Leishmania major: culture media, mouse strains, and promastigote virulence and infectivity

Promastigotes of Leishmania major were isolated from an infected mouse in two media, blood agar and Schneider's medium + 30% fetal calf serum, and maintained continuously for over 1 year. Infectivity studies in two strains of mice, outbred CD1 strain and inbred BALB/c strain, showed that promastigotes grown in Schneider's medium maintained infectivity to BALB/c mice throughout the period of cultivation. Infectivity to CD1 strain mice was progressively lost. Promastigotes grown in blood agar medium, however, lost infectivity to both strains of mice at a faster rate than promastigotes grown in Schneider's medium.     

Correlation between the distribution pattern of virulence genes and virulence of Aeromonas hydrophila strains

Nine strains of Aeromonas hydrophila isolated from diseased fish or soft-shelled tortoise were tested for the presence of three virulence genes including the genes encoding aerolysin,hemolysin,and extracellular serine protease (i.e.,aerA,hlyA,and ahpA,respectively).These genes were investigated using polymerase chain reaction (PCR)with specific primers for each gene.And the pathogenicities to Carrassius auratus ibebio of these strains were also assayed.PCR results demonstrated that the distribution patterns of aerA,hlyA,and ahpA were different in these strains.6/9 of A.hydrophila strains were aer A positive,8/9 of strains hly A positive,7/9 of strains ahp A positive,respectively.However,the assay for pathogenesis showed that two strains (A.hydrophila XS91-4-1 and C2)were strong virulent,two strains (A.hydrophila ST78-3-3 and 58-20-9)avirulent and the rest middle virulent was to the fish.In conclusion,there are significant correlation between the distribution pattern of the three virulence genes and the pathogenicity to Carrassius auratus ibebio.All strong virulent A.hydrophila strains were aerA+hlyA+ahpA+genotype,and all aerA+hlyA+ahpA+strains were virulent.Strains with the genotype of aerA-hlyA-ahpA+have middle pathogenicity.In the present study,we found for the first time that all A.hydrophila isolated from the ahpA positive were virulent to Carrassius auratus ibebio.Additionally,there was a positive correlation between the virulence of A.hydrophila and the presence of aerA and ahpA.     

Sex and virulence in Escherichia coli: an evolutionary perspective

Pathogenic Escherichia coli cause over 160 million cases of dysentery and one million deaths per year, whereas non-pathogenic E. coli constitute part of the normal intestinal flora of healthy mammals and birds. The evolutionary pathways underlying this dichotomy in bacterial lifestyle were investigated by multilocus sequence typing of a global collection of isolates. Specific pathogen types [enterohaemorrhagic E. coli, enteropathogenic E. coli, enteroinvasive E. coli, K1 and Shigella] have arisen independently and repeatedly in several lineages, whereas other lineages contain only few pathogens. Rates of evolution have accelerated in pathogenic lineages, culminating in highly virulent organisms whose genomic contents are altered frequently by increased rates of homologous recombination; thus, the evolution of virulence is linked to bacterial sex. This long-term pattern of evolution was observed in genes distributed throughout the genome, and thereby is the likely result of episodic selection for strains that can escape the host immune response.     

Sex against virulence: the coevolution of parasitic diseases

Reciprocal selection is the underlying mechanism for host-parasite coevolutionary arms races. Its driving force is the reduction of host lifespan or fecundity that is caused by a parasite. Parasites evolve to optimize host exploitation, while hosts evolve to minimize the 'parasite-induced' loss of fitness (virulence). Research on the evolution of virulence has mostly emphasized the role of parasite evolution in determining virulence. However, host evolution, accelerated by sexual recombination, contributes to the evolution and expression of virulence as well. The Red Queen hypothesis predicts that genetic variation among host offspring facilitates selection for reduced virulence. Here, we outline a synthesis between current thinking about the evolution of virulence and the evolution of sex.     

Experimental bacteriophage-mediated virulence in strains of Vibrio harveyi

Vibriosis is a major disease problem in prawn aquaculture. Until now there has been no clear explanation why some strains of Vibrio are pathogenic, while others are not. This study demonstrated that the presence of the bacteriophage V. harveyi myovirus like (VHML) may confer virulence to V. harveyi Strain 642. This was demonstrated by infecting na?ve avirulent V. harveyi Strains 12, 20, 45 and 645 with the bacteriophage and converting them into virulent strains. The previously na?ve strains of Vibrio infected with Bacteriophage VHML from V. harveyi Strain 642 demonstrated up-regulation of haemolysin, up-regulation of protein excretion, additional proteins which were recognised as toxic proteins from Strain 642 by monoclonal antibodies specific to the exotoxin sub-units, and a significant increase in mortality of larval Penaeus monodon. It was concluded that Bacteriophage VHML conferred virulence to V. harveyi Strains 12, 20, 45 and 645 and that Bacteriophage VHML either fully or partly confers virulence in V. harveyi Strain 642.     

Sex ratio of inbred strains of mice

A study of the sex ratio in mice of the inbred strains (CBA and C3H) and connection of the postimplantation embryonic mortality in mice of these strains with the sex distribution of embryos demonstrated that the sex ratio in these mice was 1:1. Literature and the author's personal data suggested that genetic features of mice of the inbred strains failed to influence significantly the sex ratio of the offspring. The postimplantation embryonic death rate in the C3H mice exceeded that in the CBA mice (14.4 and 9.3%, respectively). However, the balanced sex ratio in mice of these strains points to the absence of selective mortality of the embryos of any one sex during embryogenesis.     

Correlation between the distribution pattern of virulence genes and virulence of Aeromonas hydrophila strains

Nine strains of Aeromonas hydrophila isolated from diseased fish or soft-shelled tortoise were tested for the presence of three virulence genes including the genes encoding aerolysin, hemolysin, and extracellular serine protease (i.e., aerA, hlyA, and ahpA, respectively). These genes were investigated using polymerase chain reaction (PCR) with specific primers for each gene. And the pathogenicities to Carrassius auratus ibebio of these strains were also assayed. PCR results demonstrated that the distribution patterns of aerA, hlyA, and ahpA were different in these strains. 6/9 of A. hydrophila strains were aerA positive, 8/9 of strains hlyA positive, 7/9 of strains ahpA positive, respectively. However, the assay for pathogenesis showed that two strains (A. hydrophila XS91-4-1 and C2) were strong virulent, two strains (A. hydrophila ST78-3-3 and 58-20-9) avirulent and the rest middle virulent was to the fish. In conclusion, there are significant correlation between the distribution pattern of the three virulence genes and the pathogenicity to Carrassius auratus ibebio. All strong virulent A. hydrophila strains were aerA ⁺ hlyA ⁺ ahpA ⁺ genotype, and all aerA ⁺ hlyA ⁺ ahpA ⁺ strains were virulent. Strains with the genotype of aerA ⁻ hlyA ⁻ ahpA ⁺ have middle pathogenicity. In the present study, we found for the first time that all A. hydrophila isolated from the ahpA positive were virulent to Carrassius auratus ibebio. Additionally, there was a positive correlation between the virulence of A. hydrophila and the presence of aerA and ahpA. __________ Translated from Acta Scientiarum Naturalium Universitatis Sunyatseni, 2006, 45(1): 82–85 [译自: 中山大学学报 (自然科学版)]     

Variation of virulence and other properties among Sendai virus strains

The virulence of five Sendai virus strains (MN, Z, KN, Mol, and Hm) isolated from laboratory rodents was compared, using 3-week-old female Jcl-ICR mice. The virulence of the strains was Mol, MN, KN, Z, and Hm in decreasing order. The 50% lethal dose and 50% lung consolidation inducing dose of the highest virulent strain differed by the order of more than 10(3) and 10(6), respectively, from those of the lowest virulent one. Other properties such as the growth rate in LLC-MK2 cells, neuraminidase activities, and molecular weights of structural proteins also differed among the virus strains. These results indicate that Sendai virus prevailing in laboratory rodents is not homogenous with respect to virulence and some other properties.     

Sequenced dermatophyte strains: growth rate, conidiation, drug susceptibilities, and virulence in an invertebrate model

Although dermatophytes are the most common cause of fungal infections in the world, their basic biology is not well understood. The recent sequencing and annotation of the genomes of five representative dermatophyte species allows for the creation of hypotheses as to how they cause disease and have adapted to their distinct environments. An understanding of the microbiology of these strains will be essential for testing these hypotheses. This study is the first to generally characterize these five sequenced strains of dermatophytes for their microbiological aspects. We measured the growth rate on solid medium and found differences between species, with Microsporum gypseum CBS118893 having the fastest growth and Trichophyton rubrum CBS118892 the slowest. We also compared different media for conidia production and found that the highest numbers of conidia were produced when dermatophytes were grown on MAT agar. We determined the Minimum Inhibitory Concentration (MIC) of nine antifungal agents and confirmed susceptibility to antifungals commonly used as selectable markers. Finally, we tested virulence in the Galleria mellonella (wax moth) larvae model but found the results variable. These results increase our understanding of the microbiology and molecular biology of these dermatophyte strains and will be of use in advancing hypothesis-driven research about dermatophytes.     

Diversity, persistence, and virulence of Aeromonas strains isolated from drinking water distribution systems in Sweden

The Aeromonas populations in 13 Swedish drinking water distribution systems, representing different treatments, were investigated. From each system, water samples were collected four times during the period from May to September 1994 from raw water and water after treatment and at two to five sites within the distribution system. In total, 220 water samples were collected. From samples containing presumptive Aeromonas, up to 32 colonies were analyzed by the PhenePlate Aeromonas (PhP-AE) system, which is a highly discriminating biochemical fingerprinting method. Selected isolates from different phenotypes (PhP types) were further identified by the API 20 NE system and by gas-liquid chromatography analysis of fatty acid methyl esters (FAMEs). Selected isolates were also assayed for their potential to produce hemolysin and cytotoxin and for their ability to adhere to human intestinal cells. In total, 117 water samples (53%) contained presumptive Aeromonas which numbered up to 10(6) CFU/100 ml in raw water and up to 750 CFU/100 ml in tap water. Among the 2,117 isolates that were subjected to typing by the PhP-AE system, more than 300 distinct PhP types were found, of which the majority occurred only sporadically. Raw (surface) water samples usually contained many different PhP types, showing high diversity indices (Di) (median Di = 0.95). The Aeromonas populations in samples collected from within the distribution systems were less diverse (median Di = 0.58) and were often dominated by one major PhP type that was found on several sampling occasions. Seventeen such major PhP types could be found and were represented in 1,037 isolates (49%). Identification by API 20 NE and FAME analysis revealed that most of the major PhP types were Aeromonas hydrophila or belonged to unidentified Aeromonas species. Hemolysin and cytotoxin production was observed in most major PhP types (representing 87 and 54% of the assayed isolates, respectively), and adherence was found in 89% of the isolates that produced cytotoxin. Thus, the data presented here show that although raw water may contain very diverse Aeromonas populations, the populations seemed to be remarkably stable within the studied water distribution systems, and that some potentially pathogenic Aeromonas strains could persist for several months in drinking water.     

Superoxide dismutase, catalase and peroxidase in four strains of Neisseria meningitidis of different virulence

Abstract The effects of growth media on superoxide dismutase (SOD), catalase and peroxidase were compared in cell-free extracts from four strains of Neisseria meningitidis . The highly virulent strains, DRES-14 and M-1011, were consistently higher in SOD and catalase than the less virulent strains, DRES-03 and DRES-04. Cells grown in brain-heart infusion medium contained the highest levels of catalase. N. meningitidis contained one electrophoretic SOD band which was identified as iron-containing SOD (FeSOD). It was also shown that the presence of catalase could yield an artifactual SOD-band when the SOD activity stain is performed in the presence of 10 mM H₂O₂, normally required to inactivate and identify FeSODs.     

Genetic variation in virulence among chalkbrood strains infecting honeybees

Ascosphaera apis causes chalkbrood in honeybees, a chronic disease that reduces the number of viable offspring in the nest. Although lethal for larvae, the disease normally has relatively low virulence at the colony level. A recent study showed that there is genetic variation for host susceptibility, but whether Ascosphaera apis strains differ in virulence is unknown. We exploited a recently modified in vitro rearing technique to infect honeybee larvae from three colonies with naturally mated queens under strictly controlled laboratory conditions, using four strains from two distinct A. apis clades. We found that both strain and colony of larval origin affected mortality rates. The strains from one clade caused 12-14% mortality while those from the other clade induced 71-92% mortality. Larvae from one colony showed significantly higher susceptibility to chalkbrood infection than larvae from the other two colonies, confirming the existence of genetic variation in susceptibility across colonies. Our results are consistent with antagonistic coevolution between a specialized fungal pathogen and its host, and suggest that beekeeping industries would benefit from more systematic monitoring of this chronic stress factor of their colonies.     

Presence of virulence markers in environmental Vibrio vulnificus strains

Aims

This work aims to demonstrate the presence of several genes and factors associated with virulence in strains isolated from the environment at Pueblo Viejo Lagoon, State of Veracruz, Mexico.

Methods and Results

In this study, we investigated the production of V. vulnificus virulence factors, as cytolysin (haemolysin), RTX toxin, metalloprotease, siderophores, capsular polysaccharide, adhesion structures (like type IV pili), and polar and lateral flagella, involved in swimming and swarming (or, at least, the presence of genes encoding some of them) in 40 strains of V. vulnificus isolated from water and food. The results indicate that strains of environmental origin possess potential virulence characteristics.

Conclusions

Caution should be exercised when consuming raw shellfish (especially by those more susceptible risk groups).

Significance and Impact of the Study

This is the first work focused on the evaluation of V. vulnificus virulence factors in Mexico.