Demonstration of intracellular Staphylococcus aureus in bovine mastitis alveolar cells and macrophages isolated from naturally infected cow milk

Abstract

Numerous in vitro studies have demonstrated that Staphylococcus aureus may be internalized and survive in a bovine mammary epithelial cell line. We report here the presence of internalized and living S. aureus in alveolar cells and macrophages in milk samples of bovine mastitis. We used fluorochrome labeled monoclonal antibodies, specifically recognizing surface cell markers of bovine alveolar cells and macrophages, to isolate these two types of cells using fluorescence activated cell sorting. Extracellular bacteria and DNA were previously eliminated to exclude possible contamination. In order to detect intracellular bacterial DNA inside the isolated cells, we used PCR amplification of bacterial DNA and the PCR products were analyzed by Southern blot with a specific probe for Staphylococcus. The results showed the presence of Staphylococcus DNA inside the two isolated populations of cells, confirming that S. aureus could penetrate alveolar cells and macrophages. The demonstration of the presence of intracellular living S. aureus was determined by bacteriological culture of positive samples plated onto blood agar plates and by its further identification. Our results showed for the first time that living S. aureus and its DNA are present in both alveolar cells and macrophages in chronically infected cow milk. ß

Escherichia coli, but notStaphylococcus aureustriggers an early increased expression of factors contributing to the innate immune defense in the udder of the cow

“…The lack of response towards S. aureus is unclear. It may reside in a differential presence of humoral milk factors which may alter the ability of bacteria to attach to MEC [1,16], or to survive intracellular in macrophages [15] or epithelial cells [25].…”

Capsule-Negative Staphylococcus aureus Induces Chronic Experimental Mastitis in Mice

“…aureus internalization into bovine epithelial cells is well documented (12), and this intracellular environment may provide a niche in which S. aureus can persist and avoid killing by PMN cells and certain antibiotics (3). Our results indicate that capsule production diminished S. aureus internalization by MAC-T cells in vitro, but neither CP5 nor CP8 affected bacterial survival once S. aureus was internalized.…”

Antimicrobial bacteriophage-derived proteins and therapeutic applications

“…52 Certain pathogens such as S. aureus evade both antibiotics and the host immune system by residing intracellularly within their host eukaryotic cells. 54 Protein transduction domains (PTD) are cationic peptides that naturally facilitate protein transport across eukaryotic cell membranes. 55 Fusion of an endolysin to a PTD is also possible.…”