Sensitivity pattern of gram negative bacilli to three beta-lactam/beta-lactamase inhibitor combinations using the automated API system

PURPOSE: To evaluate the spectrum of activity of three beta-lactamase inhibitors such as amoxicillin/ clavulanic acid, ticarcillin/ clavulanic acid and piperacillin/ tazobactam in comparison to cephalosporins against gram negative bacilli. METHODS: Gram-negative bacilli isolated from the clinical specimens received in the laboratory were included in the study. Using the API system (bioMiotarieux) during a one-year period, a total of 1,252 Enterobacteriaceae and 385 non-fermenters were evaluated. RESULTS: The percentage resistance of the Enterobacteriaceae isolates was 82.92% to amoxicillin/ clavulanic acid, 58.22% to ticarcillin/clavulanic acid and 22.44% to piperacillin/tazobactam respectively. Pseudomonas aeruginosa showed resistance of 96% to ticarcillin/ clavulanic acid and 61% to piperacillin/ tazobactam and Acinetobacter baumannii showed 49% resistance to ticarcillin/ clavulanic acid and 77% resistance to piperacillin/ tazobactam respectively. The isolates exhibited high resistance to all the generations of cephalosporins and the other groups of antibiotics except carbapenems. CONCLUSIONS: Piperacillin/tazobactam was found to be the most active combination of the three against Enterobacteriaceae and Pseudomonas spp. and ticarcillin/clavulanic acid against Acinetobacter spp. and Stenotrophomonas maltophilia.     

Antimicrobial resistance patterns among aerobic Gram-negative bacilli isolated from patients in intensive care units: results of a multicenter study in Russia

Objective: To determine the antimicrobial resistance patterns among aerobic Gram-negative bacilli isolated from patients in intensive care units (ICUs) in different parts of Russia.
Methods: During 1995–96, 10 Russian hospitals from different geographic areas were asked to submit 100 consecutive Gram-negative isolates from patients with ICU-acquired infections. Minimal inhibitory concentrations (MICs) of 12 antimicrobials were determined by Etest and results were interpreted according to National Committee for Clinical Laboratory Standards (NCCLS) guidelines.
Results: In total, 1005 non-duplicate strains were obtained from 863 patients. The most common species were Pseudomonas aeruginosa (28.8%), Escherichia coli (21.4%), Klebsiella pneumoniae (16.7%), Proteus mirabilis (9.7%), Enterobacter spp. (8.2%) and Acinetobacter spp. (7.7%). High levels of resistance were seen to second- and third-generation cephalosporins, ureidopenicillins, β-lactam/β-lactamase inhibitor combinations and gentamicin. The most active agents were imipenem (no resistance in Escherichia coli, Klebsiella pneumoniae, Proteus mirabilis, Enterobacter spp. and Acinetobacter spp., 7% resistance in Pseudomonas aeruginosa ), amikacin (7% resistance in Pseudomonas aeruginosa and Acinetobacter spp., 4% in Enterobacter spp., 1% in Escherichia coli and Proteus mirabilis, no resistance in Klebsiella pneumoniae ) and ciprofloxacin (15% resistance in Pseudomonas aeruginosa, 5% in Enterobacter spp. and Proteus mirabilis, 2% in Klebsiella pneumoniae, 1% in Escherichia coli ).
Conclusions: Second- and third-generation cephalosporins, ureidopenicillins, β-lactam/β-lactamase inhibitor combinations and gentamicin cannot be considered as reliable drugs for empirical monotherapy for aerobic Gram-negative infections in ICUs in Russia.     

Detection of resistance due to inducible beta-lactamase in Enterobacter aerogenes and Enterobacter cloacae.

Thirty-six of 36 strains of Enterobacter cloacae and E. aerogenes with inducible beta-lactamase developed resistance when cefoxitin (inducer) was added to cefuroxime disks. Constitutive beta-lactamase producers (n = 23) were all resistant to cefuroxime. Cefuroxime resistance correlated with the amount of induced or constitutive beta-lactamase. Cefuroxime was a better indicator of induced resistance than cefamandole, cefazolin, cephalothin, ceftriaxone, cefotaxime, ticarcillin with or without clavulanic acid, or cefotetan. Induction by addition of cefoxitin to disks occasionally reduced zone sizes but not enough to change interpretations for ceftazidime, ceftizoxime, aztreonam, cefoperazone with or without sulbactam, and piperacillin with or without tazobactam. Most enterobacters were resistant to cefmetazole. The cefoxitin inducer-cefuroxime indicator method can be used in routine clinical laboratories to detect latent resistance due to chromosomally mediated inducible beta-lactamase in enterobacters.     

Predicting Susceptibility of Streptococcus pneumoniae to Ceftriaxone and Cefotaxime by Cefuroxime and Ceftizoxime Disk Diffusion Testing

In this study, disk diffusion testing with ceftizoxime and cefuroxime was evaluated for use in predicting the susceptibility of Streptococcus pneumoniae to ceftriaxone and cefotaxime. Of the 194 isolates included in this study, 138 were susceptible, 34 were intermediate, and 22 were resistant to cefotaxime by MIC testing; 138 isolates were susceptible, 35 were intermediate, and 21 were resistant to ceftriaxone by MIC testing. A zone of inhibition around the cefuroxime disk of >/=32 mm correctly categorized 101 of 138 isolates as susceptible to cefotaxime and ceftriaxone. A zone of inhibition around the ceftizoxime disk of >/=26 mm correctly categorized 111 of 138 isolates as susceptible to cefotaxime and 114 of 138 as susceptible to ceftriaxone. We conclude that disk diffusion can separate S. pneumoniae isolates susceptible to ceftriaxone and cefotaxime from those that are not susceptible. Isolates not falling into the susceptible category by disk diffusion require additional testing to determine the MIC.     

Different trends in antibiotic resistance rates at a university teaching hospital

Objectives  To investigate long-term trends in antibiotic resistance of common bacterial species isolated at a university hospital and in its intensive care units (ICUs).
Methods  Levels of antibiotic resistance of common bacterial pathogens were investigated at the Karolinska Hospital during the 12-year period 1988–99. Resistance rates were analyzed for the entire hospital, as well as for ICUs combined.
Results  At the Karolinska Hospital, we found increased ciprofloxacin resistance among Escherichia coli isolates, from 0% in 1991 to 11% in 1999. In the ICUs, the corresponding increase was from 0% to 4.8% during the same period. Co-trimoxazole resistance levels increased from 7.5% to 14%, with lower levels for the ICUs. For ampicillin, cefuroxime, and gentamicin, the levels of resistance were similar in the whole hospital and in the ICUs. Among Pseudomonas aeruginosa isolates, imipenem resistance was higher in the ICUs. For ciprofloxacin, resistance increased from 2.5% in 1991 to 13% in 1999 in the whole hospital, with similar figures for the ICUs.
Conclusion  The resistance rates at the Karolinska Hospital were still generally low, but were increasing for some antibiotic–microbe combinations. The results emphasize the importance of including all sectors of a hospital in resistance surveillance studies, and also the value of long surveillance periods.     

Antibiotic resistance monitoring of nosocomial clinical isolates

The authors evaluate the epidemiological trend of in vitro resistance of 2,196 clinical isolates, chiefly Gram-negative, in Caltagirone hospital in 1998/99 to piperacillin-tazobactam, piperacillin, cefotaxime, ceftazidime, ceftriaxone, imipenem, ciprofloxacin and tobramicin. The resistance percentage is reported for each year in order to study the phenomenon in time. The following results were obtained: resistance frequently increases or rarely stays constant in time for all antibiotics used; the resistance percentage is very high for some strains of bacteria; monitoring of resistance in a hospital can help in choosing the empirical therapy. Piperacillin-tazobactam, imipenem and ciprofloxacin were the most active drugs against clinical isolates.     

Resistance to second- and third-generation cephalosporins among Escherichia coli and Klebsiella species is rare in Finland

Objective: To investigate the antimicrobial resistance of Escherichia coli and Klebsiella spp. from pus, urine and respiratory specimens, with particular emphasis on the detection of third-generation cephalosporin resistance.
Methods: E. coli (698) and Klebsiella sp. (476) strains from pus, respiratory and urinary specimens from hospital patients were collected from 19 laboratories. Data about consumption of third-generation cephalosporins and cefuroxime were collected from 24 hospitals. Antimicrobial susceptibility was tested with disk diffusion in primary laboratories and by an agar dilution method. Extended-spectrum β-lactamase (ESBL) production was studied with a double disk synergy test and an ESBL Etest. The β-lactamase classes were characterized with polymerase chain reaction probes of the TEM and SHV β-lactamase families and isoelectric focusing.
Results: Only 0.6% of E. coli and 2.3% of Klebsiella spp. strains were resistant or intermediately resistant to cefotaxime, ceftriaxone and/or ceftazidime. The ESBL producers detected comprised one E. coli harboring TEM-like genes and five Klebsiella pneumoniae strains, two of which harbored SHV-like genes, two TEM-like genes and one both. Although consumption of cefuroxime has increased in the years 1990–1994, from 3.48 to 5.84 defined daily doses/100 bed-days, and the consumption of third-generation cephalosporins from 1.25 to 1.94 defined daily doses/100 bed-days, cefuroxime resistance of E. coli was only 3%.
Conclusion: Although the use of broad-spectrum cephalosporins has increased, resistance to second- and thirdgeneration cephalosporins is still rare in Finland.     

Automated direct screening for resistance of Gram-negative blood cultures using the BD Kiestra WorkCell

Early detection of resistance in sepsis due to Gram-negative organisms may lead to improved outcomes by reducing the time to effective antibiotic therapy. Traditional methods of resistance detection require incubation times of 18 to 48 h to detect resistance. We have utilised automated specimen processing, digital imaging and zone size measurements in conjunction with direct disc susceptibility testing to develop a method for the rapid screening of Gram-negative blood culture isolates for resistance. Positive clinical blood cultures with Gram-negative organisms were prospectively identified and additional resistant mock specimens were prepared. Broth was plated and antibiotic-impregnated discs (ampicillin, ceftriaxone, piperacillin–tazobactam, meropenem, ciprofloxacin, gentamicin) were added. Plates were incubated, digitally imaged and zone sizes were measured using the BD Kiestra WorkCell laboratory automation system. Minimum, clinically useful, incubation times and optimised zone size cut-offs for resistance detection were determined. We included 187 blood cultures in the study. At 5 h of incubation, > 90% of plates yielded interpretable results. Using optimised zone size cut-offs, the sensitivity for resistance detection ranged from 87 to 100%, while the specificity ranged from 84.7 to 100%. The sensitivity and specificity for piperacillin–tazobactam resistance detection was consistently worse than for the other agents. Automated direct disc susceptibility screening is a rapid and sensitive tool for resistance detection in Gram-negative isolates from blood cultures for most of the agents tested.     

Correlation of TEM, SHV and CTX-M extended-spectrum beta lactamases among Enterobacteriaceae with their in vitro antimicrobial susceptibility

Purpose: The present study was carried out to characterize the ESBL types and evaluated their in vitro activity against a collection of Gram negative bacteria (GNB) from a multicentric Indian surveillance study. Material and Methods: During January 2005 to June 2006, six tertiary care centres in India forwarded 778 non-duplicate GNB to our reference laboratory. Three hundred GNB from this collection were selected based on clinical significance and were used in the present study. Tested isolates included Escherichia coli (167), Klebsiella spp. (122) and Enterobacter spp. (11). ESBL screening and confirmation was performed for all the isolates. Minimum inhibitory concentration of imipenem, meropenem, ertapenem, levofloxacin, amikacin, piperacillin/tazobactam and ceftriaxone was determined by the E-test method. Molecular typing of the ESBLs was performed by polymerase chain reaction among the 121 selected isolates. Results: The study showed excellent susceptibility among the strains to imipenem (100%), meropenem (100%) and ertapenem (98.7%); good susceptibility to amikacin (89.7%) and piperacillin/tazobactam (85.3%) was observed. TEM and CTX-M were predominantly found in E. coli (39.2%) while, among the Klebsiella spp., TEM, SHV and CTX-M occurred together in 42.6% of the isolates. Conclusion: More than one ESBL was produced by many strains, and this was correlated with increased resistance levels. Carbapenems continue to show good in vitro activity and ertapenem is a potential alternative to imipenem and meropenem. Continued antimicrobial resistance surveillance is warranted in light of these findings.     

Mechanisms of resistance in Enterobacteriaceae towards beta-lactamase antibiotics

Except for Salmonella spp., all Enterobacteriaceae produce intrinsic chromosomal encoded beta-lactamases which, beside their physiologic role in cell-wall synthesis and natural beta-lactam protection, are responsible for intrinsic resistance of individual species among Enterobacteriaceae. E. coli and Shigella spp. produce a small amount of AmpC beta-lactamases and are susceptible to ampicillin and other beta-lactam antibiotic agents. Enterobacter spp, C. freundii, Serratia spp., M. morganii, P. stuarti and P. rettgeri produce small amounts of inducible AmpC beta-lactamases which are not inhibited by beta-lactamases inhibitor, causing intrinsic resistance to ampicillin, co-amoxiclav and first-generation cephalosporins. K. pneumoniae produces small amounts of SHV-1 beta-lactamases, and K. oxytoca chromosomal K1 beta-lactamase, causing resistance to ampicillin, carbencillin, ticarcillin and attenuated zone of inhibition to piperacillin, compared to piperacillin with tazobactam. They are susceptible to beta-lactamase inhibitors. Whereas P. mirabilis shows a minor chromosomal expression of beta-lactamases, P. vulgaris produces chromosomal beta-lactamases of class A (cefuroximases), causing resistance to ampicillin, ticarcillin, and first- and second-generation cephalosporins. Antibiotics have caused the appearance of acquired or secondary beta-lactamases, with the sole function of protecting bacteria from antibiotics. The production of broad-spectrum beta-lactamases (TEM-1, TEM-2, SHV-1, OXA-1) results in resistance to ampicillin, ticarcillin, first-generation cephalosporins and piperacillin. A high level of beta-lactamases leads to resistance to their inhibitors. The plasmid-mediated extended-spectrum beta-lactamases (ESBLs) are of increasing concern. Most are mutants of classic TEM- and SHV-beta-lactamases types. Unlike these parent enzymes, ESBLs hydrolyze oxymino-cephalosporins such as cefuroxime, cefotaxime, ceftriaxone, ceftizoxime, ceftazidime, cefpirome and cefepime, aztreonam, as well as penicillins and other cephalosporins, except for cephamycin (cefoxitin and cefotetan). They are inhibited by beta-lactamase inhibitors. AmpC beta-lactamases are chromosomal and inducible in most Enterobacter spp., C. freundii, Serratia spp., M. morganii and Providentia spp. They are resistant to almost all penicillins and cephalosporins, to beta-lactamase inhibitors and aztreonam, and are susceptible to cefepime and carbapenems as well. Plasmid-mediated AmpC beta-lactamases have arisen through the transfer of chromosomal genes for the inducible AmpC beta-lactamase onto plasmids. All plasmid-mediated AmpC beta-lactamases have similar substrate profiles to the parental enzymes from which they appear to be derived. With one exception, plasmid-mediated AmpCs differ from chromosomal AmpCs in being uninducible. The National Committee for Clinical Laboratory Standards (NCCLS) has issued recommendations for ESBL screening and confirmation for isolates of E. coli, K. pneumoniae and K. oxytoca. No NCCLS recommendations exist for ESBLs detection and reporting for other organisms or for detecting plasmid-mediated AmpC beta-lactamases. High-level expression of AmpC may prevent recognition of an ESBL in species that produce a chromosomally encoded inducible AmpC beta-lactamase. AmpC-inducible species (e. g. Enterobacter spp. and C. freundii) can be recognized by cefoxitin/cefotaxime disk antagonism tests. Since clinical laboratories are first to encounter bacteria with new forms of antibiotic resistance, they need appropriate tools to recognize these bacteria, including trained staff with sufficient time and equipment to follow up important observations. Because bacterial pathogenes are constantly changing, training must be an ongoing process.     

中国重症监护病房1994～2001年间不常见肠杆菌科细菌耐药监测

目的　调查近 7年全国 3 2家医院重症监护病房分离的 10 2 79株革兰阴性菌中 577株不常见的肠杆菌科细菌对 7种 β 内酰胺抗生素的耐药变迁。方法　 8年中共分离 577株产酸克雷伯菌、黏质沙雷菌、奇异变形杆菌、普通变形杆菌和摩根摩根菌。并分成 3组 :1994～ 1996年 ,1998～19 99年 ,2 0 0 0～ 2 0 0 1年。用Etest检测它们对下列 7种抗生素的最小抑菌浓度 (MIC) :包括亚胺培南(IPM)、头孢他啶 (CAZ)、头孢噻肟 (CTX)、头孢曲松 (CRO)、头孢哌酮 舒巴坦 (CSL)、哌拉西林 三唑巴坦 (PTZ)、头孢吡肟 (FEP)。按照美国临床实验标准委员会 2 0 0 3年标准指南 (NCCLSA10 0S 13 ) 〔10〕解释MIC值为耐药、中介和敏感 ,用WHONET 5.2软件分析数据。结果　这 5种不常见肠杆菌科细菌在2 0 0 1年所有分离菌株数中的排位是 :产酸克雷伯菌第 8位 ,敏感的抗生素 (即敏感率绝大多数年份 >80 % )依次为IPM、FEP、CAZ、TZP、CSL(10 0 %～ 83 .3 % )。黏质沙雷菌第 14位 ,敏感的抗生素依次为IPM、CAZ、TZP、CSL(10 0 %～ 87% )。奇异变形杆菌第 9位 ,敏感的抗生素依次为FEP、CAZ、IPM、TZP、CTX、CRO、CSL(10 0 %～ 83 .8% )。普通变形杆菌和摩根摩根菌分别为第 16位、17位 ,敏感的抗生素依次为CSL、IPM、FEP、TZP、CRO(1     

The role of surveillance cultures in the prediction of susceptibility patterns of Gram-negative bacilli in the intensive care unit

Surveillance cultures may detect colonisation with drug-resistant Gram-negative bacteria and can be hypothesised to guide appropriate initial antibiotic treatment for intensive care unit (ICU) patients. We investigated the microbiological data of 228 episodes of nosocomial bloodstream infection (BSI) due to Gram-negative bacteria in an ICU in which piperacillin/tazobactam or meropenem was used empirically for serious infections, to evaluate the contribution of surveillance cultures to an appropriate choice of initial antibiotic therapy. Surveillance cultures were taken in advance of BSI in 218 (95.6%) of 228 episodes. Concordant organisms with identical identification and susceptibilities were found in prior surveillance cultures and subsequent blood cultures in 65 (29.8%) of 218 episodes. Surveillance cultures predicted resistance in 52.9% and 51.4% of BSIs caused by resistant pathogens to piperacillin/tazobactam and meropenem, respectively. The negative predictive value of surveillance cultures negative for a resistant organism also exceeded 90% for piperacillin/tazobactam and meropenem. Given that the overall resistant rates of BSI pathogens of our study were 11.3% to piperacillin/tazobactam and 16.4% to meropenem, surveillance cultures in our setting may provide important information on the probability of drug resistance of the causative pathogens and some utility in aiding empiric antibiotic therapy for ICU patients who subsequently develop BSI.     

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.     

Relationship between phylogenetic groups,antibiotic resistance and patient characteristics in terms of adhesin genes in cystitis and pyelonephritis isolates of Escherichia coli

Extraintestinal pathogenic Escherichia coli (E. coli) is considered as the main causative agent of urinary tract infections worldwide. The relationship between antimicrobial resistance, phylogenetic groups, patient characteristics and adhesin virulence genes are complex and not fully understood. In this study, among 146 urinary isolates of E. coli, phylogenetic groups and various adhesin virulence genes were examined with multiplex Polymerase Chain Reaction methods. Patient characteristics divided into sex, cystitis and pyelonephritis; community-acquired and hospital-acquired; complicated and uncomplicated infection. Antimicrobial resistance was also determined. The papAH gene was seen more often in pyelonephritis than cystitis and female than male patients. iha gene was more frequent in hospital-acquired infections than in community-acquired infections. sfa/focDE was more frequent in ampicillin, amikacin, gentamicin, nalidixic acid, norfloxacin, cefuroxime, ceftriaxone, cefazolin, cefotaxime, ciprofloxacin and trimethoprim/sulfamethoxazole susceptible and extended-spectrum β-lactamase (ESBL) and multi-drug resistance (MDR) negative isolates. focG was seen more often in nalidixic acid, norfloxacin, cefuroxime, ceftriaxone, ciprofloxacin susceptible and MDR negative isolates. fimH and papAH were more commonly observed in amoxicillin/clavulanic acid and cefotaxime susceptible isolates, respectively. iha and afa/draBC genes were more frequent in resistant isolates than the susceptible ones; for iha, in ampicillin, amoxicillin/clavulanic acid, nalidixic acid, cefuroxime, ceftriaxone resistant and ESBL and MDR positive isolates; for afa/draBC, in cefotaxime, cefuroxime, ciprofloxacin, trimethoprim/sulfamethoxazole resistant and ESBL and MDR positive isolates, this trend was observed. ST 131 E. coli virulence gene pattern has a direct effect on resistance profile. Isolates belong to that clonal group has MDR and commonly harbour afa/draBC and iha genes. Our findings may provide new insights into the relationships between pathogenesis, patient characteristics and resistance of E. coli UTI.     

Concentration-dependency of β-lactam-induced filament formation in Gram-negative bacteria

Ceftazidime and cefotaxime are β-lactam antibiotics with dose-related affinities for penicillin-binding protein (PBP)-3 and PBP-1. At low concentrations, these antibiotics inhibit PBP-3, leading to filament formation. Filaments are long strands of non-dividing bacteria that contain enhanced quantities of endotoxin molecules. Higher concentrations of ceftazidime or cefotaxime cause inhibition of PBP-1, resulting in rapid bacterial lysis, which is associated with low endotoxin release. In the present study, 37 isolates of Escherichia coli , Klebsiella spp . , Pseudomonas aeruginosa and Acinetobacter spp . were studied over a 4-h incubation period in the presence of eight concentrations of ceftazidime or cefotaxime. As resistance of Gram-negative bacteria is an emerging problem in clinical practice, 14 isolates of E. coli and Klebsiella pneumoniae that produced extended-spectrum β-lactamases (ESBLs) were also investigated. Morphological changes after exposure to the β-lactam antibiotics revealed recognisable patterns in various bacterial families, genera and isolates. In general, all isolates of Enterobacteriaceae produced filaments within a relatively small concentration range, with similar patterns for E. coli and K. pneumoniae . Pseudomonas and Acinetobacter spp. produced filaments in the presence of clinically-relevant concentrations of both antibiotics as high as 50 mg/L. In all genera, filament-producing capacity was clearly related to the MIC. Ceftazidime induced filament production in more isolates and over wider concentration ranges than did cefotaxime. Interestingly, ESBL-producing isolates were not protected against filament induction. The induction of filament production may lead to additional risks during empirical treatment of severe infections.     

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.     

Molecular surveillance of European quinolone-resistant clinical isolates of Pseudomonas aeruginosa and Acinetobacter spp. using automated ribotyping

Nosocomial isolates of Pseudomonas aeruginosa and Acinetobacter spp. exhibit high rates of resistance to antibiotics and are often multidrug resistant. In a previous study (D. Milatovic, A. Fluit, S. Brisse, J. Verhoef, and F. J. Schmitz, Antimicrob. Agents Chemother. 44:1102-1107, 2000), isolates of these species that were resistant to sitafloxacin, a new advanced-generation fluoroquinolone with a high potency and a broad spectrum of antimicrobial activity, were found in high proportion in 23 European hospitals. Here, we investigate the clonal diversity of the 155 P. aeruginosa and 145 Acinetobacter spp. sitafloxacin-resistant isolates from that study by automated ribotyping. Numerous ribogroups (sets of isolates with indistinguishable ribotypes) were found among isolates of P. aeruginosa (n = 34) and Acinetobacter spp. (n = 16), but the majority of the isolates belonged to a limited number of major ribogroups. Sitafloxacin-resistant isolates (MICs > 2 mg/liter, used as a provisional breakpoint) showed increased concomitant resistance to piperacillin, piperacillin-tazobactam, ceftriaxone, ceftazidime, amikacin, gentamicin, and imipenem. The major ribogroups were repeatedly found in isolates from several European hospitals; these isolates showed higher levels of resistance to gentamicin and imipenem, and some of them appeared to correspond to previously described multidrug-resistant international clones of P. aeruginosa (serotype O:12) and Acinetobacter baumannii (clones I and II). Automated ribotyping, when used in combination with more discriminatory typing methods, may be a convenient library typing system for monitoring future epidemiological dynamics of geographically widespread multidrug-resistant bacterial clones.     

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.     

Screening for cephalosporin-resistant Streptococcus pneumoniae with the Kirby-Bauer disk susceptibility test.

Kirby-Bauer disk susceptibility tests with five standard cephalosporin disks were performed on 23 penicillin-resistant Streptococcus pneumoniae isolates for which ceftriaxone MICs were 0.125 to 4 micrograms/ml. Cefuroxime disk inhibition zone diameters distinguished clearly isolates for which ceftriaxone MICs were > or = 2 micrograms/ml from more susceptible strains, whereas cephalothin, ceftizoxime, cefotaxime, and ceftriaxone disks distinguished these isolates less clearly than the cefuroxime disk did.     

beta-Lactam antibiotic modulation of murine neutrophil cytokinesis.

Fourteen cephalosporins, 11 penicillins and 1 monobactam were evaluated for their in vitro modulation of murine neutrophil cytokinesis. As a result, the beta-lactam antibiotics were placed into 6 groups based on their effect on random (R) and FMLP-directed (D) migration [Group 1 (no effect): cephalosporin C; Group 2 (R-->D decreases): cloxacillin, cefotaxime, ceftazadime, cefuroxime, cephalothin, cephapirin, cephadine, nafcillin, piperacillin, ticarcillin, ampicillin, oxacillin, aztreonam; Group 3 (R increases D-->): cephaloridine; Group 4 (R increases D increases): cefsulodin; Group 5 (R increases D decreases): cefoperazone, cefoxitin, ceftriaxone, 6-amino-penicillanic acid; Group 6 (R decreases D decreases): cefadroxil, cefazolin, penicillin G, methicillin]. Trypan blue exclusion studies showed that inhibition of R and D by Group 6 beta-lactam antibiotics is not due to overt cytotoxicity. beta-lactam antibiotics inhibiting D also increased neutrophil adherence to plastic at a concentration of 1000 microM. Finally, the [Ca++] inhibitor chlorpromazine significantly abrogates beta-lactam- and FMLP-directed migration at a test concentration of 1 microM.