Identification of a structural determinant for resistance to beta-lactam antibiotics in Gram-positive bacteria

Streptococcus pneumoniae is the main causal agent of pathologies that are increasingly resistant to antibiotic treatment. Clinical resistance of S. pneumoniae to beta-lactam antibiotics is linked to multiple mutations of high molecular mass penicillin-binding proteins (H-PBPs), essential enzymes involved in the final steps of bacterial cell wall synthesis. H-PBPs from resistant bacteria have a reduced affinity for beta-lactam and a decreased hydrolytic activity on substrate analogues. In S. pneumoniae, the gene coding for one of these H-PBPs, PBP2x, is located in the cell division cluster (DCW). We present here structural evidence linking multiple beta-lactam resistance to amino acid substitutions in PBP2x within a buried cavity near the catalytic site that contains a structural water molecule. Site-directed mutation of amino acids in contact with this water molecule in the "sensitive" form of PBP2x produces mutants similar, in terms of beta-lactam affinity and substrate hydrolysis, to altered PBP2x produced in resistant clinical isolates. A reverse mutation in a PBP2x variant from a clinically important resistant clone increases the acylation efficiency for beta-lactams and substrate analogues. Furthermore, amino acid residues in contact with the structural water molecule are conserved in the equivalent H-PBPs of pathogenic Gram-positive cocci. We suggest that, probably via a local structural modification, the partial or complete loss of this water molecule reduces the acylation efficiency of PBP2x substrates to a point at which cell wall synthesis still occurs, but the sensitivity to therapeutic concentrations of beta-lactam antibiotics is lost.

Epileptic seizures progressing into nonepileptic conversion seizures

BACKGROUND

Epileptic and nonepileptic seizures can occur in the same patient, but usually occur at different times. In 1885, Gowers suggested that minor seizures can elaborate into hysterical seizures, but the concurrence of epileptic and nonepileptic seizures is not well documented.

METHODS

We reviewed all patients with nonepileptic seizures documented with video-EEG recordings at our center to identify those with temporally associated epileptic seizures.

RESULTS

Four patients were identified in whom video-EEG-documented epileptic seizures were temporally associated with nonepileptic seizures. In one woman, the nonepileptic event followed an absence seizure. Given the high frequency of absence seizures, the occurrence of the nonepileptic seizure may have been coincidental. In three patients, the seizures were partial and arose from right frontotemporal regions. In these patients, epileptic seizures were infrequent.

CONCLUSIONS

Epileptic and nonepileptic seizures can be temporally related, and in patients with partial seizures, there may be a pathophysiologic relation in which ictal changes facilitate the development of conversion symptoms. Ictal activation or disinhibition of emotions or impulse control may contribute to these nonepileptic events.

Relative impact of oxidative stress on the functional competence and genomic integrity of human spermatozoa

Reactive oxygen metabolites are known to disrupt sperm-oocyte fusion, sperm movement, and DNA integrity; however, the relative sensitivities of these elements to oxidative stress are unknown. In this study these factors were assessed in human spermatozoa exposed to increasing levels of oxidative stress achieved through the stimulation of endogenous oxidant generation with NADPH or direct exposure to hydrogen peroxide. At low levels of oxidative stress, DNA fragmentation was significantly reduced while the rates of sperm-oocyte fusion were significantly enhanced. As the level of oxidative stress increased, the spermatozoa exhibited significantly elevated levels of DNA damage (p < 0.001) and yet continued to express an enhanced capacity for sperm-oocyte fusion. At the highest levels of oxidative stress, extremely high rates of DNA fragmentation were observed but the spermatozoa exhibited a parallel loss in their capacities for movement and oocyte fusion. These studies emphasize how redox mechanisms can either enhance or disrupt the functional and genomic integrity of human spermatozoa depending on the intensity of the oxidative stimulus. Because these qualities are affected at different rates, spermatozoa exhibiting significant DNA damage are still capable of fertilizing the oocyte. These results may have long-term implications for the safety of assisted conception procedures in cases associated with oxidative stress.

A zinc based self setting ceramic bone substitute for local delivery of testosterone

Testosterone has been shown to stimulate bone healing. However, large doses of testosterone are associated with liver damage and prostate enlargement. Continuous release of testosterone at the traumatized bone site could enhance healing without inducing systemic side effects. In this investigation a self-setting zinc sulfate calcium phosphate (ZSCAP) ceramic with and without testosterone was used to fill experimentally induced bone defects in rats. Each treatment group consisted of six albino, Holtzman rats. Groups I and II consisted of non-operated and sham-operated animals. Rats in Group III, IV, V, and VI were implanted with ZSCAP particulate ceramic powders (63-75 microns) containing 0.0, 0.5, 1.0, or 1.5 mg testosterone in a 2.3 mm defect in the femur of each rat. Radiographic and morphologic examination of the implant site at four, eight, and twelve weeks post surgery showed integration of the implant in the femur of each rat. Serum testosterone of all rats was assayed at four, eight, and twelve weeks post surgery. Differences in the serum testosterone levels of rats in the six groups were not significant. Results of this study suggest that a ZSCAP-testosterone composite can be used to repair traumatized bone without increasing the levels of testosterone in the systemic circulation.

Prestimulus EEG alpha phase synchronicity influences N100 amplitude and reaction time

The influence of the level of prestimulus alpha phase synchronicity on the N100 component and reaction time (RT) was examined, in target auditory oddball data from 25 normal subjects. Alpha phase synchronicity is a new measure consisting (for a given stimulus presentation) of the angular or circular variance of the alpha phase at stimulus onset across the parieto-occipital sites. The lower the angular variance, the higher the phase synchronicity (the more closely in phase the alpha activity across these sites) and vice versa. Subaveraged event-related potentials (ERPs) were formed for high and low prestimulus alpha phase synchronicity stimulus presentations. N100 amplitude was significantly greater in the high than the low phase synchronicity subaverages. In addition, RT was significantly reduced in the high prestimulus alpha phase synchronicity cases. Alpha phase synchronicity reflects an aspect of brain state that influences subsequent stimulus processing.

Fast and slow reaction times and associated ERPs in patients with schizophrenia and controls

A number of studies have examined across-trial averaged late component. Event Related Potentials (EPR) and Reaction Times (RT) in response to multiple target stimuli. In this study, within-trial relatively fast and slow sub averages are additionally examined, in 20 patients with schizophrenia and 20 age and sex matched controls. A conventional auditory oddball paradigm. Across-trial ERP average analysis showed smaller N200 amplitude and delayed latency (but larger P200 amplitude) in patients with schizophrenia compared with controls. Within-trial ERP analysis revealed a number of additional findings. Controls showed distinctive differences in fast compared with slow ERP sub averages (smaller P200 amplitude, increased N200/P300 amplitudes and earlier latencies). The schizophrenic group on the other hand, showed relatively similar fast versus slow subaverages (no differences in P200 amplitude and N200 latency). In addition, between-group (within-trial) analyses highlighted significant differences in earlier stages of processing (compared with across-trial averages) in both fast and slow subaverages (increased N100 amplitude in controls). The complementary within-trial (compared with across-trial) data are interpreted with respect to a possible disturbance in inhibitory function in patients with schizophrenia.

Hydroepithelial Keratectomy in Rabbits with a Waterjet-based Instrument

BACKGROUND

Corneal epithelial removal finds multiple applications in ophthalmic surgery (epithelial herpes infections, recurrent epithelial erosion, corneal ulcers and plaques, and intraoperative epithelial clouding). Photorefractive keratectomy is initiated by removal of the epithelium. Current techniques for epithelial removal are suboptimal. We studied the safety and effectiveness of a new technique, hydroepithelial keratectomy, performed with the HydroBrush keratome on live rabbits.

METHODS

Eighteen rabbits (18 eyes) underwent hydroepithelial keratectomy and 18 rabbits (18 eyes) underwent epithelial removal with a surgical blade (blade group). Twelve rabbits were euthanized immediately after the procedure. Twenty-four rabbits were followed for up to 120 hours after treatment. Ultrastructural analysis was performed with light and electron microscopy.

RESULTS

The hydroepithelial keratectomy group healed a mean 53 hours after treatment; the blade group healed a mean 78 hours after treatment. The HydroBrush keratome exposed the basement membrane and the basal cell membrane of the epithelium. The blade exposed patches of basement membrane, as well as stroma and cell debris.

CONCLUSIONS

Hydroepithelial keratectomy with the HydroBrush keratome is effective and safe. Wound healing after hydroepithelial keratectomy is faster than after blade removal. Unlike the blade, the HydroBrush keratome exposed a smooth surface, devoid of debris, with well-defined edges and round shape without hydration nor dehydration of the tissue.

Hepatitis C virus-specific CTL responses in PBMC from chimpanzees with chronic hepatitis C: determination of CTL and CTL precursor frequencies using a recombinant canarypox virus (ALVAC)

The aim of this study was to evaluate HCV-cytotoxic T lymphocyte response from PBMC in bulk CTL assays and in CTL precursor analyses using in vitro stimulation with canarypox virus (ALVAC) expressing HCV-capsid/E1/E2/NS2/NS3 antigens. Canarypox virus is naturally host-range restricted and does not replicate or cause cytopathology on mammalian cells. PBMC were obtained from four chimpanzees with chronic hepatitis C infection and one uninfected chimpanzee. CTL from bulk culture of PBMC and CTL precursor frequencies were found in three of the four chronically infected chimpanzees using ALVAC in vitro stimulation. No CTL response was detected in PBMC from the uninfected chimpanzee. The precursor frequencies of CTL specific for capsid, NS2 and NS3 proteins ranged between 1/2663 and 1/27202. No correlation was observed between percent cytolysis in bulk culture and CTL precursor frequencies. This method may prove useful in assessing the correlation between HCV-CTL response and virological or histological status.

Principles and Microscopic Confirmation of Surface Quality of Two New Waterjet-based Microkeratomes

PURPOSE

The HydroBlade and the HydroBrush keratomes are waterjet-based devices for corneal surgery that operate at normal intraocular pressure in two different modes: removal of parallel or shaped lenticules or hinged flaps with a small diameter, high speed waterjet; and removal of the epithelium with a waterjet sheet. The operating principles as well as histology of the cut surfaces are described.

METHODS

A flap was made in one cadaver eye with a Chiron ACS keratome and in the second eye with the HydroBlade keratome. The epithelium was removed in one cadaver eye with a surgical blade and in the second eye by the HydroBrush keratome. Scanning and transmission electron microscopy and light microscopy was obtained.

RESULTS

The HydroBlade keratome cleaved only cross-linking fibrils and left intact keratocytes. Shape and dimensions of the flap were accurate. There was no observable hydration or significant heating of the tissue. Mechanical forces on the cornea were small. The HydroBrush keratome removed the epithelium quickly, left no epithelial debris, and did not damage Bowman's layer.

CONCLUSION

With the HydroBlade keratome, the cuts are ideal blunt dissections. Epithelial removal with the HydroBrush keratome is effective and quick.

Dynamic spectral analysis of event-related potentials

This paper presents a new method for the identification of individual event related potential (ERP) components in both frequency and time domains. Using the similar basis function (SBF) algorithm the method provides a time to frequency transform, representing a frequency domain equivalent of the component waveform. Notable features of the SBF algorithm are that it allows for unevenly spaced sampled functions in both the time and frequency domains, and estimates of spectral densities are obtained by numerical computation of finite Fourier integrals. Application of this method to ERP data from 20 normal subjects demonstrated a similar shape of component amplitude frequency characteristics for traditional late component waveforms (N1, P2, N2 and P3). On this basis, a low-frequency band was found where the component amplitude frequency characteristic was described by a Gaussian function, while the component phase frequency characteristic was a linear function of frequency. These relationships are interpreted as frequency domain equivalents of the component. Transformed to the time domain, they provided an analytical description of the ERP as the sum of positive- and negative-going monopolar waves. The study points to similar mechanisms underlying these component waveforms, and analytically defines dynamic properties for the components both in the frequency and time domains.

Late components of the event-related potentials and their topography in Parkinson's disease

Late components of the event-related potential (ERP; N100, P200, N200, and P300) were elicited using an auditory oddball paradigm (with a button-press response to target stimuli) in 15 Parkinson's disease (PD) patients and 50 normal control subjects. Compared with control subjects, PD subjects showed a significant decrease in N200 amplitude. Between-group topographical differences in N200 amplitude were evident at central (C3, Cz, C4) and temporal (T5, T3, T4, T6) regions. The results may reflect a deficit in response selection in PD possibly resulting from a dysfunction associated with the abnormalities in the central and temporal regions found to have a decreased N200 amplitude compared with normal control subjects in this study.

EEG alpha phase at stimulus onset significantly affects the amplitude of the P3 ERP component

Analysis of the relationship between prestimulus EEG alpha phase and the subsequent ERP has proved difficult because of the non-Euclidean nature of phase measurements. In this study, we employed a conventional P3 templating method of single-trial analysis to identify the P3 component in target auditory oddball data from 25 normals. As in previous studies, the absence or near absence of P3 from a subset of single-trials was clearly demonstrated. We investigated this phenomenon to determine whether those single-trials with a large P3 had a different prestimulus alpha phase from those with a small or no P3. Statistical analysis of phase required the use of circular statistical analysis and the development of a new form of topographic mapping, circular topography. The alpha phase at stimulus onset in single-trials with a large P3 was significantly different from that in single-trials with a small or no P3 (p = .02).

Fast and slow reaction time changes reflected in ERP brain function

A number of studies have examined the average late component Event Related Potential (ERP) and Reaction Time (RT) in response to multiple target stimuli (across-trial averages). This study demonstrates within-trial differences in ERP brain function associated with relatively fast and slow RTs in 50 normal subjects. A conventional auditory oddball paradigm (with a 1 ISI) was employed. Increased ERP N100 and N200 amplitude (and decreased P200 amplitude), as well as earlier P200, N200 and P300 latency were found in the fast compared with the slow ERP subaverages. These results show the potential to elucidate temporal and spatial dynamics of brain function associated with changes in performance, in conventional "cognitive" paradigms applicable to both health and disease states.

Quantified EEG activity in adolescent attention deficit hyperactivity disorder

The aim of this study was to explore elements of the maturational and cortical hypoarousal models in adolescent ADHD, by examining EEG activity in a rest eyes open condition, in 26 adolescent unmedicated ADHD males and 26 age and sex matched normal controls. ADHD adolescents were found to have increased anterior EEG absolute theta activity and reduced posterior relative beta activity compared with controls. These results lend some support to the continuation of a maturational lag and reduced cortical arousal in adolescent ADHD. These measures need to be further explored using concomitant EEG with electrodermal measures of arousal.

Dysfunctions of automatic (P300a) and controlled (P300b) processing in Parkinson's disease

P300 Event Related Potentials components (P300a and P300b) were investigated using an auditory oddball paradigm (with a button press response to target stimuli) in 15 Parkinson's disease patients and 50 normal controls whilst simultaneously measuring electrodermal activity. Cluster analysis showed that the first 10 target stimuli generated the largest skin conductance responses. The first 10 single-trial ERP epochs were therefore analysed as an ERP sub-average for each individual. The P300a component (associated with the automatic 'Orienting Reflex') was expected to be most prevalent in this sub-average (compared with sub-averages of subsequent blocks of 10 target stimuli). Twenty-nine out of 50 normal controls (58%) elicited a P300a in the first 10 target sub-average, compared with only 2 out of 15 Parkinson's disease subjects (13%). The conventional P300b component (associated with controlled processing) was found to be significantly delayed for all sub-averages for the Parkinson's disease group when compared with controls. These preliminary findings suggest a possible dysfunction in both automatic and controlled processing in this disorder.

Automatic processing dysfunction in Parkinson's disease

Simultaneous measures of Event Related Potentials (ERP) and electrodermal activity (EDA) allow the delineation of ERPs that did, and did not, evoke an electrodermal 'Orienting Reflex' (OR). The OR is an automatic reflex invoked by novel or significant stimuli. Our group have developed a model to quantify electrodermal OR activity acquired in conventional late component ERP paradigms with short interstimulus intervals. Target late component (N100, P200, N200, P300) ERPs (acquired in an auditory oddball paradigm) and EDA was examined in 15 Parkinson's disease (PD) subjects and 50 normal controls. Single-trial target ERPs were averaged according to whether or not they elicited an electrodermal OR. Compared with controls, the PD group showed significantly decreased N100 and N200 amplitudes in the OR related ERPs ('Orienting ERPs'). These preliminary findings suggest that conventional late component ERPs can be delineated according to whether or not they evoked an OR. The 'orienting ERPs' in PD showed more significant disturbances compared with controls, than ERPs that did not evoke an OR.

Single trial variability within the P300 (250-500 ms) processing window in adolescents with attention deficit hyperactivity disorder

The traditional averaging process used to derive event related potential components (ERPs) is a soundly based method of determining the underlying ERP. Averaging, however, ignores the variability due to the single-trial ERPs that constitute the traditional average ERP. This variability may reflect complementary functional information to the average measure. Our group applied a simple procedure, the response variance curve (RVC), which measures single-trial ERP variability relative to their average. In this study, the average ERP and RVC measures (generated from the same single-trial task-relevant target ERPs) were assessed in an auditory oddball paradigm, in 17 unmedicated male adolescents with attention deficit hyperactivity disorder (ADHD) and in 17 age- and sex-matched normal controls. P300 amplitude, latency and point of maximum variability of the RVC were measured within the P300 processing window (250-500 ms post-stimulus). There were no significant differences in P300 amplitude or latency between the groups. Unmedicated ADHD patients, however, showed significantly increased single-trial variability within the P300 window compared with controls. This variability was significantly reduced with stimulant medication.

Serious brain injury from traffic-related causes: priorities for primary prevention

This study evaluated the incidence and outcome of serious brain injury from traffic-related causes in 695 patients admitted to the Department of Neurosurgery at Karolinska Hospital during 1981-1992. A total of 37.3% of patients were car occupants, 28.1% pedestrians, 12.9% bicyclists, 12.2% car-bicycle/car-moped and 9.5% motorcycle riders. The dominating injury was brain contusion (61.6%) verified with computerized tomography. The level of consciousness was evaluated by the Glasgow Coma Scale (GCS) and outcome by the Glasgow Outcome Scale (GOS) at discharge and 6-36 months thereafter. The final outcome was 67.5% good recovery (GOS 4-5), 11.5% severely disabled (GOS 2-3) and 21.0% GOS 1 or brain dead. Patients with GOS < 4 (32.5%) were severely disabled and motivate priorities for injury prevention. Car occupants represent 40.7% of the total, followed by pedestrians at 33.6% and bicyclists at 18.2%. Much remains to be done in the primary prevention of disabling brain injury to car occupants and pedestrians. In order to achieve a more-effective primary prevention, future research should be directed toward biomechanical aspects of brain contusion as a dominating brain injury.

Evoked related potentials associated with and without an orienting reflex

Late component event related potentials (ERP) and concomitant electrodermal activity (EDA) measures of the orienting reflex (OR) were undertaken in 50 normal subjects. Our group recently developed a model to quantify electrodermal activity in conventional ERP paradigms (auditory oddball) with short interstimulus intervals (ISI). The method was used to classify the presence or absence of skin conductance response following each auditory target stimulus. Using a conventional paradigm in which data is traditionally averaged, single-trial target ERPs were sorted into those with a skin conductance response OR (ERP[+OR]) and those without (ERP[-OR]) an OR, and ERP sub-averages of the two groups were derived. The ERP(+OR) showed significantly larger P300 amplitudes and relatively earlier N200 and P300 latency than those of the ERP(-OR). These findings suggest that using concomitant SCR-ERP measures, separate ERP related processes can be determined, that are complementary to the traditional average measure.

To scale or not to scale: McCarthy and Wood revisited

We dispute McCarthy and Wood's (1985) claim that some form of scaling should be applied routinely to ERP data before determining differences in scalp distributions between conditions (or groups). Their simulation study involved assumptions about the nature of the variability within each condition, most significantly that the standard deviations are identical at all electrodes, irrespective of the means. Alternative plausible assumptions may be proposed for which scaling is unnecessary. Furthermore, we show that the two main forms of scaling they proposed may distort or even completely eliminate real differences in scalp topography reflecting genuinely different underlying sources.

Hiding worries from One's spouse: associations between coping via protective buffering and distress in male post-myocardial infarction patients and their wives

The relationship between protective buffering, a style of coping in which the individual hides his/her concerns from spouse, and level of distress was studied among post-myocardial infarction (MI) patients and their spouses. Forty-three male married MI survivors and their wives completed measures of psychological distress and protective buffering at 4 weeks and 6 months post-hospital discharge. At both time periods, a greater propensity for protective buffering by the patient was related to higher levels of patient distress. Protective buffering by wife was also associated with higher levels of wife distress. In addition, patient buffering at 4 weeks predicted increased patient distress at 6 months. The results suggest that male MI patients who conceal their worries from their spouses adjust more poorly over time.

Decomposing skin conductance into tonic and phasic components

Overlapping phasic skin conductance responses (SCRs) obtained using short interstimulus interval (ISI) paradigms such as those employed in cognitive research, confound measurement of each discrete phasic SCR as well as the tonic skin conductance level (SCL). We report a method of resolving this problem using a modelling technique that takes advantage of the stereotyped nature of the within-subject SCR waveform. A four-parameter sigmoid-exponential SCR model that describes the entire response, was developed and extended to five-, six- and eight-parameter skin conductance (SC) models. These SC models were successfully curve-fitted to more than 60 SC segments, each containing one SCR or two overlapping SCRs on a sloping baseline obtained from 20 normal subjects. The SC segments were consequently decomposed into their components: the tail of the previous response, one or two SCRs and the SCL. The SCRs free of the complication of overlap were then quantified. The raw SCRs of the same data set were also measured using a standard method. The standard measurement showed a significant reduction of 15% in amplitude and 140 ms in peak latency compared to our method. The basic four SCR model parameters--onset time, rise time, decay time constant and gain--showed increasing inter-subject variability in that order. These SCR model parameters may be studied as variables in normal and patient groups and as indices of treatment response. This quantitative method also provides a means to assess the relationships between central and autonomic psychophysiologic measures.