In Vitro Adhesion of N2-Fixing Enteric Bacteria to Roots of Grasses and Cereals

Nitrogen-fixing Klebsiella and Enterobacter strains isolated from several plants were assayed for fimbriae and for adhesion to plant roots in vitro. All eight Klebsiella strains formed type 3 fimbriae, and five strains also formed type 1 fimbriae; all 21 Enterobacter strains had type 1 fimbriae. Three strains of Klebsiella carrying either type 1, type 3, or no fimbriae were used as model organisms in developing an in vitro adhesion test. Adhesion was assayed with bacterial cells labeled with [³H]leucine. Fifteen N₂-fixing strains and the three model strains were compared for adhesion to the roots of seven grasses and five cereals. Type 3-fimbriated Klebsiella strains adhered better than the other strains, and type 3 fimbriae appeared to be major adhesins for the Klebsiella strains. Although variations between plants were observed, no host specificity for bacterial adhesion was found.     

Identification by PCR of Fusarium culmorum Strains Producing Large and Small Amounts of Deoxynivalenol

Thirty deoxynivalenol-producing F. culmorum strains, isolated from wheat grains, were incubated in vitro and analyzed for trichothecene production. Seventeen strains produced more than 1 ppm of deoxynivalenol and acetyldeoxynivalenol and were considered high-deoxynivalenol-producing strains, whereas 13 F. culmorum strains produced less than 0.07 ppm of trichothecenes and were considered low-deoxynivalenol-producing strains. For all strains, a 550-base portion of the trichodiene synthase gene (tri5) was amplified and sequenced. According to the tri5 data, the F. culmorum strains tested clustered into two groups that correlated with in vitro deoxynivalenol production. For three high-producing and three low-producing F. culmorum strains, the tri5-tri6 intergenic region was then sequenced, which confirmed the two separate clusters within the F. culmorum strains. According to the tri5-tri6 sequence data, specific PCR primers were designed to allow differentiation of high-producing from low-producing F. culmorum strains.     

Characterization and Determination of Origin of Lactic Acid Bacteria from a Sorghum-Based Fermented Weaning Food by Analysis of Soluble Proteins and Amplified Fragment Length Polymorphism Fingerprinting

The group that includes the lactic acid bacteria is one of the most diverse groups of bacteria known, and these organisms have been characterized extensively by using different techniques. In this study, 180 lactic acid bacterial strains isolated from sorghum powder (44 strains) and from corresponding fermented (93 strains) and cooked fermented (43 strains) porridge samples that were prepared in 15 households were characterized by using biochemical and physiological methods, as well as by analyzing the electrophoretic profiles of total soluble proteins. A total of 58 of the 180 strains were Lactobacillus plantarum strains, 47 were Leuconostoc mesenteroides strains, 25 were Lactobacillus sake-Lactobacillus curvatus strains, 17 were Pediococcus pentosaceus strains, 13 were Pediococcus acidilactici strains, and 7 were Lactococcus lactis strains. L. plantarum and L. mesenteroides strains were the dominant strains during the fermentation process and were recovered from 87 and 73% of the households, respectively. The potential origins of these groups of lactic acid bacteria were assessed by amplified fragment length polymorphism fingerprint analysis.     

Marine mammal Brucella isolates with different genomic characteristics display a differential response when infecting human macrophages in culture

Marine mammal Brucella strains with different genomic characteristics according to distribution of IS711 elements in their genomes were analysed for their intracellular behaviour in human THP-1 macrophage-like cells. Seven different groups of marine mammal strains were identified including a human isolate from New Zealand presumably from marine origin. Entry and intracellular survival of strains representative of these groups in THP-1 human macrophage-like cells were analysed at several times of infection. Three patterns of infection were identified. The Brucella strain isolated from the human case from New Zealand, and two other groups of strains belonging to B. ceti or B. pinnipedialis were able to infect THP-1 macrophage cells to the same extent as the virulent strains B. suis 1330 or B. melitensis 16M. Three other groups of strains belonging to B. ceti or B. pinnipedialis were able to enter the cells as classical virulent strains but were eliminated after 48 h. The last group was composed only of strains isolated from hooded seals (Cystophora cristata) and was even unable to enter and infect THP-1 macrophage cells. Thus, several groups of marine mammal Brucella strains appear to be non-infectious for human macrophages.     

Molecular genetic characteristics of Saccharomyces cerevisiae distillers’ yeasts

Genomes of 36 Saccharomyces distillers’ strains, mainly of domestic origin, were studied by PCR-RFLP analysis of rDNA 5.8S-ITS fragment, molecular karyotyping, and Southern hybridization. Molecular analysis revealed that all the strains belonged to the species S. cerevisiae. According to the karyotypic analysis, many of the strains were aneuploid. Accumulation of polymeric genes SUC and MAL was detected in S. cerevisiae distillers’ strains. Accumulation of polymeric genes of sugar fermentation may be of adaptive importance and may result in increased fermentation activity of the strains. It was demonstrated that most strains fermenting maltose after one day of fermentation possessed several MAL genes. Thermotolerant strains with high fermentation activity were selected.     

New Pseudomonas spp. Are Pathogenic to Citrus

Five putative novel Pseudomonas species shown to be pathogenic to citrus have been characterized in a screening of 126 Pseudomonas strains isolated from diseased citrus leaves and stems in northern Iran. The 126 strains were studied using a polyphasic approach that included phenotypic characterizations and phylogenetic multilocus sequence analysis. The pathogenicity of these strains against 3 cultivars of citrus is demonstrated in greenhouse and field studies. The strains were initially grouped phenotypically and by their partial rpoD gene sequences into 11 coherent groups in the Pseudomonas fluorescens phylogenetic lineage. Fifty-three strains that are representatives of the 11 groups were selected and analyzed by partial sequencing of their 16S rRNA and gyrB genes. The individual and concatenated partial sequences of the three genes were used to construct the corresponding phylogenetic trees. The majority of the strains were identified at the species level: P. lurida (5 strains), P. monteilii (2 strains), P. moraviensis (1 strain), P. orientalis (16 strains), P. simiae (7 strains), P. syringae (46 strains, distributed phylogenetically in at least 5 pathovars), and P. viridiflava (2 strains). This is the first report of pathogenicity on citrus of P. orientalis, P. simiae, P. lurida, P. moraviensis and P. monteilii strains. The remaining 47 strains that could not be identified at the species level are considered representatives of at least 5 putative novel Pseudomonas species that are not yet described.     

Physiological Properties and Phylogenetic Affiliations of Anaerobic Bacteria Isolated from Roots of Rice Plants Cultivated on a Paddy Field

Anaerobic bacteria associated with roots of rice plants cultivated on a paddy field were isolated, and their physiological properties and phylogenetic affiliations were investigated. The roots harbored culturable populations of anaerobic microorganisms at 10⁷ levels of viable counts (CFU/g dry roots), and the isolates were thought to represent numerically abundant populations of culturable anaerobic microorganisms present on the roots. Among 18 strains isolated in pure culture, five strains were obligately anaerobic and others were facultatively anaerobic. Eight strains including four obligately anaerobic strains were selected for further study. Of eight strains, seven strains were saccharolytic, and one strain was a non-saccharolytic sulfate-reducer. Glucose was fermented into ethanol and/or acetate by the saccharolytic strains, lactate, succinate or H₂ was also produced by some strains. Four facultatively anaerobic strains were saccharolytic and grew with the fermentative metabolism even under the oxic condition. Three facultatively anaerobic strains and one obligately anaerobic strain exhibited the Fe(III)-reducing ability. The comparative analysis of 16S rRNA gene sequences indicated that the sequence of any strain did not completely match to the sequences available in the database. The seven saccharolytic strains represented diverse phylogenetic groups: the classes ‘Alphaproteobacteria’ (two strains) and ‘Gammaproteobacteria’ (one strain), the family Bacteroidaceae (one strain), the orderActinomycetales (two strains), and the family Clostridiaceae. The sulfate-reducing strain was a close relative ofDesulfovibriodesulfuricans . At least five strains were considered to represent novel species. In particular, two strains were considered to represent novel lines of descent at the family level within the order ‘Rhizobiales’. These results suggested that phylogenetically different bacteria with a common physiological trait as the saccharolytic fermentative acidogen formed numerically most abundant populations of culturable anaerobes in the microbial community on rice roots.     

Phenotypic Characteristics and Virulence of Vibrio anguillarum-Related Organisms

The phenotypic, molecular, and virulence properties of 46 Vibrio anguillarum-related (VAR) strains isolated from diseased fish and shellfish and from the environment were investigated. Twelve reference strains belonging to the 10 serotypes of V. anguillarum and the Vibrio splendidus type strain were included for comparison. Numerical taxonomy studies allowed us to group the isolates into four phena. The main phenotypic traits to differentiate VAR strains from V. anguillarum were fermentation of arabinose and mannitol, indole and Voges-Proskauer reactions, gelatin and casein hydrolysis, hemolytic activity, growth at 37 and 4°C, and resistance to ampicillin. Serological analysis confirmed that phena I and II were composed mainly of strains of V. anguillarum, while phena III and IV included VAR strains. Excluding the reference strains, the typeable isolates belonged to serotypes O3 (15 strains), O4 (3 strains), and O5 (2 strains) of V. anguillarum. The infectivity trials showed that only 9 of a total of 24 strains tested displayed virulence for rainbow trout. Virulent strains (50% lethal dose ranging from 10² to 10⁶ cells) included V. anguillarum strains belonging to serotypes O1 (one strain), O2 (one strain), O3 (three isolates), and O4 (one isolate) and only three strains of the VAR group. Sodium dodecyl sulfate-polyacrylamide gel electrophoresis analysis of lipopolysaccharide and outer membrane proteins showed heterogeneity not only among the 10 V. anguillarum serotypes but also within the VAR group. Immunoblot assays demonstrated a close relationship among V. anguillarum strains from the same serotype, while strains from different serotypes were not antigenically related. The VAR strains did not share antigenic components with the serotypes of V. anguillarum tested (serotypes O1 to O5). Plasmids were detected in only 19 of the total of 59 strains. The majority of the strains carrying plasmids were grouped within phenon IV, in which plasmid bands of 27 and 36 MDa were found in all the isolates. No correlation between the plasmid content of VAR microorganisms and their phenotypic or virulence characteristics was observed. From these results it can be concluded that VAR strains associated with disease should be included together with V. anguillarum in the formulation of vaccines against vibriosis.     

Multiple-Locus Sequence Typing Analysis of Bacillus cereus and Bacillus thuringiensis Reveals Separate Clustering and a Distinct Population Structure of Psychrotrophic Strains

We used multilocus sequence typing (MLST) to characterize phylogenetic relationships for a collection of Bacillus cereus group strains isolated from forest soil in the Paris area during a mild winter. This collection contains multiple strains isolated from the same soil sample and strains isolated from samples from different sites. We characterized 115 strains of this collection and 19 other strains based on the sequences of the clpC, dinB, gdpD, panC, purF, and yhfL loci. The number of alleles ranged from 36 to 53, and a total of 93 allelic profiles or sequence types were distinguished. We identified three major strain clusters—C, T, and W—based on the comparison of individual gene sequences or concatenated sequences. Some less representative clusters and subclusters were also distinguished. Analysis of the MLST data using the concept of clonal complexes led to the identification of two, five, and three such groups in clusters C, T, and W, respectively. Some of the forest isolates were closely related to independently isolated psychrotrophic strains. Systematic testing of the strains of this collection showed that almost all the strains that were able to grow at a low temperature (6°C) belonged to cluster W. Most of these strains, including three independently isolated strains, belong to two clonal complexes and are therefore very closely related genetically. These clonal complexes represent strains corresponding to the previously identified species Bacillus weihenstephanensis. Most of the other strains of our collection, including some from the W cluster, are not psychrotrophic. B. weihenstephanensis (cluster W) strains appear to comprise an effectively sexual population, whereas Bacillus thuringiensis (cluster T) and B. cereus (cluster C) have clonal population structures.     

Comparative Characteristics of Human and Porcine Staphylococci and Their Differentiation in Burn Xenografting Procedures

Staphylococcus epidermidis from porcine skin differed from human cutaneous S. epidermidis in that the former strains were principally of the Baird-Parker biotype III group. The porcine-type strains were more proteolytic on casein and gelatin than were human strains, which were primarily of biotype II. Porcine strains were also elastolytic. Using supernatant fluids of broth cultures, the biotype II strains, but not the type III strains, were lipolytic in action on triolein. Both types of staphylococci were similar in enzymatic activities on Tween 80, egg yolk, and tributyrin. Elastase activity was not found in broth supernatant fluid of these bacteria. The porcine strains were retarded or inhibited from growing in media at pH 5.5. Action on casein agar followed by demonstration of elastase activity were used as markers to detect the porcine S. epidermidis strains in xenografts and on human burn wound grafting sites.     

Mycelial interactions inSclerotinia sclerotiorum

Mycelial interactions were examined among 35 isolates ofSclerotinia sclerotiorum and two Asian species,Sclerotinia asari and an unnamed, Japanese species. Pairings were scored as compatible when strains merged to form one colony and incompatible when strains grew to form two distinct colonies. Incompatible mycelial pairings resulted in an interaction zone in which a distinct reaction line and abundant aerial mycelium or thin mycelium were observed with some variation among replicates. All pairings of a strain with itself were compatible. Of the 31 strains ofS. sclerotiorum tested, 21 were mycelially incompatible with all others. Among the remaining 10 strains ofS. sclerotiorum, there were four mycelial compatibility groups consisting of two or three strains each. Pairings ofS. asari with all other strains resulted in a unique incompatible reaction, a mycelium-free interaction zone. Two of three strains of the Japanese species were intercompatible, but pairings of each of the three strains with all other strains were incompatible. Microscopically, mycelial interactions in pairings of strains were complex. Anastomosis between paired strains was not always observed. This may be due in part to the conversion of many hyphal tips, in both compatible and incompatible interactions, to sites of microconidiogenesis no longer capable of hyphal fusion. Incompatible pairings were followed by hyphal deterioration in one or both strains; hyphal deterioration was not observed in compatible interactions. Of the 31 strains tested, 4 strains ofS. sclerotiorum produced apothecia. Pairings between single ascospore isolates within each strain were compatible, as were pairings with the parent isolate. Mycelial interactions of single ascospore isolates with other strains were identical to those of the parent isolate, indicating that the parent fruitbody was homozygous for any determinant(s) of mycelial incompatibility. The data from this study suggest that a high level of mycelial incompatibility exists among strains ofS. sclerotiorum, comparable to levels of vegetative incompatibility reported in other ascomycetes, that the extent of mycelial incompatibility indicates that genetic heterogeneity exists within the species, and that mycelial compatibility/incompatibility reactions may be an effective way of categorizing intraspecific heterogeneity.     

Comparative genomics of a subset of Adherent/Invasive Escherichia coli strains isolated from individuals without inflammatory bowel disease

There is increased evidence demonstrating the association between Crohn's Disease (CD), a type of Inflammatory Bowel Disease (IBD), and non-diarrheagenic Adherent/Invasive Escherichia coli (AIEC) isolates. AIEC strains are phenotypically characterized by their adhesion, invasion and intra-macrophage survival capabilities. In the present study, the genomes of five AIEC strains isolated from individuals without IBD (four from healthy donors and one from peritoneal liquid) were sequenced and compared with AIEC prototype strains (LF82 and NRG857c), and with extra-intestinal uropathogenic strain (UPEC CFT073). Non-IBD-AIEC strains showed an Average Nucleotide Identity up to 98% compared with control strains. Blast identities of the five non-IBD-AIEC strains were higher when compared to AIEC and UPEC reference strains than with another E. coli pathotypes, suggesting a relationship between them. The SNPs phylogeny grouped the five non-IBD-AIEC strains in one separated cluster, which indicates the emergence of these strains apart from the AIEC group. Additionally, four genomic islands not previously reported in AIEC strains were identified. An incomplete Type VI secretion system was found in non-IBD-AIEC strains; however, the Type II secretion system was complete. Several groups of genes reported in AIEC strains were searched in the five non-IBD-AIEC strains, and the presence of fimA, fliC, fuhD, chuA, irp2 and cvaC were confirmed. Other virulence factors were detected in non-IBD-AIEC strains, which were absent in AIEC reference strains, including EhaG, non-fimbrial adhesin 1, PapG, F17D-G, YehA/D, FeuC, IucD, CbtA, VgrG-1, Cnf1 and HlyE. Based on the differences in virulence determinants and SNPs, it is plausible to suggest that non-IBD AIEC strains belong to a different pathotype.     

Genetic diversity,core collection and breeding history of Pleurotus ostreatus in China

Pleurotus ostreatus is one of the most widespread and favourably cultivated mushrooms in China. The cultivated strains of this species have been frequently exchanged domestically and internationally, but no detailed breeding history has been documented. The frequent domestic and international exchange of strains combined with a non-detailed historical documentation of breeding might have led to confusion about strain names and genetic background. In this study, 91 strains of P. ostreatus, including 57 cultivated and 34 wild strains, were analysed using 21 simple sequence repeat markers developed from the genomic sequence of “P. cf. floridanus”. Among the cultivated strains, 46 were found to possess different allelic patterns. The remaining 11 strains were clustered into five groups, each with their own private alleles, suggesting that 10.5% (6/57) of the cultivated strains were previously labelled with improper names. Our analyses indicate that wild strains harbored greater genetic diversity than the cultivated strains. With regard to the cultivation history of P. ostreatus, the cultivated strains in China have three sources: direct introduction from Europe, domestication from wild strains from China, or hybridisation of the European and Chinese strains. Furthermore, we propose a core collection of P. ostreatus with 34 strains, including 13 wild and 21 cultivated strains. The allele retention proportion of the core collection for the entire collection was 100%.     

Multilocus Sequence Typing and Phylogenetic Analyses of Pseudomonas aeruginosa Isolates from the Ocean

Recent isolation of Pseudomonas aeruginosa strains from the open ocean and subsequent pulsed-field gel electrophoresis analyses indicate that these strains have a unique genotype (N. H. Khan, Y. Ishii, N. Kimata-Kino, H. Esaki, T. Nishino, M. Nishimura, and K. Kogure, Microb. Ecol. 53:173-186, 2007). We hypothesized that ocean P. aeruginosa strains have a unique phylogenetic position relative to other strains. The objective of this study was to clarify the intraspecies phylogenetic relationship between marine strains and other strains from various geographical locations. Considering the advantages of using databases, multilocus sequence typing (MLST) was chosen for the typing and discrimination of ocean P. aeruginosa strains. Seven housekeeping genes (acsA, aroE, guaA, mutL, nuoD, ppsA, and trpE) were analyzed, and the results were compared with data on the MLST website. These genes were also used for phylogenetic analysis of P. aeruginosa. Rooted and unrooted phylogenetic trees were generated for each gene locus and the concatenated gene fragments. MLST data showed that all the ocean strains were new. Trees constructed for individual and concatenated genes revealed that ocean P. aeruginosa strains have clusters distinct from those of other P. aeruginosa strains. These clusters roughly reflected the geographical locations of the isolates. These data support our previous findings that P. aeruginosa strains are present in the ocean. It can be concluded that the ocean P. aeruginosa strains have diverged from other isolates and form a distinct cluster based on MLST and phylogenetic analyses of seven housekeeping genes.     

In Vitro Susceptibility of Atypical Mycobacteria To Rifampin

Atypical mycobacteria (209 strains) were examined for susceptibility to rifampin by the proportion method by using Middlebrook 7H-10 agar. All strains of Mycobacterium kansasii and tap-water scotochromogens were inhibited by 0.25 to 1 μg of the drug per ml. Seventy-six per cent of M. scrofulaceum and 61% of M. intracellulare strains were susceptible to 4 μg/ml or less; 5% of the former and 8% of the latter were resistant to 16 μg/ml. All strains of M. gastri and M. triviale and most strains of M. terrae were sensitive to 1 to 4 μg/ml. Two strains of M. borstelense were both inhibited by 8 μg/ml. Nearly all strains of M. fortuitum were resistant to the drug. The results of this study suggest that rifampin may be a valuable agent for the treatment of many atypical mycobacterial infections.     

Amplified Fragment Length Polymorphism Analysis of Campylobacter jejuni Strains Isolated from Chickens and from Patients with Gastroenteritis or Guillain-Barré or Miller Fisher Syndrome

The high-resolution genotyping method of amplified fragment length polymorphism (AFLP) analysis was used to study the genetic relationships between Campylobacter jejuni strains infecting chickens (n = 54) and those causing gastroenteritis in humans (n = 53). In addition, C. jejuni strains associated with the development of Guillain-Barré syndrome (GBS) (n = 14) and Miller Fisher syndrome (MFS) (n = 4), two related acute paralytic syndromes in human, were included. Strains were isolated between 1989 and 1998 in The Netherlands. The AFLP banding patterns were analyzed with correlation-based and band-based similarity coefficients and UPGMA (unweighted pair group method using average linkages) cluster analysis. All C. jejuni strains showed highly heterogeneous fingerprints, and no fingerprints exclusive for chicken strains or for human strains were obtained. All strains were separated in two distinct genetic groups. In group A the percentage of human strains was significantly higher and may be an indication that genotypes of this group are more frequently associated with human diseases. We conclude that C. jejuni from chickens cannot be distinguished from human strains and that GBS or MFS related strains do not belong to a distinct genetic group.     

The proportion of non-aflatoxigenic strains of the Aspergillus flavus/oryzae complex from meju by analyses of the aflatoxin biosynthetic genes

Strains of the Aspergillus flavus/oryzae complex are frequently isolated from meju, a fermented soybean product, that is used as the starting material for ganjang (soy sauce) and doenjang (soybean paste) production. In this study, we examined the aflatoxin producing capacity of A. flavus/oryzae strains isolated from meju. 192 strains of A. flavus/oryzae were isolated from more than 100 meju samples collected from diverse regions of Korea from 2008 to 2011, and the norB-cypA, omtA, and aflR genes in the aflatoxin biosynthesis gene cluster were analyzed. We found that 178 strains (92.7%) belonged to non-aflatoxigenic group (Type I of norB-cypA, IB-L-B-, IC-AO, or IA-L-B- of omtA, and AO type of aflR), and 14 strains (7.3%) belonged to aflatoxin-producible group (Type II of norB-cypA, IC-L-B+/B- or IC-L-B+ of omtA, and AF type of aflR). Only 7 strains (3.6%) in the aflatoxin-producible group produced aflatoxins on Czapek yeast-extract medium. The aflatoxin-producing capability of A. flavus/oryzae strains from other sources in Korea were also investigated, and 92.9% (52/56) strains from air, 93.9% (31/33) strains from rice straw, 91.7% (11/12) strains from soybean, 81.3% (13/16) strains from corn, 82% (41/50) strains from peanut, and 73.2% (41/56) strains from arable soil were included in the non-aflatoxigenic group. The proportion of non-aflatoxigenicity of meju strains was similar to that of strains from soybean, air and rice straw, all of which have an effect on the fermentation of meju. The data suggest that meju does not have a preference for non-aflatoxigenic or aflatoxin-producible strains of A. flavus/oryzae from the environment of meju. The non-aflatoxigenic meju strains are proposed to be named A. oryzae, while the meju strains that can produce aflatoxins should be referred to A. flavus in this study.     

Deoxyribonucleic Acid Homology Among Lactic Streptococci

A comparison was made by deoxyribonucleic acid homology of 45 strains of lactic streptococci, using two strains of Streptococcus cremoris and three strains of Streptococcus lactis as reference strains. All S. cremoris strains were grouped together by deoxyribonucleic acid homology. S. lactis strains formed a second group, except that three strains of S. lactis showed a high degree of homology with S. cremoris strains. The three Streptococcus diacetylactis strains could not be differentiated from S. lactis strains. In spite of these differences between S. lactis and S. cremoris strains, the majority of S. cremoris, S. lactis, and S. diacetylactis strains studied had at least 50% of their base sequences in common. In contrast, Streptococcus thermophilus strains generally showed little relationship with the other strains of lactic streptococci. The relevance of these findings to the selection of starter strains for cheese making is discussed.     

Drug Resistance of Enteric Bacteria IX. Distribution of R Factors in Gram-negative Bacteria from Clinical Sources

Many isolates belonging to the Enterobacteriaceae were collected in 1965 from the inpatients at geographically scattered hospitals in Japan. Among 2,650 Shigella strains examined, 58.4% were found to be drug-resistant; 95.0% of these resistant strains were multiply resistant. Among 434 resistant strains examined, 81% carried R factors that were transferable by cell-to-cell contact. Of 160 isolates of other enteric bacteria, drug-resistant strains included 84.2% of the Escherichia coli, 93.0% of the Klebsiella, and 90.0% of the Proteus cultures. Among these resistant strains, 70.3% of the E. coli, 66.7% of the Klebsiella, and 52.0% of the Proteus were multiply resistant. Of these resistant strains, 84.0% of the E. coli, 88.0% of the Klebsiella, and 50.0% of the Proteus strains carried R factors. These results indicate that R factors are widespread among gram-negative bacteria of clinical significance.     

Numerical Taxonomic Analysis of Some Strains of Rhizobium spp. That Uses a Qualitative Coding of Immunodiffusion Reactions

Antigenic relationships among seven strains of Bradyrhizobium japonicum were examined by immunodiffusion reactions, in which cells of each strain were reacted against each of the seven corresponding antisera. Similar analyses were performed with Rhizobium trifolii (28 strains), Rhizobium meliloti (9 strains), and rhizobia of the cowpea miscellany (13 strains). Antigens and antisera were reacted within each species only; serological interspecies cross-reactions were not performed. The results, scored qualitatively as reactions of identity, cross-reactions, or no reaction, were formed into datum matrices and used to analyze the relationships between strains by applying the association measure of Bray and Curtis (J. R. Bray and J. T. Curtis, Ecol. Monogr. 27:325-349, 1957) and the UPGMA clustering algorithm (P. H. A. Sneath and R. R. Sokal, Numerical Taxonomy, 1973). No two strains were regarded as being serologically identical unless each gave the same results as the other in each immunodiffusion reaction against every antiserum. Despite the high level of cross-reactions and reactions of identity (totalling 93% of all cell-antiserum combinations) among strains of R. trifolii and R. meliloti, no strains were identical by the criterion described above; however, the strains of these species clustered rapidly and fused at the 70% similarity level. The B. japonicum strains and the rhizobia of the cowpea miscellany were much less cross-reactive (67 and 86% of all combinations were negative, respectively), and they clustered more slowly. The strains of B. japonicum fused completely only at the 4% similarity level, whereas of the 13 cowpea-nodulating strains, 4 reacted as two pairs of identical strains and 6 remained unfused.