Evaluation of the VITEK 2 cards for identification and antimicrobial susceptibility testing of non‐glucose‐fermenting Gram‐negative bacilli

We evaluated VITEK 2 cards (NGNC and AST‐GN10) for the accuracy of identification (ID) and antimicrobial susceptibility testing (AST) of non‐glucose‐fermenting Gram‐negative bacilli (NGF‐GNB). In a total of 201 strains, 190 strains (94.5%) were correctly identified, seven strains (3.5%) showed low discrimination, four strains (2.0%) had discrepancies, and no strain remained unidentified. Reference AST of amikacin, aztreonam, cefepime, cefotaxime, ceftazidime, ciprofloxacin, imipenem, levofloxacin, piperacillin‐tazobactam, and trimethoprim‐sulfamethoxazole was performed by the agar dilution method. Approximately 82.5% of ID and 72.9% of AST were completed within 7 and 14 h, respectively. For NGF‐GNB, other than Pseudomonas aeruginosa, Acinetobacter spp., Stenotrophomonas maltophilia, and the Burkholderia cepacia group, essential agreements (EAs) were 93.6–100.0%. Severe disagreements (resistant by the reference method to susceptible by AST‐GN10) were observed for amikacin (0.9%), cefepime (1.8%), cefotaxime (1.8%), imipenem (0.9%), and piperacillin‐tazobactam (0.9%). One major disagreement (susceptible to resistant) was observed for ceftazidime (0.1%). For P. aeruginosa, EAs were 85.7–100%, with severe disagreements observed for cefepime (4.8%) and piperacillin‐tazobactam (4.8%). For Acinetobacter spp., EAs were 86.4–100% without disagreements. The VITEK 2 cards appear to be promising for rapid ID and reliable AST for most species of NGF‐GNB.     

Differential effects of bismuth and salicylate salts on the antibiotic susceptibility ofPseudomonas aeruginosa

The influence of salicylate or bismuth salts on antibiotic action againstPseudomonas aeruginosa was assessed in broth cultures. Sodium salicylate (2.5 mM) had no significant effect on the activity of any antibiotic tested. In contrast, bismuth compounds (0.5 mM) produced a significant change in the inhibitory activity of several antibiotics against all strains. Bismuth salts reduced imipenem activity by up to 20-fold, enhanced gentamicin or amikacin activity three to five-fold, and enhanced cefpirome or cefepime activity by as much as 10-fold against antibiotic-sensitive and resistant strains. Bismuth salts had little effect on cefoperazone, ceftazidime, or mezlocillin activity. Combining bismuth salts with aminoglycosides or fourth-generation cephalosporin antibiotics may help to combat the growing problem of resistantPseudomonas aeruginosa.     

Antibacterial activity of the new carbapenem meropenem (SM-7338) against clinical isolates

The in vitro antibacterial activity of the new carbapenem antibiotic meropenem (SM-7338) against 567 clinical isolates was evaluated. SM-7338 exhibited activity against a broad spectrum of organisms, including aerobes and anaerobes, and was superior to the other beta-lactam drugs tested (piperacillin, cefotaxime, ceftazidime, ceftriaxone, cefoxitin). SM-7338 was more active than imipenem, gentamicin and amikacin againstEnterobacter cloacae andPseudomonas aeruginosa. SM-7338 was less potent than imipenem against staphylococci and enterococci, but the activity of the two antibiotics against anaerobes was similar. SM-7338 and imipenem showed a high bactericidal activity at a concentration of 2–4 x MIC.     

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.     

In vitro activity of fosfomycin combined with ceftazidime, imipenem, amikacin, and ciprofloxacin againstPseudomonas aeruginosa

The in vitro activity of fosfomycin in combination with ceftazidime, imipenem, amikacin, or ciprofloxacin was studied by an agar plate checkerboard method against 40 clinical isolates ofPseudomonas aeruginosa with various antibiotic resistance profiles. Fosfomycin/ciprofloxacin appeared to be the most effective combination (synergy 15%, addition 80%, indifference 5%), followed by fosfomycin/amikacin (synergy 7.5%, addition 52.5%, indifference 40%), fosfomycin/imipenem (addition 37%, indifference 63%), and fosfomycin/ceftazidime (addition 20%, indifference 80%). The effects of the combinations were not significantly infl enced by the antibiotic susceptibility patterns of the strains.     

Development of a combination antibiogram for empirical treatments of Pseudomonas aeruginosa at a university-affiliated teaching hospital

IntroductionThe significantly higher mortality rate in the critical illness patients with Pseudomonas aeruginosa (PA) infection is linked to inappropriate selecting of empirical treatment. Traditional local antibiogram provides clinicians the resistant rate of a single antimicrobial agent to the pathogen in the specific setting. The information is valuable to the clinicians in selecting suitable empirical antibiotic therapy. However, traditional local antibiogram can only provide information for single agent empirical antibiotic not combination regimens. The combination antibiogram should be developed to facilitate the selection of appropriate antibiotics to broader the coverage rate of resistant PA.MethodsThe susceptibility to the β-lactam antibiotics (piperacillin/tazobactam (PTZ), ceftazidime, cefepime, imipenem, or meropenem) or to those administered in combination with an aminoglycoside (gentamicin or amikacin) or fluoroquinolone (ciprofloxacin or levofloxacin) was calculated. The chi-square test was used to compare the differences of combination coverage rates between non-ICU and ICU isolates.Results880 PA isolates were isolated during study period. The susceptibility of single agents ranged from 83.1% to 89.7%. The combination regimens containing amikacin provide the highest cover rate (98.9%–99.1%) and those containing levofloxacin provide less coverage rate (92.3%–93.9%). The susceptibility to five β-lactam single agents in ICU isolates significantly lower than non-ICU isolates. The non-ICU isolates exhibited significantly higher susceptibility to the PTZ–gentamicin (p = 0.002) and ceftazidime–gentamicin (p = 0.025) than ICU isolates.ConclusionOur results support the use of aminoglycosides instead of fluoroquinolones as additive agents in empirical combination treatments for patients with critical infections caused by PA.     

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.     

In vitro activity of carumonam (RO 17-2301) and twelve other antimicrobials against clinical isolates ofPseudomonas aeruginosa

Minimal inhibitory concentrations of the monobactam carumonam (RO 17-2301) and twelve other antimicrobials were determined using agar dilution against 140 recent nonreplicate clinical isolates of Pseudomonas aeruginosa.The most active drugs were ciprofloxacin, amikacin, imipenem and ceftazidime, inhibiting 96, 91, 90 und 86 percent of the strains, respectively, at or below the susceptibility threshold. The monobactams carumonam and aztreonam were active against 78 and 65 percent of the strains, respectively. Tobramycin inhibited 68 percent of the strains, and gentamicin and netilmicin 50 and 21 percent, respectively. Analysis of correlation coefficients revealed a low correlation between imipenem and the other beta-lactams and a remarkably good correlation between the beta-lactams (excepting imipenem) and the aminoglycosides.     

Epidemiology of community-acquiredPseudomonas aeruginosa infections in children

The epidemiology of community-acquiredPseudomonas aeruginosa infections in children during a one-year period (January through December 1993) was evaluated. A total of 6,859 clinical samples, each one representing a separate individual with suspected infection, were cultured.Pseudomonas aeruginosa was isolated from 218 children with various infections occurring in the following order of frequency: chronic suppurative otitis media, 76.3%; appendicitis/peritonitis, 10.3%; osteomyelitis, 8.9%; skin or soft tissue infection, 6.3%; acute conjunctivitis, 3.0%; and urinary tract infection, 0.1%. A variety of O serogroups were identified: O1 (15.2%), 06 (14.7%), O11 (12.4%), O10 (11.5%), O3 (10.6%), O5 (5.1 %), and O9 (4.6%). Other serogroups and nontypable strains were recovered at a frequency of 11.2% and 14.7%, respectively. Nontypable strains predominated in chronic otitis media (18.9%), while serogroups O1 (18.3%), O6 (17.5%), and O11 (17.5%) were recovered most frequently among the typable isolates. Susceptibility ofPseudomonas aeruginosa to antipseudomonadal agents was extremely high. The rate of susceptibility to ceftazidime was 99.6%, to azlocillin 98.6%, to piperacillin 98.2%, to aztreonam 97.3%, to gentamicin and netilmicin 97.7%, and to ciprofloxacin 99.1%. All isolates were susceptible to tobramycin, imipenem, and amikacin. The results might suggest that community-acquiredPseudomonas aeruginosa infections in children can be treated successfully with any antipseudomonadal antibiotic.     

Analysis of quorum sensing-dependent virulence factor production and its relationship with antimicrobial susceptibility in Pseudomonas aeruginosa respiratory isolates

Pseudomonas aeruginosa is an opportunistic pathogen causing severe respiratory infections. The pathogenesis of these infections is multifactorial and the production of many virulence factors is regulated by quorum sensing (QS), a cell-to-cell communication mechanism. The two well defined QS systems in P. aeruginosa, the las and rhl systems, rely on N-acyl homoserine lactone signal molecules, also termed autoinducers. We assessed the activity of QS-dependent virulence factors (including elastase, alkaline protease, pyocyanin and biofilm production) in respiratory isolates of P. aeruginosa and their relationship with antimicrobial susceptibility. We identified sixteen isolates displaying impaired phenotypic activity; among them, eleven isolates were also defective in autoinducer production, and therefore considered QS-deficient. Six of the QS-deficient isolates failed to amplify one or more of the four QS regulatory genes (lasI, lasR, rhlI, rhlR) with PCR: one isolate was negative for rhlR, two isolates were negative for rhlI and rhlR and three isolates were negative for all four genes. The isolates that were negative for virulence factor production were generally less susceptible to the antimicrobials and statistically significant correlations were observed between the lack of elastase production and resistance to piperacillin and ceftazidime; between failure in alkaline protease production and resistance to tobramycin, piperacillin, piperacillin-tazobactam, cefepime, imipenem and ciprofloxacin; and between failure in pyocyanin production and resistance to amikacin, tobramycin, ceftazidime, ciprofloxacin and ofloxacin. The results obtained indicate that, despite the pivotal role of QS in the pathogenesis of P. aeruginosa respiratory infections, QS-deficient strains are still capable of causing infections and tend to be less susceptible to antimicrobials.     

Effect of β-lactam antibiotics on the in vitro development of resistance in Pseudomonas aeruginosa

Objective   To investigate whether stepwise selection of resistance mutations may mirror the continued bacterial exposure to antibiotics that occurs in the clinical setting.
Methods   We examined the in vitro development of resistance to a number of commonly used antibiotics (cefepime, cefpirome, ceftazidime, cefotaxime, piperacillin and imipenem) in Pseudomonas aeruginosa , a significant nosocomial pathogen. Stepwise resistance was assessed by serial passage of colonies located nearest to the inhibition zone on antibiotic-containing gradient plates.
Results   The lowest frequencies of spontaneous resistance mutations were found with cefepime and imipenem; these drugs also resulted in the slowest appearance of resistance of spontaneous resistance mutations. In five wild-type P. aeruginosa strains, cefepime-selected isolates required a mean of 30 passages to reach resistance; resistance occurred more rapidly in strains selected with other cephalosporins. P. aeruginosa strains that produced β -lactamase or non-enzymatic resistance generally developed resistance more rapidly than wild-type strains. For most strains, resistance to all antibiotics except imipenem correlated with increased levels of β -lactamase activity. Cross-resistance of cephalosporin-selected resistant mutants to other cephalosporins was common. Cephalosporin-resistant strains retained susceptibility to imipenem and ciprofloxacin.
Conclusions   From our in vitro study, we can conclude that the rate of development of resistance of P. aeruginosa is lower with cefepime compared with other cephalosporines.     

Correlation between antibiotic consumption and resistance of Pseudomonas aeruginosa in a teaching hospital implementing an antimicrobial stewardship program: A longitudinal observational study

Background/purposeThe rapid emergence of Pseudomonas aeruginosa resistance made selecting antibiotics more challenge. Antimicrobial stewardship programs (ASPs) are urging to implant to control the P. aeruginosa resistance. The purpose of this study is to evaluate the relationship between antimicrobial consumption and P. aeruginosa resistance, the impact of ASPs implemented during the 14-year study period.MethodsA total 14,852 P. aeruginosa isolates were included in our study. The resistant rate and antimicrobial consumption were investigated every six months. Linear regression analysis was conducted to examine the trends in antibiotics consumption and antimicrobial resistance over time. The relationship between P. aeruginosa resistance and antimicrobial consumption were using Pearson correlation coefficient to analysis. The trend of resistance before and after ASPs implanted is evaluated by segment regression analysis.ResultsP. aeruginosa resistance to ceftazidime, gentamicin, amikacin, ciprofloxacin and levofloxacin significantly decreased during the study period; piperacillin/tazobactam (PTZ), cefepime, imipenem/cilastatin and meropenem remained stable. The P. aeruginosa resistance to ciprofloxacin and levofloxacin increasing initial then decreased after strictly controlled the use of levofloxacin since 2007. As the first choice antibiotic to treat P. aeruginosa, the consumption and resistance to PTZ increase yearly and resistance became stable since extended-infusion therapy policy implant in 2009.ConclusionOur ASP intervention strategy, which included extended infusion of PTZ and restrict use of levofloxacin, may be used to control antimicrobial resistance of P. aeruginosa in medical practice.     

Evaluation of VITEK 2 rapid identification and susceptibility testing system against gram-negative clinical isolates

A total of 281 strains of miscellaneous members of the family Enterobacteriaceae, Pseudomonas aeruginosa, and other gram-negative bacteria were evaluated by use of identification tests with the VITEK 2 system (bioMérieux) and an API identification system (bioMérieux). A total of 237 (95%) strains were correctly identified to the species level. Only six (2.1%) strains were misidentified, and eight (2.8%) strains were not identified. Among 14 strains with discrepant identifications, 8 (57.1%) strains were nonfermenters. The susceptibilities of 228 strains to 11 antibiotics including amikacin, netilmicin, tobramycin, gentamicin, ciprofloxacin, imipenem, meropenem, ceftazidime, cefepime, piperacillin, and piperacillin in combination with tazobactam were tested with the VITEK 2 AST-No. 12 card and by the broth microdilution (MB) method, according to NCCLS guidelines, as a reference. For the 2,508 organism-antibiotic combinations, the rates at which duplicate MICs correlated within +/-1 dilution ranged from 84.2 to 95.6%. Only 13 (0.5%) and 10 (0.4%) of the susceptibility tests gave major errors (resistant with the VITEK 2 system but sensitive by the MB method) and very major errors (sensitive with the VITEK 2 system but resistant by the MB method), respectively. Both VITEK 2 ID-GNB (an identification system) and VITEK 2 AST-No. 12 (a susceptibility testing system) card systems gave rapid, reliable, and highly reproducible results.     

Multicenter study of the in vitro activity of cefepime in comparison with five other broad-spectrum antibiotics against clinical isolates of Gram-positive and Gram-negative bacteria from hospitalized patients in Switzerland

Objective: To assess the in vitro susceptibility of clinical isolates to cefepime and five other antimicrobial agents with broad-spectrum activity.
Methods: The minimal inhibitory concentrations of 1521 Gram-positive cocci and 3170 Gram-negative rods were determined by the Etest procedure.
Results: The susceptibilities were as follows. Gram-positive bacteria: cefepime, 92.7%; ceftazidime, 60.5%; ceftriaxone, 87.8%; imipenem, 92.6%; amikacin, 56.5%; ciprofloxacin, 72.5%. Gram-negative bacteria: cefepime, 97.8%; ceftazidime, 94.3%; ceftriaxone, 83.1%; imipenem, 95.7%; amikacin, 96.6%; ciprofloxacin, 95.8%.
Conclusions: Cefepime had the best activity when compared with the other broad-spectrum β-lactams ceftazidime, ceftriaxone, imipenem, and the non-β-lactams amikacin and ciprofloxacin.     

Multicentre comparative study on the antibacterial activity of FK-037, a new parenteral cephalosporin

The in vitro antibacterial activity of FK-037, a new parenteral cephalosporin structurally related to cefpirome and cefepime, was compared with that of cefotaxime, ceftazidime, aztreonam, cefpirome, cefepime, imipenem and meropenem against 1,837 clinical isolates obtained from three Spanish hospitals. FK-037 inhibited 90 % ofEnterobacteriaceae isolates at 0.25 µg/ml, with the exception ofEnterobacter aerogenes (MIC90 1 µg/ml),Enterobacter cloacae andCitrobacter freundii (MIC90 8 µg/ml). In cefotaxime-and ceftazidime-resistantKlebsiella pneumoniae strains producing SHV-2 and SHV-6 -lactamases, the activity of FK-037, cefpirome and cefepime was similar (MIC range 0.25–32 µg/ml). InEnterobacteriaceae strains hyperproducing chromosomally inducible -lactamases, FK-037 (MIC90 range, 0.25–8 µg/ml) was 8- to 16-fold more active than cefotaxime and ceftazidime but two- to eightfold less active than cefpirome and cefepime. FK-037 and cefpirome were twofold more active than ceftazidime and cefepime againstPseudomonas aeruginosa isolates, with MIC90 values of 16 µg/ml. The activity of FK-037, cefpirome and cefepime was two- to eightfold lower in ceftazidime-resistant derepressedPseudomonas aeruginosa mutants. FK-037 (MIC range, 0.12–2 µg/ml) and the other -lactam agents tested were active against methicillin-susceptible staphylococci; however, only cefpirome and, particularly, FK-037 (MIC90 of 32 µg/ml) displayed some activity against methicillin-resistant strains. In penicillin-susceptible,-intermediate and -resistantStreptococcus pneumoniae isolates, the MIC90s of FK-037 were 0.03, 0.5 and 1 µg/ml, respectively. The corresponding values forStreptococcus viridans isolates were 0.12, 1 and 8 µg/ml, respectively. In bothStreptococcus pneumoniae andStreptococcus viridans isolates, FK-037 displayed activity similar to that of cefotaxime and cefpirome and slightly higher than that of cefepime.     

Bacteria involved in the blockage of biliary stents and their susceptibility to antibacterial agents

Endoscopically inserted stents are used for the palliation of obstructive jaundice, but infections and blockage of these stents by biliary sludge and bacterial biofilm may develop, presenting major complications. To analyze which bacteria are involved in this process, 25 biliary stents were examined. Eighty-one microorganisms were isolated: 59 gram-negative bacteria (54Enterobacteriaceae and 5Pseudomonas aeruginosa), 19 gram-positive bacteria (allEnterococcus spp.), and 3Candida albicans. TheEnterobacteriaceae were sensitive to netilmicin (100%), imipenem (98%), ciprofloxacin (96%), cefotaxime (69%), and piperacillin (57%), whereasEnterococcus spp. were sensitive to imipenem (79%), piperacillin (75%), ciprofloxacin (63%), and ampicillin (58%). The unpredictable aetiology and high rates of antibiotic resistance suggest that bacteriological monitoring is mandatory to avoid treatment failures in these patients.     

Comparative in vitro activity of lomefloxacin,a new difluoroquinolone

The in vitro activity of lomefloxacin, a new difluoroquinolone, was compared with that of norfloxacin, ciprofloxacin, gentamicin and ceftazidime against a total of 577 recent clinical isolates. MICs were determined by a standard agar dilution procedure, and two inocula (10⁴ and 10⁶ CFU) were used throughout. Lomefloxacin inhibited most species of theEnterobacteriaceae, Staphylococcus aureus (including methicillin-resistant strains) andHaemophilus influenzae at 1 mg/l.Pseudomonas aeruginosa (MIC 90, 4 mg/l) was somewhat more resistant, andPseudomonas maltophilia (MIC 90, 16 mg/l) and theBacteroides fragilis group (MIC 90, 32 mg/l) were considerably more resistant. Overall, lomefloxacin was as active as norfloxacin, but was two- to eightfold less active than ciprofloxacin against most species tested.     

Évolution de la résistance aux antibiotiques de Pseudomonas aeruginosa dans un centre hospitalier universitaire entre 2002 et 2006

Aim of study

Monitor evolution of antibiotic resistance of Pseudomonas aeruginosa from 2002 to 2006 in our hospital to optimize antibiotherapy.

Patients and method

The infections/colonizations with P. aeruginosa have been identified by the hospital's informatic database. Bacteriological samples realized 48 hours after patient's admission was considered as nosocomial. A Cochran-Armitage test was conducted to assess the evolution of resistance.

Results

During this period, 2098 infections/colonizations with P. aeruginosa have been identified. Bacteriological samples (68.5%) were nosocomial. Among the β-lactam antibiotics, ceftazidime and imipenem were the most active (R = 16.8% and 15.2%, respectively), followed by piperacillin and piperacillin–tazobactam (R = 24.8%, 18.4%, respectively). Amikacin and tobramycin were more active than gentamicin (R = 19.9%; 22.2% and 40.6%, respectively). 28.9% of strains were resistant to ciprofloxacin. Nosocomial strains were significantly more resistant than non-hospital strains: ceftazidime: 17.9% versus 14.2%, p = 0.0346; ticarcillin–clavulanic acid: 47.5% versus 39.6%, p = 0.0009; piperacillin–tazobactam: 20.0% versus 14.8%, p = 0.0046; ciprofloxacin: 30.7% versus 25.2%, p = 0.0112. A significant increase in the resistance of nosocomial strains to ceftazidime, ticarcillin–clavulanic acid and piperacillin–tazobactam was noted. Resistance from non-hospital strains to fluoroquinolones, aminoglycosides, ceftazidime, piperacillin and ticarcillin–clavulanic acid decreased significantly.

Conclusion

P. aeruginosa is a predominantly nosocomial microorganism. There is a decrease of resistance for non-hospital strains. But the resistance of nosocomial strains to antibiotics widely prescribed in hospital is worrying.     

河源地区铜绿假单胞菌碳青霉烯耐药机制分析

目的研究本院铜绿假单胞菌耐碳青霉烯类抗生素的耐药现况及主要耐药机制。方法用E-test方法检测铜绿假单胞菌对哌拉西林、头孢他啶、亚胺培南、美洛培南、庆大霉素、妥布霉素、环丙沙星7种抗生素的最小抑菌浓度,用EDTA双纸片扩散法及三维实验分别对金属酶及AmpC、KPC酶表型进行确证。结果从1 068例致病菌中共分离出108例铜绿假单胞菌,18例是对亚胺培南和/或美罗培南不敏感的菌株,耐药率为16.7%,其中有9例金属酶确证实验阳性,3例为AmpC酶持续高产型菌株,KPC酶确证实验尚没有检测出阳性菌株。结论耐碳青霉烯类铜绿假单胞菌多表现为多重耐药,这是多因素共同作用的结果 。     

Evaluation of novel antipseudomonal drugs using the serum bactericidal activity test

Serum bactericidal activity against Pseudomonas aeruginosa was determined in six volunteers 1 and 4 h after administration of 2 g ceftazidime, 4 g piperacillin, 500 mg imipenem, 80 mg tobramycin and four combinations of these agents. Ceftazidime produced the highest serum bactericidal titers, killing 100% and 86% of the 50 Pseudomonas aeruginosa strains tested after 1 and 4 h respectively at a serum dilution of 18. Imipenem had lower serum bactericidal titers than ceftazidime, killing 88 % of the isolates after 1 h at a serum dilution of 18. The combination showed only slightly higher titers. Killing curves were determined for nine strains of Pseudomonas aeruginosa using undiluted volunteer serum drawn 1 h after administration of the antibiotics. The combinations ceftazidime/tobramycin and piperacillin/ tobramycin exhibited higher killing activity than the single drugs. As the activity of the aminoglycosides could be underestimated on the basis of their low serum bactericidal titers, it is concluded that determination of these titers is inappropriate for evaluating the efficacy of the aminoglycosides.