Abstract
Bartonellahenselae (Bh) is a Gram-negative rod transmitted to humans by a scratch from the common house cat. Infection of humans with Bh can result in a range of clinical diseases including lymphadenopathy observed in cat-scratch disease and more serious disease from persistent bacteremia. It is a common cause of blood-culture negative endocarditis as the bacterium is capable of growing as aggregates, and forming biofilms on infected native and prosthetic heart valves. The aggregative growth requires a trimeric autotransporter adhesin (TAA) called Bartonella adhesin A (BadA). TAAs are found in all Bartonella species and many other Gram-negative bacteria. Using Bh Houston-1, Bh Houston-1 ∆badA and Bh Houston-1 ∆badA/pNS2PTrcbadA (a partial complement of badA coding for a truncated protein of 741 amino acid residues), we analyze the role of BadA in adhesion and biofilm formation. We also investigate the role of environmental factors such as temperature on badA expression and biofilm formation. Real-time cell adhesion monitoring and electron microscopy show that Bh Houston-1 adheres and forms biofilm more efficiently than the Bh Houston-1 ∆badA. Deletion of the badA gene significantly decreases adhesion, the first step in biofilm formation in vitro, which is partially restored in Bh Houston-1 ∆badA/pNS2PTrcbadA. The biofilm formed by Bh Houston-1 includes polysaccharides, proteins, and DNA components and is susceptible to enzymatic degradation of these components. Furthermore, both pH and temperature influence both badA expression and biofilm formation. We conclude that BadA is required for optimal adhesion, agglutination and biofilm formation.
Highlights
Trimeric autotransporter adhesins (TAAs) are outer membrane proteins found on Gram-negative bacteria and shown to be involved in bacterial auto-agglutination as well as facilitating adhesion to extracellular matrix components and host cells.[1]
Bartonella henselae (Bh) forms a biofilm To examine biofilm formation by Bh Houston-1, 106 bacteria in a 150 μl volume were inoculated into a 96 well polystyrene plate with a nitrocellulose membrane on the bottom
We investigate the major adhesin, Bartonella adhesin A (BadA), found on the outer membrane of Bh Houston-1 and its effect on biofilm formation
Summary
Trimeric autotransporter adhesins (TAAs) are outer membrane proteins found on Gram-negative bacteria and shown to be involved in bacterial auto-agglutination as well as facilitating adhesion to extracellular matrix components and host cells.[1]. Bh is a Gram-negative, facultative intracellular zoonotic pathogen able to grow as auto-adherent aggregates or as non-adherent individual bacilli.[6] Its native host is the cat, and it is transmitted by the cat flea (Ctenocephalides felis).[7] Out of 45 known spp. in the Bartonella genus, 13 are known to cause human infection. While the cat is the predominant host for Bh, other Bartonella species have been isolated from a range of other mammals as reviewed in Okaro et al.[8] In the case of Bh, humans become infected through a scratch from an infected cat causing cat scratch disease (CSD)—a condition characterized by self-limiting lymphadenopathy.[9] Annually, CSD affects about 24,000 people in the United States.[10]
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