Modeling and experiment yields the structure of acireductone dioxygenase from Klebsiella pneumoniae

Here we report the structure of acireductone dioxygenase (ARD), the first determined for a new family of metalloenzymes. ARD represents a branch point in the methionine salvage pathway leading from methylthioadenosine to methionine and has been shown to catalyze different reactions depending on the type of metal ion bound in the active site. The solution structure of nickel-containing ARD (Ni-ARD) was determined using NMR methods. X-ray absorption spectroscopy, assignment of hyperfine shifted NMR resonances and conserved domain homology were used to model the metal-binding site because of the paramagnetism of the bound Ni2+. Although there is no structure in the Protein Data Bank within 3 A r.m.s deviation of that of Ni-ARD, the enzyme active site is located in a conserved double-stranded b-helix domain. Furthermore, the proposed Ni-ARD active site shows significant post-facto structural homology to the active sites of several metalloenzymes in the cupin superfamily.

Extended-spectrum beta-lactamase-producing Escherichia coli and Klebsiella pneumoniae bloodstream infection: risk factors and clinical outcome

OBJECTIVES

To study the risk factor for nosocomial bacteremia caused by Escherichia coli or Klebsiella pneumoniae producing extended-spectrum beta-lactamase (ESBL) and the influence on patient outcome.

DESIGN

Retrospective, single-center study of consecutive bacteremic patients.

SETTINGS

A university-affiliated teaching hospital.

PATIENTS

A total of 85 patients with nosocomial bacteremia due to E. coli or K. pneumoniae were enrolled.

INTERVENTION

None.

MEASUREMENTS AND MAIN RESULTS

The demographic characteristics and clinical information including treatment were recorded upon review of patients' records. The primary end point was hospital mortality. Twenty-seven percent of isolates produced ESBLs. Previous treatment with 3rd-generation cephalosporins was the only independent risk factor for bacteremia due to ESBL-producing pathogens [odds ratio (OR) 4.146, P=0.008]. Antibiotic treatment was considered appropriate in 71 cases (83%), and failed in 23 patients (27%). Twenty-one patients (25%) died in the hospital. Antibiotic treatment failure was the only independent risk factor for hospital mortality (OR 15.376, P=0.001). Inappropriate antibiotic treatment might lead to significantly higher mortality rate (7/14 vs 14/71, P=0.016). Patients treated with imipenem were more likely to survive while those receiving cephalosporin treatment tended to have a poorer outcome (1/19 vs 14/40, P=0.023).

CONCLUSIONS

More judicious use of cephalosporins, especially 3rd-generation cephalosporins, may decrease ESBL-producing E. coli or K. pneumoniae bacteremia, and also improve patient outcome.

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

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

Molecular epidemiology of extended-spectrum beta-lactamase-producing, fluoroquinolone-resistant isolates of Klebsiella pneumoniae in Taiwan

Strains of extended-spectrum beta-lactamase-producing Klebsiella pneumoniae (ESBL-KP) have emerged worldwide. Concomitant ciprofloxacin resistance with ESBL production in K. pneumoniae isolates would severely restrict treatment options. Among 39 (18.5%) of 211 ESBL-KP isolates resistant to ciprofloxacin (MIC, >/=4 micro g/ml), 37 (95%) were high level resistant (MIC, >/=16 micro g/ml). These isolates were also cross resistant to the newer fluoroquinolones, including levofloxacin, gatifloxacin, gemifloxacin, and garenoxacin (BMS 284756). Sitafloxacin was most active against these ciprofloxacin-resistant ESBL-KP isolates with MICs for 67% of the isolates being </=2 micro g/ml. The molecular epidemiology of these multiresistant isolates was investigated by automated ribotyping and pulsed-field gel electrophoresis (PFGE). Ribotyping identified 18 different strains among the 39 ciprofloxacin-resistant ESBL-KP isolates. The majority (67%) of these isolates were contained in six ribogroups which were further confirmed by PFGE. The distribution of the six major strains of ciprofloxacin-resistant ESBL-KP within Taiwan included one (ribogroup 255.3-PFGE type E) with a nationwide distribution and several institution-specific strains. Interhospital cooperation appears necessary, with strict infection control practices coupled with restriction of fluoroquinolone and extended-spectrum beta-lactam use to control both the major epidemic strain and the more diverse strains observed within individual institutions.

Energy-dependent accumulation of norfloxacin and porin expression in clinical isolates of Klebsiella pneumoniae and relationship to extended-spectrum beta-lactamase production

The relationships between porin deficiency, active efflux of fluoroquinolones, and extended-spectrum beta-lactamase (ESBL) production were determined for 53 clinical isolates of Klebsiella pneumoniae. Thirty-two ESBL-positive strains (including 22 strains expressing porins and 10 strains lacking porins) and 21 ESBL-negative strains were evaluated. Active efflux of norfloxacin was defined as a >/=50% increase in the accumulation of norfloxacin in the presence of carbonyl cyanide m-chlorophenylhydrazone (CCCP) in comparison with the corresponding basal value in the absence of CCCP. The quinolone resistance-determining regions of both gyrA and parC from 13 strains, representing all isolates with different porin profiles and with or without active efflux, were determined. Porin loss was significantly more common among ESBL-positive strains (10 of 32 [31.2%]) than among ESBL-negative strains (0 of 2 [0%]) (P < 0.01). Active efflux was observed in 7 of 10 (70%) strains lacking porins and in 4 of 43 (9.3%) strains producing porins (P < 0.001). The 11 strains showing active efflux corresponded to 3 of 21 (14.3%) ESBL-negative strains and 8 of 32 (25.5%) ESBL-positive strains (P > 0.05). Basal values of norfloxacin accumulation were higher in strains lacking active efflux than in those that had this mechanism (P < 0.05). In the absence of topoisomerase changes, the contribution of either porin loss or active efflux to fluoroquinolone resistance in K. pneumoniae was negligible. It is concluded that among K. pneumoniae strains of clinical origin, porin loss was observed only in those producing ESBL, and that a significant number of porin-deficient strains also expressed active efflux of norfloxacin. In terms of fluoroquinolone resistance, both mechanisms are significant only in the presence of topoisomerase modifications.

[Extended-spectrum beta-lactamase in Klebsiella pneumoniae and Escherichia coli isolates]

OBJECTIVE

To investigate the prevalence, drug resistance, gene typing, and epidemicity of extended-spectrum beta-lactamases (ESBL) Klebsiella pneumoniae and Escherichia coli isolates.

METHODS

559 strains of K. pneumoniae and 427 strains of E.coli were isolated form Huanshan Hospital from 1 January to 31 December 1999. The ESBL-producing strains were detected by double disc test and confirmed by minimal inhibitory concentration (MIC). The MIC of ESBL-producing strains was detected by agar dilution test. The beta-lactamase genes were detected by PCR. DNA fingerprinting was made by pulsed-field gel electrophoresis (PFGE).

RESULTS

The incidence of ESBL-producing strains was 51% among the isolated K. pneumoniae (285/559) and 23.6% among the isolated E. coli (101/427), most of which were collected from the patients in the intensive care unit and neurosurgical ward. 63.5% of the ESBL-producing K. pneumoniae strains were collected from sputum specimens, and 64.3% of the ESBL-producing E. coli strains were collected from the urine specimens. Most ESBL-producing strains were resistant to most beta-lactam antibiotics, including the third-generation cephalosporins, and non- beta-lactam antimicrobial drugs, such as fluoroquinolones, aminoglycosides, tetracycline, and chloramphenicol. Most of the ESBL-producing strains were susceptible to imipenam, cefmetazole, and beta-lactam antibiotic/clavulanic acid. TEM type beta-lactamase was the main type among those EBSL-producing strains, followed by SHV type and CTX-M type. Some ESBL-producing E. coli and most ESBL-producing K. pneumoniae produced more than one type of beta-lactamase.

CONCLUSION

ESBL-producing strains are common among hospital strains of E. coli and K. pneumoniae. Most of them are multidrug resistant. Prevalence and transmission of these strains exist in hospital.

Multiple inequivalent metal-nucleotide coordination environments in the presence of the VO2+-inhibited nitrogenase iron protein: pH-dependent structural rearrangements at the nucleotide binding site

Nitrogenase naturally requires adenosine nucleoside triphosphates and divalent metal cations for catalytic activity. Their energy of hydrolysis controls several mechanistic functions, most probably via separate structural conformers of the nitrogenase Fe protein. To characterize the ligand environment of the divalent metal in the ternary complex, with ADP or ATP and the Fe protein from Klebsiella pneumoniae, the hyperfine structures have been investigated by electron paramagnetic resonance (EPR) spectroscopy by substituting naturally occurring diamagnetic Mg(2+) by paramagnetic oxovanadium. This metal replacement leads to inhibition of nitrogenase activity. Moreover, depending on pH, two distinctly different VO(2+) EPR spectra are detected. At pH 7.4 each of the vanadyl EPR hyperfine lines is further split into two. This indicates that several spectroscopically distinguishable metal coordination environments coexist for VO(2+)-nucleotide chelate complexes in the presence of the reduced Fe protein. Overall, a total of at least three distinct local metal coordination environments have been identified. We report the EPR parameters for each of the disparate metal coordinations measured at different pH values with ADP and ATP bound. EPR spectra have also been recorded for the oxidized Fe protein showing essentially similar spectra to that of the reduced protein. The EPR parameters of VO-nucleotides in the presence of the Fe protein are consistent, for all metal coordination environments, with direct metal ligation by nucleotide phosphate groups and the formation of mononucleotide complexes. The nucleotide binding environment with the highest ligand field strength is compatible with a metal coordination structure that is also found in various G-proteins with GTP bound. No significant EPR line width change is detected after exchange into D(2)O buffer solution for any of the pH forms although differences exist between the pH forms. The missing difference between the EPR parameters in the presence of ADP or ATP suggests that there is little or no conformational rearrangement between these two forms; this contrasts with behavior of G-proteins that undergo substantial conformational changes upon hydrolysis. This could be related to the inhibition of nitrogenase by VO(2+).

Further modification of the Hodge test to screen AmpC beta-lactamase (CMY-1)-producing strains of Escherichia coli and Klebsiella pneumoniae

Cefoxitin-resistant Escherichia coli and Klebsiella pneumoniae are widespread in Korea. Significant proportions of them are considered to be CMY-1 producers. For effective screening of CMY-1 producers, the Hodge test was modified by using a cefoxitin disk and the performance was evaluated. The sensitivity and specifity of the test were 100% and 94.9%, respectively. The test was easier to perform than the three-dimensional extract test. This modified test should be suitable for screening CMY-1-producing strains of E. coli and K. pneumoniae.

Comparison of screening methods for TEM- and SHV-derived extended-spectrum beta-lactamase detection

OBJECTIVE

To compare common extended-spectrum beta-lactamase (ESBL) screening methods and beta-lactams for their ability to detect TEM- and SHV-related ESBL enzymes.

METHODS

This study compared disk diffusion testing by NCCLS methodology, the Jarlier double disk test, a disk-on-disk test, a modified three-dimensional test and the E test method for their sensitivity and specificity in detecting TEM- and SHV-related ESBL producers. Three negative and 22 positive controls were studied. These were two Klebsiella pneumoniae and 23 Escherichia coli transconjugants. Seventeen beta-lactam antibiotics were tested: cefamandole, cefotetan, cefoxitin, cefuroxime, cefixime, cefoperazone, cefotaxime, cefpodoxime, cefsulodin, ceftazidime, ceftibuten, ceftizoxime, ceftriaxone, moxalactam, cefepime, cefpirome and aztreonam.

RESULTS

NCCLS disk diffusion was 14% sensitive with ceftriaxone, 36% with cefotaxime, 64% with aztreonam, 68% with cefpodoxime, and 73% with ceftazidime. Cefoperazone, cefamandole, cefpodoxime and cefpirome showed 91% sensitivity using the Jarlier test. Using the disk-on-disk test, cefsulodin showed 95% sensitivity, and cefoperazone, cefepime and cefamandole showed 91% sensitivity. With the modified three-dimensional test, cefoperazone, cefpodoxime and cefpirome showed 91% sensitivity.

CONCLUSIONS

For practical reasons, we would recommend use of either the Jarlier test or the commercial cephalosporin disks containing clavulanic acid to screen for ESBL producers. Cefoperazone, cefamandole, cefpodoxime and cefpirome showed good sensitivity across the methods tested.

Expression of SHV-2 beta-lactamase and of reduced amounts of OmpK36 porin in Klebsiella pneumoniae results in increased resistance to cephalosporins and carbapenems

A Klebsiella pneumoniae clinical isolate was resistant to cefoxitin, cefotaxime, ceftazidime, ceftazidime-clavulanate, piperacillin-tazobactam (MICs, >256 micro g/ml in all cases), and meropenem (MIC, 16 micro g/ml) and was intermediate to imipenem (MIC, 8 micro g/ml). Decreased expression of the OmpK36 porin and expression of an SHV-2 beta-lactamase contributed to the observed resistance to these beta-lactam-containing agents.

Characterization of CMY-type beta-lactamases in clinical strains of Proteus mirabilis and Klebsiella pneumoniae isolated in four hospitals in the Paris area

We isolated five clinical strains (three Proteus mirabilis and two Klebsiella pneumoniae) with beta-lactam resistance phenotypes consistent with production of an AmpC-type beta-lactamase. The predicted amino acid sequences of the enzymes were typical of class C beta-lactamases. The enzymes were identified as CMY-2, CMY-4 and a new CMY-variant beta-lactamase, CMY-12. The AmpC beta-lactamases from the two K. pneumoniae isolates were found to be encoded on self-transferable plasmids. The genes encoding the AmpC-type beta-lactamase produced by the three P. mirabilis isolates were chromosomal. Four of the five clinical isolates were from patients transferred from Greece, Algeria and Egypt; one of the K. pneumoniae strains was recovered from a French patient. PFGE analysis and rep-PCR fingerprinting showed that the two P. mirabilis isolates from Greek patients were closely related.

How the mutation glycine96 to alanine confers glyphosate insensitivity to 5-enolpyruvyl shikimate-3-phosphate synthase from Escherichia coli

The enzyme 5-enolpyruvyl shikimate-3-phosphate (EPSP) synthase (EC 2.5.1.19) is essential for the biosynthesis of aromatic compounds in plants and microbes and is the unique target of the herbicide glyphosate. One of the first glyphosate-insensitive enzymes reported was a Gly96Ala mutant of EPSP synthase from Klebsiella pneumoniae. We have introduced this single-site mutation into the highly homologous EPSP synthase from Escherichia coli. The mutant enzyme is insensitive to glyphosate with unaltered affinity for its first substrate, shikimate-3-phosphate (S3P), but displays a 30-fold lower affinity for its second substrate, phosphoenolpyruvate (PEP). Using X-ray crystallography, we solved the structure of Gly96Ala-EPSP synthase liganded with S3P to 0.17 nm resolution. The crystal structure shows that the additional methyl group from Ala96 protrudes into the active site of the enzyme. While the interactions between enzyme and S3P remain unaffected, the accessible volume for glyphosate binding is substantially reduced. Exploiting the crystallographic results for molecular modeling, we demonstrate that PEP but not glyphosate can be docked in the Gly96Ala-modified binding site. The predicted PEP binding site satisfies the earlier proposed interaction pattern for PEP with EPSP synthase and corroborates the assumption that glyphosate and PEP target the same binding site.

Epidemiological and antibiotic resistant study on extended-spectrum beta-lactamase-producing Escherichia coli and Klebsiella pneumoniae in Zhejiang Province

OBJECTIVE

To investigate the epidemiological status of extended-spectrum beta-lactamase (ESBL) producing Escherichia coli (E. coli) and Klebsiella pneumoniae (K. pneumoniae) and the drug resistance profiles of such organisms.

METHODS

A total of 282 clinical isolates of E. coli and 180 of K. pneumoniae were collected from different districts of Zhejiang Province. Inhibitor potentiated broth dilution tests were performed for detecting extended-spectrum beta-lactamases. Etests were performed to detect the drug resistance of these strains against nine commonly used antibiotics.

RESULTS

The prevalence of extended-spectrum beta-lactamases in E. coli and K. pneumoniae was 34.0% and 38.3%, respectively. The average prevalence of extended-spectrum beta-lactamases in E. coli and K. pneumoniae was 35.7%. The resistance prevalence of extended spectrum beta-lactamase producing strains to ceftazidime and cefotaxime was 40% and 26% respectively, so were those to cefepime, cefoxitin, piperacillin-tazobactam, cefoperazone-sulbactam, amikacin and ciprofloxacin. All these strains were sensitive to imipenem.

CONCLUSION

The results in this study showed that the prevalence of extended-spectrum beta-lactamases was high, while extended-spectrum beta-lactamase producing strains were resistant to most antimicrobial agents except imipenem.

Molecular epidemiology of a citywide outbreak of extended-spectrum beta-lactamase-producing Klebsiella pneumoniae infection

Multidrug-resistant strains of Klebsiella pneumoniae are a problem in many hospitals. In 1999, the molecular epidemiology of K. pneumoniae with extended-spectrum beta-lactamases (ESBLs) was studied at 15 hospitals in Brooklyn. Of 824 unique patient isolates, 34% were presumptive ESBL producers. Of this subset, 34% were susceptible to cefoxitin, 42% to ciprofloxacin, 48% to ceftriaxone, 55% to piperacillin-tazobactam, 57% to amikacin, and 86% to cefepime. Ribotype analysis revealed 87 unique types. However, 2 clusters accounted for 35% of isolates and were present in most of the hospitals. One cluster was significantly more resistant to most antibiotics. Although there was a predominance of SHV-5, considerable heterogeneity of beta-lactamases was evident, even among isolates of the same cluster. A correlation was found between the use of cephalosporins and the prevalence of ESBL-producing strains of K. pneumoniae at each hospital. Our data suggest that there is an advanced outbreak of multidrug-resistant K. pneumonia infection that is affecting all Brooklyn hospitals.

Investigation of extended-spectrum beta-lactamase in Klebsiellae pneumoniae and Escherichia coli from China

Extended-spectrum beta-lactamases (ESBLs) are an increasing cause of resistance to third-generation cephalosporins in Enterobacteriaceae. However, they have not been well studied in China. We investigated the prevalence, resistance, and probable gene type of ESBLs using MICs testing and polymerase chain reaction in 559 Klebsiellae pneumoniae and 427 Escherichia coli isolates collected from patients in Huashan Hospital from 1 January to 31 December 1999. The incidence of ESBL-producing strains was 51% among Klebsiellae pneumoniae (285/559) and 23.6% among Escherichia coli (101/427), most of which were collected from patients in intensive care unit and neurosurgical ward. PFGE showed that some epidemic ESBL-producing strains were present in the ICU, especially among ESBL-producing Klebsiellae pneumoniae. The major source of ESBL-producing Klebsiellae pneumoniae and Escherichia coli was sputum specimen (63.5%) and urine (64.3%), respectively. These strains were resistant to most beta-lactams (including the third-generation cephalosporins and monobactams) and non-beta-lactams (such as fluoroquinolones, aminoglycosides, tetracycline, and chloramphenicol), all or most ESBL producers were susceptible to imipenem, cefmetazole and beta-lactam/clavulanic acid. TEM was the main type of beta-lactamases and the CTX-M type of ESBLs was common in these isolates. Some ESBL-producing Escherichia coli and most ESBL-producing Klebsiellae pneumoniae produced more than one type of beta-lactamase. These data confirm that ESBL producers are common among hospital strains of Escherichia coli and Klebsiellae pneumoniae in China. It is important to monitor such strains closely and prevent their spread.

Crystallographic analysis of the MoFe protein of nitrogenase from a nifV mutant of Klebsiella pneumoniae identifies citrate as a ligand to the molybdenum of iron molybdenum cofactor (FeMoco)

The x-ray crystal structure of NifV(-) Klebsiella pneumoniae nitrogenase MoFe protein (NifV(-) Kp1) has been determined and refined to a resolution of 1.9 A. This is the first structure for a nitrogenase MoFe protein with an altered cofactor. Moreover, it is the first direct evidence that the organic acid citrate is not just present, but replaces homocitrate as a ligand to the molybdenum atom of the iron molybdenum cofactor (FeMoco). Subsequent refinement of the structure revealed that the citrate was present at reduced occupancy.

Beta-glucoside kinase (BglK) from Klebsiella pneumoniae. Purification, properties, and preparative synthesis of 6-phospho-beta-D-glucosides

ATP-dependent beta-glucoside kinase (BglK) has been purified from cellobiose-grown cells of Klebsiella pneumoniae. In solution, the enzyme (EC ) exists as a homotetramer composed of non-covalently linked subunits of M(r) approximately 33,000. Determination of the first 28 residues from the N terminus of the protein allowed the identification and cloning of bglK from genomic DNA of K. pneumoniae. The open reading frame (ORF) of bglK encodes a 297-residue polypeptide of calculated M(r) 32,697. A motif of 7 amino acids (AFD(7)IG(9)GT) near the N terminus may comprise the ATP-binding site, and residue changes D7G and G9A yielded catalytically inactive proteins. BglK was progressively inactivated (t(12) approximately 19 min) by N-ethylmaleimide, but ATP afforded considerable protection against the inhibitor. By the presence of a centrally located signature sequence, BglK can be assigned to the ROK (Repressor, ORF, Kinase) family of proteins. Preparation of (His6)BglK by nickel-nitrilotriacetic acid-agarose chromatography provided high purity enzyme in quantity sufficient for the preparative synthesis (200-500 mg) of ten 6-phospho-beta-d-glucosides, including cellobiose-6'-P, gentiobiose-6'-P, cellobiitol-6-P, salicin-6-P, and arbutin-6-P. These (and other) derivatives are substrates for phospho-beta-glucosidase(s) belonging to Families 1 and 4 of the glycosylhydrolase superfamily. The structures, physicochemical properties, and phosphorylation site(s) of the 6-phospho-beta-d-glucosides have been determined by fast atom bombardment-negative ion spectrometry, thin-layer chromatography, and (1)H and (13)C NMR spectroscopy. The recently sequenced genomes of two Listeria species, L. monocytogenes EGD-e and L. innocua CLIP 11262, contain homologous genes (lmo2764 and lin2907, respectively) that encode a 294-residue polypeptide (M(r) approximately 32,200) that exhibits approximately 58% amino acid identity with BglK. The protein encoded by the two genes exhibits beta-glucoside kinase activity and cross-reacts with polyclonal antibody to (His6)BglK from K. pneumoniae. The location of lmo2764 and lin2907 within a beta-glucoside (cellobiose):phosphotransferase system operon, may presage both enzymatic (kinase) and regulatory functions for the BglK homolog in Listeria species.

The respiratory complex I (NDH I) from Klebsiella pneumoniae, a sodium pump

The electrogenic NADH:Q oxidoreductase from the enterobacterium Klebsiella pneumoniae transports Na(+) ions. The complex was purified with an increase of the specific Na(+) transport activity from 0.2 micromol min(-1) mg(-1) in native membrane vesicles to 4.7 micromol min(-1) mg(-1) in reconstituted enzyme specimens. The subunit pattern resembled that of complex I from Escherichia coli, and two prominent polypeptides were identified as the NuoF and NuoG subunits of complex I. During purification the typical cofactors of complex I were enriched to yield approximately 17 nmol mg(-1) iron, 24 nmol mg(-1) acid-labile sulfide, and 0.79 nmol mg(-1) FMN in the purified sample. The enzyme contained approximately 1.2 nmol mg(-1) Q6 and 1.5 nmol mg(-1) Q8. The reduction of ubiquinone by NADH was Na(+)-dependent, which indicates coupling of the chemical and the vectorial reaction of the pump. The Na(+) activation profile corresponded to the Hill equation with a Hill coefficient K(H)(Na(+)) = 1.96 and with a half-maximal saturation at 0.33 mm Na(+). The reconstituted complex I from Klebsiella pneumoniae catalyzed deamino-NADH oxidation, Q1 reduction, and Na(+) translocation with specific activities of 2.6 units mg(-1), 2.4 units mg(-1), and 4.7 units mg(-1), respectively, which indicate a Na(+)/electron stoichiometry of one.

[Antimicrobial susceptibility and beta-lactamase types among clinical isolates during January and February 2000 in the Kinki area of Japan]

We studied antimicrobial susceptibility and beta-lactamase types among clinical isolates in the Kinki area of Japan. Eight hundreds isolates of eight organisms were collected by seven medical institutions during January and February 2000. The rates of beta-lactamase producing by using the chromogenic nitrocephin test were 68.0% against Staphylococcus aureus isolates, 6.0% against Haemophilus influenzae isolates, 98.0% against Moraxella catarrhalis isolates. The rate of beta-lactamase negative ampicillin-resistant H. influenzae was 4.0% (4 out of 100). The result of beta-lactamase producing by using the acid-metric method were as follows the penicillinase and cephalosporinase: 27.0% and 37.0% against Escherichia coli isolates, 37.0% and 1.0% against Klebsiella pneumoniae isolates, 21.8% and 100% against Enterobacter cloacae isolates, 24.2% and 96.0% against Serratia marcescens isolates, 7.0% and 22.0% against Pseudomonas aeruginosa isolates. We identified beta-lactamase type of each isolate detected by polymerase chain reaction: SHV-derived extended-spectrum beta-lactamase (ESBLs) (1 isolate of E. coli and 1 isolate of K. pneumoniae), CTX-M-1-derived ESBLs (1 isolate of K. pneumoniae, 1 of E. cloacae and 4 of S. marcescens), and IMP-1-derived metallo beta-lactamases (2 isolates of S. marcescens).

[Antimicrobial susceptibility and beta-lactamase producibility of bacteria clinically isolated during the period from December 1999 to February 2000]

Antimicrobial susceptibility and beta-lactamase producibility were tested in 848 clinical strains collected at 8 hospitals in Kanagawa prefecture during the period from December 1999 to February 2000. Positive rates of beta-lactamase used the nitrocefin method (Cefinase) were 21.9% of Staphylococcus aureus, 10.0% of Haemophilus influenzae, and 99.0% of Moraxella catarrhalis. Furthermore, on the acidometric method (P/Case test) penicillinase (PCase), cephalosporinase (CEPase), and both of PCase and CEPase were found to be positive in 19.0%, 16.0%, and 16.0% for Escherichia coli, 6.2/0/3.1% for Klebsiella pneumoniae, 0/66.3/26.5% for Enterobacter cloacae, 2.8/57.7/15.5% for Serratia marcescens, and 4.0/15.0/22.0% for Pseudomonas aeruginosa, respectively. Based on the assessment of minimal inhibitory concentrations (MICs) of antibacterial agents among beta-lactamase producing strains, there were 5 strains (4 strains of K. pneumoniae and 1 strain of E. coli) that may be ESBLs producing bacteria out of a total of 466 strains of Enterobacteriaceae and P. aeruginosa. During this process, 1 strain of class-B beta-lactamase-producing E. cloacae was isolated. MRSA were found in 79.2% of S. aureus, and BLNAR were found in 8.9% of H. influenzae.

[Beta-lactamase activity and susceptibilities to antibiotics among some species of bacteria isolated from medical institution between December 1999 and February 2000]

We studied the beta-lactamase activity and susceptibilities to antibiotics in 604 strains among 10 species of bacteria isolated from 10 medical institutions in Tottori and Shimane Prefectures between December 1999 and February 2000. beta-Lactamase activity was measured by the nitrocefin test and penicillinase/cephalosporinase activities were measured by acidometry. beta-Lactamase activity was detected in 72.1% of S. aureus, 18.8% of H. influenzae, and 96.3% of M. catarrhalis. Penicillinase/cephalosporinase activities were detected in 17.8%/22.2% of E. coli, 9.7%/0.0% of K. pneumoniae, 18.6%/95.3% of E. cloacae, 12.7%/79.4% of S. marcescens, and 7.1%/31.8% of P. aeruginosa. Three of 72 strains (4.2%) of K. pneumoniae and 5 of 90 strains (5.6%) of E. coli were assessed as ESBL-producing bacteria using the NCCLS proposed screening method based on routine susceptibility testing results. BLNAR were detected in 13 of 69 strains (18.8%) of H. influenzae.

Emergence of Klebsiella pneumoniae isolates producing inducible DHA-1 beta-lactamase in a university hospital in Taiwan

Ten nonrepetitive clinical isolates of Klebsiella pneumoniae exhibiting an unusual inducible beta-lactam resistance phenotype were identified between January 1999 and September 2001 in a university hospital in Taiwan. In the presence of 2 micro g of clavulanic acid, the isolates showed a one to four twofold concentration increase in the MICs of ceftazidime, cefotaxime, and aztreonam but remained susceptible to cefepime (MICs, </=0.5 micro g/ml) and imipenem (MICs, </=0.5 micro g/ml). PCR, sequence analysis, and isoelectric focusing revealed production by these isolates of TEM-1, SHV-11, and DHA-1, a plasmid-encoded inducible AmpC beta-lactamase originally found in a Salmonella enterica serovar Enteritidis strain. Transfer of the resistance by conjugation experiments was not successful, but Southern hybridization showed that bla(DHA-1) was located on 70-kb plasmids, suggesting that the bla(DHA-1)-containing plasmids in the K. pneumoniae isolates were non-self-transmissible. Five isolates were recovered from patients in two surgery wards and two intensive care units. Acquisition of the DHA-1 producers could be traced back to previous hospitalizations 1 to 5 months earlier for the other five patients. Six and seven patterns among the isolates were demonstrated by plasmid analysis and ribotyping, respectively, indicating that the spread of the DHA-1 producers was due to both horizontal transfer of bla(DHA-1) and dissemination of endemic clones.

[Antimicrobial susceptibility and prevalence of beta-lactamase producing clinical isolates in southern Kyushu. The results of collaborative study from 1999 to 2000]

The positivity of beta-lactamase and antimicrobial susceptibility were determined in a total of 1,358 clinical isolates at 15 hospitals and clinics in four prefectures in southern Kyushu (Okinawa, Miyazaki, Kagoshima and Kumamoto) during the period from December 1999 to February 2000. The isolates collected comprised of 176 strains of S. aureus, 203 of H. influenzae, 102 of M. catarrhalis, 206 of E. coli, 153 of K. pneumoniae, 99 of E. cloacae, 95 of S. marcescens, 201 of P. aeruginosa, 79 of E. faecalis, and 44 of E. faecium. The frequency of CPDX resistance among E. coli in particular varied geographically, and was found to be higher in Kumamoto and Kagoshima. The strains of K. pneumoniae and E. cloacae resistant to common antimicrobial agents were particularly found in Kagoshima, and one strain of IPM-resistant E. cloacae was isolated in Miyazaki. Also, the geographical difference in the frequency of LVFX resistance among the isolates of E. cloacae was noted, the results indicating the higher prevalence in Okinawa and Kagoshima. Resistant isolates of P. aeruginosa were less common in Kagoshima, and four isolates of P. aeruginosa from Miyazaki were found to be resistant to CAZ and IPM. None of the isolates of S. aureus and Enterococcus spp. was resistant to VCM or TEIC at all. The isolates of E. faecalis resistant at high-level GM (500 micrograms/ml) and SM (1,000 micrograms/ml) were found in 27.8% and 22.8%, and those of E. faecium were 6.8% and 38.6%, respectively. Overall, the ratio of MRSA among S. aureus was 67.6%, and three isolates were resistant to ABK with no less than 8 micrograms/ml of MIC. The frequency of BLNAR (beta-lactamase-negative, ampicillin resistant) among H. influenzae isolated in Okinawa was markedly higher (isolation ratio, 37.9%) when compared with other prefectures, and the isolates of BLPACR (beta-lactamase-positive, AMPC/CVA resistant) were found only in Okinawa with a ratio of 41.6%. A total of 18 strains of ESBL defined by the NCCLS criteria (M100-S11) were isolated, eight strains of K. pneumoniae and 10 strains of E. coli. Of 18 isolates of ESBL, 13 were from Kagoshima and the remaining five were from Kumamoto.