staphylococcus aureus biochemical test (clear explain)
Staphylococcus epidermidis and S. Recent advances in staphylococcal molecular biology have provided more detailed insight into the basis of biofilm formation in these opportunistic pathogens. A series of surface proteins mediate initial attachment to host matrix proteins, which is followed by the expression of a cationic glucosamine-based exopolysaccharide that aggregates the bacterial cells.
In some cases, proteins may function as alternative aggregating substances. Furthermore, surfactant peptides have now been recognized as key factors involved in generating the 3-dimensional structure of a staphylococcal biofilm by cell-cell disruptive forces, which eventually may lead to the detachment of entire cell clusters. Transcriptional profiling experiments have defined the specific physiology of staphylococcal biofilms and demonstrated that biofilm resistance to antimicrobials is due to gene-regulated processes.
Finally, novel animal models of staphylococcal biofilm-associated infection have given us important information on which factors define biofilm formation in vivo. These recent advances constitute an important basis for the development of anti-staphylococcal drugs and vaccines. Staphylococci are recognized as the most frequent causes of biofilm-associated infections.
This exceptional status among biofilm-associated pathogens is due to the fact that staphylococci are frequent commensal bacteria on the human skin and mucous surfaces and those of many other mammals. Thus, staphylococci are among the most likely germs Staphylococcus epidermidis und Prostata infect any medical device that penetrates those surfaces, such as when being inserted during surgery Vuong and Otto For a long time, research on the molecular basis of biofilm formation was focused on gram-negative pathogens, predominantly Pseudomonas aeruginosawhich is more easily accessible to molecular genetic investigation.
More recently, advances in staphylococcal molecular biology have allowed researchers to determine the molecular basis of biofilm formation in staphylococci.
In addition, animal models of staphylococcal biofilm-associated infection have been established. Therefore, we now find staphylococci, and particularly S. This review will give an overview of the role of staphylococci in biofilm-associated human diseases and focus on the mechanism of biofilm development and the molecular basis of virulence in biofilm-forming S. In addition to Staphylococcus epidermidis und Prostata antibiotic resistance, which is based on the acquisition of genetic resistance factors and may be chromosomally, or more often plasmid-encoded, staphylococci have non-specific mechanisms of resistance, of Staphylococcus epidermidis und Prostata biofilm formation is undoubtedly the most important.
In otherwise healthy patients, S. These patients may develop septicemia or endocarditis Arber et al. Notably, a device-related infection of S. The reasons for these Staphylococcus epidermidis und Prostata are not understood, but may involve yet undiscovered host factors that predispose for S.
Thus, whether indwelling medical devices are contaminated with S. To some extent, biofilm-associated infections with S. However, the involvement of S. Often, S. In addition, they represent a reservoir Staphylococcus epidermidis und Prostata dissemination of S. In this regard, it is critical from a perspective of molecular pathogenesis, whether biofilm-forming S. Similar to S. In comparison with S. It is not known if this is due to a difference in virulence Staphylococcus epidermidis und Prostata abundance on the Staphylococcus epidermidis und Prostata skin, or — which appears most likely — a combination of both factors.
CoNS found in humans colonize different parts of the human skin and mucous membranes, with each species having a certain predominance on specific parts of the body Kloos and Schleifer Notably, every species Staphylococcus epidermidis und Prostata CoNS that has been characterized as a resident of the human body S.
The specific sites and frequency of infection seem to be related to those of normal colonization. In these infections, biofilm formation is probably a crucial determinant of disease, although this remains to be investigated.
In general, the specific molecular determinants of biofilm Staphylococcus epidermidis und Prostata in CoNS may be different from S. In contrast to many other medical biofilms, such as multi-species dental plaque formation, biofilm-associated infections with staphylococci are usually not mixed with other species Arciola et al.
In addition, it is rare to find more than one strain in an infection. A possible explanation for this phenomenon is interspecies communication by quorum-sensing signals, which in staphylococci leads to interspecies inhibition of virulence factor expression Ji et al. Similarly, bacterial interference by quorum-sensing signals may explain why P. However, these phenomena are poorly understood and there may be a simpler explanation based on the evolutionary adaptation of the bacteria to a specific environment, such as of S.
Research performed in many biofilm-forming organisms has revealed that the development of a biofilm is a 2-step process involving an initial attachment and a subsequent maturation phase, which are physiologically different from each other and require phase-specific factors. A final detachment or dispersal phase involves the detachment of single cells or cell clusters by various mechanisms and is believed to be crucial for the dissemination of the bacteria, in the case of pathogens to new infection sites in the human body Fig.
Phases of biofilm development in staphylococci. Biofilms form by initial attachment to a surface, which can occur on tissues or after covering of an abiotic surface by host matrix proteins in the human body specific, protein-protein interactionor directly to an abiotic Staphylococcus epidermidis und Prostata non-specific.
Subsequently, biofilms grow and mature. The molecules that connect the cells in a staphylococcal biofilm are predominantly the exopolysaccharide PIA, teichoic acids, and some proteins such as the accumulation-associated protein Aap.
Finally, cell clusters detach. Staphylococcus epidermidis und Prostata is facilitated by expression of the surfactant-like PSM peptides, which are also important in producing the 3-dimensional structure of the biofilm. During infection, attachment is a crucial part of the colonization on host tissues or on indwelling medical devices, whereas detachment is a prerequisite for the dissemination of an infection. In the human body, the attachment to human matrix proteins represents the first step of biofilm formation.
MSCRAMMs have a common structure that includes an exposed binding domain, a cell-wall spanning domain, which often has a repeat structure, and a domain that is responsible for the Staphylococcus epidermidis und Prostata or non-covalent attachment to the bacterial surface. The only functional equivalents between the two species appear to be several members of the serine-aspartate-repeat family Sdr proteins.
This family comprises several Staphylococcus epidermidis und Prostata proteins that have a characteristic serine-aspartate repeat cell-wall spanning domain McCrea et al. In addition, both species have the accumulation-associated protein Aap and several non-covalently bound surface proteins, such as the autolysin Atl, in common.
The most important examples are autolysins, which often represent some of the most abundant proteins on the staphylococcal cell surface. There is some evidence to suggest that autolysins are non-covalently attached to teichoic acids Peschel et al. These enzymes, in addition to their primary role in cell wall turnover, also facilitate attachment to plastic surfaces and harbor binding sites for human matrix proteins Heilmann et al.
Thus, they have a crucial bi-functional importance for bacterial attachment. Similar to the autolysins, the lipase GehD has a primary catalytic role, but there is evidence to suggest that it has an additional adhesive function Bowden et al. Staphylococci are known for their extraordinary ability to stick to plastic surfaces.
While this ability has been the basis for most of the in vitro biofilm research performed in staphylococci and in other biofilm-forming pathogensStaphylococcus epidermidis und Prostata is not clear if direct attachment to plastic Staphylococcus epidermidis und Prostata a significant role in the pathogenesis of medical device-associated infection.
Host matrix proteins cover the devices soon after insertion and thus, the specific interaction between these proteins and MSCRAMMs most likely is of much greater importance for colonization. The classic microtiter plate assay for biofilm formation on abiotic surfaces has been a valuable tool especially in large screens for biofilm-related factors.
However, it is far from representing the detailed characteristics of biofilm-associated infection in vivo and might have led to an over-estimation of the importance of some molecules in biofilm formation. It should thus optimally be accompanied by more elaborate in vitro methods, such as flow cells and confocal laser scanning microscopy, and animal models of biofilm-associated infection.
For example, subcutaneous infection models with catheter tubing Rupp et al. The maturation phase of biofilm formation is characterized by 1 intercellular Staphylococcus epidermidis und Prostata that can be accomplished by a variety of molecules such as adhesive proteins Staphylococcus epidermidis und Prostata — usually polysaccharide-based - exopolymers, and 2 biofilm structuring forces that lead to the typical 3-dimensional appearance of mature biofilms with its mushroom-like cell towers surrounding fluid-filled channels.
In staphylococci, the main molecule responsible for intercellular adhesion is the polysaccharide intercellular adhesin PIAwhich is also called poly-N-acetylglucosamine PNAG according to its chemical composition Mack et al. More recently, PIA homologs have been detected in a variety of biofilm-forming pathogens, suggesting that this polymer has a widespread function in biofilms and biofilm-associated infections Darby et al.
The biofilm exopolysaccharide PIA. A, PIA covers staphylococcal cells and sticks them together as the major component of the extracellular matrix backscatter scanning electron microscopic picture of S. The IcaA transferase needs the presence of IcaD for full activity.
The de-acetylation of N-acetylglucosamine residues in PIA is of major biological importance. It introduces a positively charged character in the otherwise neutral molecule by liberating free amino groups that become charged at neutral or acid pH, such as found in the natural habitat of staphylococci, the human skin Vuong et al. As the bacterial cell surface is negatively charged, PIA supposedly works like glue that sticks the cells together by electrostatic interaction.
Teichoic acids may represent the negatively charged molecules that interact with PIA on the cell surface. Interestingly, the relative amounts of teichoic Staphylococcus epidermidis und Prostata and PIA are subject to environmental control — the biological role of which is not yet understood Sadovskaya et al. Expression of the ica gene locus is regulated by a variety of environmental factors and regulatory proteins see 4. The production of PIA and its deacetylation have been recognized as key virulence factors in S.
Several animal models have confirmed this key role, although some conflicting results exist Kristian et al. However, PIA production does not seem to be of universal importance for biofilm formation and biofilm-associated infection, as PIA-independent biofilm formation has been demonstrated Rohde et al.
Furthermore, some strains isolated from biofilm-associated infection do not have the ica genes Arciola et al. Interestingly, invasiveness of non-invasive S. The most important protein involved in PIA-independent biofilm formation appears to be Aap Hussain et al. In this study, S. Furthermore, biofilm formation was less pronounced when exclusively dependent on proteins. Thus, although PIA does not have an absolutely universal importance for staphylococcal biofilms, this study confirms its key role in staphylococcal biofilm formation.
Aap is a kD protein that needs to be proteolytically cleaved to a smaller kD form to induce biofilm formation Rohde et al. Aap may be identical Staphylococcus epidermidis und Prostata the SSP-1 and SSP-2 proteins, which have been implicated in biofilm Staphylococcus epidermidis und Prostata but whose identity was not investigated further Veenstra et al.
Interestingly, it was shown that SSP forms protein strands on the S. This capacity could explain how proteins contribute to the aggregation step of biofilm development. A very recent publication has Staphylococcus epidermidis und Prostata fact demonstrated that the formation of fibril-like structures on the S. There is evidence for the significance of Bap during infection of bovine mammary glands Cucarella et al.
A homolog of bap named bhp occurs in human strains of S. Bap homologs are also found in other bacteria, suggesting that the Bap family of surface proteins may have widespread importance in biofilm formation Latasa et al. TA can be linked to the cell wall in which case they are referred to as cell wall TA WTAor they can be linked to the cell membrane via a lipid anchor, known as lipoteichoic acid LTA.
Furthermore, the importance of the D-alanylation of S. In between those towers, there are fluid-filled channels that are believed to have a vital function in delivering nutrients to cells in deeper biofilm layers. The mechanisms that lead to channel formation and biofilm structuring are far less well understood than those governing intercellular adhesion.