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

Prevalence of extended-spectrum beta-lactamase and molecular detection of blaTEM, blaSHV, and blaCTX-M genotypes among gram-negative Bacilli isolates from hospital acquired infections in pediatrics, one institutional study

BACKGROUND

Gram-negative bacilli represents an important pathogen in hospital-acquired infections (HAIs) worldwide. The emergence of antibiotic resistance in these pathogens warrants attention for the proper management of infections. Extended-spectrum beta-lactamase (ESBL) resistance represents a major therapeutic problem in infections due to Gram-negative bacilli. The present study aimed to study the extended-spectrum beta-lactamase genes blaTEM, blaSHV, and blaCTX-M by multiplex polymerase reaction in isolated Gram-negative bacilli from HAIs in pediatric patients.

METHODS

The study included one hundred-five isolates of Gram-negative bacilli from pediatric patients with different types of HAIs. The isolates were subjected to full microbiological identification, antibiotics susceptibility by disc diffusion method, the phenotypic study of ESBL, and the genetic study of ESBL genes by multiplex PCR.

RESULTS

Fifty isolates of Gram-Negative bacilli showed ESBL activity by a phenotypic study by double disc diffusion method (50/105). All ESBL producers' isolates were positive by PCR for ESBL genes. The most frequent gene was blaTEM (64%), followed by blaSHV (30%) and CTX-M (22%). Mixed genes were found in 4 isolates (8%) for blaTEM and blaSHV, blaTEM and CTX-M. There was a significant association between PCR for ESBL genes and phenotypic ESBL detection (P = 0.001). There was significant detection of ESBL genes in E. coli (28%), followed by Enterobacter spp. (26%), Klebsiella spp. (24%), Serratia (14%), Pseudomonas spp. (6%) and Proteus (2%), P = 0.01. There Seventy percent of isolates positive for ESBL production had an insignificant association between MDR and PCR for ESBL genes (P = 0.23).

CONCLUSION

The present study highlights the prevalence of ESBL activity among clinical isolates of Gram-negative bacilli isolated from hospital-acquired infections in pediatric patients. The most common gene responsible for this activity was blaTEM gee followed by blaSHV and blaCTX-M. There was a high prevalence of multiple antibiotic resistance among isolates with ESBL activity. The finding of the present study denotes the importance of screening extended beta-lactamase among Gram-negative bacilli associated with HAIs in pediatric patients.

Prevalence of extended-spectrum β-lactamase (ESBL) and molecular detection of blaTEM, blaSHV and blaCTX-M genotypes among Enterobacteriaceae isolates from patients in Khartoum, Sudan

Introduction

the emergence of antibiotic resistance pathogens is an important health risk. Usually Gram negative bacteria acquire resistance to beta-lactam antibiotics by beta-lactamase production. The objectives of this study was to assess the prevalence of ESBL and to detect the frequency of blaTEM, blaSHV and blaCTX-M genotypes among ESBL producing Enterobacteriaceae isolates from patients in Khartoum, Sudan.

Methods

a total of 171 isolates of Enterobacteriaceae were recovered from hospitals in Khartoum, Sudan (2014 -2015) were used to detect ESBL production using disc diffusion method. blaTEM, blaSHV and blaCTX-M genes were investigated by PCR based methods using gene-specific primers.

Results

the high resistance among Enterobacteriaceae was noticed in ciprofloxacin (72%) and ofloxacin (73%). ESBL production was mainly in Escherichia Coli (38%) and Klebsiella pneumonia (34%). Prevalent genotypes were blaTEM (86%), blaCTX-M (78%) and blaSHV (28%). These were found mainly in Escherichia Coli (38%, 37%, 2%) and K. pneumonia (34%, 31%, 26.1%). The majority of ESBL producing isolates possess more than one ESBL genes.

Conclusion

the ESBL production in Enterobacteriaceae was high, with blaTEM and blaCTX-M genotypes more prevalent. Public health and laboratory standard of excellence is needed to reducing the spread of resistant pathogens.

Prevalence of blaTEM, blaSHV, and blaCTX-M Genes among ESBL-Producing Klebsiella pneumoniae and Escherichia coli Isolated from Thalassemia Patients in Erbil, Iraq

Background

Due to the recent appearance of organisms that are resistant to several drugs (multidrug-resistant) like Enterobacteriaceae that produce extended-spectrum β-lactamase (ESBL, concerns have remarkably increased regarding the suitable treatment of infections. The present study was an investigation into ESBL molecular characteristics among clinical isolates of Klebsiella pneumoniae and Escherichia coli resulting in urinary tract infections (UTIs) and their pattern of antimicrobial resistance in order to come up with helpful information on the epidemiology of these infections and risk factors accompanied with them.

Methods

In order to conduct the study, 20 K. pneumoniae and 48 E. coli were isolated and retrieved from thalassemia center in Erbil, Iraq during July 2016 and September 2016. The collected strains were analyzed and the profile of their antimicrobial susceptibility was specified. In order to spot β-lactamase genes (i.e. blaTEM, blaSHV, and blaCTX-M), polymerase chain reaction was conducted.

Results

The findings obtained from multiplex PCR assay showed that out of the collected strains of ESBL-producing E. coli, had 81% blaTEM, 16.2% blaSHV, and 32.4% blaCTX-M genes. Similarly, 64.7% blaTEM, 35.2% blaSHV, and 41.1% blaCTX-M genes existed in the isolates of K. pneumoniae. It was found that antibiotic resistance pattern of E. coli and K. pneumoniae isolates to 20 antibiotics varied widely. It was also concluded that the majority of the K. pneumoniae and E. coli isolates were multi-drug resistant (MDR). Moreover, 75% and 87.5% of respectively K. pneumoniae and E. coli isolates showed the MDR phenotypes.

Conclusion

TEM prevalence was high among other types of ESBLs. Over all, the most active antimicrobial agents in vitro remained to be the carbapenems.

The Role of Cefepime in the Treatment of Extended-Spectrum Beta-Lactamase Infections

OBJECTIVE

To review the efficacy of cefepime for use in infections caused by extended-spectrum beta-lactamase (ESBL)-producing organisms.

DATA SOURCES

A PubMed literature search (May 2000 to June 2017) was performed using the keyword cefepime and the MeSH terms beta-lactamases, cephalosporinases, and Enterobacteriaceae infections.

STUDY SELECTION AND DATA EXTRACTION

All human, English language studies evaluating cefepime use for the treatment of ESBL-producing Escherichia coli and Klebsiella pneumoniae infections were included.

DATA SYNTHESIS

Studies assessing the use of cefepime for ESBL infections are few, and clinical studies are limited by design and sample size. The largest pharmacokinetic/pharmacodynamic study, a Monte Carlo simulation using data from the U.S. SENTRY antimicrobial surveillance program, evaluating cefepime use for infections due to ESBL-producing organisms found a 95% to 100% probability of target attainment with traditional cefepime dosing regimens. Most clinical studies found that patients treated with cefepime empirically and definitively had higher rates of mortality than those treated with carbapenems. However, in concordance with other studies reporting minimum inhibitory concentration (MIC) data, lower MICs were associated with lower mortality.

CONCLUSIONS

Cefepime should be avoided for empiric treatment of suspected ESBL infections and should only be considered for definitive treatment if the MIC ≤1 µg/mL. However, the site and severity of infection, local resistance patterns, and patient-specific risk factors should also help guide antimicrobial selection.

Should the patients colonized with extended-spectrum beta-lactamase-producing Gram-negative bacilli (E-GNB) coming to hospital from the community with pneumonia get anti-E-GNB active empirical treatment?

Extended-spectrum beta-lactamases are responsible for resistance of Gram-negative bacilli to several beta-lactam antibiotics, including those prescribed for treatment pneumonia. To evaluate the importance of colonization with E-GNB for the choice of empirical treatment we performed a retrospective case-control study including 156 patients, hospitalized for treatment of pneumonia from 2009 through 2013. Empirical treatment success and in-hospital survival were significantly lower in patients colonized with E-GNB compared to non-colonized (p = 0.002, p = 0.035). When comparing subgroups of colonized patients, treatment success was significantly lower in patients who were colonized with E-GNB resistant to empirical antibiotic (p = 0.010), but not in those colonized by E-GNB susceptible to empirically given antibiotic (p = 0.104). Difference in in-hospital mortality was insignificant in both subgroups (p = 0.056, p = 0.331). The results of study suggest that an anti-E-GNB active antibiotic should be used for empirical treatment of pneumonia in E-GNB colonized patients.

Phenotypic detection of extended spectrum β-lactamase and Amp-C β-lactamase producing clinical isolates in a Tertiary Care Hospital: A preliminary study

Background:

Production of β-lactamase enzymes by Gram-negative bacteria is the most common mechanism to acquire drug resistance to β-lactam antibiotics. Limitations in detecting extended spectrum β-lactamases (ESBL) and Amp-C β-lactamases have contributed to the uncontrolled spread of bacterial resistance and are of significant clinical concern.

Materials and Methods:

A total of 148 samples was selected on the basis of resistance against third-generation cephalosporin for screening ESBLs and Amp-C β-lactamases production. These multidrug-resistant strains were phenotypically screened for ESBL production by phenotypic confirmatory disc diffusion test and double disc synergy test. Modified three-dimensional method was used for Amp-C β-lactamases detection.

Result:

Among the 148 isolates, 82 (55.40%) were ESBL producers, and 115 (77.70%) were Amp-C β-lactamases producers. Co-existence of ESBL and Amp-C was observed in 70 (47.29%) isolates. Escherichia coli was the most common ESBL and Amp-C β-lactamase producer. All ESBL producers were highly resistant to ciprofloxacin (83.10%), cotrimoxazole (95.27%), and gentamicin (89.18%). However, these bacterial strains were sensitive to imipenem 146 (98.64%) and piperacillin/tazobactam 143 (96.62%).

Conclusion:

Our study showed that ESBL producing organisms were not only resistant to cephalosporins but also to other group of drugs and also that multiple mechanisms play a role in drug resistance among Gram-negative bacteria.

Epidemiology of infections due to extended-spectrum Beta-lactamase-producing bacteria in a pediatric intensive care unit

OBJECTIVES

To determine the proportion of infections caused by extended-spectrum ß-lactamase (ESBL)-producing Klebsiella or Escherichia coli Gram-negative organisms in the pediatric intensive care unit (PICU), and to identify risk factors for these infections.

METHODS

A retrospective, single-center chart review of patients admitted to a PICU in a 5-year period with infections caused by Klebsiella species or E coli was completed. Data collected include demographics, length of stay, outcome, and relevant risk factors previously defined in the literature.

RESULTS

A total of 110 isolates were cultured from 94 patients. A total of 53% of the isolates were E coli, and the remainder were Klebsiella subspecies. Of the 110 isolates, 13 isolates (11.8%) in 7 patients were ESBL positive. The ESBL-producing isolates were equally distributed amongE coli and Klebsiella and were primarily cultured from tracheal aspirates. Most of the ESBL-positive isolates (9 of 13; 69%) were cultured from patients who received ceftazidime and/or cefotaxime in the preceding 30 days. Patients infected with E coli had higher PRISM 1 scores and were more likely to have a Foley catheter, whereas infections with Klebsiella were more common in mechanically ventilated males. Although not statistically significant, 80% of patients who were infected with non-ESBL-producing organisms survived to hospital discharge versus 57% of those infected with ESBL-producing E coli and Klebsiella.

CONCLUSIONS

Almost 12% of E coli and Klebsiella isolates in this patient population tested positive for ESBL production. ESBL production was equally distributed between E coli and Klebsiella species. These organisms were cultured from 7% of the study patients. As reported in previous studies, patients infected with ESBL-producing organisms most often had received prior cephalosporins and had a longer length of stay in the PICU.

Study of extended spectrum β-lactamase producing Enterobacteriaceae and antibiotic coresistance in a tertiary care teaching hospital

Aims:

To study the prevalence of extended spectrum β-lactamase (ESBL) producing Enterobacteriaceae and coresistance to other commonly used antibiotics from the Bhopal region of Central India.

Settings and Design:

A prospective study was conducted from September 2011 to August 2012 in Microbiology Department of our tertiary health care center.

Materials and Methods:

A total of 1044 Enterobacteriaceae isolates were recovered from various specimens. ESBL production was detected by using Clinical Laboratory Standard Institute (CLSI) that described the phenotypic confirmatory test along with routine antibiotic susceptibility testing.

Statistical Analysis:

Two-tailed Z-test.

Results:

Escherichia coli was the most common isolate (65.32%). ESBL production was confirmed in 504 (48.27%) isolates. The isolates of E. coli (50.14%) were the most common ESBL producers. Maximum ESBL isolates were obtained from urine samples (52.28%) and male patients (52.54%). Sensitivity to imipenem was 100% followed by piperacillin–tazobactam (89.28%), meropenem (87.5%), and amikacin (83.92%). Significant resistance was detected against trimethoprim–sulfomethoxazole, fluoroquinolones, and gentamicin.

Conclusion:

This is the only study conducted from Central India and shows high prevalence of ESBL production among Enterobacteriaceae. Imipenem seems to be more sensitive than meropenem. Piperacillin–tazobactam combination was found to be the best among the β-lactam–β-lactamase inhibitor combinations. Prevalence of ESBL producers were more in males than females.

Global dissemination of β2-lactamases mediating resistance to cephalosporins and carbapenems

While the main era of beta-lactam discovery programs is over, these agents continue to be the most widely prescribed antimicrobials in both community and hospital settings. This has led to considerable beta-lactam pressure on pathogens, resulting in a literal explosion of new beta-lactamase variants of existing enzyme classes. Recent advances in the molecular tools used to detect and characterize beta-lactamases and their genes has, in part, fueled the large increase in communications identifying novel beta-lactamases, particularly in Gram-negative bacilli. It now seems clear that the beta-lactams themselves have shaped the field of new enzymes, and the evolution of key amino acid substitutions around the active sites of beta-lactamases continues to drive resistance. Over 130 variants of TEM beta-lactamase now exist, and more are reported in the scientific literature each month. The most disturbing current trend is that many bla structural genes normally limited to the chromosome are now mobilized on plasmids and integrons, broadening the spread of resistance to include carbapenems and cephamycins. Furthermore, in some Enterobacteriaceae, concomitant loss of outer membrane porins act in concert with these transmissible beta-lactamase genes to confer resistance to the most potent beta-lactams and inhibitor combinations available. Continued reviews of the literature are necessary in order to keep abreast of the ingenuity with which bacteria are changing the current genetic landscape to confer resistance to this important class of antimicrobials.

Cephalosporin resistance among animal-associatedEnterobacteria: a current perspective

Beta-lactam antimicrobials are an important class of drugs used for the treatment of infection. Resistance can arise by several mechanisms, including the acquisition of genes encoding beta-lactamases from other bacteria, alterations in cell membrane permeability and over expression of endogenous beta-lactamases. The acquisition of beta-lactamase resistance genes by both Salmonella and Escherichia coli appears to be on the rise, which may pose potential problems for the treatment of infections in both human and animal medicine. The prudent use of clinically important antimicrobials is therefore critical to maintain their effectiveness. Where possible, the use of newer generation cephalosporins should be limited in veterinary medicine.

Detection of ESBL among AmpC producing enterobacteriaceae using inhibitor-based method

Introduction

The occurrence of multiple β-lactamases among bacteria only limits the therapeutic options but also poses a challenge. A study using boronic acid (BA), an AmpC enzyme inhibitor, was designed to detect the combined expression of AmpC β-lactamases and extended-spectrum β-lactamases (ESBLs) in bacterial isolates further different phenotypic methods are compared to detect ESBL and AmpC.

Methods

A total of 259 clinical isolates of Enterobacteriaceae were isolated and screened for ESBL production by (i) CLSI double-disk diffusion method (ii) cefepime- clavulanic acid method (iii) boronic disk potentiation method. AmpC production was detected using cefoxitin alone and in combination with boronic acid and confirmation was done by three dimensional disk methods. Isolates were also subjected to detailed antibiotic susceptibility test.

Results

Among 259 isolates, 20.46% were coproducers of ESBL and AmpC, 26.45% were ESBL and 5.40% were AmpC. All of the 53 AmpC and ESBL coproducers were accurately detected by boronic acid disk potentiation method.

Conclusion

The BA disk test using Clinical and Laboratory Standards Institute methodology is simple and very efficient method that accurately detects the isolates that harbor both AmpCs and ESBLs.

Modified Double Disc Synergy Test to Detect ESBL Production in Urinary Isolates of Escherichia coli and Klebsiella pneumoniae

BACKGROUND AND OBJECTIVES

Various phenotypic methods are recommended in the routine practice to detect the ESBL production in gram negative bacilli. Among them, the Double Disc Synergy Test (DDST) which uses the third generation cephalosporins (3GC), is a simple and a reliable method. But the coexistence of AmpC may give false negative results. In such cases, the ESBL detection can be improved by using cefepime along with the third generation cephalosporins in DDST.

METHODS

A total of 350 urinary isolates (224 Escherichia coli and 126 Klebsiella pneumoniae) were studied for ESBL production by the modified double disc test (MDDST) i.e. by using cefotaxime, ceftriaxone, cefpopdoxime (third generation cephalosporins) and cefepime ( fourth generation cephalosporin) along with a amoxicillin-clavulanate disc.

RESULTS AND INTERPRETATION

ESBL production was seen in 63.4% (142/224) Escherichia coli and in 60.3% (76/126) Klebsiella pneumoniae isolates by MDDST. Among these, in twelve E.coli and five K.pneumoniae strains, only cefepime but none of the third generation cephalosporins showed synergism with amoxicillin-clavulanate. All these seventeen strains showed a clear extension of the edge of inhibition which was produced by cefepime towards the amoxicillin-clavulanate disc. These strains were further tested for AmpC co-production by the AmpC disc test and all these strains were found to be AmpC positive, thus revealing the superior activity of cefepime in detecting ESBLs in the bacteria which co-produced AmpC. A high degree of coresistance was found in the ESBL producers.

CONCLUSION

The ESBL detection can be improved by MDDST by using cefepime along with the third generation cephalosporins.

Clinical outcomes with ertapenem as a first-line treatment option of infections caused by extended-spectrum β-lactamase producing gram-negative bacteria

BACKGROUND

Infections caused by extended-spectrum β-lactamase (ESBL)-producing gram-negative organisms are a growing concern in hospitalized patients. Traditionally, these infections can be effectively treated by the carbapenem class of drugs. In 2005, our institution initiated a protocol for use of ertapenem, a carbapenem, as the first-line treatment option for these infections. It is unknown whether ertapenem is associated with similar clinical response and microbiologic cure rates as those achieved with group 2 carbapenems (imipenem, meropenem, doripenem).

OBJECTIVE

To describe clinical response and microbiologic cure rates associated with ertapenem as first-line treatment of infections caused by ESBL-producing organisms.

METHODS

This case series included patients who received ertapenem for more than 48 hours to treat a documented infection with a positive culture for an ESBL-producing organism. Efficacy was determined by the clinical response and microbiologic cure rates achieved with ertapenem.

RESULTS

Seventy-three patients received ertapenem for a mean (SD) of 10.7 (5.9) days. The most common (59%) infection site was urine. The most common causative organisms were ESBL-producing Klebsiella pneumoniae (47%) and Escherichia coli (48%). Clinical response was observed in 78% of patients. Microbiologic cure was achieved in 92% of the evaluable population (n = 50). There were no significant differences in clinical or microbiologic cure rates across important subgroups.

CONCLUSIONS

Patients treated with ertapenem achieved favorable clinical response and microbiologic cure rates. Our data suggest that ertapenem can be used as an alternative to group 2 carbapenems for the treatment of infections caused by ESBL-producing gram-negative organisms.

Combination antibiotic therapy for empiric and definitive treatment of gram-negative infections: insights from the Society of Infectious Diseases Pharmacists

The widespread emergence of antibiotic-resistant gram-negative organisms has compromised the utility of current treatment options for severe infections caused by these pathogens. The rate of gram-negative multidrug resistance is worsening, threatening the effectiveness of newer broad-spectrum antibiotic agents. Infections associated with multidrug-resistant Pseudomonas aeruginosa, Acinetobacter baumannii, and Enterobacteriaceae are having a substantial impact on hospital costs and mortality rates. The potential for these resistant gram-negative nosocomial pathogens must always be a primary consideration when selecting antibiotic therapy for critically ill patients. Empiric combination therapy directed at gram-negative pathogens is a logical approach for patients with suspected health care-associated infections, particularly those with risk factors for infections caused by multidrug-resistant pathogens. Although in vitro synergy tests have shown potential benefits of continued combination therapy, convincing clinical data that demonstrate a need for combination therapy once susceptibilities are known are lacking. Thus, deescalation to a single agent once susceptibilities are known is recommended for most patients and pathogens. Use of polymyxins, often in combination with other antimicrobials, may be necessary for salvage therapy.

Diversity and complexity of urinary tract infection in diabetes mellitus

Urinary tract infections (UTIs) are a common burden in patients with diabetes mellitus. Cystitis, ascending infections leading to pyelonephritis, emphysematous complications and renal and perinephric abscesses are well recognised in this group of patients especially if glycaemic control is poor. Despite the clinical significance of UTI in diabetes, it is inadequately understood and management regimens are mostly not evidence based. Anticipation of potential complications and earlier interventions are vital to reduce serious adverse outcomes. Herein we discuss the aetiology, pathogenesis and management of UTI and its local and more remote complications.

In vitro activity of cefepime, imipenem, tigecycline, and gentamicin, alone and in combination, against extended-spectrum beta-lactamase-producing Klebsiella pneumoniae and Escherichia coli

STUDY OBJECTIVE

To evaluate the activity of cefepime, imipenem, tigecycline, and gentamicin, alone and in combination, against extended-spectrum beta-lactamase (ESBL)-producing Klebsiella pneumoniae and Escherichia coli.

DESIGN

In vitro susceptibility and time-kill analysis.

SETTING

University-affiliated research laboratory. ISOLATES: Ten K. pneumoniae and 10 E. coli clinical strains known to produce ESBL.

MEASUREMENTS AND MAIN RESULTS

Minimum inhibitory concentration (MIC) testing was performed at 5.5 and 7.0 log(10) colony-forming units (cfu)/ml. Time-kill studies were performed over 24 hours with a high inoculum of 7.0 log(10) cfu/ml for cefepime, imipenem, tigecycline, and gentamicin at 1 times MIC. Combination studies were tested for cefepime plus tigecycline, cefepime plus imipenem, imipenem plus tigecycline, and for adjunctive gentamicin with cefepime, imipenem, or tigecycline. At the high inoculum, the MIC ranges for cefepime, imipenem, tigecycline, and gentamicin were 0.25-256 (MIC for 90% of tested strains [MIC(90)] = 32), 0.125-2 (MIC(90) = 1), 0.25-16 (MIC(90) = 4), and 0.25-4 mg/L (MIC(90) = 1), respectively, for all isolates. At the higher inoculum, MICs shifted for cefepime, imipenem, and tigecycline. Change in log(10) cfu/ml from baseline to 24 hours for cefepime, imipenem, and tigecycline alone ranged from 4.85-0.71, 5-4.22, and 3.5-1.01, respectively, for all isolates. Bactericidal activity was observed for cefepime alone (10 [50%] of 20 isolates), imipenem alone (20 [100%] of 20), and tigecycline alone (3 [15%] of 20). Combination studies with cefepime plus tigecycline resulted in synergy against 4 (20%) of 20 isolates. Combination studies with gentamicin resulted in synergy against 6 isolates (30%) with cefepime and 4 isolates (20%) with tigecycline. No synergy was observed with imipenem combinations. No antagonism was observed. With the exception of cefepime, correlations were observed between MIC and terminal densities for studied agents.

CONCLUSIONS

Cefepime exhibited bactericidal activity but was unrelated to susceptibility. Tigecycline exhibited predictable bacteriostatic activity and synergy in combination against a subset of study isolates. Imipenem exhibited predictable bactericidal activity against all isolates. The utility of combination regimens with novel agents requires further exploration.

Infections due to Escherichia coli producing extended-spectrum beta-lactamase among hospitalised patients: factors influencing mortality

We performed a retrospective matched-cohort study to determine the risk factors for mortality among patients with Escherichia coli infections. From January 1996 to December 2003, 100 hospitalised patients with extended-spectrum beta-lactamase (ESBL)-producing E. coli infections were compared with patients not infected with ESBL-producing E. coli. These patients were selected according to the same site of infection and the closest date of admission. Comparison of the two groups showed that empirical antibiotic therapy was more often inadequate in patients infected with ESBL-producing E. coli (44% vs 15%; P<0.01), and that early mortality (16% vs 6%; P=0.02) and overall mortality (25% vs 11%; P=0.01) were also significantly higher in patients with ESBL-producing E. coli infections. A multivariate model identified the urinary tract focus as the only independent risk factor influencing early mortality for E. coli infections [odds ratio (OR): 0.1; 95% confidence interval (CI): 0.03-0.7; P=0.01]. All 12 patients with ESBL-producing E. coli urinary tract infections treated initially with an oxyimino-beta-lactam survived. Subsequent analysis of the factors influencing early mortality in the cohort of 130 patients with a non-urinary E. coli infection found inadequate empirical antibiotic therapy as an independent risk factor for mortality only for non-urinary E. coli infections (adjusted OR: 3.0; 95% CI: 1.0-8.6; P=0.03). The study showed that hospitalised patients with ESBL-producing E. coli infections more often receive inadequate empiric antibiotic therapy and have a higher mortality rate than those infected with non-ESBL-producing strains. The site of infection strongly influences mortality. The administration of inadequate empirical antibiotic therapy is independently associated with higher mortality only among patients with non-urinary tract infections.

The continuing challenge of ESBLs

Since their first description more than 20 years ago, Escherichia coli and Klebsiella pneumoniae possessing extended-spectrum class A beta-lactamases (ESBLs) continue to thwart our best clinical efforts. In the 'early years' the most common beta-lactamases were of the TEM and SHV varieties. Now, CTX-M enzymes are being discovered throughout the world and are becoming the most prevalent beta-lactamases found in clinical isolates. The K. pneumoniae carbapenemases (KPC) (ESBL-type enzymes that confer resistance to extended-spectrum cephalosporins and carbapenems) present the most significant challenge to date. Structural studies of ESBLs indicate that active site expansion and remodeling are responsible for this extended hydrolytic activity. Continuing questions still exist regarding the optimal detection method for ESBLs. Most relevant are the increasing concerns regarding the status of carbapenems as 'best therapy' for ESBL-producing bacteria in light of the emergence of carbapenemases.

Diagnosis and treatment of extended-spectrum and AmpC beta-lactamase-producing organisms

OBJECTIVE

To review the laboratory diagnosis of extended-spectrum beta-lactamase (ESBL) and AmpC beta-lactamase-producing bacteria and evaluate potential treatment options.

DATA SOURCES

A PubMed search, restricted to English-language articles, was conducted (1966-May 2007) using the search terms ESBL, AmpC, diagnosis, detection, carbapenem, ertapenem, fluoroquinolone, cephalosporin, cefepime, tigecycline, and colistin. Additional references were identified through review of bibliographies of identified articles.

STUDY SELECTION AND DATA EXTRACTION

All studies that evaluated laboratory methods for the detection of ESBLs and AmpC beta-lactamases and/or the treatment of these organisms were reviewed. All articles that were deemed to be clinically pertinent were included and critically evaluated.

DATA SYNTHESIS

Numerous laboratory techniques are available for the detection of ESBLs. In contrast, laboratory techniques for detection of AmpC beta-lactamases are limited, particularly for plasmid-mediated AmpC beta-lactamases. Routine microbiologic testing may not detect ESBLs or AmpC beta-lactamases. Optimal antibiotic treatment options are derived from limited observational studies and case reports. Randomized clinical trials evaluating appropriate antibiotic treatment options are lacking. In vitro susceptibility does not always correlate with clinical outcomes. The use of imipenem was associated with the lowest incidence of mortality in patients with bacteremia due to ESBL-producing organisms.

CONCLUSIONS

Laboratory detection of ESBLs for most organisms is possible with Clinical and Laboratory Standards Institute-recommended testing. However, these tests can be associated with both false negative and false positive results, particularly with organisms that harbor both ESBL- and plasmid-mediated AmpC beta-lactamases. No established guidelines exist for the detection of AmpC beta-lactamases. Imipenem and meropenem are superior to other antibiotics for the treatment of serious infections due to ESBL and AmpC beta-lactamase-producing gram-negative bacteria. While in vitro data demonstrate that tigecycline, ertapenem, and colistin might be potential choices, clinical experience is lacking.

Impact of extended-spectrum beta-lactamase-producing Escherichia coli and Klebsiella species on clinical outcomes and hospital costs: a matched cohort study

OBJECTIVES

To evaluate the economic and clinical impact of infection with extended-spectrum beta -lactamase (ESBL)-producing Escherichia coli and Klebsiella species (ESBL-EK).

DESIGN

A matched-cohort analysis of the cost of illness.

SETTING

An 810-bed, urban, community hospital in Hartford, Connecticut.

PATIENTS

Twenty-one case patients infected with ESBL-EK at a site other than the urinary tract were matched with 21 control subjects infected with a non-ESBL-producing organism on the basis of pathogen species, age, anatomic site of infection, hospitalization in the intensive care unit (ICU) during the time of infection, date of hospitalization, and initial antibiotics received.

RESULTS

Mean infection-related costs per patient were significantly greater for case patients than for control patients ($41,353 vs $24,902; P=.034). Infection-related length of stay was the main driver of cost, which was prolonged for case patients, compared with control patients (21 vs 11 days; mean difference, 9.7 days [95% confidence interval {CI}, 3.2-14.6 days]; P=.006). The additional cost attributed to the presence of an ESBL-EK infection was $16,450 per patient (95% CI, $965-$31,937). Case patients were more likely than control patients to have clinical failure (P=.027), and the rate of treatment success for case patients whose initial treatment involved antibiotics other than carbapenems was lower than that for their matched control patients (39% vs 83%; P=.013). Treatment was successful in patients for whom initial treatment was with a carbapenem, regardless of the ESBL status of the pathogen.

CONCLUSION

The cost of non-urinary tract infections caused by ESBL-EK was 1.7 times the cost of non-urinary tract infections caused by non-ESBL producers. Prompt recognition and appropriate antimicrobial selection may minimize this ESBL-related impact on hospital costs.

Clinical implications of extended spectrum beta-lactamase (ESBL) producing Klebsiella species and Escherichia coli on cefepime effectiveness

OBJECTIVE

To determine the affect of ESBL production among Klebsiella species and Escherichia coli on cefepime effectiveness.

METHODS

This was a retrospective, case-controlled study comparing the clinical and microbiologic responses of patients receiving cefepime for ESBL producing Klebsiella species or E. coli from a non-urine source with matched controls receiving cefepime for non-ESBL strains. Cases with ESBLs were included if they received monotherapy and were clinically evaluable. Non-ESBL controls were matched in a 2:1 ratio based on age, infection site, intensive care unit (ICU) stay, pathogen species and date of hospitalization.

RESULTS

Ten patients receiving cefepime for ESBLs were matched to 20 controls. Most patients received cefepime 1g q12h. Patients receiving cefepime for an ESBL infection were 9.7 (95% CI: 1.4-68.8) and 28.5 (95% CI: 2.6-306.6) times as likely to have an unsuccessful clinical and microbiological response compared with those with a non-ESBL infection. The presence of an ESBL did not have a statistically significant effect on all cause or infection-related mortality.

CONCLUSION

These data indicate that ESBL production among non-urinary Klebsiella species and E. coli negatively affected cefepime effectiveness. Further studies are required to evaluate if higher doses of cefepime may improve responses in ESBLs that are initially susceptible.

Extended-Spectrum β-Lactamases and Clinical Outcomes: Current Data

Nosocomial infections caused by extended-spectrum beta-lactamase (ESBL)-producing gram-negative bacteria complicate therapy and limit treatment options. However, the clinical significance of infections caused by ESBL-producing bacteria remains unclear. A critical examination of the literature provides divergent views of the effect of ESBL carriage on morbidity and mortality and suggests that ESBL production may have its most marked effect on ceftazidime. Effective strategies for the empirical and directed treatment of infections caused by ESBL-producing pathogens include the use of carbapenems and, possibly, the fourth-generation cephalosporin cefepime. Studies indicate that the use of cefepime to treat serious nosocomial infections (e.g., bacteremia, pneumonia, and urinary tract infections) is associated with high rates of microbiological and clinical success. The probability of attaining time above the minimum inhibitory concentration targets of at least 70% of the dosing interval, an important pharmacodynamic indicator of clinical success, is higher with cefepime than with other antimicrobials against Escherichia coli and Klebsiella pneumoniae strains exhibiting ESBL phenotypes. However, for non-ESBL-producing strains, there is no difference in the time above the minimum inhibitory concentration between ceftazidime and cefepime. When used appropriately in institutional settings, cefepime reduces the overall use of cephalosporins, thereby decreasing selection pressure for presumptive ESBL-producing pathogens.

Extended-spectrum beta-lactamases: a clinical update

Extended-spectrum beta-lactamases (ESBLs) are a rapidly evolving group of beta-lactamases which share the ability to hydrolyze third-generation cephalosporins and aztreonam yet are inhibited by clavulanic acid. Typically, they derive from genes for TEM-1, TEM-2, or SHV-1 by mutations that alter the amino acid configuration around the active site of these beta-lactamases. This extends the spectrum of beta-lactam antibiotics susceptible to hydrolysis by these enzymes. An increasing number of ESBLs not of TEM or SHV lineage have recently been described. The presence of ESBLs carries tremendous clinical significance. The ESBLs are frequently plasmid encoded. Plasmids responsible for ESBL production frequently carry genes encoding resistance to other drug classes (for example, aminoglycosides). Therefore, antibiotic options in the treatment of ESBL-producing organisms are extremely limited. Carbapenems are the treatment of choice for serious infections due to ESBL-producing organisms, yet carbapenem-resistant isolates have recently been reported. ESBL-producing organisms may appear susceptible to some extended-spectrum cephalosporins. However, treatment with such antibiotics has been associated with high failure rates. There is substantial debate as to the optimal method to prevent this occurrence. It has been proposed that cephalosporin breakpoints for the Enterobacteriaceae should be altered so that the need for ESBL detection would be obviated. At present, however, organizations such as the Clinical and Laboratory Standards Institute (formerly the National Committee for Clinical Laboratory Standards) provide guidelines for the detection of ESBLs in klebsiellae and Escherichia coli. In common to all ESBL detection methods is the general principle that the activity of extended-spectrum cephalosporins against ESBL-producing organisms will be enhanced by the presence of clavulanic acid. ESBLs represent an impressive example of the ability of gram-negative bacteria to develop new antibiotic resistance mechanisms in the face of the introduction of new antimicrobial agents.

Clinical features of nosocomial infections by extended-spectrum beta-lactamase-producing Enterobacteriaceae in neonatal intensive care units

AIM

To determine the risk factors for the acquisition of nosocomial extended-spectrum beta-lactamase (ESBL)-producing Enterobacteriaceae infection in infants hospitalized in neonatal intensive care units (NICUs) and to evaluate the therapeutic outcome of these infants.

METHODS

We retrospectively reviewed the medical records of infants with nosocomial ESBL-producing Enterobacteriaceae infection hospitalized in NICUs at Chang Gung Children's Hospital in 2001. The clinical features of these infants were compared with a cohort of non-ESBL-producing Enterobacteriaceae-infected infants during the same period. The therapeutic outcome of the infants in the ESBL group was analysed.

RESULTS

Seventy infants were included in this study. Thirty-one infants with 34 isolates were identified in the ESBL group and 39 infants with 42 isolates in the non-ESBL group. Of the parameters analysed, including gestational age, birthweight, length of hospital stay before onset, the number of antibiotics used, the duration of third-generation cephalosporin usage and the number of patients receiving a third-generation cephalosporin prior to the onset of infection, no significant difference was found between the two groups. The infection-contributed case fatality rate was 3.0% (1 of 33) in the ESBL group, not significantly different from that in the non-ESBL group (1 of 41, 2.4%). Of the 31 patients in the ESBL group, 18 were treated with a carbapenem as definitive therapy while 13 were treated with a non-carbapenem antibiotic regimen. No significant difference was noted in terms of mortality rate between the two subgroups.

CONCLUSION

The outcome of the infants hospitalized in the NICU with ESBL-producing enterobacterial infections was not indispensably grave, even when treated with a non-carbapenem antibiotic regimen. The risk factors for the acquisition of ESBL-producing enterobacterial infections in these infants were not identified in this series.

Multidrug resistance in Gram-negative bacteria that produce extended-spectrum beta-lactamases (ESBLs)

In 1983, just two years after the introduction of the oxymino-beta-lactams to the market , the first extended-spectrum beta-lactamases were isolated in Germany from Klebsiella pneumoniae strains. Since then several outbreaks have been reported in many European countries and the USA, and nowadays in several places worldwide the problem seems to reach endemic dimensions, with rates exceeding 50% in some countries, such as Portugal and Turkey. On the other hand not only K. pneumoniae but also Escherichia coli strains, with Enterobacter aerogenes predominating among the other enterobacteriaceal species, are increasingly reported as ESBL producers. In this review types, molecular characteristics, detection methods, epidemiology as well as interventions for therapy and antibiotic strategies to prevent and control infections caused by ESBL-producing microorganisms, are presented and discussed.

Antimicrobial Management of Complicated Skin and Skin Structure Infections in the Era of Emerging Resistance

BACKGROUND

Complicated skin and skin structure infections (cSSSIs) are among the most common infections treated in the hospital setting. The mainstays of treatment continue to be antimicrobial therapy combined with appropriate surgical intervention. Due to increasing resistance among pathogens commonly implicated in cSSSIs, the objectives of this review were to describe the potential pathogens causing skin infections, the implications of resistance to currently used drug therapy, and the role of new antibiotics with activity for pathogens causing cSSSIs.

METHODS

Relevant information from the primary literature and review articles were identified through a MEDLINE search of the medical literature (1980 to the present) using the terms abscess, wound infection, skin and skin structure infection, antibiotics, resistance, quinupristin- dalfopristin, linezolid, daptomycin, tigecycline, oritavancin, and dalbavancin. Meeting posters and slides were identified from the Interscience Conference of Antimicrobial Agents and Chemotherapy (1998-2004) for supplemental data.

RESULTS

The most commonly implicated pathogens in cSSSIs include gram-positive bacteria, specifically Staphylococcus aureus. Gram-negative and mixed organisms are additionally encountered in serious cSSSI. Antimicrobial resistance among both gram-positive and gramnegative bacteria has increased significantly during the last decade, with methicillin resistance among S. aureus approaching 60% in hospitals and becoming more frequent in the community as well. As a result, resistance is the driving factor for treatment failure and rising costs for infection management. Few antimicrobial agents are available currently to treat resistant bacteria in cSSSIs; vancomycin is currently the drug of choice against resistant grampositive cocci; however, resistance to this agent has appeared in enterococci and S. aureus. Several new antibiotics such as linezolid and daptomycin are now available for the management of cSSSIs. Other agents such as tigecycline are under investigation and should be available soon to increase treatment options for cSSSIs caused by resistant bacteria.

CONCLUSIONS

Although the resistance of cSSSI pathogens is problematic, new antibiotics with broad-spectrum activity against resistant gram-positive and gram-negative bacteria are promising for the management of severe cSSSIs.

Extended spectrum β-lactamase–producing Klebsiella pneumoniae chronic ambulatory peritoneal dialysis peritonitis treated successfully with polymyxin B

Peritonitis is not an infrequent complication of inpatients with chronic ambulatory peritoneal dialysis (CAPD). CAPD peritonitis may be related to the catheter or secondary to perforation of an intra-abdominal viscus. The most common organisms usually associated with CAPD peritonitis are Staphylococcus aureus and Staphylococcus epidermidis (coagulase-negative staphylococci). Rarely, aerobic gram-negative bacilli have been the causative agents of CAPD peritonitis. The treatment of CAPD peritonitis usually requires removal of the peritoneal catheter and treatment with parenteral antibiotics active against the causative pathogen. We report a case of CAPD-associated peritonitis caused by an extended spectrum beta-lactamase-producing strain of Klebsiella pneumoniae. The case presented had this strain of multidrug-resistant K. pneumoniae present in blood cultures and the peritoneal fluid. Extended spectrum beta-lactamase-producing bacteria, for example, K. pneumoniae, are multidrug-resistant and sensitive to few antibiotics. This isolate was intermediately sensitive to amikacin and meropenem, but the patient did not clinically improve on these 2 antibiotics. Polymyxin B therapy was initiated after lack of clinical improvement after dialysis catheter removal and 1 week of meropenem and amikacin therapy. The patient responded rapidly to therapy with polymyxin B. Polymyxin B has a unique mechanism of action on bacterial cells and is highly active against all multidrug-resistant gram-negative organisms except Proteus species and Serratia marcescens. No toxicity was observed during therapy. Polymyxin B is being used increasingly as a therapeutic alternative to multidrug-resistant gram-negative organisms.

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.

Risk Factors for Increasing Multidrug Resistance among Extended-Spectrum -Lactamase-Producing Escherichia coli and Klebsiella Species

BACKGROUND

The importance of infections due to extended-spectrum beta -lactamase-producing Escherichia coli and Klebsiella species (ESBL-EK) has been increasingly recognized in recent years. ESBL-EK infections are of clinical concern, because few antimicrobials are available as therapeutic options. Increased reliance on carbapenems has led to increasing carbapenem resistance. Efforts to maintain current therapeutic options for ESBL-EK infections are essential.

METHODS

We conducted a case-control study to identify risk factors for multidrug resistance (MDR) among ESBL-EK. All patients at our institution who had an inpatient clinical culture result positive for an ESBL-EK during the period of 1 June 1997 through 31 December 2002 were eligible for inclusion. An MDR ESBL-EK was defined as ESBL-EK demonstrating resistance to trimethoprim-sulfamethoxazole, aminoglycosides, and quinolones. All available ESBL-EK isolates were characterized by pulsed-field gel electrophoresis (PFGE).

RESULTS

Of 361 total ESBL-EK isolates, 68 (18.8%) were MDR. During the study period, the prevalence of MDR among ESBL-EK isolates increased from 12.5% to 26.9%. The only independent risk factor for MDR ESBL-EK was the infecting organism (i.e., Klebsiella pneumoniae; adjusted odds ratio, 11.7; 95% confidence interval, 4.77-28.51; P < .001). Prior antibiotic use was not independently associated with MDR ESBL-EK. PFGE patterns from K. pneumoniae isolates indicated close genetic relatedness among a substantial proportion of isolates.

CONCLUSIONS

The emergence of MDR among ESBL-EK has important implications for the future ability to treat these infections. The strong association between the species of infecting organism and MDR suggests that the epidemiology in K. pneumoniae may be unique. PFGE results suggest that horizontal spread is important in the emergence of MDR ESBL-EK.

Cepas de Escherichia coli productoras de betalactamasas de espectro extendido: origen, características e incidencia en el sur de la provincia de Alicante en el período 1999-2003

INTRODUCTION

In the last years, we have verified the increasing emergence of bacteria, specially Escherichia coli, that produce expanded spectrum beta-lactamases (ESBL), enzymes which confer resistance to all cephalosporins (except cephamycins) and aztreonam. These bacteria are frequently resistant also to non-beta-lactam antibiotics, a fact which poses an important clinical problem.

METHODS

Descriptive study of ESBL-producing strains of E. coli isolated in all kind of specimens in two hospitals of Southern Alicante (Spain), throughout a period of 57 months (January 1999 to September 2003), paying a close attention to their origin (outpatients or admitted patients), co-resistance to non beta-lactam antibiotics and evolution of their incidence.

RESULTS

Respectively, 3% and 2.25% of E. coli strains isolated in each hospital produce ESBL (3.83% and 2.85% of strains from admitted and 2.74% and 2.1% from outpatients). 30.73% and 24.58% of strains ESBL were isolated in admitted patients. We found in both hospitals much higher percentages of co-resistance to ciprofloxacin, gentamicin and trimetoprim-sulfamethoxazole in ESBL-producing strains.

CONCLUSION

The percentage of ESBL-producing E. coli is high in our environment, but it is even more noteworthy its clear trend to increase. It is very remarkable the high percentage of ESBL-producing strains isolated from outpatients. Finally, we emphasize the high percentages of co-resistance to non-beta-lactam antibiotics.

Treating Serious Infections: Focus on Cefepime

Antibiotic resistance among medically important pathogens is curtailing the therapeutic value of many of the standard broad-spectrum antibiotics used for empiric treatment of serious infections. This article presents a brief overview of the etiology of serious infections and the threat of emerging resistance, and reviews the adverse impact of inadequate empiric treatment on patient outcomes and hospital ecology. The treatment of two clinically important infections with cefepime--pneumonia in hospitalized patients and febrile neutropenia--also is discussed.

In vitro killing of parenteral beta-lactams against standard and high inocula of extended-spectrum beta-lactamase and non-ESBL producing Klebsiella pneumoniae

Minimum inhibitory concentrations and time-kill curves were performed against 8 Klebsiella pneumoniae (4 non-extended-spectrum beta-lactamase[ESBL] and 4 ESBL) for piperacillin/tazobactam (40/5 microg/mL), cefepime (20 microg/mL), and meropenem (4 microg/mL) by using a standard and high inocula. Imipenem was evaluated only at the standard inoculum for the non-ESBL and ESBL isolates. Samples were withdrawn at 7 predetermined time-points over 24 hours and plated on trypticase soy agar plates. Minimum inhibitory concentrations were: piperacillin/tazobactam 4 to 8 microg/mL (ESBL and non-ESBL), cefepime 1 to 2 microg/mL (ESBL) and 0.06 to 0.125 microg/mL (non-ESBL), imipenem 0.125 to 0.25 microg/mL (ESBL and non-ESBL), and meropenem 0.03 to 0.06 microg/mL (ESBL and non-ESBL). Each antibiotic reached and maintained bactericidal killing (> or =3 log killing) for 24 hours against all non-ESBL isolates for both the standard and high inoculum. Cefepime, imipenem, and meropenem showed the same bactericidal activity against each ESBL isolate at the standard inoculum, whereas piperacillin/tazobactam showed bactericidal killing against only 1 ESBL isolate. At the high inoculum, cefepime and piperacillin/tazobactam were unable to maintain bactericidal activity against any of the ESBL isolates. Only meropenem was able to maintain bactericidal killing over 24 hours against the ESBL isolates at the high inoculum. In summary, meropenem and imipenem maintained bactericidal activity against non-ESBL and ESBL K. pneumoniae irrespective of the inoculum size. While piperacillin/tazobactam and cefepime are bactericidal against non-ESBL K. pneumoniae, their activity against ESBL K. pneumoniae is limited and based on the size of the inoculum. Until more data are available, piperacillin/tazobactam and cefepime should not be used for the treatment of ESBL K. pneumoniae.

In vitro activity of parenteral Beta-lactams, levofloxacin and tobramycin alone or in combination against extended-spectrum Beta-lactamase producing Klebsiella pneumoniae

MICs and time-kill studies were performed for four clinical isolates of extended-spectrum Beta-lactamase (ESBL)-producing Klebsiella pneumoniae. MICs (mg/L) were: piperacillin/tazobactam 8, cefepime 1-2, meropenem 0.03-0.06, levofloxacin 0.5-8 and tobramycin 0.25-32. For monotherapy, only meropenem maintained bactericidal activity over the 24 h for all isolates. Levofloxacin and tobramycin maintained bactericidal activity against the isolate susceptible to each drug. Piperacillin/tazobactam and cefepime did not maintain bactericidal activity against any isolate. Combination therapy with piperacillin/tazobactam or cefepime combined with levofloxacin or tobramycin were able to provide dramatic killing against ESBL K. pneumoniae, but did not always maintain bactericidal activity. Future studies should evaluate different antimicrobial combinations against pathogens producing specific ESBL enzymes to define their utility as an alternative to carbapenems.

Clinical and microbiologic analysis of a hospital's extended-spectrum beta-lactamase-producing isolates over a 2-year period

STUDY OBJECTIVE

To evaluate the microbiologic and clinical outcomes of patients with extended-spectrum beta-lactamase (ESBL)-producing isolates over a 2-year period.

DESIGN

Retrospective analysis.

SETTING

Tertiary care teaching hospital.

PATIENTS

Twenty-one patients with cultures of confirmed ESBL-producing Escherichia coli, Klebsiella pneumoniae, or Klebsiella oxytoca.

MEASUREMENTS AND MAIN RESULTS

Antimicrobial susceptibilities of piperacillin-tazobactam, cefotetan, carbapenems, aminoglycosides, fluoroquinolones, trimethoprim-sulfamethoxazole, and nitrofurantoin (nitrofurantoin for urinary isolates only) of confirmed ESBL producers at our institution were determined, as well as clinical outcomes of patients with ESBL-producing isolates. Microbiologic and medical records were reviewed for patient sex and age, antimicrobial susceptibilities, antimicrobial therapy, and clinical and microbiologic outcomes. From January 2000-December 2001, 31 isolates were confirmed as ESBL producers (6 E. coli, 11 K. pneumoniae, and 14 K. oxytoca). A statistically significant increase occurred over the 2-year period from 9 (0.6%) of 1414 isolates in 2000 to 22 (1.8%) of 1218 isolates in 2001 (p = 0.0055). All isolates were susceptible to carbapenems, and more than 88% were susceptible to amikacin, cefotetan, or nitrofurantoin. Less than 70% of isolates were susceptible to gentamicin, fluoroquinolones, piperacillin-tazobactam, or trimethoprim-sulfamethoxazole. All patients treated with a carbapenem experienced clinical cure. Piperacillin-tazobactam alone and in combination resulted in an overall clinical cure rate of 55%, with a 50% cure rate for isolates susceptible to piperacillin-tazobactam. All patients in whom antibiotic therapy failed had been treated with piperacillin-tazobactam or cefepime, either alone or in combination with a fluoroquinolone.

CONCLUSION

Carbapenems remain the treatment of choice for ESBL-producing pathogens. Piperacillin-tazobactam and cefepime should not be routinely administered for the treatment of these organisms.

Extended spectrum beta-lactamase (ESBL)-producing Enterobacteriaceae: considerations for diagnosis, prevention and drug treatment

Extended spectrum beta-lactamase (ESBL)-producing organisms pose unique challenges to clinical microbiologists, clinicians, infection control professionals and antibacterial-discovery scientists. ESBLs are enzymes capable of hydrolysing penicillins, broad-spectrum cephalosporins and monobactams, and are generally derived from TEM and SHV-type enzymes. ESBLs are often located on plasmids that are transferable from strain to strain and between bacterial species. Although the prevalence of ESBLs is not known, it is clearly increasing, and in many parts of the world 10-40% of strains of Escherichia coli and Klebsiella pneumoniae express ESBLs. ESBL-producing Enterobacteriaceae have been responsible for numerous outbreaks of infection throughout the world and pose challenging infection control issues. Clinical outcomes data indicate that ESBLs are clinically significant and, when detected, indicate the need for the use of appropriate antibacterial agents. Unfortunately, the laboratory detection of ESBLs can be complex and, at times, misleading. Antibacterial choice is often complicated by multi-resistance. Many ESBL-producing organisms also express AmpC beta-lactamases and may be co-transferred with plasmids mediating aminoglycoside resistance. In addition, there is an increasing association between ESBL production and fluoroquinolone resistance. Although in in vitro tests ESBLs are inhibited by beta-lactamase inhibitors such as clavulanic acid, the activity of beta-lactam/beta-lactamase inhibitor combination agents is influenced by the bacterial inoculum, dose administration regimen and specific type of ESBL present. Currently, carbapenems are regarded as the drugs of choice for treatment of infections caused by ESBL-producing organisms. Unfortunately, use of carbapenems has been associated with the emergence of carbapenem-resistant bacterial species such as Stenotrophomonas sp. or Pseudomonas sp.

Carriage of methicillin-resistant Staphylococcus aureus, ceftazidime-resistant Gram-negative bacilli, and vancomycin-resistant enterococci before and after intensive care unit admission

OBJECTIVE

To measure patients' risk for acquiring antibiotic-resistant microorganisms associated with intensive care unit admission.

DESIGN

Prospective, observational study.

SETTING

Ten public hospitals including one university medical center.

PATIENTS

Consecutive patients admitted to ten intensive care units.

INTERVENTIONS

Serial patient surveillance cultures were screened for vancomycin-resistant enterococci, methicillin-resistant Staphylococcus aureus (MRSA), ceftazidime-resistant Gram-negative bacilli (CR-GNB), Acute Physiology and Chronic Health Evaluation II score, and antibiotic and medical device exposures.

MEASUREMENTS AND MAIN RESULTS

A total of 1,697 patient admissions in ten intensive care units were enrolled. The overall carriage rate of antibiotic-resistant bacteria at intensive care unit entry was 12.1% for MRSA, 14% for CR-GNB and 4.7% for both. At discharge from the intensive care unit, new carriage of MRSA, CR-GNB, and both was found in 11.1%, 14.2%, and 2.4% of the patients, respectively. The acquisition rates in the individual units correlated highly and positively with proportion of patients with carriage at intensive care unit entry for both MRSA (n = 10, Pearson's r =.89, p < 0.001) and CR-GNB (n = 10, Pearson's r =.92, p < 0.001). By logistic regression, severity of illness (odds ratio, 1.4), length of stay (odds ratio, 1.7), use of penicillins (odds ratio, 1.9), and number of antibiotics (odds ratio, 1.2) and medical devices (odds ratio, 1.2) were independently associated with intensive care unit acquisition of MRSA. In comparison, variables independently associated with intensive care unit acquisition of CR-GNB were Acute Physiology and Chronic Health Evaluation II score (odds ratio, 1.5), number of antibiotics (odds ratio, 1.1), and artificial airway (odds ratio, 1.5).

CONCLUSIONS

These data suggest that hospitalization in the intensive care unit introduces significant risk to patients in terms of transmission of MRSA and/or CR-GNB. This risk seems to be influenced strongly by the proportion of patients with colonization at intensive care unit admission and is associated with severity of illness, length of stay, and exposures to antibiotics and medical devices.

Risk factors in the acquisition of extended-spectrum beta-lactamase Klebsiella pneumoniae: a case-control study in a district teaching hospital in Taiwan

A case-control study was performed to find the risk factors in the acquisition of extended-spectrum beta-lactamase (ESBL) Klebsiella pneumoniae. From 1 May 2001 to 30 September 2001, 422 isolates ofK. pneumoniae identified by the microbiological laboratory in Hsin-Chu hospital were collected, 59 of which were ESBL-producing strains. The prevalence rate was 14% (59/422). There were 43 case patients (ESBL-producing K. pneumoniae) and 86 controls (non-ESBL-producing K. pneumoniae). Tracheostomy, insertion of a Foley catheter, endotracheal tube, nasogastric tube and central venous catheter were found to be risk factors in the acquisition of K. pneumoniae with ESBLs by univariate analysis. Tracheostomy (odds ratio, 5.13; 95% CI, 1.24-21.1;P =0.023) and ceftazidime use (odds ratio, 13.40; 95% CI, 1.21-148.85; P=0.035) remained as risk factors by multivariate analysis with logistic regression. Other anti-pseudomonal agents should be used as empirical therapy to treat possible Pseudomonas aeruginosa infection in order to reduce ceftazidime use and thereby decrease the prevalence of ESBL producing strains of Enterobacteriaceae.

A decade of antimicrobial susceptibilities at the University of Kentucky Hospital

OBJECTIVE

To determine the antimicrobial susceptibility rates for key antimicrobial agents and selective bacterial pathogens in the decade of the 1990s.

METHODS

Data from 1990 to 2000 from the University of Kentucky Clinical Microbiology Laboratory were analyzed by linear regression analysis to identify agents and pathogens that show a decline in susceptibility. For selected pathogens and antimicrobial agents, predictions were made for further declines in susceptibility for 2005 and 2010.

RESULTS

Significant declines in susceptibility to selected antimicrobial agents were found for Pseudomonas aeruginosa, Klebsiella pneumoniae, Enterobacter cloacae, Escherichia coli, Staphylococcus aureus, Staphylococcus epidermidis, and Streptococcus pneumoniae. Further declines were predicted for 2005 and 2010.

CONCLUSIONS

Examination of susceptibility rates over time in a university hospital medical center provides useful data for future planning. In our institution, antimicrobial susceptibility rates have significantly declined during the 1990s for certain antimicrobial agents and bacterial pathogens. We are attempting to change our antimicrobial use patterns through formulary manipulation and clinician education, which may retard or prevent such declines in the future.

Extended-Spectrum β-Lactamase Resistance in the ICU

Despite the recent focus on gram-positive infections in the intensive care unit (ICU), gram-negative resistance mechanisms continue to challenge the critical care practitioner. A recent national surveillance study of United States ICUs found Escherichia coli, Enterbacter species, Klebsiella species, and Pseudomonas aeruginosa represented 72% of all gram-negative bacilli recovered. E coli, Klebsiella pneumoniae, and Enterobacter species are significant producers of a β -lactamase that inactivates almost all β -lactam antibiotics, so-called extended-spectrum β -lactamases or ESBLs. Many clinical laboratories may not test for ESBL-production in these organisms, thus clinicians may be unaware of the rising incidence of this plasmid-mediated resistance mechanism. Since initial reports of ESBLs in the 1980s, investigators have found an association with ESBL-producing organisms and the critically ill population. Risk factors for ESBL-related infection in the ICU include arterial, central-venous, and urinary-catheters; mechanical ventilation; abdominal surgery; prior antibiotic therapy with ceftazidime or other extended spectrum cephalosporins; length of time in the ICU; and overall acuity of illness. This article reviews the emergence and epidemiology of the ESBL evolution, describes the clinical implications of ESBL production in the ICU, and outlines a strategy for management of infection in patients at risk for ESBL-producing organisms.