Human Leukocytes Adhere to, Penetrate, and Respond to Staphylococcus aureus Biofilms

Abstract

Staphylococcus aureus is a common pathogen responsible for nosocomial and community infections. It readily colonizes indwelling catheters, forming microbiotic communities termed biofilms. S. aureus bacteria in biofilms are protected from killing by antibiotics and the body's immune system. For years, one mechanism behind biofilm resistance to attack from the immune system's sentinel leukocytes has been conceptualized as a deficiency in the ability of the leukocytes to penetrate the biofilm. We demonstrate here that under conditions mimicking physiological shear, leukocytes attach, penetrate, and produce cytokines in response to maturing and fully matured S. aureus biofilm.Bacterial biofilms are mechanisms used by bacteria that cause chronic infections in humans (5). They are associated with a number of diseases including cystic fibrosis (24), endocarditis (3), osteomyelitis (23), and various nosocomial diseases related to central venous catheters (19), urinary catheters (20), prosthetic heart valves (12), and orthopedic devices (10). Biofilms are well suited for resistance to antibiotics and evasion of the immune system's defenses, and the biofilm mode of growth may be a specific form of microbial development (18,21,27).The bacterial pathogen Staphylococcus aureus has the ability to form biofilms under physiological conditions (4,13,19). The increased prevalence of antibiotic resistance, including recent isolates demonstrating intermediate resistance to vancomycin, has induced a surge in efforts to better understand the nature of S. aureus virulence both in vitro and in vivo (15,25). The mechanisms behind biofilm resistance, especially with regard to leukocytes, are not clear and have been explained by the paradigm of a lack of penetration by the leukocytes and a decreased ability of phagocytes to actively kill the bacteria, a process termed "frustrated phagocytosis" (11,27).The ability of leukocytes to traffic to sites of inflammation and exert their respective effector functions is vital in maintaining overall health. One of the important parameters of leukocyte trafficking is the ability of adhesion molecules to function optimally under laminar-shear conditions. Indeed, the selectin family of adhesion proteins, which are responsible for the first step in the trafficking cascade, have a requirement of a threshold amount of shear for optimal function (8). Here we have investigated the interactions of freshly isolated human leukocytes with 2-day-old (early, maturing) and 7-day-old (fully mature) S. aureus biofilms under static and dynamic conditions that mimic physiological shear in vivo. MATERIALS AND METHODSStrains and plasmids. The S. aureus strains used is this study were Seattle 1945 and a clinical isolate from the University of Texas Medical Branch in Galveston that we refer to as MRSA. The Seattle 1945 strain of S. aureus was transformed with a green fluorescent protein (GFP)-producing plasmid to produce 1945 GFPuvr . The plasmid was constructed by inserting the promoter for the global regulator sarA into...

Medical biofilms

“…Leid et al (2002) documented such penetration in an in vitro study of freshly isolated human leukocytes contacting 2-day-old (early, maturing) and 7-day-old (fully developed) S. aureus biofilms, under static and flowing fluid conditions that mimic physiological shear. Leukocytes penetrated 7-day-old S. aureus biofilms under laminar-shear conditions but do not penetrate 2-dayold S. aureus biofilms grown under static conditions.…”

Study on biofilm-forming properties of clinical isolates of Staphylococcus aureus

“…It is difficult to treat long-term staphylococcal infections such as endocarditis, osteomyelitis and especially those infections associated with implanted medical devices. One reason these organisms are capable of defending themselves from host immune systems is their capability to form biofilms [1,2]. The interior of the bacterial biofilms presents greater resistance to the opsonization by antibodies and to phagocytosis, which explains the chronic character of these infections [3].…”

Diabetic foot ulcers and biofilm formation- The culprits

“…They have an antiphagocytic property, which inactivates leukocytes in the polysaccharide matrix. [37] There is also an element within the matrix that disables both complement and host antibodies. [38] In our study 46.34% of the isolates showed biofilm formation.…”