Cefotaxime-hydrolysing beta lactamases in Morganella morganii

An Overview of the Antimicrobial Activity of Polymeric Nanoparticles Against Enterobacteriaceae

Bacterial resistance is considered one of the most important public health problems of the century, due to the ability of bacteria to rapidly develop resistance mechanisms, which makes it difficult to treat infections, leading to a high rate of morbidity and mortality. Based on this, several options are being sought as an alternative to currently available treatments, with a particular focus on nanotechnology. Nanomaterials have important potential for use in medical interventions aimed at preventing, diagnosing and treating numerous diseases by directing the delivery of drugs. This review presents data on the use of polymeric nanoparticles having in vitro and in vivo activity against bacteria belonging to the Enterobacteriaceae family.

Defining Substrate Specificity in the CTX-M Family: the Role of Asp240 in Ceftazidime Hydrolysis

The natural diversification of CTX-M β-lactamases led to the emergence of Asp240Gly variants in the clinic that confer reduced susceptibility to ceftazidime (CAZ). In this study, we compared the impact of this substitution on CAZ and ceftazidime-avibactam (CZA) MICs against isogenic Escherichia coli strains with different porin deficiencies. Our results show a noticeable increase in CAZ resistance in clones expressing Asp240Gly-harboring CTX-M when combined with OmpF porin deficiency. Kinetic analysis revealed that the k_cat/K_m for CAZ was 5- to 15-fold higher for all Asp240Gly variants but remained 200- to 725-fold lower than that for cefotaxime (CTX). In vitro selection of CAZ-resistant clones yielded nonsusceptible CTX-M producers (MIC of >16 μg/ml) only after overnight incubation; the addition of avibactam (AVI) decreased MICs to a susceptible range against these variants. In contrast, the use of CZA as a selective agent did not yield resistant clones. AVI inactivated both CTX-M-12 and CTX-M-96, with an apparent inhibition constant comparable to that of SHV-2 and 1,000-fold greater than that of PER-2 and CMY-2, and k₂/K for CTX-M-12 was 24- and 35-fold higher than that for CTX-M-96 and CTX-M-15, respectively. Molecular modeling suggests that AVI interacts similarly with CTX-M-96 and CTX-M-15. We conclude that the impact of Asp240Gly in resistance may arise when other mechanisms are also present (i.e., OmpF deficiency). Additionally, CAZ selection could favor the emergence of CAZ-resistant subpopulations. These results define the role of Asp240 and the impact of the -Gly substitution and allow us to hypothesize that the use of CZA is an effective preventive strategy to delay the development of resistance in this family of extended-spectrum β-lactamases.

Crystal structure and kinetic analysis of the class B3 di-zinc metallo-β-lactamase LRA-12 from an Alaskan soil metagenome

We analyzed the kinetic properties of the metagenomic class B3 β-lactamase LRA-12, and determined its crystallographic structure in order to compare it with prevalent metallo-β-lactamases (MBLs) associated with clinical pathogens. We showed that LRA-12 confers extended-spectrum resistance on E. coli when expressed from recombinant clones, and the MIC values for carbapenems were similar to those observed in enterobacteria expressing plasmid-borne MBLs such as VIM, IMP or NDM. This was in agreement with the strong carbapenemase activity displayed by LRA-12, similar to GOB β-lactamases. Among the chelating agents evaluated, dipicolinic acid inhibited the enzyme more strongly than EDTA, which required pre-incubation with the enzyme to achieve measurable inhibition. Structurally, LRA-12 contains the conserved main structural features of di-zinc class B β-lactamases, and presents unique structural signatures that differentiate this enzyme from others within the family: (i) two loops (α3-β7 and β11-α5) that could influence antibiotic entrance and remodeling of the active site cavity; (ii) a voluminous catalytic cavity probably responsible for the high hydrolytic efficiency of the enzyme; (iii) the absence of disulfide bridges; (iv) a unique Gln116 at metal-binding site 1; (v) a methionine residue at position 221that replaces Cys/Ser found in other B3 β-lactamases in a predominantly hydrophobic environment, likely playing a role in protein stability. The structure of LRA-12 indicates that MBLs exist in wild microbial populations in extreme environments, or environments with low anthropic impact, and under the appropriate antibiotic selective pressure could be captured and disseminated to pathogens.

Structural and Kinetic Insights into the "Ceftazidimase" Behavior of the Extended-Spectrum β-Lactamase CTX-M-96

Diversification of the CTX-M β-lactamases led to the emergence of variants responsible for decreased susceptibility to ceftazidime, like the Asp240Gly-harboring "ceftazidimases". We solved the crystallographic structure of the Asp240Gly variant CTX-M-96 at 1.2 Å and evaluated the role of Asp240 in the activity toward oxyimino-cephalosporins through simulated models and kinetics. There seem to be subtle changes in the conformation of the active site cavity of CTX-M-96, compared to enzyme variants harboring the Asp240, and these small rearrangements could be due to localized shifts in the environment of the β3 strand. According to the crystallographic evidence, CTX-M-96 presents a "compact" active site, which in spite of its reduced cavity seems to allow the proper interaction with oxyimino-cephalosporins, as suggested by simulated models. The term "ceftazidimases" that is currently applied for the Asp240Gly-harboring CTX-M variants should be used carefully. Structural differences between CTX-M harboring the Asp240Gly mutation (and also probably others like those at Pro167) do not seem to be conclusive to determine the "ceftazidimase" behavior observed in vivo, which is in turn partially supported by the mild improvement in the catalytic efficiency toward ceftazidime by CTX-M-96 and similar enzymes, compared to "parental" Asp240-harboring variants. In addition, it is observed that alterations in OmpF expression could act synergistically with CTX-M-96 for yielding clinical resistance toward ceftazidime. We therefore propose that the observed resistance in vivo is due to the sum of synergic mechanisms, and the term "cefotaximases associated with ceftazidime resistance" could be conveniently used to describe CTX-M harboring the Asp240Gly substitution.

Crystal structure of the extended-spectrum β-lactamase PER-2 and insights into the role of specific residues in the interaction with β-lactams and β-lactamase inhibitors

PER-2 belongs to a small (7 members to date) group of extended-spectrum β-lactamases. It has 88% amino acid identity with PER-1 and both display high catalytic efficiencies toward most β-lactams. In this study, we determined the X-ray structure of PER-2 at 2.20 Å and evaluated the possible role of several residues in the structure and activity toward β-lactams and mechanism-based inhibitors. PER-2 is defined by the presence of a singular trans bond between residues 166 to 167, which generates an inverted Ω loop, an expanded fold of this domain that results in a wide active site cavity that allows for efficient hydrolysis of antibiotics like the oxyimino-cephalosporins, and a series of exclusive interactions between residues not frequently involved in the stabilization of the active site in other class A β-lactamases. PER β-lactamases might be included within a cluster of evolutionarily related enzymes harboring the conserved residues Asp136 and Asn179. Other signature residues that define these enzymes seem to be Gln69, Arg220, Thr237, and probably Arg/Lys240A ("A" indicates an insertion according to Ambler's scheme for residue numbering in PER β-lactamases), with structurally important roles in the stabilization of the active site and proper orientation of catalytic water molecules, among others. We propose, supported by simulated models of PER-2 in combination with different β-lactams, the presence of a hydrogen-bond network connecting Ser70-Gln69-water-Thr237-Arg220 that might be important for the proper activity and inhibition of the enzyme. Therefore, we expect that mutations occurring in these positions will have impacts on the overall hydrolytic behavior.

Antimicrobial resistance among Enterobacteriaceae in South America: history, current dissemination status and associated socioeconomic factors

South America exhibits some of the higher rates of antimicrobial resistance in Enterobactericeae worldwide. This continent includes 12 independent countries with huge socioeconomic differences, where the ample access to antimicrobials, including counterfeit ones, coexists with ineffective health systems and sanitation problems, favoring the emergence and dissemination of resistant strains. This work presents a literature review concerning the evolution and current status of antimicrobial resistance threats found among Enterobacteriaceae in South America. Resistance to β-lactams, fluoroquinolones and aminoglycosides was emphasized along with description of key epidemiological studies that highlight the success of specific resistance determinants in different parts of the continent. In addition, a discussion regarding political and socioeconomic factors possibly related to the dissemination of antimicrobial resistant strains in clinical settings and at the community is presented. Finally, in order to assess the possible sources of resistant bacteria, we compile the current knowledge about the occurrence of antimicrobial resistance in isolates in South American' food, food-producing animals and off-hospitals environments. By addressing that intensive intercontinental commerce and tourism neutralizes the protective effect of geographic barriers, we provide arguments reinforcing that globally integrated efforts are needed to decelerate the emergence and dissemination of antimicrobial resistant strains.

Whole-genome sequencing and identification of Morganella morganii KT pathogenicity-related genes

BACKGROUND

The opportunistic enterobacterium, Morganella morganii, which can cause bacteraemia, is the ninth most prevalent cause of clinical infections in patients at Changhua Christian Hospital, Taiwan. The KT strain of M. morganii was isolated during postoperative care of a cancer patient with a gallbladder stone who developed sepsis caused by bacteraemia. M. morganii is sometimes encountered in nosocomial settings and has been causally linked to catheter-associated bacteriuria, complex infections of the urinary and/or hepatobiliary tracts, wound infection, and septicaemia. M. morganii infection is associated with a high mortality rate, although most patients respond well to appropriate antibiotic therapy. To obtain insights into the genome biology of M. morganii and the mechanisms underlying its pathogenicity, we used Illumina technology to sequence the genome of the KT strain and compared its sequence with the genome sequences of related bacteria.

RESULTS

The 3,826,919-bp sequence contained in 58 contigs has a GC content of 51.15% and includes 3,565 protein-coding sequences, 72 tRNA genes, and 10 rRNA genes. The pathogenicity-related genes encode determinants of drug resistance, fimbrial adhesins, an IgA protease, haemolysins, ureases, and insecticidal and apoptotic toxins as well as proteins found in flagellae, the iron acquisition system, a type-3 secretion system (T3SS), and several two-component systems. Comparison with 14 genome sequences from other members of Enterobacteriaceae revealed different degrees of similarity to several systems found in M. morganii. The most striking similarities were found in the IS4 family of transposases, insecticidal toxins, T3SS components, and proteins required for ethanolamine use (eut operon) and cobalamin (vitamin B12) biosynthesis. The eut operon and the gene cluster for cobalamin biosynthesis are not present in the other Proteeae genomes analysed. Moreover, organisation of the 19 genes of the eut operon differs from that found in the other non-Proteeae enterobacterial genomes.

CONCLUSIONS

This is the first genome sequence of M. morganii, which is a clinically relevant pathogen. Comparative genome analysis revealed several pathogenicity-related genes and novel genes not found in the genomes of other members of Proteeae. Thus, the genome sequence of M. morganii provides important information concerning virulence and determinants of fitness in this pathogen.

Association of broad-spectrum antibiotic use with faecal carriage of oxyiminocephalosporin-resistant enterobacteriaceae in an intensive care unit

The link between administration of antibiotics and detection of third-generation-cephalosporin-resistant (TGCR) enterobacteriaceae in faeces was studied in patients in a burns intensive care unit (ICU). The presence of extended-spectrum beta-lactamase producers was also determined in these isolates. At least two rectal swab samples were taken from 43 of 72 patients admitted to the ICU from January 1998 to June 1999. Antibiotic resistance tests were performed for all isolated enterobacteriaceae using the methods of the National Committee for Clinical Laboratory Standards. Only 10 out of 30 antibiotic-treated patients showed TGCR enterobacteriaceae in faeces. Fisher's exact test showed a relationship between the administration of oxyiminocephalosporins (third-generation cephalosporins) (P=0.002) or carbapenems (P=0.003) and the isolation of TGCR enterobacteriaceae from faeces. The administration of oxyiminocephalosporins led to the selection of resistant strains in the faecal flora.

Biochemical and molecular characterization of three new variants of AmpC beta-lactamases from Morganella morganii

Morganella morganii produces an inducible, chromosomally encoded AmpC beta-lactamase. We describe in this study three new variants of AmpC within this species with apparent pIs of 6.6 (M19 from M. morganii strain PP19), 7.4 (M29 from M. morganii strain PP29), and 7.8 (M37 from M. morganii strain PP37). After gene sequencing, deduced amino acid sequences displayed one to six substitutions when compared to the available Morganella AmpC sequences. An AmpR-encoding gene was also found upstream of ampC, including the LysR regulators' helix-turn-helix DNA-binding domain and the putative T-N11-A-protected region in the ampR-ampC intercistronic sequence. All three AmpC variants were purified from in vitro-generated derepressed mutants and showed overall similar kinetic parameters. None of the observed amino acid changes, occurring at the surface of the protein, appear to have a major influence in their catalytic properties. Morganella AmpCs exhibit the highest catalytic efficiencies (k(cat)/K(m)) on classical penicillins, cefoxitin, narrow-spectrum cephalosporins, and cefotaxime. Cefotaxime was more effectively hydrolyzed than other oxyimino-cephalosporins, whereas cefepime was 3 log-fold less efficiently hydrolyzed than other cephalosporins such as cephalothin. Several differences with other AmpC beta-lactamases were found. Ampicillin was more efficiently hydrolyzed than benzylpenicillin. High k(cat)/K(m) values were observed for oxacillin and piperacillin, which are usually poor substrates for AmpC. A fairly efficient hydrolysis of imipenem was detected as well. Aztreonam, carbenicillin, and tazobactam were effective transient inactivators of these variants.

New TEM-derived extended-spectrum beta-lactamase and its genomic context in plasmids from Salmonella enterica serovar derby isolates from Uruguay

A small (8.2-kb) ColE1 plasmid encoding TEM-144 (a new beta-lactamase with a ceftazidimase profile) was sequenced by a gene-walking strategy. The bla(TEM) allele was carried on a Tn2 element, disrupting a Rom protein gene. TEM-144 differs from TEM-1 by two mutations (R164C and E240K) and from the ceftazidime-hydrolyzing TEM-91 by one mutation (T182M).

Dissemination of CTX-M-type extended-spectrum beta-lactamase genes to unusual hosts

A Citrobacter amalonaticus and a Morganella morganii producing the CTX-M-1 extended-spectrum beta-lactamase (ESBL) were isolated from an area where this enzyme is now widespread in Escherichia coli. This is the first report of CTX-M-1 in the former species. In both cases the ESBL determinant was possibly acquired by these unusual hosts in vivo, after coinfection with E. coli strains carrying conjugative plasmids encoding CTX-M-1.

Transcriptional analysis of the bla(CTX-M-2) gene in Salmonella enterica serovar Infantis

Transcriptional organization of bla(CTX-M-2) present in a multiresistance plasmid of Salmonella enterica serovar Infantis suggests the presence of more than one promoter involved in the expression of the beta-lactamase gene. At least two bla(CTX-M-2)-specific mRNAs (near to 1 kb and 5 kb) were evidenced. Two +1 signals were detected at -22 bp and -59 bp of bla(CTX-M-2) defining two putative promoters.

Enteropathogenic Escherichia coli strains carrying genes encoding the PER-2 and TEM-116 extended-spectrum beta-lactamases isolated from children with diarrhea in Uruguay

We studied 13 extended-spectrum beta-lactamase (ESBL)-producing enteropathogenic Escherichia coli isolates from children suffering acute diarrhea in Uruguay. ESBL characterization in crude extracts showed a single band at pI 5.4. PCR amplification and sequencing data allowed identification of blaPER-2 and blaTEM-116. Retrospective analysis suggests that these strains were disseminated in the community, even if unnoticed, prior to their access to the hospital environment more than a decade ago.

[Enzymatic resistance to beta lactam antibiotics within the genus Proteus and evaluation of Proteus mirabilis phenotypes and genotypes for resistance to third- and fourth-generation cephalosporins]

INTRODUCTION

The aim of this study was to evaluate betalactam resistance within the genus Proteus and characterize the betalactamases responsible for this resistance.

METHODS

We analyzed 99 strains (87, P. mirabilis; 10 P. vulgaris, and 2, P. penneri) isolated from patients at one University Hospital. Antibiotic susceptibility tests were performed according to NCCLS recommendations. Presence of extended spectrum betalactamases (ESBL) was inferred by both double disk diffusion tests and minimum inhibitory concentration (MIC) of third and fourth generation cephalosporins alone and in the presence of clavulanic acid. Isoelectric points (pI) of the enzymes were estimated by isoelectrofocusing and the presence of the encoding genes was confirmed by polymerase chain reaction (PCR).

RESULTS

A broad spectrum betalactamase could be detected in those isolates (28%) resistant to penicillin and first generation cephalosporins while CTX-M-2 enzyme could be detected in P. mirabilis isolates resistant to third and fourth generation cephalosporins (18%). One of the P. vulgaris displayed reduced susceptibility to cefotaxime due to an enzyme of pI 7.4, while resistance to cefotaxime in one P. penneri was related to an enzyme of pI 6.8. Both enzymes were active on cefotaxime (1,000 mg/l) in the iodometric assay.

CONCLUSION

The broad extended spectrum betalactamase within genus Proteus was TEM-1, while CTX-M-2 was the ESBL responsible for the third and fourth generation cephalosporins in P. mirabilis. In P. vulgaris and P. penneri this resistance was associated with the hyperproduction of the chromosomal encoded betalactamase.

Description of In116, the first blaCTX-M-2-containing complex class 1 integron found in Morganella morganii isolates from Buenos Aires, Argentina

OBJECTIVES

We analysed the architecture and probable origin of a class 1 integron from cefotaxime-resistant Morganella morganii isolates.

METHODS

bla genes and class 1 integron elements were detected by PCR and DNA-DNA hybridization in a M. morganii strain isolated in 1996. PCR-mapping and sequencing of different fragments were carried out to determine the integron's architecture.

RESULTS AND CONCLUSIONS

A class 1 integron (In116), strongly related to the In6/In7 family, was detected in a plasmid from an oxyimino-cephalosporin-resistant M. morganii strain, producing CTX-M-2 beta-lactamase. The variable region of In116 contains aacA4, bla(OXA-2) and orfD cassettes. Downstream of the 3'-conserved-segment (3'-CS), an orf513-containing common region is followed by bla(CTX-M-2) and flanking regions, having 96-99% nucleotide identity with Kluyvera ascorbata's kluA-1 and neighbouring sequences. Some of the evidence supporting the incorporation of foreign DNA is as follows: a partial deletion in a second 3'-CS (3'-CS2), and the absence of 59-base element or IS-like structures upstream of bla(CTX-M-2).

Chromosome-encoded CTX-M-3 from Kluyvera ascorbata: a possible origin of plasmid-borne CTX-M-1-derived cefotaximases

A gene identical to plasmid-borne bla(CTX-M-3) is present in the chromosome of one Kluyvera ascorbata strain. It is associated with a structure including an inverted repeat right and an open reading frame 477-like gene probably involved in the mobilization of bla(CTX-M-3). Two other K. ascorbata strains rendered the previously described bla(KLUA-9) gene.

Cefotaximases (CTX-M-ases), an expanding family of extended-spectrum β-lactamases

Among the extended-spectrum β-lactamases, the cefotaximases (CTX-M-ases) constitute a rapidly growing cluster of enzymes that have disseminated geographically. The CTX-M-ases, which hydrolyze cefotaxime efficiently, are mostly encoded by transferable plasmids, and the enzymes have been found predominantly in Enterobacteriaceae, most prevalently in Escherichia coli, Salmonella typhimurium, Klebsiella pneumoniae, and Proteus mirabilis. Isolates of Vibrio cholerae, Acinetobacter baumannii, and Aeromonas hydrophila encoding CTX-M-ases have also been reported. The CTX-M-ases belong to the molecular class A β-lactamases, and the enzymes are functionally characterized as extended-spectrum β-lactamases. This group of β-lactamases confers resistance to penicillins, extended-spectrum cephalosporins, and monobactams, and the enzymes are inhibited by clavulanate, sulbactam, and tazobactam. Typically, the CTX-M-ases hydrolyze cefotaxime more efficiently than ceftazidime, which is reflected in substantially higher MICs to cefotaxime than to ceftazidime. Phylogenetically, the CTX-M-ases are divided into four subfamilies that seem to have descended from chromosomal β-lactamases of Kluyvera spp. Insertion sequences, especially ISEcp1, have been found adjacent to genes encoding enzymes of all four subfamilies. The class I integron-associated orf513 also seems to be involved in the mobilization of blaCTX-M genes. This review discusses the phylogeny and the hydrolytic properties of the CTX-M-ases, as well as their geographic occurrence and mode of spread.Key words: extended-spectrum β-lactamases, cefotaximases, phylogeny, dissemination, hydrolytic properties.

Prevalence and molecular epidemiology of CTX-M extended-spectrum beta-lactamase-producing Escherichia coli and Klebsiella pneumoniae in Russian hospitals

A total of 904 consecutive nosocomial isolates of Escherichia coli and Klebsiella pneumoniae collected from 28 Russian hospitals were screened for production of extended-spectrum beta-lactamases (ESBLs). The ESBL phenotype was detected in 78 (15.8%) E. coli and 248 (60.8%) K. pneumoniae isolates. One hundred fifteen isolates carried the genes for CTX-M-type beta-lactamases, which, as shown by PCR-restriction fragment length polymorphism analysis, were distributed into the two genetic groups of CTX-M-1 (93%)- and CTX-M-2 (7%)-related enzymes. Isolates producing the enzymes of the first group were found in 20 hospitals from geographically distant regions of the country and were characterized by considerable diversity of genetic types, as was demonstrated by enterobacterial repetitive consensus PCR typing. Within this group the CTX-M-3 and the CTX-M-15 beta-lactamases were identified. In contrast, the enzymes of the CTX-M-2 group (namely, CTX-M-5) were detected only in eight clonally related E. coli isolates from a single hospital. Notably, the levels of resistance to ceftazidime were remarkably variable among the CTX-M producers. This study provides further evidence of the global dissemination of CTX-M type ESBLs and emphasizes the need for their epidemiological monitoring.

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.

Extended-spectrum beta-lactamases in enterobacteriaceae in Buenos Aires, Argentina, public hospitals

Resistance to extended-spectrum cephalosporins is often associated with plasmid encoded extended spectrum beta-lactamases (ESBL). In order to evaluate the prevalence and diversity of ESBLs in enterobacteria in our city, a 1-month-period survey was carried out from April to May 2000. Extended-spectrum-cephalosporin-resistant strains, isolated from inpatient clinical specimens other than stools, were collected among 17 participating hospitals. From a total of 427 enterobacterial strains that were collected during this period, 39 were extended-spectrum cephalosporin resistant. The National Committee for Clinical Laboratory Standards' Screening and Confirmatory Tests for ESBL production were performed using cefotaxime and ceftazidime; cefepime and cefepime-clavulanic acid-containing disks were included. beta-Lactamases were characterized by isoelectric focusing and PCR amplification using specific primers. Three different ESBLs were detected: SHV-related (4 isolates), PER-2-type (9 isolates), and CTX-M-2-related (26 isolates). Sequencing of the corresponding genes confirmed CTX-M-2 in 19 of 21 and CTX-M-31 (an allelic variant) in the remaining 2 of 21. CTX-M-2 (or its variant) was detected in all Escherichia coli, Enterobacter aerogenes, Serratia marcescens, Proteus mirabilis, and Providencia stuartii strains, while PER-2 was detected in Enterobacter cloacae, E. aerogenes, and Klebsiella pneumoniae; SHV-related ESBL were found only in K. pneumoniae. These results clearly show that CTX-M-2 is the most prevalent ESBL produced by enterobacterial species isolated from public hospitals in Buenos Aires.

Novel class 1 integron (InS21) carrying blaCTX-M-2 in Salmonella enterica serovar infantis

The genetic organization of the region coding for CTX-M-2 in Salmonella enterica serovar Infantis was determined by PCR mapping. This gene seems to have been mobilized from the Kluyvera ascorbata chromosome to a complex sulI-type integron, similar to In6 and In7.

Plasmidic extended-spectrum beta-lactamases in Vibrio cholerae O1 El Tor isolates in Argentina

Since 1992 there have been seven major outbreaks of cholera in Argentina. Susceptibility analysis of 1,947 isolates (40% of reported cases) of Vibrio cholerae O1 biotype El Tor suggested the presence of extended-spectrum beta-lactamases (ESBLs) in 28 isolates. Because of their different susceptibility profiles, V. cholerae isolates M1502, M1516, M1573, and M3030 (all of which are of the Ogawa serotype) were selected for the present study. By susceptibility analysis, isoelectric focusing, and PCR-based restriction fragment length polymorphism analysis, CTX-M-type enzymes were identified in three isolates, whereas a PER-2-type enzyme, in addition to a TEM-1-like enzyme, was identified in the other isolate. The presence of these ESBLs in V. cholerae isolates resulted in MICs well below those commonly observed for members of the family ENTEROBACTERIACEAE: Genes that encode both ESBLs were transferred to Escherichia coli by conjugation, together with all determinants of resistance to non-beta-lactam antibiotics (gentamicin, kanamycin, and sulfamethoxazole for all isolates; amikacin and streptomycin for three isolates; trimethoprim, tetracycline, and chloramphenicol for two isolates). Plasmid profile analysis and Southern blotting revealed the presence of single plasmids of about 150 kb in the four V. cholerae isolates and their respective transconjugants and revealed that the plasmids harbored genes encoding CTX-M-type or PER-2-type ESBLs. These results strongly suggest the broad spread of these ESBLs among genera belong to families other than the ENTEROBACTERIACEAE:

Epidemiology of extended-spectrum beta-lactamase-producing Enterobacter isolates in a Spanish hospital during a 12-year period

Fifteen Enterobacter clinical isolates (11 Enterobacter cloacae isolates, 3 Enterobacter aerogenes isolates, and 1 Enterobacter gergoviae isolate), representing 0.4% of all Enterobacter isolates recovered in our hospital from 1989 to 2000, were suspected of harboring an extended-spectrum beta-lactamase (ESBL). These isolates were recovered from 14 different patients. ESBLs were transferred by conjugation into an Escherichia coli recipient strain. Pulsed-field gel electrophoresis (PFGE) revealed a single clone of E. aerogenes and six different clones of E. cloacae. Four of these E. cloacae clonal types were represented by only one isolate each, but the other two were represented by three and four isolates, respectively. Isoelectric focusing, susceptibility phenotyping, PCR analysis, and sequencing demonstrated the presence of three different ESBLs. The most frequent was the recently characterized CTX-M-10 ESBL, which was found in the E. gergoviae isolate and in all but one of the E. cloacae isolates. The remaining E. cloacae isolate harbored a TEM-27 ESBL, and the three E. aerogenes isolates harbored a TEM-24 ESBL. PFGE revealed that our E. aerogenes strain was indistinguishable from the French TEM-24-producing E. aerogenes endemic clone. Although a low prevalence of ESBL-producing Enterobacter isolates was found in our institution over a 12-year period, a diversity of nonepidemic E. cloacae clones was detected, as was the persistence of the CTX-M-10 beta-lactamase. The presence of the TEM-24-producing E. aerogenes French clone in our institution also demonstrates the intercountry dissemination of ESBL-producing isolates.

Third-generation cephalosporin resistance in Shigella sonnei, Argentina

Shigella sonnei resistant to cefotaxime (but not to ceftazidime) was isolated for the first time in stool samples from a pediatric patient with vomiting and bloody diarrhea in northern Argentina. Microbiologic and biochemical tests confirmed the presence of an extended spectrum beta-lactamase displaying an apparent isoelectric point value of 8.2.