Perceptual errors increase with movement duration and may contribute to hypokinesia in Parkinson's disease

People with Parkinson's disease (PD) perceive that their movement amplitude is greater than what they actually perform. The neural mechanisms underlying one's perception of movement are believed to involve the sensorimotor integration process (SIP). How PD affects the SIP is not well understood. A previous study interrogating the SIP showed healthy adults (HAs) overestimated their limb position in the direction of movement and the error and its variance (VOE) depended on movement duration. We asked if PDs showed errors in perceived limb position and if the dependence on movement duration was different from HAs. We used an existing computational model of the SIP to explore mechanisms for the error and VOE as a function of movement duration. Twenty PDs, off medication, and 20 age-matched HAs were asked to estimate the position of their hand after performing 50, slow, non-visually guided wrist flexion or extension movements for a random period of time (<4.0 s). Both groups overestimated the amount they moved; however, the PDs' error and VOE were larger (p<0.001). HAs showed increasing error/VOE for small movement durations that reduced/stabilized for longer movement durations. PDs however showed increasing error/VOE with increasing movement duration that did not significantly improve/stabilize. The model suggested that the basis for such perceptual deficits may be abnormal proprioceptive feedback and/or processing of an abnormal internal impression (prediction) that underestimates movement amplitude. Simulation results imply that the PD's SIP could no longer effectively access sensory (proprioceptive) feedback to correct errors in other components of the SIP due to the abnormal processing of sensory feedback. We suggest from this study that an impaired perception of movement amplitude and sensory processing deficits contribute to hypokinesia in PD.

Successful urgent transplantation of an adult kidney into a child with inferior vena cava thrombosis

Poor venous drainage options following inferior vena cava (IVC) thrombosis have been considered to complicate or preclude renal transplantation of adult kidneys into pediatric patients. We describe urgent renal transplantation in a 5-year-old (15.3 kg) male with IVC thrombosis using an adult living donor. Preoperative magnetic resonance venography revealed a patent infrahepatic/suprarenal vena cava and portal system. In surgery, the right liver lobe was mobilized sufficiently to anastomose the graft renal vein to the native IVC at the confluence of the native left renal vein and proximal vena cava. Graft function has remained excellent with serum creatinine of 0.5 mg/dL at 36 months. IVC thrombosis need not preclude successful transplantation of adult-sized kidneys into children.

Transient-state reduction and steady-state kinetic studies of menaquinol oxidase from Bacillus subtilis, cytochrome aa3-600 nm. Spectroscopic characterization of the steady-state species

Cytochrome aa3-600 or menaquinol oxidase, from Bacillus subtilis, is a member of the heme-copper oxidase family. Cytochrome aa3-600 contains cytochrome a, cytochrome a3, and CuB, and each is coordinated via histidine residues to subunit I. Subunit II of cytochrome aa3-600 lacks CuA, which is a common feature of the cytochrome c oxidase family members. Anaerobic reduction of cytochrome aa3-600 by the substrate analogue 2,3-dimethyl-1,4-naphthoquinone (DMN) resolves two distinct kinetic phases by stopped-flow, single-wavelength spectrometry. Global analysis of time-resolved, multiwavelength spectra shows that during these distinct phases cytochromes a and a3 are both reduced. Cyanide binding to cytochrome a3 enhances the fast phase rate, which in the presence of cyanide can be assigned to cytochrome a reduction, whereas cytochrome a3-cyanide reduction is slow. The steady-state activity of cytochrome aa3-600 exhibits saturation kinetics as a function of DMN concentration with a Km of 300 microM and a maximal turnover of 63.5 s(-1). Global kinetic analysis of steady-state spectra reveals a species that is characteristic of a partially reduced oxygen adduct of cytochrome a3-CuB, whereas cytochrome a remains oxidized. Electron paramagnetic resonance (EPR) spectroscopy of the oxidase in the steady state shows the expected signal from ferricytochrome a, and a new EPR signal at g = 2.01. A model of the catalytic cycle for cytochrome aa3-600 proposes initial electron delivery from DMN to cytochrome a, followed by rapid heme to heme electron transfer, and suggests possible origins of the radical signal in the steady-state form of the enzyme.

Control of vancomycin-resistant enterococcus in health care facilities in a region

BACKGROUND

In late 1996, vancomycin-resistant enterococci were first detected in the Siouxland region of Iowa, Nebraska, and South Dakota. A task force was created, and in 1997 the assistance of the Centers for Disease Control and Prevention was sought in assessing the prevalence of vancomycin-resistant enterococci in the region's facilities and implementing recommendations for screening, infection control, and education at all 32 health care facilities in the region.

METHODS

The infection-control intervention was evaluated in October 1998 and October 1999. We performed point-prevalence surveys, conducted a case-control study of gastrointestinal colonization with vancomycin-resistant enterococci, and compared infection-control practices and screening policies for vancomycin-resistant enterococci at the acute care and long-term care facilities in the Siouxland region.

RESULTS

Perianal-swab samples were obtained from 1954 of 2196 eligible patients (89 percent) in 1998 and 1820 of 2049 eligible patients (89 percent) in 1999. The overall prevalence of vancomycin-resistant enterococci at 30 facilities that participated in all three years of the study decreased from 2.2 percent in 1997 to 1.4 percent in 1998 and to 0.5 percent in 1999 (P<0.001 by chi-square test for trend). The number of facilities that had had at least one patient with vancomycin-resistant enterococci declined from 15 in 1997 to 10 in 1998 to only 5 in 1999. At both acute care and long-term care facilities, the risk factors for colonization with vancomycin-resistant enterococci were prior hospitalization and treatment with antimicrobial agents. Most of the long-term care facilities screened for vancomycin-resistant enterococci (26 of 28 in 1998 [93 percent] and 23 of 25 in 1999 [92 percent]) and had infection-control policies to prevent the transmission of vancomycin-resistant enterococci (22 of 25 [88 percent] in 1999). All four acute care facilities had screening and infection-control policies for vancomycin-resistant enterococci in 1998 and 1999.

CONCLUSIONS

An active infection-control intervention, which includes the obtaining of surveillance cultures and the isolation of infected patients, can reduce or eliminate the transmission of vancomycin-resistant enterococci in the health care facilities of a region.

Assignment of CDC weak oxidizer group 2 (WO-2) to the genus Pandoraea and characterization of three new Pandoraea genomospecies

CDC weak oxidizer group 2 (WO-2) consists of nine phenotypically similar human clinical isolates received by the Centers for Disease Control and Prevention between 1989 and 1998. Four of the isolates were from blood, three were from sputum, and one each was from bronchial fluid and maxillary sinus. All are aerobic nonfermentative, motile gram-negative rods with one to eight polar flagella per cell. All grew at 25 and 35 degrees C and were positive for catalase, urease (usually delayed 3 to 7 days), citrate, alkalinization of litmus milk, oxidization of glycerol (weakly), and growth on MacConkey agar and in nutrient broth without NaCl. All except one strain were oxidase positive with the Kovács method, and all except one isolate weakly oxidized D-glucose. All were negative for oxidation of D-xylose, D-mannitol, lactose, sucrose, maltose, and 20 other carbohydrates, esculin hydrolysis, indole production, arginine dihydrolase, and lysine and ornithine decarboxylase. Only two of nine isolates reduced nitrate. Broth microdilution susceptibilities were determined for all strains against 13 antimicrobial agents. Most of the strains were resistant to ampicillin, extended-spectrum cephalosporins, and aminoglycosides, including gentamicin, tobramycin, and amikacin, but they varied in their susceptibility to fluoroquinolones. High-performance liquid chromatographic and mass spectrometric analyses of the WO-2 group identified ubiquinone-8 as the major quinone component. The percent G+C of the WO-2 strains ranged from 65.2 to 70.7% (thermal denaturation method). All shared a common cellular fatty acid (CFA) profile, which was characterized by relatively large amounts (7 to 22%) of 16:1omega7c, 16:0, 17:0cyc, 18:1omega7c, and 19:0cyc(11-12); small amounts (1 to 3%) of 12:0 and 14:0; and eight hydroxy acids, 2-OH-12:0 (4%), 2-OH-14:0 (trace), 3-OH-14:0 (12%), 2-OH-16:1 (1%), 2-OH-16:0 (3%), 3-OH-16:0 (4%), 2-OH-18:1 (2%), and 2-OH-19:0cyc (3%). This profile is similar to the CFA profile of Pandoraea, a recently described genus associated with respiratory infections in cystic fibrosis patients (T. Coenye et al., Int. J. Syst. Evol. Microbiol., 50:887-899, 2000). Sequencing of the 16S rRNA gene (1,300 bp) for all nine strains indicated a high level (> or =98.8%) of homogeneity with Pandoraea spp. type strains. DNA-DNA hybridization analysis (hydroxyapatite method; 70 degrees C) confirmed the identity of WO-2 with the genus Pandoraea and assigned three strains to Pandoraea apista and three to Pandoraea pnomenusa, and identified three additional new genomospecies containing one strain each (ATCC BAA-108, ATCC BAA-109, ATCC BAA-110). This study also shows that Pandoraea isolates may be encountered in blood cultures from patients without cystic fibrosis.

Characterization of YpmQ, an accessory protein required for the expression of cytochrome c oxidase in Bacillus subtilis

A search of the Bacillus subtilis genome identifies a potential homolog, ypmQ, of the inner mitochondrial membrane protein Sco1 from yeast. Sco1 has been found to aid the delivery of copper to cytochrome c oxidase. B. subtilis expresses two members of the cytochrome oxidase family, a cytochrome c oxidase that has two copper centers, Cu(A) and Cu(B), and a menaquinol oxidase that has only Cu(B). Deletion of ypmQ in B. subtilis depresses expression of cytochrome c oxidase but not menaquinol oxidase. Levels of cytochrome c oxidase recover when copper is added to the growth medium of the DeltaypmQ strain or when ypmQ is expressed from a plasmid. Neither treatment affects the amount or activity of menaquinol oxidase. YpmQ in which two conserved cysteines are replaced by serines and a conserved histidine is replaced by alanine do not complement the deletion of ypmQ even though these mutant forms are found in the membrane extract at a level similar to the wild type protein. We propose that the two cysteines and the histidine are critical for the function of YpmQ and suggest they are involved in copper exchange between YpmQ and the Cu(A) site of cytochrome c oxidase.

Classification of Proteus vulgaris biogroup 3 with recognition of Proteus hauseri sp. nov., nom. rev. and unnamed Proteus genomospecies 4, 5 and 6

Strains traditionally identified as Proteus vulgaris formed three biogroups. Biogroup 1, characterized by negative reactions for indole production, salicin fermentation and aesculin hydrolysis, is now known as Proteus penneri. Biogroup 2, characterized by positive reactions for indole, salicin and aesculin, was shown by DNA hybridization (hydroxyapatite method) to be a genetic species separate from biogroup 1 and from biogroup 3 which is positive for indole production and negative for salicin and aesculin. In this study, 52 strains were examined, of which 36 strains were Proteus vulgaris biogroup 3, which included the current type strain of the species P. vulgaris (ATCC 29905T), and compared to seven strains of Proteus vulgaris biogroup 2 and nine type strains of other species in the genera Proteus, Providencia and Morganella. By DNA hybridization, these 36 strains were separated into four distinct groups, designated as Proteus genomospecies 3, 4, 5 and 6. DNAs within each separate Proteus genomospecies were 74-99% related to each other in 60 degrees C hybridization reactions with < or = 4.5% divergence between related sequences. Proteus genomospecies 3 contained the former P. vulgaris type strain and one other strain and was negative in reactions for salicin fermentation, aesculin hydrolysis and deoxyribonuclease, unlike the reactions associated with strains considered as typical P. vulgaris which are positive in reactions for salicin, aesculin and DNase. Genomospecies 3 can be distinguished from Proteus genomospecies 4, 5 and 6 because it is negative for Jordan's tartrate. Proteus genomospecies 4, containing five strains, was differentiated from Proteus penneri, genomospecies 3 and 6 and most, but not all, strains of genomospecies 5, by its ability to ferment L-rhamnose. Proteus genomospecies 5 and 6, containing 18 and 11 strains, respectively, could not be separated from each other by traditional biochemical tests, by carbon source utilization tests or SDS-PAGE of whole-cell proteins. In an earlier publication, a request was made to the Judicial Commission that the former type strain of P. vulgaris (ATCC 13315) be replaced by P. vulgaris biogroup 2 strain ATCC 29905T, a strain considered more biochemically typical of P. vulgaris strains. This would have the effect of assigning the name P. vulgaris to P. vulgaris biogroup 2. Since this request has been acceded to, the name Proteus hauseri is herein proposed for Proteus vulgaris genomospecies 3. Its type strain is ATCC 700826T. Proteus genomospecies 4, 5 and 6 will remain unnamed until better phenotypic differentiation can be accomplished. All Proteus genomospecies were similar in their antimicrobial susceptibility patterns. Nineteen strains were isolated from urine, four from faeces, two from wounds, nine from other human sources and two from animals.

Characterization of a structural model of membrane bound cytochrome c-550 from Bacillus subtilis

A structural model of Bacillus subtilis cytochrome c-550 has been built based upon hydropathy analysis, sequence alignment, homology modeling, and energy minimization. The model has a single transmembrane alpha-helix and a water-soluble domain folded around covalently attached heme C. Physical measurements on purified, recombinant cytochrome c-550 have been made to test aspects of the model. Excitation at either 280 or 295 nm yields fluorescence with an emission maximum at 334 nm and a quantum yield of 25% relative to n-acetyltryptophanamide. The model places one (i.e., W115) of the two tryptophans of cytochrome c-550 in the heme domain and the second (i.e., W3) in the transmembrane domain. The indole ring of W115 is within 5 A of the heme macrocycle and is expected to be highly quenched via resonance energy transfer to the heme. In contrast, W3 is at the start of the putative transmembrane helix and could be located a considerable distance from the heme. Förster theory assigns a distance of 42 A from W3 to the heme. This distance is important in adjusting the relative positions of the membrane-spanning and heme-binding domains. Circular dichroism measurements in the ultraviolet region indicate increased alpha-helical content of B. subtilis cytochrome c compared to mitochondrial cytochrome c in support of an alpha-helical transmembrane domain. The ionic strength dependence of redox kinetics for cytochrome c-550 indicates an overall negative charge that is consistent with a calculated pI of 5.4. However, the charge distribution specified by the model indicates a surface for electron exchange that is different from the classical front face used by mitochondrial cytochrome c.

A simplified method for testing Bordetella pertussis for resistance to erythromycin and other antimicrobial agents

Present methods of antimicrobial susceptibility testing of Bordetella pertussis are time consuming and require specialized media that are not commercially available. We tested 52 isolates of B. pertussis for resistance to erythromycin, trimethoprim-sulfamethoxazole, chloramphenicol, and rifampin by agar dilution with Bordet-Gengou agar (BGA) containing 20% horse blood (reference method), Etest using BGA and Regan-Lowe agar without cephalexin (RL-C), and disk diffusion using BGA and RL-C. The organisms tested included four erythromycin-resistant isolates of B. pertussis from a single patient, a second erythromycin-resistant strain of B. pertussis from an unrelated patient in another state, and 47 nasopharyngeal surveillance isolates of B. pertussis from children in the western United States. The results of agar dilution testing using direct inoculation of the organisms suspended in Mueller-Hinton broth were within +/-1 dilution of those obtained after overnight passage of the inoculum in Stainer-Scholte medium, which is the traditional method of testing B. pertussis. The Etest method produced MICs similar to those of the agar dilution reference method for three of the four antimicrobial agents tested; the trimethoprim-sulfamethoxazole results were lower with Etest, particularly when the direct suspension method was used. Most of the Etest MICs, except for that of erythromycin, were on scale. Disk diffusion testing using RL-C medium was helpful in identifying the erythromycin-resistant strains, which produced no zone of inhibition around the disk; susceptible isolates produced zones of at least 42 mm. Thus, the antimicrobial susceptibility testing of B. pertussis can be simplified by using the Etest or disk diffusion on RL-C to screen for erythromycin-resistant isolates of B. pertussis.

Isolation of Providencia heimbachae from human feces

Providencia heimbachae was first described in 1986. It has been isolated from penguin feces and an aborted bovine fetus. To date, there has been no reported isolation of this organism from human specimens. We now report the isolation of P. heimbachae from the stool of a 23-year-old woman with idiopathic diarrhea. The identity of the human strain was determined biochemically and by DNA relatedness to the type strain of P. heimbachae.

Regional dissemination of vancomycin-resistant enterococci resulting from interfacility transfer of colonized patients

During early 1997, the Siouxland District Health Department (SDHD; Sioux City, IA) reported an increased incidence of vancomycin-resistant enterococcal (VRE) isolates at area health care facilities. To determine the prevalence and risk factors for colonization with VRE strains at 32 health care facilities in the SDHD region, a prevalence survey and case-control study were performed. Of 2266 patients and residents, 1934 (85%) participated, and 40 (2.1%) were positive for (gastrointestinal) VRE colonization. The prevalence of VRE isolates was significantly higher in acute care facilities (ACFs) than in long-term care facilities (LTCFs) (10/152 [6.6%] vs. 30/1782 [1.7%]; odds ratio [OR], 4.1; 95% confidence interval [CI], 1.8-9.0). LTCF case patients were significantly more likely than controls to have been inpatients at any ACF (19/30 vs. 12/66; OR, 8.0; 95% CI, 2.7-23.8). Of 40 VRE isolates, 34 (85%) were a related strain. The predominant strain was present in all 12 LTCFs that had at least 1 case patient in each facility. Soon after the introduction of VRE isolates into this region, dissemination to multiple LTCFs resulted from resident transfer from ACFs to LTCFs.

Lithium and valproate differentially regulate brain regional expression of phosphorylated CREB and c-Fos

Previous studies in our laboratory have shown that the mood stabilizers, lithium and valproate (VPA), regulate the transcription factors, cyclic AMP responsive element binding protein (CREB), c-Fos and c-Jun, differentially in cultured human neuroblastoma SH-SY5Y cells. Here, we confirm these findings in rat brain and further study the brain-regional effects of these drugs using immunohistochemistry. We found that although chronic treatment with LiCl or VPA did not change the expression of c-Fos and c-Jun, acute treatment with either drugs increased c-Fos expression but not c-Jun expression in CA1 and CA3 regions of hippocampus. Chronic treatment with LiCl, but not VPA, decreased CREB phosphorylation in rat cerebral cortex and hippocampus. These results suggest that lithium and VPA may act on different pathways to bring about their long-term prophylactic effects on bipolar disorder (BD). The regulation of CREB phosphorylation may be relevant to lithium effect. VPA, which is also effective in BD, may be linked to other pathways.

Expression, purification, and characterization of recombinant forms of membrane-bound cytochrome c-550nm from Bacillus subtilis

Bacillus subtilis expresses a cytochrome c-550nm that participates in respiratory electron transfer and is an integral membrane protein. Analysis of the B. subtilis cytochrome c-550nm amino acid sequence predicts a single N-terminal transmembrane helix attached to a water-soluble heme binding domain [C. von Wachenfeldt and L. Hederstedt (1990) J. Biol. Chem. 265, 13939-13948]. We have purified cytochrome c-550nm from wild-type B. subtilis and B. subtilis transformed with the shuttle vector pHP13 containing the gene for B. subtilis cytochrome c-550nm (cccA). In B. subtilis transformed with pHP13/cccA there is better than eightfold more membrane-bound cytochrome c-550nm than in wild-type B. subtilis. The overexpressed cytochrome c-550nm can be purified by chromatography on hydroxylapatite and Q-Sepharose media. A six-histidine tag has been added to the C-terminus of cytochrome c-550nm from B. subtilis as a further aid for purification. This strain produces cytochrome c-550nm to a level fourfold greater than wild type and allows for one-step purification using metal affinity chromatography. UV-Vis spectroscopy detects no change in the heme C spectrum due to the addition of six histidines. Neither form of B. subtilis cytochrome c-550nm is stable in its reduced state in aerated buffer, unless EDTA is added. The two forms, wild-type and his-tagged, of cytochromes c have similar midpoint redox potentials of 195 and 185 mV, respectively, and are equally good substrates for B. subtilis cytochrome c oxidase. We conclude that the addition of the histidine tag eases the purification of cytochrome c-550nm from B. subtilis plasma membranes and that the additional metal binding site does not compromise the stability or functional properties of the protein.

Staphylococcus aureus with reduced susceptibility to vancomycin isolated from a patient with fatal bacteremia

A Staphylococcus aureus isolate with reduced susceptibility to vancomycin was obtained from a dialysis patient with a fatal case of bacteremia. Comparison of the isolate with two methicillin-resistant S. aureus (MRSA) isolated obtained from the same patient 4 months earlier suggests that the S. aureus with reduced susceptibility to vancomycin emerged from the MRSA strain with which the patient was infected. Atypical phenotypic characteristics, including weak or negative latex-agglutination test results, weak or negative-slide coagulase test results, heterogeneous morphologic features, slow rate of growth, and vancomycin susceptibility (by disk diffusion test) were observed.

Electron transfer kinetics during the reduction and turnover of the cytochrome caa3 complex from Bacillus subtilis

The cytochrome caa3 complex from Bacillus subtilis is a member of the cytochrome oxidase superfamily of respiratory enzyme complexes. The key difference in the cytochrome caa3 complex lies in the addition of a domain, homologous with mitochondrial cytochrome c, that is fused to the C-terminal end of its subunit II. Measurements of steady-state and transient reduction kinetics have been carried out on the cytochrome caa3 complex. Reduction of the cyanide-bound enzyme with ascorbate and N,N,N',N'-tetramethyl-p-phenylenediamine (TMPD) supports a sequence of electron transfer in which cytochromec is reduced initially, and this is followed by rapid internal electron transfer from cytochrome c to CuA and from CuA to cytochrome a. Steady-state kinetics with exogenous cytochrome c as the substrate demonstrates the capability of the cytochrome caa3 complex to act as a cytochrome c oxidase. The cytochrome c from B. subtilis is the most efficient cytochrome c of those tested. Steady-state kinetics with ascorbate-TMPD as the reductant, in the absence of exogenous cytochrome c, reveals a biphasic pattern even though only a single, covalent cytochrome c interaction site is present. The two-phase kinetics are characterized by a low activity phase associated with a high apparent affinity for TMPD and a high activity phase with a low affinity for TMPD. This pattern is observed over a wide range of ionic strengths and enzyme concentrations, and with both purified and membrane extract forms of cytochrome caa3. It is proposed that the biphasic steady-state kinetics of this oxidase, and other members of the cytochrome oxidase superfamily, do not result directly from different interactions with cytochrome c but are due to a change in the redox kinetics within the centers of the conventional oxidase unit itself. Our results will be related to models that account for the biphasic steady-state kinetics exhibited by cytochrome oxidase.

Characterization of staphylococci with reduced susceptibilities to vancomycin and other glycopeptides

During the last several years a series of staphylococcal isolates that demonstrated reduced susceptibility to vancomycin or other glycopeptides have been reported. We selected 12 isolates of staphylococci for which the vancomycin MICs were > or =4 microg/ml or for which the teicoplanin MICs were > or =8 microg/ml and 24 control strains for which the vancomycin MICs were < or =2 microg/ml or for which the teicoplanin MICs were < or =4 microg/ml to determine the ability of commercial susceptibility testing procedures and vancomycin agar screening methods to detect isolates with reduced glycopeptide susceptibility. By PCR analysis, none of the isolates with decreased glycopeptide susceptibility contained known vancomycin resistance genes. Broth microdilution tests held a full 24 h were best at detecting strains with reduced glycopeptide susceptibility. Disk diffusion did not differentiate the strains inhibited by 8 microg of vancomycin per ml from more susceptible isolates. Most of the isolates with reduced glycopeptide susceptibility were recognized by MicroScan conventional panels and Etest vancomycin strips. Sensititre panels read visually were more variable, although with some of the panels MICs of 8 microg/ml were noted for these isolates. Vitek results were 4 microg/ml for all strains for which the vancomycin MICs were > or =4 microg/ml. Vancomycin MICs on Rapid MicroScan panels were not predictive, giving MICs of either < or =2 or > or =16 microg/ml for these isolates. Commercial brain heart infusion vancomycin agar screening plates containing 6 microg of vancomycin per ml consistently differentiated those strains inhibited by 8 microg/ml from more susceptible strains. Vancomycin-containing media prepared in-house showed occasional growth of susceptible strains, Staphylococcus aureus ATCC 29213, and on occasion, Enterococcus faecalis ATCC 29212. Thus, strains of staphylococci with reduced susceptibility to glycopeptides, such as vancomycin, are best detected in the laboratory by nonautomated quantitative tests incubated for a full 24 h. Furthermore, it appears that commercial vancomycin agar screening plates can be used to detect these isolates.

Spectral and cyanide binding properties of the cytochrome aa3 (600 nm) complex from Bacillus subtilis

The cytochrome aa3 (600 nm) complex, or menaquinol oxidase, from Bacillus subtilis is a member of the cytochrome oxidase superfamily of respiratory membrane protein complexes. We have characterized some spectral properties of this enzyme and its reaction with cyanide. The magnetic circular dichroism (MCD) spectrum of the oxidized enzyme has a single band at 1560 nm in the near-infrared region assigned to bis-histidine-ligated, low-spin ferricytochrome a. The other heme, cytochrome a3, is presumably high-spin in the oxidized enzyme, as isolated. The absence of a trough in the MCD spectrum at 790 nm, observed previously with mammalian cytochrome c oxidase and assigned to CuA (Greenwood et al., Biochem. J. 215, 303-316, 1983), is consistent with the absence of this center from the menaquinol oxidase. When the heme ligand cyanide is added to oxidized menaquinol oxidase, a new MCD band appears at 2010 nm, while the band at 1560 nm is unperturbed. The new band is assigned to low-spin ferricytochrome a3 bound with cyanide. The long-wavelength position of this cyanide-induced band is proposed to arise from the close interaction of cytochrome a3 with the copper atom, CuB. The kinetics of cyanide binding to oxidized cytochrome aa3(600 nm) reveal a spectrally simple, yet kinetically complex process. The reaction is biphasic with second-order rate constants of 45 and 0.61 M-1s-1 at 1 mM KCN, with each phase constituting about 50% of the overall reaction. When the enzyme is subjected to a cycle of anaerobic reduction and air oxidation, the subsequent reaction with cyanide occurs in a single phase at the faster rate. This behavior is ascribed to different conformations of the binuclear center exhibiting different reactivities with cyanide, and is in keeping with that previously established for the structurally more complex mitochondrial cytochrome c oxidase. However, the electronic spectral characteristics of some of the species involved in these reactions are different in the present bacterial case from those of reported eukaryotic systems.

First report of a human isolate of Erwinia persicinus

Erwinia persicinus was first described in 1990 after being isolated from a variety of fruits and vegetables, including bananas, cucumbers, and tomatoes. In 1994, it was shown to be the causative agent of necrosis of bean pods. We now report the first human isolate of E. persicinus. The strain was isolated from the urine of an 88-year-old woman who presented with a urinary tract infection. By the hydroxyapatite method, DNA from this strain was shown to be 94.5% related at 60 degrees C and 86% related at 75 degrees C to the type strain of E. persicinus. The biochemical profile of E. persicinus is most similar to those of Erwinia rhapontici, Pantoea agglomerans, and Enterobacter species. It is negative in tests for lysine, arginine, ornithine, dulcitol, and urea. It is motile and positive in tests for D-sorbitol and sucrose. It is susceptible to the expanded-spectrum cephalosporins, aminoglycosides, and fluoroquinolones, but it is resistant to ampicillin, ticarcillin, and cefazolin.

Risk factors for carriage of drug-resistant Streptococcus pneumoniae among children in Memphis, Tennessee

OBJECTIVES

To determine risk factors for carriage of drug-resistant Streptococcus pneumoniae to understand better the factors promoting spread of these isolates.

STUDY DESIGN

We obtained medical and demographic information and nasopharyngeal swab specimens from 216 children less than 6 years old with upper respiratory tract infections, seeking medical care at five Memphis, Tenn, study sites. We evaluated risk factors for carriage of penicillin-nonsusceptible S. pneumoniae (NSSP) among 100 children with S. pneumoniae isolates. Patterns of antimicrobial prescription were recorded for enrolled children.

RESULTS

Independent risk factors for carriage of NSSP included an increased number of antimicrobial treatment courses during the previous 3 months and white race. Day care attendance approached statistical significance (p = 0.07). Most children with upper respiratory tract infection received a prescription for antimicrobial drugs. These prescriptions were more common for white children than for black children.

CONCLUSIONS

Increased use of antimicrobial drugs enhances the risk of carriage of NSSP. This may contribute to the higher risk among white children of NSSP infection; however, after control for antimicrobial use, white children were still at an increased risk of infection with NSSP, possibly through greater exposure to resistant strains.

Stopped-flow, laser-flash photolysis studies on the reactions of CO and O2 with the cytochrome caa3 complex from Bacillus subtilis: conservation of electron transfer pathways from cytochrome c to O2

The reaction of CO and O2 with fully reduced cytochrome caa3 from Bacillus subtilis has been studied by rapid reaction spectrophotometry. The fully reduced caa3 complex reacts with CO to give a spectrum that is characteristic of formation of ferrocytochrome a3-CO. This adduct is photosensitive, and its recombination rate is proportional to CO concentration with a bimolecular value of 1.2 x 10(5)M-1 s-1. When the CO compound of the reduced complex is exposed to O2, the rate of oxidation proceeds at 0.1 s-1, which is assigned as the CO off rate. These kinetic constants give an equilibrium dissociation constant for the CO complex of 0.83 microM. Photolysis of the CO adduct in the presence of O2 reveals three reaction phases over the first 3 ms and an additional phase on the second time scale. A kinetic model is proposed in which fully reduced oxidase first combines with O2 and then electron transfer commences from both cytochrome a and a3, followed rapidly by electron input from CuA and the cytochrome c domain. An equivalent kinetic model has been used to account for the reactivity of mammalian cytochrome c oxidase in its electrostatic complex with soluble cytochrome c [Hill, B. C., (1994) J. Biol. Chem. 269, 2419-2425]. However, unlike the mitochondrial complex, the reactivity of cytochrome c in the B. subtilis caa3 complex is unaffected by ionic strength. Thus the cytochrome c moiety in the B. subtilis caa3 complex seems to be fixed in a reactive orientation by its covalent association with the rest of the oxidase complex. The pathway of electron transfer from cytochrome c to O2 appears very well conserved from B. subtilis to the mammalian respiratory chain, making the B. subtilis protein a good model to probe intersite electron transfer within the cytochrome c-cytochrome oxidase complex.

Respiration gated radiotherapy treatment: a technical study

In order to optimize external-beam conformal radiotherapy, patient movement during treatment must be minimized. For treatment on the upper torso, the target organs are known to move substantially due to patient respiration. This paper deals with the technical aspects of gating the radiotherapy beam synchronously with respiration: the optimal respiration monitoring system, measurements of organ displacement and linear accelerator gating. Several respiration sensors including a thermistor, a thermocouple, a strain gauge and a pneumotachograph were examined to find the optimal sensor. The magnitude of breast, chest wall and lung motion were determined using playback of fluoroscopic x-ray images recorded on a VCR during routine radiotherapy simulation. Total dose, beam symmetry and beam uniformity were examined to determine any effects on the Varian 2100C linear accelerator due to gating.

Effects of bipolar point and line stimulation in anisotropic rabbit epicardium: assessment of the critical radius of curvature for longitudinal block

Excitation front shape and velocity were studied in anisotropic perfused rabbit epicardium stained with potentiometric fluorescent dye. In the combined results from all experiments, convex excitation fronts produced by stimulation with a single electrode propagated longitudinally 13.3% slower than flat excitation fronts produced by stimulation with a line of electrodes. For transverse propagation, the two stimulation methods produced similar flat excitation fronts and velocities. The critical excitation front radius of curvature for longitudinal block (Rcr), calculated from excitable media theory, was 92 microns in control hearts. In hearts exposed to diacetyl monoxime (20 mmol/L), which decreases inward sodium current, Rcr was 175 microns. The slower longitudinal propagation velocity of convex fronts versus flat fronts and the theoretically predicted critical radius of curvature may be important for propagation and block of ectopic depolarizations in the heart.

High-yield purification of cytochrome aa3 and cytochrome caa3 oxidases from Bacillus subtilis plasma membranes

When grown in aerated shaking culture, Bacillus subtilis expresses two different haem A-containing terminal oxidases: cytochrome aa3-quinol oxidase and cytochrome caa3 oxidase. This paper describes a high-yield conventional procedure for purifying the two haem A-containing oxidases from the same aerobic culture of Bacillus subtilis. Yields of close to 40% of the total haem A are achieved and about 6 mg of each of the purified oxidases is obtained from 4 litres of liquid culture. Both of the purified enzymes have two subunits, with apparent molecular masses of 71.6 kDa and 34.3 kDa for the cytochrome caa3 oxidase, and 67.6 kDa and 37.2 kDa for aa3-quinol oxidase. These features are in agreement with the sequence data for the corresponding structural genes in the aa3 and caa3 operons of B. subtilis. Some spectral and enzymic features of the two purified oxidases are reported that are consistent with the inclusion of both of these enzymes as members of the cytochrome oxidase superfamily.

The room temperature reaction of carbon monoxide and oxygen with the cytochrome bd quinol oxidase from Escherichia coli

When grown under O2-limited conditions, Escherichia coli expresses a cytochrome bd quinol oxidase that has an unusually high affinity for O2. We have studied the reaction of cytochrome bd with CO and O2 by rapid-reaction spectrophotometry. The reduced enzyme forms a photosensitive ferrocytochrome d-CO complex, and following photolysis, CO recombines with the reduced enzyme with a bimolecular rate of 8 x 10(7) M-1 s-1. Reaction of CO-bound enzyme with O2 gives a CO off-rate of 1.6 s-1. The O2 reaction is followed by a flow-flash procedure in which CO-ligated enzyme is mixed with O2, and the reaction commenced by photolysis of cytochrome d-CO. In the presence of O2, two processes are resolved on a time-scale of 300 microseconds. The absorbance at 645 nm first increases at a rate that is dependent on O2 concentration with a value of 2 x 10(9) M-1 s-1. The second phase results in decreased absorbance at 645 nm and increased absorbance at 680 nm. The rate of the second process is independent from O2 concentration above 50 microM O2 and reaches a first-order limit of 1 x 10(4) s-1. A model for the reaction of the cytochrome bd quinol oxidase with O2 is proposed in which an initial ferrocytochrome d-oxy adduct forms, and then decays to a ferryl-oxo species. The oxidation of the low-spin cytochrome b component of the oxidase, monitored at 560 nm, occurs at the same time as the ferryl species forms. We suggest that the suitability of the cytochrome bd quinol oxidase to function at low O2 concentration is conferred by its rapid rate of binding O2.

The pathway of CO binding to cytochrome c oxidase. Can the gateway be closed?

Addition of cyanide to the CO complex of cytochrome oxidase reduces the apparent photosensitivity of the Fe-CO bond. This effect is not seen with azide, or when cyanide is added to ferromyoglobin-CO. It is proposed that cyanide binds to CuB, and restricts the passage of CO out of the protein. This restriction favors geminate recombination of CO and ferrocytochrome a3, thereby lowering the apparent quantum yield for CO photolysis. The apparent Kd of cyanide for CuB is 15.4 mM. These data support a direct role for CuB in ligand binding by cytochrome c oxidase.

Epidemic gram-negative bacteremia in a neonatal intensive care unit in Guatemala

BACKGROUND

Nosocomial bloodstream infection is an important cause of morbidity and mortality among neonates. From September 1 through December 5, 1990 (epidemic period), gram-negative bacteremia developed in 26 neonates after their admission to the neonatal intensive care unit (NICU) of Hospital General, a 1000-bed public teaching hospital in Guatemala with a 16-bed NICU. Twenty-three of the 26 patients (88%) died.

METHODS

To determine risk factors for and modes of transmission of gram-negative bacteremia in the NICU, we conducted a cohort study of NICU patients who had at least one blood culture drawn at least 24 hours after admission to the NICU and performed a microbiologic investigation in the NICU.

RESULTS

The rate of gram-negative bacteremia was significantly higher among patients born at Hospital General, delivered by cesarian section, and exposed to selected intravenous medications and invasive procedures in the NICU during the 3 days before the referent blood culture was obtained. During the epidemic period, the hospital's chlorinated well-water system malfunctioned; chlorine levels were undetectable and tap water samples contained elevated microbial levels, including total and fecal coliform bacteria. Serratia marcescens was identified in 81% of case-patient blood cultures (13/16) available for testing and from 57% of NICU personnel handwashings (4/7). Most S. marcescens blood isolates were serotype O3:H12 (46%) or O14:H12 (31%) and were resistant to ampicillin (100%) and gentamicin (77%), the antimicrobials used routinely in the NICU.

CONCLUSIONS

We hypothesize that gram-negative bacteremia occurred after invasive procedures were performed on neonates whose skin became colonized through bathing or from hands of NICU personnel.

Virtual electrode effects in myocardial fibers

The changes in transmembrane potential during a stimulation pulse in the heart are not known. We have used transmembrane potential sensitive dye fluorescence to measure changes in transmembrane potential along fibers in an anisotropic arterially perfused rabbit epicardial layer. Cathodal or anodal extracellular point stimulation produced changes in transmembrane potential within 60 microns of the electrode that were positive or negative, respectively. The changes in transmembrane potential did not simply decrease to zero with increasing distance, as would occur with a theoretical fiber space constant, but instead became reversed beyond approximately 1 mm from the electrode consistent with a virtual electrode effect. Even stimulation from a line of terminals perpendicular to the fibers produced negative changes in transmembrane potential for cathodal stimulation with the largest negative changes during a 50-ms pulse at 3-4 mm from the electrode terminals. Negative changes as large as the amplitude of the action potential rising phase occurred during a 50-ms pulse for 20-volt cathodal stimulation. Switching to anodal stimulation reversed the directions of changes in transmembrane potential at most recording spots, however for stimulation during the refractory period negative changes in transmembrane potential were significantly larger than positive changes in transmembrane potential. Anodal stimulation during diastole with 3-ms pulses produced excitation in the region of depolarization that accelerated when the stimulation strength was increased to > 3 times the anodal threshold strength. Thus, virtual electrode effects of unipolar stimulation occur in myocardial fibers, and for sufficiently strong stimuli the virtual electrode effects may influence electrical behavior of the myocardium.

Modeling the sequence of electron transfer reactions in the single turnover of reduced, mammalian cytochrome c oxidase with oxygen

Single-turnover studies of the reaction of reduced cytochrome oxidase with oxygen has led to a mechanistic model that specifies a linear sequence of electron transfer from cytochrome c to O2 via the four redox active metals of mitochondrial cytochrome oxidase. Fully reduced oxidase initially forms a dioxygen adduct within which two electrons are transferred at a rate of 6 x 10(4) s-1 to form a peroxy adduct. This two-electron step results in single-electron oxidation of cytochrome alpha 3 and cytochrome alpha. Cytochrome alpha is then re-reduced by CuA in an intramolecular reaction. Subsequent reoxidation of cytochrome alpha occurs at a rate nearly 100-fold slower than its initial oxidation. Oxidation of CuB in this sequence has been the most difficult to determine and here is specified as the third electron transfer step. This reaction sequence is unchanged in the presence of tightly bound cytochrome c, although cytochrome c is rapidly oxidized via CuA and cytochrome alpha. The linear model advanced here has CuA as the acceptor of electrons from cytochrome c, with cytochrome alpha serving as a bridge to deliver electrons from CuA (and cytochrome c) to the binuclear center, cytochrome alpha 3-CuB.

Characterization of glycopeptide-resistant enterococci from U.S. hospitals

We examined 105 clinical isolates of glycopeptide-resistant enterococci collected from 31 U.S. hospitals in 14 states during May 1988 to July 1992. The isolates included 82 Enterococcus faecium, 8 E. faecalis, 6 Enterococcus spp., 5 E. gallinarum, 3 E. casseliflavus, and 1 E. raffinosus. The isolates were categorized into the following four phenotypes of glycopeptide resistance on the basis of their MIC patterns: (i) 70 VanA (vancomycin [Vm] MIC, > or = 64 micrograms/ml; teicoplanin [Tei] MIC, 16 to > or = 128 micrograms/ml), (ii) 26 VanB (Vm MIC, 16 to 1,024 micrograms/ml; Tei MIC, < or = 2 micrograms/ml), (iii) 5 VanC (Vm MIC, 4 to 16 micrograms/ml; Tei MIC, < or = 2 micrograms/ml) in E. gallinarum, and (iv) 3 E. casseliflavus and 1 E. raffinosus isolates for which Vm MICs were 4 to 16 micrograms/ml and Tei MICs were < or = 1 micrograms/ml were called unclassified. Of the 101 isolates with the VanA, VanB, and VanC phenotypes, 99 were confirmed by production of a specific 1,030-, 433-, or 796-bp polymerase chain reaction product, respectively, and hybridization with the respective gene probe. The vanA gene was also detected in the E. raffinosus isolate for which the Vm MIC was 16 micrograms/ml and the Tei MIC was 1 microgram/ml. The vanA gene was located on either a 34- or a 60-kb plasmid in all of the U.S. isolates examined. Pulsed-field gel electrophoresis demonstrated both intrahospital and interhospital diversity among Vmr enterococci in the United States and was more useful than plasmid analysis for epidemiologic studies.

Optical recordings of the effect of electrical stimulation on action potential repolarization and the induction of reentry in two-dimensional perfused rabbit epicardium

BACKGROUND

Prolonged membrane depolarization induced by an electric shock in the heart may produce propagation block leading to repetitive beats. We studied prolonged depolarization and its role in repetitive beats in a thin epicardial layer of endocardially prefrozen arterially perfused rabbit heart.

METHODS AND RESULTS

A laser scanner recorded optical action potentials at 63 sites within a 1-cm2 area on the left ventricle of hearts stained with potentiometric fluorescent dye. Pacing (S1) produced propagation across the myofibers; then, a 3-millisecond shock (S2) given in the S1 refractory period produced an electric field that decreased in strength with distance along the fibers. The S2 strengths at the center of the scanned region (C) were 2.1 +/- 0.2 or 5.6 +/- 0.3 V/cm (mean +/- SD, n = 4). Repetitive beats occurred in 50% of hearts when C was 2.1 V/cm and in 100% of hearts when C was 5.6 V/cm. With each occurrence of repetitive beats, prolonged depolarization of the shocked action potential occurred within 1 mm of the S2 electrode when C was 2.1 V/cm and within 3 mm when C was 5.6 V/cm. Transient block immediately after S2 occurred between tissue with prolonged depolarization (S2 strength, 6 to 9 V/cm) and tissue without prolonged depolarization (S2 strength, 1 to 3 V/cm). Propagation in the scanned region after S2 occurred first on the side of the block distal to the S2 electrode, propagated from the most recovered to the least recovered tissue, and then turned toward the S2 electrode. When C was 5.6 V/cm, reentry by retrograde propagation near the S2 electrode produced repetitive beats. The center of the reentrant circuit exhibited further transient block and small depolarizations associated with the circulating activation.

CONCLUSIONS

Prolonged depolarization occurs where the S2 strength is more than 6 V/cm, block occurs between regions of prolonged depolarization and no prolonged depolarization, and reentry occurs around the block. Shock-induced prolonged depolarization can be proarrhythmic and may account for electrically induced arrhythmias.

Quenching of intrinsic fluorescence of yeast cytochrome c peroxidase by covalently- and noncovalently-bound quenchers

The intrinsic steady-state fluorescence of the heme enzyme cytochrome c peroxidase (CCP) has been characterized as a probe of its structure in solution. The fluorescence is dominated by tryptophan emission, which has a quantum yield of 7% relative to the tryptophan standard N-acetyltryptophanamide, and an emission maximum at 324 nm indicative of a relatively hydrophobic environment for the fluorescent residues. These fluorescence properties are consistent with the known structure of CCP; six of the seven tryptophan residues are well within quenching distance for efficient Förster energy transfer to the heme, so that the intrinsic fluorescence arises largely from Trp101 which is approximately 26 A from the heme and partially buried. Quenching studies using Cs+, I-, and acrylamide are also consistent with this picture, since the charged species are poor quenchers, but acrylamide, which can penetrate the protein matrix, is a more effective quencher. The intrinsic fluorescence of two CCP derivatives with the quencher pentaammineruthenium(III) covalently attached to His6 and His60 has also been characterized. The His60 derivative, shown by X-ray analysis to be essentially structurally identical to native CCP, is 17% less fluorescent than native CCP, consistent with the quenching expected from distance calculations and the assignment of Trp101 as the major fluorescent center. The observed quenching of 38% in the second derivative is close to that predicted for ruthenation of His6 assuming that Trp101 is the major fluorophore. The fluorescence of compound I of CCP is also reported. This species, which has a ferryl (FeIV = O) heme and a protein radical purportedly on Trp191, exhibits 9% higher fluorescence than native CCP.(ABSTRACT TRUNCATED AT 250 WORDS)

The reaction of Bacillus subtilis aa3-600 oxidase with oxygen: an aa3-oxidase lacking the CuA site

The reaction of reduced cytochrome aa3-600 nm oxidase from Bacillus subtilis with oxygen has been measured. The reaction of fully reduced oxidase with oxygen was studied by the flow-flash method which employs the photosensitive CO complex to protect the enzyme from oxygen until the reaction is initiated by a photolytic flash. The rate of the reaction, measured in the Soret region, is oxygen concentration dependent at low levels of oxygen and becomes independent from oxygen above 200 microM. The reaction reaches a rate limit of 9500 s-1 at high oxygen. This type of oxygen concentration dependence indicates that the oxidation reaction is preceded by another event, probably an oxygen combination reaction. When compared to mammalian cytochrome oxidase the Bacillus oxidase exhibits a simpler reaction profile. This simpler observed reaction profile can be accounted for by the absence of CuA in the Bacillus oxidase using the same model developed for the single turnover of mammalian cytochrome oxidase.

The sequence of electron carriers in the reaction of cytochrome c oxidase with oxygen

Kinetic studies of the electron transfer processes performed by cytochrome oxidase have assigned rates of electron transfer between the metal centers involved in the oxidation of ferrocytochrome c by molecular oxygen. Transient-state studies of the reaction with oxygen have led to the proposal of a sequence of carriers from cytochrome c, to CuA, to cytochrome a, and then to the binuclear (i.e., cytochrome a3-CuB) center. Electron exchange rates between these centers agree with relative center-to-center distances as follows; cytochrome c to CuA 5-7 A, cytochrome c to cytochrome a 20-25 A, CuA to cytochrome a 14-16 A and cytochrome a to cytochrome a3-CuB 8-10 A. It is proposed that the step from cytochrome a to the binuclear center is the key control point in the reaction and that this step is one of the major points of energy transduction in the reaction cycle.

Kinetic and ligand binding evidence for two heme A-based terminal oxidases in plasma membranes from Bacillus subtilis

Detergent-solubilized plasma membranes from Bacillus subtilis have been characterized for their cytochrome oxidase content. Triton X-100-solubilized membranes show high O2 turnover with ascorbate plus TMPD. Reduced-oxidized difference spectroscopy of ascorbate-TMPD-reduced membranes reveals the presence of cytochrome c and cytochrome a. An additional, b-type cytochrome appears when the membranes are reduced with dithionite. Time-resolved difference spectra taken during reduction by ascorbate-TMPD reveal two kinetic forms of heme A-containing cytochromes. There is a high-turnover form that is rapidly reduced upon anaerobiosis, and a second type which is only slowly reduced upon anaerobiosis. The slowly reduced oxidase is distinguished by an alpha-band blue-shifted to 600 nm relative to the 603-nm position observed for high-turnover oxidase. Addition of CO to ascorbate-TMPD-reduced membranes gives a spectrum typical of ferrocytochrome a3-CO, and the intensity corresponds to the total ferrocytochrome a3 concentration. Photolysis of ascorbate-TMPD-reduced, CO-bound membranes indicates that both species are photosensitive with similar rates of recombination. Addition of CO to dithionite-reduced membranes shows an additional CO reactive center that has a spectrum characteristic of cytochrome o. Cyanide blocks complete reduction of high-turnover oxidase by ascorbate plus TMPD, but does not appear to effect slowly reduced oxidase. These results indicate the presence of two different types of cytochrome aa3 oxidase in plasma membranes of B. subtilis.

Optical measurements of transmembrane potential changes during electric field stimulation of ventricular cells

We evaluated transmembrane potential changes at the ends of isolated rabbit ventricular myocytes during defibrillation-strength shocks given in the cellular refractory period. The myocytes were stimulated (S1 pulse) to produce an action potential. Then a constant-field shock (S2 pulse) with an electric field of 20 or 40 V/cm was given at an S1-S2 interval of 50 msec. The cells were stained with potentiometric dye (di-4-ANEPPS), and the cell end facing the S2 anode or cathode was illuminated with a laser while the fluorescence was recorded. During S2, the cell end facing the S2 cathode became more positive intracellularly, whereas the cell end facing the S2 anode became more negative intracellularly. The S2-induced transmembrane potential change at the cell end (delta Vm) was determined relative to the amplitude of the S1-induced action potential (APA) in each recording (i.e., delta Vm/APA). In Tyrode's solution containing 4.5 mM potassium, delta Vm/APA for 40-V/cm S2 was 1.36 +/- 0.34 at the cell end facing the S2 cathode and -1.65 +/- 0.61 at the cell end facing the S2 anode (n = 9). For the 20-V/cm S2, delta Vm/APA was 0.61 +/- 0.33 at the cell end facing the S2 cathode and -0.71 +/- 0.33 at the cell end facing the S2 anode (n = 6). The delta Vm/APA was not significantly influenced by 20 mM diacetyl monoxime. These results indicate that large delta Vm values occurred at the ends of the cells during S2. The calculated values of delta Vm, assuming a nominal APA of 130 mV, were 177 and -214 mV for the 40-V/cm S2 and 79 and -93 mV for the 20-V/cm S2. The delta Vm was correlated with cell size (r > or = 0.95) and agreed with values predicted by the S2 electric field strength multiplied by half of the cell length to within 27%. When the potassium concentration was increased to 20 mM, delta Vm/APA for 40 V/cm S2 increased 85% and 67% at the cell ends facing the S2 cathode and anode, respectively (n = 9, p < 0.005 versus 4.5 mM potassium), consistent with reduced APA. Thus, with normal or elevated extracellular potassium, transmembrane potential changes at the ends of cells during defibrillation-type stimulation are large enough to produce activation or recovery of voltage-dependent ion channels and may produce the effects responsible for defibrillation.

Analysis of multiply antimicrobial-resistant isolates of Streptococcus pneumoniae from the United States

Streptococcus pneumoniae isolates resistant to penicillin, chloramphenicol, tetracycline and sulfamethoxazole-trimethroprim are being recovered with increasing frequency in the United States. We analyzed the penicillin-binding proteins (PBPs), multilocus enzyme electrophoresis (MLEE) genotypes, and ribotypes of 22 multiresistant serotype 23F isolates of S. pneumoniae from the United States and 1 isolate each from Spain and South Africa. Also included were seven multiresistant isolates of other serotypes, three penicillin-resistant but chloramphenicol-susceptible serotype 23F isolates, and two penicillin-susceptible isolates (one penicillin-susceptible isolate was serotype 23F). Fifteen of the 22 multiresistant isolates from the United States and the isolates from Spain and South Africa had identical PBP patterns, MLEE profiles, and ribotypes. Six of the remaining seven multiresistant isolates were related by PBP pattern, but demonstrated slightly different MLEE and/or ribotype profiles, possibly because of acquisition of additional resistance markers (four of the six isolates were also resistant to erythromycin). The remaining multiresistant serotype 23F isolate had a unique PBP pattern and ribotype and was only distantly related to the other pneumococcal isolates by MLEE analysis. The PBP patterns, MLEE profiles, and ribotypes of the multiresistant serotype 23F isolates were easily distinguished from those of six multiresistant isolates of other serotypes; three other penicillin-resistant, chloramphenicol-susceptible, serotype 23F isolates; and two penicillin-susceptible isolates. One exception was a multiresistant serotype 19A isolate that was highly related to the clonal group by PBP pattern and MLEE analysis and that had a ribotype similar to those of the other erythromycin-resistant serotype 23F isolates. MLEE analysis and ribotyping were more discriminating than were the PBP patterns in discerning strain differences. These data strongly suggest that a multiresistant clone of S. pneumoniae serotype 23F that is related to multiresistant isolates from Spain and South Africa has become disseminated in the United States. Clinicians should be alerted to the spread of these multiresistant strains in the United States.

Antimicrobial susceptibility patterns of common and unusual species of enterococci causing infections in the United States. Enterococcal Study Group

We collected 705 isolates of enterococci (1 per patient) from cultures of a variety of anatomic sites from patients at eight tertiary-care hospitals in six geographic regions of the United States. A total of 632 (90%) Enterococcus faecalis, 58 (8%) E. faecium, 5 E. gallinarum, 4 E. avium, 3 E. casseliflavus, 1 E. raffinosus, and 1 E. hirae isolate and 1 biochemical variant of E. faecalis were identified; 606 (86%) of these isolates were associated with clinical infections. The most common sites of isolation were the urinary tract (402 [57%]), nonsurgical wounds (94 [13%]), the bloodstream (74 [10%]), and surgical wounds (62 [9%]). High-level resistance to gentamicin or streptomycin or both was detected in 265 (38%) of the isolates. We identified two E. faecalis isolates resistant to vancomycin (MICs, 32 and 128 micrograms/ml) and 11 beta-lactamase-producing E. faecalis isolates. E. faecium isolates were significantly more resistant than E. faecalis isolates to penicillin, ampicillin, piperacillin, imipenem, and ciprofloxacin (P less than 0.001). The MICs for the 15 non-E. faecalis, non-E. faecium enterococci indicated variable resistance to ciprofloxacin and the penicillins. Antimicrobial susceptibility patterns vary among species of enterococci, and these organisms, while commonly resistant to high-level aminoglycosides, can also acquire resistance to vancomycin or the ability to produce beta-lactamase. Because of these diverse antimicrobial resistance mechanisms, successful treatment and control of enterococcal infections with current antimicrobial agents are becoming increasingly difficult.

Effect of diethyl pyrocarbonate modification on spectral and steady-state kinetic properties of bovine heart cytochrome oxidase

The histidine-specific reagent diethyl pyrocarbonate has been used to chemically modify bovine heart cytochrome oxidase. Thirty-two of sixty-seven histidine residues of cytochrome oxidase are accessible to modification by diethyl pyrocarbonate. Effects on the Soret and alpha bands of the heme spectrum indicate disturbance in the environment of one or both of the heme groups. However, diethyl pyrocarbonate modification does not alter the 830-nm absorbance band, suggesting that the environment of CuA is unchanged. Maximal modification of cytochrome oxidase by diethyl pyrocarbonate results in loss of 85-90% of the steay-state electron transfer activity, which can be reversed by hydroxylamine treatment. However, modification of the first 20 histidines does not alter either activity or the heme spectrum, but only when 32 residues have been modified are the activity and heme spectral changes complete. The steady-state kinetic profile of fully modified oxidase is monophasic; the phase corresponding to tight cytochrome c binding and low turnover is retained, whereas the high turnover phase is abolished. Proteoliposomes incorporated with modified oxidase have a 65% lower respiratory control ratio and 40% lower proton pumping stoichiometry than liposomes containing unmodified oxidase. These results are discussed in terms of a redox-linked proton pumping model for energy coupling via cytochrome oxidase.

Infections and pseudoinfections due to povidone-iodine solution contaminated with Pseudomonas cepacia

In 1989 we investigated the first instance of Pseudomonas cepacia infections due to intrinsic contamination of a povidone-iodine product. Six patients in a Texas pediatric facility had P. cepacia infection or pseudoinfection (three, peritonitis; one, pseudoperitonitis; and two, pseudobacteremia). Epidemiological studies showed one risk factor for infection of peritoneal fluid with P. cepacia: performance of peritoneal dialysis in the dialysis unit with use of one lot of povidone-iodine later found to be intrinsically contaminated (4/5 vs. 0/16, P = .001). Blood cultures yielded P. cepacia after nurses wiped the tops of blood culture bottles with the povidone-iodine solution before inoculation. P. cepacia was cultured from three povidone-iodine containers used at the hospital and from four containers of the same lot obtained from other health-care facilities in Texas and California. Isolates from patients and the povidone-iodine had similar antibiograms, identical plasmid profiles, and identical DNA banding patterns on the basis of results of ribonucleotide typing. This investigation demonstrates that intrinsic contamination of povidone-iodine solution with P. cepacia can result in infections in addition to colonization and/or pseudoinfection.

d-Sotalol has opposite effects from encainide and propafenone on the proportion of episodes of ventricular tachycardia that are sustained in an experimental substrate for reentry

Conversion of sustained ventricular tachycardia (VT) to nonsustained VT may be a potent mode of antiarrhythmic drug action, whereas a drug's conversion of nonsustained VT to sustained VT could produce serious clinical complications. We tested the effects of two class Ic drugs [encainide (1, 2, and 4 microM) and propafenone (0.1, 0.3, and 0.6 microM)) and a class III drug (d-sotalol (25, 50, and 100 microM)] on the proportion of VT episodes that were sustained (duration greater than 1 min) in an acute in vitro model of reentrant VT in left ventricular (LV) epicardium: a Langendorff-perfused rabbit heart whose LV endocardial and midwall cells have been killed by a selective freezing procedure. Multiple VT episodes were generated by increasing the stimulation rate until self-sustained activity occurred. Some episodes spontaneously terminated in less than 1 min; others lasted longer and were terminated by transient cooling of the heart. Both encainide and propafenone increased the fraction of episodes of sustained VT in all preparations; the increase was significant in 4 of the 5 encainide preparations (p less than 0.02) and 4 of the 5 propafenone preparations (p less than 0.003). d-Sotalol, on the other hand, decreased the fraction of sustained VT in all preparations; the decrease was significant (p less than 0.002) in 4 of the 5 preparations. All 3 drugs increased the basic cycle length of pacing at which VT was induced and the cycle time of the resulting VT. These results of this new assay of drug action may be related to the drugs' different mechanisms of prolonging refractoriness.

A cluster of vancomycin-resistant Enterococcus faecium in an intensive care unit

OBJECTIVE

To describe the epidemiology of a cluster of vancomycin-resistant Enterococcus faecium (VAREC) in a cardiothoracic surgery intensive care unit.

DESIGN

A case series of patients identified through review of surveillance data on nosocomial infections, review of microbiologic records, and culture survey of patients in the unit.

RESULTS

Six patients in the cardiothoracic surgery intensive care unit had VAREC with identical antimicrobic susceptibility patterns over a 6-month period. Four patients were identified with VAREC through prospective surveillance and 2 through retrospective review. Prior vancomycin use was seen more commonly in patients with VAREC (6/6, 100%) than in those without VAREC (3/12, 25%) (Fisher's exact test, p = .01). Six of the 7 patients with prior infection developed VAREC (85.7%). A prior nosocomial infection and prior exposure to vancomycin were found to be important variables in a logistic regression analysis. VAREC also was isolated from the environment. A combination of cohorting of patients and staff, and modifications of standard contact isolation practices eliminated the presence of VAREC from the cardiothoracic surgery intensive care unit.

CONCLUSIONS

The results suggest that prior administration of vancomycin, especially in the patient who develops nosocomial infection, can influence the acquisition of vancomycin-resistant enterococci and that VAREC may be transmitted from patient to patient. Using a modification of the standard infection control practice of isolation, we were able to control the spread of this resistant strain of E faecium.

Photochemical and ligand-exchange properties of the cyanide complex of fully reduced cytochrome c oxidase

Cytochrome oxidase, in its fully reduced state, forms a complex with CN having a Kd of 230 microM with a stoicheiometry of 1 CN molecule per cytochrome oxidase. We do not detect a second CN-binding site as seen by i.r. spectroscopy [Yoshikawa & Caughey (1990) J. Biol. Chem. 265, 7945-7958]. The ferrocytochrome a3-CN complex, like the analogous ferrocytochrome a3-CO complex, is photosensitive but with a 15-fold lower quantum yield for photolysis. Analysis of the recombination kinetics after CN photolysis establishes a simple bimolecular binding constant of 235 M-1.s-1, in agreement with the value obtained from stopped-flow studies [Antonini, Brunori, Greenwood, Malmström & Rotillo (1971) Eur. J. Biochem. 23, 396-400]. A rate of 0.07 s-1 for the first-order dissociation of CN from cytochrome a3 is found by the rate of exchange of CO with ferrocytochrome a3-CN, and is consistent with the value calculated from the equilibrium binding constant and the CN on rate. However, O2 is able to oxidize the fully reduced CN compound at a rate well in excess of the CN off rate. The product of this oxidation reaction is a partially reduced CN complex. This implies that O2 either promotes CN dissociation or is able to oxidize the CN-bound enzyme directly. These results are discussed in the context of the structure and dynamics of the ligand-binding site of cytochrome oxidase.

Serratia marcescens surgical wound infection following breast reconstruction

Surgical wound infections due to gram-negative bacilli have been rarely reported following breast implant surgery. From April to November 1989, four patients from one plastic surgeon's practice developed Serratia marcescens surgical wound infection (SWI) following breast reconstruction procedures with implantation of six expandable mammary implants. All six implants were removed for unabated S. marcescens SWI. Symptoms developed 13-161 days (median, 66 days) after surgery. When compared with nonexpandable silicone breast implants used during the period November 1, 1988, to October 31, 1989, expandable implants were associated with a greater risk of S. marcescens SWI (4/10 versus 0/11 patients, p = 0.04). Epidemiologic studies revealed that infection was associated with saline expansion of the implants performed in the surgeon's office. S. marcescens was cultured from a bag of commercial saline used on at least two of the four patients with SWI; the isolate from the saline and the three available patient isolates had identical serotype (O-undetermined:H4) and antimicrobial susceptibility patterns. Review of office procedures revealed that hands were not routinely washed before and aseptic technique was not used during the expansion procedure. Cultures of unopened bags of saline and an unused expandable implant were sterile. We hypothesize that multiple use of saline bags and nonsterile expansion technique extrinsically contaminated saline solutions and resulted in implant and/or surgical site infection. This investigation underscores the importance of avoiding multiple use of solutions intended for single use and of using aseptic technique when manipulating prosthetic devices.

The reaction of the electrostatic cytochrome c-cytochrome oxidase complex with oxygen

The reaction of the electrostatic cytochrome c-cytochrome oxidase complex with oxygen is measured by transient absorption spectroscopy. The oxygen reaction is initiated by photolytic removal of CO from cytochrome oxidase, using a flash-pumped dye laser. The subsequent reaction of the cytochrome c-cytochrome oxidase complex with oxygen is reported at 550, 605, 744, and 830 nm at different cytochrome c:cytochrome oxidase ratios and different oxygen concentrations. In the absence of cytochrome c the time course of the reaction of the oxidase is well described by a triple exponential process at any of the measured wavelengths. The three processes are well resolved at high O2 levels (i.e. greater than 200 microM), where they reach first-order rate limits of 2.4 x 10(4), 7.5 x 10(3), and 650 s-1. When cytochrome c is added the oxidation of cytochrome a and one of the redox active cooper centers (CuA) are interrupted. The maximal effect of cytochrome c on the oxidation of the oxidase occurs at a c:aa3 ratio of 1. Cytochrome c reacts in a biphasic process with rates of up to 7 x 10(3) and 550 s-1 at high oxygen. The fast phase takes up 60% of the process, and this is independent of the cytochrome c:cytochrome oxidase ratio. The results are discussed in the context of a model in which electron entry into cytochrome oxidase from cytochrome c is via CuA, and cytochrome a functions to mediate electron transfer from CuA to the oxygen binding site. The role of CuA as initial electron acceptor in cytochrome c oxidase is related to its physical proximity to cytochrome c is the cytochrome c-cytochrome oxidase complex.

Reentrant tachycardia in a thin layer of ventricular subepicardium: effects of d-sotalol and lidocaine

Ventricular tachycardia (VT) was induced by premature stimulation or fast pacing in 14 Langendorff-perfused rabbit hearts whose left ventricular endocardial and intramural cells had been selectively killed by freezing. VTs were caused by apparent reentrant excitation in the surviving thin (1 mm thick) subepicardial layer of anisotropically oriented cells having ostensibly normal membrane characteristics. During VT, 100 microM d-sotalol (seven hearts) or 30 microM lidocaine (seven hearts) was added to the perfusate. Electrophysiological variables were measured before and during drug exposure at both slow (S1 = 300 ms) and fast (S1 = 150-180 ms) pacing rates. Sotalol prevented VT reinduction in six of seven preparations, compared to only two of seven with lidocaine. Lidocaine prolonged the functional refractory period (FRP) and slowed conduction velocity (CV). Lidocaine prolonged the wavelength of the cardiac impulse (= FRP x CV) by 18% at slow rates but reduced it by 21% at fast rates. Sotalol, however, since it increased the FRP without reducing CV, caused wavelength prolongation at both rates (43% at slow rates, 26% at fast rates). Thus, this VT model may provide an important contrast of class I and class III drug action, with the drug effects on wavelength predicting susceptibility to VT induction.

Epidemiologic typing of Enterobacter sakazakii in two neonatal nosocomial outbreaks

Two unrelated hospital outbreaks of Enterobacter sakazakii, involving meningitis, bacteremia, and colonization of neonates, were investigated. In each of these outbreaks, E. sakazakii was isolated from both patients and dried infant formula. In previous outbreaks, the source and mode of transmission of E. sakazakii in neonatal infections was not determined. In this study, we used a combination of typing methods (plasmid analysis, antibiograms, chromosomal restriction endonuclease analysis, ribotyping, and multilocus enzyme electrophoresis) to evaluate the isolates from each outbreak as to their relatedness. The typing results differed among outbreaks, but in each one, patient and formula isolates shared the same typing pattern. The only exceptions were disk antibiograms, which often varied among colonies selected from each of the isolates. Plasmid analysis, chromosomal restriction endonuclease analysis, ribotyping, and multilocus enzyme electrophoresis all were effective as epidemiological typing methods for E. sakazakii, especially when used in combination. By using this typing scheme, we have confirmed that E. sakazakii from intrinsically contaminated dried infant formula was the source of neonatal infection.

Characterization of reductant-induced, tryptophan fluorescence changes in cytochrome oxidase

We have measured the steady-state tryptophan fluorescence spectrum of cytochrome oxidase in its oxidized and fully reduced states. Reduction of the oxidized enzyme by sodium dithionite causes an apparent shift in the fluorescence emission maximum from 328 nm, in the oxidized enzyme, to 348 nm, in the reduced enzyme. This spectroscopic change has been observed previously and assigned to a redox-linked, conformational change in cytochrome oxidase [Copeland, R. A., Smith, P. A., & Chan, S. I. (1987) Biochemistry 26, 7311-7316]. When dithionite-reduced enzyme sits in an open cuvette, the enzyme returns to the oxidized state, and the fluorescence maximum shifts back to 328 nm. However, the time course of the fluorescence change does not follow the redox state of the enzyme, monitored spectrophotometrically at 445,605, and 820 nm, but follows the disappearance of dithionite, which absorbs at 315 nm. Moreover, when the fluorescence emission spectrum of the dithionite-reduced enzyme is corrected for the absorbance due to dithionite, the fluorescence maximum is found 2 nm blue shifted, relative to that of the oxidized enzyme, at 326 nm. This dithionite-induced, red-shifted steady-state tryptophan fluorescence is also seen with the non-heme-containing enzyme carboxypeptidase A. The tryptophan emission spectrum of untreated carboxypeptidase A is at 332 nm, whereas in the presence of dithionite the emission spectrum of carboxypeptidase A is at 350 nm. When corrected for the absorbance of dithionite, the tryptophan emission maximum is at 332 nm. We have also used the photoreductant 3,10-dimethyl-5-deazaisoalloxazine (deazaflavin) to reduce cytochrome oxidase.(ABSTRACT TRUNCATED AT 250 WORDS)

Enterobacter hormaechei, a new species of the family Enterobacteriaceae formerly known as enteric group 75

The name Enterobacter hormaechei is proposed for a new species of the family Enterobacteriaceae, formerly called Enteric Group 75, which consists of 23 strains, 22 of which were isolated from humans. DNAs from 12 E. hormaechei strains tested were highly related to the type strain (ATCC 49162) by DNA hybridization, using the hydroxyapatite method (80 to 97% in 60 degrees C reactions; 80 to 90% in 75 degrees C reactions). The strains were most closely related (50 to 63%) to Enterobacter cloacae, Enterobacter dissolvens, Enterobacter taylorae, and Enterobacter nimipressuralis. E. hormaechei strains were positive within 48 h for the following: Voges-Proskauer test; citrate utilization (Simmons and Christensen); urea hydrolysis (87%); ornithine decarboxylase; growth in potassium cyanide (KCN); malonate utilization; production of acid from D-glucose, L-arabinose, cellobiose, dulcitol (87%), D-galactose, maltose, D-mannitol, D-mannose, L-rhamnose, sucrose, trehalose, and D-xylose; acid production from mucate; nitrate reduction; and o-nitrophenyl-beta-D-galactopyranoside. Delayed positive reactions were seen in tests for arginine dihydrolase, gas from D-glucose, acid from alpha-methyl-D-glucoside, and acetate utilization. E. hormaechei was negative in tests for indole production; H2S production; phenylalanine deaminase; lysine decarboxylase; gelatin hydrolysis; acid production from D-adonitol, D-arabitol, erythritol, glycerol, i(myo)-inositol, melibiose, raffinose, and D-sorbitol; esculin hydrolysis; DNase; lipase; and tyrosine clearing. Variable reactions occurred in tests for methyl red, motility, and tartrate. All strains tested were susceptible or moderately susceptible to amikacin, azlocillin, cefotaxime, ceftazidime, ceftriaxone, chloramphenicol, gentamicin, mezlocillin, moxalactam, piperacillin, trimethoprim-sulfamethoxazole, sulfisoxazole, thienamycin, tobramycin, and trimethoprim. All strains tested were resistant to nitrofurantoin; the majority were resistant to ampicillin, cefoxitin, and cephalothin. Four isolates were from blood; most other isolates were from wounds or sputum.