Gram-positive cocci, isolated from the feces of koalas and identified as Streptococcus bovis biotype I, formed a distinct clear zone on tannin-treated brain heart infusion agar, suggesting that this isolate has the unique characteristic of degrading the tannin-protein complex.
Pulsed-field gel electrophoresis and lectin blotting were performed on a total of 41 B. longum strains isolated from 27 human fecal samples and 14 probiotic products in order to characterize their clonality and variation in expression of exopolysacchrides (EPSs; cell-bound polysaccharides). The probiotic isolates formed several distinct clonal clusters, and most of them shared the same lectin blotting profile. Almost all human fecal isolates were distinct from the probiotic isolates not only clonally but also in terms of EPS expression. Most of the fecal isolates within each clonal cluster presented different lectin blotting profiles, suggesting that the structures of EPSs from B. longum were of a labile nature independent of their clonality. Lectin blotting was also performed on a total 38 B. longum strains that had been isolated periodically (at the 1st, 23 rd, and 68th weeks) from fecal samples of 12 human subjects in order to evaluate whether EPS expression was host-specific. B. longum strains that had been isolated from fecal samples of the same individual at different times presented identical or almost identical lectin blotting profiles in 9 out of 12 subjects despite being clonally distant from each other. These findings suggest that variations in EPS expression are related to the hosts but not to the strains' clonality. This in turn suggests that human hosts can discriminate indigenous strains from exogenous ones based on EPS expression profiles.
Near infrared spectroscopy (NIRS) is a promising new tool for quick and accurate bacterial quantification in water-rich samples like food. However, we still do not know what this spectroscopic method takes into account in order to measure bacterial counts at food safety limits. This study tries to identify which part of the bacterial culture has a more significant impact on spectral models for bacterial quantification in an aqueous environment. Two type strains of E. coli and S. aureus were evaluated, at a concentration range 0.1–8 log10 CFU. Spectra from bacterial cells, separated by filtration, and extracellular metabolites were acquired separately and then combined in a reciprocal ratio in order to identify the spectral combination that would provide the best partial least squares quantification model for each strain. Spectral data were evaluated in the first wavelength overtone region of water 1300–1600 nm. The best model was achieved at a cells : extracellular metabolites spectral combination ratio of 40 : 60 for the E. coli strain and 20 : 80 for the S. aureus strain. While the best ratio was different for each species, extracellular metabolite spectra had a consistent significantly higher impact on PLS models. It can be concluded that species-specific extracellular metabolite spectra give more valuable information on bacterial quantification, and it is the spectral detection of changes in extracellular water conformations, due to extracellular bacterial metabolites, that represents the most significant factor for successful bacterial quantification. Finding out that bacteria influence the water matrix is an important step in understanding the mechanism of NIRS detection of low bacterial concentrations.
Escherichia coli O157 strains belonging to a distinct lineage and expressing different O-antigen (Oag) lengths were isolated. Although the function of wzz in E. coli has not been adequately investigated, this gene is known to be associated with regulation of Oag length. Using E. coli O157:H7 ATCC43888 (wild-type), several wzz mutants of E. coli O157, including a wzz deletion mutant, were generated and the relationship between the length of Oag modulated by the wzz gene and sensitivities to serum complement investigated. SDS-PAGE, immunoblot analyses and sensitivity tests to human serum complement were performed on these strains. The lengths of the O157-antigen could be modulated by the wzz gene mutations and were classified into long, intermediate and short groups. The short chain mutant was more serum sensitive than the wild-type strain and the other wzz mutants (P < 0.001). In conclusion, Oag chain length modulated by the wzz gene in E. coli O157 influences its sensitivities to serum complement. The present findings suggest that E. coli O157 strains with intermediate or long length Oag chains might show greater resistance to serum complement than those with short chains.
Pulsed-field gel electrophoresis (PFGE) analysis revealed that enterohaemorrhagic Escherichia coli (EHEC) O157:H7 strains had considerable variations in their genomes. This study investigated whether or not the molecular profile of Shiga toxin (Stx) 1- and Stx2-converting phages isolated from EHEC O157:H7 strains, derived from various sources in the USA and Japan, corresponded to the variations of host strains’ genotypes as determined by PFGE. A total of 51 Stx-converting phages including 12 Stx1-converting phages and 37 Stx2-converting phages was isolated from seven USA isolates and 20 Japanese isolates. The average Dice coefficient values showed 44% similarity between phage DNAs in Stx2-converting phages digested with Sma I and 55% in Stx1-converting phages digested with Hin dIII, indicating considerable variation among phage DNA. In particular, restriction fragment length polymorphism (RFLP) patterns of Stx2-converting phage DNA varied according to the PFGE type of their host strain, which suggests that the phage genomes have altered their genotypic characteristics with those of host genomes. However, there are several exceptions: the RFLP patterns of some Stx2-converting phages were quite similar irrespective of the different genotypes of the host strains, indicating that horizontal transfer of Stx2-converting phage may also occur under some circumstances.
Escherichia coli O157 strains starved in sterile deionized water (SDW) and filter-sterilized natural river water (SRW) were investigated with specific reference to their culturability in selective and non-selective media. Growth of the strains starved in both SDW and SRW were markedly suppressed with time in selective liquid media such as modified trypticase soy broth supplemented with novobiocin (mTSB+n) and modified E. coli broth supplemented with novobiocin (mEC+n). This suppression was more pronounced when incubated at 42 C than at 37 C, especially with mEC+n. By contrast, such growth suppression was seldom observed when cultured at 37 C in non-selective liquid media such as trypticase soy broth (TSB) and buffered peptone water. In mEC+n at 42 C, the non-starved cells from overnight cultures with an initial density of less than 10(3) colony-forming units (CFU)/ml grew to the density of over 10(7) CFU/ml after 24 hr incubation, whereas those starved for 6 weeks in SRW were only to maintain their initial density or died off after 24 hr incubation under the same culturing conditions. These results indicated that the isolation of starved cells of E. coli O157 from water samples would be most difficult with selective enrichment or direct plating on the selective plate media. It is thus highly recommended that a "resuscitation" of the cells with non-selective enrichment should be performed as a routine practice for maximum recovery of E. coli O157 from water systems.
A total of 127 road-kills of the swamp wallaby, Wallabia bicolor, on North Stradbroke Island in south-east Queensland was recorded between May 1981 and April 1982. The majority of kills were of adults. Road-kills occurred mainly at night, suggesting that W. bicolor is nocturnal, and were significantly correlated with the number of vehicles brought onto the island by ferries. Faecal pellet counts were made in classified habitats along the road in order to determine the relationship between the population density and road-kills of W. bicolor. Road-kills were significantly correlated with the faecal pellet counts in the Disturbed Ares (narrow, artificially cleared areas adjacent to the road) but not with the counts in the Native Area (i.e. native forest). This indicates that the wallabies were attracted to the disturbed area and became more susceptible to being killed by vehicles. There was no significant variation in the number of road-kills between lunar phases.
We had previously isolated Enterococcus gallinarum AH4, a strain capable of degrading rat milk oligosaccharides. In this study, we determined the whole-genome sequence of AH4. This whole-genome information will expand our understanding of milk oligosaccharide-mediated symbioses between bacteria and host mammals.
