Nucleotide sequence of a plasmid-mediated cephalosporinase gene (blaLAT-1) found in Klebsiella pneumoniae

A Sustainable Combined Approach to Control the Microbial Bioburden in the School Environment

The indoor microbiome is a dynamic ecosystem including pathogens that can impact human health. In this regard, the school environment represents the main living space of humans for many years, and an unhealthy environment can significantly condition students' health. School rooms can suffer from insufficient ventilation and the use of building materials that may favor pathogen contamination, mostly sanitized by conventional chemical-based methods, which can impact pollution, have temporary effects, and induce the selection of antimicrobial resistance (AMR) in persistent microbes. In the search for sustainable and effective methods to improve the healthiness of the classroom environment, a pre-post case-control study was performed in an Italian high school. Over a year, different interventions were sequentially placed and evaluated for their impact on bioburden and air quality, including the introduction of plants, a mechanical ventilation system, and probiotic-based sanitation (PBS) in substitution for chemical sanitation. Through continuous microbial monitoring of the enrolled school rooms, via culture-dependent and -independent methods, a remarkable bioburden level was detected at baseline (around 12,000 and 20,000 CFU/m2, before and after classes, respectively), composed mostly of Staphylococcus spp. and fungi. Some decrease in fungal contamination was observed following the introduction of plants. Still, the most significant decrease in pathogens and associated AMR was detected following the introduction of ventilation and PBS, which decreased pathogen level by >80% (p < 0.001) and AMR by up to 3 Log10 (p < 0.001) compared to controls. Collected data support the use of combined strategies to improve indoor microbial quality and confirm that PBS can effectively control bioburden and AMR spread not only in sanitary environments.

Class C β-Lactamases: Molecular Characteristics

Class C β-lactamases or cephalosporinases can be classified into two functional groups (1, 1e) with considerable molecular variability (≤20% sequence identity). These enzymes are mostly encoded by chromosomal and inducible genes and are widespread among bacteria, including Proteobacteria in particular. Molecular identification is based principally on three catalytic motifs (⁶⁴SXSK, ¹⁵⁰YXN, ³¹⁵KTG), but more than 70 conserved amino-acid residues (≥90%) have been identified, many close to these catalytic motifs. Nevertheless, the identification of a tiny, phylogenetically distant cluster (including enzymes from the genera Legionella, Bradyrhizobium, and Parachlamydia) has raised questions about the possible existence of a C2 subclass of β-lactamases, previously identified as serine hydrolases. In a context of the clinical emergence of extended-spectrum AmpC β-lactamases (ESACs), the genetic modifications observed in vivo and in vitro (point mutations, insertions, or deletions) during the evolution of these enzymes have mostly involved the Ω- and H-10/R2-loops, which vary considerably between genera, and, in some cases, the conserved triplet ¹⁵⁰YXN. Furthermore, the conserved deletion of several amino-acid residues in opportunistic pathogenic species of Acinetobacter, such as A. baumannii, A. calcoaceticus, A. pittii and A. nosocomialis (deletion of residues 304-306), and in Hafnia alvei and H. paralvei (deletion of residues 289-290), provides support for the notion of natural ESACs. The emergence of higher levels of resistance to β-lactams, including carbapenems, and to inhibitors such as avibactam is a reality, as the enzymes responsible are subject to complex regulation encompassing several other genes (ampR, ampD, ampG, etc.). Combinations of resistance mechanisms may therefore be at work, including overproduction or change in permeability, with the loss of porins and/or activation of efflux systems.

Identification of CMY-2-type cephalosporinases in clinical isolates of Enterobacteriaceae by MALDI-TOF MS

This study exploited the possibility to detect Citrobacter freundii-derived CMY-2-like cephalosporinases in Enterobacteriaceae clinical isolates using matrix-assisted laser desorption ionization-time of flight mass spectrometry (MALDI-TOF MS). Periplasmic proteins were prepared using a modified sucrose method and analyzed by MALDI-TOF MS. A ca. 39,850-m/z peak, confirmed to represent a C. freundii-like β-lactamase by in-gel tryptic digestion followed by MALDI-TOF/TOF MS, was observed only in CMY-producing isolates. We have also shown the potential of the assay to detect ACC- and DHA-like AmpC-type β-lactamases.

Plasmid-encoded ACC-4, an extended-spectrum cephalosporinase variant from Escherichia coli

ACC-4, an omega loop mutant (Val(211)-->Gly) of the Hafnia alvei-derived cephalosporinase ACC-1, was encoded by an Escherichia coli plasmid. The genetic environment of bla(ACC-4) shared similarities with plasmidic regions carrying bla(ACC-1). Kinetics of beta-lactam hydrolysis and levels of resistance to beta-lactams showed that ACC-4 was more effective than ACC-1 against expanded-spectrum cephalosporins.

First detection of the Ambler class C 1 AmpC beta-lactamase in Citrobacter freundii by a new, simple double-disk synergy test

We report on the first detection of an AmpC-type Ambler class C 1 (ACC-1) beta-lactamase in Citrobacter freundi isolated from a patient also harboring ACC-1-producing Escherichia coli and Klebsiella pneumoniae. We propose a simple cefoxitin-based double-disk synergy test (DDST) for the specific detection of ACC-1 in members of the family Enterobacteriaceae, including natural AmpC producers, in association with a cloxacillin-based DDST as a first-line AmpC-type beta-lactamase screening test.

Antibiotic resistance in the institutionalized elderly

Geriatric patients frequently are cared for in long term care facilities (LTCFs), which are now a major component of our health care delivery system. Nearly half of the 2.2 million people who turned 65 years old in 1990 will enter an LTCF at least once before they die. Infections are one of the principal causes of morbidity and mortality in LTCFs. Because LTCFs are a less costly alternative to hospitalization, clinicians are treating many serious infections in the nursing home. As a result of antibiotic use, LTCFs will increasingly be recognized as sources of organisms resistant to multiple antibiotics. b-Lactams are a valuable class of potent antimicrobials with broad-spectrum activity against Gram-negative and Gram-positive organisms. The safety and efficacy of this class of antibiotics make them easy choices for empiric treatment of infections in the elderly. Unfortunately, excessive use of these antibiotics has created serious threats to our therapeutic armamentarium: the emergence of methicillin-resistant Staphylococcus aureus and of Gram-negative pathogens resistant to third-generation cephalosporins such as cefotaxime, ceftazidime, and ceftriaxone. Of these third-generation cephalosporins, resistance to ceftazidime is most frequently recognized. The major mechanism responsible for ceftazidime resistance in Gram-negative bacteria is the production of b-lactamases. This article summarizes the diversity of b-lactamases, highlights the important enzymes that confer ceftazidime resistance in LTCFs, and details some methods used to identify and characterize these enzymes. A clear challenge is to apply these techniques to epidemiologic and molecular studies conducted in LTCFs.

Escherichia coli with a self-transferable, multiresistant plasmid coding for metallo-beta-lactamase VIM-1

An Escherichia coli strain exhibiting decreased susceptibility to carbapenems was isolated from a hospitalized patient in Greece. The strain carried a self-transferable plasmid coding for metallo-beta-lactamase VIM-1. bla(VIM-1), along with aacA7, dhfrI, and aadA, was included as a gene cassette in a novel class 1 integron. A Citrobacter freundii ampC-derived gene, not associated with the integron, was also located in the same plasmid.

Cefcapene inactivates chromosome-encoded class C beta-lactamases

The stability of cefcapene and cefpodoxime, oral antibacterial cephalosporins, toward different classes of beta-lactamases was evaluated. For the class A beta-lactamases, TEM-1, SHV-1, and NMC-A, only the steady-state kinetic parameter ( k(cat)/ Km) values were calculated (3100 - 1.1 x 10(7) M(-1) x s(-1)), because these enzymes have very high Km values for cefpodoxime and cefotaxime. As for class B beta-lactamases L1, IMP-1, and CcrA, in general, similar k(cat)/ Km values were obtained. However, regarding class C beta-lactamases from Enterobacter cloacae, Escherichia coli, Pseudomonas aeruginosa, and Citrobacter freundii, we found major differences in stability between the two compounds. Cefpodoxime acted as a good substrate for the class C beta-lactamases, except for the enzyme from E. cloacae; its k(cat) and Km values were successfully calculated ( k(cat)/ Km, 1.8 x 10(5) - 1.2 x 10(7) M(-1) x s(-1)). On the other hand, cefcapene acted as a poor substrate or an inactivator for class C beta-lactamases; its k(2)/ K value was successfully calculated (8.7 x 10(5) - 7.0 x 10(6) M(-1) x s(-1)). In addition, k(3) values were determined for beta-lactamases from P. aeruginosa (2.3 x 10(-2) x s(-1)) and C. freundii (2.1 x 10(-1) x s(-1)). Even though these values could be calculated, transient inactivation as an enzyme reactivation reaction for all these enzymes was observed. These findings suggest the potential of cephem compounds as inhibitors of class C beta-lactamases.

Detection of plasmid-mediated AmpC beta-lactamase genes in clinical isolates by using multiplex PCR

Therapeutic options for infections caused by gram-negative organisms expressing plasmid-mediated AmpC beta-lactamases are limited because these organisms are usually resistant to all the beta-lactam antibiotics, except for cefepime, cefpirome, and the carbapenems. These organisms are a major concern in nosocomial infections and should therefore be monitored in surveillance studies. Six families of plasmid-mediated AmpC beta-lactamases have been identified, but no phenotypic test can differentiate among them, a fact which creates problems for surveillance and epidemiology studies. This report describes the development of a multiplex PCR for the purpose of identifying family-specific AmpC beta-lactamase genes within gram-negative pathogens. The PCR uses six sets of ampC-specific primers resulting in amplicons that range from 190 bp to 520 bp and that are easily distinguished by gel electrophoresis. ampC multiplex PCR differentiated the six plasmid-mediated ampC-specific families in organisms such as Klebsiella pneumoniae, Escherichia coli, Proteus mirabilis, and Salmonella enterica serovar Typhimurium. Family-specific primers did not amplify genes from the other families of ampC genes. Furthermore, this PCR-based assay differentiated multiple genes within one reaction. In addition, WAVE technology, a high-pressure liquid chromatography-based separation system, was used as a way of decreasing analysis time and increasing the sensitivity of multiple-gene assays. In conclusion, a multiplex PCR technique was developed for identifying family-specific ampC genes responsible for AmpC beta-lactamase expression in organisms with or without a chromosomal AmpC beta-lactamase gene.

Plasmid-borne AmpC beta-lactamases

Historically, it was thought that ampC genes encoding class C beta-lactamases were located solely on the chromosome but, within the last 12 years, an increasing number of ampC genes have been found on plasmids. These have mostly been acquired by ampC-deficient pathogenic bacteria, which consequently are supplied with new and additional resistance phenotypes. This review discusses the phylogenetic origin of the plasmid-encoded AmpC beta-lactamases, their occurrence, and mode of spread, as well as their hydrolytic properties.

Amino acid sequence determinants of extended spectrum cephalosporin hydrolysis by the class C P99 beta-lactamase

Class C beta-lactamases are commonly encoded on the chromosome of Gram-negative bacterial species. Mutations leading to increased expression of these enzymes are a common cause of resistance to many cephalosporins including extended spectrum cephalosporins. Recent reports of plasmid- and integrin-encoded class C beta-lactamases are a cause for concern because these enzymes are likely to spread horizontally to susceptible strains. Because of their increasing clinical significance, it is critical to identify the determinants of catalysis and substrate specificity of these enzymes. For this purpose, the codons of a set of 21 amino acid residues that encompass the active site region of the P99 beta-lactamase were individually randomized to create libraries containing all possible amino acid substitutions. The amino acid sequence requirements for the hydrolysis of ceftazidime, an extended spectrum cephalosporin commonly used to treat serious infections, were determined by selecting resistant mutants from each of the 21 libraries. DNA sequencing identified the residue positions that are critical for ceftazidime hydrolysis. In addition, it was found that certain amino acid substitutions in the omega-loop region of the P99 enzyme result in increased ceftazidime hydrolysis suggesting the loop is an important determinant of substrate specificity.

Detection of amp C in Enterobacter cloacae in China

PCR amplification of 55 strains of Enterobacter cloacae indicated 51 of them had amp C structural gene verified by DNA sequence and Southern blotting. All PCR products were cleaved into 666- and 328-bp fragments by Kpn1 restriction enzyme. Imipenem was the most potent inducer for mRNA expression of amp C gene and beta-lactamase activity. The beta-Lactamase inhibitor R0481220 strongly inhibited Amp C beta-lactamases; 96.4% (53/55) of Enterobacter cloacae producing Amp C enzyme were susceptible to cefepime.

Dissemination of CTX-M-3 and CMY-2 beta-lactamases among clinical isolates of Escherichia coli in southern Taiwan

A total of 1,210 clinical isolates of Escherichia coli collected from a university hospital in southern Taiwan were screened for production of extended-spectrum beta-lactamases (ESBLs). Expression of classical ESBLs (resistant to extended-spectrum beta-lactam agents and susceptible to beta-lactam inhibitors) was inferred in 18 isolates by the phenotypic confirmatory test. These included 10 isolates producing CTX-M-3, 2 strains carrying SHV-12, 1 strain harboring SHV-5, 1 strain expressing TEM-10, and 4 strains producing unidentifiable ESBLs with a pI of 8.05, 8.0, or 7.4. Eighteen isolates that showed decreased susceptibilities to ceftazidime and/or cefotaxime, negative results for the confirmatory test, and high-level resistance to cefoxitin (MICs of >/=128 microg/ml) were also investigated. Five isolates were found to produce CMY-2 AmpC enzymes, one isolate carried both CTX-M-3 and CMY-2, and the remaining three and nine isolates expressed putative AmpC beta-lactamases with pIs of >9.0 and 8.9, respectively. Thus, together with the isolate producing CTX-M-3 and CMY-2, 19 (1.6%) isolates produced classical ESBLs. Pulsed-field gel electrophoresis revealed that all isolates carrying CTX-M-3 and/or CMY-2 were genetically unrelated, indicating that dissemination of resistance plasmids was responsible for the spread of these two enzymes among E. coli in this area. Among the 16 isolates expressing CTX-M-3 and/or CMY-2, 5 might have colonized outside the hospital environment. Our data indicate that CTX-M-3 and CMY-2, two beta-lactamases initially identified in Europe, have been disseminated to and are prevalent in Taiwan.

Prevalence of SHV-12 among clinical isolates of Klebsiella pneumoniae producing extended-spectrum beta-lactamases and identification of a novel AmpC enzyme (CMY-8) in Southern Taiwan

Twenty (8.5%) of 234 nonrepetitive clinical isolates of Klebsiella pneumoniae from southern Taiwan were found to produce extended-spectrum beta-lactamases (ESBLs): 10 strains produced SHV-12, 4 produced SHV-5, 2 produced a non-TEM non-SHV ESBL with a pI of 8.3, 3 produced a novel AmpC beta-lactamase designated CMY-8 with a pI of 8.25, and 1 produced SHV-12 and an unidentified AmpC enzyme with a pI of 8.2. The CMY-8 enzyme confers a resistance phenotype similar to CMY-1 and MOX-1, and sequence comparisons showed high homologies (>95%) of nucleotide and amino acid sequences among these three enzymes. Plasmid and pulse-field gel electrophoresis analyses revealed that all isolates harboring an SHV-derived ESBL were genetically unrelated, indicating that dissemination of resistance plasmids is responsible for the spread of SHV ESBLs among K. pneumoniae in this area. All three isolates carrying CMY-8 had identical genotypic patterns, suggesting the presence of an epidemic strain.

Outbreak of Klebsiella pneumoniae producing transferable AmpC-type beta-lactamase (ACC-1) originating from Hafnia alvei

Fifty-two strains of Klebsiella pneumoniae producing an AmpC-type plasmid-mediated beta-lactamase were isolated from 13 patients in the same intensive care unit between March 1998 and February 1999. These strains were resistant to ceftazidime, cefotaxime and ceftriaxone, but susceptible to cefoxitin, cefepime and aztreonam. Plasmid content and genomic DNA restriction pattern analysis suggested dissemination of a single clone. Two beta-lactamases were identified, TEM-1 and ACC-1. We used internal bla(ACC-1) primers, to sequence PCR products obtained from two unrelated strains of Hafnia alvei. Our results show that the ACC-1 beta-lactamase was derived from the chromosome-encoded AmpC-type enzyme of H. alvei.

Prevalent mechanisms of resistance among common enterobacterial isolates in Greek hospitals

The recent data concerning antibiotic resistance of the enterobacteria isolated in Greek hospitals are reviewed. A variety of mechanisms of resistance, clustered in most of the cases, was observed. Epidemics of plasmids were responsible for dissemination of third-generation cephalosporins, aminoglycosides, and trimethoprim resistance among Klebsiella pneumoniae and, to a lesser extent, Escherichia coli isolates. Stable depression of the expression of chromosomal cephalosporinase is the main cause of resistance to third-generation cephalosporins observed at high frequencies in Enterobacter spp. strains.

Carbapenem resistance in Escherichia coli associated with plasmid-determined CMY-4 beta-lactamase production and loss of an outer membrane protein

Three cefoxitin-resistant Escherichia coli isolates from stool specimens of a patient with leukemia were either resistant, intermediate, or sensitive to imipenem. Conjugation experiments showed that cefoxitin resistance, but not imipenem resistance, was transferable. All isolates were shown by isoelectric focusing to produce two beta-lactamases with isoelectric points of 5.4 (TEM-1, confirmed by sequencing of a PCR product) and >8.5 (consistent with a class C beta-lactamase). The gene coding for the unknown beta-lactamase was cloned and sequenced and revealed an enzyme which had 99.9% sequence identity with the plasmid-determined class C beta-lactamase CMY-2. The cloned beta-lactamase gene differed from blaCMY-2 at one nucleotide position that resulted in an amino acid change, tryptophan to arginine at position 221. We propose that this enzyme be designated CMY-4. Both the imipenem-resistant and -intermediate isolates lacked a 38-kDa outer membrane protein (OMP) that was present in the imipenem-sensitive isolate. The lack of an OMP alone did not explain the difference in carbapenem susceptibilities observed. However, measurement of beta-lactamase activities (including measurements under conditions where TEM-1 beta-lactamase was inhibited) indicated that the imipenem-intermediate isolate expressed six- to eightfold less beta-lactamase than did the other isolates. This study illustrates that carbapenem resistance in E. coli can arise from high-level expression of plasmid-mediated class C beta-lactamase combined with an OMP deficiency. Furthermore, in the presence of an OMP deficiency, the level of expression of a plasmid-mediated class C beta-lactamase is an important factor in determining whether E. coli isolates are fully resistant to carbapenems.

Use of an isogenic Escherichia coli panel to design tests for discrimination of beta-lactamase functional groups of Enterobacteriaceae

A study was designed to determine if an isogenic panel of Escherichia coli strains containing many different beta-lactamases could be used for the preliminary screening of a large number of beta-lactam agents to identify which might be most useful in the development of a definitive test for specific beta-lactamases found among the members of family Enterobacteriaceae. The susceptibilities of 46 strains, comprising the isogenic panel, to expanded-spectrum cephalosporins, cephamycins, and aztreonam were determined in the presence and absence of beta-lactamase inhibitors in broth microdilution tests. The results indicated that strains producing extended-spectrum beta-lactamases (ESBLs) could be distinguished from strains producing other Bush-Jacoby-Medeiros functional group 2 or group 1 beta-lactamases. For strains producing group 1 beta-lactamases, cefpodoxime and ceftazidime MICs were > or = 4 micrograms/ml and addition of clavulanate did not reduce the MICs more than fourfold. For strains producing group 2 enzymes other than ESBLs, cefpodoxime and ceftazidime MICs were < or = 2 micrograms/ml. With a single exception (ceftazidime for the strain producing SHV-3), among strains producing ESBLs, cefpodoxime and ceftazidime MICs were > or = 4 micrograms/ml and addition of clavulanate reduced the MICs by more than eightfold. Cephamycins could also be used to discriminate between strains producing group 1 beta-lactamases and ESBLs, since only the former required cefotetan concentrations as high as 8 micrograms/ml or cefoxitin concentrations of > 16 micrograms/ml for inhibition. Other cephalosporins provided some discrimination between the various beta-lactamase producers, although they were not as reliable as either cefpodoxime or ceftazidime. These results indicate the utility of an isogenic panel for identification of candidate drugs among many for further testing with clinical isolates of the family Enterobacteriaceae to determine the best agents for detection of specific beta-lactamases in this family.

Characterisation of CMY-4, an AmpC-type plasmid-mediated beta-lactamase in a Tunisian clinical isolate of Proteus mirabilis

A strain of Proteus mirabilis resistant to beta-lactams, including cefoxitin, was isolated from the urine of a woman from Tunisia. Its antibiotic susceptibility pattern and that of the Escherichia coli transconjugant suggested the presence of an AmpC-type beta-lactamase. Two bands of beta-lactamase activity (pI 5.4 and 9.2) were detected by isoelectric focusing. The nucleotide sequence of the gene encoding the AmpC-type enzyme was determined. The deduced amino acid sequence was 98-99% identical to CMY-3 and to those of the plasmid-mediated AmpC-type beta-lactamases originated from Citrobacter freundii and 97% identical to the chromosome-encoded beta-lactamase of a Tunisian clinical isolate of C. freundii. This enzyme differs from CMY-2 by one substitution (Arg for Trp at position 221) and from CMY-3 by two substitutions (Glu for Gly at position 42 and Ser for Asn at position 363) and we propose the denomination CMY-4.

Salmonella enteritidis: AmpC plasmid-mediated inducible beta-lactamase (DHA-1) with an ampR gene from Morganella morganii

DHA-1, a plasmid-mediated cephalosporinase from a single clinical Salmonella enteritidis isolate, conferred resistance to oxyimino-cephalosporins (cefotaxime and ceftazidime) and cephamycins (cefoxitin and moxalactam), and this resistance was transferable to Escherichia coli HB101. An antagonism was observed between cefoxitin and aztreonam by the diffusion method. Transformation of the transconjugant E. coli strain with plasmid pNH5 carrying the ampD gene (whose product decreases the level of expression of ampC) resulted in an eightfold decrease in the MIC of cefoxitin. A clone with the same AmpC susceptibility pattern with antagonism was obtained, clone E. coli JM101(pSAL2-ind), and its nucleotide sequence was determined. It contained an open reading frame with 98. 7% DNA sequence identity with the ampC gene of Morganella morganii. DNA sequence analysis also identified a gene upstream of ampC whose sequence was 97% identical to the partial sequence of the ampR gene (435 bp) from M. morganii. The gene encoded a protein with an amino-terminal DNA-binding domain typical of transcriptional activators of the LysR family. Moreover, the intercistronic region between the ampC and ampR genes was 98% identical to the corresponding region from M. morganii DNA. AmpR was shown to be functional by enzyme induction and a gel mobility-shift assay. An ampG gene was also detected in a Southern blot of DNA from the S. enteritidis isolate. These findings suggest that this inducible plasmid-mediated AmpC type beta-lactamase, DHA-1, probably originated from M. morganii.

A plasmid-mediated CMY-2 beta-lactamase from an Algerian clinical isolate of Salmonella senftenberg

Multiresistance to antibiotics including beta-lactams, e.g. cefoxitin, was transferred by conjugation to Escherichia coli strain C1a from a clinical isolate of Salmonella senftenberg recovered from stools of an Algerian child. The susceptibility pattern to beta-lactams was similar to the profile mediated by an AmpC-type beta-lactamase. By biochemical analysis, typical AmpC-type enzyme substrate and inhibition profiles were obtained. Finally, an ampC plasmid-encoded beta-lactamase gene was cloned and sequenced. Its deduced amino acid sequence confirmed its identity as a class C beta-lactamase. It showed 99.5% sequence identity with the plasmid-mediated beta-lactamase CMY-2. The differences in the amino acid sequences of the two enzymes were located in the signal peptide.

Imipenem resistance in Klebsiella pneumoniae is associated with the combination of ACT-1, a plasmid-mediated AmpC beta-lactamase, and the foss of an outer membrane protein

Six Escherichia coli and 12 Klebsiella pneumoniae isolates from a single hospital expressed a common beta-lactamase with a pI of approximately 9.0 and were resistant to cefoxitin and cefotetan (MIC ranges, 64 to > 128 and 16 to > 128 micrograms/ml, respectively). Seventeen of the 18 strains produced multiple beta-lactamases. Most significantly, three K. pneumoniae strains were also resistant to imipenem (MICs, 8 to 32 micrograms/ml). Spectrophotometric beta-lactamase assays with purified enzyme indicated hydrolysis of cephamycins, in addition to cephaloridine and benzylpenicillin. The 4ene encoding the pI 9.0 beta-lactamase (designated ACT-1 for AmpC type) was cloned and sequenced, which revealed an ampC-type beta-lactamase gene that originated from Enterobacter cloacae and that had 86% sequence homology to the P99 beta-lactamase and 94% homology to the partial sequence of MIR-1. Southern blotting revealed that the gene encoding ACT-1 was on a large plasmid in some of the K. pneumoniae strains as well as on the chromosomes of all of the strains, suggesting that the gene is located on an easily mobilized element. Outer membrane protein profiles of the K. pneumoniae strains revealed that the three imipenem-resistant strains were lacking a major outer membrane protein of approximately 42 kDa which was present in the imipenem-susceptible strains. ACT-1 is the first plasmid-mediated AmpC-type beta-lactamase derived from Enterobacter which has been completely sequenced. This work demonstrates that in addition to resistance to cephamycins, imipenem resistance can occur in K. pneumoniae when a high level of the ACT-1 beta-lactamase is produced in combination with the loss of a major outer membrane protein.

Comparative evaluation of the inhibitory activities of the novel penicillanic acid sulfone Ro 48-1220 against beta-lactamases that belong to groups 1, 2b, and 2be

The inhibitory activity of the penicillanic acid sulfone Ro 48-1220 against group 1, 2b, and 2be beta-lactamases was evaluated. Ro 48-1220 inhibited TEM and SHV as effectively as clavulanate and tazobactam. It also inhibited group 1 beta-lactamases at lower concentrations than tazobactam. Ro 48-1220, at a concentration of 4 micrograms/ml, protected ceftriaxone and ceftazidime against strains producing group 1 and 2be beta-lactamases.

Study of an outbreak of cefoxitin-resistant Klebsiella pneumoniae in a general hospital

During a 3-month period, six Klebsiella pneumoniae isolates resistant to cefoxitin and penicillin-inhibitor combinations were derived from patients in the intensive care unit of a hospital in Athens, Greece. Enterobacterial repetitive intergenic consensus PCR and pulsed-field gel electrophoresis provided evidence of the clonal origin of the isolates. Conventional techniques and ribotyping were inadequate in proving that the isolates were related. Resistance was due to a plasmidic class C beta-lactamase.

Transferable cefoxitin resistance in enterobacteria from Greek hospitals and characterization of a plasmid-mediated group 1 beta-lactamase (LAT-2)

Cefoxitin resistance in Klebsiella pneumoniae from Escherichia coli strains isolated in Greek hospitals was found to be due to the acquisition of similar plasmids coding for group 1 beta-lactamases. The plasmids were not self-transferable but were mobilized by conjugative plasmids. These elements have also been spread to Enterobacter aerogenes. The most common enzyme was a Citrobacter freundii-derived cephalosporinase (LAT-2) which differed from LAT-1 by three amino acids.

In vitro activity of cefpirome against selected clinical enterobacterial isolates with beta-lactamase-mediated resistance

Previous studies have shown that there is a high incidence of resistance to cephalosporins among enterobacteria isolated in Greek hospitals. This resistance is mainly due to either the derepression of chromosomal cephalosporinases or the acquisition of plasmids coding for SHV-5 type beta-lactamase. In the present study the activity of cefpirome against a number of enterobacteria (Escherichia coli, Klebsiella pneumoniae, Enterobacter cloacae, Enterobacter aerogenes and Serratia marcescens) possessing the mechanisms mentioned above was examined. Cefpirome was found active against all the strains characterized by stable derepression of chromosomal class-C enzymes. The antibiotic was less potent against strains expressing SHV-5 type beta-lactamase due to its hydrolysis by the enzyme. Also cefpirome exhibited good activity against E. aerogenes strains with reduced susceptibility to imipenem. These in vitro data suggest that cefpirome might be useful in treating infections caused by these resistant microorganisms that are frequently encountered in Greek hospitals.