Bacillus subtilis is the best-characterized member of the Gram-positive bacteria. Its genome of 4,214,810 base pairs comprises 4,100 protein-coding genes. Of these protein-coding genes, 53% are represented once, while a quarter of the genome corresponds to several gene families that have been greatly expanded by gene duplication, the largest family containing 77 putative ATP-binding transport proteins. In addition, a large proportion of the genetic capacity is devoted to the utilization of a variety of carbon sources, including many plant-derived molecules. The identification of five signal peptidase genes, as well as several genes for components of the secretion apparatus, is important given the capacity of Bacillus strains to secrete large amounts of industrially important enzymes. Many of the genes are involved in the synthesis of secondary metabolites, including antibiotics, that are more typically associated with Streptomyces species. The genome contains at least ten prophages or remnants of prophages, indicating that bacteriophage infection has played an important evolutionary role in horizontal gene transfer, in particular in the propagation of bacterial pathogenesis.
A new multiplex PCR assay was developed to separate the four major Listeria monocytogenes serovars isolated from food and patients (1/2a, 1/2b, 1/2c, and 4b) into distinct groups. The PCR test, which constitutes a rapid and practical alternative to laborious classical serotyping, was successfully evaluated with 222 Listeria strains.Listeria monocytogenes is a facultative intracellular pathogen that can cause serious illness in susceptible individuals. Persons with specific immunocompromising conditions, pregnant women, newborns, and the elderly are particularly at risk for listeriosis (9, 23). Although rare, listeriosis remains of great public health concern due to its high mortality rate (20 to 30%) (16). Ingestion of contaminated foods is considered to be the primary source of infection for both sporadic and epidemic human listeriosis cases (19). Because of the importance of L. monocytogenes strain characterizations for epidemiological investigations, a number of discriminatory subtyping methods have been described for this organism (2,4,5,18,20,24,25). Pulsed-field gel electrophoresis (PFGE) typing, which has provided the most sensitive strain discrimination up to now, has rapidly become the standard subtyping method to detect listeriosis outbreaks (4, 11). However, this method is labor-intensive and time-consuming and thus for practical purposes is often preceded by serotyping. Since all major outbreaks of the invasive form of listeriosis are due to serovar 4b strains, an infrequent serovar in foods compared to 1/2a strains (6, 9), the procedure adopted for outbreak investigations relies upon serovar characterization to provide valuable information for rapid screening of groups of strains. Indeed, the serovar information allows discrimination between isolates probably belonging to an outbreak and those that are not part of the outbreak and thus decreases the number of strains which need to be characterized by PFGE in order to improve discrimination beyond the serovar level. Moreover, serotyping is widely used for long-term microbiological surveillance of human listeriosis. For the food industry, where the presence of L. monocytogenes is a big concern, tracing contaminating strains within the food chain and the plant environment is of primary importance. Again serotyping is often used as a first-line typing method. Although 13 serovars are described for the species L. monocytogenes, at least 95% of the strains isolated from foods and patients are of serovars 1/2a, 1/2b, 1/2c, and 4b (12,21,22). Routine analysis of L. monocytogenes by serotyping with traditional agglutination methods is limited by cost, availability, and the need for technical expertise to perform the assay. Furthermore, the reproducibility of serotyping is not always satisfactory. Schonberg et al. (20) concluded in a multicenter study that a critical need exists for high-quality antisera. A new enzyme-linked immunosorbent assay serotyping format used in conjunction with a commercially available kit to make serotyping more efficient and more ...
A multilocus sequence typing (MLST) system was developed for group B streptococcus (GBS). The system was used to characterize a collection (n ؍ 152) of globally and ecologically diverse human strains of GBS that included representatives of capsular serotypes Ia, Ib, II, III, V, VI, and VIII. Fragments (459 to 519 bp) of seven housekeeping genes were amplified by PCR for each strain and sequenced. The combination of alleles at the seven loci provided an allelic profile or sequence type (ST) for each strain. A subset of the strains were characterized by restriction digest patterning, and these results were highly congruent with those obtained with MLST. There were 29 STs, but 66% of isolates were assigned to four major STs. ST-1 and ST-19 were significantly associated with asymptomatic carriage, whereas ST-23 included both carried and invasive strains. All 44 isolates of ST-17 were serotype III clones, and this ST appeared to define a homogeneous clone that was strongly associated with neonatal invasive infections. The finding that isolates with different capsular serotypes had the same ST suggests that recombination occurs at the capsular locus. A web site for GBS MLST was set up and can be accessed at http://sagalactiae.mlst.net. The GBS MLST system offers investigators a valuable typing tool that will promote further investigation of the population biology of this organism.Streptococcus agalactiae, group B streptococcus (GBS), is an important human pathogen. It is the leading cause of neonatal sepsis in the United Kingdom (18) and the United States (23). It is regarded as an emerging pathogen in the elderly (13) and is a frequent cause of maternal sepsis. However, GBS is usually a commensal organism and can be isolated from the genitourinary and gastrointestinal tracts of up to 35% of healthy adults (1).Capsular serotyping has been one of the mainstays in the descriptive epidemiology of GBS. Nine capsular serotypes have been described (Ia, Ib, and II to VIII). Serotype III GBS strains are of particular importance, as they are responsible for the majority of infections, including meningitis, in neonates worldwide (22). Diverse lineages of serotype III strains can be distinguished with multilocus enzyme electrophoresis (12, 19), pulsed-field gel electrophoresis (20), and restriction digest pattern (RDP) analysis (2), and the lineages appear to vary in pathogenic potential.Multilocus sequence typing (MLST) is an unambiguous sequence-based typing method that involves sequencing approximately 500-bp fragments of seven housekeeping genes and has been used successfully to type strains and investigate the population structure of a number of human bacterial pathogens, including Neisseria meningitidis (16) and Streptococcus pneumoniae (9). MLST is particularly suitable for epidemiological studies because it provides data that can easily be compared between laboratories over the Internet.The primary aim of this study was to develop an MLST system for GBS. Secondary aims were to show that the system could be used on a di...
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