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

In vitro efficacy of humanized regimen of flomoxef against extended-spectrum β-lactamase-producing Escherichia coli and Klebsiella pneumoniae

This study compared the efficacy of flomoxef with other β-lactam antibiotics against extended-spectrum β-lactamases (ESBL)-producing bacteria of clinical relevance. First, the prevalence and β-lactamase genotypes of ESBL-producing strains among Escherichia coli and Klebsiella pneumoniae isolates collected in Japan from 2004 to 2018 were investigated. High MIC90 values (>64 µg/mL) of ceftriaxone, cefepime, and ceftazidime and low MIC90 values (≤0.06-2 µg/mL) of flomoxef, cefmetazole, and meropenem against both species were observed. Second, a chemostat model was used to analyze the efficacy of humanized regimens of three oxacephem/cephamycin antibiotics (flomoxef, cefmetazole, cefoxitin) and two other antibiotics (meropenem and piperacillin/tazobactam) in suppressing the growth of five ESBL-producing E. coli and two K. pneumoniae strains. Flomoxef, piperacillin/tazobactam, and meropenem showed good bactericidal effects with >4 log10 CFU/mL reduction without bacterial regrowth at 24 h even when the MIC of test isolates was >MIC90. Cefmetazole and cefoxitin resulted in regrowth of test isolates with MIC ≥MIC90 at 24 h. Cefmetazole, cefoxitin, flomoxef, and meropenem showed increased MICs for regrown samples. A clear relationship between the proportion of time that the free drug concentration exceeded the MIC (%fT>MIC) and antibiotic efficacy was found for flomoxef, cefoxitin, and cefmetazole, and flomoxef had the highest %fT>MIC, whereas discrepancies between Clinical and Laboratory Standards Institute breakpoint and bactericidal activity were observed for cefmetazole. Flomoxef was effective in preventing the growth of all ESBL-producing strains, even those with an MIC eight times the MIC90. Thus, flomoxef may be a good alternative to meropenem in context of carbapenems sparing stewardship.

Prevalence of Carbapenem-Resistant Enterobacteriaceae in Western Saudi Arabia and Increasing Trends in the Antimicrobial Resistance of Enterobacteriaceae

PURPOSE

 The aim of the study is to estimate the prevalence rate of carbapenem-resistant Enterobacteriaceae (CRE) and to determine the types of carbapenemase genes present in patients admitted to King Abdulaziz Medical City (KAMC-J) and King Abdulaziz University Hospital (KAUH), both in Jeddah, Saudi Arabia.

METHODS

 A total of 180 isolates were analyzed which were included on the basis of retrospective chart review of patients from KAMC-J and KAUH between 1^st April 2017 to 30^th March 2019. The prevalence of carbapenemase genes ( ^blaIMP, ^blaVIM, ^blaKPC, ^blaNDM-1, and ^blaOXA-48) was evaluated by Xpert® Carba-R (Cepheid, Sunnyvale, CA, USA). We assessed the CRE prevalence and described their susceptibility to antimicrobial agents based on antibiogram reports.  Results: Klebsiella pneumoniae showed a higher frequency of ^bla OXA-48 (79%) than ^bla NDM (11.7%) genes (p=0.007). The CRE prevalence in KAUH was 8% in 2017 and increased to 13% in 2018. In KAMC-J, the prevalence was 57% in 2018 and 61% in 2019. K. pneumoniae was found to be the most frequently isolated causative organism followed by Escherichia coli . The  ^bla OXA-48 (76.1%) gene was predominant among overall isolates followed by ^bla NDM (13.9%); both genes coexisted in 6.1% of the isolates.

CONCLUSION

 During the study period, the prevalence of CRE considerably rose in the two tertiary care institutions from western Saudi Arabia. In the CRE isolates, ^bla OXA-48 was discovered to be the most common gene. We recommend an antimicrobial resistance surveillance system to detect the emergence of resistant genes through use of new rapid diagnostic tests and monitor antimicrobial use in order to improve clinical outcomes of CRE infections given the severity of infection associated with the CRE isolates as well as the limited treatment options available.

Magnitude of Extended-Spectrum Beta-Lactamase-Producing Gram-Negative and Beta-Lactamase-Producing Gram-Positive Pathogens Isolated from Patients in Dar es Salaam, Tanzania: A Cross-Sectional Study

Background

The worldwide emergence of antibiotic-resistant bacteria threatens to overshadow the dramatic advances in medical sciences since the discovery of antibiotics. Antibiotic resistance has rendered some antibiotics obsolete, creating a reliance on synthetic drugs. In some instances, bacteria can be resistant to all antibiotics. The problem of antibiotic resistance is eminent in resource-limited countries like Tanzania, where systematic surveillance and routine susceptibility tests are rarely conducted. Therefore, this study aimed to investigate the magnitude of beta-lactamase-producing Gram-positive pathogens and Enterobacteriaceae with extended-spectrum beta-lactamase (ESBL) in Dar es Salaam, Tanzania.

Methodology

This multi-site cross-sectional study involved three private hospitals in Dar es Salaam, Tanzania. The study was conducted between July and September 2008. Bacterial isolates were collected, identified, and subjected to antibiotic-sensitivity testing against cephalosporins, including ceftriaxone, cefuroxime and cefotaxime, and clavulanic acid, which are antibiotics readily available on the Tanzanian market at the time of the study. The microdilution method was employed to determine beta-lactamase and ESBL production per the Clinical Laboratory and Standards Institute (CLSI) protocol. Cephalosporins, including ceftriaxone, cefuroxime and cefotaxime, the beta-lactamase inhibitor, and clavulanic acid, were serially diluted with concentrations ranging from 0.011 mg/ml to 200 mg/ml. Each of these antibiotics was subjected to sensitivity tests by determining the minimum inhibitory concentrations (MIC) of the clinical isolates of bacteria using a 96-well microdilution plate. Five microliters of bacterial suspension were inoculated into each well-containing 120µl of sterile Mueller-Hinton broth before incubation overnight.

Results

A total of 111 bacterial isolates were tested. Of the 111 tested bacterial isolates, 85 (76.6%) and 26 (23.4%) were Gram-negative and Gram-positive bacteria, respectively. Fifty-six clinical isolates (50.4%) were Escherichia coli, and 13 Salmonella species (11.7%) were among the Gram-negative isolates. On the other hand, 15 (13.5%) and 11 (9.9%) Gram-positive bacteria were Staphylococcus aureus and Streptococcus species, respectively, of all isolates. The majority of these clinical isolates, 71 (64.0%), were obtained from mid-stream urine, while the remaining were from stool, vaginal secretions, blood, pus, catheter sip, and urethra. A high proportion of tested Gram-negative bacteria, 58 (68.2%), were identified as ESBL producers, and 16 (61.5%) of the Gram-positive bacteria were identified as beta-lactamase producers. Cefuroxime was the least effective, exhibiting the largest MIC (18.47 ± 22.6 mg/ml) compared to clavulanic acid alone (5.28 ± 8.0 mg/ml) and clavulanic acid-cefuroxime (5.0± 12.32 mg/ml). Of all isolates, 78.2% were sensitive to chloramphenicol. Only five isolates had MIC larger than 32.23 mg/ml as opposed to cefotaxime and ampicillin, which had more isolates in that similar MIC range.

Conclusion

There is a high proportion of beta-lactamase, particularly ESBL-producing pathogens, in Dar es Salaam, Tanzania. Therefore, regular detection of beta-lactamase and ESBL production may help detect resistance to beta-lactam antibiotics.

The role of tazobactam-based combinations for the management of infections due to extended-spectrum β-lactamase-producing Enterobacterales: Insights from the Society of Infectious Diseases Pharmacists

Extended-spectrum β-lactamase (ESBL)-producing Enterobacterales are a global threat to public health due to their antimicrobial resistance profile and, consequently, their limited available treatment options. Tazobactam is a sulfone β-lactamase inhibitor with in vitro inhibitory activity against common ESBLs in Enterobacterales, including CTX-M. However, the role of tazobactam-based combinations in treating infections caused by ESBL-producing Enterobacterales remains unclear. In the United States, two tazobactam-based combinations are available, piperacillin-tazobactam and ceftolozane-tazobactam. We evaluated and compared the roles of tazobactam-based combinations against ESBL-producing organisms with emphasis on pharmacokinetic/pharmacodynamic exposures in relation to MIC distributions and established breakpoints, clinical outcomes data specific to infection site, and considerations for downstream effects with these agents regarding antimicrobial resistance development. While limited data with ceftolozane-tazobactam are encouraging for its potential role in infections due to ESBL-producing Enterobacterales, further evidence is needed to determine its place in therapy. Conversely, currently available microbiologic, pharmacokinetic, pharmacodynamic, and clinical data do not suggest a role for piperacillin-tazobactam, and we caution clinicians against its usage for these infections.

Cefepime Therapy for Cefepime-Susceptible Extended-Spectrum β-Lactamase-Producing Enterobacteriaceae Bacteremia

The role of cefepime for extended-spectrum β-lactamase (ESBL) bacteremia is unclear if susceptible in vitro. In a propensity score-matched study of patients with ESBL bacteremia, risk of death was 2.87 times higher for patients receiving cefepime compared with carbapenems (95% confidence interval [CI], .88–9.41). We compared 14-day mortality of patients with ESBL bacteremia receiving empiric cefepime versus empiric carbapenem therapy in a propensity score-matched cohort. There was a trend towards increased mortality in the cefepime group (hazard ratio, 2.87; 95% CI, .88–9.41), which enhances the existing literature suggesting that cefepime may be suboptimal for invasive ESBL infections.

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.

Which Multidrug-Resitant Bacteria are Emerging in Patients with Hematological Malignancies?: One-Year Report

The aim of this retrospective, observational study was to evaluate the outcomes of bacteremia attacks during neutropenic episodes caused by chemotherapy in patients with hematological cancers by assessing mortality, involved pathogens, antimicrobial therapy and treatment responses. Patients who were older than 14 years of age and developed at least one neutropenic episode after chemotherapy to treat hematological cancer between November 2011 and November 2012 were included in the study. We retrospectively collected demographic, treatment, and survival data for 68 patients with 129 neutropenic episodes. The mean age was 59.36 ± 15.22 years (range 17-80 years), and 41 cases were male. The mean Multinational Association of Supportive Care in Cancer score was 19.56 ± 9.04. A total of 37 (28 %) bacteremia attacks were recorded in 20 cases (29 %). Fatality rates were 50 % in the six cases with bacteremia caused by carbapenem-resistant Gram-negative bacteria; death occurred in two patients with carbapenem-resistant Acinetobacter baumannii and in one patient with carbapenem-resistant Pseudomonas aeruginosa. Clinical and microbiological responses were achieved using PIP-TAZ or CEP-SUL treatment in 80 % (16/20) of the cases with bacteremia caused by carbapenem-sensitive Gram-negative bacteria (CS-GNB). During 547 colonization-days in 21 (30 %) vancomycin-resistant enterococci (VRE)-colonized cases among 68 patients, vancomycin-resistant Enterococcus faecium bacteremia developed in two patients. Non-carbapenem-based therapy can cure most bacteremia attacks caused by CS-GNB in patients with hematological cancer. However, bacteremia and other infections caused by drug-resistant pathogens, such as A. baumannii, P. aeruginosa, and VRE, are a growing concern in hematological patients.

β-lactam and β-lactamase inhibitor combinations in the treatment of extended-spectrum β-lactamase producing Enterobacteriaceae: time for a reappraisal in the era of few antibiotic options?

The spread of extended-spectrum β-lactamase (ESBL) genes in Enterobacteriaceae such as Escherichia coli or Klebsiella spp is a major challenge to modern medical practice. Carbapenems are the treatment of choice for serious infections caused by ESBL producers; however, carbapenem resistance has increased globally. ESBL producers might be susceptible to β-lactam-β-lactamase inhibitor (BLBLI) combination antibiotics such piperacillin-tazobactam or amoxicillin-clavulanate. These drugs are frequently avoided in serious infections caused by ESBL producers because of the inoculum effect in-vitro (especially for piperacillin-tazobactam), animal data suggesting inferior efficacy when compared with carbapenems, concerns about pharmacokinetic-pharmacodynamic drug target attainment with standard doses, and poor outcomes shown in some observational studies. Prospective cohort data and a meta-analysis suggest that BLBLIs are non-inferior to carbapenems in the treatment of bloodstream infections caused by ESBL producers. We examine why BLBLIs are perceived as inferior in the treatment of infection with ESBL producers, and discuss data that suggest these concerns might not be strongly supported by clinical evidence.

Possibility of CTX-M-14 Gene Transfer from Shigella sonnei to a Commensal Escherichia coli Strain of the Gastroenteritis Microbiome

Objectives

To investigated whether the CTX-M-14 gene could be transferred from a clinical Shigella sonnei strain to commensal Escherichia coli strain in the gastroenteritis microbiome.

Methods

E. coli strains were isolated from 30 stool samples of S. sonnei infected students in a gastroenteritis outbreak in 2004 and were characterized by antibiotic resistance analysis, in vitro conjugation and in vivo transfer of CTX-M-14 gene and molecular assays.

Results

One strain of Escherichia coli that had high levels of resistance to cefotaxime was isolated from a patient infected with S. sonnei. Isoelectric focusing showed that the E. coli and S. sonnei strains produced a β-lactamase with an isoelectric point of 8.1. Moreover, polymerase chain reaction analysis indicated that both strains possessed the same DNA sequences for CTX-M-14. The results of in vitro and in vivo conjugation showed that the efficiency of CTX-M-14 transfer from S. sonnei to E. coli was similar to CTX-M-14 transfer between E. coli strains.

Conclusion

The data suggest that the acquisition of the extended-spectrum β-lactamases gene by pathogenic bacteria in the human intestinal tract to commensal microbiome bacteria can cause serious infectious diseases.

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.

The outcome of non-carbapenem-based empirical antibacterial therapy and VRE colonisation in patients with hematological malignancies

BACKGROUND

Febrile neutropenia (FN) is generally a complication of cancer chemotherapy.

OBJECTIVES

We retrospectively evaluated the febrile neutropenia episodes and their outcomes with respect to modification rates of non-carbapenem-based empirical antibacterial therapy and vancomycin-resistant enterococcus (VRE) colonisation that caused to VRE bacteremia in patients with hematological malignancies.

METHODS

All consecutive patients, who were older than 14 years of age and developed febrile neutropenia episodes due to hematological malignancies from September 2010 to November 2011 at the hematology department were included into the study.

RESULTS

In total, 86 consecutive neutropenic patients and their 151 febrile episodes were evaluated. The mean MASCC prognostic index score was 18,72 ± 9,43. Among 86 patients, 28 patients experienced a total of 30 bacteremia episodes of bacterial origin. Modification rates of both, empirical monotherapy and combination therapies, were found similar, statistically (P = 0,840).

CONCLUSIONS

Our results suggest that initiating of non-carbapenem based therapy does not provide high response rates in the treatment of febrile neutropenia attacks. Furthermore, non-carbapenem-based empirical therapy provides benefit in regard to cost-effectiveness and antimicrobial stewardship when local antibiotic resistance patterns of gram-negative bacteria are considered. Patients who are colonized with VRE are more likely to develop bacteremia with VRE strains as a result of invasive procedures and severe damage of mucosal barriers observed in this group of patients.

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.

Efficacy of ertapenem for treatment of bloodstream infections caused by extended-spectrum-β-lactamase-producing Enterobacteriaceae

Ertapenem is active against extended-spectrum-β-lactamase (ESBL)-producing Enterobacteriaceae organisms but inactive against Pseudomonas aeruginosa and Acinetobacter baumannii. Due to a lack of therapeutic data for ertapenem in the treatment of ESBL bloodstream infections (BSIs), group 2 carbapenems (e.g., imipenem or meropenem) are often preferred for treatment of ESBL-producing Enterobacteriaceae, although their antipseudomonal activity is unnecessary. From 2005 to 2010, 261 patients with ESBL BSIs were analyzed. Outcomes were equivalent between patients treated with ertapenem and those treated with group 2 carbapenems (mortality rates of 6% and 18%, respectively; P = 0.18).

Clinical characteristics and outcomes of patients with extended-spectrum β-lactamase-producing bacteremias in the emergency department

Extended-spectrum β-lactamase (ESBL)-producing bacteria have been spreading from hospitals to communities. Despite this, there are limited emergency department (ED) patient-based studies about these bacteremias. A retrospective matched case-control study with a ratio of 1:3 was conducted at a university hospital. The case group consisted of patients aged >16 years with ESBL-producing bacteremias in the ED. Patients matched for age and sex with non-ESBL-producing bacteremias were sampled as the control group. Finally, 64 episodes of ESBL-producing Escherichia coli, Klebsiella pneumoniae, and Proteus mirabilis bacteremias were included in our study. The median age of case patients was 71 years, and 29 (45.3%) were males. The most common type of infection was urinary tract infection (71.9%), followed by intra-abdominal infection (12.5%). Inappropriate empirical antibiotics therapy was prescribed in 87.5% of case patients, which was significantly higher than the control group (13.0%; p < 0.001). Patients with inappropriate empirical antibiotics had a significantly longer hospital stay than those with appropriate empirical antibiotics (p < 0.001). Multivariate analysis showed that hospital-acquired infection, urinary catheterization, and previous antibiotics use were independent risk factors for the acquisition of ESBL-producing bacteremia. The 28-day mortality rate of case patients was 18.8%. Whether they received appropriate empirical antibiotics treatment or not, there was no statistical difference in the mortality of patients with ESBL-producing bacteremias (p = 0.167). To face these emerging multidrug-resistant bacteria and to guide the empirical antibiotics therapy, it is crucial for emergency physicians to recognize the characteristics and risk factors for ESBL-producing organisms.

ESBLs: A Clear and Present Danger?

Extended spectrum β-lactamases (ESBLs) are enzymes produced by a variety of Gram negative bacteria which confer an increased resistance to commonly used antibiotics. They are a worrying global public health issue as infections caused by such enzyme-producing organisms are associated with a higher morbidity and mortality and greater fiscal burden. Coupled with increasing prevalence rates worldwide and an ever diminishing supply in the antibiotic armamentarium, these enzymes represent a clear and present danger to public health. This article aims to give an overview of the current situation regarding ESBLs, with a focus on the epidemiology and management of such infections.

Extended-spectrum beta-lactamase-producing bacterial infections in adult solid organ transplant recipients

BACKGROUND

Limited research is available evaluating infections due to extended-spectrum β-lactamase (ESBL)-producing organisms in adult recipients of solid organ transplant (SOT).

OBJECTIVE

To evaluate clinical response and rate of recurrence of ESBL-producing organisms in 20 SOT recipients.

METHODS

In a retrospective case series, records of adult SOT recipients with an admitting diagnosis of infection and a positive culture for an ESBL-producing organism from January 2003 through August 2006 were reviewed.

RESULTS

Twenty patients met inclusion criteria. The median time to infection following transplant was 3.5 years (range 1-23 years). Overall, 85% of the patients received inadequate empiric antibiotic therapy, including ciprofloxacin or piperacillin/tazobactam, to manage their infection. Nineteen patients had clinical resolution; however, 12 patients required at least 1 readmission due to infection recurrence. One patient's death occurred during the study period. The median time to readmission for a recurrence was 41 days (18-455 days). All recurrent infections were caused by the same ESBL-producing pathogen and 10 of 12 (83%) infections occurred at the same site as the initial infection. Among patients with recurrent infections, 75% received inadequate empiric therapy upon readmission. All 12 patients with recurrent infections had successful clinical responses to both initial and recurrent infections.

CONCLUSIONS

The provision of inadequate empiric therapy for new and recurrent infections due to ESBL-producing pathogens was common in this study population. SOT recipients with a history of infection due to an ESBL-producing organism presenting with a new infection should receive adequate empiric therapy with a carbapenem agent until a definitive diagnosis can be established.

National multicenter study of predictors and outcomes of bacteremia upon hospital admission caused by Enterobacteriaceae producing extended-spectrum beta-lactamases

Extended-spectrum β-lactamase (ESBL)-producing Enterobacteriaceae are pathogens that may lead to a spectrum of clinical syndromes. We aimed to identify predictors and outcomes of ESBL bacteremia upon hospital admission (UHA) in a nationwide prospective study. Thus, a multicenter prospective study was conducted in 10 Israeli hospitals. Adult patients with bacteremia due to Enterobacteriaceae diagnosed within 72 h of hospitalization were included. Patients with ESBL producers (cases) were compared to those with non-ESBL producers (controls), and a 1:1 ratio was attempted in each center. A case-control study to identify predictors and a cohort study to identify outcomes were conducted. Bivariate and multivariate logistic regressions were used for analyses. Overall, 447 patients with bacteremia due to Enterobacteriaceae were recruited: 205 cases and 242 controls. Independent predictors of ESBL were increased age, multiple comorbid conditions, poor functional status, recent contact with health care settings, invasive procedures, and prior receipt of antimicrobial therapy. In addition, patients presenting with septic shock and/or multiorgan failure were more likely to have ESBL infections. Patients with ESBL producers suffered more frequently from a delay in appropriate antimicrobial therapy (odds ratio [OR], 4.7; P, <0.001) and had a higher mortality rate (OR, 3.5; P, <0.001). After controlling for confounding variables, both ESBL production (OR, 2.3; P, 9.1) and a delay in adequate therapy (OR, 0.05; P, 0.001) were significant predictors for mortality and other adverse outcomes. We conclude that among patients with bacteremia due to Enterobacteriaceae UHA, those with ESBL producers tend to be older and chronically ill and to have a delay in effective therapy and severe adverse outcomes. Efforts should be directed to improving the detection of patients with ESBL bacteremia UHA and to providing immediate appropriate therapy.

Clinical outcome of empiric antimicrobial therapy of bacteremia due to extended-spectrum beta-lactamase producing Escherichia coli and Klebsiella pneumoniae

Background

Prompt administration of adequate empiric antimicrobial therapy is a major determinant influencing the outcome of serious infections. The objective of this study was to describe empiric antimicrobial therapy employed and assess its effect on the outcome of patients bacteremic with extended-spectrum beta-lactamase (ESBL) producing Escherichia coli and Klebsiella pneumoniae.

Findings

A retrospective surveillance study of all patients with bacteremias caused by ESBL-producing E. coli and K. pneumoniae (EK-ESBL) from 2000-2007 in the Calgary Health Region was conducted. Data were available for 79 episodes of bacteremia among 76 patients. Forty-four (56%) were male, the median age was 70.0 yrs [interquartile range (IQR) 60.6-70.1 yrs], and 72 (91%) episodes were E. coli. Seventy-four episodes (94%) were treated with empiric therapy within the first 48 hours. A non-statistically significant increased mortality occurred in those treated empirically with a beta-lactam/beta-lactamase inhibitor combination (6/16; 38% vs. 10/53; 18%; p = 0.063) while empiric carbapenem therapy was associated with lower mortality (0/10 died vs. 16/53 (30%), p = 0.089). Only 42 (53%) episodes received adequate therapy within the first 48 hours. The median time to first adequate antibiotic therapy was 41.0 hours [IQR 5.8-59.5] (n = 75). The case-fatality rate was not different among those that received adequate compared to inadequate therapy by 48 hours as compared to inadequate empiric therapy (9/42; 21% vs. 7/37; 19%; p = 1.0).

Conclusion

Inadequate empiric therapy is common among patients with EK-ESBL bacteremia in our region but was not associated with adverse mortality outcome.

Prevalence of extended-spectrum beta-lactamase-producing Enterobacteriaceae in Bahrain

OBJECTIVES

To determine the occurrence of extended-spectrum beta-lactamase (ESBL)-producing Enterobacteriaceae in Bahrain.

METHODS

Retrospective analysis of records (January 2005-December 2006) at the Microbiology Laboratory of the Salmaniya Medical Complex, Bahrain which is the major national diagnostic laboratory.

RESULTS

Out of a total of 11,886 member of family of Enterobacteriaceae isolated, 2695 (22.6%) were ESBL producers. Majority of ESBL isolates were from inpatients (n=2363; 87.7%). Escherichia coli (52.2%) and Klebsiella pneumoniae (24.3%) were predominant and distributed comparatively in the hospital wards while Proteus spp. (17.6%) was predominant in medical wards. Urine was the major source (52.2%) with low occurrence in blood cultures. No carbapenem resistant isolates was identified but resistance to three classes of antibiotics was exhibited by >25% of the isolated ESBL strains. Nitrofurantoin resistance was identified in 38.2% of urinary isolates.

CONCLUSION

This is the first report from Bahrain and it indicates that the prevalence of ESBL-producing isolates is high. Carbapenems were the most active drug against the ESBL-producing isolates. We recommend strict infection control to prevent trafficking into the community.

Comparative assessment of inoculum effects on the antimicrobial activity of amoxycillin-clavulanate and piperacillin-tazobactam with extended-spectrum beta-lactamase-producing and extended-spectrum beta-lactamase-non-producing Escherichia coli isolates

A significant inoculum-size effect has been observed with piperacillin-tazobactam, and has been associated with beta-lactamase production in extended-spectrum beta-lactamase (ESBL) producers. This association has not been previously studied in the case of amoxycillin-clavulanate. Piperacillin-tazobactam and amoxycillin-clavulanate were compared, using high inocula of susceptible strains either harbouring ESBLs or not. Two non-ESBL-producing and 15 amoxycillin-clavulanate-susceptible and piperacillin-tazobactam-susceptible ESBL-producing Escherichia coli isolates, and their respective transconjugants, were tested in dilution susceptibility tests using standard and 100-fold higher inocula. Three ESBL-producing strains and E. coli ATCC 25922 were selected for time-kill studies using standard and high initial inocula. At high inocula, MICs of piperacillin increased >eight-fold for non-ESBL-producing strains, and MICs of piperacillin-tazobactam (8:1 ratio or with tazobactam fixed at 4 mg/L) increased>eight-fold for all ESBL-producing strains. However, amoxycillin MICs were not affected by a high inoculum with non-ESBL-producing strains, whereas the MICs of amoxycillin-clavulanate (2:1 and 4:1) increased <or=four-fold for ESBL producers, using the broth and agar dilution methods. In kinetic studies at a high inoculum, amoxycillin and amoxycillin-clavulanate were bactericidal against E. coli ATCC 25922, whereas piperacillin and piperacillin-tazobactam yielded decreases of <1 log(10) CFU/mL. Similarly, at a high inoculum, only amoxycillin-clavulanate was able to maintain bactericidal rates of killing over 24 h against the ESBL-positive E. coli isolates. The stability of amoxycillin-clavulanate and the contrasting results obtained with piperacillin-tazobactam against high inocula of ESBL-non-producing and ESBL-producing E. coli strains appear to be related to aspects other than the amount of beta-lactamase production.

Extended-spectrum beta-lactamase-producing organisms

Extended-spectrum beta-lactamases (ESBLs), which hydrolyse extended-spectrum cephalosporins and are inhibited by clavulanic acid, are spreading among Enterobacteriaceae. The CTX-M enzymes are replacing SHV and TEM enzymes as the prevalent type of ESBLs, principally in community-acquired infections caused by Escherichia coli. Associated infectious syndromes include mainly urinary tract infections, and secondly bloodstream and intra-abdominal infections, and may be serious enough to warrant hospitalisation. Affected patients commonly have various underlying risk factors. This is also observed in hospital-acquired infections. The rates of ESBL-expression among nosocomial Enterobacteriaceae isolates, particularly Klebsiella pneumoniae, have risen substantially in several countries. The hospital epidemiology of these infections is often complex; multiple clonal strains causing focal outbreaks may co-exist with sporadic ones. Relevant infection-control measures should focus on reducing patient-to-patient transmission via the inanimate environment, hospital personnel, and medical equipment. Wise use of antibiotics is also essential. The available therapeutic options for the treatment of ESBL-associated infections are limited by drug resistance conferred by the ESBLs, along with frequently observed co-resistance to various antibiotic classes, including cephamycins, fluoroquinolones, aminoglycosides, tetracyclines, and trimethoprim/sulfamethoxazole. Relevant clinical data regarding the effectiveness of different regimens for ESBL-associated infections are limited. Although certain cephalosporins may appear active in vitro, associated clinical outcomes are often suboptimal. beta-Lactam/beta-lactamase inhibitor combinations may be of value, but the supporting evidence is weak. Carbapenems are regarded as the agents of choice, and may be more effective than fluoroquinolones for serious infections. Tigecycline and polymyxins have substantial antimicrobial activity against ESBL-producing Enterobacteriaceae, and, along with fosfomycin, merit further evaluation.

Prevalence of multiresistant gram-negative organisms in a tertiary hospital in Mwanza, Tanzania

Background

Antimicrobial resistance is fast becoming a global concern with rapid increases in multidrug-resistant Gram negative organisms. The prevalence of extended spectrum beta-lactamase (ESBL)-producing clinical isolates increases the burden on implementing infectious disease management in low socio-economic regions. As incidence can vary widely between regions, this study was done to determine resistance patterns of Gram-negative organisms at Bugando Medical Center, a tertiary hospital in Mwanza, Tanzania.

Methods

A total of 800 clinical samples (urine, wound swab, pus, blood, aspirate, sputum etc) were processed over a period of 6 months. Gram-negative bacteria were identified using conventional in-house biochemical tests and susceptibility to common antibiotics done using disc diffusion methods. The disc approximation method was used to identify ESBL producers.

Results

A total of 377 Gram-negative bacteria (GNB) recovered from 377 clinical specimens were analyzed of which 76.9% were Enterobacteriaceae. Among all GNB, 110/377 (29.2%) were found to be ESBL producers. Species specific ESBLs rate among Klebsiella pneumoniae, Escherichia coli, Acinetobacter spp, Proteus spp and other enterobacteria were 63.7%, 24.4%, 17.7%, 6.4% and 27.9% respectively. A statistically significant higher number of inpatients 100/283 (35.3%) compared to 10/94 (10.6%) of outpatients had ESBL-producing organisms (p = 0.000023). Rates of resistances to gentamicin, tetracycline, sulphamethaxazole/trimethoprim and ciprofloxacin were significantly higher among ESBLs isolates than non-ESBL isolates (p = 0.000001).

Conclusion

ESBL producing organisms are common at BMC (Bugando Medical Center) and pose a challenge to antibiotic therapy. Successful implementation of a routine detection of ESBL production is essential in designing appropriate antibiotic prescribing policies and infection control intervention programmes.

Extended-spectrum beta-lactamase-producing Enterobacteriaceae: an emerging public-health concern

The medical community relies on clinical expertise and published guidelines to assist physicians with choices in empirical therapy for system-based infectious syndromes, such as community-acquired pneumonia and urinary-tract infections (UTIs). From the late 1990s, multidrug-resistant Enterobacteriaceae (mostly Escherichia coli) that produce extended-spectrum beta lactamases (ESBLs), such as the CTX-M enzymes, have emerged within the community setting as an important cause of UTIs. Recent reports have also described ESBL-producing E coli as a cause of bloodstream infections associated with these community-onset UTIs. The carbapenems are widely regarded as the drugs of choice for the treatment of severe infections caused by ESBL-producing Enterobacteriaceae, although comparative clinical trials are scarce. Thus, more rapid diagnostic testing of ESBL-producing bacteria and the possible modification of guidelines for community-onset bacteraemia associated with UTIs are required.

First report of the emergence of CTX-M-type extended-spectrum beta-lactamases (ESBLs) as the predominant ESBL isolated in a U.S. health care system

CTX-M-type extended-spectrum beta-lactamases (ESBLs) have become increasingly common worldwide, with the notable exception of the United States, where TEM- and SHV-type ESBLs have appeared to predominate. We have noted the emergence of ESBLs in our health care system (the University Health System in San Antonio, TX), especially in Escherichia coli isolates, that preferentially hydrolyze cefotaxime rather than ceftazidime, suggesting the possibility of CTX-M-type enzymes. Microbiology laboratory records were reviewed to identify ESBL-producing isolates and to compare the diameters of ceftazidime disk diffusion zones of inhibition to cefotaxime zone diameters. All isolates had been initially detected and confirmed using the procedures recommended by the Clinical and Laboratory Standards Institute. A total of 94 stored ESBL-producing isolates recovered between January 2000 and June 2006 (predominately from blood and normally sterile fluids) were retrieved for further study and screened using PCR primers specific for the presence of CTX-M, TEM, and SHV ESBLs. Only small numbers of retained ESBL-producing isolates were available for study in 2000 and 2002. The percentages of available ESBL-producing organisms in the following years were found to produce CTX-M enzymes: 2000, 25%; 2001, 10%; 2002, 0%; 2003, 60%; 2004, 69%; 2005, 89%; and 2006, 70%. The most common CTX-M-type ESBL was CTX-M-15, followed by CTX-M-16, CTX-M-8, and CTX-M-14. Comparing the disk diffusion zone diameters of cefotaxime and ceftazidime was helpful with the initial recognition of CTX-M-producing E. coli, which had an average cefotaxime zone diameter 7 mm smaller than the ceftazidime zone. However, comparing ceftazidime and cefotaxime zones for CTX-M-producing Klebsiella spp. was not helpful with initial recognition. CTX-M enzymes were also identified in Proteus mirabilis, Enterobacter spp., and Morganella morganii. Based on pulsed-field gel electrophoresis typing of the E. coli isolates, the CTX-M-producing isolates did not represent the spread of a single clone in the institution or in the community. In conclusion, CTX-M-type ESBLs are now the most common ESBL type isolated from patients in our health care system and may also be present but unrecognized in other U.S. locales.

Comparison of Essential Oils from Three Plants for Enhancement of Antimicrobial Activity of Nitrofurantoin against Enterobacteria

BACKGROUND

Piperitone from plant essential oils enhancesbactericidal activities of nitrofurantoin and furazolidone against bacteria from the family Enterobacteriaceae. In this study, the essential oils of spearmint (Mentha spicata L.), dill (Anethum graveolens L.) and peppermint (Mentha piperita L.)were screened for augmentation of nitrofurantoin activity and the most active components were determined.

METHOD

The effects of essential oils and their components on the bactericidal activity of nitrofurantoin against Enterobacter cloacae were studied using disk-diffusion and agar-dilution methods. The composition of essential oils was studied using gas chromatography-mass spectrometry.

RESULTS

M. spicata and A. graveolens oils exhibited the highest effects. Gas chromatography-mass spectrometry analysis showed that the oils of these two plants contained 40.12 and 20.32% carvone, respectively. Pure carvone and piperitone equally increased the bactericidal activity of nitrofurantoin. Other ingredients of essential oils, including camphor, limonene and menthone, were less effective.

Cefepime pharmacodynamics in patients with extended spectrum beta-lactamase (ESBL) and non-ESBL infections

OBJECTIVE

This study was designed to compare cefepime exposures with microbiological outcomes in ESBL and non-ESBL infections and determine the pharmacodynamic profiles associated with successful outcome.

METHODS

Cefepime pharmacodynamic exposures of unbound drug [time above MIC (fT>MIC), minimal concentration over MIC (fC(min)/MIC), and area under the curve over MIC (fAUC/MIC)] for 18 patients with ESBL and non-ESBL infections were determined by using a published population pharmacokinetic model. Classification and regression tree analysis was used to identify pharmacodynamic breakpoints that predicted eradication. A 5000-patient Monte Carlo Simulation was conducted to estimate the probability of target attainment for the goal pharmacodynamic exposures.

RESULTS

Eradication was 80% when fT>MIC was 50% compared with 0% when T>MIC was less than 50% (p<0.05). The median fC(min)/MIC ratio for ESBL group was statistically lower than that for the non-ESBL group (1.54 versus 138, p<0.001). Regardless of ESBL production, all pathogens were eradicated when fC(min)/MIC>7.6 and only 33.3% were eradicated when fC(min)/MIC< or =7.6 (p<0.05). Pharmacodynamic exposures of 50% fT>MIC and fAUC/MIC>1654 were also predictive of eradication. While conventional dosage regimens of 2g q 12h and q 8h failed to achieve adequate target attainment, 4 g continuous infusion and 2g q 6-8h prolonged infusion could attain more than 90% of target attainment at the MIC of 2 microg/ml for the breakpoint of fCmin/MIC=7.6.

CONCLUSION

Microbiological eradication in patients receiving cefepime was best predicted by fCmin/MIC ratio greater than 7.6 regardless of the presence of an ESBL. Continuous or prolonged infusion regimens provided the greatest probability of attaining this exposure.

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.

Clinical correlation of the CLSI susceptibility breakpoint for piperacillin- tazobactam against extended-spectrum-beta-lactamase-producing Escherichia coli and Klebsiella species

We assessed infections caused by extended-spectrum-beta-lactamase-producing Escherichia coli or Klebsiella spp. treated with piperacillin-tazobactam to determine if the susceptibility breakpoint predicts outcome. Treatment was successful in 10 of 11 nonurinary infections from susceptible strains and in 2 of 6 infections with MICs of >16/4 mug/ml. All six urinary infections responded to treatment regardless of susceptibility.

Applying antimicrobial pharmacodynamics to resistant gram-negative pathogens

PURPOSE

Guided antibiotic adjustment for the treatment of multidrug-resistant, gram-negative pathogens is explored.

SUMMARY

Multidrug-resistant pathogens are being isolated with increasing frequency, while the production of novel agents to circumvent resistance has slowed to a near halt. Hence, antimicrobial adjustment based on drug pharmacokinetic and pharmacodynamic properties has moved to the forefront of treatment. Pharmacodynamic principles for major classes of antimicrobials are reviewed, and the use of susceptibility reports to optimize pharmacodynamics to treat gram-negative infections is described. The need for the application of antimicrobial pharmacodynamics continues to grow as resistance to the agents becomes more common. Susceptibility reports, including antibiograms, and their limitations are briefly discussed. The resistance profiles of the beta-lactams (including carbapenems), aminoglycosides, fluoroquinolones, tetracyclines and glycylcyclines, and the polymyxins are reviewed, and the pharmacodynamic optimization of these profiles is explored.

CONCLUSION

Various mechanisms account for resistance of bacteria to antibiotics. The appropriate use of pharmacokinetics and pharmacodynamics can guide antibiotic therapy and enhance the likelihood of success.

Application of molecular techniques to the study of hospital infection

Nosocomial infections are an important source of morbidity and mortality in hospital settings, afflicting an estimated 2 million patients in United States each year. This number represents up to 5% of hospitalized patients and results in an estimated 88,000 deaths and 4.5 billion dollars in excess health care costs. Increasingly, hospital-acquired infections with multidrug-resistant pathogens represent a major problem in patients. Understanding pathogen relatedness is essential for determining the epidemiology of nosocomial infections and aiding in the design of rational pathogen control methods. The role of pathogen typing is to determine whether epidemiologically related isolates are also genetically related. To determine molecular relatedness of isolates for epidemiologic investigation, new technologies based on DNA, or molecular analysis, are methods of choice. These DNA-based molecular methodologies include pulsed-field gel electrophoresis (PFGE), PCR-based typing methods, and multilocus sequence analysis. Establishing clonality of pathogens can aid in the identification of the source (environmental or personnel) of organisms, distinguish infectious from noninfectious strains, and distinguish relapse from reinfection. The integration of molecular typing with conventional hospital epidemiologic surveillance has been proven to be cost-effective due to the associated reduction in the number of nosocomial infections. Cost-effectiveness is maximized through the collaboration of the laboratory, through epidemiologic typing, and the infection control department during epidemiologic investigations.

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.

Why is the microbiology lab calling about an extended-spectrum beta-lactamase bacterium from a wound culture?

As more and more gram-negative bacteria produce extended-spectrum beta-lactamases, it is important that physicians know what to do when these bacteria cause postoperative infections in patients.

Pharmacodynamics of intermittent and continuous infusion piperacillin/tazobactam and cefepime against extended-spectrum β-lactamase-producing organisms

The pharmacodynamics of piperacillin/tazobactam and cefepime were evaluated against extended-spectrum beta-lactamase (ESBL)-producing organisms. Ten thousand patients were simulated based on ESBL minimum inhibitory concentrations (MICs) from our laboratory (N=39) and on pharmacokinetic data from peer-reviewed literature. The desired proportion of the dosing interval that the concentration remains above the MIC (%T>MIC) for the intermittent bolus regimens was >/=40% for piperacillin/tazobactam and >/=60% for cefepime. The desired C(ss)/MIC ratio (where C(ss) is the concentration at steady state) was >/=2 for all continuous infusion (CI) regimens. MIC(50), MIC(90) and %S were, respectively, 64/4mug/mL, 1024/4mug/mL and 33% for piperacillin/tazobactam and 8mug/mL, 16mug/mL and 0% for cefepime. For piperacillin/tazobactam, 3.375g every 4h (q4h) achieved the highest probability of target attainment (43%), followed by 13.5g CI (31%), 3.375g q6h (27%), 4.5g q8h (17%) and 6.75g CI (10%). However, for cefepime, 4g CI had the highest probability of target attainment (77%), followed by 1g q8h (65%), 2g q12h (58%), 3g CI (46%) and 1g q12h (27%). Although the probabilities of target attainment for cefepime were higher than for piperacillin/tazobactam, neither agent achieved a high probability of target attainment and should not be used routinely for the treatment of ESBL infections.

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.

Antibacterial agents in pediatrics

Antibiotics are among the most widely prescribed therapeutic agents in children. Several new trends in antibiotic usage for pediatric care have emerged. New mechanisms of antibacterial resistance have required a broader repertoire of antibiotic usage, including new agents directed at multidrug resistance. After promotion of judicious antibiotic use, there has been a decline in the number of pediatric prescriptions for antibiotics. Recent legislation addresses the necessity for pediatric clinical drug trials, ensuring development of further antibacterial agents for use in pediatric patients.

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.

Antibiotic therapy for Klebsiella pneumoniae bacteremia: implications of production of extended-spectrum beta-lactamases

The prevalence of extended-spectrum beta -lactamase (ESBL) production by Klebsiella pneumonia approaches 50% in some countries, with particularly high rates in eastern Europe and Latin America. No randomized trials have ever been performed on treatment of bacteremia due to ESBL-producing organisms; existing data comes only from retrospective, single-institution studies. In a prospective study of 455 consecutive episodes of Klebsiella pneumoniae bacteremia in 12 hospitals in 7 countries, 85 episodes were due to an ESBL-producing organism. Failure to use an antibiotic active against ESBL-producing K. pneumoniae was associated with extremely high mortality. Use of a carbapenem (primarily imipenem) was associated with a significantly lower 14-day mortality than was use of other antibiotics active in vitro. Multivariate analysis including other predictors of mortality showed that use of a carbapenem during the 5-day period after onset of bacteremia due to an ESBL-producing organism was independently associated with lower mortality. Antibiotic choice is particularly important in seriously ill patients with infections due to ESBL-producing K. pneumoniae.