Dietary influences on resistance to Salmonella infection in chicks.

Studies on the influence of nutritional factors on the resistance of chicks to Salmonella gallinarum have been reviewed. Increased dietary protein decreased the resistance of chicks to this infection although resistance to Escherichia coli infections was not appreciably affected. The administration of high levels of iron, particularly when accompanied by a chelating agent such as EDTA, resulted in increased resistance to this infection. The additional iron resulted in the prevention of the transient hypoferremia and anemia during the course of the disease. Fewer viable S. gallinarum were present in the blood, liver, and spleen in the presence of increased dietary or injected iron. Cadmium added to the diet at a nontoxic level also enhanced resistance to this infection.     

Differentiation of Salmonella enterica serotype gallinarum biotype pullorum from biotype gallinarum by analysis of phase 1 flagellin C gene (fliC)

Salmonella enterica serotype gallinarum biotype gallinarum and biotype pullorum are non-motile and pathogenic avian strains. Biotype gallinarum causes fowl typhoid and biotype pullorum is the cause of pullorum disease in chickens. The two biotypes could be differentiated based on biochemical characteristics. However, conventional culture and biochemical assays are time-consuming, laborious and need sterile laboratory practices. Although the two biotypes, gallinarum and pullorum are non-motile, they possess the phase 1 flagellin C gene. The variable regions of the flagellin C gene from 41 biotype pullorum and 52 biotype gallinarum were amplified by colony-PCR and analyzed by single strand conformational polymorphism (SSCP) method. Differences in SSCP electrophoretic patterns were confirmed by nucleotide sequencing. In addition, PCR-RFLP with Hinp1I was also successfully applied to differentiate the two biotypes. These results suggested that the variable regions of fliC could be used as a genetic marker to differentiate biotype gallinarum from biotype pullorum.     

Spacing behaviour and habitat use of rock ptarmigan (Lagopus mutus) at low density in the Italian Alps

Studies of rock ptarmigan Lagopus mutus in northern latitudes have shown that, in the breeding season, the majority of cocks pair monogamously and defend small territories, whilst in most populations, a small proportion of cocks are polygynous or remain unmated. Little is known, however, on spacing behaviour and habitat use of alpine rock ptarmigan populations occurring at low densities at the southern edge of the species’ range. From 1995 to 1997, we trapped, radio-tracked and observed birds in the Central Italian Alps (elevation 2,000–3,000 m) in order to investigate spacing behaviour and habitat use in alpine landscapes where habitats offering rich food and cover are patchy. Both sexes were selective in their habitat use, and cocks did not establish territories on bare ground, artificial or nutrient rich grasslands or bogs. In the breeding season, cocks had larger home ranges than hens (cocks 99 ± 57 ha, hens 50 ± 25 ha) that overlapped with the ranges of neighbouring cocks and hens. Cocks were monogamous and defended relatively large territories (core areas of home ranges: cocks 37 ± 26 ha, hens 24 ± 12 ha), which corresponded with low spring densities (0.47–2.29 cocks km⁻² and 0.35–1.60 pairs km⁻²). Territory size of individual cocks was negatively correlated with the amount of high quality habitat in the core-area. Our results suggest increased home ranges and large breeding territories in low density alpine rock ptarmigan populations, compared to populations occurring at higher densities in the central and northern alps, and on subarctic and arctic grounds at northern latitudes, confirming the predictions of models on food-based territoriality.     

A short-term divergent selection for resistance to Teladorsagia circumcincta in Romanov sheep using natural or artificial challenge

This experiment was conducted to assess the efficiency of selection on the basis of response to artificial challenges in order to breed sheep resistant to natural infection. A short-term divergent selection process was designed to estimate the genetic parameters of these two traits. Two flocks, including 100 Romanov ram lambs each, were challenged in 1990 when they were 6 months old. One flock received three artificial infections with 20 000 third-stage Teladorsagia circumcincta larvae, at intervals of 7 weeks. Faecal egg counts (FEC) were performed on Days 22, 25 and 28 post infection (p.i.) and the animals were drenched on Day 28 p.i. The other flock was grazed for 5 months on a pasture contaminated with the same species. Faecal samples were taken from the lambs at similar ages. About 5 rams with the lowest FEC and 5 with the highest FEC were selected in each flock and mated with unselected ewes. Their offspring (200 animals) were challenged in 1992, half in the same way as their sires, and the other half by the other method. Because of a drought in the summer of 1990, it was necessary to repeat part of the experiment, and in 1992 the 5 and 8 rams with the lowest and highest FEC, respectively, were selected from the offspring challenged on the pasture in 1992 and were mated with unselected ewes. Their progeny (about 80 animals) were challenged in 1994, half by natural infection, half by artificial infection. The mean FEC of the flock increased from the first to the third artificial infection. The natural infection was highly variable in different years, reflecting the difficulty of assessing resistance using this mode of challenge. Genetic parameters were estimated using animal models and REML solutions. The repeatabilities of the FEC following artificial and natural infection were 0.49 and 0.70 respectively within a period of one week, and 0.22 and 0.41 respectively for periods separated by intervals of 7 weeks; the heritabilities of the single egg count were 0.22 and 0.38 respectively. The genetic correlation was 0.87: the FEC recorded under natural or artificial infection appear to depend on the same genetic potential.     

Unusual recovery of animal staphylococci from septic wounds of hospital patients in Ile-Ife, Nigeria

Two Staphylococcus species— Staphylococcus gallinarum and Staphylococcus sciuri —previously known to be of animal origin have been isolated from infected wounds of hospital patients in Ile-Ife, Nigeria. These organisms were non-typable at both RTD and 100×RTD and did not produce β-lactamase detectable by the normal methods. Their actual involvement in the infection is not immediately clear, but their resistance to most common antibiotics, in addition to the production of DNase and phosphatase, may be indicating that these species could become important skin contaminants in humans and opportunistic zoonotics.     

Allele-specific PCR method based on rfbS sequence for distinguishing Salmonella gallinarum from Salmonella pullorum: serotype-specific rfbS sequence polymorphism

Cloning and sequence analysis of rfbS gene identified two polymorphic nucleotides, one at position 598 (Salmonella gallinarum-specific) and other at position 237 (Salmonella pullorum-specific). Based on S. gallinarum-specific nucleotide found at position 598, an allele-specific PCR method was developed for serotype-specific detection of S. gallinarum. This PCR method was able to discriminate pure cultures of S. gallinarum from S. pullorum and other Salmonella serotypes from serogroup D in less than 3 h. Serotype-specific detection of S. gallinarum was possible in less than 24 h when the PCR was applied on the presumptive Salmonella colonies obtained after overnight incubation of selective media plates streaked with the clinical material from diseased chickens. As little as 100 pg of genomic DNA could be detected with S. gallinarum-specific primers; no PCR product was detected in non-S. gallinarum serotypes of serogroup D and other closely related non-salmonella organisms. This rfbS allele-specific amplification assay is specific, reproducible and less time consuming than the standard bacteriological methods used to detect S. gallinarum and could be an effective molecular tool for rapid definitive diagnosis of fowl typhoid in the areas of endemicity where fowl typhoid infection exists.     

内生真菌对植物生长发育及抗逆性的影响

本文从内生真菌的涵义和基本生物学特征出发,对国内外近二十年来关于内生真菌与植物关系的研究情况作了综述,主要包括内生真菌的检测、鉴定和转染,内生真菌对植物生长发育与抗逆性的影响,以及内生真菌在农业及其他相关领域的应用前景。文中提及作者近期开展的关于内生真菌对黑麦草抗旱性影响的研究课题及其初步进展。     

内生真菌对植物生长发育及抗逆性的影响

本文从内生真菌的涵义和基本生物学特征出发,以国内外近二十年来关于内生真菌与植物关系的研究情况作了综述。主要包括内生真菌的检测、鉴定和转染,内生真菌对植物生长发育与抗逆性的影响,以及内生真菌在农业及其他相关领域的应用前景。文中提及作者近期开展的关于内生真菌对黑麦草抗旱性影响的研究课题及其初步进展。     

The effect of growth-promoting antibiotics on the faecal enterococci of healthy young chickens

Small groups of chickens were given feed containing either avoparcin, nitrovin, vir-giniamycin or zinc bacitracin from the day of their purchase as day-olds. Differences between the birds receiving growth promoters and the untreated controls were observed during the last third of the 23 d survey period. The enterococcal population of the 'dosed' birds contained a greater proportion of Enterococcus faecium than did that of the control birds while the converse was true for Ent. gallinarum . This apparent selection of Ent. faecium by the growth-promoting antibiotics had an influence on the incidence of resistance to therapeutic antibiotics among the enterococcal population as a whole. This was because this species was generally more resistant than Ent. gallinarum to cephalothin, the MLS antibiotics (erythromycin, lincomycin and tylosin) and tetracycline.     

Tetratrichomonas gallinarum in the Blood of Chickens Infected with Spirochetes

SYNOPSIS. Tetratrichomonas gallinarum was found in the blood of 3 chickens experimentally infected with Borrelia anserina . The blood infection was successfully reproduced in healthy chickens and was accompanied by evidence that the trichomonads multiplied in the blood, ingested red blood cells, and were themselves phagocytized by leucocytes. T. gallinarum was maintained in serial passage in chicken embryos as well as in the usual trichomonad culture media.     

The effect of recreational homes on willow ptarmigan (Lagopus lagopus) in a mountain area of Norway

The increasing development of recreational resorts and second homes in mountain regions worldwide require substantial infrastructure, and have large impact on habitats and ecosystems. We hypothesized that developed areas would attract predators and lead to higher predation on willow ptarmigan and lower their abundance. In a 500-km² study area in south-central Norway, we sampled the density of territorial cocks in spring and the breeding success of willow ptarmigan along a 3-km gradient extending out from clusters of cabins. We also sampled red fox scats and corvid birds and measured nest predation on artificial nests across this gradient. Densities of cocks in the spring and of adults and brood sizes in August did not vary along the gradient. However, the density of chicks in August was higher beyond 1.5 km from cabin areas, presumably because more hens lost their clutches in the vicinity of cabins. This was supported by the results from the artificial nest experiment where significantly more nests were depredated near cabin areas than further away. The number of scats of red fox along trails increased with distance from cabins, whereas more corvid birds were observed near cabins. We conclude that corvid birds were the main cause of higher loss of ptarmigan nests near cabin areas, which led to lower production of chicks. Breeding density, however, did not seem to vary along the gradient, presumably because of suitable habitat for breeding and little human activity in these areas during the period of pair formation and nesting.     

Development of the testes in female domestic fowls submitted to an experimental sex reversal during embryonic life

The sex differentiation of the female chick embryo can be totally inverted toward the male sex by an early extraembryonic testis grafting. This sex reversal remains permanent, as shown by three adult fowls described in this paper. They possess two testes associated with normally differentiated male excretory ducts and their Müllerian ducts have regressed. The development of male sex characteristics such as external features, behavior and complete spermatogenesis is evidence that these cocks have endocrine and exocrine capabilities similar to those of normal cocks. Although these cocks were able to mate with female fowls, they were sterile. A mechanism is discussed by which grafted testes induce such modifications in females. Hypotheses considering the heterogametic sex (female in birds) as exerting a dominant influence on the phenotypic sexual differentiation can be discarded in light of our results because a homogametic testis provokes the definitive sex inversion of a female.     

Genetic variation in herbivore resistance and tolerance: the role of plant life‐history stage and type of damage

Information of the patterns of genetic variation in plant resistance and tolerance against herbivores and genetic trade‐offs between these two defence strategies is central for our understanding of the evolution of plant defence. We found genetic variation in resistance to two specialist herbivores and in tolerance to artificial damage but not to a specialist leaf herbivore in a long‐lived perennial herb. Seedlings tended to have genetic variation in tolerance to artificial damage. Genetic variation in tolerance of adult plants to artificial damage was not consistent in time. Our results suggest that the level of genetic variation in tolerance and resistance depends on plant life‐history stage, type of damage and timing of estimating the tolerance relative to the occurrence of the damage, which might reflect the pattern of selection imposed by herbivory. Furthermore, we found no trade‐offs between resistance and tolerance, which suggests that the two defence strategies can evolve independently.     

Selection for resistance to a fungal pathogen in Drosophila melanogaster

An artificial selection experiment designed to explore the evolution of resistance to a fungal pathogen, Beauveria bassiana, in Drosophila melanogaster is reported here. The experiment was designed to test whether there is sufficient additive genetic variation in this trait for increased resistance to evolve, and, if so, whether there are correlated responses that might represent a cost to defence. After 15 generations of selection, flies from selected lines did not have higher overall fitness after infection compared with control lines. The response to selection for resistance against this pathogen is thus much weaker than against other species, in particular, parasitoids. There was, however, evidence for increased late-life fecundity in selected lines, which may indicate evolved tolerance of fungal infection. This increase was accompanied by reduced early-life fitness, which may reflect the well-known trade-off between early and late reproduction. In the absence of fungal infection, selected flies had lower fitness than control flies, and the possibility that this is also a trade-off with increased tolerance is explored.     

PCR-RFLP和测交方法对进口祖代蛋鸡异性个体间的遗传同质性检测

对进口Ｘ祖代鸡Ｂ系和Ｄ系共１４３羽异性公鸡的Ｋ座位羽速型作了Ｋ座位隐性测交,杂合子占４１．９６％,慢羽纯合子占３５．６６％,另有９羽和２羽公鸡分别因后裔数少于７羽或是后裔快慢羽鸡比例严重偏离１：１而被判为无效,对８羽进口祖代Ｄ系异性公鸡的ＰＣＲ－ＲＦＬＰ分析的结果表明,６羽公鸡为Ｋ座位显性纯合子（仅检到１４５０ｂｐＤＮＡ片段）,２羽为杂合子（检到１４５０ｂｐ、１０６８ｂｐ和３８２ｂｐ共３条带）。通     

Cost of resistance: relationship between reduced fertility and increased resistance in a snail—schistosome host—parasite system

Natural host populations often exhibit genetic variability in resistance to parasitism. One possible mechanism for maintaining such diversity is a trade-off between fitness costs associated with resistance and fitness costs associated with parasitism. However, little is known about the nature or magnitude of these costs in animal populations. Using artificial selection experiments in a Biomphalaria glabrata–Schistosoma mansoni host–parasite system, we demonstrated that resistance and susceptibility to infection are heritable. We then investigated whether resistance had any associated costs in terms of snail reproductive success. Susceptible-selected snail lines showed significantly higher fertility (number of offspring produced) than resistant-selected or unselected control snail lines, irrespective of current infection status. There were no consistent differences between snail lines in fecundity, proportion of abnormal egg masses produced, or mean number of eggs per egg mass. Mortality rate was higher among infected than uninfected snails. These results are consistent with snails incurring costs of resistance to schistosome infection in the absence of the parasite.     

Artificial microRNA-mediated virus resistance in plants

RNA silencing in plants is a natural defense system against foreign genetic elements including viruses. This natural antiviral mechanism has been adopted to develop virus-resistant plants through expression of virus-derived double-stranded RNAs or hairpin RNAs, which in turn are processed into small interfering RNAs (siRNAs) by the host's RNA silencing machinery. While these virus-specific siRNAs were shown to be a hallmark of the acquired virus resistance, the functionality of another set of the RNA silencing-related small RNAs, microRNAs (miRNAs), in engineering plant virus resistance has not been extensively explored. Here we show that expression of an artificial miRNA, targeting sequences encoding the silencing suppressor 2b of Cucumber mosaic virus (CMV), can efficiently inhibit 2b gene expression and protein suppressor function in transient expression assays and confer on transgenic tobacco plants effective resistance to CMV infection. Moreover, the resistance level conferred by the transgenic miRNA is well correlated to the miRNA expression level. Comparison of the anti-CMV effect of the artificial miRNA to that of a short hairpin RNA-derived small RNA targeting the same site revealed that the miRNA approach is superior to the approach using short hairpin RNA both in transient assays and in transgenic plants. Together, our data demonstrate that expression of virus-specific artificial miRNAs is an effective and predictable new approach to engineering resistance to CMV and, possibly, to other plant viruses as well.     

Characterization of glycopeptide resistant enterococci isolated from a hospital in Naples (Italy)

A study on the antibiotic resistance of enterococcal isolates (n = 280) was carried out in a teaching hospital in Naples. Strains were isolated from different sources, identified by conventional tests and their antibiotic susceptibility was tested by E-test method. Thirty-two enterococcal isolates (11.5%), phenotypically identified as E. faecium (n = 26), E. gallinarum (n = 3), E. faecalis (n = 2) and E. hirae (n = 1), showed resistance to glycopeptides. The vanA gene was found in all 32 VRE. Molecular typing was performed by RAPD analysis which showed two majors patterns.     

Does multiple paternity influence offspring disease resistance?

It has been suggested that polyandry allows females to increase offspring genetic diversity and reduce the prevalence and susceptibility of their offspring to infectious diseases. We tested this hypothesis in wild‐derived house mice (Mus musculus) by experimentally infecting the offspring from 15 single‐ and 15 multiple‐sired litters with two different strains of a mouse pathogen (Salmonella Typhimurium) and compared their ability to control infection. We found a high variation in individual infection resistance (measured with pathogen loads) and significant differences among families, suggesting genetic effects on Salmonella resistance, but we found no difference in prevalence or infection resistance between single‐ vs. multiple‐sired litters. We found a significant sex difference in infection resistance, but surprisingly, males were more resistant to infection than females. Also, infection resistance was correlated with weight loss during infection, although only for females, indicating that susceptibility to infection had more harmful health consequences for females than for males. To our knowledge, our findings provide the first evidence for sex‐dependent resistance to Salmonella infection in house mice. Our results do not support the hypothesis that multiple‐sired litters are more likely to survive infection than single‐sired litters; however, as we explain, additional studies are required before ruling out this hypothesis.     

Prevalence and pathology of the nematode Heterakis gallinarum, the trematode Paratanaisia bragai, and the protozoan Histomonas meleagridis in the turkey, Meleagris gallopavo

The prevalence of infection and associated pathology induced by two helminth and one protozoan species infecting Brazilian turkeys are reported. The intestinal nematode Heterakis gallinarum appeared with a prevalence of 70% in the infected birds, without gross lesions when not associated to the protozoan Histomonas meleagridis. Histological findings in the ceca were represented by the presence of H. gallinarum worms, intense chronic diffuse inflammatory processes with mononuclear and polymorphonuclear (heterophils) leucocyte infiltrations. The prevalence of the protozoan H. meleagridis associated to H. gallinarum was of 2.5% and microscopic examination revealed a severe inflammatory process in the liver and cecum with the presence of small clear areas with round eosinophilic parasites. Gross lesions were absent in turkeys infected with the renal digenetic trematode Paratanaisia bragai; the parasite was prevalent in 20% of the cases and cross-sections of the kidneys showed a remarkable distension of the collecting ducts with several worms in the lumen. The walls of the ducts presented a discrete heterophilic infiltrate among mononuclear cells.