Imaging of shear waves induced by Lorentz force in soft tissues.

This study presents the first observation of elastic shear waves generated in soft solids using a dynamic electromagnetic field. The first and second experiments of this study showed that Lorentz force can induce a displacement in a soft phantom and that this displacement was detectable by an ultrasound scanner using speckle-tracking algorithms. For a 100 mT magnetic field and a 10 ms, 100 mA peak-to-peak electrical burst, the displacement reached a magnitude of 1 µm. In the third experiment, we showed that Lorentz force can induce shear waves in a phantom. A physical model using electromagnetic and elasticity equations was proposed. Computer simulations were in good agreement with experimental results. The shear waves induced by Lorentz force were used in the last experiment to estimate the elasticity of a swine liver sample.

Passive elastography of the esophagus: from model to preliminaryin-vivoexperiments using diameter measurements.

Numerous diseases alter the esophagus elasticity, such as eosinophilic esophagitis and esophageal motility disorders like achalasia. The possibility to measure these modifications using minimally invasive techniques is a key issue for the diagnosis of such pathologies. The commercially available EndoflipTM(endoluminal functional lumen imaging probe) can be used to measure the luminal cross-sectional diameter of the esophagus at different points and over time, and is used in clinical routine to assess esophageal distensibility. We used this probe to track the propagation of shear waves similar to those that are produced naturally by natural waves, to compute wavelength of the esophagus using passive elastography algorithms. To assess the feasibility of such measurements, we compared the wavelengths obtained with the probe in polyvinyl alcohol (PVA) gel tubes to those obtained for the same tubes with optical tracking of their edges using a camera. We first compared the wavelength obtained with homogeneous gel tubes with both techniques, and then used paired gel tubes of different elasticities to investigate the possibility to measure different wavelengths. Although, the wavelength computed using the probe and the camera showed some small differences, qualitative differentiation of the tubes was achieved when using paired tubes with different elasticities. Using the camera, a wavelength of 61 mm was measured for the hard tube, and 35 mm for the soft tube. Using the probe, wavelengths of 61 mm and 38 mm were measured, respectively. Therefore, we demonstrate here the feasibility of using this probe to track wave propagation and to determine the wavelengths in gel tubes of different stiffnesses. This analysis was also taken to a preliminaryin-vivostudy that allowed tracking of natural waves in the esophagus using the luminal probe, which indicates that this technique can also be usedin vivoto measure the stiffness of the esophagus.

Location of the three major agglutinogens of Bordetella pertussis by immuno-electronmicroscopy.

When the three serotypes of Bordetella pertussis (types 1,2,3; 1,2 and 1,3) were labelled with agglutinins and protein-A gold, agglutinogen 1 was found on fimbriae and on the cell surface of types 1,2,3 and 1,2 but on the cell surface only of non-fimbriate type 1,3 organisms. In contrast, agglutinogen 2 was located on fimbriae only. Agglutinogen 3 was not labelled. When protein-A gold was replaced by immunoglobulin-G gold, agglutinogen 3 was found on the cell surface only, even of fimbriate bacteria of type 1,2,3. The implications of these findings for acellular vaccines are discussed.

Inhibitory effect of saliva from secretors and non-secretors on binding of meningococci to epithelial cells.

Carriage of Neisseria meningitidis B:4:P1.15 was higher among non-secretors during a school outbreak of meningitis; non-secretors had lower levels of anti-meningococcal salivary IgM. Flow cytometry was used to assess effects of secretor and non-secretor saliva on binding of B:4:P1.15 to buccal epithelial cells: (1) to assess inhibition by IgA and IgM; and (2) to assess contributions of salivary antibodies to inhibitory activities. Greater inhibition was obtained with secretor saliva: pooled (P = 0.049); fresh (P = 0.0001). Purified IgA (P = 0.02) and IgM (P = 0.03) were equally inhibitory. After absorption of anti-meningococcal antibodies, there was still significant inhibitory activity in the pools: secretors (P = 0.018); non-secretors (P = 0.005). These results indicate that both secretory immunoglobulins and other factors contribute to protection against colonisation by meningococci and might explain the increased carriage of B:4:1.15 in this population.

Serum bactericidal activity in a secondary school population following an outbreak of meningococcal disease: effects of carriage and secretor status.

Sera obtained from 106 children following an outbreak of Neisseria meningitidis (B:4:P1.15) were screened for bactericidal antibodies against isolates of meningococci and Neisseria lactamica. Most had high titres of antibodies to N. lactamica and N. meningitidis NG:4:- but not to capsulate isolates: B:4:P1.15; B:15:P1.16; B:4:-; C:4:-. Bactericidal activity was higher for both carriers and secretors but the differences were not significant. Bactericidal activity was not associated with total or specific IgA or IgM. Carriers had significantly higher levels of IgG to N. lactamica but not to NG:4:- in sera with bactericidal activity for each of the capsulate strains. Among non-carriers, higher levels of IgG to N. lactamica were associated with killing of B:4:P1.15 and B:4:-. Secretors' sera with bactericidal activity had significantly higher levels of IgG to N. lactamica compared with sera that were not bactericidal. This was not observed among non-secretors. Antibodies to the outbreak strain were adsorbed by all Neisseria isolates tested and absorption of sera with N. lactamica alone completely removed the bactericidal activity against the outbreak strain.

Toxigenic bacteria and sudden infant death syndrome (SIDS): nasopharyngeal flora during the first year of life.

Many developmental and environmental risk factors for sudden infant death syndrome (SIDS) are similar to those for susceptibility to respiratory tract infection, and toxigenic bacteria have been implicated in some SIDS cases. We assessed nasopharyngeal flora of healthy infants in relation to risk factors to determine which species best lit the mathematical model proposed for the common bacterial toxin hypothesis and if these findings complemented results obtained from SIDS cases which occurred during the period of the survey. Longitudinal studies were carried out between April 1993 and March 1996 on 253 healthy infants and their mothers. 150 from a multiply deprived area, 103 from an affluent area. Concurrent SIDS infants (37) were screened for nasopharyngeal flora. Among healthy infants < or = 3 months of age, the predominant isolate was Staphylococcus aureus 57% compared with 86% for SIDS infants in that age range (P< 0.02). There were significant associations between isolation of different species from both mother and baby but no association between isolation of any species with: area of residence: parental smoking habits; breast or bottle feeding; symptoms of viral infection: seasonality. We conclude that S. aureus fits the mathematical model for SIDS. Both staphylococci and/or their toxins were identified in a significant proportion of SIDS cases. Isolation of staphylococci from healthy infants was associated with the 2-4-month age range, a risk factor consistently found in all epidemiological studies of SIDS. This might reflect the developmental stage in which 80-90% of infants express the Lewis(a) antigen which we have shown to be one of the receptors for S. aureus.

The protective effect of immunisation against diphtheria, pertussis and tetanus (DPT) in relation to sudden infant death syndrome.

Epidemiological evidence indicates infants immunised against diphtheria, pertussis and tetanus (DPT) are at decreased risk of sudden infant death syndrome (SIDS). Asymptomatic whooping cough and pyrogenic toxins of Staphylococcus aureus have been implicated in the aetiology of SIDS. The objectives of the present study were: (1) to determine if the DPT vaccine induced antibodies cross-reactive with the staphylococcal toxins; (2) to determine if antibodies to the pertussis toxin (PT) and the staphylococcal toxins were present in the sera of women during late pregnancy; (3) to examine the effects of infant immunisation on levels of antibodies to PT and the staphylococcal toxins; (4) to assess the effects of changes in immunisation schedules in the UK on the incidence and age distribution of SIDS. Enzyme-linked immunosorbent assays (ELISA) were used to measure binding of rabbit or human IgG to the DPT vaccine, PT, toxic shock syndrome toxin-1 (TSST-1) and staphylococcal enterotoxins A (SEA), B (SEB) and C (SEC). Neutralisation activity of anti-DPT serum was assessed by a bioassay for induction of nitric oxide from human monocytes by the staphylococcal toxins. Anti-DPT serum bound to the DPT vaccine, PT and each of the staphylococcal toxins. It also reduced the ability of the four toxins to induce nitric oxide from monocytes. In pregnant women, levels of IgG to PT, SEC and TSST-1 decreased significantly in relation to increasing weeks of gestation while antibodies to SEA and SEB increased. In infants' sera there were significant correlations between levels of IgG bound to DPT and IgG bound to PT, TSST-1 and SEC but not SEA or SEB. Antibody levels to the toxins in infants declined with age; sera from infants < or = 2 months of age had higher levels of IgG bound to the toxins than those older than 2 months. This pattern was observed for infants whose immunisation schedules began at 2 months of age or 3 months of age. The decrease in IgG bound to the toxins was, however, less for those immunised at 2 months. The decrease in SIDS deaths after the change in immunisation schedules was greatest in the 4-6-month age range. While DPT immunisation might prevent some unexplained infant deaths due to asymptomatic whooping cough, these data indicate that immunisation with DPT also induces antibodies cross-reactive with pyrogenic staphylococcal toxins implicated in many cases of SIDS. Passive immunisation of infants who have low levels of these antibodies might reduce further the numbers of these infant deaths.

Detection of pyrogenic toxins of Staphylococcus aureus in sudden infant death syndrome.

It has been suggested that pyrogenic toxins of Staphylococcus aureus are involved in the series of events leading to some cases of sudden infant death syndrome (SIDS). The objectives of the study were to screen tissues from SIDS infants for pyrogenic toxins and to compare incidence of identification of these toxins among these infants from different countries. An enzyme-linked immunosorbent assay (ELISA) and a flow cytometry method were used to screen body fluids and frozen or formalin-fixed tissues for pyrogenic toxins of S. aureus, toxic shock syndrome toxin 1 (TSST), staphylococcal enterotoxins A (SEA), B (SEB), and C1 (SEC). Toxins were identified in tissues of 33/62 (53%) SIDS infants from three different countries: Scotland (10/ 19, 56%); France (7/13, 55%); Australia (16/30, 53%). In the Australian series, toxins were identified in only 3/19 (16%) non-SIDS deaths (chi2 = 5.42, P < 0.02). The flow cytometry method was useful for toxin detection in both frozen and fixed tissues, but ELISA was suitable only for frozen tissues or those fixed for less than 12 months. Identification of pyrogenic toxins in > 50% of SIDS infants from three different countries indicated further investigation into the role the toxins play in cot deaths might result in development of additional measures to reduce further the incidence of these infant deaths.

Bacterial toxins and sudden unexpected death in a young child.

The sudden unexpected death of a six year old child following an upper respiratory tract infection is reported. Laboratory investigations revealed the presence of staphylococcal toxic shock syndrome toxin-1 (TSST-1) in samples of brain tissue. The significance of this finding is discussed.

Trends in nosocomial bloodstream infections in a burn intensive care unit: an eight-year survey.

This study was designed to evaluate the frequency and profile of bloodstream infection (BSI) in a burn intensive care unit (BICU) in Tripoli, Libya, from 1st January 2000 to 31st December 2007 and to determine the prevalence of different bacteria involved in such infections and their antimicrobial susceptibilities. During the eight-year study period, 995 patients were admitted to the BICU. Blood cultures were collected from each septicaemic case and reviewed for age, sex, total body surface area burned, isolated micro-organisms, and antibiotic sensitivity. There were 430 episodes of BSI among 830 cases; the annual true positive rate varied between 40.0 and 59.4%, the majority (87.9%) being caused by one species only. However, 22% had two or more episodes with different pathogens during hospitalization. The leading isolate was Staphylococcusaureus (40.4%) (methicillinresistant, 55.7%). Pseudomonas spp ranked second (23.9%). Klebsiella spp were third, responsible for 7.4%; the rate of extended spectrum beta lactamase among Klebsiella isolates was 47%. Candida spp were the fourth most common pathogen (6.7%), the majority (55%) being C. albicans. Staphylococci were generally resistant to trimethoprim (91%) and fusidic acid (80%). Pseudomonas spp proved moderately resistant (38-43%) to tobramicin, ciprofloxacin, amikacin, and impenem but remained relatively susceptible to cefepime (72%). Klebsiella isolates demonstrated moderate resistance (46-58%) to most agents tested, and relatively low resistance (19-27%) to meropenem, impenem, and cefepime. We suggest that extra infection control measures should be implemented and antibiotic policy and guidelines introduced to reduce the high resistance rate among isolates such as Pseudomonas, Acinetobacter, and MRSA.

Inducible Clindamycin Resistance among Staphylococci Isolated from Burn Patients.

Clindamycin has been used successfully to treat pneumonia and soft-tissue infections caused by methicillin-resistant Staphylococcus aureus. However, inducible clindamycin resistance has been described as a cause of treatment failure of such infections. A total of 159 staphylococcal isolates from different clinical specimens from burn patients in Tripoli Burn Center were tested for inducible clindamycin resistance by the disk-diffusion induction test. Inducible clindamycin resistance was detected in 66.2% of 65 methicillin-resistant S. aureus isolates and in none of 55 methicillin-sensitive S. aureus, 10 methicillin-resistant coagulase negative staphylococci and 29 methicllin-sensitive coagulase negative staphylococci isolates. In our setting, clindamycin can be used for the treatment of infections due to staphylococci, but we recommend that staphylococci isolates, particularly methicillin-resistant S. aureus, are tested by the D-test before treatment.

A profile and spectrum of four cases of methicillin-resistant Staphylococcus aureus in a burns intensive care unit.

This report describes and evaluates four patients with hospital-acquired methicillin-resistant Staphylococcus aureus (MRSA) and Pseudomonas infections at the Burns and Plastic Surgery Hospital, in Libya, between August 1999 and August 2002. Neither rifampicin nor vancomycin was used to treat these patients. Inhalation injury with major burns (> 60% total body surface area), a major degree of burns (3rd degree), and septicaemia caused by both MRSA and multi-resistant P. aeruginosa invariably proved fatal. One patient responded well to antibiotic therapy, but the other three died in spite of similar therapy. Vancomycin and rifampicin should be established as the first choice to treat MRSA infection, and infected wounds need aggressive management with antibiotics prior to skin grafting.

Secretor status and humoral immune responses to Neisseria lactamica and Neisseria meningitidis.

Non-secretors of ABO blood group antigens are over-represented among patients with meningococcal diseases. Lower levels of secretory IgA reported for non-secretors have been suggested to compromise mucosal defences. Total serum and salivary IgG, IgA and IgM and levels of these isotypes specific for Neisseria lactamica and five isolates of meningococci were determined by ELISA for 357 pupils and staff of a secondary school in which an outbreak of meningitis occurred. There were no differences in total or specific levels of serum IgG, IgA or IgM or salivary IgG or IgA of secretors compared with non-secretors. Non-secretors had significantly lower levels of salivary IgM (P = 0.022). A similar pattern was observed for levels of IgM specific for N. lactamica and five meningococcal isolates. The significance of these results is discussed with reference to the role of secretory IgM in protection of mucosal surfaces in infants.

The type IV bundle-forming pilus of enteropathogenic Escherichia coli undergoes dramatic alterations in structure associated with bacterial adherence, aggregation and dispersal.

BFP, a plasmid-encoded type IV bundle-forming pilus produced by enteropathogenic Escherichia coli (EPEC), has recently been shown to be associated with the aggregation of bacteria and dispersal of bacteria from bacterial microcolonies. In standard 3 h HEp-2 cell assays, EPEC adhere in localized microcolonies; after 6 h, bacterial microcolonies are no longer present, indicating that bacterial aggregation and dispersal occurs in vitro during EPEC adhesion to cultured epithelial cells. To examine the role of BFP in EPEC aggregation and dispersal, we examined HEp-2 cell adhesion of strain E2348/69 and defined E2348/69 mutants by immunofluorescence and immunoelectron microscopy. BFP was expressed initially as approximately 40 nm diameter pilus bundles that promoted bacteria-bacteria interaction and microcolony formation. BFP subsequently underwent a striking alteration in structural organization with the formation of much longer and thicker ( approximately 100 nm diameter) pilus bundles, which frequently aggregated laterally to form even thicker bundles often arranged in a loose three-dimensional network; EPEC dispersal from bacterial microcolonies was associated with this transformation of BFP from thin to thick bundles. Bacterial dispersal and transformation of BFP from thin to thick bundles did not occur with a bfpF mutant of strain E2348/69. It is concluded that BFP promotes both the formation and the dispersal of EPEC microcolonies, that the dispersal phase requires BfpF and that dispersal is associated with dramatic alterations in the structure of BFP bundles.