The virulence of Staphylococcus aureus correlates with strain genotype in a chicken embryo model but not a nematode model.

Staphylococcus aureus infections are of major importance in human and veterinary medicine. Studies of the virulence of this bacterium are complicated by inconsistent results obtained in different animal models. We searched for an uncomplicated and inexpensive model suitable to study virulence of poultry strains of S. aureus using a genome-wide approach. We determined that a useful model would clearly differentiate strains of high and low virulence, and that this would generally correlate with the genetic relatedness among strains. To this end Gallus gallus (chicken) embryo and Caenorhabditis elegans (nematode) models were selected, and their response to challenge by a set of well-characterized Staphylococcus strains was evaluated. The chicken embryo model allowed to determine variation in virulence among strains of poultry and human origin. The survival of embryos ranged from 0% to almost 100% for the various strains. In contrast, variation in virulence of most strains in the nematode model was comparable, regardless of their origin or genotype, demonstrating limited usefulness of this model. Most importantly, a clear correlation was found between the virulence level in the embryo model and the genotype of the tested poultry strains. Our findings indicate the potential usefulness of embryo model for future identification of host-specific adaptations and virulence factors in S. aureus.

Protective effect of zinc on cadmium embryotoxicity and antioxidant status of blood plasma in newly hatched chicks.

Among the multiple mechanisms of cadmium toxicity proposed, the most common is the disruption of the cellular antioxidant system, which may be limited by pre- or co-treatment with zinc. The aim of this study was to determine if simultaneous zinc supplementation of hen's egg could reduce embryotoxic effect of cadmium. Egg albumen was injected on day 4 of incubation with cadmium alone (50 nmol per egg) or in combination with zinc (100 and 500 nmol). Hatching results and antioxidant activity in plasma of newly hatched chicks were determined by photochemiluminescence (PCL) and FRAP methods. Administration of cadmium markedly reduced hatchabilty (30.2 %), while both zinc doses used were embryotoxic (43.2 and 48.9 %) as compared to the control group (61.9 %). This adverse effect was reduced by simultaneous zinc administration (completely at 10-fold higher molar concentration). This observation was confirmed by examination of the antioxidant capacity in plasma of Cd-treated chicks. A slight decrease in the hydrophilic and lipophilic antioxidant capacity induced by cadmium was compensated by a co-treatment with higher zinc dose administration, whereas the exposure of hen embryos to zinc caused an increase in antioxidant potential in the plasma of chicks. It is concluded that Zn supply in conditions of exposure to Cd can protect against Cd-induced oxidative stress in chicken embryos.

Effect of cadmium injected in ovo on hatching results and the activity of plasma hydrolytic enzymes in newly hatched chicks.

The aim of the study was to determine the toxicity of cadmium ions in chick embryos, using plasma hydrolytic enzyme as its biomarker. Hatching eggs (n = 300) from Ross 308 broilers were incubated under standard conditions. On day 4 of incubation, 50 µl of saline solution, containing Cd ions at a concentration from 0 (control group) to 24 µg, was injected in ovo into the egg albumen. The results indicate that the administration of cadmium at doses exceeding 1 µg/egg caused a gradual decrease in hatchability, with an LD50 of 3.9 µg/egg. The greatest differences between the groups in the enzymatic activities studied were found for N-acetyl-ß-D-glucosaminidase (NAG), ß-D-mannosidase (ß-MAN) and arylsulphatase (ARYL). Compared to the control group, in the blood serum of chicks from the groups receiving 3, 6 and 12 µg Cd/egg the NAG activity increased by 79, 108 and 54% and ß-MAN activity by 33, 119 and 108%, respectively. Exposure to cadmium at a dose of 1 to 6 µg per egg caused an about 60% increase in ARYL activity while a dose of 12 µg decreased the activity by about 35% below the level observed in the control group. These findings show that cadmium has a similar toxicity mechanism in mammals and birds, which opens the possibility of using NAG activity as a biomarker of the cytotoxic effect of cadmium in birds.