Antimicrobial activity against strains of Escherichia coli and Klebsiella spp. with resistance phenotypes consistent with an extended-spectrum beta-lactamase in Europe

Antibimicrobial Susceptibility of Trimethoprim-Sulfamethoxazole and 3rd-Generation Cephalosporin-Resistant Escherichia coli Isolates Enumerated Longitudinally from Feedlot Arrival to Harvest in High-Risk Beef Cattle Administered Common Metaphylactic Antimicrobials

Multidrug resistant (MDR) Escherichia coli threaten the preservation of antimicrobials to treat infections in humans and livestock. Thus, it is important to understand where antimicrobial-resistant E. coli persist and factors that contribute to its their development. Crossbred cattle (n = 249; body weight = 244 kg ±25 kg standard deviation) were blocked by arrival date and assigned metaphylactic antimicrobial treatments of sterile saline control, tulathromycin (TUL), ceftiofur, or florfenicol at random. Trimethoprim-sulfamethoxazole (COTR) and third-generation cephalosporin (CTXR)-resistant E. coli were isolated from fecal samples on days 0, 28, 56, 112, 182, and study END (day 252 for block 1 and day 242 for block 2). Then, susceptibility testing was conducted on all confirmed isolates. MDR was detected in both COTR and CTXR E. coli isolates. In COTR isolates, the number of antimicrobials each isolate was resistant to and the minimum inhibitory concentration (MIC) for amoxicillin-clavulanic acid, ceftriaxone, and gentamicin was greatest on day 28 compared with all other days (p ≤ 0.04). Similarly, chloramphenicol MIC was greater on day 28 than on day 0 (p < 0.01). Overall, sulfisoxazole MIC was less for TUL than all other treatments (p ≤ 0.02), and trimethoprim-sulfamethoxazole MIC was greater for TUL than all other treatments (p ≤ 0.03). Finally, there was no effect of treatment, day, or treatment × day for tetracycline or meropenem MIC (p ≥ 0.07). In CTXR isolates, there was an effect of day for all antimicrobials tested except ampicillin and meropenem (p ≤ 0.06). In conclusion, administering a metaphylactic antimicrobial at feedlot arrival did influence the susceptibility of COTR and CTXR E. coli. However, MDR E. coli are widely distributed, and the MIC for most antimicrobials was not different from the initial value upon completion of the feeding period.

The bacterial pathogen and resistance spectrum in a dermatological inpatient ward: a six-year, retrospective, epidemiological study

Aim

Treatment of bacterial soft tissue infections is an essential part of clinical dermatology, and the choice of antibiotic therapy is often empirical. The aim of this longitudinal retrospective study was to evaluate bacterial epidemiology, resistance patterns and antibiotic consumption in a dermatological inpatient ward.

Method

Bacterial isolates and antimicrobial susceptibility testing from a dermatological inpatient ward were recorded retrospectively from 2011 to 2016. The antibiotic consumption was evaluated and given as the assumed defined daily dose [DDD] per 100 days of covering per year.

Results

A total of 4,800 bacterial isolates were included (skin, mucous membrane and wounds 87%, urine 9.5%, blood 1.7%, tissue and tissue fluids 1.6%). The proportion of Gram-positive bacteria was 58% (Staphy loc occus aureus 37.8%, coagulase-negative staphylococci 21.5%, Enterococcus spp. 16.7%). Pseudomonas aeruginosa (27.2%), Escherichia coli (17.5%) and Proteus spp. (13.1%) were the most common Gram-negative bacteria. The proportion of multi-resistant pathogens was 5.8% for methicillin-resistant S. aureus, 0.9%, 0.8% and 1.8% for multi-resis tant P. aeruginosa, ESBL-producing E. coli and ESBL-producing Klebsiella pneumoniae of all isolates. Beta-lactam antibiotics were the most used drugs (14.4, 10.8, and 9.6 DDD/100 for aminopenicillins, cefalexin, and penicillin G), followed by clindamycin (9.0 DDD/100 patient days).

Conclusion

In view of the frequency of bacterial soft tissue infections and their need for inpatient treatment with mostly empirically chosen antibiotics, systematic microbiological surveillance should be recommended for dermatological inpatient wards.

Extended spectrum β-lactamase producing Escherichia coli and Klebsiella pneumoniae: critical tools for antibiotic resistance pattern

Drug resistance is a phenomenon where by an organism becomes fully or partially resistant to drugs or antibiotics being used against it. Antibiotic resistance poses an exacting intimidation for people with underlying medical immune conditions or weakened immune systems. Infections caused by the enzyme extended spectrum β-lactamase (ESBL) producing multi drug resistance (MDR) Enterobacteriaceae especially Escherichia coli and Klebsiella pneumoniae are resistant to a broad range of beta lactams, including third generation cephalosporins. Among all the pathogens, these two MDR E. coli and K. pneumoniae have emerged as one of the world's greatest health threats in past two decades. The nosocomial infections caused by these ESBL producing MDR E. coli and K. pneumoniae complicated the therapy and limit treatment options.

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.

Extended-Spectrum Beta-Lactamases Producing Klebsiella Species Isolated from Several Major Hospitals in Iran

Klebsiella pneumoniae is a common hospital-acquired pathogen, causing urinary tract infections, nosocomial pneumoniae, and intra-abdominal infections. K.pneumoniae is also a potential community acquired pathogen. The aims of this study are to determine epidemiology of ESBL-producing K.pneumoniae and Koxytoca in Iran during different seasons, to determine the prevalence of blaTEM, SHV and CTX-M responsible for ESBL production among ESBL-producing K.pneumoniae and Koxytoca in the different wards and hospitals in Iraa Klebsiella spp producing ESBLs were identified by phenotypic and genotyping methods. The findings in this study revealed that 36.5%, 51.7% and 45.6% of K.pneumoniae were producing ESBLs in Ham, Milad and Emam Reza hospitals, respectively. The results revealed blaSHV was responsible for ESBLs production. The analysis showed significant difference of ESBLs production by K.pneumoniae in winter (53%) in comparison to the other seasons P≤ 0.01. The results also showed a significant difference in blaSHV that was the dominant gene responsible for ESBL production P≤ 0.049 but no significant difference was observed between blaTEM and blaSHV. The results showed that the highest ESBL production was found in Koxytoca isolated from patients in Emam Reza Hospital and the lowest frequency of ESBL production was found among Koxytoca in Ham hospital. BlaSHV was found as dominant gene responsible for ESBLs production by K.pneumoniae and Koxytoca, followed by blaCTX-M.

Carbapenems versus alternative antibiotics for the treatment of bacteraemia due to Enterobacteriaceae producing extended-spectrum β-lactamases: a systematic review and meta-analysis

OBJECTIVES

To study the comparative mortality associated with carbapenems and alternative antibiotics for the treatment of patients with extended-spectrum β-lactamase (ESBL)-positive Enterobacteriaceae bacteraemia.

METHODS

We searched systematically PubMed and Scopus databases for studies providing data for mortality among patients treated with carbapenems, β-lactam/β-lactamase inhibitor combinations (BL/BLIs) or non-BL/BLIs (mainly cephalosporins and fluoroquinolones), preferably as monotherapy. Studies focusing on patients of all ages with community- and healthcare-associated bacteraemia were eligible. Data were pooled using the technique of meta-analysis.

RESULTS

Twenty-one articles, studying 1584 patients, were included. Escherichia coli and Klebsiella pneumoniae were the most commonly studied bacteria. Delay in appropriate treatment up to 6 days was reported. Carbapenems were used mainly as definitive therapy. Carbapenems were associated with lower mortality than non- BL/BLIs for definitive [risk ratio (RR) 0.65, 95% CI 0.47-0.91] and empirical (RR 0.50, 95% CI 0.33-0.77) treatment. No statistically significant differences in mortality were found between carbapenems and BL/BLIs administered as definitive (RR 0.52, 95% 0.23-1.13) or empirical (RR 0.91, 95% CI 0.66-1.25) treatment. BL/BLIs were not associated with lower mortality than non-BL/BLIs administered either definitively (RR 1.59, 95% 0.83-3.06) or empirically (RR 0.82, 95% 0.48-1.41). Data regarding subgroups according to the setting, comorbidity and bacterial species could not be extracted.

CONCLUSIONS

Based on data from non-randomized studies, carbapenems may be considered the treatment of choice for empirical treatment of patients with ESBL-producing Enterobacteriaceae bacteraemia. The role of BL/BLIs should be further evaluated for definitive treatment. Further research should focus on faster identification of ESBL-positive pathogens and potential differences in the treatment of each bacterial species.

Nosocomial infection and characterization of extended-spectrum β-lactamases-producing Enterobacteriaceae in Northeast Brazil

INTRODUCTION: Extended spectrum β-lactamases (ESBLs) are enzymes that degrade β-lactam antibiotics and have been reported to be an important cause of nosocomial infection in worldwide. METHODS: During 2009, 659 enterobacteria strains were isolated from different clinical specimens and tested for ESBL production. The disk approximation test, combined disk method and addition of clavulanic acid were used for phenotypic detection of the ESBL-producing strains and PCR for detection of the blaTEM and blaCTX-M genes. RESULTS: Among the isolates, 125 were ESBL producers. The blaCTX-M and blaTEM genes were detected in 90.4% and 75% of the strains, respectively. Most strains were isolated from urine. Klebsiella pneumoniae was the most prevalent organism. Microorganisms presented high resistance to the antibiotics. CONCLUSIONS: These results support the need for extending ESBL detection methods to different pathogens of the Enterobacteriaceae family because these methods are only currently standardized by the CLSI for Escherichia coli, Klebsiella pneumoniae, Klebsiella oxytoca and Proteus mirabilis. Carbapenems were the antibiotic class of choice for the treatment of infections caused by ESBL-producing Enterobacteriaceae.

Antibiotic resistance in orthopaedic surgery: acute knee prosthetic joint infections due to extended-spectrum beta-lactamase (ESBL)-producing Enterobacteriaceae

The aim of this study was to describe the prevalence and characteristics of knee prosthetic joint infections due to extended-spectrum beta-lactamase (ESBL)-producing Enterobacteriaceae. From 2000 to 2007, 132 infections out of 5,076 arthroplasties (2.6%) were registered. Seven out of 132 infections (5.3%) were due to ESBL-producing Enterobacteriaceae, Escherichia coli in six cases and Klebsiella pneumoniae in one. Open debridement and retention of the implant was the first surgical approach and all patients received intravenous carbapenems. Relapse was documented in four cases and remission in three. Therefore, debridement without prosthesis removal was associated with a high failure rate.

Prevalence of extended-spectrum beta-lactamase-producing Escherichia coli in a tertiary care hospital in Tehran, Iran

The prevalence of extended-spectrum beta-lactamase (ESBL) production by consecutive, non-repeated Escherichia coli isolates from hospitalised patients was determined over the period from July 2005 to November 2006. A total of 201 E. coli were isolated from various clinical specimens, 135 (67.2%) of which were confirmed as ESBL-positive using the combination disk synergy test. By univariate analysis, male sex, intravascular or urinary catheterisation, recent surgery or hospitalisation and isolation of E. coli from wound or respiratory tube specimens were found to be risk factors for acquisition of resistant bacteria (chi(2) test, P<0.05). However, binary logistic multivariate regression analysis confirmed that isolation of E. coli from urine samples of either males in any hospital ward (odd ratio (OR) 7.52, 95% confidence interval (CI) 1.21-47.62; P=0.031) or patients with prior surgery (OR 13.16, 95% CI 1.81-100.00; P=0.011) were significantly associated with ESBL production. Imipenem, amikacin and piperacillin/tazobactam were found to be highly active against ESBL-positive isolates in vitro (100%, 91.1% and 85.2% susceptibility, respectively). They showed co-resistance with other antibiotics such as fluoroquinolones, gentamicin and trimethoprim/sulfamethoxazole. Of the 135 ESBL-positive isolates, 22 (16.3%) appeared to be of the CTX-M type based on a phenotypic determination method.

Clinical impact of a PCR assay for rapid identification of Klebsiella pneumoniae in blood cultures

The clinical impact of a rapid PCR identification assay for Klebsiella pneumoniae in positive blood cultures was prospectively evaluated. Multivariate analysis identified the rapid PCR assay as the only significant factor in decreasing the time lapse preceding the initiation of appropriate antimicrobial therapy (hazards ratio, 3.03; confidence interval, 1.62 to 5.68; P, 0.001).

Piperacillin-tazobactam: a beta-lactam/beta-lactamase inhibitor combination

Piperacillin-tazobactam is a beta-lactam/beta-lactamase inhibitor combination with a broad spectrum of antibacterial activity that includes Gram-positive and -negative aerobic and anaerobic bacteria. Piperacillin-tazobactam retains its in vitro activity against broad-spectrum beta-lactamase-producing and some extended-spectrum beta-lactamase-producing Enterobacteriaceae, but not against isolates of Gram-negative bacilli harboring AmpC beta-lactamases. Piperacillin-tazobactam has recently been reformulated to include ethylenediaminetetraacetic acid and sodium citrate; this new formulation has been shown to be compatible in vitro with the two aminoglycosides, gentamicin and amikacin, allowing for simultaneous Y-site infusion, but not with tobramycin. Multicenter, randomized, double-blinded clinical trials have demonstrated piperacillin-tazobactam to be as clinically effective as relevant comparator antibiotics. Clinical trials have demonstrated piperacillin-tazobactam to be effective for the treatment of patients with intra-abdominal infections, skin and soft tissue infections, lower respiratory tract infections, complicated urinary tract infections, gynecological infections and more recently, febrile neutropenia. Piperacillin-tazobactam has an excellent safety and tolerability profile and continues to be a reliable option for the empiric treatment of moderate-to-severe infections in hospitalized patients.

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

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

Contemporary activity of meropenem and comparator broad-spectrum agents: MYSTIC program report from the United States component (2005)

The Meropenem Yearly Susceptibility Test Information Collection Program is a 9-year-old antimicrobial resistance surveillance network of more than 100 medical centers worldwide, including 15 sites in the United States (US) that monitors the susceptibility of Gram-negative and Gram-positive bacterial pathogens especially to carbapenems. In 2005, the antimicrobial activity of 11 broad-spectrum agents was assessed against 2910 bacterial isolates (2493 Gram-negative and 417 staphylococci) submitted from the US medical centers to a reference laboratory using Clinical and Laboratory Standards Institute susceptibility testing methods and interpretative criteria. Meropenem continued to demonstrate 1) high potency with MIC(90) values 4- to 16-fold lower than imipenem against the Enterobacteriaceae, 2) equal activity against Pseudomonas aeruginosa, 3) 2-fold less activity compared with imipenem against Acinetobacter spp., and 4) 4- to 8-fold less activity compared with imipenem against the oxacillin-susceptible staphylococci. The wide spectrum of activity for carbapenems against Enterobacteriaceae (1657 strains) was confirmed by the overall rank order by percentage susceptibility at breakpoint criteria: imipenem (98.9%) > meropenem (98.7%) > cefepime (97.6%) > piperacillin/tazobactam (92.0%) > ceftriaxone (91.2%) > aztreonam (90.6%) > gentamicin = tobramycin (90.5%) > ceftazidime (90.4%) > levofloxacin (84.9%) > ciprofloxacin (83.9%). Against Acinetobacter spp. isolates, only tobramycin (92.0% susceptible) and carbapenems (92.0-85.6%) exhibited acceptable levels of activity. A continued increase in the resistance rate for both ciprofloxacin and levofloxacin was observed with highest rates found among indole-positive Proteae species (36.5-33.3%) and Escherichia coli (21.6-20.4%) isolates, some documented by molecular typing methods as clonally related. Ongoing surveillance of meropenem and other broad-spectrum antimicrobial agents appears warranted to monitor the potency and spectrum of activity against indicated Gram-negative and-positive pathogens causing serious infections in the hospital setting, and to detect the emergence of new or novel resistance mechanisms that could compromise clinical utility (serine and metallo-carbapenemases).

An overview of the Meropenem Yearly Susceptibility Test Information Collection (MYSTIC) Program: 1997-2004

This overview provides a summary of the Meropenem Yearly Susceptibility Test Information Collection (MYSTIC) Program over an 8-year period from 1997 to 2004. The evolution of the MYSTIC Program is described, as well as its design compared with other surveillance programs. In addition, the global MYSTIC Program data, published to date, are summarized, and the empiric use of carbapenems, their current indications, and meropenem usage versus resistance was discussed. From 1997 to 2004, 120 medical centers that were actively prescribing meropenem in 32 countries worldwide participated in the program. The MYSTIC Program results demonstrate the sustained potency and continued effectiveness of meropenem globally against clinically relevant Gram-negative and Gram-positive pathogens including extended spectrum beta-lactamase- and AmpC beta-lactamase-producing organisms, which may also display resistance to the fluoroquinolones and/or aminoglycosides. Furthermore, in centers actively prescribing meropenem, resistance to meropenem is not increasing despite greater resistance among the comparator antimicrobial agents. Thus, antipseudomonal carbapenems such as meropenem and imipenem remain an effective treatment option.

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.

Influx of extended-spectrum beta-lactamase-producing enterobacteriaceae into the hospital

BACKGROUND

The prevalence of infections caused by extended-spectrum beta -lactamase (ESBL)-producing Enterobacteriaceae is increasing worldwide. The influx of these bacteria into hospitals has major implications for infection-control and empirical treatment strategies.

METHODS

Isolates from 2 patient cohorts--patients with gram-negative bacteremia within 2 days after admission and patients screened for fecal colonization at admission--were assessed for ESBL production. ESBL phenotype was confirmed according to Clinical and Laboratory Standards Institute guidelines. Predictors of ESBL phenotype were examined by univariate and multivariate analyses.

RESULTS

Of 80 Enterobacteriaceae isolates from blood samples obtained at admission to the hospital, 13.7% produced ESBL. Thirty-eight patients with ESBL-positive isolates and 72 with ESBL-negative isolates were included in a case-control study. Predictors of ESBL production were male sex and nursing home residence (area under receiver operator characteristic curve, 0.7). Of 241 persons screened at admission, 26 (10.8%) had fecal carriage of ESBL-producing Enterobacteriaceae. Predictors of fecal carriage were poor functional status, antibiotic use, chronic renal insufficiency, liver disease, and use of histamine2 blockers (area under receiver operator characteristic curve, 0.8). Four (15.4%) of the 26 individuals with fecal carriage had subsequent bacteremia with ceftazidime-resistant Enterobacteriaceae, compared with 1 (0.5%) noncarrier (odds ratio, 38.9; P<.001). Of 80 ESBL-producing Enterobacteriaceae isolates obtained at admission, 65 were health care associated, and 15 were community acquired. The 15 community-acquired ESBL-producing Enterobacteriaceae belonged to diverse clones. The most prevalent ESBL gene among these isolates was CTX-M-2 (found in 53.3% of the isolates).

CONCLUSIONS

We report high rates of bacteremia and colonization with ESBL-producing Enterobacteriaceae at admission to our institution, which may undermine infection-control measures and complicate the selection of empirical treatment.

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.

Pharmacodynamic modeling of carbapenems andfluoroquinolones against bacteria that produce extended-spectrum beta-lactamases

BACKGROUND

Bacteria that produce extended-spectrum beta-lactamases (ESBLs) are resistant to penicillins,cephalosporins, and monobactams. The results of clinical studies suggest that the carbapenems imipenem and meropenem may be effective against bacteria that produce ESBLs, although it is not known whether the new once-daily carbapenem ertapenem or the fluoroquinolones are useful against infections caused by ESBL-producing bacteria.

OBJECTIVE

The present study compared the simulated pharmacodynamics of the carbapenems imipenem,meropenem, and ertapenem; the simulated pharmacodynamics of the fluoroquinolones levofloxacin, gatifloxacin, and ciprofloxacin with those of the carbapenems; and the simulated pharmacodynamics of levofloxacin 750 mg with those of levofloxacin 500 mg, all against gram-negative isolates that did and did not produce ESBLs

METHODS

Pharmacokinetic data were obtained from studies in healthy humans. Minimum inhibitory concentrationsMICs) for bacteria that did and did not produce ESBLs were determined in triplicate using broth-microdilution techniques as recommended by National Committee for Clinical Laboratory Standards guidelines. Monte Carlo simulation was used to construct pharmacodynamic models for imipenem, meropenem, ertapenem, levofloxacin, gatifloxacin, and ciprofloxacin. Pharmacodynamic measures of interest were the probability of the free concentration remaining above the MIC >-40% of the time (T>MIC > or =40%) for carbapenems and the likelihood of achieving a free AUC:MIC ratio > or =125 for fluoroquinolones.

RESULTS

MICs were determined for 39 isolates that produced ESBLs and 45 isolates that did not Bacteria that did not produce ESBLs were > or =93% susceptible to all carbapenems and fluoroquinolones tested. Among bacteria that produced ESBLs, rates of susceptibility to the specific agents were as follows: imipenem, 100%; meropenem, 97%; ertapenem, 87%; levofloxacin, 54%; gatifloxacin, 44%; and ciprofloxacin, 36%. In the pharmacodynamic models, imipenem and meropenem had an equal likelihood of achieving a free T>MIC > or =40% against bacteria that produced ESBLs (> or =97%) and bacteria that did not produce ESBLs (> or =98%). In contrast, the likelihood of ertapenem achieving a free T>MIC > or =40% was lower against bacteria that produced ESBLs (78%) than against bacteria that did not produce ESBLs (94%). Similarly, the fluoroquinolones were less likely to achieve a free AUC:MIC ratio > or =125 against bacteria that produced ESBLs (2%-13%) than against bacteria that did not produce ESBLs (85%-91%).

CONCLUSIONS

Carbapenems had superior in vitro activity against bacteria that produced ESBLs compared with fluoroquinolones. Pharmacodynamic modeling based on local ESBL-producing isolates and pharmacokinetic data from healthy humans indicated that imipenem and meropenem may have a greater likelihood of achieving pharmacodynamic targets against bacteria that produce ESBLs than ertapenem or fluoroquinolones.

Appropriate antimicrobial treatment in nosocomial infections—the clinical challenges

Resistance to antimicrobial agents is emerging in a wide variety of pathogens, particularly those that cause nosocomial infections. As a consequence of this increasing resistance, morbidity and mortality in nosocomial infections is also increasing. It is therefore critical to treat nosocomial infections appropriately by starting antimicrobial treatment early in the course of infection, using the correct agent, at the most appropriate dose, and for an adequate duration. Indeed, early 'appropriate' antibiotic prescribing has been shown significantly to reduce mortality, length of intensive care unit and hospital stay and overall costs. Early use of the correct antibiotic at the appropriate dose and for an adequate duration are key to initial appropriate antibiotic prescribing. Choosing the right antibiotic depends mainly on the likely pathogen(s) and the expected local susceptibility patterns. Selection of appropriate antimicrobial therapy requires a thorough understanding of the likely microbial cause of the infection, including local susceptibility patterns, as well as the properties of the antimicrobials available for treating these infections, namely spectrum of activity and potency (including activity versus known resistance mechanisms), pharmacokinetic profile and tolerability and safety. This review, based on a series of presentations at the 5th International Conference of the Hospital Infection Society (Edinburgh, 2002) examines the importance of appropriate antimicrobial therapy in nosocomial infections, and provides guidance on how to achieve this.