Detection and reporting of organisms producing extended-spectrum beta-lactamases: survey of laboratories in Connecticut

CON: Testing for ESBL production is unnecessary for ceftriaxone-resistant Enterobacterales

Phenotypic testing for Enterobacterales that harbour ESBLs is not additive to accurate in vitro β-lactam MICs for clinical decision-making. ESBL testing is an outdated practice established in an era of higher cephalosporin breakpoints to prevent resistant Enterobacterales carrying Ambler class A β-lactamases with affinity for later-generation β-lactams from being reported as susceptible to later-generation cephalosporins, leading to clinical failures. ESBL testing is problematic because of inaccuracies when multiple classes of β-lactamases are produced by the same organism, thus limiting the testing application to specific species and resistance types. Clinical laboratories should instead focus finite resources on accurate susceptibility testing using contemporary interpretative criteria to help guide therapeutic decisions. With continued emergence of antimicrobial resistance and in the setting of accurate susceptibility testing and current breakpoints the use of ESBL phenotypic testing is not helpful in clinical decision-making.

Predominance of CTX-M Type Extended Spectrum β-lactamase (ESBL) Producers Among Clinical Isolates of Enterobacteriaceae in a Tertiary Care Hospital, Kathmandu, Nepal

Background:

ESBL problem is increasing worldwide and only limited studies on genes of ESBL are performed in Nepal.

Objectives:

We aimed to focus on the molecular detection of plasmid-mediatedblaTEM,blaSHVandblaCTX-Mgenes among the ESBL producing Enterobacteriaceae from different clinical samples.

Methods:

A total of 550 clinical samples were processed and organisms of Enterobacteriaceae were identified using standard microbiological process. ESBL producers were screened and confirmed using modified Kirby Bauer disc diffusion method by CLSI guidelines. Plasmids extracted from the confirmed ESBL positives were the template for PCR.blaSHV,blaTEMandblaCTX-Mgenes were amplified using specific primers of respective genes by uniplex PCR. The presence of these genes was confirmed by gel electrophoresis.

Results:

Among 550 different clinical samples 343 (62.36%) were culture positive. Of which, 157 (45.57%) belonged to Enterobacteriaceae.Escherichia coli(45.9%) was predominant. Of these 33.2% (52/157) isolates ESBL positive. ESBL-E. coli(52.8%) were prevalent. All ESBL positive organisms were sensitive to imipenem. Of confirmed ESBL positives, 34.6% harboringblaTEMgene, 30.8% harboringblaSHVgene andblaCTX-Mgenes were present in all ESBL producers. Twenty-eightout of 52 (53.9%) isolates harbored multipleblagenes, the most common combination beingblaCTX-M+blaTEM(21.2%).

Conclusion:

We report 100% plasmid mediated CTX-M genotype among ESBL producers which might indicate rapid dissemination ofblaCTX-Mgenes from the community to the patients. Besides, there is a need for regular monitoring of antibiotic resistance in the country and de-escalate the use of antibiotics so as to preserve the antibiotics for future generation.

Detection, characterization, and antibiogram of extended-spectrum beta-lactamase Escherichia coli isolated from bovine milk samples in West Bengal, India

Background:

Milk is considered as complete food and an important part of human diet throughout the world including India. Bacterial contamination of milk such as Escherichia coli due to unhygienic condition and poor udder health can cause infections, especially in infants and elders or in immunocompromised persons. Possession of antimicrobial resistance genes by commensal bacteria present in milk makes the issue more serious.

Aim:

The study was aimed to isolate and characterize extended-spectrum beta-lactamase (ESBL)-producing E. coli from milk samples collected from different parts of West Bengal, India, to assess the potential risk associated with the food.

Materials and Methods:

Around 182 milk samples were collected from apparently healthy cows reared by organized dairy farms in West Bengal. E. coli was isolated from collected samples as per standard methods followed by serotyping. The detection of ESBL-producing E. coli was done both phenotypically and genotypically by detecting the presence of bla_CTX-M gene. Antibiogram of the ESBL-positive isolates was done using common 12 antibiotics by disc diffusion method.

Results:

A total of 22 (12.1%) samples were found to be positive for E. coli in this study. Different serotypes such as O11, O20, O22, O34, O35, O128, O149, and UT were isolated from the collected samples. 12 (54.5%) E. coli strains showed the capability of producing ESBL, both phenotypically and genotypically with the presence of bla_CTX-M gene. Antibiogram of these ESBL-positive isolates revealed the drugs such as colistin (100%), levofloxacin (83.33%), and imipenem (66.67%) to be highly sensitive against this pathogen but drugs such as cefotaxime (100%), ceftazidime (91.67%), amoxicillin/clavulanic acid (83.33%), tetracycline (75.00%), and gentamicin (58.33%) to be very much resistant.

Conclusion:

More than 50% of the E. coli strains prevalent in the bovine milk samples were positive for ESBL production and are resistant to most of the common antimicrobials which may be alarming for human health.

Dissemination and genetic support of broad-spectrum beta-lactam-resistant Escherichia coli strain isolated from two Tunisian hospitals during 2004-2012

BACKGROUND

The dissemination of extended-spectrum β-lactamase (ESBL)-producing bacteria presented a great concern worldwide. Gram-negative organisms such as Escherichia coli and Klebsiella pneumoniae are the most frequently isolated pathogens responsible for nosocomial infections.

OBJECTIVES

The aim of this study was to investigate and to follow the emergence of resistance and the characterization of Extended-Spectrum Beta-Lactamases (ESBL) among broad-spectrum beta-lactam-Escherichia coli clinical isolates recovered from the military hospital and Habib Thameur hospital in Tunisia.

METHODS

A total of 113 E.coli isolates obtained during the period 2004 through 2012 showed a significant degree of multi-resistance. Among these strains, the double-disk synergy test confirmed the ESBL phenotype in 46 isolates. These included 32(70%) strains from Hospital A and 14(30%) from Hospital B.

RESULTS

The ESBL was identified as CTX-M-15. The ESBL resistance was transferred by a 60 kb plasmid CTXM-15-producing isolates were unrelated according to the PFGE analysis and characterization of the regions surrounding the blaCTX-M-15 showed the ISEcp1 elements located in the upstream region of the bla gene and 20 of them truncated by IS26.

CONCLUSION

ESBL producing E. coli strains are a serious threat in the community in Tunisia and we should take into consideration any possible spread of such epidemiological resistance.

Sites of colonization in hospitalized patients with infections caused by extended-spectrum beta-lactamase organisms: a prospective cohort study

Background

The objective of this study was to determine whether patients infected with extended-spectrum beta-lactamase (ESBL)-producing organisms are colonized at multiple body sites.

Methods

This was a prospective cohort study at a tertiary care center in Beirut, Lebanon. Hospitalized patients with infections caused by ESBL-producing organisms were included. Cultures were obtained from the primary site of infection as well as from other sites (skin, nasopharynx, urine, rectum). Molecular analysis was performed on isolates to determine clonal relatedness.

Results

One hundred patients were included in the study. Only 22 patients had positive cultures from sites other than the primary site of infection. The most common ESBL gene was CTX-M-15 followed by TEM-1. In 11 of 22 patients, isolates collected from the same patient were 100% genetically related, while in the remaining patients, genomic relatedness ranged from 42.9% to 97.1%.

Conclusions

Colonization at sites other than the primary site of infection was not common among our patient population infected with ESBL-producing organisms. The dynamics of transmission of these bacterial strains should be studied in further prospective studies to determine the value of routine active surveillance and the need for expanded precautions in infected and colonized patients.

Extended-spectrum β-lactamase infections during pregnancy: a growing threat

Extended-spectrum β-lactamases (ESBLs) are rapidly evolving plasmid transferrable enzymes that confer unique patterns of antibiotic resistance on various bacterial species. Such organisms pose special challenges to laboratory identification, as well as antibiotic selection, administration, and follow-up. Although such infections are increasingly common in the obstetric population, issues surrounding ESBLs are not widely recognized by practicing obstetricians, and controversies exist regarding diagnosis and management. This article provides the practitioner with a summary of clinically pertinent information that will assist in the proper care of pregnant patients with ESBL infection.

Genetic Environment of Plasmid Mediated CTX-M-15 Extended Spectrum Beta-Lactamases from Clinical and Food Borne Bacteria in North-Eastern India

Background

The study investigated the presence of CTX-M-15 type extended spectrum beta-lactamases (ESBL), compared their genetic arrangements and plasmid types in gram negative isolates of hospital and food origin in north-east India. From September 2013 to April 2014, a total of 252 consecutive, non-duplicate clinical isolates and 88 gram negative food isolates were selected. Phenotypic and molecular characterization of ESBL genes was performed. Presence of integrons and gene cassettes were analyzed by integrase and 59 base-element PCR respectively. The molecular environments surrounding bla_CTX-M and plasmid types were investigated by PCR and PCR-based replicon typing respectively. Transformation was carried out to assess plasmid transfer. Southern blotting was conducted to localize the bla_CTX-M-15 genes. DNA fingerprinting was performed by ERIC-PCR.

Results

Prevalence of ESBL was found to be 40.8% (103/252) in clinical and 31.8% (28/88) in food-borne isolates. Molecular characterization revealed the presence of 56.3% (58/103) and 53.5% (15/28) bla_CTX-M-15 in clinical and food isolates respectively. Strains of clinical and food origin were non-clonal. Replicon typing revealed that IncI1 and IncFII plasmid were carrying bla_CTX-M-15 in clinical and food isolates and were horizontally transferable. The ISEcp1 element was associated with bla_CTX-M-15 in both clinical and food isolates.

Conclusions

The simultaneous presence of resistance determinants in non-clonal isolates of two different groups thus suggests that the microbiota of common food products consumed may serve as a reservoir for some of the drug resistance genes prevalent in human pathogens.

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

Background:

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

Materials and Methods:

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

Result:

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

Conclusion:

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

Extended-Spectrum β-Lactamase-Producing and Third-Generation Cephalosporin-Resistant Enterobacteriaceae in Children: Trends in the United States, 1999-2011

BACKGROUND

Enterobacteriaceae infections resistant to extended-spectrum β-lactams are an emerging problem in children. We used a large database of clinical isolates to describe the national epidemiology of extended-spectrum β-lactamase (ESBL)-producing and third-generation cephalosporin-resistant (G3CR) Enterobacteriaceae.

METHODS

Antimicrobial susceptibilities of Klebsiella pneumoniae, Escherichia coli, and Proteus mirabilis reported to ∼300 laboratories participating in The Surveillance Network (TSN) between January 1999 and December 2011 were used to phenotypically identify G3CR and ESBL isolates cultured from patients <18 years. Bi-annual trends in the prevalence of each phenotype were stratified by species, patient location, culture site, age, and region. Children of age 0-1 years were excluded from analysis as data were only available from 2010 onwards.

RESULTS

Out of 368,398 pediatric isolates, 1.97% (7255) were identified as G3CR, and 0.47% (1734) as ESBL producers. The prevalence of both phenotypes increased, respectively, from 1.39% and 0.28% in 1999-2001 to 3% and 0.92% in 2010-2011. Trends were significant across all demographic and age groups, including outpatients, with the highest proportion of isolates in the 1-5-year-old age group. The majority of G3CR and ESBL isolates were E. coli (67.8% and 65.2%, respectively). Among ESBLs, resistance to ≥3 antibiotic classes was 74%. The lower regional prevalence of ESBL-producing bacteria in the upper Midwest relative to the rest of the country is consistent with recent local data.

CONCLUSIONS

Rates of G3CR and ESBL infections in children are increasing in both inpatient and ambulatory settings nationally. The identification of host factors and exposures leading to infection in children is essential.

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.

Extended-spectrum β lactamase-producing gram-negative bacteria: clinical profile and outcome in a neonatal intensive care unit

BACKGROUND & AIMS

Multidrug-resistant extended-spectrum 3 lactamase-producing bacteria (ESBL) have emerged as a common problem globally. However, data regarding clinical profile and outcome in neonates infected with ESBL-producing gram-negative bacteria are sparse.

METHODS

A retrospective study was undertaken of all neonates admitted between April 2002 and May 2003 to the neonatal intensive care unit, Safdarjang Hospital, New Delhi who had blood cultures positive for gram-negative bacteria. The clinical profile and outcome in each patient was obtained from the case notes. The mortality and morbidity of the ESBL (cases) and non-ESBL groups were compared. Data were analysed using the chi(2) and Student's t-tests.

RESULTS

There were 75 cases of gram-negative septicaemia, 46 newborns (61.3%) were infected with ESBL-producing strains and 63 case records were available. ESBL production was associated with prematurity (24/38 vs 9/25, p=0.03), prolonged rupture of membranes (14/38 vs 2/25, p=0.01) and previous antibiotic administration to the infant (15/38 vs 1/25, p=0.002). Fifty per cent of infants with early-onset sepsis and 82.1% with late-onset sepsis were infected with ESBL strains. Newborns with ESBL sepsis were more likely to manifest persistent thermal instability (13/38 vs 3/25, p=0.04) and pre-feed gastric aspirates (18/38 vs 3/25, p=0.004). More than 90% of ESBL isolates were susceptible to carbapenems, cefperazone-sulbactam and piperacillin-tazobactam. The mean length of nursery stay (15.8 vs 10.7, p=0.02) and mortality (23.6 vs 4.0%, p= 0.07) were higher in the ESBL group and onset of feeds was delayed (7.6 vs 3.9 days, p=0.007) in this group.

CONCLUSIONS

Isolation of ESBL in cases of early-onset sepsis indicates that ESBL producers might have percolated into the community. Early suspicion of ESBL-producing isolates in cases of neonatal sepsis can facilitate prompt institution of appropriate empirical therapy and lead to an improved outcome.

Increasing prevalence of ESBL production among Irish clinical Enterobacteriaceae from 2004 to 2008: an observational study

Background

Extended spectrum β-lactamase (ESBL) producing Enterobacteriaceae infections are associated with delayed initiation of appropriate treatment, poor outcomes and increased hospital stay and expense. Although initially associated with healthcare settings, more recent international reports have shown increasing isolation of ESBLs in the community. Both hospital and community ESBL epidemiology in Ireland are poorly defined.

Methods

This report describes clinical and laboratory data from three hospitals over 4.5 years. All significant isolates of Enterobacteriaceae were subjected to standardized antimicrobial susceptibility testing and screening for ESBL production. Available patient data from hospital databases were reviewed.

Results

The database included 974 ESBL producing organisms from 464 patients. Urine and blood isolates represented 84% and 3% of isolates respectively. E. coli predominated (90.9%) followed by K. pneumoniae (5.6%). The majority of patients (n = 246, 53.0%) had been admitted to at least one of the study hospitals in the year prior to first isolation of ESBL. The overall 30-day all-cause mortality from the date of culture positivity was 9.7% and the 1 year mortality was 61.4%. A Cox regression analysis showed age over 60, male gender and previous hospital admissions were significant risk factors for death within 30 days of ESBL isolation. Numbers of ESBL-producing E. coli isolated from urine and blood cultures increased during the study. Urine isolates were more susceptible than blood isolates. Co-resistance to other classes of antimicrobial agents was more common in ESBL producers from residents of long stay facilities (LSF) compared with hospital inpatients who lived at home.

Conclusions

This work demonstrates a progressively increasing prevalence of ESBL Enterobacteriaceae in hospital, LSF and community specimens in a defined catchment area over a long time period . These results will improve clinician awareness of this problem and guide the development of empiric antimicrobial regimens for community acquired bloodstream and urinary tract infections.

Using nucleic acid microarrays to perform molecular epidemiology and detect novel β-lactamases: a snapshot of extended-spectrum β-lactamases throughout the world

The worldwide dissemination of extended-spectrum-β-lactamase (ESBL)- and carbapenemase-producing Enterobacteriaceae is a major concern in both hospital and community settings. Rapid identification of these resistant pathogens and the genetic determinants they possess is needed to assist in clinical practice and epidemiological studies. A collection of Escherichia coli, Klebsiella pneumoniae, Klebsiella oxytoca, and Proteus mirabilis isolates, including phenotypically ESBL-positive (n = 1,093) and ESBL-negative isolates (n = 59), obtained in 2008-2009 from a longitudinal surveillance study (SMART) was examined using an in vitro nucleic acid-based microarray. This approach was used to detect and identify bla(ESBL) (bla(SHV), bla(TEM), and bla(CTX-M) genes of groups 1, 2, 9, and 8/25) and bla(KPC) genes and was combined with selective PCR amplification and DNA sequencing for complete characterization of the bla(ESBL) and bla(KPC) genes. Of the 1,093 phenotypically ESBL-positive isolates, 1,041 were identified as possessing at least one bla(ESBL) gene (95.2% concordance), and 59 phenotypically ESBL-negative isolates, used as negative controls, were negative. Several ESBL variants of bla(TEM) (n = 5), bla(SHV) (n = 11), bla(CTX-M) (n = 19), and bla(KPC) (n = 3) were detected. A new bla(SHV) variant, bla(SHV-129), and a new bla(KPC) variant, bla(KPC-11), were also identified. The most common bla genes found in this study were bla(CTX-M-15), bla(CTX-M-14), and bla(SHV-12). Using nucleic acid microarrays, we obtained a "molecular snapshot" of bla(ESBL) genes in a current global population; we report that CTX-M-15 is still the dominant ESBL and provide the first report of the new β-lactamase variants bla(SHV-129) and bla(KPC-11).

Phenotypic detection of broad-spectrum beta-lactamases in microbiological practice

Background

Enterobacteriaceae producing ESBL and AmpC enzymes can be associated with failure of antibiotic therapy and related morbidity and mortality. Their routine detection in microbiology laboratories is still a problem. The aim of this study was to compare the sensitivity of selected phenotypic methods.

Material/Methods

A total of 106 strains of the Enterobacteriaceae family were tested, in which molecular biology methods confirmed the presence of genes encoding ESBL or AmpC. In ESBL-positive strains, the sensitivity of the ESBL Etest (AB Biodisk) and a modified double-disk synergy test (DDST) were evaluated. AmpC strains were tested by a modified AmpC disk method using 3-aminophenylboronic acid. For simultaneous detection of ESBL and AmpC, the microdilution method with a modified set of antimicrobial agents was used.

Results

The sensitivity of the ESBL Etest was 95%; the modified DDST yielded 100% sensitivity for ESBL producers and the AmpC test correctly detected 95% of AmpC-positive strains. The sensitivity of the modified microdilution method was 87% and 95% for ESBL and AmpC beta lactamases, respectively.

Conclusions

The detection of ESBL and AmpC beta lactamases should be based on specific phenotypic methods such as the modified DDST, ESBL Etest, AmpC disk test and the modified microdilution method.

Are we ready for novel detection methods to treat respiratory pathogens in hospital-acquired pneumonia?

Hospital-acquired pneumonia represents one of the most difficult treatment challenges in infectious diseases. Many studies suggest that the timely administration of appropriate, pathogen-directed therapy can be lifesaving. Because results of culture and antimicrobial susceptibility testing can take 48 h or longer, physicians currently rely on clinical, epidemiological, and demographic factors to assist with the choice of empiric therapy for antibiotic-resistant pathogens. At present, a number of rapid molecular tests are being developed that identify pathogens and the presence of genetic determinants of antimicrobial resistance (eg, GeneXpert [Cepheid], ResPlex [Qiagen], FilmArray [Idaho Technologies], and Microarray [Check-Points]). In this review, the potential impact that molecular diagnostics has to identify and characterize pathogens that cause hospital-acquired bacterial pneumonia at an early stage is examined. In addition, a perspective on a novel technology, polymerase chain reaction followed by electrospray ionization mass spectrometry, is presented, and its prospective use in the diagnosis of pneumonia is also discussed. The complexities of the pulmonary microbiome represent a novel challenge to clinicians, but many questions still remain even as these technologies improve.

Evolution of β-lactams resistance in Gram-negative bacteria in Tunisia

Antimicrobial resistance is a major health problem worldwide, but marked variations in the resistance profiles of bacterial pathogens are found between countries and in different patient settings. In Tunisia, the strikingly high prevalence of resistance of bacteria to penicillins and cephalorosporins drugs including fourth generation in clinical isolates of Gram negative bacteria has been reported. During 30 years, the emerging problem of extended-spectrum β-lactamase-producing Escherichia coli and Klebsiella pneumoniae isolates is substantial, and some unique enzymes have been found. Recently, evidence that Gram-negative bacteria are resistant to nearly all available antimicrobial agents, including carbapenems, have emerged.

Evaluation of a commercial microarray system for detection of SHV-, TEM-, CTX-M-, and KPC-type beta-lactamase genes in Gram-negative isolates

We evaluated the ability of a commercial microarray system (Check KPC/ESBL; Check-Points Health BV) to detect clinically important class A beta-lactamase genes. A total of 106 Gram-negative strains were tested. The following sensitivity and specificity results were recorded, respectively: for bla(SHV), 98.8% and 100%; for bla(TEM), 100% and 96.4%; and for bla(CTX-M) and bla(KPC), 100% and 100%.

Risk factors for extended-spectrum beta-lactamase producing Escherichia coli and Klebsiella pneumoniae acquisition in a neonatal intensive care unit

This study was made to find the prevalence of extended-spectrum beta-lactamase (ESBL)-producing Escherichia coli and Klebsiella pneumoniae in neonatal intensive care unit (NICU) and to identify the risk factors associated with the acquisition of these organisms. Risk factors associated with ESBL-producing E. coli and/or K. pneumoniae acquisition status of neonates were assessed. Of 253 neonates admitted, 238 entered the active surveillance system. ESBL-producing K. pneumoniae was responsible for 7 infections and 51 colonizations while ESBL-producing E. coli was responsible for 9 infections and 88 colonizations. Concurrent isolation of both the organisms occurred in 30 neonates. The logistic regression model identified 'length of stay in the NICU' as the single independent risk factor. Imipenem, cefepime and amikacin can be suggested as the drugs of choice in our study.

Resistance against broad-spectrum beta-lactams among uropathogens in children

The aim of this study was to investigate the prevalence trends and risk factors for urinary tract infection (UTI) caused by Enterobacteriaceae resistant to broad-spectrum beta-lactams in children. All Enterobacteriaceae uropathogens from children <15 years during the 11-year period 1997-2007 were included, and risk factors were evaluated. Of 523 Enterobacteriaceae isolated from 473 children, 30 (5.73%) were phenotypically resistant to broad-spectrum beta-lactams (18 Escherichia coli, ten Klebsiella spp, one Enterobacter spp, and one Citrobacter spp). The prevalence of resistance increased during the study period (p = 0.031). Resistance to cefoxitin was common (26/30), pointing to AmpC enzyme expression, and 2/30 isolates were resistant to carbapenems. Resistant Enterobacteriaceae were often community acquired (22/30, 73.3%) and related to male gender (p < 0.05), urinary tract abnormalities (p < 0.05), prophylactic antibiotics (p < 0.0001), longer hospitalization (p < 0.001), and UTI recurrences (p < 0.001). Co-resistance was more likely for cotrimoxazole, gentamicin, and ciprofloxacin (p < 0.0001). In conclusion, our study points to increasing prevalence of Enterobacteriaceae uropathogens resistant to broad-spectrum beta-lactams in the community setting, which limits the utility of first-line antibiotics and questions the validity of using prophylaxis after a first UTI episode.

Molecular characterization of extended-spectrum β-lactamase-producing Escherichia coli isolates from chickens in Henan Province, China

Extended-spectrum β-lactamase (ESBL)-producing Escherichia coli has spread rapidly worldwide and poses a serious threat to human and animal health. This study collected 51 non-replicate E. coli isolates from 14 different chicken farms in Henan Province in China from December 2007 to August 2008. The prevalence of ESBL-producing E. coli, molecular characterization of the ESBL-related bla genes, including bla TEM, bla SHV and bla CTX-M, and the susceptibilities of these bacteria to various antimicrobial agents were determined. Thirty-one of the 51 isolates were positive for an ESBL phenotype and 29 of these isolates carried one or more bla genes. Twenty-two isolates harboured bla TEM genes and 15 isolates carried bla CTX-M genes (one CTX-M-14, three CTX-M-24 and 11 CTX-M-65). One isolate carried bla TEM -57; the remaining bla TEM isolates carried bla TEM-1 with one silent nucleotide base variation (T18C). We believe that this is the first study to report TEM-57 in E. coli isolates. All isolates harbouring bla CTX-M-24 and bla CTX-M-14 and five of the bla CTX-M-65 isolates also harboured the bla TEM-1 gene. To our knowledge, this study is the first to describe detection of CTX-M-65-producing E. coli isolated from chickens. None of the isolates contained the bla SHV gene. Conjugation experiments demonstrated that bla CTX-M and bla TEM genes could be transferred to E. coli DH5α. The results indicate that ESBL frequency has reached an alarming level in chicken isolates in China, with TEM-1 and CTX-M-65 enzymes being the two predominant β-lactamases detected.

Extended-spectrum beta-lactamase-producing Escherichia coli isolated in the Al-Amiri Hospital in 2003 and compared with isolates from the Farwania hospital outbreak in 1994-96 in Kuwait

Extended-spectrum beta-lactamases (ESBLs) are a major problem in Kuwait and an accurate method for their detection is essential. This study was designed to evaluate the efficacy of the commercial system (Vitek 2) to identify ESBLs in clinical isolates of Escherichia coli and relate this to their identification by agar dilution methods for use in a diagnostic laboratory. The presence of the major ESBLs parental enzyme groups was confirmed by PCR and the similarity of the strains was determined by pulsed field gel electrophoresis (PFGE) on DNA, cleaved using XbaI endonuclease, to identify clonal spread.Seventy-one separate E. coli isolates from 65 patients were tested. Sixty-two isolates were from 56 patients from the Al-Amiri Hospital and nine isolates from neonates from Farwania Hospital. The isolates were screened for ESBL activity by the Vitek 2 system. Isolates showing positive results were further tested with Etest ESBL strips and by the disc approximation methods. All the isolates were flagged as ESBL-positive by the Vitek 2 advanced expert system (AES). Isolates from all the 65 patients were detected as ESBL positive by the Etest, only if both ESBL strips were used. The double disc approximation test using five different antibiotics could detect ESBL presence in isolates from only 46 patients. In this test, the synergy with cefepime was the most sensitive in ESBL detection, showing their presence in 41 isolates. PCR with primers for bla(TEM) and bla(SHV) demonstrated that one or both of these enzymes in all isolates. PFGE revealed that many different clones were present amongst the isolates. The epidemiology of ESBL E. coli in Kuwait is complex. Many distinct strains are already present in the population, as shown by the results of PFGE. Several testing methods may be required to detect all strains harboring ESBLs.

The continuing challenge of ESBLs

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

Performance in detection and reporting beta-lactam resistance phenotypes in Enterobacteriaceae: a nationwide proficiency study in Italian laboratories

We evaluated the ability of 60 Italian clinical microbiology laboratories in detecting and reporting beta-lactam resistance phenotypes in Enterobacteriaceae. Laboratories received 5 well-characterized isolates producing extended-spectrum beta-lactamases (ESBLs), 2 hyperproducers of chromosomal enzymes, and 3 quality control strains. The performances in antimicrobial susceptibility testing (AST) were different depending on the species and type of ESBL produced. High rates of very major errors (up to 56%) were observed for ESBL producers when testing cephalosporins and aztreonam, especially in the case of CTX-M-1-producing Escherichia coli and TEM-52-producing Proteus mirabilis. Isolates hyperproducing chromosomal enzymes were erroneously reported as ESBL producers in approximately 20% of cases. Detection of ESBLs is still a problem for clinical microbiology laboratories. Overall, performances in AST appear to be better with Klebsiella spp. producing well-known enzymes (e.g., SHV type) than with strains producing emerging enzymes (e.g., CTX-M type) or organisms not well recognized as ESBL producers (e.g., P. mirabilis).

Overview of the epidemiological profile and laboratory detection of extended-spectrum beta-lactamases

Extended-spectrum beta-lactamases (ESBLs) are plasmid-mediated bacterial enzymes that confer resistance to a broad range of beta-lactams. They are descended by genetic mutation from native beta-lactamases found in gram-negative bacteria, especially infectious strains of Escherichia coli and Klebsiella species. Genetic sequence modifications have broadened the substrate specificity of the enzymes to include third-generation cephalosporins, such as ceftazidime. Because ESBL-producing strains are resistant to a wide variety of commonly used antimicrobials, their proliferation poses a serious global health concern that has complicated treatment strategies for a growing number of hospitalized patients. Another resistance mechanism, also common to Enterobacteriaceae, results from the overproduction of chromosomal or plasmid-derived AmpC beta-lactamases. These organisms share an antimicrobial resistance pattern similar to that of ESBL-producing organisms, with the prominent exception that, unlike most ESBLs, AmpC enzymes are not inhibited by clavulanate and similar beta-lactamase inhibitors. Recent technological improvements in testing and in the development of uniform standards for both ESBL detection and confirmatory testing promise to make accurate identification of ESBL-producing organisms more accessible to clinical laboratories.

Detection of bacterial strains producing sulbactam- or tazobactam-sensitive beta-lactamases by the use of disks containing the inhibitors alone instead of combining them with antibiotics

The author demonstrated that disks containing beta-lactamase inhibitors sulbactam or tazobactam combined with ampicillin (SAM) and piperacillin (TZP) are not suitable for performing the double-disk synergy test (DDST) with the aim of determining the sensitivity of beta-lactamases to these inhibitors. The presence of antibiotics (especially of piperacillin) is so disturbing that the results of testing are not specific. In contrast, the use of disks containing sulbactam or tazobactam alone yields very specific results. The author suggested to the firms producing sensi-disks that they make these commercially available to laboratory workers.

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.

Emergence of Enterobacteriaceae producing extended-spectrum beta-lactamases (ESBLs) in the community

Enterobacteriaceae, especially Klebsiella spp. producing extended-spectrum beta-lactamases (ESBLs) such as SHV and TEM types, have been established since the 1980s as a major cause of hospital-acquired infections. Appropriate infection control practices have largely prevented the dissemination of these bacteria within many hospitals, although outbreaks have been reported. However, during the late 1990s and 2000s, Enterobacteriaceae (mostly Escherichia coli) producing novel ESBLs, the CTX-M enzymes, have been identified predominantly from the community as a cause of urinary tract infections. Resistance to other classes of antibiotics, especially the fluoroquinolones, is often associated with ESBL-producing organisms. Many clinical laboratories are still not aware of the importance of screening for ESBL-producing Enterobacteriaceae originating from the community. A heightened awareness of these organisms by clinicians and enhanced testing by laboratories, including molecular surveillance studies, is required to reduce treatment failures, to limit their introduction into hospitals and to prevent the spread of these emerging pathogens within the community.

Update on Resistance among Nosocomial Gram-Negative Pathogens to Extended-Spectrum Cephalosporins and Fluoroquinolones: Results of the Antimicrobial Resistance Management (ARM) Program

Objective

To evaluate trends in antibiotic resistance among Escherichia coli, Klebsiella pneumoniae, Proteus mirabilis, and Pseudomonas aeruginosa isolates submitted to the Antimicrobial Resistance Management (ARM) program between 1990 and 2002.

Design

The ongoing Antimicrobial Resistance Management (ARM) program is a queriable Web-based surveillance system that tracks resistance patterns among U.S. inpatient and outpatient isolates. This report represents data from 285 institutions and over 17 million isolates. Using a Web-based analysis tool, antibiogram and sensitivity reports of E. coli, K. pneumoniae, P. mirabilis, and P. aeruginosa isolates were reviewed for resistance to extended-spectrum cephalosporins and fluoroquinolones.

Setting

285 teaching and non-teaching U.S Hospitals nationwide.

Results

For E. coli, resistance was 3.2% to ciprofloxacin (n = 444,947), 5.4% to levofloxacin (n = 201,532), and 0.8% to cefotaxime (n = 107,394), ceftriaxone (n = 464,931), and cefepime (n = 81,980), respectively. K. pneumoniae isolate resistance was 4.6% to ciprofloxacin (n = 144,698), 4.5% to levofloxacin (n = 57,462), 1.9% to cefotaxime (n = 33,189), 2.0% to ceftriaxone (n = 145,328) and 1.9% to cefepime (n = 25,503). For P. mirabilis, resistance was 12.5% to ciprofloxacin (n = 83,186), 12.2% to levofloxacin (n = 35,277), 1.0% to cefotaxime (n = 18,802), 0.7% to ceftriaxone (83,652), and 2.3% to cefepime (n = 13,968). P. aeruginosa resistance was also higher for fluoroquinolones (only 65.2% of isolates were susceptible to ciprofloxacin) compared to extended-spectrum cephalosporins, with ceftazidime exhibiting the greatest antipseudomonal activity. Clinically significant regional variations in the activity of fluoroquinolones and cephalosporins were apparent.

Conclusion

Resistance to the fluoroquinolones is increasing dramatically, whereas the third generation cephalosporins remain inherently more active. P. aeruginosa exhibits the most formidable resistance pattern with neither the antipseudomonal cephalosporins nor fluoroquinolones representing acceptable monotherapy options. Given the association between fluoroquinolone resistance and extended-spectrum β-lactamase production, continued surveillance is vital to preserve the activity of existing therapies.

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.

Risk factors for and outcomes of bloodstream infection caused by extended-spectrum beta-lactamase-producing Escherichia coli and Klebsiella species in children

OBJECTIVE

The increasing prevalence of infections caused by extended-spectrum beta-lactamase-producing Escherichia coli and Klebsiella species (ESBL-EK) has become a growing concern in the hospitalized patient population. Previous studies on risk factors for infection with ESBL-EK have mainly focused on adult populations, and these findings may not be relevant among the pediatric population that experiences a unique set of health care exposures and underlying conditions. The objective of this study was to define the risk factors and outcomes associated with ESBL-EK bloodstream infections in children.

METHODS

We conducted a nested case-control study using data from the Children's Hospital of Philadelphia from May 1, 1999, to September 30, 2003. Eligible patients were identified from the hospital database of microbiology laboratory records. All patients with ESBL-EK bloodstream infections were compared to a random sample of patients with non-ESBL-EK bloodstream infections. Risk factors analyzed included prior antimicrobial use, comorbid conditions, and demographic characteristics. Pulsed-field gel electrophoresis was performed to determine genetic relatedness of the ESBL-EK isolates.

RESULTS

Thirty-five cases and 105 control subjects were included in the study. The median age among the cases was 2 years (interquartile range: 0-11), compared with 1 year (interquartile range: 0-8) among control subjects. Patients with ESBL-EK infections were 5.8 times (95% confidence interval: 1.9-17.7) more likely to have had exposure to an extended-spectrum cephalosporin in the 30 days before infection than those with non-ESBL-EK infections. Other independent predictors of ESBL-EK infection were being female, infection with a Klebsiella species, and steroid use in the 30 days before infection. All ESBL-EK isolates were susceptible to carbapenem antibiotics. Pulsed-field gel electrophoresis analysis revealed that the ESBL-EK isolates were polyclonal. Although a substantially higher proportion of children with ESBL-EK died (in-hospital mortality: 36% vs 13%), this difference was not statistically significant.

CONCLUSIONS

Receipt of extended-spectrum cephalosporins in the 30 days before infection by an Escherichia coli or Klebsiella species is significantly associated with having an ESBL-EK infection in hospitalized children. Curtailed use of cephalosporins among high-risk groups may reduce the occurrence of ESBL-EK infections. Future studies on identifying high-risk children and investigating the impact of curtailed third-generation cephalosporin use to limit additional emergence of ESBL-EK infections should be undertaken.

Phenotypic and molecular detection of CTX-M-beta-lactamases produced by Escherichia coli and Klebsiella spp

Organisms producing CTX-M-beta-lactamases are emerging around the world as a source of resistance to oxyiminocephalosporins such as cefotaxime (CTX). However, the laboratory detection of these strains is not well defined. In this study, a molecular detection assay for the identification of CTX-M-beta-lactamase genes was developed and used to investigate the prevalence of these enzymes among clinical isolates of Escherichia coli and Klebsiella species in the Calgary Health Region during 2000 to 2002. In addition, National Committee for Clinical Laboratory Standards (NCCLS) recommendations were evaluated for the ability to detect isolates with CTX-M extended-spectrum beta-lactamases (ESBLs). The PCR assay consisted of four primer sets and demonstrated 100% specificity and sensitivity for detecting different groups of CTX-M-beta-lactamases in control strains producing well-characterized ESBLs. Using these primer sets, 175 clinical strains producing ESBLs were examined for the presence of CTX-M enzymes; 24 (14%) were positive for bla(CTX-M-1-like) genes, 95 (54%) were positive for bla(CTX-M-14-like) genes, and the remaining 56 (32%) were negative for bla(CTX-M) genes. Following the NCCLS recommendations for ESBL testing, all of the control and clinical strains were detected when screened with cefpodoxime and when both cefotaxime and ceftazidime with clavulanate were used as confirmation tests.

Evaluation of the current National Committee for Clinical Laboratory Standards guidelines for screening and confirming extended-spectrum beta-lactamase production in isolates of Escherichia coli and Klebsiella species from bacteremic patients

The National Committee for Clinical Laboratory Standards (NCCLS) recommendations for screening and confirming the production of extended-spectrum beta-lactamases (ESBLs) were evaluated in 115 isolates of Escherichia coli and 157 isolates of Klebsiella spp. from Israeli patients with bacteremia. All isolates were screened using cefotaxime, ceftazidime, and cefpodoxime discs. Confirmatory tests using pairs of discs containing ceftazidime, cefotaxime, or cefpodoxime in which clavulanic acid was added to one of the discs in each pair [inhibitor-potentiated disc diffusion test (IPDDT)] and two double-sided E test strips containing ceftazidime or cefotaxime with and without clavulanic acid were performed on all isolates regardless of the results of screening tests. Isolates that tested positive by one or more confirmatory tests were considered ESBL producers. Overall, 69 (25.4%) strains were found to be ESBL producers. The sensitivity of the NCCLS screening criteria ranged between 98.6% for cefotaxime and 92.8% for ceftazidime, and the specificity ranged between 100% for cefotaxime and cefpodoxime and 99.0% for ceftazidime. The sensitivity of the confirmatory tests ranged between 97.1% for the cefotaxime E test and only 75.4% for the ceftazidime IPDDT discs. All 64 isolates that fell in the intermediate and resistant categories for cefotaxime, as well as all 41 in the same categories for ceftazidime and 68 of 69 in these categories for cefpodoxime, were confirmed as ESBL producers. The use of multiple antimicrobial discs for screening isolates and combinations of IPPDT discs is needed to improve the sensitivity of confirmatory testing. It is recommended that isolates falling in the intermediate and resistant categories in disc diffusion testing be reported as ESBL producers. The use of confirmatory tests should be limited to organisms with inhibition zone diameters ranging between the NCCLS recommendations for ESBL screening and the intermediate category breakpoints.

Nosocomial bacteremia and urinary tract infections caused by extended-spectrum beta -lactamase-producing Klebsiella pneumoniae with plasmids carrying both SHV-5 and TLA-1 genes

We describe the prevalence and molecular characteristics of extended-spectrum beta -lactamase (ESBL)-producing Klebsiella pneumoniae causing nosocomial bacteremia and urinary tract infections in a Mexican general hospital. We analyzed 82 episodes of bacteremia (approximately 60% of episodes) and urinary tract infection (approximately 40% of episodes) due to K. pneumoniae during a 23-month surveillance period. The neonatal intensive care unit accounted for 49% of all episodes. All strains were imipenem susceptible; 62.2% of the strains were resistant to ceftazidime, cefotaxime, and aztreonam; 69.5% were resistant to amikacin; 58.5% were resistant to gentamicin; and 7.3% were resistant to ciprofloxacin. All strains were associated with 28 pulsed-field gel electrophoresis patterns, and dissemination of 2 ceftazidime-resistant clones produced 44% of the cases. The ESBL phenotype in these clones was transferred by identical or highly related megaplasmids. The ESBL activity corresponded to SHV-5 and TLA-1. Cross-transmission of 2 ceftazidime-resistant clones and the horizontal spread of identical or highly related megaplasmids explain the high prevalence of ESBL phenotype in these infections.

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

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

Detection of antimicrobial resistance by small rural hospital microbiology laboratories: comparison of survey responses with current NCCLS laboratory standards

Microbiology laboratory personnel from 77 rural hospitals in Idaho, Nevada, Utah, and eastern Washington were surveyed in July 2000 regarding their routine practices for detecting antimicrobial resistance. Their self-reported responses were compared to recommended laboratory practices. Most hospitals reported performing onsite bacterial identification and susceptibility testing. Many reported detecting targeted antimicrobial resistant organisms. While only 5/61 hospitals (8%) described using screening tests capable of detecting all 8 targeted types of resistance, most (57/61, 93%) were capable of accurately screening for at least 6 types. Conversely, most hospitals (58/61, 95%) reported confirmatory testing capable of identifying only 3 or fewer resistance types with high-level penicillin resistance among pneumococci, methicillin and vancomycin resistance among staphylococci and enterococci, and extended spectrum beta-lactamase production by Gram-negative bacilli presenting the greatest difficulties. Furthermore, only 50% of hospitals compiled annual antibiogram reports to help physicians choose initial therapy for suspected infectious illnesses. This survey suggests that the antimicrobial susceptibility testing in many rural hospitals may be unreliable.

Extended-spectrum beta-lactamases in Ireland, including a novel enzyme, TEM-102

Organisms producing extended-spectrum beta-lactamases (ESBLs) have been reported in many countries, but there is no information on the prevalence of ESBL-producing members of the family Enterobacteriaceae in Ireland. A total of 925 isolates of ampicillin-resistant members of the Enterobacteriaceae were received from six hospitals in Ireland over a 3-year period from September 1996 to September 1999. Isolates were screened for ESBL production by the double-disk diffusion (DDD) method. DDD-positive isolates that were (i) confirmed as ESBL producers by National Committee for Clinical Laboratory Standards (NCCLS) confirmatory testing and (ii) susceptible to cefoxitin by disk diffusion were considered ESBL producers. By these criteria, 27 (3%) of the ampicillin-resistant members of the Enterobacteriaceae studied were categorized as ESBL producers. Molecular typing suggested that some intra- and interhospital spread of ESBL-producing isolates had occurred. DNA sequencing of amplified bla(TEM) and bla(SHV) genes resulted in the detection of a novel bla(TEM) ESBL gene, bla(TEM-102) in two isolates (Klebsiella pneumoniae and Enterobacter cloacae) received from the same hospital but isolated from different patients. The study suggests dissemination of ESBL-producing bacteria within the health care system in Ireland and emphasizes the need for measures to control such spread.

Evaluation of the NCCLS extended-spectrum beta-lactamase confirmation methods for Escherichia coli with isolates collected during Project ICARE

To determine whether confirmatory tests for extended-spectrum beta-lactamase (ESBL) production in Escherichia coli are necessary, we selected 131 E. coli isolates that met the National Committee for Clinical Laboratory Standards (NCCLS) screening criteria for potential ESBL production from the Project ICARE (Intensive Care Antimicrobial Resistance Epidemiology) strain collection. For all 131 isolates, the broth microdilution (BMD) MIC of at least one extended-spectrum cephalosporin was >/=2 micro g/ml. For 21 of 131 (16%) isolates, the ESBL confirmatory test was positive; i.e., the BMD MICs of ceftazidime or cefotaxime decreased by >/=3 doubling dilutions in the presence of clavulanic acid (CA) or the disk diffusion zone diameters increased by >/=5 mm around ceftazidime or cefotaxime disks in the presence of CA. All 21 isolates were shown by PCR to contain at least one of the genes bla(TEM), bla(SHV), and bla(OXA), and in isoelectric focusing (IEF) tests, all isolates demonstrated at least one beta-lactamase band consistent with a TEM, SHV, or OXA enzyme. Of the 21 isolates, 3 showed a CA effect for cefotaxime by BMD but not by disk diffusion testing. A total of 59 (45%) of the 131 isolates demonstrated decreased susceptibility to cefpodoxime alone (MIC = 2 to 4 micro g/ml), and none had a positive ESBL confirmatory test result. These were classified as false positives according to ESBL screen test results. For the remaining 51 (39%) isolates, the cefpodoxime MICs ranged from 16 to >128 micro g/ml and the MICs for the other extended-spectrum cephalosporins were highly variable. All 51 isolates gave negative ESBL confirmatory test results. Most showed IEF profiles consistent with production of both a TEM and an AmpC beta-lactamase, and representative isolates of several phenotypic groups showed changes in porin profiles; these 51 isolates were considered true negatives. In all, only 16% of 131 E. coli isolates identified as potential ESBL producers by the current NCCLS screening criteria were confirmed as ESBL producers. Thus, changing the interpretation of extended-spectrum cephalosporins and aztreonam results from the susceptible to the resistant category without confirming the presence of an ESBL phenotype would lead to a large percentage of false resistance results and is not recommended. However, by increasing the cefpodoxime MIC screening breakpoint to >/=8 micro g/ml, 45% of the false-positive results could be eliminated. NCCLS has incorporated this change in the cefpodoxime screening breakpoint in its recent documents.

Contamination of bone marrow products with an actinomycete resembling Microbacterium species and reinfusion into autologous stem cell and bone marrow transplant recipients

Bacterial contamination of bone marrow or peripheral blood stem cell transplant products typically occurs with skin flora or, rarely, gram-negative organisms. We describe a clonal outbreak of contamination in transplant products caused by contamination with an aerobic actinomycete that occurred at our institution during the summer of 2001. From 1 July through 12 September 2001, 73 peripheral blood or bone marrow stem cell products were obtained from 39 patients, and 34 products were found to be contaminated with the outbreak strain. Fourteen patients were reinfused with contaminated cells, and the outbreak strain was isolated from the blood cultures for one patient. Investigation revealed multiple potential sources for contamination during the product cryopreservation process. The outbreak of contamination was aborted upon modification of the cryopreservation process.

Antimicrobial proficiency testing of National Nosocomial Infections Surveillance System hospital laboratories

OBJECTIVE

The National Nosocomial Infections Surveillance (NNIS) System personnel report trends in antimicrobial-resistant pathogens. To validate select antimicrobial susceptibility testing results and to identify test methods that tend to produce errors, we conducted proficiency testing among NNIS System hospital laboratories.

SETTING

NNIS System hospital laboratories in the United States.

METHODS

Each laboratory received five organisms (ie, an imipenem-resistant Serratia marcescens, an oxacillin-resistant Staphylococcus aureus, a vancomycin-resistant Enterococcus faecalis, a vancomycin-intermediate Staphylococcus epidermidis, and an extended-spectrum beta-lactamase (ESbetaL)-producing Klebsiella pneumoniae). Testing results were compared with reference testing results from the Centers for Disease Control and Prevention.

RESULTS

Of 138 laboratories testing imipenem against the Serratia marcescens strain, 110 (80%) correctly reported minimum inhibitory concentrations (MICs) or zone sizes in the resistant range. All 193 participating laboratories correctly reported the Staphylococcus aureus strain as oxacillin resistant Of the 193 laboratories, 169 (88%) reported correct MICs or zone sizes for the vancomycin-resistant Enterococcus faecalis. One hundred sixty-two (84%) of 193 laboratories demonstrated the ability to detect a vancomycin-intermediate strain of Staphylococcus epidermidis, however, disk diffusion performed poorly when testing both staphylococci and enterococci with vancomycin. Although laboratory personnel correctly reported nonsusceptible extended-spectrum cephalosporins and aztreonam results for K. pneumoniae, only 98 (51%) of 193 correctly reported this organism as an ESbetaL producer.

CONCLUSION

Overall, NNIS System hospital laboratory personnel detected most emerging resistance patterns. Disk diffusion continues to be unreliable for vancomycin testing of staphylococci and must be used cautiously for enterococci. Further education on the processing of ESbetaL-producing organisms is warranted.

Serious bacterial infections in febrile infants younger than 90 days of age: the importance of ampicillin-resistant pathogens

BACKGROUND

Intrapartum antibiotic prophylaxis against group B Streptococcus (GBS) has reduced the occurrence of serious bacterial infections (SBI) in young infants caused by GBS. Recommendations for initial antibiotic therapy for the febrile infant 1 to 90 days old were developed when infections with GBS were common and antibiotic resistance was rare.

OBJECTIVE

To document the pathogens responsible for SBI in recent years in febrile infants 1 to 90 days old and the antibiotic susceptibility of these organisms.

METHODS

The results of bacterial cultures from infants 1 to 90 days old evaluated for fever at Primary Children's Medical Center in Salt Lake City, Utah, between July 1999 and April 2002 were analyzed. Antibiotic susceptibility profiles were collected and patient records were reviewed to determine if initial antibiotic therapy was changed following the identification of the organism.

RESULTS

Of 1298 febrile infants enrolled from the Primary Children's Medical Center emergency department, 105 (8%) had SBI. The mean age of the infants with SBI was 39 days (range 2-82 days) and 2 (2%) were <7 days. SBI included urinary tract infection (UTI; 67%), bacteremia (16%), bacteremia and UTI (6%), bacteremia and meningitis (5%), meningitis (2%), abscess (2%), meningitis and UTI (1%), and meningitis and gastroenteritis (1%). Eighty-three (79%) of 105 episodes of SBI were caused by Gram-negative bacteria, including 92% of UTI, 54% of bacteremia, and 44% of meningitis cases. The most common pathogen was Escherichia coli (61%). Other Gram-negative pathogens were responsible for 19% of SBI. Staphylococcus aureus was the most common Gram-positive pathogen, causing 8% of SBI. GBS accounted for 6% of SBI. Of the 105 pathogens, 56 (53%) were resistant to ampicillin. Of the pathogens causing meningitis, UTI, and bacteremia, 78%, 53%, and 50%, respectively, were resistant to ampicillin. Antibiotic therapy was changed in 54% of cases of SBI following identification of the organism.

CONCLUSIONS

In Utah, ampicillin-resistant Gram-negative bacteria are the most common cause of SBI in febrile infants <90 days old. This finding impacts antibiotic selection, especially in cases of meningitis. Local surveillance of pathogens and antibiotic susceptibility patterns is critical to determine appropriate antibiotic therapy.

Quality control for beta-lactam susceptibility testing with a well-defined collection of Enterobacteriaceae and Pseudomonas aeruginosa strains in Spain

Eighteen Enterobacteriaceae and Pseudomonas aeruginosa strains, 16 of them with well-defined beta-lactam resistance mechanisms, were sent to 52 Spanish microbiology laboratories. Interpretative categories for 8 extended-spectrum beta-lactams were collected. Participating laboratories used their own routine susceptibility testing procedures (88% automatic systems, 10% disk diffusion, and 2% agar dilution). Control results were established by two independent reference laboratories by applying the NCCLS microdilution method and interpretative criteria. Interpretative discrepancies were observed in 16% of the results (4.4% for cefepime, 3.0% for aztreonam, 2.8% for piperacillin-tazobactam, 1.7% for cefotaxime [CTX] and ceftazidime, 1.1% for ceftriaxone, 0.9% for meropenem, and 0.3% for imipenem). High consistency with reference values (<5% of major plus very major errors) was observed with (i) American Type Culture Collection quality control strains; (ii) strains with low-efficiency mechanisms inactivating extended-spectrum beta-lactams, such as OXA-1-producing Escherichiacoli or SHV-1-hyperproducing Klebsiella pneumoniae; (iii) strains with highly efficient mechanisms, such as SHV-5 porin-deficient K. pneumoniae, CTX-M-10 in Enterobacter cloacae hyperproducing AmpC, and P. aeruginosa with the MexAB OprM efflux phenotype or hyperproducing AmpC. Low consistency (>30% major plus very major errors) was detected in K1-producing Klebsiella oxytoca, CTX-M-9-producing E. coli, and in OprD(-) P. aeruginosa strains. Extended-spectrum beta-lactamase (ESBL)-producing strains accounted for 86% of very major errors. Recognition of the ESBL phenotype was particularly low in Enterobacter cloacae strains (<35%), due to the lack of NCCLS-specific rules in this genus. A K1-producing K. oxytoca was misidentified by 10% of laboratories as an ESBL producer. The use of well-defined resistant strains is useful for improving proficiency in susceptibility testing in clinical laboratories.

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

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

[Phenotypes of resistance in community urinary tract isolates of Escherichia coli: therapeutic implications]

BACKGROUND AND OBJECTIVE

Urinary tract infectious (UTI) are very frequent in the community and are managed through empirical treatment guidelines. The knowledge of patterns of susceptibility of patients at the time of establishing an empirical treatment is fundamental to avoid therapeutic failures. The aim of this study was to know the pattern of resistance to betalactams and other antimicrobials used in the treatment of non-complicated urinary infections in the area 11 of Madrid.

PATIENTS AND METHOD

Retrospective study of susceptibility of Escherichia coli isolated in cultures of urine of outpatients of area 11 of Madrid during a period of 12 months.

RESULTS

We found high rates of resistance to ampicillin and trimethoprim-sulfamethoxazole (57 and 29%, respectively). We observed high rates of resistance to cefuroxime (24%) and amoxicillin-clavulanic acid (27%). Resistance to ciprofloxacine was 16%. Resistance to phosphomicin and nitrofurantoin was very low (5 and 4%). Most frequent resistance association was ampicillin + cephalothin (20,2%). The mechanisms of resistance having more clinical relevance was the production and hyper-production of betalactamase.

CONCLUSIONS

Changes were detected as to the pattern of susceptibility of certain antimicrobials frequently used in the empirical treatment of UTI such as cefuroxime and amoxicillin-clavulanic acid. It is important to support a condition of active surveillance for the evolution of resistances.

Occurrence of newer beta-lactamases in Klebsiella pneumoniae isolates from 24 U.S. hospitals

Despite the discovery of novel beta-lactamases such as extended-spectrum beta-lactamases (ESBLs), imported AmpC, and carbapenem-hydrolyzing beta-lactamases at least a decade ago, there remains a low level of awareness of their importance and how to detect them. There is a need to increase the levels of awareness of clinical laboratories about the detection of newer beta-lactamases. Therefore, a study was conducted in 2000 to investigate the occurrence of these beta-lactamases in Klebsiella pneumoniae isolates at 24 U.S. medical centers. To enhance the likelihood of detecting imported AmpC and carbapenem-hydrolyzing beta-lactamases, participating laboratories were permitted to include archived strains (1996 to 2000) that were intermediate or resistant to either cefoxitin or imipenem. The beta-lactamase production of 408 isolates positive by screening of 1,123 isolates was investigated by ESBL phenotypic confirmation tests; and for AmpC and carbapenem-hydrolyzing beta-lactamases, three-dimensional tests, isoelectric focusing, beta-lactamase inhibitor studies, spectrophotometric assays, induction assays, and molecular tests were used. ESBL-producing isolates were detected at 18 of the 24 sites (75%), imported AmpC-producing isolates were detected at 10 sites (42%), inducible imported AmpC-producing isolates were detected at 3 sites (12.5%), and a molecular class A carbapenem-hydrolyzing enzyme was detected at 1 site (4%). No class B or D carbapenem-hydrolyzing enzymes were detected. ESBLs and imported AmpC beta-lactamases were detected at a significant number of sites, indicating widespread penetration of these enzymes into U.S. medical institutions. Because these enzymes may significantly affect therapeutic outcomes, it is vital that clinical laboratories be aware of them and be able to detect their occurrence.

Detection of extended spectrum beta-lactamases in the routine clinical microbiology laboratory

AIMS

To compare three methods of confirming the presence of an extended spectrum beta-lactamase (ESBL) enzyme with the initial detection (i.e., screening) by the Vitek AMS.

METHODS

Gram-negative bacteria which flagged as ESBL-positive in the Vitek GNS card, or were suspected of harbouring an enzyme, were further tested by each of the following methods: (a) combination disc test using cefpodoxime, ceftazidime and cefotaxime with and without clavulanate; (b) cefotaxime ESBL Etest; and (c) Jarlier keyhole method with cefpodoxime (10 microg), cefotaxime (5 microg) and aztreonam (30 microg) placed 15mm away from an augmentin (30 microg) disc.

RESULTS

A total of 52 isolates were investigated, representing an 18-month time period. Fifty of these were positive by Vitek. Twenty-eight (56%) were confirmed by other methods (true positives). Of the 44% Vitek-positive/confirmatory test-negative (false positives), eight were Escherichia coli which was 53% of all E. coli tested. The majority of other false-positive isolates were Klebsiella oxytoca (24% overall) which were all Vitek- and Etest-positive but negative by the combination disc test.

CONCLUSIONS

All ESBL-positive strains by Vitek should be confirmed by the combination disc test using all three antibiotics. This will enable differentiation of 'true' ESBLs from false-positive organisms, including K1 hyperbetalactamase-producing Klebsiella oxytoca and AmpC-producing organisms. The cefpodoxime combination discs gave the best differentiation in this study with only one ESBL organism being missed.

Detection of antimicrobial resistance and extended-spectrum beta-lactamase production in Klebsiella pneumoniae strains from infected neonates

The present study was designed to determine the antimicrobial resistance and extended-spectrum beta-lactamase (ESBL) activities of Klebsiella pneumoniae strains isolated from the neonatal intensive care unit of Atatürk University Hospital, Erzurum, Turkey. Antibiotic susceptibility of 40 isolates was detected by the standard disk diffusion method according to the National Committee for Clinical Laboratory Standards Guidelines. The double-disk synergy method was used to determine ESBL activity, which is associated with resistance to beta-lactam antibiotics. Twenty-four (60%) of 40 K. pneumoniae strains were found to produce ESBL. Of the antibiotics tested, meropenem was found to be the most effective (100%), and ampicillin the least effective (0%). With the increasing incidence of antimicrobial resistance, which poses a clinically significant risk to vulnerable patients, it is important that clinical microbiology laboratories have accurate and timely information concerning the strains of bacteria present to enable them to predict which antibiotics are likely to be effective in treating the infections they may cause.