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Coagulase Positive Pathogen Is Staphylococcus Aureus Biology Essay

1.0 Introduction

Staphylococci are a Gram-positive group of bacteria, most of which are harmless and found on the skin. The range of pathogenic species, however, are able to cause a wide array of diseases usually by toxin production or invasion of the skin and mucous membrane. The genus can be split into two groups: coagulase positive and coagulase negative depending on their ability to produce the enzyme coagulase and therefore clot blood.

A major coagulase positive pathogen is Staphylococcus aureus. This species is most commonly recognised as the cause of food poisoning due to the consumption of toxins the bacteria produces which contaminate food. It is the most common and pathogenic in the genus and causes diseases such as septic shock syndrome and meningitis (Weiss et al., 2009). S. aureus displays a wide selection of virulence factors, including the production of toxins and surface arrangements that help the bacteria to colonise tissue (O'Neill et al., 2007). S. aureus is known for the growing threat associated with its resistance to the large antibiotic group beta-lactams.

A less pathogenic species is Staphylococcus epidermidis, which is a member of the commensal flora. S. epidermidis is an opportunistic pathogen as it predominately causes infection in immunocompromised patients (Rachid et al., 2000) and patients with medical implants. Both S. aureus and S. epidermidis, are only able to cause harm after penetration of the skin or mucous membranes, where they cause infections such as septicaemia and endocarditis (Otto, 2008). The bacteria are easily introduced into the body as a contaminant during surgical implantations of medical devices (Otto, 2008) for example, indwelling catheters and prosthetic joints for hips and knees.

Staphylococcal intermedius is a coagulative positive member of the genus and is very closely related to S. aureus. It is predominantly found on animals (mostly dogs) and is the cause of canine inflicted wounds. It is able to cause infection in patients who are both immunocompromised and have medical implants where, similarly to the other species of the same genus, they are able to form biofilms. All these staphylococci species are recognized as the most common causes of biofilm associated infections (Otto, 2008), with S. epidermidis as the leading species causing over 80% of biofilm infections (Gotz, 2002).

A biofilm is a complex aggregation of microorganisms embedded in an extrcellular polymeric substance (EPS) that attach to the surfaces of both living and non-living surfaces (Stobie et al., 2008). The formation of a biofilm is the first step in disease initiation, biofilm infections have recently been shown to occur in vivo in the mouse pathogen M. pulmonis (Simmons et al., 2007). Maturation of the biofilm occurs over a variable timescale, once mature, the biofilm has is a hydrated structure which allows diffusion of nutrients and oxygen (Fitzpatrick et al., 2005).

Biofilms anchor the bacteria to a surface (Frank and Patel, 2008) and so are directly introduced into a patient and therefore able to cause infection. Staphylococci within a biofilm capsule are impaired against neutrophil phagocytosis (Otto, 2008). Biofilm resistance is a phenotypic phenomenon, this suggests multi-cellular defence mechanism (Gilbert et al., 2002). Consequently unnecessary biofilm formation is a major concern (Chiang et al., 2009) as the bacteria are able to grow inside the dense polysaccharide layer, protected from the action of the antibodies, phagocytic cells and antimicrobial treatments (Houari and Di Martino, 2007). Even patients with exceptional immune systems find it hard to resolve infections caused by biofilms (Aparna and Yadav, 2008). However changes in environmental conditions have been shown to effect biofilm formation by Fitzpatrick (2005). Biofilm colonization is of particular concern in immunocompromised patients as they have a weak immune system, the introduction of large numbers of virulent bacteria could be lethal.

The formation of a biofilm involves many sequential steps and interlinked pathways; this is the main reason for no available single method of preventing the formation of biofilms. Their formation predominantly depends on two bacterial properties: the ability to remain to cells and the accumulation to form multi-layered cell groups (Gotz, 2002), which gives the bacteria appearance of slime (Fitzpatrick et al., 2005). Formation of a biofilm is very complicated and many surface proteins are involved which share several structural and functional features. Molecular microbiologists have identified many biofilm formation pathways involving many operons during all stages of biofilm development (Petrova and Sauer, 2009). In S. aureus the biofilm associated protein, Bap, was one of the first found (Lasa, 2006). There have been many genes implicated, some of the main ones along with their functions can be found in table1.

Table 1. Shows some of the main genes involved in biofilm formation in the staphylococcus genus.



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