Dipstick test for rapid diagnosis of Shigella dysenteriae 1 in bacterial cultures and its potential use on stool samples

BACKGROUND

We describe a test for rapid detection of S. dysenteriae 1 in bacterial cultures and in stools, at the bedside of patients.

METHODOLOGY/PRINCIPAL FINDINGS

The test is based on the detection of S. dysenteriae 1 lipopolysaccharide (LPS) using serotype 1-specific monoclonal antibodies coupled to gold particles and displayed on a one-step immunochromatographic dipstick. A concentration as low as 15 ng/ml of LPS was detected in distilled water and in reconstituted stools in 10 minutes. In distilled water and in reconstituted stools, an unequivocal positive reaction was obtained with 1.6×10⁶ CFU/ml and 4.9×10⁶ CFU/ml of S. dysenteriae 1, respectively. Optimal conditions to read the test have been determined to limit the risk of ambiguous results due to appearance of a faint yellow test band in some negative samples. The specificity was 100% when tested with a battery of Shigella and unrelated strains in culture. When tested on 328 clinical samples in India, Vietnam, Senegal and France by laboratory technicians and in Democratic Republic of Congo by a field technician, the specificity (312/316) was 98.7% (95% CI:96.6-99.6%) and the sensitivity (11/12) was 91.7% (95% CI:59.8-99.6%). Stool cultures and the immunochromatographic test showed concordant results in 98.4 % of cases (323/328) in comparative studies. Positive and negative predictive values were 73.3% (95% CI:44.8-91.1%) and 99.7% (95% CI:98-100%).

CONCLUSION

The initial findings presented here for a simple dipstick-based test to diagnose S. dysenteriae 1 demonstrates its promising potential to become a powerful tool for case management and epidemiological surveys.

Microbacterium binotii sp. nov., isolated from human blood

Two strains of non-spore-forming, rod-shaped, Gram-positive bacteria, CIP 101303(T) and CIP 102116, were isolated from human blood in 1976 and 1977, respectively. These strains had chemotaxonomic markers that were consistent with classification in the genus Microbacterium, i.e. MK-10, MK-11 and MK-12 as the major menaquinones, predominant iso- and anteiso-branched cellular fatty acids, galactose, mannose and rhamnose as the cell-wall sugars and ornithine as the diamino acid in the cell-wall peptidoglycan. The DNA G+C content was 70-72 mol%. Comparative 16S rRNA gene sequence studies revealed that strains CIP 101303(T) and CIP 102116 belonged to the genus Microbacterium and that they were related closely to Microbacterium halotolerans. The level of DNA-DNA relatedness showed that the two isolates represented a separate genomic species. Based on phenotypic and genotypic results, it is proposed that strains CIP 101303(T) and CIP 102116 be assigned to a novel species, Microbacterium binotii sp. nov. The type strain is CIP 101303(T) (=DSM 19164(T)).

Arthrobacter bergerei sp. nov. and Arthrobacter arilaitensis sp. nov., novel coryneform species isolated from the surfaces of cheeses

Fourteen isolates of two different bacterial species isolated from the surface of smear-ripened cheeses were found to exhibit many characteristics of the genus Arthrobacter. The isolates were aerobic, Gram-positive, catalase-positive, non-spore-forming and non-motile. The cell-wall peptidoglycan contained lysine, alanine and glutamic acid. rrs sequence analysis indicated that the new isolates Re117T and Ca106T are closely related to the Arthrobacter nicotianae group and showed highest sequence similarity (>98 %) to Arthrobacter nicotianae and Arthrobacter protophormiae. However, DNA-DNA hybridization studies indicated that the strains represented two novel genomic species within the genus Arthrobacter and did not belong to A. nicotianae or A. protophormiae (<43 % DNA-DNA relatedness). On the basis of the phylogenetic and phenotypic distinctiveness of the new isolates, these bacteria should be classified as two novel Arthrobacter species, for which the names Arthrobacter bergerei sp. nov. and Arthrobacter arilaitensis sp. nov. are proposed. Type strains have been deposited in culture collections as Arthrobacter bergerei Ca106T (=CIP 108036T=DSM 16367T) and Arthrobacter arilaitensis Re117T (=CIP 108037T=DSM 16368T).

Taxonomic characterization of nine strains isolated from clinical and environmental specimens, and proposal of Corynebacterium tuberculostearicum sp. nov

Nine unidentified Gram-positive, lipophilic corynebacteria were isolated from clinical and food samples and subjected to a polyphasic taxonomic analysis. The bacteria were distinguished from Corynebacterium species with validly published names by biochemical tests, fatty acid content and whole-cell protein analysis. Comparative 16S rRNA gene sequence analysis demonstrated unambiguously that the nine strains were related phylogenetically to the species ‘Corynebacterium tuberculostearicum’ and represented a distinct subline within the genus Corynebacterium. On the basis of both phenotypic and phylogenetic evidence, the formal description of Corynebacterium tuberculostearicum sp. nov. is proposed. The type strain of C. tuberculostearicum is Medalle XT (=LDC-20T=CIP 107291T=CCUG 45418T=ATCC 35529T).

Clonal diversity among streptogramin A-resistant Staphylococcus aureus isolates collected in French hospitals

We analyzed 62 clinical isolates of streptogramin A-resistant (SGA(r)) Staphylococcus aureus collected between 1981 and 2001 in 14 hospitals located in seven French cities. These isolates, including five with decreased susceptibility to glycopeptides, were distributed into 45 antibiotypes and 38 SmaI genotypes. Each of these genotypes included between 1 and 11 isolates, the SmaI patterns of which differed by no more than three bands. Although numerous clones were identified, we observed the spread of monoclonal isolates either within the same hospital or within hospitals in distinct cities and at large time intervals. Hybridization with probes directed against 10 SGA(r) genes (vatA, vatB, vatC, vatD, vatE, vgaA, vgaB, vgaAv, vgbA, and vgbB) revealed six patterns: vgaAv (21 isolates), vatA-vgbA (24 isolates), vgaAv-vatB-vgaB (14 isolates), vgaAv-vatA-vgbA (1 isolate), vgaAv-vatA-vgbA-vatB-vgaB (1 isolate), and vgaA (1 isolate). We detected at least one SGA(r) determinant in all of the tested isolates. vgaAv, which is part of the recently characterized transposon Tn5406, was found in 59.7% of the tested isolates. Of the 16 streptogramin B-susceptible isolates, 14 carried vgaAv alone and were susceptible to the mixtures of streptogramins, whereas the 2 isolates carrying vgaAv-vatB-vgaB were resistant to these mixtures. vatA-vgbA was found on plasmids of the same apparent size in 26 (42%) of the tested clinical isolates from 18 unrelated SmaI genotypes. The possible dissemination of some of the multiple clones characterized in the present study with an expected increased selective pressure of streptogramins following the recent licensing of Synercid (quinupristin-dalfopristin) must be carefully monitored.

[First confirmed case of laryngeal diphtheria in Djibouti]

The first bacteriologically confirmed case of laryngeal diphtheria in Djibouti was reported in 1998. It involved a three-year-old native-born infant who had been vaccinated during the first year of life with three doses of a combined vaccine against diphtheria, tetanus, poliomyelitis, and pertussis. A rapid clinical improvement was observed under erythromycin treatment. Other cases of laryngeal diphtheria have been observed. It is important to reverse decreasing vaccinal coverage in Djibouti and to warn incoming travelers of the need to be adequate immunized against diphtheria. Enhanced epidemiologic surveillance of this disease is also needed.

Comparison of traditional and molecular methods for typing nontoxigenic strains of Corynebacterium diphtheriae

Thirty-eight nontoxigenic strains of Corynebacterium diphtheriae isolated between 1987 and 1992 from clinical specimens of French patients were typed by biotyping, antibiograms, bacteriophage typing, ribotyping, and restriction analysis by pulsed-field gel electrophoresis (PFGE). Excellent correlation occurred between the genotypes defined by PFGE SfiI profiles or by ribotype BstEII profiles. Genotyping revealed seven genotype patterns among the 26 biotype mitis isolates, five among the nine biotype gravis isolates, and three among the three biotype belfanti isolates. Phage typing was nonreactive for nine of the 38 isolates. A combination of all the typing methods led to the identification of 19 different types of Corynebacterium diphtheriae.

Clinical and molecular study of Corynebacterium diphtheriae systemic infections in France. Coryne Study Group

Diphtheria is a disease with a long history that almost completely disappeared from developed countries. In addition, until 1987, systemic infections involving Corynebacterium diphtheriae were rare. However, in 1990, an epidemic occurred in Russia. These two circumstances have provided the stimulus to gain insight into the situation in France. In fact, between 1987 and 1993, a total of 59 C. diphtheriae strains were isolated. Epidemiological data were collected for patients from whom 40 strains were isolated from normally sterile sites, including 34 from blood cultures, and half of the bacteremic patients developed endocarditis. Osteoarticular involvement was noted in 11 of these 40 patients, including 5 bacteremic patients. The fatality rate following bacteremia was 36%, despite specific antibiotic treatment (beta-lactams and aminoglycosides). The mean age of the participants was 38 years, with half of the patients subsisting under low socioeconomic conditions and suffering from homelessness or alcoholism. Apparently, the skin turned out to be the major route of transmission in this reemerging disease. Eighty-eight percent of the isolates belonged to the C. diphtheriae biotype mitis. These were found predominantly in the Paris area, and most were of the same ribotype. Those isolates originating from the overseas territories (Guyana and New Caledonia) belonged to C. diphtheriae biotype gravis. No strains were positive for the tox gene by PCR. This study attests to the persistent circulation in France of C. diphtheriae in the form of systemic infections. The matter is especially significant since these strains are nontoxigenic and are of a unique ribotype. The strains are, however, sensitive to most antibiotics, although 20% are rifampin resistant.

Apport des méthodes de typage dans l'étude des souches de Corynebacterium diphtheriae

Corynebacterium diphtheriae is the causative agent of Diphtheria. This bacteria circulates throughout the world. Recently, two outbreaks occurred in New independent states (Russia, Ukraine...) and Algeria. Routine technics permit to study the strains of Corynebacterium diphtheriae : biotype, antibiotype, toxin gene detection. However, molecular biological tests (ribotyping, and pulsed field gel electrophoresis) are necessary to characterize these strains in the space and the time. The studies with international laboratories exchanges are recents and have permitted first results concerning the molecular epidemiology of C. diphtheriae strains.

Corynebacterium seminale sp. nov., a new species associated with genital infections in male patients

We studied 12 coryneform isolates having similar biochemical profiles which did not permit their assignment to any recognized taxa. Human semen was the source for seven of these strains, whereas the other strains were isolated from urethra, urine, and blood specimens of adult male patients. These bacteria were found in significant quantities (10(4) to 10(5) CFU/ml) in semen specimens from infertile male patients with the diagnosis of prostatitis. These strains had characteristics of the genus Corynebacterium, such as 60 mol% G + C in the DNA and corynemycolic acids, meso-diaminopimelic acid, arabinose, and galactose in the cell wall. Quantitative DNA-DNA hybridizations (S1 nuclease procedure) and phylogenies based on comparisons of almost-complete small-subunit ribosomal DNA sequences confirmed that these strains constitute a single new species within the genus Corynebacterium. All 12 strains showed similar phenotypic features, i.e., good growth on sheep blood agar in contrast with poor growth on the same medium supplemented with 1% Tween 80, a positive CAMP test in the presence of Staphylococcus aureus, glucose and sucrose fermentation, and the presence of beta-glucuronidase. Some strains reduced nitrate and hydrolyzed urea or esculin. These features allowed us to distinguish these strains from members of any other coryneform taxon, and the proposed name is Corynebacterium seminale with strain IBS B12915 (CIP 104297) as the type strain. The description and delineation of these strains as a new species should be useful for further studies, including evaluations of their prevalence among the normal flora and their clinical implications.

Corynebacterium argentoratense sp. nov., from the human throat

A new Corynebacterium species, Corynebacterium argentoratense was isolated from the throats of four human patients. It is characterized by the presence of chemotype IV, a cell wall, corynomycolic acids, and a G+C content ranging from 60 to 61 mol%. Strains belonging to this species exhibit high levels of DNA relatedness as determined by DNA-DNA hybridization experiments (S1 nuclease procedure) but no close DNA relatedness with related Corynebacterium species. Phylogenies based on comparative analyses of nearly complete small-subunit rDNA sequences confirmed the inclusion of this new species within the genus Corynebacterium and grouped it in a cluster with C. diphtheriae, C. ulcerans, C. pseudotuberculosis, and C. kutscheri. PCR experiments revealed an absence of the gene coding for diphtheria toxin. This new species can be identified by its mycolic acid pattern, fermentation of sugars, and enzymatic activities. Strain IBS B10697 (CIP 104296) is the type strain of C. argentoratense.

Polymerase chain reaction assay for diagnosis of potentially toxinogenic Corynebacterium diphtheriae strains: correlation with ADP-ribosylation activity assay

We have developed a polymerase chain reaction assay for the clinical diagnosis of potentially toxinogenic strains of Corynebacterium diphtheriae, the causative agent of diphtheria. A 910-bp amplification product, overlapping a DNA portion encoding both fragments of the diphtheria toxin, has been found in 28 among the 36 strains tested. In addition, effective toxin production, as evidenced by the ability of bacterial culture supernatants to ADP ribosylate eukaryotic elongation factor 2, was determined. In every case, the presence of an amplification product correlated with an ADP-ribosylation activity, thus confirming the diagnosis. The polymerase chain reaction assay herein described is very rapid (2 h) compared with the Elek immunodiffusion test or the guinea pig lethality test. It can provide a convenient and reliable method for laboratories involved in the identification of toxinogenic corynebacteria.

Comparative chemotaxonomic studies of mycolic acid-free coryneform bacteria of human origin

Forty-two clinical isolates were classified as Corynebacterium minutissimum, Corynebacterium striatum, and Corynebacterium CDC group I by the API Coryne system. The chemotaxonomic characteristics of the isolates were determined by thin-layer chromatographic analysis. Twenty-six isolates were found to have a type IV cell wall (meso-di-aminopimelic acid arabinose, galactose) but did not contain mycolic acids. These 26 isolates shared chemotaxonomic characteristics with those of mycolic acid-free reference strains (including the Corynebacterium amycolatum NCFB 2768 type strain, "Corynebacterium asperum," and coryneform CDC groups I2 and F2). The total protein profiles of the isolates determined by sodium dodecyl sulfate-polyacrylamide gel electrophoresis were similar to each other and to that of the C. amycolatum type strain. The profiles of the reference strains "Corynebacterium asperum" (CIP 100836, CIP 80.54, CIP 79.37, CIP 52.13), coryneform bacteria CDC groups I2 and F2 (CDC F5771, F5890, G723, G1970), and C. amycolatum were closely related. Thus, the mycolic acid-negative strains with a chemotype IV wall may belong to a single taxon. DNA hybridization studies could confirm this hypothesis. The present study shows the importance of chemotaxonomic analysis for verifying strain identifications and completing results from biochemical tests, particularly for coryneform bacteria.

In vitro susceptibility of Corynebacterium group D2 and Corynebacterium jeikeium to twelve antibiotics

The in vitro susceptibility of 83 Corynebacterium group D2 strains and 44 Corynebacterium jeikeium strains to 12 antimicrobial agents was determined by an agar dilution technique using Mueller-Hinton agar supplemented with Tween 80 (0.025%). All strains of Corynebacterium group D2 were highly sensitive to fusidic acid, pristinamycin, teicoplanin and vancomycin (geometric mean MICs 0.047, 0.048, 0.338 and 0.396 mg/l respectively). Most of the strains were resistant to other antibiotics tested (ciprofloxacin, erythromycin, gentamicin, lincomycin, rifampin and tetracycline). However, a few strains were highly sensitive (MICs less than or equal to 0.2 mg/l). The overall pattern of susceptibility of 44 strains of Corynebacterium jeikeium was similar; the geometric mean MICs of fusidic acid, pristinamycin, vancomycin and teicoplanin were 0.234, 0.235, 0.557 and 0.652 mg/l respectively.

[Kingella denitrificans endocarditis on an aortic valve prosthesis]

Kingella denitrificans is a Gram-negative bacillus which does not grow readily on the usual media. This organism, normally a commensal of the upper airways, may exceptionally be responsible for endocarditis. We report here the sixth case known in the literature. Cure was obtained with an intravenous combination of vancomycin and rifampicin.