Effect of Staphylococcus aureus infection on the heat stress protein 70 (HSP70) level in chicken embryo tissues

Abstract

Staphylococcus aureus bacteria are components of physiological biocenosis of skin or mucous membranes in some animals' genera but also they are dangerous opportunistic pathogens responsible for infections of various localization, course or manifestations. Proteins produced by these bacteria destroy tissues, leukocytes and cause haemolysis of erythrocytes. Host organisms respond by defence mechanisms. Production of heat stress proteins (HSPs) is one of defence responses of infected host organism. To evaluate infection and host defence mechanisms some animal models of experimental infection are reported. Use of chick embryo model allows demonstrating adequate differences in staphylococcal virulence depending on the strain genotype. The aim of the study was to examine the changes in heat shock protein HSP70 levels in chick embryo tissues after infection caused by S. aureus strains no. tu2, pa3, ch5, ch10, ch24, and ch25 isolated from chickens. The bacteria were injected directly into fluid of amnion cavity and incubated for 10 days. The mortality of particular chick embryos was reported and the tissues for further analysis were taken every day from day 13 to day 19. The levels of heat stress protein HSP70 were determined by dot-blot method. Results showed that the strains no. ch5, ch24, and ch25 were the most virulent. HSP70 levels increased in all groups of injected embryos at the same time the hatching process was started. The presented study showed that the infected chick embryos were characterized by higher HSP level from 12.3% up to 19.7% compared to the control group. The morphological analysis showed numerous erythrocytes with damaged cell membranes and morphological changes of erythrocytes. Changes in the level of HSP70 protein can be a useful indicator of infection caused by S. aureus bacteria. Additionally, chicken embryo is a helpful research model in studies of pathogenesis of diseases caused by bacteria.

Keywords: defence mechanisms; hatchability; in ovo model; staphylococci.

Figure 1

The level of HSP70 (mean ± SEM) in the liver of chicken embryos from the control group on the following days of incubation. ^abc- values marked with different letters differ statistically significantly (P ≤ 0.05).

Figure 2

The average level of HSP70 (mean ± SEM) in the liver of chicken embryos infected with selected strains of Staphylococcus aureus in the period from 13 to 19 day of incubation. ^abc- values marked with different letters differ statistically significantly (P ≤ 0.05).

Figure 3.

The microscopic view (60 × magnification) of blood smear of a chick embryo at 14th day of incubation. The eggs were in ovo injected by selected Staphylococcus aureus strains at 10th day of incubation; (A) the normal red blood cells of the control group; (B) lysed erythrocyte in the group infected by ch24 strain; (C) the swollen erythrocytes in the group infected by pa3 strain; (D) damaged cell membranes of erythrocytes in the group infected by ch5 strain; (E) changes of erythrocyte morphology in the group infected by tu2 strain.