing of many of the antimicrobial agents used against P. aeruginosa and A. baumannii. It would be desirable if new versions of the VITEK 2 software were able to determine MICs and the corresponding clinical categories of agents active against S. maltophilia.     

Synergy of fosfomycin with carbapenems, colistin, netilmicin, and tigecycline against multidrug-resistant Klebsiella pneumoniae, Escherichia coli, and Pseudomonas aeruginosa clinical isolates

Fosfomycin represents a potential last-resort treatment option for infections with certain multidrug-resistant (MDR) Gram-negative pathogens. We evaluated double-drug combinations of fosfomycin with imipenem, meropenem, doripenem, colistin, netilmicin, and tigecycline for in vitro synergy against 100 MDR Klebsiella pneumoniae, Escherichia coli, and Pseudomonas aeruginosa clinical isolates, using the Etest method. Synergy was defined as a fractional inhibitory concentration index ≤0.5. The isolates were consecutively collected at a university hospital in Greece from various clinical specimens. Against 50 serine carbapenemase-producing K. pneumoniae isolates, synergy of fosfomycin with imipenem, meropenem, doripenem, colistin, netilmicin, and tigecycline was observed for 74.0%, 70.0%, 74.0%, 36.0%, 42.0%, and 30.0% of the isolates, respectively. Against 14 extended-spectrum β-lactamase (ESBL)-producing K. pneumoniae isolates, synergy of fosfomycin with imipenem, meropenem, doripenem, colistin, netilmicin, and tigecycline was observed for 78.6%, 42.9%, 42.9%, 7.1%, 42.9%, and 21.4%, respectively; for 20 ESBL-producing E. coli isolates, the corresponding values were 55.0%, 25.0%, 30.0%, 15.0%, 25.0%, and 25.0%; and for 15 MDR P. aeruginosa isolates, the corresponding values were 46.7%, 53.3%, 73.3%, 13.3% , 13.3%, and 13.3%. Antagonism was not observed for any of the combinations tested. Further studies are needed in order to confirm the clinical relevance of the above findings.     

Doripenem vs meropenem against Pseudomonas and Acinetobacter

Recently, doripenem has been approved for the treatment of nosocomial pneumonia (NP), including ventilator-associated pneumonia (VAP). The E-test was performed to determine the MICs of doripenem and meropenem in 203 endotracheal aspirate isolates that consisted of 140 Acinetobacter calcoaceticus-Acinetobacter baumannii complexes and 63 Pseudomonas aeruginosa. Doripenem showed minimum concentration necessary for inhibition of 50% (MIC 50 ) of P. aeruginosa isolates at 0.38 mg/L which is several times (84.2 times) lower than the corresponding MIC 50 value of >32 mg/L for meropenem. The MIC 50 and MIC 90 were similar for both the drugs against A. baumannii. Thus, P. aeruginosa was consistently more susceptible than the A. baumannii.     

Activity of doripenem against extended-spectrum β-lactamase-producing Enterobacteriaceae and Pseudomonas aeruginosa isolates

The in vitro activity of doripenem was evaluated against a recent collection of extended-spectrum β-lactamase (ESBL)-producing Enterobacteriaceae and Pseudomonas aeruginosa isolates (201 ESBL-producing Enterobacteriaceae [153 Escherichia coli and 48 Klebsiella pneumoniae] and 201 P. aeruginosa). Comparator agents included amikacin, tobramycin, ciprofloxacin, cefepime, cefotaxime, ceftazidime piperacillin-tazobactam, imipenem, and meropenem. Both doripenem and meropenem inhibited 100% of the ESBL-producing Enterobacteriaceae at ≤0.5 μg/mL. For these isolates, the MIC₉₀ of doripenem (0.12 μg/mL) was 4-fold lower than that of imipenem (0.5 μg/mL). Against P. aeruginosa, the MIC₉₀ of doripenem and meropenem was 2 μg/mL, 4-fold lower than that of imipenem (8 μg/mL). At an MIC of ≤2 μg/mL, doripenem, meropenem, and imipenem inhibited 90.5%, 89.6%, and 82.1% of P. aeruginosa isolates, respectively. Doripenem maintained activity against imipenem-nonsusceptible isolates of P. aeruginosa; at an MIC of ≤4 μg/mL, it inhibited 15 of the 25 isolates with MICs for imipenem of >4 μg/mL. Doripenem is active against ESBL-producing Enterobacteriaceae and P. aeruginosa isolates. Its activity is similar to that of meropenem and slightly better than that of imipenem. The results of this study suggest that doripenem could be an alternative therapeutic agent for infections caused by these organisms.     

P594 Intracellular killing of drug-resistant Staphylococcus aureus by different antibiotics

Objectives:  The aim of this study was to assess the carbapenem susceptibility of four nosocomial pathogens and to evaluate the reliability of the susceptibility results determined by E-test and disc diffusion (DD) methods.
Methods:  Escherichia coli ( n  = 73), Klebsiella pneumoniae ( n  = 60), Pseudomonas aeruginosa ( n  = 70) and Acinetobacter spp. ( n  = 70) isolated from nosocomial infections in 2002–2003 were included in the study. Thirty-five per cent of the strains were isolated from intensive care units. After determining antimicrobial susceptibility against imipenem and meropenem by DD (10  μ g; Oxoid, UK) and Etest (AB Biodisk, Solna, Sweden) methods, the results were categorised as susceptible (S), intermediate (I) and resistant (R) according to the NCCLS criteria. For statistical analyses, the intermediate group was included in the resistant category because of the low numbers of bacteria in the former group.
Results:  None of E. coli or K. pneumoniae strains were resistant to carbapenems, whereas, resistance reached up to 59.0% in Acinetobacter spp. and P. aeruginosa isolates. By either method, the pattern of the susceptibility of the four bacteria was not statistically significantly different for imipenem vs. meropenem. Total agreement of DD and E-test methods for susceptibility to imipenem was 95.7%, and 90.0% in Acinetobacter spp. and P. aeruginosa , respectively; and susceptibility to meropenem was 90.0% for both bacteria. However, the difference of the results obtained by either method was statistically significant for Acinetobacter spp.
Conclusion:  Study results suggest a high resistance rate for Acinetobacter spp. and P. aeruginosa strains against carbapenem antibiotics in our hospital. Further studies are needed to clarify whether E-test should be used to confirm meropenem resistance of Acinetobacter spp. determined by DD method.     

Phenotypic and genotypic characteristics of non fermenting atypical strains recovered from cystic fibrosis patients

We used partial 16S rRNA gene (16S DNA) sequencing for the prospective identification of nonfermenting Gram-negative bacilli recovered from patients attending our cystic fibrosis center (h?pital Necker-Enfants malades), which gave problematic results with conventional phenotypic tests. During 1999, we recovered 1093 isolates of nonfermenting Gram-negative bacilli from 702 sputum sampled from 148 patients. Forty-six of these isolates (27 patients) were not identified satisfactorily in routine laboratory tests. These isolates were identified by 16S DNA sequencing as Pseudomonas aeruginosa (19 isolates, 12 patients), Achromobacter xylosoxidans (10 isolates, 8 patients), Stenotrophomonas maltophilia (9 isolates, 9 patients), Burkholderia cepacia genomovar I/III (3 isolates, 3 patients), Burkholderia vietnamiensis (1 isolate), Burkholderia gladioli (1 isolate) and Ralstonia mannitolilytica (3 isolates, 2 patients). Fifteen isolates (33%) were resistant to all antibiotics in routine testing. Sixteen isolates (39%) resistant to colistin were recovered on B. cepacia-selective medium: 2 P. aeruginosa, 3 A. xylosoxidans, 3 S. maltophilia and the 8 Burkholderia--Ralstonia isolates. The API 20NE system gave no identification for 35 isolates and misidentified 11 isolates (2 P. aeruginosa, 2 A. xylosoxidans and 1 S. maltophilia classified as B. cepacia ). Control measures and/or treatment were clearly improved as a result of 16S DNA sequencing in three of these cases. This study confirms the weakness of phenotypic methods for identification of atypical nonfermenting Gram-negative bacilli recovered from cystic fibrosis patients. The genotypic methods, such as 16S DNA sequencing which allows identification of strains in routine practice, appears to have a small, but significant impact on the clinical management of CF patients.     

Comparison of Etest, Vitek and agar dilution for susceptibility testing of colistin

In total, 172 isolates of Enterobacteriaceae, Acinetobacter spp., Pseudomonas aeruginosa and Stenotrophomonas maltophilia were tested for susceptibility to colistin by agar dilution, Etest and the Vitek 2 system. Isolates with a colistin MIC < or =2 mg/L were considered to be susceptible. Fifty-four (31%) Gram-negative isolates were resistant to colistin. Categorical agreement between agar dilution and Etest was 87%, and between agar dilution and Vitek 2 was 82%. Based on the data obtained, the Vitek 2 system was unreliable for detecting colistin resistance, and results obtained by Etest may require confirmation by a standard MIC susceptibility testing method.     

Carbapenem resistance mediated by Beta-lactamases in clinical isolates ofAcinetobacter baumannii in Spain

Four patients colonized/infected with carbapenem-resistant strains ofAcinetobacter baumannii are described. The first patient had a decubitus ulcer infection and had been on intravenous imipenem for 50 days. Two other patients, from whomAcinetobacter baumannii was isolated from urine, were hospitalized in the same ward as the first patient. The fourth patient had been mechanically ventilated in the intensive care unit for 4 month and had nosocomial pneumonia. He had been on intravenous meropenem for 1 month. Minimum inhibitory concentrations (MICs) of imipenem (128 mg/l) and meropenem (>128 mg/l) were the same for the isolates from the first three patients, and all of these isolates had the same repetitive extragenic palindromic polymerase chain reaction (rep-PCR) pattern. The MICs of carbapenems were lower for patient 4's isolate, which also had a different rep-PCR pattern. Beta-lactamases that hydrolyzed imipenem were detected in all four isolates; isoelectric points were 8.6–7.7 in the first three isolates and 6.8–7 in the fourth isolate.     

Comparative analysis of antimicrobial susceptibility among organisms from France, Germany, Italy, Spain and the UK as part of the tigecycline evaluation and surveillance trial.

As part of the tigecycline evaluation and surveillance trial (TEST), bacterial isolates were collected from 39 centres in France, Germany, Italy, Spain and the UK between January 2004 and August 2006. Antimicrobial susceptibilities were determined according to CLSI guidelines. Italy had the highest rate of methicillin-resistant Staphylococcus aureus (36.4%), and was the only country to report vancomycin-resistant Enterococcus faecalis (8.6%). Tigecycline was the only agent to which all Gram-positive isolates were susceptible. For many of the Gram-negative organisms collected, antimicrobial susceptibilities were lowest among isolates from Italy and highest among isolates from Spain. The notable exception was Acinetobacter baumannii, where the poorest susceptibility profile was among isolates from Spain. For A. baumannii, MIC(90)s of imipenem varied from 1 mg/L for isolates in France and Germany to > or =32 mg/L for isolates from Italy and Spain. Tigecycline was the only agent to maintain an MIC(90) of < or =1 mg/L against isolates from all five countries. The in-vitro activity of tigecycline against both Gram-positive and Gram-negative isolates may make it valuable in the treatment of hospital infections, including those caused by otherwise antimicrobial-resistant organisms.     

The activity of meropenem and comparators against Acinetobacter strains isolated from European hospitals, 1997–2000

In vitro susceptibilities to meropenem and comparators of Acinetobacter strains isolated from serious infections in 37 European hospital centers participating in the Meropenem Yearly Susceptibility Test Information Collection (MYSTIC) Program (1997–2000) were tested. There were 635 Acinetobacter strains collected: 490 A. baumannii ; 51 A. calcoaceticus var . lwoffii ; and 94 other Acinetobacter strains. Overall, meropenem and imipenem were the most effective agents tested. Resistance to the antimicrobials was: 14%, meropenem; 16%, imipenem; 39%, piperacillin–tazobactam; 41%, tobramycin; 45%, ceftazidime; and 53%, ciprofloxacin. Thus, the carbapenems have useful activity against Acinetobacter spp. and represent a viable choice for treating infections caused by these organisms.     

Global assessment of the antimicrobial activity of polymyxin B against 54 731 clinical isolates of Gram-negative bacilli: report from the SENTRY antimicrobial surveillance programme (2001–2004)

In total, 54 731 Gram-negative bacilli isolated worldwide between 2001 and 2004 from diverse sites of infection were tested for susceptibility to polymyxin B by the broth reference microdilution method, with interpretation of results according to CLSI (formerly NCCLS) guidelines. Polymyxin B showed excellent potency and spectrum against 8705 Pseudomonas aeruginosa and 2621 Acinetobacter spp. isolates (MIC50, < or = 1 mg/L and MIC90, 2 mg/L for both pathogens). Polymyxin B resistance rates were slightly higher for carbapenem-resistant P. aeruginosa (2.7%) and Acinetobacter spp. (2.8%), or multidrug-resistant (MDR) P. aeruginosa (3.3%) and Acinetobacter spp. (3.2%), when compared with the entire group (1.3% for P. aeruginosa and 2.1% for Acinetobacter spp.). Among P. aeruginosa, polymyxin B resistance rates varied from 2.9% in the Asia-Pacific region to only 1.1% in Europe, Latin America and North America, while polymyxin B resistance rates ranged from 2.7% in Europe to 1.7% in North America and Latin America among Acinetobacter spp. Polymyxin B also demonstrated excellent activity (MIC90, < or = 1 mg/L; > 98% susceptible) against Citrobacter spp., Escherichia coli and Klebsiella spp., but activity was more variable against Enterobacter spp. (MIC50, < or = 1 mg/L; 83.3% susceptible) and Stenotrophomonas maltophilia (MIC50, < or = 1 mg/L; 72.4% susceptible), and was very limited (MIC50, > 8 mg/L) against Burkholderia cepacia (11.8% susceptible), Serratia spp. (5.4% susceptible), indole-positive Proteus spp. (1.3% susceptible) and Proteus mirabilis (0.7% susceptible).     

Comparative bactericidal activities of daptomycin, glycopeptides, linezolid and tigecycline against blood isolates of Gram-positive bacteria in Taiwan.

In-vitro MICs and minimum bactericidal concentrations (MBCs) of daptomycin, linezolid, tigecycline, vancomycin and teicoplanin against Gram-positive bacteria were determined using the broth microdilution method for ten blood isolates each of methicillin-susceptible Staphylococcus aureus (MSSA), methicillin-resistant S. aureus (MRSA), including two vancomycin-intermediate S. aureus (VISA), vancomycin-resistant Enterococcus faecium and Enterococcus faecalis. One strain of VISA was tested in a time-kill synergism assay of daptomycin combined with oxacillin, imipenem, rifampicin and isepamicin. Daptomycin showed excellent in-vitro bactericidal activity against all the isolates tested, with no tolerance or synergism effects when combined with other agents, except with rifampicin against VISA. Vancomycin had better bactericidal activity against MRSA and MSSA than did teicoplanin. Linezolid had the poorest bactericidal activity against the isolates tested, with 100% tolerance by the MSSA and VRE isolates, and 80% tolerance by the MRSA isolates. Tolerance towards tigecycline was exhibited by 40% of the MRSA isolates, 100% of the MSSA and vancomycin-resistant E. faecalis isolates, and 90% of the vancomycin-resistant E. faecium isolates.     

Antimicrobial activity of the new carbapenem biapenem compared to imipenem,meropenem and other broad-spectrum beta-lactam drugs

The in vitro activity of biapenem was compared to that of imipenem, meropenem and other broad-spectrum beta-lactams. A total of 716 isolates from recent cases of clinical septicemia and an additional 137 stock strains possessing known beta-lactamases or other well-characterized resistance mechanisms were tested. The minimal concentrations inhibiting 90 % of strains (MIC90) ofEnterobacteriaceae species were for biapenem 0.03 to 1 mg/l and for imipenem 0.25 to 2 mg/l. No member of theEnterobacteriaceae was found to be resistant to biapenem. Biapenem and meropenem were the most active drugs againstPseudomonas aeruginosa, with an MIC90 of 1 mg/l. Biapenem was more active than ceftazidime against most gram-negative and gram-positive bacteria tested. Biapenem was as potent as imipenem against anaerobic bacteria (includingBacteroides fragilis), with an MIC90 of 0.25 mg/l. High MICs of biapenem were demonstrated forXanthomonas maltophilia, oxacillin-resistantStaphylococcus spp. andEnterococcus spp. These species have demonstrated resistance to other carbapenems and to most of the newer cephalosporins. The results of this study, coupled with previously documented favorable qualities of biapenem, endorse further investigation of this broad-spectrum antibacterial agent for clinical use.     

Use of 16S rRNA gene sequencing for identification of "Pseudomonas-like" isolates from sputum of patients with cystic fibrosis

Since nonfermenting, Gram negative bacilli recovered from patients with cystic fibrosis could be misidentified with phenotypic procedures, we used partial 16S ribosomal RNA gene (16S gene) sequencing to identify these "Pseudomonas-like" isolates. 473 isolates were recovered from 66 patients in 2003. Sequencing was used to identify 29 (from 24 patients) of the 473 isolates, showing unclear results with routine tests. PCR with specific primers was carried out to amplify a 995 bp fragment, which was then sequenced. The sequences were analyzed with GenBank database for species assignment. Phenotypic and genotypic results were concordant for 20/29 isolates (10 Pseudomonas aeruginosa, 5 Burkholderia cepacia, 3 Stenotrophomonas maltophilia, 2 Achromobacter xylosoxidans). However, 3 of the 5 B. cepacia isolates were then identified as Burkholderia multivorans with a PCR-RFLP procedure. Phenotypic misidentification was observed for 9/29 isolates: 4 A. xylosoxidans, 1 P. aeruginosa, 1 Bordetella petrii, 1 Bordetella bronchiseptica, 1 Ralstonia respiraculi and 1 Ralstonia mannitolilytica. Partial 16S gene sequencing improved the identification of "Pseudomonas-like" isolates from cystic fibrosis patients, but the accuracy to distinguish between genomovars of the B. cepacia complex was inadequate.     

Heteroresistance to Meropenem in Carbapenem-Susceptible Acinetobacter baumannii

The characteristics of carbapenem heteroresistance were studied in 14 apparently carbapenem-susceptible Acinetobacter baumannii isolates. The MICs for carbapenems were determined, and the isolates were genotyped by pulsed-field gel electrophoresis (PFGE) and sequence typing (ST). Population analysis, testing of the stability of the heteroresistant subpopulations, and time-killing assays were performed. The agar dilution MICs of both imipenem and meropenem for the native isolates ranged from 0.25 to 4 mg/liter. The isolates belonged to nine PFGE types and exhibited seven ST allelic profiles. Population analysis revealed subpopulations that grew in the presence of imipenem at concentrations of up to 8 mg/liter and meropenem at concentrations of up to 32 mg/liter. The meropenem-heteroresistant subpopulations of 11 isolates exhibited stable resistance with MICs that ranged from 16 to >32 mg/liter; their PFGE profiles were identical to those of the native isolates. Time-kill assays with meropenem revealed less pronounced killing for 10 isolates. These findings indicate that meropenem pressure can produce meropenem-heteroresistant subpopulations that might subsequently select for highly resistant strains.Acinetobacter baumannii is an opportunistic pathogen associated with severe hospital infections (1, 16), which often need the use of carbapenems as the treatment of last resort. However, reduced susceptibility or resistance to carbapenems is increasingly being observed among A. baumannii clinical isolates (2, 5, 25).In a preliminary work, we reported on the growth of distinct colonies within the inhibition halo around carbapenem disks or Etest strips and assessed these colonies as having the phenotypic manifestation of carbapenem heteroresistance (17). Likewise, a recent study (12) has described colistin-heteroresistant subpopulations among apparently colistin-susceptible A. baumannii clinical isolates, implying an intrinsic potential of the species to overcome drug pressure. These observations suggest that the use of carbapenems or colistin to treat severe multidrug-resistant A. baumannii infections may lead to the development of resistance.The present study aimed to evaluate in vitro the incidence of carbapenem heteroresistance, to characterize the traits of the heteroresistant subpopulations, and to assess the efficacies of carbapenems against heteroresistant A. baumannii isolates. The study included carbapenem-susceptible A. baumannii clinical isolates that cause infections; such infections are commonly treated with carbapenems, although it is recognized that the heterogeneity of resistance might affect the outcome. The study also determined how the heterogeneity of resistance might affect the treatment outcome.