Stable Configurations of Charged Sedimenting Particles.

The qualitative behavior of charged particles in a vacuum is given by Earnshaw's theorem, which states that there is no steady configuration of charged particles in a vacuum that is asymptotically stable to perturbations. In a viscous fluid, examples of stationary configurations of sedimenting uncharged particles are known, but they are unstable or neutrally stable-they are not attractors. In this Letter, it is shown by example that two charged particles settling in a fluid may have a configuration that is asymptotically stable to perturbations for a wide range of charges, radii, and densities. The existence of such "bound states" is essential from a fundamental point of view and it can be significant for dilute charged particulate systems in various biological, medical, and industrial contexts.

Verification of a PCR-based typing method for Acinetobacter baumannii in a pseudo-outbreak investigation.

Acinetobacter spp. isolates were increasingly obtained from clinical specimens and sterility samples, and a subsequent epidemiological investigation implicated an intermittently contaminated supply of commercially acquired enrichment broths. Typing was performed with DNA amplification by the polymerase chain reaction (PCR) using enterobacterial repetitive intergenic consensus sequence primers, ERIC2 and reverse ERIC1R. The reliability of this PCR-based typing method was verified by the ability of the technique to demonstrate homology and differences among isolates from an epidemiologically well-defined pseudo-outbreak.

Oxacillin susceptibility of coagulase-negative staphylococci: role for mecA genotyping and E-test susceptibility testing.

For 115 clinical isolates of coagulase-negative staphylococci which were acquired from 100 patients, we compared the results of routine critical agar dilution susceptibility testing (4% NaCl, 6 mg/ml oxacillin) with mecA gene detection by a polymerase chain reaction amplification. Discrepant results were subsequently reassessed with critical agar dilution testing, repeat mecA genotyping, disc radial diffusion susceptibility testing, E-test and determination of beta-lactamase status. For the initial comparisons, 36 isolates were susceptible and lacked mecA whereas 54 isolates were resistant and had evidence of mecA. Among 17 mecA positive/agar dilution susceptible bacteria, four were clearly resistant by E-test, one isolate had borderline resistance (MIC, 2-4 mg/l), and 12 were resistant when E-test was applied to resistant subpopulations. Initial E-tests facilitated the recognition of the heteroresistant isolates. For eight mecA negative/agar dilution resistant isolates, two were confirmed as oxacillin susceptible and six were mecA positive upon retesting. Although 53.9% had been classified initially as resistant by agar dilution, 67.0% were finally deemed resistant. Critical agar dilution underestimates oxacillin resistance among coagulase-negative staphylococci, and accurate detection of resistance is facilitated by mecA genotyping and E-test.

Markers of virulence among prospectively acquired putative enteropathogenic Escherichia coli serogroups.

We assessed the frequency of proposed enteropathogenic virulence factor genes (eaeA and eaf) by genetic amplification for a series of prospectively collected putative enteropathogenic Escherichia coli serogroup isolates that were acquired from the stool specimens of children. Among 102 isolates, eaeA and eaf markers were determined among 27.5% and 4.9%, respectively. Eaf positivity was found to be coexisting in only a minority of eaeA+ E. coli; the eaeA+/eaf- genotype was most common among strains that had evidence of at least one virulence marker. When clinical variables were compared for two groups of patients whose strains did or did not possess eaeA, the eaeA+ group was more likely to have had an acute diarrheal illness (P = .05) and less likely to have had an underlying chronic illness (P = .03). Localized adherence in vitro was easily recognized for eaeA+/eaf+ E. coli but eaeA+/eaf- isolates were less consistent in manifesting this phenotype. The availability of genetic amplification technologies has the potential to rekindle diagnostic interests in this area, although a rational approach has yet to be defined.

Heterogeneous Serratia marcescens genotypes from a nosocomial pediatric outbreak.

OBJECTIVE: Define the applicability of a rapid molecular typing scheme to study the epidemiology of a Serratia marcescens outbreak. DESIGN: With the assistance of a simple bacterial lysis technique, isolates of S marcescens from a putative outbreak were genotyped with the polymerase chain reaction technology for which primers were chosen on the basis of previously defined enterobacterial repetitive intergenic consensus sequences. SETTING: Pediatric ICU. PATIENTS: Intensively monitored patients who were found to yield S marcescens from any body site during the epidemic period. RESULTS: Over an 8-month period, 12 ICU patients were either infected or colonized with S marcescens. All of these patients were transiently supported by artificial ventilation. During the epidemiologic investigation, a dilution error in a high-level glutaraldehyde disinfectant, which was being used for some ventilator components, was observed. Rectification of the error was associated with an abrupt termination of the outbreak. Enterobacterial repetitive intergenic consensus polymerase chain reaction was easily applicable to this setting and it defined 4 distinct genotypes among the 12 isolates. CONCLUSION: The typing method is easily implemented and offers great promise as an epidemiologic tool. The associated investigation served to emphasize that an outbreak may occur with more than one epidemic strain and that strain heterogeneity itself does not exclude an outbreak.

Correlation of erythromycin agar dilution susceptibility testing with disc diffusion susceptibility for Bordetella pertussis.

Agar dilution and disc diffusion susceptibility testing of erythromycin were performed for contemporary isolates of Bordetella pertussis with the use of charcoal media. Minimum inhibitory concentration (MIC) values ranged from < or = 0.016-0.5 mg/l and the MIC(50) and MIC(95) were 0.125 and 0.25 mg/l respectively. Disc diffusion zone sizes were interpretable after either 48 or 72 h of incubation and all inhibition diameters were > or = 37 mm.

Diagnosis of whooping cough: a new era with rapid molecular diagnostics.

A rapid diagnostic procedure, which is based upon the polymerase chain reaction (PCR) genetic amplification technology, was utilized to establish the presence of Bordetella pertussis in nasopharyngeal washes from children. Overall, 14.7% of 456 specimens were positive by either culture or the rapid assay. Culture and PCR were concordant for 62.7% of positive samples; PCR provided an additional increment of 37.3%. PCR-positive, culture-negative specimens were more likely to be found among older patients with more prolonged illness and previous erythromycin therapy (P < 0.01 for all three comparisons). As a single laboratory assay, PCR should be recognized as the current standard for diagnosis.

Insertional sequence primers for Bordetella pertussis diagnostic polymerase chain reaction differentiate strains of Pseudomonas cepacia.

Insertion sequence primers originally intended to amplify a singular specific product for the rapid diagnosis of Bordetella pertussis respiratory infection were used to differentiate strains of Pseudomonas (Burkholderia) cepacia. A modified sample preparation of proteinase K treatment and boiling was used in lieu of DNA extraction. The method was simple, rapid, and reproducible. This scheme identified 10 variations among 35 strains. Repeat strains from patients with cystic fibrosis and epidemiologically linked strains from an infection associated with a jet gun injection device were homologous in each setting.

Selective media for isolation of Burkholderia (Pseudomonas) cepacia from the respiratory secretions of patients with cystic fibrosis.

One hundred and six specimens from 90 patients with cystic fibrosis were evaluated for the presence of Burkholderia cepacia using a current routine diagnostic protocol as well as a research protocol involving polymyxin B-MacConkey agar without crystal violet, PC agar, OFPVL agar, and a selective brain-heart infusion broth. Ten specimens from eight patients (8.9%) were positive by any method. The selective enrichment broth was the only medium that yielded B cepacia from all 10 positive samples, although the routine protocol was successful for eight of these. Transient carriage was identified in one patient. Epidemiological studies may be better served by the use of selective enrichment rather than selective solid media alone. Carrier status for B cepacia requires more strict definition if positive carrier status is to be accepted as having medical importance.

Appraisal of the stability of leukocytes in refrigerated urine.

There is limited evidence that urinary leukocytes are rapidly destroyed in alkaline hypotonic urine. We assessed the stability of leukocytes in urine specimens provided by 90 children with neurogenic bladder who attended a meningomyelocele clinic. No significant correlation was found between urine specific gravity and leukocyte survival after an interval of 4 h in a sample of 30 specimens from these patients. The survival of leukocytes was determined at 2 h and at 4 h in aliquots of these 30 specimens directly, and after adjustment to pH values of 5.0, 7.0, 8.0, 8.5, and 9.0. Statistically significant leukocyte destruction only occurred at pH 9.0 at 2 h (16%), at pH 8.5 at 4 h (19%), and at pH 9.0 at 4 h (57%). Only one of a further sample of 180 routine specimens had both a pH of > or = 8.5 and an interval to laboratory examination of > 2 h. No specimen had a specific gravity of < 1.002, and 93.9% had values of > or = 1.005. Urine pH and tonicity were not therefore important determinants of leukocyte stability in refrigerated samples examined within 4 h from this clinic population.

Implications of Yersinia enterocolitica biotyping.

The utility of a simple biotyping scheme to differentiate pathogenic and non-pathogenic strains of Yersinia enterocolitica was determined for 79 patients who were admitted to or attended a reference children's hospital in western Canada. Biotyping defined predominantly two subsets of Y enterocolitica. 'Pathogenic' strains were more likely to have been obtained from younger patients (mean age 61.9 months) who experienced an acute gastrointestinal illness that was occasionally associated with bloody diarrhoea or a surgical procedure. Growth of Y enterocolitica from selective solid bacteriological growth media were often in the moderate to heavy range (82.0%). In contrast, 'non-pathogenic' strains were more often obtained from older patients (mean 116.0 months) who were already recognised to have suffered from a chronic illness and who were likely to have been admitted to hospital. Moderate to heavy growth of bacterium in stool specimens were infrequently (17.4%) obtained from the latter patients. The use of a simple biotyping scheme for the differentiation of Y enterocolitica strains has the potential to improve patient care.

Invasive Streptococcus pyogenes infections in children.

We investigated the epidemiology and clinical features of invasive S. pyogenes infection in a pediatric population over a 7-year period (1984-90) by retrospective review. An increasing frequency in invasive infections had occurred (0-11.81/10,000 admissions). A large proportion (48%) of these were orthopedic infections. An epidemic strain was typed as M1T1. This increase appears to have occurred in the context of an overall increase in S. pyogenes infections ("scarlet fever" 1.47-11.22/10,000 outpatients; "strep throat" 4.41-46.54/10,000 outpatients).

Assessment of the BACTEC NR660 blood culture system for the detection of bacteremia in young children.

The sensitivity of the BACTEC NR660 blood culture system was assessed by using paired bottles of anaerobic (NR7A) and resin-containing aerobic (NR16A) media and conditions and organisms which simulated those found in pediatric practice. Corresponding media (7D and 16B) of the established BACTEC 460 radiometric method served as controls. The performances of the two systems were similar with 50 isolates of 10 aerobic organisms (aerobic medium) and with 21 isolates of 15 strict anaerobes (anaerobic medium).

SIGNAL blood culture system for detection of bacteremia in neonates.

In the SIGNAL (Oxoid Ltd., Basingstoke, United Kingdom) blood culture system, gas produced by bacterial metabolism displaces medium from the culture bottle into an upper reservoir via a hollow needle. Displacement of media may provide a visual indication of the presence of both aerobic and anaerobic organisms in a single medium. The single-bottle SIGNAL system was compared with paired BACTEC 16B and 7D (Johnston Laboratories, Inc., Towson, Md.) radiometric system bottles by using bacterial inocula and conditions which simulated those found in neonatal and pediatric populations. The single SIGNAL bottle was a good as the combined BACTEC media for Escherichia coli and Staphylococcus aureus, but was slower for Candida spp., Haemophilus influenzae, Pseudomonas aeruginosa, Staphylococcus epidermidis, group B streptococci, alpha-streptococci, and pneumococci. The SIGNAL system failed to detect four of five isolates of Neisseria meningitidis and four of eight anaerobic organisms. The SIGNAL system is not suitable for neonatal blood cultures at its present state of development.

Inoculation of API-20E from positive blood cultures.

The API-20E system (Analytab Products, Inc., Plainview, N. Y.) was inoculated from 4- to 6-h tryptic soy broth cultures that had been inoculated from positive blood cultures containing gram-negative bacilli. This method gave the same genus and species identification for 139 of 140 organisms (47 patient and 96 simulated positive cultures) when compared to the Analytab Products, Inc., recommended method of inoculation.