Inheritance of resistance to flumethrin in the Mexican Aldama strain of the cattle tick Boophilus microplus (Acari: Ixodidae)

The objective of this study was to evaluate the inheritance mode of resistance to flumethrin in the Mexican Aldama Boophilus microplus strain. Two Mexican strains were used, the Chiapas susceptible (SS), and the Aldama flumethrin-resistant from Tamaulipas. Six steers weighing ca. 250 kg were randomly assigned for each of six crosses: the susceptible (SS), resistant (RR), and the F1 (RS, SR) reciprocal crosses and F2 (RS x RS and SR x SR). The reciprocal crosses were made to evaluate maternal and sex linkage effects. Bioassays tested resistant and susceptible larvae along with their hybrid F1 and F2 progeny against a series of concentrations of flumethrin (0, 0.0075, 0.00150, 0.00300, 0.00600 and 0.01200 microg/g). To test the single-gene hypothesis of resistance, a nonparametric line-cross test proposed by Collins was used. The bioassay data were subjected to probit analysis and the resistance factor and effective dominance obtained. Results of this study indicated that inheritance for flumethrin resistance in the Aldama strain was autosomal and controlled for more than one gene. The F1 and F2 larvae had similar lower resistant factor (RF 2.8-4.5) while the resistant Aldama strain was 21-fold higher (RF 81.8) than the mean of the F1 and F2. The extent of flumethrin resistance in the Aldama B. microplus strain depended upon the concentration of the pesticide used. Resistance was almost dominant at the lowest dose while almost completely recessive at the highest dose. Maternal effects were shown for egg-mass. These results shown here indicate more than one gene basis of flumethrin resistance in B. microplus ticks are present. Therefore it is necessary to locate and understand the major loci for elucidate the mechanism of resistance and improve the ability to track and delay the evolution of resistance.     

A rapid urease test for presumptive identification of Cryptococcus neoformans

A rapid method to evidence urease activity is described. Urea hydrolysis and consequent production ammonia are detected by a chemical reaction producing a blue phenol compound (indophenol blue). Three hundred and three yeast were tested. Out of 107 urease-positive organisms detected by Christensen's Urea Agar Test (CUAT) 102 were positive by our method. No false negatives were observed by this method when testing 87 Cryptococcus strains. Ths practical screening test for presumptive identification of Cryptococcus neoformans is simple, unaffected by pH changes and requires 15 minutes to be performed.     

Serogroups, K1 antigen, and antimicrobial resistance patterns of Aeromonas spp. strains isolated from different sources in Mexico

A total of 221 strains of Aeromonas species isolated in Mexico from clinical (161), environmental (40), and food (20) samples were identified using the automated system bioMérieux-Vitek. Antisera for serogroups O1 to 044 were tested using the Shimada and Sakazaki scheme. The K1 antigen was examined using as antiserum the O7:K1C of Escherichia coli. Besides, we studied the antimicrobial patterns according to Vitek AutoMicrobic system. Among the 161 clinical strains 60% were identified as A. hydrophila, 20.4% as A. caviae, and 19.25% as A. veronii biovar sobria. Only A. hydrophila and A. veronii biovar sobria were found in food (55 and 90% respectively) and environmental sources (45 and 10% respectively). Using "O" antisera, only 42.5% (94/221) of the strains were serologically identified, 55% (121/221) were non-typable, and 2.5% (6/221) were rough strains. Twenty-two different serogroups were found, O14, O16, O19, O22, and O34 represented 60% of the serotyped strains. More than 50% of Aeromonas strain examined (112/221) expressed K1 encapsulating antigen; this characteristic was predominant among Aeromonas strains of clinical origin. Resistance to ampicillin/sulbactam and cephazolin was detected in 100 and 67% of Aeromonas strain tested for their susceptibility to antibiotics. In conclusion, antibiotic-resistant Aeromonas species that possess the K1 encapsulating antigen and represent serogroups associated with clinical syndrome in man are not uncommon among Aeromonas strains isolated from clinical, food and environmental sources in Mexico.     

Responsive regions for direct organogenesis in sunflower cotyledons

Regeneration efficiency from three different regions of cotyledonary explants was examined in six sunflower inbred lines. Proximal, middle and distal regions from seedling cotyledons were cultured on regeneration medium supplemented with growth regulators. Plant regeneration by direct organogenesis was observed after four weeks. Significant differences among inbred lines were found for regeneration percentage and average number of shoots per total explants. Also a decreasing regeneration capacity was observed from proximal to distal sections for all inbred lines. Regeneration ability from cotyledonary explants in this species is strongly influenced by the genotype and by the region from which the explant was obtained. The distance to the cotyledonary node plays a preponderant role in the expression of shoot forming capacity. Shoot differentiation via seedling cotyledons depends upon the presence of the proximal region of cotyledon regardless of the genotype.     

Squid nerve Na+/Ca2+ exchanger expressed in Saccharomyces cerevisiae: Up-regulation by a phosphorylated cytosolic protein (ReP1–NCXSQ) is identical to that of native exchanger in situ

This work shows, for the first time, a properly metabolically regulated squid nerve Na⁺/Ca²⁺ exchanger (NCXSQ1) heterologous expressed in Saccharomyces cerevisiae. The exchanger was fused to the enhanced green fluorescence protein (eGFP) on its C-terminus and had two tags, a Strep-tag II and 6 histidines, added to the N-terminal region (ST–6HB–NCXSQ1–eGFP). The eGFP fluorescence signal co-localized with that of the plasma membrane marker FM1-43 in whole cells that displayed an uptake of Ca²⁺ with the expected characteristics of the reverse Na⁺/Ca²⁺ exchange mode. Similar to squid nerve membrane vesicles, inside-out yeast plasma membrane vesicles (ISOV) showed a Ca²⁺_i regulation of the forward mode that was modulated by previously phosphorylated regulatory cytosolic protein (ReP1–NCXSQ). On the other hand, a close association between NCXSQ1 and ReP1–NCXSQ, estimated by co-immunoprecipitation, was independent of ReP1–NCXSQ phosphorylation. An additional crucial observation was that in proteoliposomes containing only the ST–6HB–NCXSQ1–eGFP protein, Na⁺/Ca²⁺ exchange was stimulated by phosphorylated ReP1–NCXSQ; i.e., this up-regulation needs no other requirement besides the lipid membrane and the exchanger protein. Finally, this work provides a potential approach to obtain enough purified NCXSQ1 for structural and biochemical studies which have been delayed due to the lack of sufficient material.     

Agentes de micosis endémicas en un área rural de Argentina: estudio seroepidemiológico en perros

BackgroundThree fungal species causing human disease, namely Paracoccidioides brasiliensis, Histoplasma capsulatum and Coccidioides sp., are endemic in different areas of Argentina. Rates of infection in domestic dogs have been used in other Latin American countries as indicators of the presence of these pathogens in a given area. We used such an approach to investigate the epidemiological relevance of paracoccidiodomycosis, histoplasmosis and coccidioidomycosis in our country.AimTo investigate the presence of P. brasiliensis, H. capsulatum and Coccidioides sp. in a rural area of Argentina called Interfluvio Teuco-Bermejito, located in Chaco province.MethodsWe applied Western Blotting to determine the presence of specific antibodies in sera from 89 domestic dogs inhabiting the area. Antibodies against the following extra-cellular fungal antigens were investigated: gP43 of P. brasiliensis, H/M of H. capsulatum and 120, 82 and 48 kDa antigen bands of Coccidioides sp.ResultsSpecific antibodies against H. capsulatum were found in 9/89 (10%) sera: 8 reacted against both H and M antigens and 1 only reacted against antigen M. Of these 9 sera, one showed additional anti-gp43 activity and another reacted against all the fungal antigens tested.ConclusionsThis is the first study using dog infection to assess the presence of endemic fungal pathogens in Argentina. Our results suggest that H. capsulatum is the main dimorphic fungal pathogen in the Interfluvio Teuco-Bermejito area. Therefore, the diagnosis of histoplasmosis should be taken into account in patients living in this geographic region who show pulmonary or mucocutaneous symptoms compatible with the disease.     

Electrophoresis karyotype and chromosome-length polymorphism of Histoplasma capsulatum clinical isolates from Latin America

Intact chromosomes of 19 clinical isolates of Histoplasma capsulatum recently obtained in Argentina, Mexico and Guatemala and the laboratory reference strain G186B from Panama were analyzed using pulsed-field gel electrophoresis. Chromosomal banding patterns of the human isolates revealed 5-7 bands, ranging from 1.3 to 10 Mbp in size. Strain G186B showed five bands of approximately 1.1, 2.8, 3.3, 5.4 and 9.7 Mbp. Thirteen different electrokaryotypes were identified, indicating that the genome of H. capsulatum varies widely in nature, as observed previously in laboratory strains. No definite association was found between electrokaryotype and geographical or clinical source.