Host-microbe Interactions in Bovine Mastitis Staphylococcus Epidermidis, Staphylococcus Simulans and Streptococcus Uberis
Year: 2015
Type: dissertation
Abstract: Bovine mastitis is an inflammation of the udder that can be caused by multiple bacteria. Three major pathogens causing clinical intramammary infection are Escherichia coli, Staphylococcus aureus, and Streptococcus uberis. The most important group of minor udder pathogens is coagulase-negative staphylococci. The objective of this thesis study was to investigate the host-microbe interactions in bovine mastitis caused by a major udder pathogen, Strep. uberis, and two minor pathogens, Staphylococcus simulans and Staphylococcus epidermidis. Experimental intramammary infection was conducted to examine the host immune responses to Staph. simulans and Staph. epidermidis. Molecular methods were applied to study the genetic background of Strep. uberis for biofilm formation. In vitro models for biofilm formation, epithelial cell adhesion, and phagocytosis were used to investigate the relationship between the presence of clinical signs in 119 cases of Strep. uberis mastitis and characteristics of the corresponding bacterial isolate. Staph. simulans and Staph. epidermidis induced an infection in an experimental mastitis model. We also demonstrated that these strains were able to induce clinical signs and to persist for up to two weeks in the udder. Biofilm production among Staphylococcae has been under intensive research, and its association with persistence has been proposed. In contrast, biofilm formation by Strep. uberis has only recently been discovered. This thesis study characterized the genes involved in biofilm formation using the thermosensitive mutant library of Strep. uberis. Bacterial virulence-associated factors can be regulated by a two-component system. The twocomponent system response regulator (LiaR) was observed to negatively regulate biofilm formation by Strep. uberis, but the clear mechanism remains to be determined. Analysis of 119 Strep. uberis isolates revealed an association between biofilm formation and epithelial adhesion and susceptibility to phagocytosis, as well as the decreased susceptibility to phagocytosis among the isolates originating from infections with clinical signs. The analysis further revealed that highly adhesive strains are not phagocytosed as efficiently as weakly adhesive strains. These findings highlight the importance of adhesion, which is the key process in biofilm formation. Bacteria do not necessarily need to produce a biofilm, but they have much better possibilities to survive in the host if they can adhere, for instance, to epithelial cells. Nevertheless, the risk of an excessively intensive host response exists. Activated host response mechanisms would trigger an efficient host defense response to eliminate invading pathogens. Although we did not observe any difference in biofilm formation between clinical and subclinical isolates, a strong tendency for epithelial adhesion and resistance against phagocytosis are likely promoters of the bacterial load and intramammary infection leading to detectable clinical signs.
Source: Työväentutkimus Vuosikirja
Author: Tiina Salomäki
Language: English
Subfield: Animal Science and Zoology
Domain: Life Sciences
Open Access status: green
Funder: Helsingin Yliopisto
OpenAlex ID: W2175492209