Interleukin-1b-induced growth enhancement of Staphylococcus aureus occurs in biofilm but not planktonic cultures by McLaughlin and Hoogewerf, 2006

The interplay between biofilms and host immune system is still poorly understood.

However, in the last years several discoveries have been made that may help in the understanding of the interactions between biofilms and the host immune system response.

It seems that patients with elevated levels of cytokines develop more frequently bacterial infections. This suggests that cytokines may stimulate bacterial growth and therefore, in this paper, the authors explored the interaction between S. aureus biofilms and the some pro-inflammatory cytokines namely IL-1beta, TNF-alpha, IL-6 and MIP-alpha.

Established S. aureus biofilms were treated with the different cytokines and 6h later the biofilm biomass was determined by crystal violet staining. Planktonic cells were used as control.

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Global changes in Staphylococcus aureus gene expression in Human blood by Malachowa et al., 2011

Staphylococcus aureus is one of the leading causes of bloodstream infections worldwide, however, the mechanisms employed by the bacterium to survive in human blood, and therefore cause infection is poorly understood.

Thus, to better understand the relationship between the bacterium and the human blood, the authors have analyzed the transcriptome of the bacterium after ex vivo exposure to human blood and serum.  Additionally, they have assessed the percentage of survival of the bacterium in the human blood.

With this approach they have find:

1. After 120 minutes of exposure to human blood there were still a significant number of bacteria alive in the blood (approximately 35%).

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Immune defense against S. epidermidis biofilms: components of the extracellular polymeric substance activate distinct bactericidal mechanisms of phagocytic cells by Meyle et al., 2012

As referred before, the molecular mechanism underlying S. epidermidis biofilm formation has been extensively studied in the last years. However, when it comes to the interaction of biofilms with the host immune system effectors very little is known.

In this manuscript the authors aimed to understand the interaction between the S. epidermidis extracellular matrix and the potent phagocytic polymorphonuclear cells (PMNs). An effective phagocytic process by PMNs depends on the opsonization of the antigen by complement proteins and IgG. However, previous work developed by these authors has shown that PMNs are activated in the presence of S. epidermidis biofilms and start the phagocytic process even in the absence of opsonins, indicating that some of the biofilm matrix components may stimulate PMNs activation.

Therefore, in this study the characterization of PMNs activation by non-opsonized S. epidermidis biofilms and purified matrix fractions was performed.  Continue reading

Vaccination with SesC decreases Staphylococcus epidermidis biofilm formation by Shahrooei et al., 2012

Immunoprophylaxis and immunotherapy are the most desired and promising strategies to avoid biofilm formation on the surface of biotic and abiotic surfaces, and the serious complications related with biofilm detachment, such as pneumonia, endocarditis and sepsis.

Several vaccination studies have been performed using  bacterial cell wall proteins as targets, due to their exposure to host immune system components. In this study, 5 S. epidermidis surface protein were selected based on the presence of conserved LPXTG motifs (SesC, SesK, SesB) or ABC transporter lipoproteins (SesL ans SesM), since these motifs and transporters are important for S. epidermidis pathogenesis.

In order to evaluate the immunogenicity of  the 5 proteins selected, rabbits were immunized with each of the 5 proteins (recombinant) and with whole bacteria killed by ethanol. The antisera was then collected and tested.

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Gene expression during S. epidermidis biofilm formation on biomaterials by Patel et al., 2012

In this paper, the changes in the expression of some of the genes involved in S. epidermidis initial adhesion and biofilm formation on the surface of different biomaterials were analysed.

In order to study the genetic changes over the time, planktonic cells were incubated up to 48h with different biomaterials along with human serum proteins in order to mimic the in vivo environment.

The gene expression profile obtained was very similar in all the biomaterials used. A 10x up-regulation of atlE, gene that encodes the protein AtlE, that is known to be involved in initial adhesion, cell wall metabolism activity and pathogenesis, was detected 48h after contact with the biomaterials surface and human serum proteins.

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Detachment characteristics and Oxacillin resistance of Staphylococcus aureus biofilm emboli in an in vitro catheter infection model by Fux et al., 2004

As I wrote previously,  biofilm detachment mechanism is believed to be the origin of severe acute infections such as bacteremia and pneumonia. Therefore, the study of these released cells (either by a passive or an active mechanism), will have an important impact in the seeking for effective prophylactic and/or therapeutic strategies against biofilm-related infections.

In this paper the susceptibility of the S. aureus biofilm-detached cells to oxacillin, a penicillinase-resistant β-lactam antibiotic often used for the treatment of S. aureus infections, was tested.

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Bacterial adhesion, intracellular survival and cytokine induction upon stimulation of mononuclear cells with planktonic or biofilm phase Staphylococcus epidermidis by Spiliopoulou et al., 2012

The way how immune effector cells behave in the presence of a biofilm have been explored in the few years, however, the consequences of these interactions in the immune cells remains largely unknown.

In this work the authors studied the influence of S. epidermidis biofilms in the human mononuclear cells (PMNs) and monocyte-derived macrophages cytokine production profile. Additionaly, the ability of biofilm cells to adhere to human monocyte-derived macrophages and its intracellular survival were also assessed.

It was observed that S. epidermidis biofilm cells (formalin-fixed or alive) induced lower level of pro-inflammatory cytokines production (TNF-alpha, IL12p40, IL-12p70 and IFN-gamma) by the PMNs when compared to the stimulation produced by planktonic cells.

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