Epidemiological relatedness and clonal types of natural populations of Escherichia coli strains producing Shiga toxins in separate populations of cattle and sheep.

Two separate animal populations consisting of a herd of cattle (19 animals) and a flock of sheep (25 animals) were investigated for strains of Escherichia coli producing Shiga toxins (STEC) over a time period of 6 months. Thirty-three STEC were isolated from 63.2% of cattle and grouped into 11 serotypes and eight electrophoretic types (ETs) by multilocus enzyme analysis. In sheep, 88% of the animals excreted STEC (n = 67 isolates) belonging to 17 different serotypes and 12 different ETs. STEC from cattle and sheep differed with respect to serotype, and only 4 of the 16 ETs occurred in both animal populations. In cattle, ET14 (O116:H21) strains predominated, whereas other STEC serotypes occurred only sporadically. The predominating STEC types in sheep were ET4 (O125 strains), ET11 (O128:H2 and others), and ET14 (O146:H21). In contrast to their diversity, STEC originating from the same animal population were similar with respect to Shiga toxin (stxy genes. Almost all STEC isolated from cattle were positive for stx2 and stx2c; only one was positive for stx1. In sheep, almost all STEC isolated were positive for stx1 and stx2, whereas stx2c was not found. XbaI-digested DNAs of genetically closely related O146:H21 strains have different restriction profiles which were associated with size alterations in XbaI fragments hybridizing with stx1- and stx2-specific DNA probes. Our results indicate that stx-encoding bacteriophages might be the origin of the genetic heterogeneity in STEC from animals.     

Differentiation between Actinobacillus (Haemophilus) actinomycetemcomitans, Haemophilus aphrophilus and Haemophilus paraphrophilus by multilocus enzyme electrophoresis

Genetic relationships among isolates assigned to Actinobacillus actinomycetemcomitans, Haemophilus aphrophilus and H. paraphrophilus were determined by analysis of electrophoretically demonstrable allelic variation in 14 structural genes encoding metabolic enzymes. Among the 51 isolates analysed there were 25 electrophoretic types (ETs), among which mean genetic diversity per locus was 0.753. Cluster analysis of ETs demonstrated one well-defined group of 11 ETs representing solely the genotypes of all 17 isolates assigned to A. actinomycetemcomitans. The remaining 14 ETs represented the genotypes of the 34 isolates of H. aphrophilus and H. paraphrophilus. With the exception of ATCC 13252, all strains of H. aphrophilus were closely related, whereas strains assigned to H. paraphrophilus included distantly related lineages, some of which were similar to those of H. aphrophilus and should be assigned to this species. Thus, the study showed that there is no significant overall genetic similarity between A. actinomycetemcomitans and the two Haemophilus spp.     

Multilocus genotypes determined by enzyme electrophoresis of Neisseria meningitidis isolated from patients with systemic disease and from healthy carriers

Variation in nine enzymes in 152 isolates of Neisseria meningitidis from Norway (118 from blood or cerebrospinal fluid of patients with systemic disease and 34 from the pharynx of healthy carriers) was analysed by starch-gel electrophoresis. All nine enzymes were polymorphic and the number of allozymes (electromorphs) identified per locus ranged from 3 to 12, with a mean of 6.1. Among the 152 isolates, 55 unique combinations of electromorphs (electrophoretic types, ETs) were distinguished. Twenty ETs were represented among the carrier isolates and 37 among the systemic isolates; hence, only two ETs were found in both groups of isolates. ET-5 was identified 67 times among the 118 systemic isolates (58%), indicating an association of this ET with invasiveness; ET-5 was also the most common type among the carrier isolates (18%). Genetic similarity between ETs was analysed by pairwise comparison of all 55 ETs with respect to the number of electromorphs by which they differed. No evidence of a general genetic difference between carrier and case isolates was found. Two well-defined clusters of ETs were observed, each including one of the two most common ETs identified among the systemic isolates (ET-5 and ET-37), together with isolates differing from them only at one or two loci. All isolates of ET-5 and ET-37, as well as their closely related variants defined by the similarity matrix, were resistant to sulphonamide, independent of their antigenic characteristics and isolation site. The extensive allozyme variation among isolates of the same serogroup demonstrated the limited value of serogrouping as an epidemiological tool. All but one isolate of serotype 15:P1.16 were electrophoretically similar, as were all the 2a:P1.2 isolates. The 15:P1.15 isolates, however, were genetically heterogeneous. The distribution of alleles in genotypes identified among the systemic isolates indicated that genetic recombination may occur in natural populations of N. meningitidis.     

Genotypic and Phenotypic Comparisons of Chromosomal Types within an Indigenous Soil Population of Rhizobium leguminosarum bv. trifolii

The relative genetic similarities of 200 isolates of Rhizobium leguminosarum bv. trifolii recovered from an Oregon soil were determined at 13 enzyme loci by multilocus enzyme electrophoresis (MLEE). These isolates represented 13 antigenically distinct serotypes recovered from nodules formed on various clover species. The MLEE-derived levels of relatedness among isolates of R. leguminosarum bv. trifolii were found to be in good agreement with the levels of relatedness established by using repetitive (repetitive extragenic palindromic and enterobacterial repetitive intergeneric consensus) sequences and the PCR technique and with levels of relatedness from previously published DNA reassociation studies. BIOLOG substrate utilization patterns showed that isolates within an electrophoretic type (ET) were phenotypically more similar to each other than to isolates of other ETs. The soil isolates were represented by 53 ETs which could be clustered into seven groups (groups B, E, G, H1, H2, I, and J). Evidence for multilocus structure within the population was obtained, and group B was identified as the primary creator of the disequilibrium. Of 75 isolates belonging to the nodule-dominant serotype AS6 complex, 72 were found in group B. Isolates WS2-01 and WS2-02 representing nodule-dominant serotypes recovered from subclover grown at another Oregon site were also found in group B. Isolates representing the most numerous ETs in group B (ETs 2 and 3) were either suboptimally effective or completely ineffective at fixing nitrogen on six different clover species. Another four groups of isolates (groups A, C, D, and F) were identified when 32 strains of diverse origins were analyzed by MLEE and incorporated into the cluster analysis. Group A was most dissimilar in comparisons with other groups and contained strain USDA 2124 (T24), which produces trifolitoxin and has unique symbiotic characteristics.     

Genetic structure of Neisseria meningitidis populations in relation to serogroup, serotype, and outer membrane protein pattern.

The genetic structure of populations of Neisseria meningitidis was examined by an analysis of electrophoretically demonstrable allelic variation at 15 genes encoding enzymes in 650 isolates of eight serogroups (A, B, C, W135, X, Y, Z, and 29E) and 38 nonserogroupable isolates. A total of 331 distinctive multilocus genotypes (electrophoretic types, ETs) was identified, among which mean genetic diversity per locus (H = 0.547) was greater than in Escherichia coli and other bacterial species thus far studied. The intercontinental distribution of some ETs and the recovery of organisms of identical genotype over periods of many years strongly suggest that the genetic structure of N. meningitidis is basically clonal as a consequence of low rates of recombination of chromosomal genes. Variation among strains in serogroup, serotype, and the electrophoretic pattern of the major outer membrane proteins has little relationship to the complex structure of populations revealed by enzyme electrophoresis, which involves 14 major lineages of clones diverging from one another at genetic distances greater than 0.50. Genetic diversity among ETs of isolates of the same serogroup was, on average, 84% of that in the total sample. Clones of serogroup A were unusual in being genotypically less heterogeneous than those of other serogroups and in forming a single phylogenetic group. Isolates of the same serotype or outer membrane protein pattern were also highly heterogeneous; on average, 87 and 97%, respectively, of the total species diversity was represented by ETs of the same serotype or outer membrane protein.     

Genetic structure of populations of Legionella pneumophila.

The genetic structure of populations of Legionella pneumophila was defined by an analysis of electrophoretically demonstrable allelic variation at structural genes encoding 22 enzymes in 292 isolates from clinical and environmental sources. Nineteen of the loci were polymorphic, and 62 distinctive electrophoretic types (ETs), representing multilocus genotypes, were identified. Principal coordinates and clustering analyses demonstrated that isolates received as L. pneumophila were a heterogeneous array of genotypes that included two previously undescribed species. For 50 ETs of L. pneumophila (strict sense), mean genetic diversity per locus was 0.312, and diversity was equivalent in ETs represented by isolates recovered from clinical sources and those collected from environmental sources. Cluster analysis revealed four major groups or lineages of ETs in L. pneumophila. Genetic diversity among ETs of the same serotype was, on average, 93% of that in the total sample of ETs. Isolates marked by particular patterns of reactivity to a panel of nine monoclonal antibodies were also genetically heterogeneous, mean diversity within patterns being about 75% of the total. Both Pontiac fever and the pneumonic form of legionellosis may be caused by isolates of the same ET. The genetic structure of L. pneumophila is clonal, and many clones apparently are worldwide in distribution. The fact that L. pneumophila is only 60% as variable as Escherichia coli raises the possibility that isolates recovered from clinical cases and man-made environments are a restricted subset of all clones in the species as a whole.     

Analysis of clinical and food-borne isolates of Listeria monocytogenes in the United States by multilocus enzyme electrophoresis and application of the method to epidemiologic investigations

To investigate the microbiology and epidemiology of the 1,700 sporadic cases of listeriosis that occur annually in the United States, we developed a multilocus enzyme electrophoresis (MEE) typing system for Listeria monocytogenes. We studied 390 isolates by MEE. Eighty-two electrophoretic types (ETs) were defined. Two distinct clusters of ETs, ET group A (ETGA) and ET group B (ETGB), separated at a genetic distance of 0.440, were identified. Strains of ETGB were associated with perinatal listeriosis (P = 0.03). All strains of H antigen type a were in ETGA, while all strains of H antigen type b were in ETGB. Among 328 clinical isolates from cases of literiosis, 55 ETs of L. monocytogenes were defined. Thirty-four ETs were identified among 62 isolates from food products. The mean number of strains per ET (5.2) was significantly higher among clinical isolates than among food-borne isolates. Examination of isolates from outbreaks further documented the link between cases and contaminated food products. In one investigation, we found 11 different ETs, ruling out a single common source as a cause of that outbreak. By examining a large number of isolates collected over a specified time in diverse geographic locations in the United States, we have begun to establish a baseline for the study of the epidemiology of listeriosis by MEE.     

Analysis of clinical and food-borne isolates of Listeria monocytogenes in the United States by multilocus enzyme electrophoresis and application of the method to epidemiologic investigations.

To investigate the microbiology and epidemiology of the 1,700 sporadic cases of listeriosis that occur annually in the United States, we developed a multilocus enzyme electrophoresis (MEE) typing system for Listeria monocytogenes. We studied 390 isolates by MEE. Eighty-two electrophoretic types (ETs) were defined. Two distinct clusters of ETs, ET group A (ETGA) and ET group B (ETGB), separated at a genetic distance of 0.440, were identified. Strains of ETGB were associated with perinatal listeriosis (P = 0.03). All strains of H antigen type a were in ETGA, while all strains of H antigen type b were in ETGB. Among 328 clinical isolates from cases of literiosis, 55 ETs of L. monocytogenes were defined. Thirty-four ETs were identified among 62 isolates from food products. The mean number of strains per ET (5.2) was significantly higher among clinical isolates than among food-borne isolates. Examination of isolates from outbreaks further documented the link between cases and contaminated food products. In one investigation, we found 11 different ETs, ruling out a single common source as a cause of that outbreak. By examining a large number of isolates collected over a specified time in diverse geographic locations in the United States, we have begun to establish a baseline for the study of the epidemiology of listeriosis by MEE.     

Diversity and genetic structure of a natural population of Rhizobium leguminosarum bv. trifolii isolated from Trifolium subterraneum L.

A collection of 121 isolates of Rhizobium leguminosarum biovar (bv.) trifolii was obtained from root nodules of Trifolium subterraneum L. (subclover) plants growing in an established pasture. The collection consisted of a single isolate from each of 18 plants sampled from seven microplots. The following year, a further 28 and 27 isolates were collected from the first and seventh sampling points, respectively. Analysis of restriction fragment length polymorphisms (RFLPs) of both chromosomal and Sym (symbiotic) plasmid DNA and multilocus enzyme electrophoresis (MLEE) were used to assess the diversity, genetic relationships and structure of this population. Symbiotic effectiveness tests were used to examine the symbiotic phenotype of each isolate collected in the first year. Analysis of RFLPs of the first year isolates revealed 13 chromosomal types and 25 Sym plasmid types. Similar Sym plasmid types were grouped into 14 families containing 1–6 members. No new chromosomal types and six new Sym plasmid types were detected in the second year. The symbiotic effectiveness of the first year isolates of the same Sym plasmid type was similar. Significant differences in symbiotic effectiveness were detected between different Sym plasmid types in the same plasmid family. Representative isolates of each chromosomal type Sym plasmid type identified in the first year were analysed using multilocus enzyme electrophoresis. Mean genetic diversity per locus was high (0.559). Enzyme electrophoresis revealed 17 electrophoretic types (ETs). Ouster analysis of the enzyme data revealed large genetic diversity amongst the ETs. Strong linkage disequilibrium was observed for the population as a whole, i.e. clonal population structure, but significantly less disequilibrium was observed among a cluster of ETs suggesting that recombination occurred between ETs within the cluster. Our results revealed that a population of naturally occurring isolates of Rhizobium leguminosarum bv. trifolii can be genetically diverse and support the possibility that recombination plays a role in generating new genotypes.     

Genetic Diversity of Bacillus cereus/B. thuringiensis Isolates from Natural Sources

The genetic diversity and relationships among 154 Bacillus cereus/B. thuringiensis isolates recovered from soil samples from five geographic areas in Norway were investigated with multilocus enzyme electrophoresis (MEE). Cluster analysis revealed two major groups (designated cluster I and cluster II) separated at genetic distance greater than 0.55. Cluster I included 62 electrophoretic types (ETs) originating from all five locations, whereas, in cluster II, all but one isolate were from the same location. The isolates were also serotyped with B. thuringiensis flagellar antisera, and 28 distinct serotypes were identified. In general, serotyping did not show correlation to the genetic diversity of the isolates. The presence of IS231- and IS240-like transposable elements was detected in 14% of the strains of cluster II only. Parasporal crystals were observed in three strains; ten other strains were toxic to Trichoplusia ni. We conclude that B. cereus/B. thuringiensis from soil exhibit a high degree of recombination. Received: 15 December 1997 / Accepted: 26 January 1998     

Population Snapshot of Streptococcus pneumoniae Causing Invasive Disease in South Africa Prior to Introduction of Pneumococcal Conjugate Vaccines

We determined the sequence types of isolates that caused invasive pneumococcal disease (IPD) prior to routine use of pneumococcal conjugate vaccines (PCV) in South Africa. PCV-13 serotypes and 6C isolates collected in 2007 (1 461/2 437, 60%) from patients of all ages as part of on-going, national, laboratory-based surveillance for IPD, were selected for genetic characterization. In addition, all 134 non-PCV isolates from children <2 years were selected for characterization. Sequence type diversity by serotype and age category (children <5 years vs. individuals ≥5 years) was assessed for PCV serotypes using Simpson’s index of diversity. Similar genotypes circulated among isolates from children and adults and the majority of serotypes were heterogeneous. While globally disseminated clones were common among some serotypes (e.g., serotype 1 [clonal complex (CC) 217, 98% of all serotype 1] and 14 [CC230, 43%)]), some were represented mainly by clonal complexes rarely reported elsewhere (e.g., serotype 3 [CC458, 60%] and 19A [CC2062, 83%]). In children <2 years, serotype 15B and 8 were the most common serotypes among non-PCV isolates (16% [22/134] and 15% [20/134] isolates, respectively). Sequence type 7052 and 53 were most common among serotypes 15B and 8 isolates and accounted for 58% (7/12) and 64% (9/14) of the isolates, respectively. Serotype 19F, 14, 19A and 15B had the highest proportions of penicillin non-susceptible isolates. Genotypes rarely reported in other parts of the world but common among some of our serotypes highlight the importance of our data as these genotypes may emerge post PCV introduction.     

Genetic relatedness amongst intestinal spirochaetes isolated from rate and brids.

Multilocus enzyme electrophoresis was used to determine genetic relationships amongst 32 intestinal sprrochaetes ( Serpulina spp.) isolated from rats (17), rheas (7), chickens (4), ducks (2), a swan (1) and a flamingo (1). The strains were divided into 20 electrophoretic types (ETs), with a mean genetic diversity per locus of 0.62. The results were compared with those previously published for procine intestinal spirochaetes. One strain from a healthy rat, and three rhea strains which were recovered from cases of necrotizing typhlitis, were grouped in the same ETs as certain procine strains of Serpulina hydysenteriae . The rhea strains could be differentiated from these by pulsed-field gel electrophoresis. Fifteen of the rat strains could be differentiated from these by pulsed-field gel electrophoresis. Fifteen of the rat strains were genetically and phenotypically closely related. In contrast the avian strains were genetically more heterogeneous, with pathogenic isolates located in three different genetic groups.     

Symbiotic Characteristics of Rhizobium leguminosarum bv. trifolii Isolates Which Represent Major and Minor Nodule-Occupying Chromosomal Types of Field-Grown Subclover (Trifolium subterraneum L.)

The symbiotic effectiveness and nodulation competitiveness of Rhizobium leguminosarum bv. trifolii soil isolates were evaluated under nonsoil greenhouse conditions. The isolates which we used represented both major and minor nodule-occupying chromosomal types (electrophoretic types [ETs]) recovered from field-grown subclover (Trifolium subterraneum L.). Isolates representing four ETs (ETs 2, 3, 7, and 8) that were highly successful field nodule occupants fixed between 2- and 10-fold less nitrogen and produced lower herbage dry weights and first-harvest herbage protein concentrations than isolates that were minor nodule occupants of field-grown plants. Despite their equivalent levels of abundance in nodules on field-grown subclover plants, ET 2 and 3 isolates exhibited different competitive nodulation potentials under nonsoil greenhouse conditions. ET 3 isolates generally occupied more subclover nodules than isolates belonging to other ETs when the isolates were mixed in 1:1 inoculant ratios and inoculated onto seedlings. In contrast, ET 2 isolates were less successful at nodulating under these conditions. In many cases, ET 2 isolates required a numerical advantage of at least 6:1 to 11:1 to occupy significantly more nodules than their competitors. We identified highly effective isolates that were as competitive as the ET 3 isolates despite representing serotypes that were rarely recovered from nodules of field-grown plants. When one of the suboptimally effective isolates (ET2-1) competed with an effective and competitive isolate (ET31-5) at several different inoculant ratios, the percentages of nodules occupied by the former increased as its numerical advantage increased. Although subclover yields declined as nodule occupancy by ET2-1 increased, surprisingly, this occurred at inoculant ratios at which large percentages of nodules were still occupied by ET31-5.     

Serotypes, virulence genes, and PFGE patterns of enteropathogenic Escherichia coli isolated from Cuban pigs with diarrhea.

Thirty-six enteropathogenic Escherichia coli strains isolated from Cuban pigs with diarrhea were serotyped and screened by PCR for the presence of virulence genes. The 36 isolates belonged to 11 O serogroups and 14 O:H serotypes, with 53% of the isolates belonging to only two serotypes: O141:H- (13 isolates) and O157:H19 (6 isolates). Genes coding for STb, STa, VT2e, and LT toxins were identified in 69, 61, 53, and 6% of the isolates, respectively. The most prevalent fimbrial adhesin was F18, detected in 22 (61%) isolates. The gene encoding F6 (P987) colonization factor was identified in three (8%) isolates. None of the 36 isolates assayed contained genes encoding F4 (K88), F5 (K99), or F41. The seropathotype O141:H-:STa/STb/VT2e/F18 (13 isolates) was the most frequently detected, followed by O157:H19:VT2e/F18 (5 isolates). A genetic diversity study, carried out by pulsed-field gel electrophoresis (PFGE) of 24 representative isolates, revealed 21 distinct restriction patterns clustered in 18 groups (I-XVIII). Isolates of the same serotype were placed together in a dendrogram, but isolates of serotype O157:H19 showed a high degree of polymorphism. The results of this study demonstrate the presence in Cuba of different clusters among one of the most prevalent serotypes isolated from pigs with diarrhea. Further experiments are needed to determine whether some of these clusters have appeared recently; if so, their evolution, as well as their possible association with pathogenicity in farms should be studied.     

Characterization of urease-positive thermophilic Campylobacter subspecies by multilocus enzyme electrophoresis typing

Thirty-one urease-positive thermophilic Campylobacter (UPTC) isolates, including three reference strains (NCTC12892, NCTC12895 and NCTC12896), and three Campylobacter lari isolates, which were isolated from several countries and sources, were compared genotypically by using multilocus enzyme electrophoresis (MLEE). We examined allelic variation around seven enzyme loci, including the adenylate kinase, alkaline phosphatase, catalase, fumarase, malic enzyme, malate dehydrogenase, and L-phenylalanyl-L-leucine peptidase loci. MLEE typing revealed the presence of 23 different electrophoretic types (ETs) among the 31 UPTC isolates, and 14 isolates shared six electrophoretic profiles. Three different ETs were identified for the three C. lari isolates examined, and no ETs were shared by UPTC and C. lari isolates. Quantitative analyses were subsequently performed by using allelic variation data, and the results demonstrated that the mean genetic diversity was 0.655. In conclusion, MLEE demonstrated that the UPTC isolates examined are genetically hypervariable and form a cluster separate from the C. lari cluster.     

Chemical immobilization of adult female Weddell seals with tiletamine and zolazepam: effects of age, condition and stage of lactation

Background

Postweaning diarrhoea (PWD) in pigs is usually the main infectious problem of large-scale farms and is responsible for significant losses worldwide. The disease is caused mainly by enterotoxigenic E. coli (ETEC) and Shiga-toxin producing E. coli (STEC). In this study a total of 101 E. coli isolated from pigs with PWD in Slovakia were characterized using phenotypic and genotypic methods.

Results

These 101 isolates belonged to 40 O:H serotypes. However, 57% of the isolates belonged to only six serotypes (O9:H51, O147:H-, O149:H10, O163:H-, ONT:H-, and ONT:H4), including two new serotypes (O163:H- and ONT:H4) not previously found among porcine ETEC and STEC isolated in other countries. Genes for EAST1, STb, STa, LT and Stx2e toxins were identified in 64%, 46%, 26%, 20%, and 5% of isolates, respectively. PCR showed that 35% of isolates carried genes for F18 colonization factor, and further analyzed by restriction endonuclease revealed that all of them were F18ac. Genes for F4 (K88), F6 (P987), F17, F5 (K99), F41, and intimin (eae gene) adhesins were detected in 19 %, 5%, 3%, 0.9%, 0.9%, and 0.9% of the isolates, respectively. The study of genetic diversity, carried out by PFGE of 46 representative ETEC and STEC isolates, revealed 36 distinct restriction profiles clustered in eight groups. Isolates of the same serotype were placed together in the dendrogram, but high degree of polymorphism among certain serotypes was detected.

Conclusion

Seropathotype O149:H10 LT/STb/EAST1/F4 (14 isolates) was the most commonly detected followed by O163:H- EAST1/F18 (six isolates), and ONT:H4 STa/STb/Stx2e/F18 (five isolates). Interestingly, this study shows that two new serotypes (O163:H- and ONT:H4) have emerged as pig pathogens in Slovakia. Furthermore, our results show that there is a high genetic variation mainly among ETEC of O149:H10 serotype.     

Genetic Structure and Symbiotic Characteristics of a Bradyrhizobium Population Recovered from a Pasture Soil

We examined the genetic structure and symbiotic characteristics of Bradyrhizobium isolates recovered from four legume species (Lupinus albus [white lupine], Lupinus angustifolius [blue lupine], Ornithopus compressus [yellow serradella], and Macroptilium atropurpureum [sirato]) grown in an Oregon soil. We established that multilocus enzyme electrophoresis (MLEE) can provide insights into the genetic relatedness among Bradyrhizobium strains by showing a positive correlation (r² = ≥0.90) between the relatedness of Bradyrhizobium japonicum strains determined by MLEE at 13 enzyme loci and that determined by other workers using either DNA-DNA hybridization or DNA sequence divergence estimates. MLEE identified 17 electrophoretic types (ETs) among 95 Bradyrhizobium isolates recovered from the four hosts. Although the overall genetic diversity among the ETs (H = 0.69) is one of the largest measured to date in a local population of any soilborne bacterial species, there was no evidence of multilocus structure (linkage disequilibrium) within the population. The majority of the isolates (73%) were represented by two closely related ETs (2 and 3) which dominated the root nodules of white lupine, serradella, and siratro. In contrast, ET1 dominated nodules of blue lupine. Although representative isolates from all of the 17 ETs nodulated siratro, white lupine, blue lupine, and big trefoil (Lotus pedunculatus), they were either completely ineffective or poorly effective at fixing nitrogen on these hosts. Despite the widespread use of serradella as a surrogate host for lupine-nodulating bradyrhizobia, 7 of the 17 ETs did not nodulate this host, and the remaining 10 ETs were ineffective at fixing nitrogen.     

Genetic structure of natural populations of the nitrogen-fixing bacterium Rhizobium meliloti.

The genetic structure of populations of the symbiotic nitrogen-fixing soil bacterium Rhizobium meliloti was examined by analysis of electrophoretically demonstrable allelic variation in 14 metabolic, presumably chromosomal, enzyme genes. A total of 232 strains were examined, most of which were isolated from southwest Asia, where there is an unsurpassed number of indigenous host species for R. meliloti. The collection consisted of 115 isolates recovered from annual species of Medicago in Syria, Turkey, and Jordan; 85 isolates cultured from two perennial species of Medicago (M. sativa [alfalfa] and M. falcata) in northern Pakistan and Nepal; and 32 isolates collected at various localities in North and South America, Europe, South Africa, New Zealand, and Australia, largely from M. sativa. Fifty distinctive multilocus genotypes (electrophoretic types [ETs]) were identified, and cluster analysis revealed two primary phylogenetic divisions separated at a genetic distance of 0.83. By the criterion of genetic differentiation conventionally applied in defining species limits among members of the family Enterobacteriaceae and certain other bacteria, the two primary divisions of R. meliloti represent distinct evolutionary species. Division A included 35 ETs represented by 209 strains from the eastern Mediterranean basin, northern Pakistan, Nepal, and various other localities worldwide. This division contained the nine commercial alfalfa inoculant strains examined. Division B included 15 ETs represented by 23 isolates, 21 of which were isolated from annual medic species growing in previously uninoculated soils in the eastern Mediterranean basin. The two remaining strains in division B, both representing the same ET, were isolated in the United States and Australia.(ABSTRACT TRUNCATED AT 250 WORDS)     

Genetic structure of natural populations of the nitrogen-fixing bacterium Rhizobium meliloti.

The genetic structure of populations of the symbiotic nitrogen-fixing soil bacterium Rhizobium meliloti was examined by analysis of electrophoretically demonstrable allelic variation in 14 metabolic, presumably chromosomal, enzyme genes. A total of 232 strains were examined, most of which were isolated from southwest Asia, where there is an unsurpassed number of indigenous host species for R. meliloti. The collection consisted of 115 isolates recovered from annual species of Medicago in Syria, Turkey, and Jordan; 85 isolates cultured from two perennial species of Medicago (M. sativa [alfalfa] and M. falcata) in northern Pakistan and Nepal; and 32 isolates collected at various localities in North and South America, Europe, South Africa, New Zealand, and Australia, largely from M. sativa. Fifty distinctive multilocus genotypes (electrophoretic types [ETs]) were identified, and cluster analysis revealed two primary phylogenetic divisions separated at a genetic distance of 0.83. By the criterion of genetic differentiation conventionally applied in defining species limits among members of the family Enterobacteriaceae and certain other bacteria, the two primary divisions of R. meliloti represent distinct evolutionary species. Division A included 35 ETs represented by 209 strains from the eastern Mediterranean basin, northern Pakistan, Nepal, and various other localities worldwide. This division contained the nine commercial alfalfa inoculant strains examined. Division B included 15 ETs represented by 23 isolates, 21 of which were isolated from annual medic species growing in previously uninoculated soils in the eastern Mediterranean basin. The two remaining strains in division B, both representing the same ET, were isolated in the United States and Australia.(ABSTRACT TRUNCATED AT 250 WORDS)     

Serotypes and Genotypes of Invasive Streptococcus pneumoniae Before and After PCV10 Implementation in Southern Brazil

To reduce the burden of pneumococcal diseases, different formulations of pneumococcal conjugate vaccines (PCV) have been introduced in many countries. In Brazil, PCV10 has been available since 2010. We aimed to analyze the serotype and genetic composition of invasive pneumococci from Brazil in pre- and post- vaccination periods (2007–2012). Antibiotic susceptibility was determined and genotypes of macrolide and fluoroquinolone resistance were characterized. The genotypes of isolates of the most frequent serotypes were determined by multilocus sequence typing. The study included 325 isolates, which were primarily recovered from blood. The most common serotypes recovered were 14, 3, 4, 23F, 7F, 9V, 12F, 20, 19F, 8, 19A, and 5. Thirty-eight pneumococci (11.7%) were from children ≤5 years old. Considering the overall population, PCV10 and PCV13 serotype coverage was 50.1% and 64.9%, respectively. During the pre-vaccine period, isolates with serotypes belonging to the PVC10 represented 51.5% (100/194), whereas in the post vaccine they represented 48.0% (63/131). PCV13 serotypes represented 67.5% (131/194) and 59.2% (77/131) of total for pre- and post-vaccination periods, respectively. Seventy different sequence types [STs] were found, accounting for 9 clonal complexes [CCs] and 45 singletons. Eight STs (156, 180, 218, 8889, 53, 191, 770, and 4967) represented the majority (51.5%) of isolates. Fifty STs were associated with the pre-vaccination period (27 exclusive) and 43 (20 exclusive) with the post-vaccination period; 23 STs were identified in both periods. Some serotypes were particularly clonal (7F, 8, 12F, 20). Non-susceptibility to penicillin was associated with serotype 19A, CC320. Erythromycin resistance was heterogeneous when considering serotype and ST. A single serotype 23F (ST4967) isolate was resistant to levofloxacin. Continued surveillance is required to determine vaccine impact and to monitor changes in pneumococcal population biology post-PCV10 introduction in Brazil.