Plate Colony Sample Sizes Required for Inferences about the Uniqueness of a Lactobacillus Strain within a Human Volunteer

Making inferences about the spectrum of bacterial strains on a plate as a consequence of observing only one strain in a random sample of colonies from the plate is relatively straightforward whereas making inferences about the spectrum of strains within a human volunteer as a consequence of observing only one strain in a random sample from the plate requires some care. The issue of the appropriate number of colonies to sample from a plate to make inferences about strain uniqueness within a human volunteer is examined and illustrated with an example     

FTLD‐TDP assemblies seed neoaggregates with subtype‐specific features via a prion‐like cascade

Morphologically distinct TDP‐43 aggregates occur in clinically different FTLD‐TDP subtypes, yet the mechanism of their emergence and contribution to clinical heterogeneity are poorly understood. Several lines of evidence suggest that pathological TDP‐43 follows a prion‐like cascade, but the molecular determinants of this process remain unknown. We use advanced microscopy techniques to compare the seeding properties of pathological FTLD‐TDP‐A and FTLD‐TDP‐C aggregates. Upon inoculation of patient‐derived aggregates in cells, FTLD‐TDP‐A seeds amplify in a template‐dependent fashion, triggering neoaggregation more efficiently than those extracted from FTLD‐TDP‐C patients, correlating with the respective disease progression rates. Neoaggregates are sequentially phosphorylated with N‐to‐C directionality and with subtype‐specific timelines. The resulting FTLD‐TDP‐A neoaggregates are large and contain densely packed fibrils, reminiscent of the pure compacted fibrils present within cytoplasmic inclusions in postmortem brains. In contrast, FTLD‐TDP‐C dystrophic neurites show less dense fibrils mixed with cellular components, and their respective neoaggregates are small, amorphous protein accumulations. These cellular seeding models replicate aspects of the patient pathological diversity and will be a useful tool in the quest for subtype‐specific therapeutics.     

Patterns of genomic and allochronic strain divergence in the fall armyworm,Spodoptera frugiperda (J.E. Smith)

Speciation is the process through which reproductive isolation develops between distinct populations. Because this process takes time, speciation studies often necessarily examine populations within a species that are at various stages of divergence. The fall armyworm, Spodoptera frugiperda (J.E. Smith), is comprised of two strains (R = Rice & C = Corn) that serve as a novel system to explore population divergence in sympatry. Here, we use ddRADSeq data to show that fall armyworm strains in the field are largely genetically distinct, but some interstrain hybridization occurs. Although we detected F1 hybrids of both R‐ and C‐strain maternal origin, only hybrids with R‐strain mtDNA were found to contribute to subsequent generations, possibly indicating a unidirectional barrier to gene flow. Although these strains have been previously defined as “host plant‐associated,” we recovered an equal proportion of R‐ and C‐strain moths in fields dominated by C‐strain host plants. As an alternative to host‐associated divergence, we tested the hypothesis that differences in nightly activity patterns could account for reproductive isolation by genotyping temporally collected moths. Our data indicates that strains exhibit a significant shift in the timing of their nightly activities in the field. This divergence in phenology creates a prezygotic reproductive barrier that likely maintains the genetic isolation between strains. Thus, we conclude that it may be ecologically inaccurate to refer to the C‐ and R‐ strain as “host‐associated” and they should more appropriately be considered “allochronic strains.”     

Aerobactin production and dulcitol fermentation in clonal groups of Escherichia coli O1: K1 strains from urinary tract infections

Abstract 70 urinary Escherichia coli O1:K1 strains were characterized for O1 antigen factors, mannose-resistant hemagglutination of human erythrocytes, flagellar and fimbrial antigens, dulcitol fermentation and aerobactin production. On the basis of their O1 and H antigens the strains could be assigned to 6 distinct groups. The most prevalent groups were: O1abcd: H⁻ :F9 (33 strains; pattern II), O1abc: H⁻ :F11 (9 strains; pattern IV), and O1abc: H7: F11 (19 strains; pattern V). Strains with patterns IV and V, both expressing fimbrial antigen F11, fermented dulcitol and produced aerobactin, whereas strains with pattern II were negative for both characteristics.     

Characteristics of Ralstonia solanacearum Biovar N2 Strains in Asia

Ralstonia solanacearum biovar N2 strains isolated in Asia were compared by biochemical tests with biovar N2 strains from South America and biovar 2 (race 3) strains from Africa, America, Asia and Europe. Distinct differences were found between Asian and South American strains of biovar N2, and between Asian biovar N2 and biovar 2 strains with respect to their ability to utilize several carbon sources. Using cluster analysis based on repetitive sequence‐based polymerase chain reaction (rep‐PCR) genomic fingerprints, the Asian biovar N2 strains were divided into two groups, group 1 containing Japanese strains and group 2 containing Indonesian and Philippine strains. The fingerprints showed the genetic diversity of biovar N2 strains in Asia.     

Mouse strain variation and effects of oocyst dose in infection of mice with Eimeria falciformis, a coccidian parasite of the large intestine

Stockdale P. G. H., Stockdale M. J., Rickard M. D. and Mitchell G. F. 1985. Mouse strain variation and effects of oocyst dose in infection of mice with Eimeria falciformis, a coccidian parasite of the large intestine, International Journal for Parasitology15: 447–452. Five inbred strains of mice and three hypothymic (nude) strains were infected orally with different doses of E. falciförmis oocysts. After resolution of primary infection as determined by faecal oocyst output, mice were challenged orally with a second dose of E. falciformis. Amongst the intact mice, BALB/c proved the most resistant to primary infection, while C3H/He mice were most susceptible, in terms of faecal oocyst production. Resistance was far more dramatic in BALB/c mice given high numbers of challenge oocysts. In terms of mortality at high oocyst doses, CBA/H were the most susceptible. All of the strains of mice were highly resistant to reinfection. In the case of nude mice, BALB/c. nu/nu were more susceptible than CBA/H.nu/nu or C57BL/6.nu/nu both in terms of faecal oocyst production and mortality. Thus the most resistant inbred mouse strain (BALB/c) is the least resistant in the absence of T cells. Unlike intact mice, nude mice showed no resistance to reinfection, this result being in line with previous work on this and other Eimeria spp. in nude mice.     

IS21 insertion in the trfA replication control gene of chromosomally integrated plasmid RP1: a property of stable Pseudomonas aeruginosa Hfr strains

Summary Broad host range IncP-1 plasmids are able to integrate into the chromosome of gram-negative bacteria. Strains carrying an integrated plasmid can be obtained when the markers of a temperature-sensitive (ts) plasmid derivative are selected at non-permissive temperature; in this way Hfr (high frequency) donor strains can be formed. The integrated plasmids, however, tend to be unstable in the absence of continuous selective pressure. In order to obtain stable Hfr donor strains of Pseudomonas aeruginosa PAO, we constructed a derivative of an RP1 (ts) plasmid, pME134, which was defective in the resolvase gene (tnpR) of transposon Tn801. Chromosomal integration of pME134 was selected in a recombination-deficient (rec-102) PAO strain at 43°C. Plasmid integration occurred at different sites resulting in a useful set of Hfr strains that transferred chromosomal markers unidirectionally. The tnpR and rec-102 mutations prevented plasmid excision from the chromosome. In several (but not all) Hfr strains that grew well and retained the integrated plasmid at temperatures below 43°C, the insertion element IS21 of RP1 was found to be inserted into the trfA locus (specifying an essential trans-acting replication funtion) of the integrated plasmid. One such Hfr strain was rendered rec ⁺; from its chromosome the pME134::IS21 plasmid (=pME14) was excised and transferred by conjugation to Escherichia coli where pME14 could replicate autonomously only when a helper plasmid provided the trfA ⁺ function in trans. Thus, it appears that trfA inactivation favours the stability of chromosomally integrated RP1 in P. aeruginosa.