Antimicrobial activity and spectrum investigation of eight broad-spectrum beta-lactam drugs: a 1997 surveillance trial in 102 medical centers in the United States. Cefepime Study Group

Frequency of quinolone resistance genes among extended-spectrum β-lactamase (ESBL)-producing Escherichia coli strains isolated from urinary tract infections

Background

As an opportunistic pathogen, Escherichia coli (E. coli) is widely recognized as the main cause of nosocomial infections as well as some disorders especially those associated with urinary tract infections (UTIs). This study, therefore, sets out to determine the extent of antibiotic resistance to quinolones and to measure the frequency of qnr genes (A, B, and S) within extended-spectrum beta-lactamase (ESBL) and non-ESBL-producing strains of E. coli isolated from UTI-diagnosed patients as well as to investigate their antimicrobial susceptibility patterns for some selected antibiotics in southwest Iran.

Methods

Two hundred E. coli strains were isolated from UTI-diagnosed patients, hospitalized in nine different wards of Ahvaz Golestan Hospital between November 2015 and March 2016. The isolates were confirmed through well-practiced phenotypical methods. Moreover, the antimicrobial susceptibility test was successfully performed using a disk diffusion method. ESBL production among the isolates was screened by double disk synergism test (DDST), and the qnr genes were identified using a multiplex PCR.

Results

Out of the 200 samples collected, 167 isolates were confirmed to be E. coli strains. Maximum and minimum resistance were reported against nalidixic acid and chloramphenicol with 65.3% and 17.4%, respectively. Most of the isolates were resistant to all three types of quinolones studied in this research. Using multiplex PCR, the qnr genes were found in 100 (59.88%) strains (qnrA = 10, qnrB = 21, qnrS = 41, qnrB-S = 21, qnrB-A = 1, qnrA-S = 3, qnrA-B-S = 3), 58% of which was found among ESBL-producing isolates.

Conclusions

Resistance to quinolones antibiotics was highest among ESBL-producing isolates harboring, especially qnrS among other determinants of the qnr gene. There is a need for sensitive antibiotic stewardship especially in hospitals of Ahvaz, Khuzestan province. Further research is needed to ascertain the gravity of quinolones resistance in Iran and to quickly act against its spread among other nosocomial pathogens.

Current Issues in Gram-Negative Resistance: Extended-Spectrum Beta-Lactamases and Inducible Beta-Lactamases

The production of beta-lactamases is the most common cause of antimicrobial resistance in gram-negative bacilli. Two beta-lactamases, extended-spectrum beta-lactamases (ESBLs) and inducible beta-lactamases (IDBLs), are presently seen with increasing frequency. Treatment of severe infections due to gram-negative bacilli producing these beta-lactamases is problematic. In vitro susceptibility testing of ESBL-producing organisms remains difficult to interpret; clinical isolates sensitive to a particular antimicrobial agent at standard inoculum may become resistant when a higher inoculum is employed. Laboratory detection of IDBL-producing organisms is not yet commercially available. Due to the lack of sufficient outcome data, clinicians often have no choice but to use carbapenems empirically for the treatment of severe infections caused by organisms suspected of producing these enzymes. The widespread empiric use of carbapenems is of concern and may potentially precipitate increased bacterial resistance to this class of antimicrobial agents.

Phenotypic and molecular characterization of nosocomial K. pneumoniae isolates by ribotyping

PURPOSE

To characterize clinical isolates of Klebsiella pneumoniae by phenotypic and genotypic methods.

MATERIAL/METHODS

Over a 12-month period, 52 isolates of K. pneumoniae were isolated. Of these 52 isolates, 7 were isolated over a period of 21 days from a suspected outbreak in the Neonatal Intensive Care Unit (NICU) and 45 from sporadic cases occurring in different wards of hospital were analysed.

RESULTS

The prevalence of K. pneumoniae isolates was 4% (52/1295). Quinolones, aztreonam and amikacin showed the greatest efficacy showing >85% sensitivity. Of the 52 isolates of K. pneumoniae, 8 (15.4%) isolates were positive for ESBL-production. Among the ESBL-producing K. pneumoniae, two out of 8 (25%) and 6 out of 8 (75%) were positive for (bla)SHV and (bla)CTX-M genes respectively. Ribotyping identified 30 distinct ribogroups among 52 isolates evaluated. Seven NICU outbreak isolates were divided into 2 ribotypes, as many as 6 belonged to one ribotype while one isolate which was isolated a week later was of a different ribotype, indicating the termination of the outbreak in the NICU. The outbreak in the NICU thus, was shown to have been caused by a single clone.

CONCLUSIONS

A high discriminatory power, ease of interpretation coupled with excellent reproducibility and stability make ribotyping a very useful technique for investigating the molecular epidemiology of nosocomial infections caused by K. pneumoniae. A regular surveillance of hospital associated infections including monitoring antibiotic sensitivity pattern of K. pneumoniae, ESBL-production and molecular characterization is mandatory to control the spread of multidrug-resistant and ESBL-producing K. pneumoniae and for epidemiological purposes especially in outbreak situations.

Three-year review of bacteriological profile and antibiogram of burn wound isolates in Van, Turkey

The risk of infection in burns is well-known. In recent decades, the antimicrobial resistance of bacteria isolated from burn patients has increased. For this reason, a retrospective study was conducted at Van Training and Research Hospital to analyze the bacterial isolates from the wounds of patients admitted to the Burn Unit and to determine the susceptibility patterns of the commonly cultured organisms over a 3-year period, January 2009 to December 2011.A total of 250 microorganisms were isolated from burn wounds of 179 patients. Our results revealed that the most frequent isolate was Acinetobacter baumannii (23.6%), Pseudomonas aeruginosa (12%), Staphylococcus aureus (11.2%), Escherichia coli (10%) respectively. Multidrug-resistance has emerged as an important concern in our burn unit. Tigecycline, and colistin were found to be the most active drugs against Acinetobacter baumannii. Carbapenems and amikacin, were found to be the most active drugs against other gram negative bacteria. Vancomycin and linezolid were active against gram positive bacteria.Aggressive infection control measures should be applied to limit the emergence and spread of multidrug-resistant pathogens.

In vitro activity of cefepime against multidrug-resistant Gram-negative bacilli, viridans group streptococci and Streptococcus pneumoniae from a cross-Canada surveillance study

OBJECTIVE

To determine the in vitro activity of cefepime against multidrug-resistant Gram-negative bacilli and Gram-positive cocci obtained from an ongoing cross-Canada surveillance study.

DESIGN

Clinical isolates of aerobic Gram-negative bacilli with inducible and constitutive chromosomally mediated cephalosporinases, viridans group streptococci and Streptococcus pneumoniae were collected from laboratories serving hospitals, nursing homes and physician offices in the community from across Canada during 1996 and 1997. Laboratories were asked to submit only clinically relevant nonduplicate isolates for susceptibility testing. In vitro antimicrobial susceptibility testing was carried out on all isolates of Gram-negative and viridans group streptococci. S pneumoniae were characterized as penicillin susceptible, intermediately resistant or highly resistant. Nonsusceptible isolates were defined as being intermediately or highly resistant (minimal inhibitory concentrations [MIC] greater than 0.06 mg/L). Only isolates of S pneumoniae that were nonsusceptible to penicillin were selected for further study. MICs were determined using a microbroth dilution technique according to the National Committee of Clinical Laboratory Standards.

RESULTS

A total of 727 Gram-negative bacilli samples were collected. No resistance to cefepime was detected with Citrobacter freundii, Serratia marcescens, Morganella morganii and Enterobacter species. Of these strains, Enterobacter species and C freundii were the most resistant to ceftazidime, cefotaxime and ceftriaxone with MIC(90S) of 32 mg/L or greater and resistance rates of 6% or greater. Resistance rates of Pseudomonas aeruginosa and Acinetobacter species to cefepime were 4.8% and 3%, respectively. The two organisms had similar rates of resistance to ceftazidime. Less than 3% of the Gram-negative bacilli were resistant to imipenem and meropenem. There were 153 viridans group streptococci, of which 22 (14.4%) were resistant to penicillin. Of 1287 S pneumoniae samples, 193 (15%) were nonsusceptible to penicillin. Cefepime, ceftriaxone and cefotaxime had comparable activity against all isolates of viridans group streptococci and S pneumoniae.

CONCLUSIONS

Cefepime demonstrated excellent in vitro activity against Gram-negative bacilli with inducible and constitutive chromosomally mediated cephalosporinases, and had equal or superior activity versus comparator beta-lactams against all isolates of viridans group streptococci and S pneumoniae.

Cefepime

Cefepime (Maxipime), Maxcef, Cepimax, Cepimex, Axepim, a parenteral fourth-generation cephalosporin, is active against many organisms causative in pneumonia. Cefepime has in vitro activity against Gram-positive organisms including Staphylococcus aureus and penicillin-sensitive, -intermediate and -resistant Streptococcus pneumoniae similar to that of cefotaxime and ceftriaxone. Cefepime also has good activity against Gram-negative organisms, including Pseudomonas aeruginosa, similar to that of ceftazidime. Importantly, cefepime is stable against many of the common plasmid- and chromosome-mediated beta-lactamases and is a poor inducer of AmpC beta-lactamases. As a result, it retains activity against Enterobacteriaceae that are resistant to third-generation cephalosporins, such as derepressed mutants of Enterobacter spp. Cefepime may be hydrolyzed by the extended-spectrum beta-lactamases produced by some members of the Enterobacteriaceae, but to a lesser extent than the third-generation cephalosporins. Monotherapy with cefepime 1 or 2g, usually administered intravenously twice daily, was as effective for clinical and bacteriological response as ceftazidime, ceftriaxone or cefotaxime monotherapy (1 or 2g two or three times daily) in a number of randomized, clinical trials in hospitalized adult, or less commonly, pediatric, patients with generally moderate to severe community-acquired or nosocomial pneumonia. More limited data indicated that monotherapy with cefepime 2g three times daily was also as effective in treating patients with nosocomial pneumonia as imipenem/cilostatin 0.5g four times daily, and when combined with amikacin, cefepime was as effective as ceftazidime plus amikacin. Patients with pneumonia who failed to respond to previous antibacterial therapy with penicillins or other cephalosporins responded to treatment with cefepime. Cefepime is generally well tolerated, with a tolerability profile similar to those of other parenteral cephalosporins. In clinical trials, the majority of adverse events experienced by cefepime recipients were mild to moderate and reversible. The most common adverse events with a causal relationship to cefepime reported in clinical trials included rash and diarrhea. Other, less common, adverse events included pruritus, urticaria, nausea, vomiting oral candidiasis, colitis, headache, fever, erythema and vaginitis.

CONCLUSION

Cefepime is an established and generally well tolerated parenteral drug with a broad spectrum of antibacterial activity which, when administered twice daily, provides coverage of most of the pathogens that may be causative in pneumonia. In randomized clinical trials in hospitalized patients with generally moderate to severe community-acquired or nosocomial pneumonia, cefepime monotherapy exhibited good clinical and bacteriological efficacy. Cefepime may become a preferred antibacterial agent for infections caused by Enterobacter spp. With prudent use in order to prevent the emergence of resistant organisms, cefepime will continue to be a suitable option for the empiric treatment of pneumonia.

Molecular characteristics of extended spectrum beta-lactamases in Escherichia coli and Klebsiella pneumoniae and the prevalence of qnr in Extended spectrum beta-lactamase isolates in a tertiary care hospital in Korea

PURPOSE

Extended spectrum beta-lactamases (ESBLs) are cephalosporinases that confer resistance to a wide variety of oxyimino cephalosporins and create serious therapeutic problems. In addition, the quinolone resistance qnr genes are becoming increasingly prevalent in clinical isolates, some of which also produce ESBL. This study was designed to evaluate the occurrence and genotypic distribution of ESBL producing Escherichia coli (E. coli) and Klebsiella pneumoniae (K. pneumoniae) as well as the prevalence and distribution of qnr genes in ESBL-producing isolates in a tertiary care hospital in Korea.

MATERIALS AND METHODS

We tested a total of 111 ESBL-producing isolates of E. coli and K. pneumoniae, which were collected at Kyung Hee Medical Center from November 2006 to June 2008. ESBL production was determined by the Clinical and Laboratory Standards Institute (CLSI) ESBL confirmatory test. The cefotaxime and ceftazidime resistance of the ESBL-producers were transferred to azide-resistant E. coli J53 by conjugation. The presence and identity of ESBL and qnr genes were determined by polymerase chain reaction (PCR) and nucleotide sequencing.

RESULTS

The prevalence of ESBLs was 17.7% (297/1,680) of E. coli and 26.5% (240/904) of K. pneumoniae in our hospital during the study periods. Of the 111 collected isolates, 69 isolates were E. coli and 42 isolates were K. pneumoniae. The most prevalent ESBL genotype was CTX-M15. Among the ESBL-producing isolates, 4 E. coli (5.8%) and 17 K. pneumoniae (40.5%) contained qnr genes. qnrB4 was the most frequent type in both E. coli and K. pneumoniae.

CONCLUSION

CTX-M15 was the most frequently encountered ESBL. In addition, a high prevalence of qnr genes among ESBL-producing K. pneumoniae was identified in this study.

The technical aspects and clinical significance of detecting extended-spectrum beta-lactamase-producing Enterobacteriaceae at a tertiary-care hospital in Kuwait

Extended-spectrum beta-lactamase (ESBL) production by Enterobacteriaceae is an emerging problem. This 3-year prospective study was undertaken to determine the prevalence of such enzymes among the clinically significant isolates of the Enterobacteriaceae family gathered from patients, and to evaluate the different techniques for their detection as well as their clinical significance. Members of the Enterobacteriaceae family isolated from blood, inhibited by the third-generation cephalosporins with minimum inhibitory concentrations (MICs) of < or =2 microg/ml and MIC < or =8 microg/ml and isolates from other sources inhibited by MIC < or =8 microg/ml were also investigated for ESBL production by VITEK2 and E test. Their clinical significance in septicemic patients was analyzed. Out of 3,215 isolates, 1018 (31.7%) were ESBL-producers by both VITEK2 and E test. Of these, 428 (42%) were Klebsiella pneumoniae and 376 (37.0%) were Escherichia coli with overall prevalence rates of 13.3% and 11.7%, respectively. There were a total of 184 septicemic patients infected by ESBL-producing Enterobacteriaceae out of which 134 (73%) needed modification of therapy; most (58%) of these patients were initially on third-generation cephalosporin therapy. A total of 58 (31.5%) patients were infected by ESBL-producing blood isolates which were inhibited by cefotaxime/ceftriaxone at MICs =8 microg/ml (within the susceptibility range). Resistance to both aminoglycosides and quinolones were significantly higher among ESBLproducing isolates compared to non-producers (P <0.05). This study highlights a high prevalence of ESBL-producing Enterobacteriaceae in a major tertiary teaching hospital in our country and demonstrates that almost a third of the ESBL-producing Enterobacteriaceae blood isolates would have been released as susceptible by routine susceptibility testing; a finding inimical to optimal therapeutic success.

The safety of cefepime in the treatment of infection

BACKGROUND

Cefepime is a fourth-generation cephalosporin usually reserved for treating severe nosocomial pneumonia, as well as empirical treatment of febrile neutropenia, uncomplicated and complicated urinary tract infections, uncomplicated skin and skin structure infections, and complicated intra-abdominal infections.

OBJECTIVE

Since reports of neurotoxic effects and of an all-cause mortality higher with cefepime than with comparators have created some concerns regarding its safety, this paper reviews data available in the PubMed database up to December 2007 on cefepime safety.

METHODS

Literature data from PubMed obtained by combining cefepime and safety, or cefepime and clinical trials, were examined.

RESULTS/CONCLUSIONS

Caution in the use of cefepime should be adopted until new evidence on cefepime safety is available.

Treatment of Citrobacter kosen Infection with Ciprofloxacin and Cefotaxime in a Preterm Infant

Objective:

To report a case of successful treatment of Citrobacter koseri infection in a preterm infant as a means of challenging the current treatment recommendations on the basis of pharmacodynamic and pharmacokinetic considerations.

Case Summary:

A premature infant was diagnosed with C. koseri sepsis after 3 weeks in intensive care. Concern for meningitis was based on the propensity for central nervous system (CNS) involvement with Citrobacter infection along with new findings of ventriculomegaly and hydrocephalus shown on cranial ultrasound (CUS). The infant was treated with ciprofloxacin 10–20 mg/day and cefotaxime 100 mg/day for 21 days. After treatment, lumbar puncture was normal, follow-up CUS returned to baseline, and the Infant passed a hearing screen after discharge. A favorable outcome was achieved in this case.

Discussion:

Approximately 76% of neonatal patients Infected with C. koseri develop brain abscesses. The mortality rate for meningitis due to Citrobacter sop is approximately 30%, and of the infants who survive, more than 80% have some degree of mental retardation. Third-generation cephalosporins and aminoglycosides are traditional therapies against this infection. The current antibiotic strategies have failed to prevent the high rates of morbidity and mortality associated with Citrobacter infections. A possible basis for these poor outcomes is failure to apply appropriate pharmacokinetic and pharmacodynamic principles in selecting antibiotics that will achieve adequate concentrations to kill the bacteria in granulocytes within the CNS. Based on favorable sensitivity data, penetration into neutrophils and the CNS, and favorable toxicity profiles, ciprofloxacin and meropenem would appear to be the most appropriate antibiotic treatment options for systemic infection or meningitis caused by C. koseri.

Conclusions:

Ciprofloxacin and meropenem should be considered antibiotic treatment options for systemic infection or meningitis caused by G koseri.

Tigecycline: in-vitro performance as a predictor of clinical efficacy

The incidence of nosocomial disease caused by Gram-negative pathogens is increasing, and infections caused by Enterobacter, Klebsiella, Acinetobacter, Escherichia coli and Pseudomonas aeruginosa are more commonly refractive to traditional antimicrobial agents, including aminoglycosides, fluoroquinolones and broad-spectrum cephalosporins. The most important mechanism of resistance to beta-lactam antibiotics among Gram-negative bacilli involves the production of beta-lactamases. Extended-spectrum beta-lactamases are particularly worrisome, since they are often associated with multidrug resistance phenotypes, which can pose a significant therapeutic challenge. Novel agents for the treatment of Gram-negative infections are uncommon, as recent emphasis has been placed on the development of agents targeting drug-resistant strains of Gram-positive bacteria, e.g., streptococci, enterococci and staphylococci. Tigecycline, a semi-synthetic derivative of minocycline, has a unique and novel mechanism of action, which not only allows this agent to overcome the well-known tet gene-encoded resistance mechanisms, but also maintains its activity against Gram-negative pathogens producing a broad array of extended-spectrum beta-lactamases. Tigecycline is the first example of a new class of glycylcyclines with activity against a wide range of clinically important Gram-negative pathogens. Tigecycline has potent antimicrobial activity, and has been associated with an excellent therapeutic response in animal infection models and recently reported clinical trials, which reflect the effectiveness of tigecycline against pathogens causing intra-abdominal, skin and soft-tissue infections, including susceptible or multidrug-resistant strains of most Enterobacteriaceae, as well as anaerobic pathogens.

Intra-abdominal infections: considerations for the use of the carbapenems

Intra-abdominal infection remains a common and frequently severe medical condition, carrying with it significant morbidity and mortality. These infections are almost always polymicrobial in nature as they are caused by mixed aerobic/anaerobic intestinal flora. Despite substantial improvements in both the medical and surgical management of these infections over the last several decades, there remains an opportunity to further enhance the utilization of adjunctive antibiotic therapy. As a result of the epidemiology and the current resistance profile of the infecting pathogens, the carbapenems represent a class of antibiotics that are considered appropriate for the treatment of severe intra-abdominal infections. This review will discuss the classification and microbiology of these infections and emerging resistance in the pathogens of interest. The review also and focuses on the role of the carbapenems in the management of the constellation of diseases known as intra-abdominal infection.

Bactericidal activities of meropenem and ertapenem against extended-spectrum-beta-lactamase-producing Escherichia coli and Klebsiella pneumoniae in a neutropenic mouse thigh model

The purpose of this study was to examine the in vivo efficacies of meropenem and ertapenem against extended-spectrum-beta-lactamase (ESBL)-producing isolates with a wide range of MICs. Human-simulated dosing regimens in mice were designed to approximate the free drug percent time above the MIC (fT>MIC) observed for humans following meropenem at 1 g every 8 h and ertapenem at 1 g every 24 h. An in vivo neutropenic mouse thigh infection model was used to examine the bactericidal effects against 31 clinical ESBL Escherichia coli and Klebsiella pneumoniae isolates and 2 non-ESBL isolates included for comparison at a standard 10(5) inoculum. Three isolates were examined at a high 10(7) inoculum as well. Meropenem displayed greater in vitro potency, with a median MIC (range) (microg/ml) of 0.125 (0.03 to 32), than did ertapenem, with 0.5 (0.012 to 128). Seven of the 31 ESBL isolates were removed from the efficacy analysis due to their inability to establish infection in the mouse model. When MICs were<or=1.5 microg/ml for ertapenem (<or=0.5 microg/ml for meropenem), similar reductions in CFU (approximately 2-log kill) were observed for both ertapenem (fT>MIC>or=23%) and meropenem (fT>MIC>or=75%). Ertapenem showed bacterial regrowth for seven of eight isolates, with MICs of>or=2 microg/ml (fT>MIC<or=20%), while meropenem displayed antibacterial potency that varied from a static effect to a 1-log bacterial reduction in these isolates (fT>MIC=30 to 65%). At a 10(7) inoculum, both agents eradicated bacteria due to adequate exposures (fT>MIC=20 to 45%). Due to low MICs, no difference in bacterial kill was noted for the majority of ESBL isolates tested. However, for isolates with raised ertapenem MICs of>or=2 microg/ml, meropenem displayed sustained efficacy due to its greater in vitro potency and higher resultant fT>MIC.

Predictors of In-Hospital Mortality for Bloodstream Infections Caused byEnterobacterSpecies orCitrobacter freundii

STUDY OBJECTIVE

To identify predictors of in-hospital mortality among patients with bacteremia caused by Enterobacter cloacae, Enterobacter aerogenes, or Citrobacter freundii.

DESIGN

Retrospective cohort study.

SETTING

1300-bed tertiary academic medical center.

PATIENTS

One hundred twenty-four patients who had bloodstream infections caused by E. cloacae (3), E. aerogenes (71), or C. freundii (50) between 1998 and 2004.

MEASUREMENTS AND MAIN RESULTS

Data from patients with bloodstream infections caused by Enterobacter sp or C. freundii were retrospectively segregated according to hospital survival (98 survivors, 26 nonsurvivors). Multiple patient characteristics and processes of care were evaluated to identify factors contributing to in-hospital mortality. Multiple logistic regression was performed based on univariate comparisons to determine independent risk factors for in-hospital mortality. Among the 124 cases of bacteremia, the crude in-hospital mortality rate was 21% (26 cases). Univariate analysis revealed that survivors were more likely to receive an aminoglycoside as part of their empiric antimicrobial regimen (40% [39/98]) compared with nonsurvivors (19% [5/26], p=0.05). Other factors related to antimicrobial therapy including choice and number of agents used did not differ between survivors and nonsurvivors (p>0.05). Vasopressor use (31% [30/98] vs 62% [16/26]), care in an intensive care unit (19% [19/98] vs 54% [14/26]), and acute renal failure (13% [13/98] vs 31% [8/26]) occurred more frequently in nonsurvivors (p<0.05). Multiple logistic regression identified resistance to second- or third-generation cephalosporins (adjusted odds ratio [OR] 5.16, 95% confidence interval [CI] 2.66-10.0, p=0.013), trimethoprim-sulfamethoxazole resistance (adjusted OR 5.44, 95% CI 2.53-11.7, p=0.027), and mechanical ventilation (adjusted OR 12.2, 95% CI 5.99-24.5, p<0.001) as independent determinants of mortality.

CONCLUSION

Among patients with Enterobacter sp or C. freundii bloodstream infections, those with trimethoprim-sulfamethoxazole-resistant or second or third-generation cephalosporin-resistant strains or those who required mechanical ventilation had an increased risk of mortality.

Outcome of cephalosporin treatment of bacteremia due to CTX-M–type extended-spectrum β-lactamase–producing Escherichia coli

The aim of the study was to analyze the outcome of different antibiotic treatments for bacteremia due to CTX-M-type extended-spectrum beta-lactamase (ESBL)-producing Escherichia coli. In a prospective controlled clinical study from October 2002 to April 2005, 22 consecutive cases of bacteremia due to ESBL-producing E. coli with a ceftazidime-inhibition zone diameter of > or =18 mm were studied. The Etest method was used to determine the MIC values of cefotaxime, ceftazidime, imipenem, gentamicin, and ciprofloxacin against 22 isolates of E. coli. The polymerase chain reaction and sequencing analyses were used to determine the genotypes of the ESBLs. Of these 22 episodes, 7 were treated with ceftazidime, 8 were treated with imipenem/cilastatin, and 7 were treated with cefoperazone/sulbactam after detection of bacteremia. The demographic characteristics were comparable between the 3 groups. The treatment success ratio was similar (ceftazidime 85.7%, imipenem/cilastatin 87.5%, cefoperazone/sulbactam 71.4%, P = 0.637). Difficulties arose during treatment of peritonitis caused by CTX-M-producing E. coli bacteremia. Patients with bacteremia associated with urinary tract infection or biliary tract infection had a better chance of survival. All the 22 strains of E. coli produced CTX-M ESBLs (CTX-M-3, CTX-M-14, or CTX-M-27). The MICs of ceftazidime for 22 strains of E. coli were < or =8 microg/mL. All 7 patients who received ceftazidime survived, 6 of them were cured. Treatment in one patient with a ceftazidime MIC of 2 mug/mL failed because of abdominal abscess. Treatment with ceftazidime in vivo was effective against cases of CTX-M ESBL-producing E. coli bacteremia due to urinary tract infections and biliary tract infection when the MICs of ceftazidime were < or =8 microg/mL.

Frequency of isolation and antimicrobial susceptibility of bacteria isolated from bloodstream infections at Children's Medical Center, Tehran, Iran, 1996–2000

Antimicrobial susceptibility patterns of major bloodstream pathogens from Iran provide essential information regarding the selection of antibiotic therapy for patients with bloodstream infections (BSIs) living in Iran. Unfortunately, data regarding the isolation frequency and antimicrobial susceptibility patterns of endemic BSI pathogens are scarce in Iran. To shed some light on the susceptibility patterns of BSI pathogens endemic to Tehran, Iran, we investigated the antimicrobial susceptibility patterns of 2248 bloodstream isolates from patients in Children's Medical Center (CMC) Hospital in Tehran between January 1996 and December 2000. Microbiology reports of 24600 blood specimens collected from inpatients in CMC Hospital were retrospectively reviewed. Specimen culture, bacterial identification and disk diffusion susceptibility testing were performed according to National Committee for Clinical Laboratory Standards guidelines. Overall, Gram-positive bacteria comprised 72% (1627/2248) of recovered isolates and Gram-negative bacteria comprised 28% (621/2248). Coagulase-negative staphylococci (CoNS) comprised 48.4% of all isolates, followed by Staphylococcus aureus (16.7%) and Klebsiella spp. (8.5%). Among the 621 Gram-negative organisms, Klebsiella spp. (31%) were the most frequently isolated, followed by Escherichia coli (21%) and Pseudomonas aeruginosa (17%). The rates of oxacillin resistance for S. aureus and CoNS isolates were similar (60% versus 61%); however, the rate of S. aureus vancomycin resistance was almost twice that of CoNS resistance (21% versus 11%). Over 55% of S. pneumoniae were resistant to penicillin and co-trimoxazole. Although all isolates of enterococci were susceptible to vancomycin, only 21% were susceptible to gentamicin. Among Gram-negative isolates, amikacin was shown to be very effective, with susceptibility rates of 84%. The susceptibility of Klebsiella spp. to ampicillin and co-trimoxazole was 1% and 39%, respectively. The susceptibility of Klebsiella spp., E. coli and Enterobacter spp. to ceftriaxone was 47%, 86% and 67%, respectively. There were notable differences in the order of the five most common organisms isolated from blood cultures, which can help set priorities for focused control efforts. Our findings highlight the importance of a nationwide surveillance programme to monitor the trends in isolation frequency of bacteria and their antimicrobial resistance patterns throughout Iran.

Defining the need for new antimicrobials: clinical and economic implications of resistance in the hospitalised patient

Resistance among pathogens causing the most common infections encountered in hospitalised patients is increasing. Due to this resistance, the clinical efficacy of current antimicrobial agents is decreasing against many pathogens, including Streptococcus pneumoniae, methicillin-resistant Staphylococcus aureus, vancomycin-resistant enterococci, Pseudomonas aeruginosa, extended-spectrum beta-lactamases, and AmpC beta-lactamase-producing organisms. Studies assessing the impact of these resistance mechanisms on clinical outcomes have been performed; however, studies determining the economic impact of resistance have been limited. Strategies to retain the clinical efficacy of currently available agents include the initiation of antimicrobials with efficacy against the suspected pathogen(s) based on data obtained from local antibiograms, the use of combination therapy, and pharmacodynamic optimisation. Once a broad-spectrum regimen has been initiated, de-escalation to narrow, targeted antimicrobial therapy based on susceptibility data is warranted. Despite these efforts, new antimicrobials with novel mechanisms of action are eagerly anticipated to extend the current armamentarium against the growing population of multi-drug-resistant pathogens.

Prevalence and antimicrobial susceptibility of extended-spectrum beta-lactamase-producing Escherichia coli and Klebsiella pneumoniae in a general hospital

BACKGROUND

The prevalence of extended-spectrum beta-lactamases (ESBLs) varies between countries and institutions. We studied the prevalence of ESBL among clinical isolates of Escherichia coli and Klebsiella pneumoniae and analyzed patterns of susceptibilities to different antimicrobial agents in a general hospital in Saudi Arabia over a 15-month period.

METHODS

A total of 2455 clinical isolates of E. coli and K. pneumoniae were tested for ESBL production by double-disk diffusion. The minimum inhibitory concentration to imipenem, meropenem, piperacillin-tazobactam, cefepime, ciprofloxacin, gentamicin and amikacin were determined by the agar dilution method.

RESULTS

Of the 2455 isolates of E. coli and K. pneumoniae tested, 268 (11%) produced ESBL. The ESBL phenotype was detected in 10.3% of 1674 E. coli isolates and 12.2% of 781 K. pneumoniae isolates. The majority of these isolates were from urine (57.5%) and wounds (17%). Only 7% of the blood culture isolates were ESBL-producing. Overall, carbapenems (imipenem and meropenem) had good activity against the ESBL-producing isolates tested (over 92% of isolates were susceptible). There was no difference in the activity of imipenem and meropenem against the ESBL-producing E. coli or K. pneumoniae. Over 66% of the isolates were susceptible to piperacillin-tazobactam. Susceptibilities of the isolates to amikacin varied, ranging from 72.8% for E. coli to 62% for K. pneumoniae. Gentamicin, ciprofloxacin and cefepime were active against 58.6%, 55% and 22.8% of the isolates, respectively.

CONCLUSION

Our findings demonstrate the increasing incidence of infection with ESBL-producing bacteria, and the high rates of antimicrobial resistance encountered among them. Clinicians should be familiar with the clinical importance of these enzymes and potential strategies for dealing with them.

Pathogens resistant to antimicrobial agents: epidemiology, molecular mechanisms, and clinical management

Resistance to antimicrobial drugs is increasing at an alarming rate among both gram-positive and gram-negative bacteria. Traditionally, bacteria resistant to multiple antimicrobial agents have been restricted to the nosocomial environment. A disturbing trend has been the recent emergence and spread of resistant pathogens and resistance traits in nursing homes, the community, as well as in hospitals. This article reviews the epidemiology, molecular mechanisms of resistance, and treatment options for pathogens resistant to antimicrobial drugs.

Extended-spectrum β-lactamases: implications for the clinical microbiology laboratory, therapy, and infection control

Extended-spectrum beta-lactamase (ESBL) producing gram-negative bacilli are a growing concern in human medicine today. When producing these enzymes, organisms (mostly K. pneumoniae and E. coli) become highly efficient at inactivating the newer third-generation cephaloporins (such as cefotaxime, ceftazidime, and ceftriaxone). In addition, ESBL-producing bacteria are frequently resistant to many classes of non-beta-lactam antibiotics, resulting in difficult-to-treat infections. This review gives an introduction into the topic and is focused on various aspects of ESBLs; it covers the current epidemiology, the problems of ESBL detection and the clinical relevance of infections caused by ESBL-producing organisms. Therapeutic options and potential strategies for dealing with this growing problem are also discussed in this article.

Steady-state plasma and intrapulmonary concentrations of cefepime administered in continuous infusion in critically ill patients with severe nosocomial pneumonia

OBJECTIVE

To determine the steady-state plasma and epithelial lining fluid concentrations of cefepime administered in continuous infusion in critically ill patients with severe bacterial pneumonia.

DESIGN

Prospective, open-label study.

SETTING

An intensive care unit and research ward in a university hospital.

PATIENTS

Twenty adult patients with severe nosocomial bacterial pneumonia on mechanical ventilation were enrolled.

INTERVENTIONS

All subjects received a 30-min intravenous infusion of cefepime 2 g followed by a continuous infusion of 4 g over 24 hrs. The concentrations of cefepime in plasma and epithelial lining fluid were determined at steady state after 48 hrs of therapy with high performance liquid chromatography.

MEASUREMENTS AND MAIN RESULTS

The mean +/- sd steady-state plasma and epithelial lining fluid concentrations of cefepime 4 g in continuous infusion were 13.5 +/- 3.3 microg/mL and 14.1 +/- 2.8 microg/mL, respectively, with a mean percentage penetration of cefepime into epithelial lining fluid of about 100%.

CONCLUSIONS

The administration of 4 g of cefepime in continuous infusion in critically ill patients with severe nosocomial pneumonia appears to optimize the pharmacodynamic profile of this beta-lactam by constantly providing concentrations in excess of minimal inhibitory concentration of most of susceptible organisms over the course of therapy in both serum and epithelial lining fluid.

Surveillance for antimicrobial susceptibility among clinical isolates of Pseudomonas aeruginosa and Acinetobacter baumannii from hospitalized patients in the United States, 1998 to 2001

Pseudomonas aeruginosa and Acinetobacter baumannii are the most prevalent nonfermentative bacterial species isolated from clinical specimens of hospitalized patients. A surveillance study of 65 laboratories in the United States from 1998 to 2001 found >90% of isolates of P. aeruginosa from hospitalized patients to be susceptible to amikacin and piperacillin-tazobactam; 80 to 90% of isolates to be susceptible to cefepime, ceftazidime, imipenem, and meropenem; and 70 to 80% of isolates to be susceptible to ciprofloxacin, gentamicin, levofloxacin, and ticarcillin-clavulanate. From 1998 to 2001, decreases in antimicrobial susceptibility (percents) among non-intensive-care-unit (non-ICU) inpatients and ICU patients, respectively, were greatest for ciprofloxacin (6.1 and 6.5), levofloxacin (6.6 and 3.5), and ceftazidime (4.8 and 3.3). Combined 1998 to 2001 results for A. baumannii isolated from non-ICU inpatients and ICU patients, respectively, demonstrated that >90% of isolates tested were susceptible to imipenem (96.5 and 96.6%) and meropenem (91.6 and 91.7%); fewer isolates from both non-ICU inpatients and ICU patients were susceptible to amikacin and ticarcillin-clavulanate (70 to 80% susceptible); and <60% of isolates were susceptible to ceftazidime, ciprofloxacin, gentamicin, or levofloxacin. From 1998 to 2001, rates of multidrug resistance (resistance to at least three of the drugs ceftazidime, ciprofloxacin, gentamicin, and imipenem) showed small increases among P. aeruginosa strains isolated from non-ICU inpatients (5.5 to 7.0%) and ICU patients (7.4 to 9.1%). From 1998 to 2001, rates of multidrug resistance among A. baumannii strains isolated from non-ICU inpatients (27.6 to 32.5%) and ICU patients (11.6 to 24.2%) were higher and more variable than those observed for P. aeruginosa. Isolates concurrently susceptible, intermediate, or resistant to both imipenem and meropenem accounted for 89.8 and 91.2% of P. aeruginosa and A. baumannii isolates, respectively, studied from 1998 to 2001. In conclusion, for aminoglycosides and most beta-lactams susceptibility rates for P. aeruginosa and A. baumannii were constant or decreased only marginally (</=3%) from 1998 to 2001. Greater decreases in susceptibility rates were, however, observed for fluoroquinolones and ceftazidime among P. aeruginosa isolates.

Cefepime use in a pediatric intensive care unit reduces colonization with resistant bacilli

BACKGROUND

Cefepime has activity against many hospital-acquired Gram-negative pathogens resistant to earlier beta-lactam antibiotics. This study was designed to test whether preferential use of cefepime in a pediatric intensive care unit could reduce enteric colonization with antibiotic-resistant Gram-negative rods.

METHODS

After a 6-month period of uncontrolled antibiotic use, cefepime was preferentially used during 2 years as treatment for nosocomial or serious community-acquired infection. Rectal swab specimens were obtained daily on every patient regardless of antibiotic exposure during the 6 months of uncontrolled antibiotic use and during the first and last 6 months of the 2 years of cefepime preference. The study outcome was rectal colonization with a facultative Gram-negative rod resistant to at least one of four antibiotics: cefepime; ceftazidime; gentamicin; or piperacillin-tazobactam.

RESULTS

The incidence of colonization by a resistant organism decreased only slightly during the first 6 months of cefepime use. By contrast, the number of antibiotic-resistant bacilli isolated from rectal swab specimens diminished from 27.6/100 patients during the baseline period to 12.9/100 patients by the last 6 months of the 2 years of cefepime preference (P < 0.01). The proportion of patients harboring at least one resistant organism decreased from 11.6% to 7.4% during the same time period (P < 0.01). A decrease in colonization with resistant organisms occurred for all the tested resistance phenotypes, including cefepime.

CONCLUSION

Cefepime may possess a low potential for promoting bacillary resistance in critically ill patients, suggesting that its preferential use might be a key element in limiting the presence of antibiotic resistance in the intensive care unit.

Emergence in Klebsiella pneumoniae of a chromosome-encoded SHV beta-lactamase that compromises the efficacy of imipenem

A Klebsiella pneumoniae isolate was identified that had reduced susceptibility to several expanded-spectrum cephalosporins and imipenem. That isolate produced a chromosome-encoded SHV-type beta-lactamase, SHV-38, that had an alanine to valine substitution in position Ambler 146 compared to beta-lactamase SHV-1. The kinetic parameters for purified beta-lactamases SHV-38 and SHV-1 showed that the hydrolytic spectrum of SHV-38 included only ceftazidime and imipenem. This report is the first example of an SHV-type beta-lactamase capable of hydrolyzing imipenem.

Geographic variations in activity of broad-spectrum beta-lactams against Pseudomonas aeruginosa: summary of the worldwide SENTRY Antimicrobial Surveillance Program (1997-2000)

With reports of increasing resistance to antimicrobial agents among Pseudomonas aeruginosa clinical isolates worldwide, the activities of cefepime and eight other broad-spectrum beta-lactams against 6969 isolates collected during 1997-2000 from the four regions of the SENTRY Antimicrobial Surveillance Program. P. aeruginosa isolates were tested by the reference broth microdilution method against nine beta-lactam antimicrobial agents (aztreonam, cefepime, ceftazidime, imipenem, meropenem, piperacillin +/- tazobactam, ticarcillin +/- clavulanate), three aminoglycosides (amikacin, gentamicin, tobramycin), and two fluoroquinolones (ciprofloxacin, levofloxacin). The strains were contributed by more than 100 medical centers. National Committee for Clinical Laboratory Standards criteria were used to identify susceptible and resistant isolates. P. aeruginosa strains from Latin America were generally the most resistant to all classes of antimicrobials, compared with strains from other regions. The beta-lactams exhibited a wide range of potency, with carbapenems most active (meropenem, 80-91% susceptible; imipenem, 76-88% susceptible). Piperacillin/tazobactam was the most active penicillin (77-80% susceptible), and cefepime (67-83% susceptible) had an average 2% (range, 0.7-3.5%) greater susceptibility rate than ceftazidime (66-80% susceptible) across all regions. The rank order of beta-lactam activity according to percent resistant isolates in North American P. aeruginosa strains was: meropenem (4.8% resistant) > cefepime (6.8%) > imipenem (8.6%) > piperacillin/tazobactam (10.3%) > piperacillin (12.9%). Only 2.3% and 6.5% of isolates were resistant to amikacin or tobramycin, respectively, and nearly 16% of P. aeruginosa strains were resistant to ciprofloxacin. Compared with other geographic regions, strains of P. aeruginosa remain most susceptible in North America. In all regions, aminoglycosides in combination with carbapenems, cefepime, or piperacillin/tazobactam would provide more potential antipseudomonal activity than fluoroquinolone combinations for wide-spectrum empiric regimens.

Ceftriaxone: an update of its use in the management of community-acquired and nosocomial infections

Ceftriaxone is a parenteral third-generation cephalosporin with a long elimination half-life which permits once-daily administration. It has good activity against Streptococcus pneumoniae, methicillin-susceptible staphylococci, Haemophilus influenzae, Moraxella catarrhalis and Neisseria spp. Although active against Enterobacteriaceae, the recent spread of derepressed mutants which hyperproduce chromosomal beta-lactamases and extended-spectrum beta-lactamases has diminished the activity of all third-generation cephalosporins against these pathogens necessitating careful attention to sensitivity studies. Extensive data from randomised clinical trials confirm the efficacy of ceftriaxone in serious and difficult-to-treat community-acquired infections including meningitis, pneumonia and nonresponsive acute otitis media. Ceftriaxone also has efficacy in other community-acquired infections including uncomplicated gonorrhoea, acute pyelonephritis and various infections in children. In the nosocomial setting, extensive data also confirm the efficacy of ceftriaxone with or without an aminoglycoside in serious Gram-negative infections, pneumonia, spontaneous bacterial peritonitis and as surgical prophylaxis. Outpatient use of ceftriaxone, either as part of a step-down regimen or parenterally, is a distinguishing feature of the data gathered on the agent over the last decade. The review focuses on new applications of the drug and its use in infections in which the causative pathogens or their resistance patterns have changed over the past decade. Ceftriaxone has a good tolerability profile, the most common events being diarrhoea, nausea, vomiting, candidiasis and rash. Ceftriaxone may cause reversible biliary pseudolithiasis, notably at higher dosages of the drug (>/=2 g/day); however, the incidence of true lithiasis is <0.1%. Injection site discomfort or phlebitis can occur after intramuscular or intravenous administration.

CONCLUSIONS

As a result of its strong activity against S. pneumoniae, ceftriaxone holds an important place, either alone or as part of a combination regimen, in the treatment of invasive pneumococcal infections, including those with reduced beta-lactam susceptibility. Its once-daily administration schedule allows simplification of otherwise complex regimens in a hospital setting and has also contributed to its popularity as a parenteral agent in an ambulatory setting. These properties, together with a well characterised tolerability profile, mean that ceftriaxone is likely to retain its place as an important third-generation cephalosporin in the treatment of serious community-acquired and nosocomial infections.

Comparative pharmacokinetic and pharmacodynamic profile of piperacillin/tazobactam 3.375G Q4H and 4.5G Q6H

When piperacillin/tazobactam has been used to treat hospitalized patients with serious infections, including nosocomial pneumonia caused by Pseudomonas aeruginosa, it has usually been dosed at 3.375 g q4h to provide serum concentrations above commonly encountered organisms' MICs (T > MIC) for at least 40-50% of the dosing interval. Pharmacodynamic principles suggest that a similar efficacy can be realized with extended dosing intervals when a larger dose (e.g. 4.5 g q6h) is administered, which was the objective of this study. Twelve healthy volunteers, 29.4 +/- 8.9 years of age, were enrolled in this multiple-dose, open-labeled, randomized, two-period crossover study. Blood samples were collected after the third dose and concentrations of piperacillin/tazobactam were determined with a validated HPLC method. Pharmacokinetic profiles were determined by noncompartment analysis. T > MIC of piperacillin was calculated for a range of MIC values. Piperacillin/tazobactam was well tolerated in 11 subjects who completed both regimens. The C(max), T(1/2), K, and AUC of P were significantly different according to a paired t test (p < 0.05) between two study regimens. Significant differences (p < 0.05) in tazobactam regimens were noted for C(max), and AUC. The piperacillin/tazobactam regimen of 4.5 g q6h achieved a 44% T > MIC for MIC values of < or = 16 microg/ml, while the 3.375-gram q4h regimen achieved 42% T > MIC, for MIC values of < or = 32 microg/ml. Dosage regimens for treating serious infections can be extended safely and effectively to 4.5 g q6h and obtain at least 40-50% T > MIC in the coverage of pathogens implicated with serious infections, including P. aeruginosa.

Pharmacokinetic and pharmacodynamic evaluation of two dosing regimens for piperacillin-tazobactam

STUDY OBJECTIVE

To compare the pharmacokinetic and pharmacodynamic profiles of two dosing regimens for piperacillin-tazobactam against commonly encountered pathogens. The regimens compared were piperacillin 4.0 g-tazobactam 0.5 g administered every 8 hours, and piperacillin 3.0 g-tazobactam 0.375 g administered every 6 hours.

DESIGN

Multiple-dose, open-label, randomized, crossover study.

SETTING

Clinical research center at Hartford Hospital.

SUBJECTS

Twelve healthy volunteers.

INTERVENTION

The two dosing regimens for piperacillin-tazobactam were administered intravenously in crossover design. Blood was sampled after the third dose.

MEASUREMENTS AND MAIN RESULTS

Drug concentrations were determined by a validated high-performance liquid chromatography assay. The percentage of time above minimum inhibitory concentration (%T>MIC) for piperacillin was calculated for a range of MIC values. The maximum concentration (Cmax), area under the concentration-time curve (AUC0-tau), and total clearance of piperacillin differed significantly between the two study regimens, as did the Cmax, AUC0-tau, volume of distribution, and total clearance of tazobactam (p<0.05). The piperacillin 4.0 g-tazobactam 0.5 g regimen provided 40-50% T>MIC for MIC values 8-16 microg/ml; a similar value for the piperacillin 3.0 g-tazobactam 0.375 g regimen was 16-32 microg/ml.

CONCLUSION

Although statistically significant differences in the pharmacodynamic profile were noted for the regimens, both provide adequate T>MIC against commonly encountered pathogens considered susceptible to piperacillin-tazobactam. However, for treatment of Pseudomonas aeruginosa infection, combination therapy or higher-dosage regimens (e.g., piperacillin 3.0 g-tazobactam 0.375 g every 4 hours, piperacillin 4.0 g-tazobactam 0.5 g every 6 hours, or continuous-infusion piperacillin 12 g-tazobactam 1.5 g/day) may be a prudent option when full MIC data are unavailable.

Surveillance of antimicrobial resistance in gram-negative isolates from intensive care units in Turkey: analysis of data from the last 5 years

A multicenter antimicrobial surveillance program was established in Turkey in 1995 to monitor the predominant Gram-negative pathogens from intensive care units (ICUs) and antimicrobial resistance patterns of these isolates. Sixteen hospitals participated in the study and a total of 1479 isolates from 1,100 patients were collected. The isolates were tested for their susceptibility against 13 antibiotics by E-test method. Minimum inhibitory concentrations (MICs) for each isolate were determined for imipenem, ceftazidime, ceftazidime-clavulanate, cefoperazone-sulbactam, ceftriaxone, cefepime, cefuroxime, piperacillin-tazobactam, ticarcillin-clavulanate, gentamicin, amikacin and ciprofloxacin. The most common isolates were Pseudomonas spp. (28.2%), Escherichia coli (19.2%) and Klebsiella spp. (19.1%). We found very high resistance rates to all major antibiotics that are used to treat serious infections. Although imipenem is the most active agent, it had an overall susceptibility rate of 68%. Half of the tested Klebsiella spp. strains were found to produce ESBL. This is a very high rate when compared with the literature. Cross-resistance among species was also investigated. 52% of ciprofloxacin-resistant strains were also resistant to imipenem, 80% to ceftazidime, 97% to ceftriaxone, 86% to amikacin and 19% of imipenem-resistant strains were susceptible to ceftazidime and 18% to amikacin. When susceptibilities of the years 1995 and 1999 were compared, the most interesting finding was the decrease in resistance to 3rd generation cephalosporins. In conclusion, this national clinical isolate database shows that resistance rates are high, the change over years is not predictable and continuous surveillance is necessary to monitor antimicrobial resistance and to guide antibacterial therapy.

In vitro activities of BAL9141, a novel broad-spectrum pyrrolidinone cephalosporin, against gram-negative nonfermenters

The activities of BAL9141 (formerly Ro 63-9141), a novel pyrrolidinone-3-ylidenemethyl cephalosporin, against 244 strains of gram-negative nonfermenters were evaluated. The overall MIC at which 50% of isolates are inhibited (MIC50) and the overall MIC90 were 2 and 64 microg/ml, respectively, which are similar to those of imipenem, lower than those of the other cephalosporins tested, amoxicillin, and the ticarcillin-clavulanic acid combination, and much higher than those of ciprofloxacin. BAL9141 shows species-dependent activity in vitro against a variety of gram-negative nonfermentative pathogens.

Cefepime versus ceftazidime as empiric monotherapy for fever and neutropenia in children with cancer

BACKGROUND

Monotherapy with cefepime or ceftazidime is an effective alternative to combination therapy for the treatment of febrile neutropenic adult cancer patients. We compared the efficacy and safety of cefepime and ceftazidime as empiric monotherapy of febrile neutropenia in children with cancer.

MATERIALS AND METHODS

A prospective, open label, randomized, comparative study in pediatric cancer patients was conducted at Chang Gung Children's Hospital from January 1, 2000, to April 15, 2001. Patients with fever and neutropenia (absolute neutrophil count of < or = 500/mm3) were randomized to receive either intravenous cefepime or ceftazidime (50 mg/kg/dose as two or three doses daily). Febrile episodes were classified as microbiologically documented infection, clinically documented infection or unexplained fever. Clinical response to therapy was classified as success and failure.

RESULTS

Ninety-five pediatric cancer patients with 120 febrile neutropenic episodes were randomized to receive empiric treatment with cefepime or ceftazidime. After 72 h of treatment, 82.8% (48 of 58) of the eligible patients in the cefepime group continued with unmodified therapy, compared with 87.9% (51 of 58) in the ceftazidime group. The neutrophil count was <100/mm3 at randomization for 76% of the patients in the cefepime group and 83% of those in the ceftazidime group; the median durations of neutropenia (<500/mm3) were 8.5 and 6.5 days, respectively. Of the 96 evaluable episodes the overall success rate with unmodified empiric therapy until the end of the treatment course in the cefepime group was comparable with that in the ceftazidime group (69% vs. 71%, P = 0.95). The response rate after glycopeptides were added to the regimens was 79.2% for the cefepime group and 77.1% for the ceftazidime group. The bacterial eradication rate was 33% for the cefepime group and 20% for the ceftazidime group (P = 0.85), and the rates of new infections were 10.4% vs. 4.2% (P = 0.67), respectively. Both study drugs were well-tolerated. Three (6.4%) patients in the cefepime group and 2 (4.3%) patients in the ceftazidime group died.

CONCLUSION

Cefepime appeared to be as effective and safe as ceftazidime for empiric treatment of febrile episodes in neutropenic pediatric cancer patients.

Clinical evaluation of the Vitek automated system with cards GNS 122 and 127 and VTK-R07.01 software for antimicrobial susceptibility testing of Pseudomonas aeruginosa

The performance of the Vitek Automated Susceptibility Testing System software version VTKR07.01 (bioMerieux Vitek, Hazelwood, MO), for testing Pseudomonas aeruginosa was evaluated by comparing results for 200 clinical isolates with those of disk diffusion and manual broth microtiter dilution testing. For cefepime, the restricted major error rate was 0.53% and the minor error rate was 12.5%. For piperacillin, the restricted major error rate was 2.15%. For ticarcillin/clavulanic acid, restricted very major and major error rates of 6.5% and 3.2%, respectively, occurred. The results of our study indicate that the Vitek system performs within acceptable limits when testing piperacillin, but remains problematic for testing cefepime and ticarcillin-clavulanic acid.

Pharmacokinetics of cefepime during continuous renal replacement therapy in critically ill patients

The pharmacokinetics of cefepime were studied in 12 adult patients in intensive care units during continuous venovenous hemofiltration (CVVH) or continuous venovenous hemodiafiltration (CVVHDF) with a Multiflow60 AN69HF 0.60-m(2) polyacrylonitrile hollow-fiber membrane (Hospal Industrie, Meyzieu, France). Patients (mean age, 52.0 +/- 13.0 years [standard deviation]; mean weight, 96.7 +/- 18.4 kg) received 1 or 2 g of cefepime every 12 or 24 h (total daily doses of 1 to 4 g/day) by intravenous infusion over 15 to 30 min. Pre- and postmembrane blood (serum) samples and corresponding ultrafiltrate or dialysate samples were collected 1, 2, 4, 8, and 12 or 24 h (depending on dosing interval) after completion of the drug infusion. Drug concentrations were measured using validated high-performance liquid chromatography methods. Mean systemic clearance (CL(S)) and elimination half-life (t(1/2)) of cefepime were 35.9 +/- 6.0 ml/min and 12.9 +/- 2.6 h during CVVH versus 46.8 +/- 12.4 ml/min and 8.6 +/- 1.4 h during CVVHDF, respectively. Cefepime clearance was substantially increased during both CVVH and CVVHDF, with membrane clearance representing 40 and 59% of CL(S), respectively. The results of this study confirm that continuous renal replacement therapy contributes substantially to total CL(S) of cefepime and that CVVHDF appears to remove cefepime more efficiently than CVVH. Cefepime doses of 2 g/day (either 2 g once daily or 1 g twice daily) appear to achieve concentrations adequate to treat most common gram-negative pathogens (MIC <or= 8 microg/ml) during CVVH or CVVHDF.

Therapeutic challenges associated with extended-spectrum, beta-lactamase-producing Escherichia coli and Klebsiella pneumoniae

The emergence of extended-spectrum beta-lactamase (ESBL)-producing Enterobacteriaceae, particularly Escherichia coli and Klebsiella pneumoniae, presents significant diagnostic and therapeutic challenges to the management of infections due to these organisms. Detection of resistant isolates is difficult based on routine susceptibility testing performed by a clinical microbiology laboratory. In addition, the utility of penicillins, cephalosporins, and aztreonam in treating serious infections due to these organisms is uncertain due to reports of treatment failure despite apparent in vitro susceptibility. A critical evaluation of the English literature was performed on treatment outcomes associated with ESBL-producing Enterobacteriaceae. Imipenem and extended-spectrum cephalosporins were commonly administered. Discordant outcomes in relation to in vitro susceptibility of the agent did not occur exclusively with cephalosporins but with all drugs including imipenem. Until more outcome data are available, drug selection must take into consideration whether or not an outbreak is occurring and whether therapy is empirical or definitive.

Extended-spectrum beta-lactamases: epidemiology, detection, and treatment

Extended-spectrum beta-lactamases (ESBLs) are extremely broad spectrum beta-lactamase enzymes found in a variety of Enterobacteriaceae. Most strains producing these beta-lactamases are Klebsiella pneumoniae, other Klebsiella species (i.e., K. oxytoca), and Escherichia coli. When producing these enzymes, organisms become highly effective at inactivating various beta-lactam antibiotics. In addition, ESBL-producing bacteria are frequently resistant to many classes of antibiotics, resulting in difficult-to-treat infections. Other problems due to ESBL-producing bacteria are difficulty in detecting the presence of ESBLs, limited treatment options, and deleterious impact on clinical outcomes. Clinicians should be familiar with the clinical significance of these enzymes and potential strategies for dealing with this growing problem.

Susceptibility Patterns of Select Gram-Negative Organisms after a Formulary Switch from Ceftazidime to Cefepime

Objective:

To document changes in susceptibility patterns of gram-negative organisms, including Pseudomonas aeruginosa, Enterobacter aerogenes, Acinetobacter calcoaceticus, and Serratia marcescens after a formulary switch from ceftazidime to cefepime.

Design, Setting:

Retrospective, observational study in a tertiary care, university teaching hospital.

Participants:

Adult surgical patients with culture and susceptibility data.

Main Outcome Measures:

Percent susceptible and median minimum inhibitory concentration values were evaluated for select gram-negative organisms from culture and susceptibility results. The time periods of one year before and two years after the formulary change were evaluated. Duplicate isolates were excluded. Different culture sites of infection were assessed for P. aeruginosa, including blood, urine, and lung.

Results:

A total of 957 samples from 489 patients were included. Susceptibility results after the formulary switch favored ceftazidime over cefepime for P. aeruginosa (79% vs. 54%; n = 485) and A. calcoaceticus (65% vs. 29%; n = 140). However, cefepime demonstrated greater kill rate with E. aerogenes isolates compared with ceftazidime (95% vs. 69%; n = 208). Susceptibility results were comparable with S. marcescens (100% for cefepime vs. 98% for ceftazidime). P. aeruginosa results from isolates taken from different culture sites did not differ from the overall results, as susceptibility was higher for ceftazidime compared with cefepime for all culture sites.

Conclusions:

Susceptibility to cefepime and ceftazidime is organism-specific; therefore, it may be appropriate to include both agents on the formulary and/or implement an antibiotic rotation policy.

Cefepime microbiologic profile and update

BACKGROUND

The evolution of the cephalosporin class of antibiotics through modifications of the basic cephem structure has resulted in a new generation with improved antibacterial activity. Cefepime is a prototypic agent of this new class of fourth generation cephalosporins.

OBJECTIVE

To review the microbiologic profile of cefepime.

RESULTS

Cefepime, which is a zwitterion, has a net neutral charge that allows it to penetrate the outer membrane of Gram-negative bacteria faster than third generation cephalosporins. It is more stable against beta-lactamases because of the lower affinity of the enzymes for cefepime when compared with third generation cephalosporins. As a result of these structural attributes, cefepime has in vitro activity against pathogens that are prevalent in pediatric infections. This agent offers the advantage of Gram-positive coverage similar to that of cefotaxime and ceftriaxone, as well as good activity against Pseudomonas aeruginosa and many enteric bacilli that are resistant to third generation cephalosporins, including clinical isolates of Enterobacter spp. and Citrobacter freundii.

CONCLUSIONS

Based on its spectrum of activity cefepime is an option for the treatment of pediatric infections caused by susceptible pathogens.

Microbiologic aspects of predominant bacteria isolated from the burn patients in Korea

The risk of infection in burns is well-known. In recent decades, the antimicrobial resistance of bacteria isolated from burn patients has increased. For this reason, we have carried out a study of the predominant bacterial profiles and antimicrobial resistance patterns of isolates from a burn center in Korea. A retrospective study was undertaken at Hallym University, Hangang Sacred Heart Hospital to examine the bacterial isolates from the burn patients and to compare the antibiograms of the predominant bacteria isolated from these patients with those of the other wards over a period of 3 years. Pseudomonas aeruginosa was the most common (n=2997, 45.7%) isolate from the burn patients followed by Staphylococcus aureus (n=21261, 19.2%) and Acinetobacter baumannii (n=878, 13.4%). These bacteria, isolated from the burn patients, were almost all higher in antimicrobial resistance rate than those in the non-burn patients (P<0.05). Because these bacteria showed very high resistant rates, they must be avoided in order to control a hospital-acquired infection. Our results seem helpful in providing useful guidelines for choosing effective empiric antimicrobial therapy against bacteria isolated from the burn patients in Korea.

Hospital-acquired pneumonia: risk factors, microbiology, and treatment

Pneumonia complicates hospitalization in 0.5 to 2.0% of patients and is associated with considerable morbidity and mortality. Risk factors for hospital-acquired pneumonia (HAP) include mechanical ventilation for > 48 h, residence in an ICU, duration of ICU or hospital stay, severity of underlying illness, and presence of comorbidities. Pseudomonas aeruginosa, Staphylococcus aureus, and Enterobacter are the most common causes of HAP. Nearly half of HAP cases are polymicrobial. In patients receiving mechanical ventilation, P aeruginosa, Acinetobacter, methicillin-resistant S aureus, and other antibiotic-resistant bacteria assume increasing importance. Optimal therapy for HAP should take into account severity of illness, demographics, specific pathogens involved, and risk factors for antimicrobial resistance. When P aeruginosa is implicated, monotherapy, even with broad-spectrum antibiotics, is associated with rapid evolution of resistance and a high rate of clinical failures. For pseudomonal HAP, we advise combination therapy with an antipseudomonal beta-lactam plus an aminoglycoside or a fluoroquinolone (eg, ciprofloxacin).

Antimicrobial resistance in Streptococcus pneumoniae: implications for patients with community-acquired pneumonia

Streptococcus pneumoniae is the leading cause of community-acquired pneumonia. During the past decade, the prevalence of penicillin resistance in S pneumoniae has increased dramatically, with resistance rates approaching 45% in some areas of the United States. Streptococcus pneumoniae has also acquired resistance to other commonly used antimicrobials, including cephalosporins, macrolides, and trimethoprim-sulfamethoxazole. While vancomycin and the newer quinolones are currently highly active against most strains of S pneumoniae, reduced susceptibilities to these agents have been identified in some strains. Prior use of antimicrobial agents is the major risk factor for colonization and infection with antibiotic-resistant strains. beta-Lactam antibiotics remain the treatment of choice for infections caused by susceptible S pneumoniae. The optimum therapy for penicillin-resistant strains remains unclear. Appropriate empirical therapy for patients with community-acquired pneumonia depends in part on the community-specific resistance patterns of S pneumoniae to various antibiotics. In this article, we provide an overview of the development of S pneumoniae resistance to commonly used antibiotics and discuss the implications of the development of resistance on treatment decisions.

Multidrug-resistant Pathogens: Mechanisms of Resistance and Epidemiology

Resistance to antimicrobial agents among bacteria and fungi is a persistent problem complicating the management of critically ill patients. To understand the issues involved in resistance in critical care, it is essential to understand the epidemiology and mechanisms of resistance. beta-lactam resistance in pneumococci, and penicillin and chloramphenicol resistance in Neisseria meningitidis, have complicated the management of meningitis. Vancomycin resistance in enterococci and methicillin resistance in Staphylococcus aureus have disseminated among hospitals, nursing homes and, in some cases, community patients. Glycopeptide resistance in S. aureus has recently been described in clinical isolates; the potential for spread of this resistance trait is concerning. Resistance to broad-spectrum cephalosporins is a persistent challenge in the management of infections caused by Pseudomonas areuginosa, and Enterobacter species, as well as other Enterobacteriaceae. Azole resistance in Candida species. has also complicated the treatment of nosocomial infections. Resistance to antimicrobial drugs is a persistent and emerging problem and presents major therapeutic challenges.

Cefepime versus ceftazidime as empiric therapy for fever in neutropenic patients with cancer

OBJECTIVE

To compare the efficacies of cefepime and ceftazidime as empiric therapy during the management of fever in cancer patients with chemotherapy-induced neutropenia.

METHODS

A prospective, double-blind, randomized study of cefepime 2 g every eight hours and ceftazidime 2 g every eight hours was performed in 276 adult neutropenic (absolute neutrophil count < 500/mm3) cancer patients with fever.

RESULTS

Median duration of neutropenia was five days. Sixty-one percent (n = 188) of the patients were evaluable. Treatment was successful in 57% (58/101) of cefepime-treated patients and 60% (52/87) of ceftazidime-treated patients (95% CI -18 to 12; p = 0.77). Bacteremic clearance occurred in 71% (12/17) of cefepime-treated patients and 40% (6/15) of ceftazidime-treated patients (p = 0.3). Both drugs were well tolerated.

CONCLUSIONS

Cefepime appears to be as effective as ceftazidime in the initial treatment of febrile episodes in adult cancer patients with chemotherapy-associated neutropenia of modest duration.

Endemic carbapenem-resistant Acinetobacter species in Brooklyn, New York: citywide prevalence, interinstitutional spread, and relation to antibiotic usage

Acinetobacter species are problematic nosocomial pathogens. In November 1997, pathogens isolated by microbiology laboratories were collected from 15 hospitals in Brooklyn, New York. Acinetobacter species accounted for 10% of gram-negative isolates. Only half of Acinetobacter species were susceptible to carbapenems; 11 hospitals had at least 1 isolate resistant to carbapenems. Other Acinetobacter susceptibility rates were as follows: polymyxin, 99%; amikacin, 87%; ampicillin/sulbactam, 47%; ceftazidime, 25%; and ciprofloxacin 23%. Overall, 10% were resistant to all commonly used antibiotics. Genetic analysis by use of pulsed-field gel electrophoresis of 12 carbapenem-resistant isolates revealed 4 strains that were recovered from >1 hospital, which suggests interinstitutional spread. Antibiotic usage data from 11 hospitals revealed that the use of third-generation cephalosporins was associated significantly with the percentage of carbapenem-resistant strains (P=.03). Resistant Acinetobacter species have become endemic in Brooklyn, New York. Citywide strategies that involve surveillance, infection-control practices, and the reduction of antibiotic usage may be necessary to control the spread of these pathogens.

In vitro efficacy of six cephalosporins tested against Enterobacteriaceae isolated at 38 North American medical centres participating in the SENTRY Antimicrobial Surveillance Program, 1997-1998

The SENTRY Antimicrobial Surveillance Program is an ongoing international collaboration that monitors the predominant bacterial and fungal pathogens and antimicrobial susceptibility patterns associated with community-acquired and nosocomial infections. SENTRY data on the current cephalosporin susceptibility patterns (1997-98) of North American isolates of clinically important Enterobacteriaceae were analyzed. Susceptibility to a selection of cephalosporins was assessed at a central laboratory using reference broth microdilution methods and interpretive criteria specified by the National Committee for Clinical Laboratory Standards. The third- and fourth-generation cephalosporins tested demonstrated excellent activity against Escherichia coli and Klebsiella pneumoniae, whereas some of the older agents maintained good efficacy. Extended spectrum beta-lactamases were detected in all regions of the United States and Canada (1.8-10.7%). Cefepime was the most active agent tested against pathogens with the potential for enzyme-mediated resistance due to Amp C. The third-generation agents maintained acceptable efficacy against Serratia marcescens, but were less effective against Citrobacter and Enterobacter species. The older cephalosporins were generally inadequate against these pathogens, in contrast to cefepime, which was the widest spectrum cephalosporin overall. Some significant regional variations in spectrum were detected.

Determinants of ceftriaxone clearance by continuous venovenous hemofiltration and hemodialysis

STUDY OBJECTIVE

To guide individual ceftriaxone dosages in patients receiving continuous renal replacement therapy.

DESIGN

Prospective, outpatient study.

SETTING

University-affiliated general clinical research center.

PATIENTS

Eight patients receiving hemodialysis.

INTERVENTION

We performed controlled clearance studies with three hemofilters: an acrylonitrile copolymer 0.6 m2 (AN69), polymethylmethacrylate 2.1 m2 (PMMA), and polysulfone 0.65 m2 (PS).

MEASUREMENTS AND MAIN RESULTS

Subjects received ceftriaxone 1000 mg intravenously before the start of a clearance study. The concentration of ceftriaxone in multiple plasma and dialysate-ultrafiltrate samples was determined by high-performance liquid chromatography. The diffusional clearances (Cl(diffusion)) and sieving coefficients (SC) of ceftriaxone, urea, and creatinine were compared by a mixed-model repeated-measures analysis of variance with filter and blood, dialysate inflow, or ultrafiltration rate as the main effect and patient as a random effect. The fraction of ceftriaxone bound to plasma proteins was 43 +/- 15% (range 13-92%). Concentration dependence was evident in all three groups. The fraction unbound to plasma proteins (f(up)) at the time that SCs were determined was significantly lower in the PS group (0.16 +/- 0.07) than the AN69 group (0.30 +/- 0.17, p<0.01), but similar to that in the PMMA group (0.27 +/- 0.12). Despite the higher f(up), the SC of unbound ceftriaxone with the AN69 filter (0.48 +/- 0.13) was significantly lower than values for the PMMA (0.86 +/- 0.33) and PS (0.82 +/- 0.22) groups (p<0.05). Continuous venovenous hemofiltration clearance of urea and unbound ceftriaxone increased significantly only for the PMMA (p=0.006) and PS (p=0.015) filters when the ultrafiltration rate was increased. Significant linear relationships (p<0.0001) were observed between Cl(diffusion) of unbound ceftriaxone and clearance of urea for all three filters: AN69 slope = 0.57, PMMA slope = 0.90, and PS slope = 1.02. The slope of this relationship for the AN69 filter was significantly lower than for the other two filters.

CONCLUSION

Ceftriaxone clearance was significantly increased and membrane dependent during continuous venovenous hemofiltration and continuous venovenous hemodialysis. Thus individual ceftriaxone dosages for patients receiving continuous renal replacement therapies should incorporate extracorporeal clearance.

Respiratory tract pathogens isolated from patients hospitalized with suspected pneumonia: frequency of occurrence and antimicrobial susceptibility patterns from the SENTRY Antimicrobial Surveillance Program (United States and Canada, 1997)

Thirty-seven sentinel hospitals (29 in the United States [US]; eight in Canada) collected bacterial isolates from hospitalized patients with a diagnosis of pneumonia. The antimicrobial susceptibility patterns of these pathogens were determined to more than 60 agents (40 reported) using the reference broth microdilution method described by the National Committee for Clinical Laboratory Standards. The five most frequently recorded species among the 2757 isolates collected during the study were (no. tested/%): Staphylococcus aureus (632/22.9%), Pseudomonas aeruginosa (498/18. 1%), Haemophilus influenzae (284/10.3%), Klebsiella spp. (240/8.7%), and Streptococcus pneumoniae (213/7.7%). There was a significant difference in the susceptibility to antimicrobials between the US and Canada for S. aureus to oxacillin (50.1% versus 93.8% susceptible, respectively), gentamicin (78.7% versus 97.8%), and fluoroquinolones (49.5 to 53.0% versus 89.8 to 94.9%). Amikacin (92. 8% susceptible) was the most active antimicrobial agent against P. aeruginosa, and meropenem was the most potent beta-lactam. Against H. influenzae, most drugs retained a high level of activity, whilst against the S. pneumoniae, only the newer fluoroquinolones (gatifloxacin, levofloxacin, sparfloxacin) remained highly effective in vitro. Only two antimicrobial agents (imipenem and meropenem) were >99% active against the Klebsiella spp. and Enterobacter spp. isolated in this survey (possess extended spectrum beta-lactamases or hyperproduction of Amp C cephalosporins); cefepime (95.6-100.0% susceptible) was significantly more active than other cephalosporins tested. Clonal, epidemic outbreaks of multiply resistant strains were very rare in monitored hospitals. In conclusion, important differences exist between the US and Canada in the susceptibility patterns of some respiratory tract pathogens to commonly used antimicrobial agents with Canadian strains generally being more susceptible to currently available antimicrobial agents.