Most Enterobacter aerogenes strains in France belong to a prevalent clone

Exploring the oral-gut linkage: Interrelationship between oral and systemic diseases

The oral cavity harbors a diverse microbiota that plays a significant role in maintaining homeostasis. Disruption of this balance can lead to various oral diseases, including periodontitis. Accumulating evidence suggests a connection between periodontitis and extra-oral diseases such as cardiovascular disease, rheumatoid arthritis, obesity, and diabetes. During periodontitis, oral bacteria enter the bloodstream directly, impacting extra-oral organs. Furthermore, recent studies have uncovered another pathway, the direct oral-gut axis, where oral bacteria translocate to the gut through an enteral route, influencing gut microbiota and metabolism. Oral pathobionts associated with exacerbation of periodontal disease are implicated in gut pathology, including inflammatory bowel disease and colorectal cancer through ectopic gut colonization. Furthermore, oral bacteria can provoke host immune responses, leading to colitis and other inflammatory diseases. Conversely, mechanisms by which extra-oral conditions exacerbate oral diseases, such as periodontitis, are also beginning to be elucidated. This review discusses the bidirectional interrelationship between oral and systemic diseases based on the oral-gut linkage.

Molecular characterization of Enterobacter aerogenes isolated from urinary tract infections in Iran

The prevalence of multidrug-resistant Enterobacter aerogenes strains in UTIs is increasing. Therefore, the purpose of this study was to examine the mechanisms of resistance in Enterobacter aerogenes strains isolated from the urinary tract of infected patients. To achieve this goal, 786 urine samples from Shahrekord, Iran, were collected from June 2019 to February 2020. After isolating and identifying E. aerogenes samples, antibiotic susceptibility testing was done on the strains using Kirby-Bauer's disk diffusion method. The biofilm formation assays were performed to study the link between antibiotic resistance and biofilm formation and virulence genes. As a result, amongst the 786 urine samples, 50 strains were identified as E. aerogenes. The lowest rate of resistance was observed with imipenem (30%). This study also reports that all the strains of E. aerogenes are biofilm producers, with 50% of isolates producing a large amount, 30% a moderate amount, and 20% a small amount of biofilm. 42% were identified in the phenotypic study of ESBLs. In the PCR test, (64%) produced broad-spectrum beta-lactamases. Prevalence of qnrC, qnrB, qnrA, tetA, tet B, acc(3)IIa, acc(2)IIa, ant(2)Ia and Sul1 in strong producing isolates reported 100%, 80.95%,% 58.14, 87.5%, 81.58%, 86.67%, 82.14, 81.48% and 90% respectively. In the statistical analysis based on the chi-square test, a statistically significant relationship was reported between qnrA, qnrB, tetA, tetB, Sul1, ant(2)Ia, ant(3)I, aac(3)II, and biofilm formation. Resistance to cephalothin, ceftriaxone, cefotaxime and ceftazidime were reported 40%, 34%, 30% and 30%, respectively. Out of 50 Enterobacter aerogenes, 32 isolates (64%) were identified in the phenotypic study of ESBLS, prevalence of bla_CTX-M, bla_TEM and bla_SHV reported 30%, 20% and 14% respectively. There is a significant relationship between resistance to ceftriaxone and bla_CTX-M. Prevalence of csgA, ybtS, markD, rmpA, csgD and fimH in strong biofilm formation isolates reported 84%, 83.33%, 80%, 80%, 80% and 66% respectively. The chi-square test showed a statistically significant relationship between biofilm production and resistance genes fimH, csgA, csgD, ybtS, and mrkD. The findings of this study indicate that the ability to produce biofilms is associated with the increase of antibiotic resistance and virulence genes. These agents enable bacteria to produce biofilms that ultimately lead to colonization and bacterial survival in the body.

New Polyaminoisoprenyl Antibiotics Enhancers against Two Multidrug-Resistant Gram-Negative Bacteria from Enterobacter and Salmonella Species

A series consisting of new polyaminoisoprenyl derivatives were prepared in moderate to good chemical yields varying from 32 to 64% according to two synthetic pathways: (1) using a titanium-reductive amination reaction affording a 50/50 mixture of cis and trans isomers and (2) a direct nucleophilic substitution leading to a stereoselective synthesis of the compounds of interest. These compounds were then successfully evaluated for their in vitro antibiotic enhancer properties against resistant Gram-negative bacteria of four antibiotics belonging to four different families. The mechanism of action against Enterobacter aerogenes of one of the most efficient of these chemosensitizing agents was precisely evaluated by using fluorescent dyes to measure outer-membrane permeability and to determine membrane depolarization. The weak cytotoxicity encountered led us to perform an in vivo experiment dealing with the treatment of mice infected with Salmonella typhimurium and affording preliminary promising results in terms of tolerance and efficiency of the polyaminoisoprenyl derivative 5r/doxycycline combination.

Antimicrobial Resistance in ESKAPE Pathogens

Antimicrobial-resistant ESKAPE ( Enterococcus faecium, Staphylococcus aureus, Klebsiella pneumoniae, Acinetobacter baumannii, Pseudomonas aeruginosa, and Enterobacter species) pathogens represent a global threat to human health. The acquisition of antimicrobial resistance genes by ESKAPE pathogens has reduced the treatment options for serious infections, increased the burden of disease, and increased death rates due to treatment failure and requires a coordinated global response for antimicrobial resistance surveillance. This looming health threat has restimulated interest in the development of new antimicrobial therapies, has demanded the need for better patient care, and has facilitated heightened governance over stewardship practices.

Antimicrobial Resistance in ESKAPE Pathogens

Antimicrobial-resistant ESKAPE ( Enterococcus faecium, Staphylococcus aureus, Klebsiella pneumoniae, Acinetobacter baumannii, Pseudomonas aeruginosa, and Enterobacter species) pathogens represent a global threat to human health. The acquisition of antimicrobial resistance genes by ESKAPE pathogens has reduced the treatment options for serious infections, increased the burden of disease, and increased death rates due to treatment failure and requires a coordinated global response for antimicrobial resistance surveillance. This looming health threat has restimulated interest in the development of new antimicrobial therapies, has demanded the need for better patient care, and has facilitated heightened governance over stewardship practices.

Enterobacter spp.: Update on Taxonomy, Clinical Aspects, and Emerging Antimicrobial Resistance

The genus Enterobacter is a member of the ESKAPE group, which contains the major resistant bacterial pathogens. First described in 1960, this group member has proven to be more complex as a result of the exponential evolution of phenotypic and genotypic methods. Today, 22 species belong to the Enterobacter genus. These species are described in the environment and have been reported as opportunistic pathogens in plants, animals, and humans. The pathogenicity/virulence of this bacterium remains rather unclear due to the limited amount of work performed to date in this field. In contrast, its resistance against antibacterial agents has been extensively studied. In the face of antibiotic treatment, it is able to manage different mechanisms of resistance via various local and global regulator genes and the modulation of the expression of different proteins, including enzymes (β-lactamases, etc.) or membrane transporters, such as porins and efflux pumps. During various hospital outbreaks, the Enterobacter aerogenes and E. cloacae complex exhibited a multidrug-resistant phenotype, which has stimulated questions about the role of cascade regulation in the emergence of these well-adapted clones.

Molecular drivers of emerging multidrug resistance in Proteus mirabilis clinical isolates from Algeria

OBJECTIVES

The aim of this study was to characterise the molecular drivers of multidrug resistance in Proteus mirabilis isolated from Algerian community and hospital patients.

METHODS

A total of 166 P. mirabilis isolates were collected from two hospitals and eight private laboratories from four cities (Khemis Miliana, Aïn Defla, Oran and Chlef) located in northwestern Algeria. All isolates were identified by matrix-assisted laser desorption/ionisation time-of-flight mass spectrometry (MALDI-TOF/MS). Antimicrobial susceptibility testing was performed by the disk diffusion and Etest methods. Genes encoding AmpC β-lactamases, extended-spectrum β-lactamases (ESBLs), quinolone resistance and aminoglycoside-modifying enzymes (AMEs) as well as plasmid replicon typing were characterised by PCR. Clonal relationships were also determined by enterobacterial repetitive intergenic consensus PCR (ERIC-PCR) typing and were compared with MALDI-TOF/MS proteomic typing.

RESULTS

Of the 166 P. mirabilis isolates, 14 (8.4%) exhibited resistance to important antibiotics, including amoxicillin, amoxicillin/clavulanic acid, cefotaxime, gentamicin and ciprofloxacin, of which 4/14 (28.6%) had an ESBL genotype (bla_CTX-M-2) and 10 (71.4%) had an AmpC/ESBL genotype (bla_CMY-2/bla_TEM-1). AME genes were detected in all isolates, including ant(2'')-I, aac(3)-I, aac(6')-Ib-cr and aac(3)-IV. The qnrA gene was identified in 13 isolates (7.8%). ERIC-PCR showed one predominant clone, with eight bla_CMY-2-producing isolates from UHC Oran belonging to profile A clustering together in the MALDI-TOF/MS dendrogram.

CONCLUSION

Here we report the first description of AME and plasmid-mediated quinolone resistance genes among ESBL- and/or AmpC β-lactamase-producing P. mirabilis isolates from community- and hospital-acquired infections in northwestern Algeria.

Modulation of antimicrobial resistance in clinical isolates of Enterobacter aerogenes: A strategy combining antibiotics and chemosensitisers

OBJECTIVE

The main focus of this study was to evaluate the antimicrobial susceptibility profiles of a number of human clinical isolates of Enterobacter aerogenes isolates and to explore the effects of selected chemosensitisers on reversal of the resistant phenotype of these isolates.

METHODS

This study design was accomplished by: (i) characterising several multidrug-resistant (MDR) E. aerogenes clinical isolates; (ii) evaluating the contribution of target gene mutations to the resistance phenotype, focusing on fluoroquinolones and chloramphenicol only; (iii) evaluating the contribution of membrane permeability and efflux to the MDR phenotype; (iv) assessing the combined action of selected antimicrobials and chemosensitisers in order to identify combinations with synergistic effects able to reduce the minimum inhibitory concentration (MIC); and (v) understanding how these combinations can modulate the permeability or efflux of these isolates.

RESULTS

Resistance to ciprofloxacin could not be totally reversed owing to pre-existing mutations in target genes. Chloramphenicol susceptibility was efficiently restored by the addition of the selected chemosensitisers. From the modulation kinetics it was clear that phenothiazines were able to increase the accumulation of Hoechst dye.

CONCLUSIONS

Modulation of permeability and efflux in the presence of chemosensitisers can help us to propose more appropriate chemotherapeutic combinations that can set the model to be used in the treatment of these and other MDR infections.

Detection of CTX-M-15 beta-lactamases in Enterobacteriaceae causing hospital- and community-acquired urinary tract infections as early as 2004, in Dar es Salaam, Tanzania

Background

The spread of Extended Spectrum β-lactamases (ESBLs) among Enterobacteriaceae and other Gram-Negative pathogens in the community and hospitals represents a major challenge to combat infections. We conducted a study to assess the prevalence and genetic makeup of ESBL-type resistance in bacterial isolates causing community- and hospital-acquired urinary tract infections.

Methods

A total of 172 isolates of Enterobacteriaceae were collected in Dar es Salaam, Tanzania, from patients who met criteria of community and hospital-acquired urinary tract infections. We used E-test ESBL strips to test for ESBL-phenotype and PCR and sequencing for detection of ESBL genes.

Results

Overall 23.8% (41/172) of all isolates were ESBL-producers. ESBL-producers were more frequently isolated from hospital-acquired infections (32%, 27/84 than from community-acquired infections (16%, 14/88, p < 0.05). ESBL-producers showed high rate of resistance to ciprofloxacin (85.5%), doxycycline (90.2%), gentamicin (80.5%), nalidixic acid (84.5%), and trimethoprim-sulfamethoxazole (85.4%). Furthermore, 95% of ESBL-producers were multi-drug resistant compared to 69% of non-ESBL-producers (p < 0.05). The distribution of ESBL genes were as follows: 29/32 (90.6%) bla_CTX-M-15, two bla_SHV-12, and one had both bla_CTX-M-15 and bla_SHV-12. Of 29 isolates carrying bla_CTX-M-15, 69% (20/29) and 31% (9/29) were hospital and community, respectively. Bla_SHV-12 genotypes were only detected in hospital-acquired infections.

Conclusion

bla_CTX-M-15 is a predominant gene conferring ESBL-production in Enterobacteriaceae causing both hospital- and community-acquired infections in Tanzania.

Electronic supplementary material

The online version of this article (doi:10.1186/s12879-017-2395-8) contains supplementary material, which is available to authorized users.

In Vivo Evolution of Bacterial Resistance in Two Cases of Enterobacter aerogenes Infections during Treatment with Imipenem

Infections caused by multidrug resistant (MDR) bacteria are a major concern worldwide. Changes in membrane permeability, including decreased influx and/or increased efflux of antibiotics, are known as key contributors of bacterial MDR. Therefore, it is of critical importance to understand molecular mechanisms that link membrane permeability to MDR in order to design new antimicrobial strategies. In this work, we describe genotype-phenotype correlations in Enterobacter aerogenes, a clinically problematic and antibiotic resistant bacterium. To do this, series of clinical isolates have been periodically collected from two patients during chemotherapy with imipenem. The isolates exhibited different levels of resistance towards multiple classes of antibiotics, consistently with the presence or the absence of porins and efflux pumps. Transport assays were used to characterize membrane permeability defects. Simultaneous genome-wide analysis allowed the identification of putative mutations responsible for MDR. The genome of the imipenem-susceptible isolate G7 was sequenced to closure and used as a reference for comparative genomics. This approach uncovered several loci that were specifically mutated in MDR isolates and whose products are known to control membrane permeability. These were omp35 and omp36, encoding the two major porins; rob, encoding a global AraC-type transcriptional activator; cpxA, phoQ and pmrB, encoding sensor kinases of the CpxRA, PhoPQ and PmrAB two-component regulatory systems, respectively. This report provides a comprehensive analysis of membrane alterations relative to mutational steps in the evolution of MDR of a recognized nosocomial pathogen.

Enterobacter aerogenes and Enterobacter cloacae; versatile bacterial pathogens confronting antibiotic treatment

Enterobacter aerogenes and E. cloacae have been reported as important opportunistic and multiresistant bacterial pathogens for humans during the last three decades in hospital wards. These Gram-negative bacteria have been largely described during several outbreaks of hospital-acquired infections in Europe and particularly in France. The dissemination of Enterobacter sp. is associated with the presence of redundant regulatory cascades that efficiently control the membrane permeability ensuring the bacterial protection and the expression of detoxifying enzymes involved in antibiotic degradation/inactivation. In addition, these bacterial species are able to acquire numerous genetic mobile elements that strongly contribute to antibiotic resistance. Moreover, this particular fitness help them to colonize several environments and hosts and rapidly and efficiently adapt their metabolism and physiology to external conditions and environmental stresses. Enterobacter is a versatile bacterium able to promptly respond to the antibiotic treatment in the colonized patient. The balance of the prevalence, E. aerogenes versus E. cloacae, in the reported hospital infections during the last period, questions about the horizontal transmission of mobile elements containing antibiotic resistance genes, e.g., the efficacy of the exchange of resistance genes Klebsiella pneumoniae to Enterobacter sp. It is also important to mention the possible role of antibiotic use in the treatment of bacterial infectious diseases in this E. aerogenes/E. cloacae evolution.

Fecal Carriage of Extended-Spectrum β-Lactamase–ProducingEscherichia coliandKlebsiella pneumoniaein Patients and Asymptomatic Healthy Individuals

Fecal carriage of extended-spectrum β-lactamase (ESBL)-producing organisms was assessed in 272 inpatients, 162 outpatients, and 426 asymptomatic healthy individuals. Of 860 stool samples cultured, 152 (17.7%) yielded ESBL-producing organisms. Isolates were recovered from 71 (26.1%) of the inpatients, 25 (15.4%) of the outpatients, and 56 (13.1%) of the healthy individuals. These findings suggest that the community could be a reservoir of ESBL-producing organisms.

The rhizome of the multidrug-resistant Enterobacter aerogenes genome reveals how new "killer bugs" are created because of a sympatric lifestyle

Here, we sequenced the 5,419,609 bp circular genome of an Enterobacter aerogenes clinical isolate that killed a patient and was resistant to almost all current antibiotics (except gentamicin) commonly used to treat Enterobacterial infections, including colistin. Genomic and phylogenetic analyses explain the discrepancies of this bacterium and show that its core genome originates from another genus, Klebsiella. Atypical characteristics of this bacterium (i.e., motility, presence of ornithine decarboxylase, and lack of urease activity) are attributed to genomic mosaicism, by acquisition of additional genes, such as the complete 60,582 bp flagellar assembly operon acquired "en bloc" from the genus Serratia. The genealogic tree of the 162,202 bp multidrug-resistant conjugative plasmid shows that it is a chimera of transposons and integrative conjugative elements from various bacterial origins, resembling a rhizome. Moreover, we demonstrate biologically that a G53S mutation in the pmrA gene results in colistin resistance. E. aerogenes has a large RNA population comprising 8 rRNA operons and 87 cognate tRNAs that have the ability to translate transferred genes that use different codons, as exemplified by the significantly different codon usage between genes from the core genome and the "mobilome." On the basis of our findings, the evolution of this bacterium to become a "killer bug" with new genomic repertoires was from three criteria that are "opportunity, power, and usage" to indicate a sympatric lifestyle: "opportunity" to meet other bacteria and exchange foreign sequences since this bacteria was similar to sympatric bacteria; "power" to integrate these foreign sequences such as the acquisition of several mobile genetic elements (plasmids, integrative conjugative element, prophages, transposons, flagellar assembly system, etc.) found in his genome; and "usage" to have the ability to translate these sequences including those from rare codons to serve as a translator of foreign languages.

First detection of TEM-116 extended-spectrum β-lactamase in a Providencia stuartii isolate from a Tunisian hospital

PURPOSE

To study the resistance to third-generation cephalosporins in Providencia stuartii strain isolated from hospitalized patient in Tunisia and to identify the responsible genes

MATERIALS AND METHODS

This strain was analysed by PCR and sequencing to identify the genes responsible for the β-lactamase resistance phenotypes. The transferability of the phenotypes was tested by conjugation to Escherichia coli J53. The isoelectric point was determinate by isoelectrofocalisation.

RESULTS

This resistance was carried by a 60 kb plasmid that encoded a β-lactamase with a pI of 5.4. This β-lactamase revealed identity with the blaTEM-1 gene encoding the TEM-1 β-lactamase, except for a replacement of the Val residue at position 84 by Ile, and the Ala residue at position 184 by Val. These two mutations were encountered in TEM-116 β-lactamase.

CONCLUSION

This study demonstrates the first description of TEM-116 in the P. stuartii species in the world and the first one in a Tunisian hospital.

The porin and the permeating antibiotic: a selective diffusion barrier in Gram-negative bacteria

Gram-negative bacteria are responsible for a large proportion of antibiotic-resistant bacterial diseases. These bacteria have a complex cell envelope that comprises an outer membrane and an inner membrane that delimit the periplasm. The outer membrane contains various protein channels, called porins, which are involved in the influx of various compounds, including several classes of antibiotics. Bacterial adaptation to reduce influx through porins is an increasing problem worldwide that contributes, together with efflux systems, to the emergence and dissemination of antibiotic resistance. An exciting challenge is to decipher the genetic and molecular basis of membrane impermeability as a bacterial resistance mechanism. This Review outlines the bacterial response towards antibiotic stress on altered membrane permeability and discusses recent advances in molecular approaches that are improving our knowledge of the physico-chemical parameters that govern the translocation of antibiotics through porin channels.

[Recent evolution and characterization of extended-spectrum beta-lactamase producing enterobacteria in the CHU of Nice (2005-2007)]

AIM OF THE STUDY

ESBL producing enterobacteria (E-ESBL+) are always a public health concern, mainly due to increase of CTX-M beta-lactamase. So, 542 new strains were isolated in the CHU de Nice during the 2005-2007 period. The aim of this work was to characterize the ESBL and to type isolates suspected to be implicated in outbreaks.

METHODS

Every first E-ESBL+ was studied, the antibiotype was defined by the agar diffusion technique. Type of ESBL was determined by PCR, followed by sequencing for CTX-M and SHV enzymes. Typing was performed when several strains of one species had same antibiotype and beta-lactamase.

RESULTS

CTX-M type ESBL are predominant (45% of all E-ESBL+), mainly in Escherichia coli (34.5%). The TEM24 ESBL was the second predominant type (34.5%), mainly in Enterobacter aerogenes (18.6%) and Klebsiella pneumoniae (9.4%). SHV5/12 ESBL was found mainly in Enterobacter cloacae (7.5%). Several epidemic situations were identified, with CTX-M15 in Escherichia coli (2005/2006: 27 patients), SHV5/12 in Enterobacter cloacae (2006: 10 patients) and TEM in Proteus mirabilis (2007: nine patients). Enterobacter aerogenes is still endemic (101 patients) while an epidemic clone of TEM24 producing K. pneumoniae persists especially in an intensive care unit (26 patients during the three years).

CONCLUSION

Caracterization of E-ESBL+ is essential to better understand their mode of dissemination, monitor the emergence of new enzymes and adapt the efforts against BMR cross transmission.

Identification and evolution of drug efflux pump in clinical Enterobacter aerogenes strains isolated in 1995 and 2003

Background

The high mortality impact of infectious diseases will increase due to accelerated evolution of antibiotic resistance in important human pathogens. Development of antibiotic resistance is a evolutionary process inducing the erosion of the effectiveness of our arsenal of antibiotics. Resistance is not necessarily limited to a single class of antibacterial agents but may affect many unrelated compounds; this is termed ‘multidrug resistance’ (MDR). The major mechanism of MDR is the active expulsion of drugs by bacterial pumps; the treatment of Gram negative bacterial infections is compromised due to resistance mechanisms including the expression of efflux pumps that actively expel various usual antibiotics (ß-lactams, quinolones, …).

Methodology/Principal Findings

Enterobacter aerogenes has emerged among Enterobacteriaceae associated hospital infections during the last twenty years due to its faculty of adaptation to antibiotic stresses. Clinical isolates of E. aerogenes belonging to two strain collections isolated in 1995 and 2003 respectively, were screened to assess the involvement of efflux pumps in antibiotic resistance. Drug susceptibility assays were performed on all bacterial isolates and an efflux pump inhibitor (PAßN) previously characterized allowed to decipher the role of efflux in the resistance. Accumulation of labelled chloramphenicol was monitored in the presence of an energy poison to determine the involvement of active efflux on the antibiotic intracellular concentrations. The presence of the PAßN-susceptible efflux system was also identified in resistant E. aerogenes strains.

Conclusions/Significance

For the first time a noticeable increase in clinical isolates containing an efflux mechanism susceptible to pump inhibitor is report within an 8 year period. After the emergence of extended spectrum ß-lactamases in E. aerogenes and the recent characterisation of porin mutations in clinical isolates, this study describing an increase in inhibitor-susceptible efflux throws light on a new step in the evolution of mechanism in E. aerogenes.

Successive emergence of extended-spectrum beta-lactamase-producing and carbapenemase-producing Enterobacter aerogenes isolates in a university hospital

Sixty-two clinical isolates of Enterobacter aerogenes resistant to expanded-spectrum cephalosporins were collected between July 2003 and May 2005. Among these isolates, 23 (37.1%) were imipenem (IPM) susceptible, and 39 (62.9%) were IPM insusceptible, of which 89.7% (35/39) were resistant and 10.3% (4/39) were intermediate. Isolate genotypes were compared by pulsed-field gel electrophoresis. Of 62 isolates, 48 belonged to epidemic pulsotype A (77.4%). This pulsotype included 37.5% and 58.4% of beta-lactam phenotypes b and a, respectively. Nine isolates (14.5%) belonged to pulsotype E, which included 22.3% and 77.7% of phenotypes b and a, respectively. The beta-lactamases with pIs of 5.4, 6.5, 8.2, and 8.2 corresponded to extended-spectrum beta-lactamases (ESBLs) TEM-20, TEM-24, SHV-5, and SHV-12, respectively. Of 39 IPM-insusceptible E. aerogenes isolates, 26 (66.6%) were determined to be metallo-beta-lactamase producers, by using a phenotypic method. Of these isolates, 24 harbored a bla(IMP-1) gene encoding a protein with a pI of >9.5, and two carried the bla(VIM-2) gene encoding a protein with a pI of 5.3, corresponding to beta-lactamases IMP-1 and VIM-2, respectively. The remaining 13 (33.4%) isolates were negative for the bla(IMP-1) and bla(VIM-2) genes but showed an alteration of their outer membrane proteins (OMPs). Ten of these isolates produced the two possible OMPs (32 and 42 kDa), with IPM MICs between 8 and 32 microg/ml, and three others produced only a 32-kDa OMP with IPM MICs >32 microg/ml. This work demonstrates that, in addition to resistance to expanded-spectrum cephalosporins, IPM resistance can occur in ESBL-producing E. aerogenes isolates by carbapenemase production or by the loss of porin in the outer membrane.

The Enterobacter aerogenes outer membrane efflux proteins TolC and EefC have different channel properties

The outer membrane proteins TolC and EefC from Enterobacter aerogenes are involved in multidrug resistance as part of two resistance-nodulation-division efflux systems. To gain more understanding in the molecular mechanism underlying drug efflux, we have undertaken an electrophysiological characterization of the channel properties of these two proteins. TolC and EefC were purified in their native trimeric form and then reconstituted in proteoliposomes for patch-clamp experiments and in planar lipid bilayers. Both proteins generated a small single channel conductance of about 80 pS in 0.5 M KCl, indicating a common gated structure. The resultant pores were stable, and no voltage-dependent openings or closures were observed. EefC has a low ionic selectivity (P(K)/P(Cl)= approximately 3), whereas TolC is more selective to cations (P(K)/P(Cl)= approximately 30). This may provide a possible explanation for the difference in drug selectivity between the AcrAB-TolC and EefABC efflux systems observed in vivo. The pore-forming activity of both TolC and EefC was severely inhibited by divalent cations entering from the extracellular side. Another characteristic of the TolC and EefC channels was the systematic closure induced by acidic pH. These results are discussed in respect to the physiological functions and structural models of TolC and EefC.

An early response to environmental stress involves regulation of OmpX and OmpF, two enterobacterial outer membrane pore-forming proteins

Bacterial adaptation to external stresses and toxic compounds is a key step in the emergence of multidrug-resistant strains that are a serious threat to human health. Although some of the proteins and regulators involved in antibiotic resistance mechanisms have been described, no information is available to date concerning the early bacterial response to external stresses. Here we report that the expression of ompX, encoding an outer membrane protein, is increased during early exposure to drugs or environmental stresses. At the same time, the level of ompF porin expression is noticeably affected. Because of the role of these proteins in membrane permeability, these data suggest that OmpF and OmpX are involved in the control of the penetration of antibiotics such as beta-lactams and fluoroquinolones through the enterobacterial outer membrane. Consequently, the early control of ompX and ompF induced by external stresses may represent a preliminary response to antibiotics, thus triggering the initial bacterial line of defense against antibiotherapy.

Detecting the form of selection in the outer membrane protein C of Enterobacter aerogenes strains and Salmonella species

The types of selective pressure operating on the outer membrane protein C (ompC) of Enterobacter aerogenes strains, the causative agent for nosocomial infections, and Salmonella sp., the hazardous pathogen are investigated using the maximum likelihood-based codon substitution models. Although the rate of amino acid replacement to the silent substitution (omega) across the entire codon sites of ompC of E. aerogenes (omega=0.3194) and Salmonella sp. (omega=0.2047) indicate that the gene is subjected to purifying selection (i.e. omega<1), approximately 3.7% of ompC codon sites in E. aerogenes (omega=21.52) are under the influence of positive Darwinian selection (i.e. omega>1). Such contrast in the intensity of selective pressures in both pathogens could be associated with the differential response to the adverse environmental changes. In E. aerogenes, majority of the positively selected sites are located in the hypervariable cell-surface-exposed domains whereas the trans-membrane domains are functionally highly constrained.

Extended-spectrum beta-lactamases: a clinical update

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

Clinical and molecular analysis of extended-spectrum {beta}-lactamase-producing enterobacteria in the community setting

During a previous survey, five extended-spectrum beta-lactamase (ESBL)-producing enterobacteria (ESBLE) (two Enterobacter aerogenes isolates expressing TEM-24 b, two Escherichia coli isolates expressing TEM-21 or TEM-24 b, and one Klebsiella pneumoniae isolate expressing SHV-4/TEM-15) responsible for urinary tract infections (UTIs) were found among 1,584 strains collected from community patients. The aim of the present study was to elucidate the route of emergence of these typically nosocomial organisms in the community. Thus, the files of the five patients were analyzed over at least a decade, and potentially related ESBLE from hospitals or clinics were examined. Their enzymes were characterized at a molecular level, and the strains were typed by amplified-primed PCR, enterobacterial repetitive intergenic consensus PCR, and restriction plasmid profile. All patients (C1 to C5) had risk factors for ESBLE acquisition, including past history of hospitalization (2.5 to 23 months before). Four (C1 and C3 to C5) had previously received antibiotics (concomitantly to 35 months earlier), two (C1 and C3) had indwelling urinary catheters and recurrent UTIs, and three (C2, C3, and C5) formerly experienced ESBLE-induced UTIs (2 to 11 months before). The same ESBLE and/or an identical or similar ESBL-encoding plasmid was identified in the hospital ward (C1 to C4) or in a clinic (C5) where the patients had previously resided. Patients C1 and C4, infected with different ESBLE carrying a closely related plasmid, were hospitalized in the same unit. Persistence of ESBLE over at least a 5-year period was demonstrated for patient C3. Thus, community-acquired UTIs in these patients likely resulted from nosocomially acquired ESBLE or an ESBL-encoding plasmid followed by a prolonged digestive carriage.

Molecular typing of Klebsiella pneumoniae isolates from public hospitals in Recife, Brazil

Thirty nosocomial isolates of Klebsiella pneumoniae, collected from three public hospitals in Recife, Brazil, between 1999 and 2000, were analysed in order to determine their epidemiological relatedness and genetic characteristics. The isolates were characterised by biotyping, antibiotyping, protein analysis, plasmid profile and random amplified polymorphic DNA (RAPD). The majority of the clinical isolates were resistant to multiple antibiotics, in particular to beta-lactams, and 30% were found to be ESBLs producers. RAPD proved to be the most effective technique in discriminating unrelated K. pneumoniae isolates. It was confirmed by the highly genetic similarity found among related isolates from an hospital outbreak. We conclude that K. pneumoniae infections in Recife has been caused by a variety of bacterial genotypes. This is the first report that revealed the subtypes of K. pneumoniae in Brazil by plasmid analysis and RAPD.

The eefABC multidrug efflux pump operon is repressed by H-NS in Enterobacter aerogenes

The Enterobacter aerogenes eefABC locus, which encodes a tripartite efflux pump, was cloned by complementation of an Escherichia coli tolC mutant. E. aerogenes deltaacrA expressing EefABC became less susceptible to a wide range of antibiotics. Data from eef::lacZ fusions showed that eefABC was not transcribed in the various laboratory conditions tested. However, increased transcription from Peef was observed in an E. coli hns mutant. In addition, EefA was detected in E. aerogenes expressing a dominant negative E. coli hns allele.

Successive emergence of Enterobacter aerogenes strains resistant to imipenem and colistin in a patient

Enterobacter aerogenes is an agent of hospital-acquired infection that exhibits a remarkable resistance to beta-lactam antibiotics during therapy. Five successive isolates of E. aerogenes infecting a patient and exhibiting a multiresistance phenotype to beta-lactam antibiotics and fluoroquinolones were investigated. Among these clinical strains, four presented resistant phenotypes during successive imipenem and colistin treatments. The involved resistance mechanisms exhibited by the successive isolates were associated with alterations of the outer membrane that caused a porin decrease and lipopolysaccharide modifications.

Molecular diversity of Proteus mirabilis isolates producing extended-spectrum β-lactamases in a French university hospital

Between February 1997 and December 2002, 3340 hospitalised patients yielded samples positive for Proteus mirabilis, of whom 45 (1.3%) were colonised/infected by P. mirabilis producing extended-spectrum beta-lactamases (ESBLs). The gross incidence of patients colonised/infected by ESBL-producing P. mirabilis was 1.61/10(5) days of hospitalisation, with 20% of isolates being collected from patients in urology wards, most frequently (53.3%) from urine samples. Seventeen (37.7%) of the 43 isolates were obtained from samples collected within 48 h of hospitalisation, indicating that they were community-acquired. Isoelectric focusing assays and sequencing identified the TEM-24, TEM-92 and TEM-52 ESBLs. Pulsed-field gel electrophoresis revealed eight pulsotypes (I-VIII), with the two most common pulsotypes, IV and VI, comprising ten (23.3%) and 12 (26.6%) isolates, respectively. These pulsotypes were considered to represent epidemic strains and spread in various wards of the hospital.

Chloramphenicol and expression of multidrug efflux pump in Enterobacter aerogenes

Chloramphenicol has been reported to act as an inducer of the multidrug resistance in Escherichia coli. A resistant variant able to grow on plates containing 64 microg/ml chloramphenicol was obtained from the Enterobacter aerogenes ATCC 13048-type strain. Chloramphenicol resistance was due to an active efflux of this antibiotic and it was associated with resistance to fluoroquinolones and tetracycline, but not to aminoglycoside or beta-lactam antibiotics. MDR in the chloramphenicol-resistant variant is linked to the overexpression of the major AcrAB-TolC efflux system. This overexpression seems unrelated to the global Mar and the local AcrR regulatory pathways.

Control of Enterobacteriaceae producing extended-spectrum beta-lactamase in intensive care units: rectal screening may not be needed in non-epidemic situations

OBJECTIVE

To evaluate the usefulness of screening cultures in the control of extended-spectrum beta-lactamase (ESBL)-producing Enterobacteriaceae in intensive care units (ICUs).

DESIGN

A 4-year retrospective study.

SETTING

Two adult ICUs of a university-affiliated public hospital in France.

RESULTS

A total of 7,777 specimens were analyzed and 28 (0.97%) of 2,883 screened patients had a positive result on a screening test, among the 3,678 admitted patients. Thirteen of these 28 patients were only carriers; 4 were carriers and then were colonized or infected 2, 2, 3, and 8 days later, respectively; and 11 were colonized or infected before a screening test was positive. Cluster analysis showed that the occurrence of ESBL-producing Enterobacteriaceae cross-transmission within both ICUs was limited to 9 cases. Thus, most cases (19 of 28) were probably imported. Surveillance cultures failed to detect 9 of the 19 cases.

CONCLUSION

The low prevalence of ESBL-producing Enterobacteriaceae carriers on admission (0.45%) and the relative ineffectiveness of our screening test to detect imported cases suggest that systematic detection of ESBL-producing Enterobacteriaceae in ICU patients is not cost-effective and that the use of clinical cultures may be sufficient to control ESBL-producing Enterobacteriaceae in non-epidemic situations.

TEM-121, a novel complex mutant of TEM-type beta-lactamase from Enterobacter aerogenes

Enterobacter aerogenes clinical isolate LOR was resistant to penicillins and ceftazidime but susceptible to cefuroxime, cephalothin, cefoxitin, cefotaxime, ceftriaxone, and cefepime. PCR and cloning experiments from this strain identified a novel TEM-type beta-lactamase (TEM-121) differing by five amino acid substitutions from beta-lactamase TEM-2 (Glu104Lys, Arg164Ser, Ala237Thr, Glu240Lys, and Arg244Ser) and by only one amino acid change from the extended-spectrum beta-lactamase (ESBL) TEM-24 (Arg244Ser), with the last substitution also being identified in the inhibitor-resistant beta-lactamase IRT-2. Kinetic parameters indicated that TEM-121 hydrolyzed ceftazidime and aztreonam (like TEM-24) and was inhibited weakly by clavulanic acid and strongly by tazobactam. Thus, TEM-121 is a novel complex mutant TEM beta-lactamase (CMT-4) combining the kinetic properties of an ESBL and an inhibitor-resistant TEM enzyme.

Extended-Spectrum beta-lactamase (ESBL) producing Enterobacter aerogenes phenotypically misidentified as Klebsiella pneumoniae or K. terrigena

Background

Enterobacter aerogenes and Klebsiella pneumoniae are common isolates in clinical microbiology and important as producers of extended spectrum β-lactamases (ESBL). The discrimination between both species, which is routinely based on biochemical characteristics, is generally accepted to be straightforward. Here we report that genotypically unrelated strains of E. aerogenes can be misidentified as K. pneumoniae by routine laboratories using standard biochemical identification and using identification automates.

Results

Ten clinical isolates, identified as K. pneumoniae or K. terrigena with the routinely used biochemical tests and with API-20E, were identified as E. aerogenes by tDNA-PCR – an identification that was confirmed by 16S rRNA gene sequencing for five of these isolates. Misidentification also occurred when using the automated identification systems Vitek 2 and Phoenix, and was due to delayed positivity for ornithine decarboxylase and motility. Subculture and prolonged incubation resulted in positive results for ornithine decarboxylase and for motility. It could be shown by RAPD-analysis that the E. aerogenes strains belonged to different genotypes.

Conclusions

Clinical E. aerogenes isolates can be easily misidentified as Klebsiella due to delayed positivity for ornithine decarboxylase and motility. The phenomenon may be widespread, since it was shown to occur among genotypically unrelated strains from different hospitals and different isolation dates. A useful clue for correct identification is the presence of an inducible β-lactamase, which is highly unusual for K. pneumoniae. In several instances, the use of genotypic techniques like tDNA-PCR may circumvent problems of phenotypic identification.

Four variants of the Citrobacter freundii AmpC-Type cephalosporinases, including novel enzymes CMY-14 and CMY-15, in a Proteus mirabilis clone widespread in Poland

Twenty-nine Proteus mirabilis isolates from 17 Polish hospitals were analyzed. The isolates were resistant to a variety of antimicrobials, and their patterns of resistance to beta-lactams resembled those of the constitutive class C cephalosporinase (AmpC) producers. Indeed, beta-lactamases with a pI of approximately 9.0 were found in all of the isolates, and they were subsequently identified as four AmpC-type cephalosporinases, CMY-4, -12, -14, and -15, of which the two last ones were novel enzyme variants. The enzymes were of Citrobacter freundii origin and were closely related to each other, with CMY-4 likely being the evolutionary precursor of the remaining ones. The bla(CMY) genes were located exclusively in chromosomal DNA, within EcoRI restriction fragments of the same size of approximately 10 kb. In the CMY-12- and -15-producing isolates, an additional fragment of approximately 4.5 kb hybridized with the bla(CMY) probe as well, which could have arisen from a duplication event during the evolution of the genes. In all of the isolates, the ISEcp1 mobile element, which most probably is involved in mobilization of the C. freundii ampC gene, was placed at the same distance from the 5' ends of the bla(CMY) genes, and sequences located between them were identical in isolates carrying each of the four genes. These data suggested that a single chromosome-to-chromosome transfer of the ampC gene from C. freundii to P. mirabilis could have initiated the spread and evolution of the AmpC-producing P. mirabilis in Poland. The hypothesis seems to be confirmed by pulsed-field gel electrophoresis typing, which revealed several cases of close relatedness between the P. mirabilis isolates from distant centers and showed an overall similarity between the majority of the multiresistant isolates.

Molecular epidemiology of Enterobacteriaceae isolates producing extended-spectrum beta-lactamases in a French hospital

In 2002, 80 isolates of Enterobacteriaceae producing extended-spectrum beta-lactamases (ESBLs) were collected from infected patients in our hospital. Enterobacter aerogenes was the most common bacterium isolated from all specimens (36.5%). The ESBLs were predominantly (90%) TEM derivatives (TEM-24, TEM-3). Pulsed-field gel electrophoresis highlighted that E. aerogenes, Klebsiella pneumoniae, and Citrobacter koseri had a clonal propagation.

RamA is an alternate activator of the multidrug resistance cascade in Enterobacter aerogenes

Multidrug resistance (MDR) in Enterobacter aerogenes can be mediated by induction of MarA, which is triggered by certain antibiotics and phenolic compounds. In this study, we identified the gene encoding RamA, a 113-amino-acid regulatory protein belonging to the AraC-XylS transcriptional activator family, in the Enterobacter aerogenes ATCC 13048 type strain and in a clinical multiresistant isolate. Overexpression of RamA induced an MDR phenotype in drug-susceptible Escherichia coli JM109 and E. aerogenes ATCC 13048, as demonstrated by 2- to 16-fold-increased resistance to beta-lactams, tetracycline, chloramphenicol, and quinolones, a decrease in porin production, and increased production of AcrA, a component of the AcrAB-TolC drug efflux pump. We show that RamA enhances the transcription of the marRAB operon but is also able to induce an MDR phenotype in a mar-deleted strain. We demonstrate here that RamA is a transcriptional activator of the Mar regulon and is also a self-governing activator of the MDR cascade.

Enterobacter aerogenes OmpX, a cation-selective channel mar- and osmo-regulated

The ompX gene of Enterobacter aerogenes was cloned. Its overexpression induced a decrease in the major porin Omp36 production and consequently a beta-lactam resistance was noted. Purified outer membrane protein X (OmpX) was reconstituted into artificial membranes and formed ion channels with a conductance of 20 pS in 1 M NaCl and a cationic selectivity. Both MarA expression and high osmolarity induced a noticeable increase of the OmpX synthesis in the E. aerogenes ATCC 13048 strain. In addition, OmpX synthesis increased under conditions in which the expression of the E. aerogenes major non-specific porins, Omp36 and Omp35, decreased.

Omp35, a new Enterobacter aerogenes porin involved in selective susceptibility to cephalosporins

In Enterobacter aerogenes, beta-lactam resistance often involves a decrease in outer membrane permeability induced by modifications of porin synthesis. In ATCC 15038 strain, we observed a different pattern of porin production associated with a variable antibiotic susceptibility. We purified Omp35, which is expressed under conditions of low osmolality and analyzed its pore-forming properties in artificial membranes. This porin was found to be an OmpF-like protein with high conductance values. It showed a noticeably higher conductance compared to Omp36 and a specific location of WNYT residues in the L3 loop. The importance of the constriction region in the porin function suggests that this organization is involved in the level of susceptibility to negative large cephalosporins such as ceftriaxone by bacteria producing the Omp35 porin subfamily.

Extended-spectrum beta-lactamase-producing Enterobacteriaceae in community and private health care centers

In 1999, 39 of 2,599 isolates of the family Enterobacteriaceae (1.5%) collected by eight private laboratories in the Aquitaine region in France produced an extended-spectrum beta-lactamase (ESBL). Among these were 19 Enterobacter aerogenes isolates; 8 Klebsiella pneumoniae isolates; 6 Escherichia coli isolates; 3 Proteus mirabilis isolates; and 1 isolate each of Serratia marcescens, Morganella morganii, and Providencia stuartii. ESBL producers were isolated from 38 patients, including 33 residents of 11 clinics or nursing homes and 5 ambulatory patients. Seven different ESBLs were characterized. These mainly consisted of TEM-24 (25 isolates) and TEM-21 (9 isolates), but TEM-15 (2 isolates) and TEM-3, TEM-19, SHV-4, and CTX-M-1 (1 isolate each) were also characterized. Seven strains showed the coexistence of different TEM- and/or SHV-encoding genes, including a new SHV-1 variant, SHV-44, defined by the substitution R205L previously reported for SHV-3 in association with S238G. The epidemiology of the ESBL producers was investigated by random amplification of polymorphic DNA, typing by enterobacterial repetitive intergenic consensus PCR, analysis of resistance cotransferred with the ESBL, and analysis of the restriction profiles of the ESBL-encoding plasmids. Of the TEM-24-expressing strains, 18 were E. aerogenes isolates, including 9 from the same clinic, that were representatives of the epidemic clone disseminating in France. Of the TEM-21-producing strains that belonged to different species of the family Enterobacteriaceae (E. coli, K. pneumoniae, and P. mirabilis), 8 were isolated in the same nursing home. Outbreaks due to strain and/or plasmid dissemination in these clinic and nursing home were demonstrated. The presence of ESBL producers in five ambulatory patients probably resulted from nosocomial acquisition. Our data highlight the serious need to monitor patients for ESBL-producing Enterobacteriaceae in general practice.

Selection during cefepime treatment of a new cephalosporinase variant with extended-spectrum resistance to cefepime in an Enterobacter aerogenes clinical isolate

Enterobacter aerogenes resistant to cefepime (MIC, 32 microg/ml) was isolated from a patient treated with cefepime for an infection caused by a strain of E. aerogenes overproducing its AmpC beta-lactamase (MIC of cefepime, 0.5 microg/ml). The AmpC beta-lactamase of the resistant strain had an L-293-P amino acid substitution and a high k(cat)/K(m) ratio for cefepime. Both of these modifications were necessary for resistance to cefepime.

Antibiotic resistance rates and phenotypes among isolates of Enterobacteriaceae in French extra-hospital practice

Antibiotic resistance among members of the family Enterobacteriaceae was prospectively surveyed by eight French private laboratories over a 5-month period in 1999. A total of 2,599 consecutive and nonduplicate strains were collected, mainly (60.9%) from patients in the community. Most strains (82.9%) derived from urine. Escherichia coli was the predominant (73.9%) organism isolated. The overall rates of antibiotic resistance were as follows: amoxicillin, 53.4%; amoxicillin-clavulanic acid, 27.3%; ticarcillin, 44.2%; piperacillin-tazobactam, 3.2%; cephalothin, 29.2%; cefuroxime, 14.7%; cefoxitin, 11.5%; ceftazidime, 3.6%; cefotaxime, 2.8%; cefepime, 0.3%; imipenem, 0.1%; gentamicin (G), 3.8%; tobramycin (T), 5.0%; netilmicin (Nt), 3.7%; amikacin (A), 0.7%; nalidixic acid, 14.3%; ofloxacin, 10.4%; cotrimoxazole, 21.1%; nitrofurantoin, 12.7%; fosfomycin, 5.2%; tetracycline, 50.1%; and colistin, 12.5%. Beta-lactam resistance phenotypes essentially comprised penicillinase production (33.9%), overexpression of chromosomal cephalosporinase (4.6%), and synthesis of inhibitor-resistant TEM/OXA enzymes (1.5%) or extended-spectrum beta-lactamases (1.5%). Aminoglycoside resistance phenotypes consisted of GTNt (93 strains), TNtA (68 strains), GTNtA (14 strains), T (4 strains), GT (3 strains), G (1 strain), and reduced uptake/permeability (3 strains). Most of the nalidixic acid-resistant strains were resistant to ofloxacin (72.8%). Antibiotic resistance rates and phenotypes varied widely according to the bacterial group and the source of the strains. Significantly higher rates were observed in private healthcare centers than in the community, due to a higher proportion of both resistant species and resistant strains. However, multidrug-resistant isolates, including five extended-spectrum beta-lactamase-producing strains, were also recovered from the community.

Prevalence of extended-spectrum beta-lactamase-producing Enterobacter cloacae in the Asia-Pacific region: results from the SENTRY Antimicrobial Surveillance Program, 1998 to 2001

Enterobacter cloacae strains from hospitalized patients with a range of infections were collected by 17 laboratories in the Asia-Pacific region and South Africa. Isolates for which ceftriaxone MICs were above 1 microg/ml and/or ceftazidime MICs were above 2 microg/ml, as well as 46 strains for which ceftriaxone and/or ceftazidime MICs were at or below these values, were screened for levels of extended-spectrum beta-lactamase (ESBL) production through the use of broth microdilution for the detection of clavulanate enhancement of the activity of ceftriaxone, ceftazidime, and cefepime. Of the isolates examined, ceftriaxone and/or ceftazidime had elevated MICs for 44%, of which 36% were ESBL positive. ESBL-positive strains were commonly susceptible to piperacillin-tazobactam and more frequently resistant to several other antimicrobials studied. A cefepime MIC above 0.25 microg/ml had the highest sensitivity (100%) and specificity (74%) for predicting the presence of an ESBL.

Outbreak of TEM-24-producing Enterobacter aerogenes in a Spanish hospital

Organisms encoding multidrug resistance genes are becoming increasingly prevalent. During a 2-month period (December, 2000, to January, 2001), 83 consecutive isolates of Enterobacter spp. were collected in our microbiology department. Antibiotic susceptibility was determined using the Vitek II automatic system. We selected strains with decreased susceptibility to extended-spectrum cephalosporins. The double-disk potentiation test was positive in 10 of these strains, indicating the presence of extended-spectrum beta-lactamases (ESBLs). Polymerase chain reaction (PCR), isoelectric focusing (IEF), and sequencing identified TEM 24 beta-lactamase in the 10 selected E. aerogenes. Random amplification of polymorphic DNA (RAPD-PCR) revealed the same clonal origin for all the strains tested and strongly suggest an outbreak of multidrug-resistant E. aerogenes. To follow up the trends in ESBLs-producing Enterobacter infections in the hospital over time, we repeated the study 1 year later (December, 2001, to February, 2002). Only three ESBLs-producing Enterobacter were found. All of them corresponded to the previously characterized clone.

A seven-year survey of Klebsiella pneumoniae producing TEM-24 extended-spectrum beta-lactamase in Nice University Hospital (1994-2000)

The aim of this study was to investigate TEM-24-producing isolates of Klebsiella pneumoniae, and their clonal dissemination in Nice University Hospital. During the 1994-2000 period, a total of 263 non-repetitive isolates of ESBL-producing K. pneumoniae were collected. Most of these isolates were highly resistant in vitro to ceftazidime, cefotaxime and aztreonam, but susceptible to cefoxitin and imipenem. Resistance profile analysis revealed seven predominant antibiotypes (P1 to P7). Isoelectric focusing evidenced beta-lactamase activity, with a chromosomal penicillinase (pl 7.7), and one or two additional enzymes with pls ranging from 5.4 to 8.2 identified as presumed TEM-1 pl 5.4, TEM-3 pl 6.3, TEM-24 pl 6.5, SHV-3 pl 7.0, SHV-4 pl 7.8, SHV-5 pl 8.2, or other unidentified beta-lactamases. Among these K. pneumoniae, 130 isolates produced TEM-24, and 115 of them were highly resistant in vitro to quinolones (antibiotype P1). This phenotype was responsible for an outbreak in a medical intensive care unit from March to September 2000. Four isolates submitted were genetical sequenced, and shared 99.9% homology with tem-24 (GenBank no. X 65253). Pulsed-field gel electrophoresis and enterobacterial repetitive intergenic consensus polymerase chain reaction (PCR) (ERIC2-PCR) applied to 28 non-epidemic and six epidemic isolates yielded concordant results. Molecular typing revealed the persistence and dissemination of a single clone of TEM-24 producing K. pneumoniae in Nice Hospital during the seven-year study period.

Overexpression and purification of the three components of the Enterobacter aerogenes AcrA-AcrB-TolC multidrug efflux pump

The tripartite AcrA-AcrB-TolC system is the major efflux pump of the nosocomial pathogen Enterobacter aerogenes. AcrA is a trimeric periplasmic lipoprotein anchored in the inner membrane, AcrB is an inner membrane transporter and TolC is a trimeric outer membrane channel. In order to reconstitute the AcrA-AcrB-TolC system of E. aerogenes in artificial membranes, we overexpressed and purified the three proteins. The E. aerogenes acrA, acrB and tolC open reading frames were individually inserted in the expression vector pET24a(+), in frame with a sequence coding a C-terminal hexahistidine tag to allow purification by INAC (Immobilized Nickel Affinity Chromatography). The mature AcrA-6His was overproduced in a soluble form in the cytoplasm of Escherichia coli BL21(DE3). AcrA-6His was purified under native conditions in two steps using INAC and gel permeation chromatography. We obtained about 25 mg of 97% pure AcrA-6His per liter of culture. AcrB-6His was solubilized from the membrane fraction of E. coli C43(DE3) in 300 mM NaCl, 5% Triton X-100 and purified in one step by INAC. The AcrB-6His enriched fraction was eluted with 100 mM imidazole. The final yield was 1-2 mg of 95% pure AcrB-6His per liter of culture. The membrane fraction of E. coli BL21(DE3)pLysS containing TolC-6His was first treated with 2% Triton X-100, 30 mM MgCl(2) to solubilize the inner membrane proteins. After ultracentrifugation, the pellet was treated with 5% Triton X-100, 5 mM EDTA to solubilize the outer membrane proteins. Approximately 5 mg of 95% pure TolC-6His trimers per liter of culture was purified by INAC.