Prevalence of newer beta-lactamases in gram-negative clinical isolates collected in the United States from 2001 to 2002

Antimicrobial resistance in the intensive care unit: mechanisms, epidemiology, and management of specific resistant pathogens

Infections caused by drug-resistant and multidrug-resistant microbial pathogens pose tremendous challenges to health care systems, including challenges related to the diagnosis, treatment, and containment of these infections. These challenges are amplified in the intensive care unit (ICU), where pressures for selection and emergence of resistance and risks of transmission of resistant pathogens are highest, and where the threat of resistance drives selection of empiric antimicrobial regimens. This article reviews basic concepts of resistance to antibacterial agents including mechanisms and modes of transmission, and discusses management issues for the important drug-resistant pathogens found in the ICU.

Antibiotic resistance gene abundances associated with waste discharges to the Almendares River near Havana, Cuba

Considerable debate exists over the primary cause of increased antibiotic resistance (AR) worldwide. Evidence suggests increasing AR results from overuse of antibiotics in medicine and therapeutic and nontherapeutic applications in agriculture. However, pollution also can influence environmental AR, particularly associated with heavy metal, pharmaceutical, and other waste releases, although the relative scale of the "pollution" contribution is poorly defined, which restricts targeted mitigation efforts. The question is "where to study and quantify AR from pollution versus other causes to best understand the pollution effect". One useful site is Cuba because industrial pollution broadly exists; antibiotics are used sparingly in medicine and agriculture; and multiresistant bacterial infections are increasing in clinical settings without explanation. Within this context, we quantified 13 antibiotic resistance genes (ARG; indicators of AR potential), 6 heavy metals, 3 antibiotics, and 17 other organic pollutants at 8 locations along the Almendares River in western Havana at sites bracketing known waste discharge points, including a large solid waste landfill and various pharmaceutical factories. Significant correlations (p < 0.05) were found between sediment ARG levels, especially for tetracyclines and β-lactams (e.g., tet(M), tet(O), tet(Q), tet(W), bla(OXA)), and sediment Cu and water column ampicillin levels in the river. Further, sediment ARG levels increased by up to 3 orders of magnitude downstream of the pharmaceutical factories and were highest where human population densities also were high. Although explicit links are not shown, results suggest that pollution has increased background AR levels in a setting where other causes of AR are less prevalent.

First detection of CTX-M and SHV extended-spectrum beta-lactamases in Escherichia coli urinary tract isolates from dogs and cats in the United States

One hundred fifty canine and feline Escherichia coli isolates associated with urinary tract infections were screened for the presence of extended-spectrum beta-lactamase (ESBL) genes. Out of 60 isolates suspected to be ESBL positive based on antimicrobial susceptibility testing, 11 ESBLs were identified, including one SHV-12 gene, one CTX-M-14 gene, and nine CTX-M-15 genes. This study provides the first report of CTX-M- and SHV-type ESBLs in dogs and cats in the United States.

Differential fate of erythromycin and beta-lactam resistance genes from swine lagoon waste under different aquatic conditions

The attenuation and fate of erythromycin-resistance-methylase (erm) and extended-spectrum beta-lactamse (bla) genes were quantified over time in aquatic systems by adding 20-L swine waste to 11,300-L outdoor mesocosms that simulated receiving water conditions below intensive agricultural operations. The units were prepared with two different light-exposure scenarios and included artificial substrates to assess gene movement into biofilms. Of eleven genes tested, only erm(B), erm(F), bla(SHV) and bla(TEM) were found in sufficient quantity for monitoring. The genes disappeared rapidly from the water column and first-order water-column disappearance coefficients were calculated. However, detected gene levels became elevated in the biofilms within 2 days, but then disappeared over time. Differences were observed between sunlight and dark treatments and among individual genes, suggesting that ecological and gene-specific factors play roles in the fate of these genes after release into the environment. Ultimately, this information will aid in generating better predictive models for gene fate.

Molecular characteristics of extended-spectrum beta-lactamase-producing Escherichia coli from the Chicago area: high prevalence of ST131 producing CTX-M-15 in community hospitals

This study was designed to characterise 30 non-duplicate extended-spectrum beta-lactamase (ESBL)-producing Escherichia coli clinical isolates from the community in the Chicago metropolitan area collected during 2008. The majority of isolates (n=28) were recovered from urine and 2 isolates were from blood. Molecular characterisation was done using the following techniques: isoelectric focusing; polymerase chain reaction (PCR) and sequencing of bla(ESBL); PCR for plasmid-mediated quinolone resistance determinants; identification of ST131; phylogenetic grouping; and replicon typing. Genetic relatedness was determined by pulsed-field gel electrophoresis (PFGE) with XbaI and repetitive sequence-based PCR (rep-PCR) typing. Twenty-six (87%) of the ESBL-producing E. coli were positive for bla(CTX-M) genes (22 CTX-M-15 and 4 CTX-M-14), whilst the remaining 4 isolates produced SHV-2. Twenty-eight isolates (93%) were non-susceptible to ciprofloxacin and 16 (53%) were positive for aac(6')-Ib-cr. Overall, 16 (53%) of the ESBL-producers belonged to clonal complex ST131 that produced CTX-M-15 or CTX-M-14. Molecular characteristics of ST131 showed that it belonged to three distinct but related PFGE clones, was derived from phylogenetic group B2 and contained IncFII type plasmids. These results illustrate that E. coli clonal complex ST131 producing CTX-M-15, CTX-M-14, OXA-1, TEM-1 and aac(6')-Ib-cr has emerged as an important cause of community-onset urinary tract infections caused by ESBL-producing E. coli isolates in the Chicago area.

Citrobacter spp. simultaneously harboring blaCTX-M, blaTEM, blaSHV, blaampC, and insertion sequences IS26 and orf513: an evolutionary phenomenon of recent concern for antibiotic resistance

A collection of 40 confirmed isolates of Citrobacter spp., obtained from the culture of 5,732 clinical samples during 2006 to 2008, was studied for the presence of blaCTX-M, blaTEM, blaSHV, and blaampC by monoplex and multiplex PCRs. These isolates were also looked at for the presence of insertion elements IS26 and orf513, which play an important role in the resistance gene pool. blaCTX-M, blaTEM, blaSHV, and blaampC were noticed in 67.5%, 40%, 25%, and 40% of isolates, respectively. Sequencing for the specific CTX-M type revealed the presence of CTX-M-15-type extended-spectrum beta-lactamases (ESBL). sul1-type integrons were detected in 32.5% (13/40) of isolates, and a single plasmid of ca. approximately 22 kb was also noticed in all the isolates harboring bla genes. A total of 48.2% (13/27) of isolates harboring blaCTX-M alleles were found to carry IS26 elements and 53.4% (7/13) of isolates harboring the sul1-type integrons were found to carry orf513. Alarmingly, a few isolates simultaneously carried IS26 and orf513, reflecting the occurrence of complex evolution. All the Citrobacter isolates were noticed to produce an amplicon of 400 bp in an IS26 PCR, similar to that of the predominant UK CTX-M-15-producing Escherichia coli clone (clone A) and suggesting a probable genetic relatedness between the two, which could not be proved with British and Indian E. coli isolates in our earlier studies. Here, a first report is being presented describing the occurrence of blaCTX-M-15 in Indian Citrobacter spp. This is also the first report describing the simultaneous occurrence of blaTEM, blaSHV, and blaampC along with blaCTX-M in class 1 integrons. The recent findings indicate that the genetic environment of blaCTX-M-15 has changed through the insertion of IS26 and orf513, although the consequences of these events remain uncertain. It perhaps also suggests a "turnover" of these mobile elements in the population over time.

Evidence of increasing antibiotic resistance gene abundances in archived soils since 1940

Mass production and use of antibiotics and antimicrobials in medicine and agriculture have existed for over 60 years, and has substantially benefited public health and agricultural productivity throughout the world. However, there is growing evidence that resistance to antibiotics (AR) is increasing both in benign and pathogenic bacteria, posing an emerging threat to public and environmental health in the future. Although evidence has existed for years from clinical data of increasing AR, almost no quantitative environmental data exist that span increased industrial antibiotic production in the 1950s to the present; i.e., data that might delineate trends in AR potentially valuable for epidemiological studies. To address this critical knowledge gap, we speculated that AR levels might be apparent in historic soil archives as evidenced by antibiotic resistance gene (ARG) abundances over time. Accordingly, DNA was extracted from five long-term soil-series from different locations in The Netherlands that spanned 1940 to 2008, and 16S rRNA gene and 18 ARG abundances from different major antibiotic classes were quantified. Results show that ARG from all classes of antibiotics tested have significantly increased since 1940, but especially within the tetracyclines, with some individual ARG being >15 times more abundant now than in the 1970s. This is noteworthy because waste management procedures have broadly improved and stricter rules on nontherapeutic antibiotic use in agriculture are being promulgated. Although these data are local to The Netherlands, they suggest basal environmental levels of ARG still might be increasing, which has implications to similar locations around the world.

[Evaluation of the MicroScan NegCombo panel Type 44 for detection of extended-spectrum beta-lactamase among clinical isolates of Escherichia coli, Klebsiella species, and Proteus mirabilis]

BACKGROUND

Accurate and rapid detection of extended-spectrum beta-lactamases (ESBLs) is important in guiding proper antimicrobial therapy for infected patients. We evaluated the performance of MicroScan NegCombo Type 44 panel (Dade Behring, USA), which was developed to confirm ESBL-producing Enterobacteriaceae using ceftazidime/clavulanate and cefotaxime/clavulanate.

METHODS

From August 30 to September 20, 2007, 206 non-duplicate clinical isolates, including 106 Escherichia coli, 81 Klebsiella pneumoniae, 11 Klebsiella oxytoca, and 8 Proteus mirabilis were subcultured and tested with Type 32 and Type 44 panels. The results were compared with those of the CLSI phenotypic confirmatory test (CLSI-PCT) and disk approximation test (DAT). Isolates not susceptible to cefotetan or flagged as "Possible ESBL, unable to interpret confirm test (Possible ESBL)" on Type 44 panel were tested with boronic acid disks to confirm AmpC beta-lactamases (AmpC) production.

RESULTS

Of the 206 isolates tested, 44 (21.4%) produced ESBL by CLSI-PCT or DAT, including 27 E. coli, 14 K. pneumoniae, 2 K. oxytoca, and 1 P. mirabilis. Thirty-eight isolates flagged as "Confirmed ESBL" on Type 44 panel were all confirmed as ESBL-producers. Of 14 K. pneumoniae flagged as "Possible ESBL", 6 were confirmed as ESBL and AmpC co-producers and 8 as AmpC-producers.

CONCLUSIONS

Type 44 panel showed an excellent performance in detecting ESBL-producing E. coli, Klebsiella spp., and P. mirabilis. When flagged as "Confirmed ESBL", no other confirmatory test was necessary to report as ESBL; however, "Possible ESBL" required a differential test for AmpC production.

Activity of the antimicrobial peptide and thanatin analog S-thanatin on clinical isolates of Klebsiella pneumoniae resistant to conventional antibiotics with different structures

The treatment of infections caused by bacteria resistant to the vast majority of antibiotics is a challenge worldwide. To evaluate the effect of S-thanatin (an analog of thanatin, a cationic antimicrobial peptide isolated from the hemipteran insect Podisus maculiventris) against microbial resistant to antibiotics, we studied its bactericidal kinetics, synergistic effect, resistance, and activity on clinical isolates of Klebsiella pneumoniae resistant to conventional antibiotics with different structures. The bactericidal rate of S-thanatin was more than 99% against K. pneumoniae ATCC 700603 when bacterial cultures were monitored for 60 min. The peptide was synergistic with beta-lactam cefepime in most of the clinical MDR isolates tested (7/8). An average value of FIC was 0.3708. No synergy was found between the peptide and amoxicillin, gentamycin, tetracycline, or ciprofloxacin in all bacteria tested. A total of 48 isolates of K. pneumoniae with different resistance spectrum tested was susceptible to S-thanatin. The MICs were 6.25-25 mug/ml. No significant difference in the MICs of S-thanatin between the sensitive isolates and the resistant isolates to single antibiotic was observed (P > 0.05). The resistance of K. pneumoniae ATCC 700603 to S-thanatin was slightly higher, when cultured at sub-inhibitory concentration for 5 days. S-thanatin may be an attractive candidate for developing into an antimicrobial agent.

AmpC beta-lactamases

SUMMARY

AmpC beta-lactamases are clinically important cephalosporinases encoded on the chromosomes of many of the Enterobacteriaceae and a few other organisms, where they mediate resistance to cephalothin, cefazolin, cefoxitin, most penicillins, and beta-lactamase inhibitor-beta-lactam combinations. In many bacteria, AmpC enzymes are inducible and can be expressed at high levels by mutation. Overexpression confers resistance to broad-spectrum cephalosporins including cefotaxime, ceftazidime, and ceftriaxone and is a problem especially in infections due to Enterobacter aerogenes and Enterobacter cloacae, where an isolate initially susceptible to these agents may become resistant upon therapy. Transmissible plasmids have acquired genes for AmpC enzymes, which consequently can now appear in bacteria lacking or poorly expressing a chromosomal bla(AmpC) gene, such as Escherichia coli, Klebsiella pneumoniae, and Proteus mirabilis. Resistance due to plasmid-mediated AmpC enzymes is less common than extended-spectrum beta-lactamase production in most parts of the world but may be both harder to detect and broader in spectrum. AmpC enzymes encoded by both chromosomal and plasmid genes are also evolving to hydrolyze broad-spectrum cephalosporins more efficiently. Techniques to identify AmpC beta-lactamase-producing isolates are available but are still evolving and are not yet optimized for the clinical laboratory, which probably now underestimates this resistance mechanism. Carbapenems can usually be used to treat infections due to AmpC-producing bacteria, but carbapenem resistance can arise in some organisms by mutations that reduce influx (outer membrane porin loss) or enhance efflux (efflux pump activation).

Surveillance of carbapenem-resistant Pseudomonas aeruginosa isolates from Puerto Rican Medical Center Hospitals: dissemination of KPC and IMP-18 beta-lactamases

During a 6-month period, 37/513 (7.2%) Pseudomonas aeruginosa isolates belonging to 13 pulsed-field gel electrophoresis (PFGE) groups from Puerto Rican hospitals were carbapenem nonsusceptible. Seven of 37 isolates from four PFGE groups carried bla(IMP-18), and 25/37 isolates from seven PFGE groups carried bla(KPC). The results indicated the clonal spread of bla(KPC)-positive P. aeruginosa isolates into several Puerto Rican hospitals and the dissemination of bla(IMP-18) and bla(KPC) into genetically unrelated isolates.

NHSN annual update: antimicrobial-resistant pathogens associated with healthcare-associated infections: annual summary of data reported to the National Healthcare Safety Network at the Centers for Disease Control and Prevention, 2006-2007

OBJECTIVE

To describe the frequency of selected antimicrobial resistance patterns among pathogens causing device-associated and procedure-associated healthcare-associated infections (HAIs) reported by hospitals in the National Healthcare Safety Network (NHSN).

METHODS

Data are included on HAIs (ie, central line-associated bloodstream infections, catheter-associated urinary tract infections, ventilator-associated pneumonia, and surgical site infections) reported to the Patient Safety Component of the NHSN between January 2006 and October 2007. The results of antimicrobial susceptibility testing of up to 3 pathogenic isolates per HAI by a hospital were evaluated to define antimicrobial-resistance in the pathogenic isolates. The pooled mean proportions of pathogenic isolates interpreted as resistant to selected antimicrobial agents were calculated by type of HAI and overall. The incidence rates of specific device-associated infections were calculated for selected antimicrobial-resistant pathogens according to type of patient care area; the variability in the reported rates is described.

RESULTS

Overall, 463 hospitals reported 1 or more HAIs: 412 (89%) were general acute care hospitals, and 309 (67%) had 200-1,000 beds. There were 28,502 HAIs reported among 25,384 patients. The 10 most common pathogens (accounting for 84% of any HAIs) were coagulase-negative staphylococci (15%), Staphylococcus aureus (15%), Enterococcus species (12%), Candida species (11%), Escherichia coli (10%), Pseudomonas aeruginosa (8%), Klebsiella pneumoniae (6%), Enterobacter species (5%), Acinetobacter baumannii (3%), and Klebsiella oxytoca (2%). The pooled mean proportion of pathogenic isolates resistant to antimicrobial agents varied significantly across types of HAI for some pathogen-antimicrobial combinations. As many as 16% of all HAIs were associated with the following multidrug-resistant pathogens: methicillin-resistant S. aureus (8% of HAIs), vancomycin-resistant Enterococcus faecium (4%), carbapenem-resistant P. aeruginosa (2%), extended-spectrum cephalosporin-resistant K. pneumoniae (1%), extended-spectrum cephalosporin-resistant E. coli (0.5%), and carbapenem-resistant A. baumannii, K. pneumoniae, K. oxytoca, and E. coli (0.5%). Nationwide, the majority of units reported no HAIs due to these antimicrobial-resistant pathogens.

Spread of multidrug-resistant Proteus mirabilis isolates producing an AmpC-type beta-lactamase: epidemiology and clinical management

A remarkable increase in Proteus mirabilis strains producing acquired AmpC-type beta-lactamases (CBLs) has been observed at Ospedale di Circolo e Fondazione Macchi (Varese, Italy) over the last few years. The epidemiology and treatment outcome of infections associated with this unprecedented spread are reported. From 2004-2006, 2070 P. mirabilis isolates were investigated. Extended-spectrum beta-lactamases (ESBLs) and CBL resistance determinants were identified by gene amplification and direct sequencing. Clonal relatedness was evaluated by macrorestriction analysis. Overall, 43 CBL-positive isolates were obtained from hospitalised (n=22) and non-hospitalised (n=21) patients (median age 78.8 years). The prevalence of CBL-positive isolates increased from 0.3% in 2004 to 4.6% in 2006, whereas that of ESBL-positive isolates remained constant (ca. 10%). CBL-positive isolates were multidrug-resistant and carried the CMY-16 determinant. All but two isolates were genetically identical or closely related. Retrospective analysis of clinical records revealed that the majority of CMY-16-positive isolates were associated with urinary tract infections. Treatment with amikacin or carbapenems was consistently effective, whereas piperacillin/tazobactam produced a clinical response in seven of nine cases. This is the first report of a rapid spread of CBL-positive P. mirabilis strains endowed with remarkable antimicrobial resistance. Practical methods for CBL detection are needed for the appropriate management of related infections.

Multiresistant Enterobacteriaceae: new threat of an old problem

The Enterobacteriaceae are among the most important causes of serious nosocomial and community-onset bacterial infections in humans, and resistance to antimicrobial agents in these species has become an increasingly relevant problem for healthcare providers. beta-lactam and fluoroquinolone antibiotics are important drug classes used to treat infections caused by Enterobacteriaceae. Emerging resistance mechanisms against these agents have recently been described in Enterobacteriaceae and include the production of newer beta-lactamases and plasmid-mediated quinolone resistance. The newer beta-lactamases consist of the following: plasmid-mediated AmpC beta-lactamases (e.g., ephamycin [CMY], CMY types), extended-spectrum beta-lactamases (e.g., cefotaxime [CTX], CTX-M first isolated at Munich) and carbapenem-hydrolyzing enzymes (e.g., Klebsiella pneumoniae carbapenemase [KPC], KPC types and the metallo-beta-lactamases). Recent developments in the epidemiology, clinical relevance and laboratory detection of infections caused by multiresistant Enterobacteriaceae with these new types of resistance mechanisms will be addressed in this review.

Evaluation of screening methods to detect plasmid-mediated AmpC in Escherichia coli, Klebsiella pneumoniae, and Proteus mirabilis

There are currently no standardized phenotypic methods for the screening and detection of AmpC enzymes. This study aimed to evaluate different methods to detect AmpC enzymes in Escherichia coli, Klebsiella spp., and Proteus spp., comparing the results from two disk-based methods and an agar dilution method. AmpC activity was determined for 255 clinical isolates by use of a three-dimensional enzyme assay combined with a multiplex PCR assay for plasmid-borne ampC genes. These results were compared against a disk-based inhibitor assay using various combinations of cefpodoxime and cefoxitin as antibiotic substrates and boronic acid or cloxacillin as an AmpC inhibitor. The presence of enzyme induction by disk approximation was evaluated using imipenem, cefoxitin, and amoxicillin-clavulanate as inducing agents against ceftazidime. Finally, an agar dilution assay was performed, using cefoxitin with and without added cloxacillin. AmpC activity was present in 49.8% of test isolates, 93.7% of which were positive for plasmid-borne ampC genes. CIT-like enzymes were predominant in E. coli, and DHA-like enzymes were predominant in Klebsiella spp. The disk-based inhibitor tests performed better than the agar dilution assay, while detection of AmpC by disk induction had a poor sensitivity. The cefoxitin-cloxacillin disk combination provided the best overall performance, with a sensitivity and specificity of 95%. This study confirmed the accuracy of disk-based inhibitor screening for AmpC enzymes, which proved reliable at detecting CIT- and DHA-like plasmid-borne ampC genes. The methods are simple enough for introduction into clinical microbiology laboratories.

In vitro activity of doripenem, a carbapenem for the treatment of challenging infections caused by gram-negative bacteria, against recent clinical isolates from the United States

Doripenem, a 1beta-methylcarbapenem, is a broad-spectrum antibiotic approved for the treatment of complicated urinary tract and complicated intra-abdominal infections. An indication for hospital-acquired pneumonia including ventilator-associated pneumonia is pending. The current study examined the activity of doripenem against recent clinical isolates for the purposes of its ongoing clinical development and future longitudinal analysis. Doripenem and comparators were tested against 12,581 U.S. clinical isolates collected between 2005 and 2006 including isolates of Staphylococcus aureus, coagulase-negative staphylococci, Streptococcus pneumoniae, Enterobacteriaceae, Pseudomonas aeruginosa, and Acinetobacter spp. MICs (microg/ml) were established by broth microdilution. By MIC(90), doripenem was comparable to imipenem and meropenem in activity against S. aureus (methicillin susceptible, 0.06; resistant, 8) and S. pneumoniae (penicillin susceptible, < or =0.015; resistant, 1). Against ceftazidime-susceptible Enterobacteriaceae, the MIC(90) of doripenem (0.12) was comparable to that of meropenem (0.12) and superior to that of imipenem (2), though susceptibility of isolates exceeded 99% for all evaluated carbapenems. The activity of doripenem was not notably altered against ceftazidime-nonsusceptible or extended-spectrum beta-lactamase screen-positive Enterobacteriaceae. Doripenem was the most potent carbapenem tested against P. aeruginosa (MIC(90)/% susceptibility [%S]: ceftazidime susceptible = 2/92%S, nonsusceptible = 16/61%S; imipenem susceptible = 1/98.5%S, nonsusceptible = 8/56%S). Against imipenem-susceptible Acinetobacter spp., doripenem (MIC(90) = 2, 89.1%S) was twice as active by MIC(90) as were imipenem and meropenem. Overall, doripenem potency was comparable to those of meropenem and imipenem against gram-positive cocci and doripenem was equal or superior in activity to meropenem and imipenem against Enterobacteriaceae, including beta-lactam-nonsusceptible isolates. Doripenem was the most active carbapenem tested against P. aeruginosa regardless of beta-lactam resistance.

Surveillance of community-based reservoirs reveals the presence of CTX-M, imported AmpC, and OXA-30 beta-lactamases in urine isolates of Klebsiella pneumoniae and Escherichia coli in a U.S. community

beta-Lactamases produced by urine isolates from patients in long-term care facilities (LTCFs), outpatient, clinics, and one hospital in a U.S. community were characterized. A total of 1.3% of all Escherichia coli and Klebsiella pneumoniae isolates collected from patients in 30 LTCFs and various outpatient clinics produced extended-spectrum beta-lactamases (ESBLs) and/or imported AmpC beta-lactamases.

Bloodstream infections caused by extended-spectrum-beta-lactamase- producing Escherichia coli: risk factors for inadequate initial antimicrobial therapy

Extended-spectrum-beta-lactamase (ESBL)-producing strains of Escherichia coli are a significant cause of bloodstream infections (BSI) in hospitalized and nonhospitalized patients. We previously showed that delaying effective antimicrobial therapy in BSI caused by ESBL producers significantly increases mortality. The aim of this retrospective 7-year analysis was to identify risk factors for inadequate initial antimicrobial therapy (IIAT) (i.e., empirical treatment based on a drug to which the isolate had displayed in vitro resistance) for inpatients with BSI caused by ESBL-producing E. coli. Of the 129 patients considered, 56 (43.4%) received IIAT for 48 to 120 h (mean, 72 h). Independent risk factors for IIAT include an unknown BSI source (odds ratios [OR], 4.86; 95% confidence interval [CI], 1.98 to 11.91; P = 0.001), isolate coresistance to >or=3 antimicrobials (OR, 3.73; 95% CI, 1.58 to 8.83; P = 0.003), hospitalization during the 12 months preceding BSI onset (OR, 3.33; 95% CI, 1.42 to 7.79; P = 0.005), and antimicrobial therapy during the 3 months preceding BSI onset (OR, 2.65; 95% CI, 1.11 to 6.29; P = 0.02). IIAT was the strongest risk factor for 21-day mortality and significantly increased the length of hospitalization after BSI onset. Our results underscore the need for a systematic approach to the management of patients with serious infections by ESBL-producing E. coli. Such an approach should be based on sound, updated knowledge of local infectious-disease epidemiology, detailed analysis of the patient's history with emphasis on recent contact with the health care system, and aggressive attempts to identify the infectious focus that has given rise to the BSI.

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

STUDY OBJECTIVE

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

DESIGN

In vitro susceptibility and time-kill analysis.

SETTING

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

MEASUREMENTS AND MAIN RESULTS

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

CONCLUSIONS

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

Direct comparison of the BD phoenix system with the MicroScan WalkAway system for identification and antimicrobial susceptibility testing of Enterobacteriaceae and nonfermentative gram-negative organisms

The Phoenix automated microbiology system (BD Diagnostics, Sparks, MD) is designed for the rapid identification (ID) and antimicrobial susceptibility testing (AST) of clinically significant human bacterial pathogens. We evaluated the performance of the Phoenix instrument in comparison with that of the MicroScan WalkAway system (Dade Behring, West Sacramento, CA) in the ID and AST of gram-negative clinical strains and challenge isolates of Enterobacteriaceae (n = 150) and nonfermentative gram-negative bacilli (NFGNB; 45 clinical isolates and 8 challenge isolates). ID discrepancies were resolved with the API 20E and API 20NE conventional biochemical ID systems (bioMerieux, Durham, NC). The standard disk diffusion method was used to resolve discordant AST results. The overall percentages of agreement between the Phoenix ID results and the MicroScan results at the genus and species levels for clinical isolates of Enterobacteriaceae were 98.7 and 97.7%, respectively; following resolution with conventional biochemical testing, the accuracy of the Phoenix system was determined to be 100%. For NFGNB, the levels of agreement were 100 and 97.7%, respectively. Both systems incorrectly identified the majority of the uncommon nonfermentative nonpseudomonal challenge isolates recovered from cystic fibrosis patients; these isolates are not included in the databases of the respective systems. For AST of Enterobacteriaceae, the rate of complete agreement between the Phoenix results and the MicroScan results was 97%; the rates of very major, major, and minor errors were 0.3, 0.2, and 2.7%, respectively. For NFGNB, the rate of complete agreement between the Phoenix results and the MicroScan results was 89.1%; the rates of very major, major, and minor errors were 0, 0.5, and 7.7%, respectively. Following the confirmatory testing of nine clinical isolates initially screened by the MicroScan system as possible extended-spectrum-beta-lactamase (ESBL)-producing organisms (seven Klebsiella pneumoniae isolates and two Escherichia coli isolates), complete agreement was achieved for eight isolates (one ESBL positive and seven negative); one false positive was obtained with the Phoenix instrument. The MicroScan system correctly detected the 10 ESBL challenge isolates, versus the 6 detected by the Phoenix system. Overall, there was good correlation between the Phoenix instrument and the MicroScan system for the ID and AST of Enterobacteriaceae and common NFGNB. The Phoenix system is a reliable method for the ID and AST of the majority of clinical strains encountered in the clinical microbiology laboratory. Until additional performance data are available, results for all Klebsiella pneumoniae or Klebsiella oxytoca and E. coli isolates screened and confirmed as ESBL producers by any automated system should be confirmed by alternate methods prior to the release of final results.

Molecular survey of beta-lactamases conferring resistance to newer beta-lactams in Enterobacteriaceae isolates from Polish hospitals

The first national survey of resistance to newer beta-lactams in nosocomial populations of Enterobacteriaceae in Poland was performed. The study covered all nonrepetitive enterobacterial isolates cultured from specimens from inpatients in 13 regional secondary-care hospitals from November 2003 to January 2004. Among 2,388 isolates, the predominant species was Escherichia coli (59.6%), followed by Proteus mirabilis (14.5%) and Klebsiella spp. (8.5%). The frequency of extended-spectrum beta-lactamases (ESBLs) was very high, with ESBLs present in 11.1% of all isolates and 40.4% of Klebsiella pneumoniae isolates, the latter value greatly exceeding that for E. coli (2.5%). The contribution of outbreak isolates was significant, resulting, for example, in a particularly high rate of ESBL producers among Serratia marcescens isolates (70.8%). The pool of ESBL types was overwhelmingly dominated (81.7%) by CTX-M-like beta-lactamases CTX-M-3 (80.6%) and CTX-M-15, with SHV types (17.5%; SHV-2, SHV-5, and SHV-12) and sporadic TEM-like enzymes (0.7%; TEM-19 and TEM-48) being the next most frequent. Acquired AmpC-type cephalosporinases were observed exclusively in P. mirabilis, in 20.5% of the isolates of this species (compared with the frequency of ESBL producers of 11.5% of P. mirabilis isolates). All these cephalosporinases (CMY-12, CMY-15, and a novel variant, CMY-38) originated from Citrobacter freundii. Four isolates of E. coli (two isolates), K. pneumoniae (one isolate), and P. mirabilis (one isolate) produced class A inhibitor-resistant beta-lactamases (TEM-30, TEM-32, TEM-37, and SHV-49), being the first of such producers identified in Poland. The survey documented both specific and more global characteristics of the epidemiology of the beta-lactamase-mediated resistance in enterobacteria from Polish hospitals and demonstrated that the ESBL frequency has reached an alarming level.

Characterization of methicillin-resistant Staphylococcus aureus, vancomycin-resistant enterococci and extended-spectrum beta-lactamase-producing Escherichia coli in intensive care units in Canada: Results of the Canadian National Intensive Care Unit (CAN-ICU) study (2005-2006)

BACKGROUND

Methicillin-resistant Staphylococcus aureus (MRSA), extended-spectrum beta-lactamase (ESBL)-producing Escherichia coli and vancomycin-resistant enterococci (VRE) are important hospital pathogens in Canada and worldwide.

OBJECTIVES

To genotypically and phenotypically characterize the isolates of MRSA, VRE and ESBL-producing E coli collected from patients in Canadian intensive care units (ICUs) in 2005 and 2006.

METHODS

Between September 1, 2005, and June 30, 2006, 19 medical centres participating in the Canadian National Intensive Care Unit (CAN-ICU) study collected 4133 unique patient isolates associated with infections in ICUs. Isolates of MRSA underwent mecA polymerase chain reaction (PCR) and Panton-Valentine leukocidin analysis; they were typed using pulsed-field gel electrophoresis. All isolates of E coli with ceftriaxone minimum inhibitory concentrations greater than or equal to 1 mug/mL were tested for the presence of an ESBL using the Clinical Laboratory Standards Institute double-disk diffusion method. Subsequently, PCR and sequence analysis were used to identify bla(SHV), bla(TEM) and bla(CTX-M). Isolates of VRE were tested for the presence of vanA and vanB genes by PCR.

RESULTS

Of the 4133 ICU isolates collected, MRSA accounted for 4.7% (193 of 4133) of all isolates. MRSA represented 21.9% (193 of 880) of all S aureus collected during the study; 90.7% were health care-associated MRSA strains and 9.3% were community-associated MRSA strains. Resistance rates for the isolates of MRSA were 91.8% to levofloxacin, 89.9% to clarithromycin, 76.1% to clindamycin and 11.7% to trimethoprim-sulfamethoxazole; no isolates were resistant to vancomycin, linezolid, tigecycline or daptomycin. ESBL-producing E coli accounted for 0.4% (18 of 4133) of all isolates and 3.7% (18 of 493) of E coli isolates. All 18 ESBL-producing E coli were PCR-positive for CTX-M, with bla(CTX-M-15) occurring in 72% (13 of 18) of isolates. All ESBL-producing E coli displayed a multidrug-resistant phenotype (resistant to third-generation cephalosporins and one or more other classes of antimicrobials), with 77.8% of isolates resistant to ciprofloxacin, 55.6% resistant to trimethoprim-sulfamethoxazole, 27.8% resistant to gentamicin and 26.3% resistant to doxycycline; all isolates were susceptible to ertapenem, meropenem and tigecycline. VRE accounted for 0.4% (17 of 4133) of all isolates and 6.7% (17 of 255) of enterococci isolates; 88.2% of VRE had the vanA genotype. Isolated VRE that were tested were uniformly susceptible to linezolid, tigecycline and daptomycin.

CONCLUSIONS

MRSA isolated in Canadian ICUs in 2005 and 2006 was predominately health care-associated (90.7%), ESBL-producing E coli were all CTX-M producers (72% bla(CTX-M-15)) and VRE primarily harboured a vanA genotype (88.2%). MRSA, ESBL-producing E coli and VRE were frequently multidrug resistant.

Antimicrobial-resistant pathogens in intensive care units in Canada: results of the Canadian National Intensive Care Unit (CAN-ICU) study, 2005-2006

Between 1 September 2005 and 30 June 2006, 19 medical centers collected 4,180 isolates recovered from clinical specimens from patients in intensive care units (ICUs) in Canada. The 4,180 isolates were collected from 2,292 respiratory specimens (54.8%), 738 blood specimens (17.7%), 581 wound/tissue specimens (13.9%), and 569 urinary specimens (13.6%). The 10 most common organisms isolated from 79.5% of all clinical specimens were methicillin-susceptible Staphylococcus aureus (MSSA) (16.4%), Escherichia coli (12.8%), Pseudomonas aeruginosa (10.0%), Haemophilus influenzae (7.9%), coagulase-negative staphylococci/Staphylococcus epidermidis (6.5%), Enterococcus spp. (6.1%), Streptococcus pneumoniae (5.8%), Klebsiella pneumoniae (5.8%), methicillin-resistant Staphylococcus aureus (MRSA) (4.7%), and Enterobacter cloacae (3.9%). MRSA made up 22.3% (197/884) of all S. aureus isolates (90.9% of MRSA were health care-associated MRSA, and 9.1% were community-associated MRSA), while vancomycin-resistant enterococci (VRE) made up 6.7% (11/255) of all enterococcal isolates (88.2% of VRE had the vanA genotype). Extended-spectrum beta-lactamase (ESBL)-producing E. coli and K. pneumoniae occurred in 3.5% (19/536) and 1.8% (4/224) of isolates, respectively. All 19 ESBL-producing E. coli isolates were PCR positive for CTX-M, with bla CTX-M-15 occurring in 74% (14/19) of isolates. For MRSA, no resistance against daptomycin, linezolid, tigecycline, and vancomycin was observed, while the resistance rates to other agents were as follows: clarithromycin, 89.9%; clindamycin, 76.1%; fluoroquinolones, 90.1 to 91.8%; and trimethoprim-sulfamethoxazole, 11.7%. For E. coli, no resistance to amikacin, meropenem, and tigecycline was observed, while resistance rates to other agents were as follows: cefazolin, 20.1%; cefepime, 0.7%; ceftriaxone, 3.7%; gentamicin, 3.0%; fluoroquinolones, 21.1%; piperacillin-tazobactam, 1.9%; and trimethoprim-sulfamethoxazole, 24.8%. Resistance rates for P. aeruginosa were as follows: amikacin, 2.6%; cefepime, 10.2%; gentamicin, 15.2%; fluoroquinolones, 23.8 to 25.5%; meropenem, 13.6%; and piperacillin-tazobactam, 9.3%. A multidrug-resistant (MDR) phenotype (resistance to three or more of the following drugs: cefepime, piperacillin-tazobactam, meropenem, amikacin or gentamicin, and ciprofloxacin) occurred frequently in P. aeruginosa (12.6%) but uncommonly in E. coli (0.2%), E. cloacae (0.6%), or K. pneumoniae (0%). In conclusion, S. aureus (MSSA and MRSA), E. coli, P. aeruginosa, H. influenzae, Enterococcus spp., S. pneumoniae, and K. pneumoniae are the most common isolates recovered from clinical specimens in Canadian ICUs. A MDR phenotype is common for P. aeruginosa isolates in Canadian ICUs.

First outbreak of multidrug-resistant Klebsiella pneumoniae producing both SHV-12-type extended-spectrum beta-lactamase and DHA-1-type AmpC beta-lactamase at a Korean hospital

PURPOSE

Coexistence of different classes of beta-lactamases in a single bacterial isolate may pose diagnostic and therapeutic challenges. We investigated a spread of Klebsiella pneumoniae isolates co-producing an AmpC beta-lactamase and an extended-spectrum beta-lactamase (ESBL) in a university hospital.

MATERIALS AND METHODS

Over a three-month period, a total of 11 K. pneumoniae isolates, which exhibited resistance to cefotaxime, aztreonam, and cefoxitin, were isolated. These isolates showed positive to ESBLs by double disk tests. Minimal inhibitory concentrations (MICs) were determined by broth microdilution testing. All isolates were examined by isoelectric focusing, PCR and sequence analysis to identify bla(SHV) and bla(DHA), and molecular typing by pulsed-field gel electrophoresis (PFGE).

RESULTS

All 11 isolates were highly resistant (MIC, > or = 128microg/ml) to ceftazidime, aztreonam, and cefoxitin, while they were susceptible (MIC, < or = 2microg/ml) to imipenem. The bla(SHV-12) and bla(DHA-1) genes were detected by PCR and sequence analysis. PFGE revealed a similar pattern in 10 of the 11 strains tested.

CONCLUSION

This is the first outbreak report of K. pneumoniae in Korea which co-produced SHV-12 and DHA-1 beta-lactamase, and we suggest a clonal spread of multidrug-resistant K. pneumoniae at a hospital.

Prevalence of plasmid-mediated AmpC beta-lactamases in a Chinese university hospital from 2003 to 2005: first report of CMY-2-Type AmpC beta-lactamase resistance in China

The aim of this study was to investigate the prevalences of plasmid-mediated AmpC beta-lactamases (PABLs) in isolates of Escherichia coli and Klebsiella spp. from a university hospital in China. A total of 1,935 consecutive nonrepeat clinical isolates of Escherichia coli, Klebsiella pneumoniae, and Klebsiella oxytoca were collected between January 2003 and July 2005. The isolates with cefoxitin zone diameters less than 18 mm (screen positive) were selected for PCR of the bla(AmpC) genes and sequencing. Fifty-four (2.79%) isolates harbored PABLs, as demonstrated by PCR and isoelectric focusing. Sequence analysis revealed the presence of bla(DHA-1) and bla(CMY-2) genes. The Southern blot hybridization studies confirmed that bla(CMY-2) and bla(DHA-1) were located on plasmids. Based on species, PABLs were detected in 4.29% (29 isolates of DHA-1 and 1 isolate of CMY-2) of K. pneumoniae, 1.91% (11 isolates of DHA-1 and 12 isolates of CMY-2) of E. coli, and 3.03% (1 isolate of DHA-1) of K. oxytoca isolates. In contrast to our anticipation, the occurrence rate of DHA-1-producing K. pneumonia significantly decreased (P < 0.01), from 7.54% in 2003 to 2.72% in 2004. The results of random amplified polymorphic DNA analysis indicate that the prevalences of DHA-1-producing K. pneumoniae and CMY-2-producing E. coli strains were not due to epidemic strains. In conclusion, DHA-1 was the most prevalent acquired AmpC beta-lactamase in this collection of isolates from a medical center in China, and DHA-1-producing K. pneumoniae was the most prevalent bacterium harboring a PABL. To the best of our knowledge, this is the first report of CMY-2-type AmpC beta-lactamases in the Chinese mainland.

In vitro efficacy for some local antimicrobial products against E. coli K12

The aim of this study was to assess the in vitro activity of a number of antimicrobial agents (Sultrim, Oxytetracycline, enrofloxacin and florfenicol) produced by different Iranian manufacturers against E. coli K12. Comparison of the MICs of reference antimicrobials with Disk Diffusion (DD) results of different products made by Iranian manufacturers revealed that all products of tested antimicrobials seem to be in synergy with their reference MIC evaluation. Present data indicate that E. coli K 12 is resistant to Enrofloxacin (MIC value of 6.25 microg mL(-1)) by both MIC and DD evaluation.

Risk factors for colonization with extended-spectrum beta-lactamase-producing bacteria and intensive care unit admission

Coexisting conditions and previous antimicrobial drug exposure predict colonization.

Extended-spectrum β-lactamase (ESBL)–producing bacteria are emerging pathogens. To analyze risk factors for colonization with ESBL-producing bacteria at intensive care unit (ICU) admission, we conducted a prospective study of a 3.5-year cohort of patients admitted to medical and surgical ICUs at the University of Maryland Medical Center. Over the study period, admission cultures were obtained from 5,209 patients. Of these, 117 were colonized with ESBL-producing Escherichia coli and Klebsiella spp., and 29 (25%) had a subsequent ESBL-positive clinical culture. Multivariable analysis showed the following to be statistically associated with ESBL colonization at admission: piperacillin-tazobactam (odds ratio [OR] 2.05, 95% confidence interval [CI] 1.36–3.10), vancomycin (OR 2.11, 95% CI 1.34–3.31), age >60 years (OR 1.79, 95% CI 1.24–2.60), and chronic disease score (OR 1.15; 95% CI 1.04–1.27). Coexisting conditions and previous antimicrobial drug exposure are thus predictive of colonization, and a large percentage of these patients have subsequent positive clinical cultures for ESBL-producing bacteria.

Antimicrobial resistance prevention initiative--an update: proceedings of an expert panel on resistance

Antimicrobial resistance is a growing problem that complicates the treatment of important nosocomial and community-acquired infections. It is a worldwide problem that spans the range of human pathogens, including bacteria, fungi, and viruses. This update from the Antimicrobial Resistance Prevention Initiative (ARPI) provides a review of some important trends in antibiotic, antifungal, and antiviral resistance. Areas of focus include multidrug-resistant bacteria in the hospital setting; the growing problem of community-acquired methicillin-resistant Staphylococcus aureus; triazole and polyene resistance in nosocomial infections caused by non-Candida albicans or Aspergillus species, and the utility of in vitro susceptibility testing for these fungal infections; antiviral resistance in alpha- or beta-herpesviruses causing genital herpes or cytomegalovirus infection in immunocompromised hosts; and concerns about a possible pandemic involving avian influenza A and the importance of minimizing emergence of resistant strains of this highly pathogenic virus. The challenges in each area are different, but the general keys to addressing the growing problem of antimicrobial resistance continue to be responsible antimicrobial stewardship and the development of newer antimicrobial agents.

Screening for extended-spectrum beta-lactamase-producing Enterobacteriaceae among high-risk patients and rates of subsequent bacteremia

BACKGROUND

Bloodstream infections due to extended-spectrum beta-lactamase (ESBL)-producing Enterobacteriaceae have been associated with increased hospital costs, length of stay, and patient mortality. However, the role of routine inpatient surveillance for ESBL colonization in predicting related infection is unclear.

METHODS

From 2000 through 2005, we screened 17,872 patients hospitalized in designated high-risk units for rectal colonization with vancomycin-resistant enterococci and ESBL-producing Enterobacteriaceae using a selective culture medium. In patients with a bloodstream infection due to ESBL-producing Enterobacteriaceae (ESBL-BI) during the study period, surveillance results were evaluated for evidence of antecedent ESBL-producing Enterobacteriaceae colonization.

RESULTS

The rate of ESBL-producing Enterobacteriaceae colonization doubled during the 6-year study period, increasing from 1.33% of high-risk patients in 2000 to 3.21% in 2005. Among patients with ESBL-producing Enterobacteriaceae colonization, 49.6% also carried vancomycin-resistant enterococci. The number of ESBL-BIs increased >4-fold in 5 years, from 9 cases in 2001 to 40 cases in 2005. Of 413 patients colonized with ESBL-producing Enterobacteriaceae, 35 (8.5%) developed a subsequent ESBL-BI. Of concern, more than one-half of all ESBL-BIs occurred in patients who were not screened. These 56 patients received a diagnosis of ESBL-BI in the emergency department, when hospitalized in low-risk medical units, or at transfer from an acute or long-term health care facility.

CONCLUSIONS

Colonization with ESBL-producing Enterobacteriaceae is increasing at a rapid rate, and routine rectal surveillance for ESBL-producing Enterobacteriaceae may have clinical implications. However, in our experience, over one-half of patients with an ESBL-BI did not undergo screening through our current surveillance measures. As a result, targeted screening for ESBL-producing Enterobacteriaceae among additional patient populations may be integral to future ESBL-BI prevention and management efforts.

Antimicrobial resistance prevention initiative--an update: proceedings of an expert panel on resistance

Antimicrobial resistance is a growing problem that complicates the treatment of important nosocomial and community-acquired infections. It is a worldwide problem that spans the range of human pathogens, including bacteria, fungi, and viruses. This update from the Antimicrobial Resistance Prevention Initiative (ARPI) provides a review of some important trends in antibiotic, antifungal, and antiviral resistance. Areas of focus include multidrug-resistant bacteria in the hospital setting; the growing problem of community-acquired methicillin-resistant Staphylococcus aureus; triazole and polyene resistance in nosocomial infections caused by non-Candida albicans or Aspergillus species, and the utility of in vitro susceptibility testing for these fungal infections; antiviral resistance in alpha- or beta-herpesviruses causing genital herpes or cytomegalovirus infection in immunocompromised hosts; and concerns about a possible pandemic involving avian influenza A and the importance of minimizing emergence of resistant strains of this highly pathogenic virus. The challenges in each area are different, but the general keys to addressing the growing problem of antimicrobial resistance continue to be responsible antimicrobial stewardship and the development of newer antimicrobial agents.

Comparison of Phoenix and VITEK 2 extended-spectrum-beta-lactamase detection tests for analysis of Escherichia coli and Klebsiella isolates with well-characterized beta-lactamases

The VITEK 2 and Phoenix extended-spectrum beta-lactamase (ESBL) detection systems, which comprise confirmatory tests and expert systems, were evaluated for their ability to discriminate between 102 well-characterized strains of ESBL-positive or -negative Escherichia coli, Klebsiella pneumoniae, and Klebsiella oxytoca. At least 38 distinct ESBLs were included. The strains were chosen to include some known to cause false-positive and false-negative CLSI ESBL confirmatory test results. Therefore, enzyme characterizations, rather than CLSI tests, were the reference methods for the Phoenix and VITEK 2 evaluations. A third arm of the study was conducted with the Phoenix test using two normally inactive expert rules intended to enhance ESBL detection, in addition to using the currently available software. The Phoenix ESBL confirmatory test and unmodified expert system exhibited 96% sensitivity and 81% specificity for ESBL detection. Activation of the two additional rules increased sensitivity to 99% but reduced the specificity to 58%. The VITEK 2 ESBL confirmatory test exhibited 91% sensitivity, which was reduced to 89% sensitivity by its expert system, while its specificity was 85%. Many of the expert system interpretations of both instruments were helpful, but some were suboptimal. The VITEK 2 expert system was potentially more frustrating because it provided more inconclusive interpretations of the results. Considering the high degree of diagnostic difficulty posed by the strains, both ESBL confirmatory tests were highly sensitive. The expert systems of both instruments require modification to update and enhance their utility.

Class A carbapenemases

Carbapenems, such as imipenem and meropenem, are most often used to treat infections caused by enterobacteria that produce extended-spectrum beta-lactamases, and the emergence of enzymes capable of inactivating carbapenems would therefore limit the options for treatment. Carbapenem resistance in Enterobacteriaceae is rare, but class A beta-lactamases with activity against the carbapenems are becoming more prevalent within this bacterial family. The class A carbapenemases can phylogenetically be segregated into six different groups of which four groups are formed by members of the GES, KPC, SME, IMI/NMC-A enzymes, while SHV-38 and SFC-1 each separately constitute a group. The genes encoding the class A carbapenemases are either plasmid-borne or located on the chromosome of the host. The bla(GES) genes reside as gene cassettes on mainly class I integrons, whereas the bla(KPC) genes and a single bla(IMI-2) gene are flanked by transposable elements on plasmids. Class A carbapenemases hydrolyse penicillins, classical cephalosporins, monobactam, and imipenem and meropenem, and the enzymes are divided into four phenotypically different groups, namely group 2br, 2be, 2e and 2f, according to the Bush-Jacoby-Medeiros classification system. Class A carbapenemases are inhibited by clavulanate and tazobactam like other class A beta-lactamases.

Extended-spectrum beta-lactamases of the CTX-M type now in Switzerland

The epidemiology of clavulanic acid-inhibited extended-spectrum beta-lactamases (ESBLs) was investigated among infection-associated enterobacterial isolates at the University Hospital in Lausanne, Switzerland, from January 2004 to June 2005. Out of 57 nonrepetitive ESBL producers (prevalence rate of 0.7%), 45 produced CTX-M-like ESBLs. CTX-M enzymes were mostly from clonally nonrelated Escherichia coli isolates, from urinary infections and community-acquired infections. Pediatric patients (20 out of 57) accounted for a large number of CTX-M producers. CTX-M-15 was the most frequent CTX-M-type enzyme. The plasmid-located bla(CTX-M) genes were associated with either ISEcp1 or ISCR1 insertion sequences. This study is the first published report of CTX-M-type beta-lactamases in Switzerland.