Mechanical properties and structure of the biological multilayered material system, Atractosteus spatula scales

During recent decades, research on biological systems such as abalone shell and fish armor has revealed that these biological systems employ carefully arranged hierarchical multilayered structures to achieve properties of high strength, high ductility and light weight. Knowledge of such structures may enable pathways to design bio-inspired materials for various applications. This study was conducted to investigate the spatial distribution of structure, chemical composition and mechanical properties in mineralized fish scales of the species Atractosteus spatula. Microindentation tests were conducted, and cracking patterns and damage sites in the scales were examined to investigate the underlying protective mechanisms of fish scales under impact and penetration loads. A difference in nanomechanical properties was observed, with a thinner, stiffer and harder outer layer (indentation modulus ∼69 GPa and hardness ∼3.3 GPa) on a more compliant and thicker inner layer (indentation modulus ∼14.3 GPa and hardness ∼0.5 GPa). High-resolution scanning electron microscopy imaging of a fracture surface revealed that the outer layer contained oriented nanorods embedded in a matrix, and that the nanostructure of the inner layer contained fiber-like structures organized in a complex layered pattern. Damage patterns formed during microindentation show complex deformation mechanisms. Images of cracks identify growth through the outer layer, then deflection along the interface before growing and arresting in the inner layer. High-magnification images of the crack tip in the inner layer show void-linking and fiber-bridging exhibiting inelastic behavior. The observed difference in mechanical properties and unique nanostructures of different layers may have contributed to the resistance of fish scales to failure by impact and penetration loading.

Application of an immunoassay to determine risk factors associated with porcine cysticercosis in rural areas of Yucatan, Mexico

A Western blot assay for identification of 26 kDa and/or 8 kDa antigens in a crude saline extract (CSE) of Taenia solium metacestodes, previously developed for human cysticercosis, was evaluated for use with pigs. The test population used for assay standardisation consisted of 45 cysticercotic pigs (5 pigs positive by necropsy and 40 selected by tongue palpation and LL-Gp immunoblot but not confirmed by necropsy), 48 pigs with heterologous infections and 40 negative controls from endemic and non-endemic areas. The test detected 93% of the cysticercotic group and was 100% specific. In a field study this antigen preparation was compared by immunoblot with antibody recognition for Gp13-50 antigens in a lentil-lectin semi-purified glycoprotein extract of T. solium (LL-Gp). The seroprevalence to CSE antigen was slightly lower (26/75) when compared to LL-Gp (29/75) and this represented a non-significant difference. The CSE Western blot assay was used to assess seroprevalence of T. solium cysticercosis in pig populations in the state of Yucatan, Mexico. A total of 1099 pigs sampled at random from 25 villages revealed a seroprevalence of 23% (253/1099). Seroprevalence in intensively reared, farmed pigs was 2% (7/228). In comparison with farmed pigs, the seroprevalence was 33% (172/513) in free-roaming backyard pigs (OR=13.86, CI=4.0747.22, p<10(-6)) and 25% (74/98) in semi-confined backyard pigs (OR=14.03, CI=5.60-35.16, p<10(-6)). There was no significant difference in seroprevalence by sex (p=0.23). Seroprevalence decreased with age (chi(2)-test for linear trend=7.803, p<0.006). Results of this study demonstrate that the CSE Western blot can be applied for reliable immunodiagnosis of T. solium cysticercosis in pigs. Furthermore, variation in pig husbandry in Yucatan indicated significantly higher exposure to cysticercosis in free-roaming backyard pigs compared to intensively reared animals from the same area.

In vitro responsiveness of Babesia bovis to imidocarb dipropionate and the selection of a drug-adapted line

A South African stock of Babesia bovis was successfully resuscitated from liquid nitrogen, and cultured in microaerophilous stationary phase. The in vitro susceptibility of the B. bovis stock to titrated concentrations of imidocarb dipropionate was observed and the 50% inhibitory concentration (IC) was determined (8.7 x 10(7) g ml-1). A drug-adapted line was developed by culture in the presence of sub-inhibitory concentrations of imidocarb dipropionate and it had an IC50 eight times higher than that of its original stock (6.6 x 10(-6) g ml-1). The drug-adapted line was cryopreserved and resuscitated from liquid nitrogen. Continuous culture of the non-drug adapted line through 15 subcultures did not change the IC50 (8.3 x 10(-7) g ml-1).

Evaluation of a colorimetric Babesia bigemina-DNA probe within an epidemiological survey

An epidemiological survey was conducted in southeast Mexico, in an effort to establish the serological reactivity and carrier status to Babesia bigemina of an indigenous cattle population. The prevalence was obtained through the Indirect Fluorescent Antibody Test (IFAT), using an in vitro culture-derived B. bigemina antigen. A specific, digoxigenin-coupled, approximately 6 Kb B. bigemina-DNA probe (BBDP), was used to indicate the presence of the parasite. Serum samples from 925 animals of all ages, were obtained within the three regions (I, II, III) of the state of Yucatan and tested by IFAT. In addition, whole blood samples drawn from 136 of the same animals of region II were analyzed using the BBDP. Positive IFAT (IFAT+) reactions were observed in 531 sera for a 57% overall prevalence. Regional values were: I = 157+ (56%), II = 266+ (68%) and III 108+ (42%). Only 32 (23%) of the blood samples tested with BBDP showed distinctive hybridization signal, in contrast with 100 (73%) IFAT+ animals. The response distribution for IFAT vs. BBDP was: +/+ 23, +/- 77, -/+ 9 and -/- 27 respectively. It was found that the analytical sensitivity of BBDP appears to be low for its utilization in widespread epidemiological surveys. It was considered, however, that the colorimetric probe might be useful to safely detect transmission prone carriers, since it is able to detect parasitemias as low as 0.001%.