La construcción de género y los roles al interior de la fa- fa-milia nuclear

The biofilms of pathogenic bacteria are of great interest, as biofilm formation naturally confers a resistance phenotype (Jolivet-Gougeon and Bonnaure-Mallet, 2014). The ECM, although not the main source of antimicrobial resistance (Patel, 2005), also contributes to increased resistance phenotypes. It is able to decrease antimicrobial penetration and in some cases inactivate antimicrobials (Billings et al., 2013). Genetic material can be effectively exchanged within biofilms due to the close proximity of the bacteria, exposure of cells to sub-lethal doses of antimicrobials and their uptake of DNA directly from the ECM. These factors contribute to the spread of resistance phenotypes throughout the biofilm population (Madsen et al., 2012).

Biofilms also provide a reservoir, which pathogenic bacteria are able to utilise, moving from the biofilm to colonise new areas. Bacteria are also able to integrate into the biofilm community during periods of antimicrobial treatment, utilising the biofilms protective environment. Many important human pathogens are able to form biofilms. Three important areas of medical biofilm investigation will be reviewed in Sections 1.1.4.1 to 1.1.4.3: biofilm formation on implants, the contribution of biofilms to cystic fibrosis infections and wound infection biofilms.

1.1.4.1 Biofilm formation on implants

As surgical procedures increase in complexity, patients often require immobilisation and support of vital functions for extended periods of time (Bunker, 2001). In these instances patients are also at higher risk of infection and two well recognised biofilm infection reservoirs include ventilators (Browne et al., 2014) and catheters (Iacovelli et al., 2014). These not only are able to introduce bacteria into the body of potentially immuno- suppressed patients, but also provide bacteria within the body with a surface on which they are able to attach and form a biofilm, therefore evading antimicrobial treatment and attack by the hosts immune system.

Implant biofilms are frequently found to contain only a single species, typically an opportunistic pathogen. Ventilator associated pneumonia (VAP) is a significant risk for patients undergoing mechanical ventilation. VAP occurs in up to 30% of patients (Chastre and Fagon, 2002), with an increasing incidence as the time ventilation is required is increased. Contraction of VAP increases patient morbidity and mortality and incurs a significant treatment cost as patients require longer hospitalisation and antibiotic treatment (Chastre and Fagon, 2002). VAP can be caused by various bacterial species, including P.

Helen Louise Brown Introduction

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aeruginosa, S. aureus and Klebsiella pneumonia. A link has been identified between

patients‟ oral health and VAP, and a recent study has shown that better oral hygiene and monitoring of patients undergoing mechanical ventilation significantly reduced the incidence of VAP (Rello et al., 2010). This suggests colonisation of the ventilation tubing occurs via an oral route, with pathogenic bacteria utilising the oral biofilm prior to VAP infection.

Catheter-associated urinary tract infections (CAUTIs) are the most common hospital acquired (nosocomial) infection (Jacobsen et al., 2008), and biofilm involvement in CAUTIs leads to infection recurrence and complications in treatment of infection. E. coli, a member of the healthy urinary tract flora, is a frequent cause of urinary tract infections (Vollmerhausen et al., 2014), accounting for up to 80% of urinary tract infections (Stamm and Hooton, 1993).

E. coli‟s ability to form biofilms is a significant contributor to its persistence and pathogenicity (Bielecki et al., 2014).

1.1.4.2 Biofilm formation in the Cystic Fibrosis lung

Cystic fibrosis (CF) biofilms have received significant attention over the last two decades due to their role in increasing patient mortality (Ciofu et al., 2013) and the involvement of the model biofilm organism P. aeruginosa in CF pathology (Hoiby et al., 2010b). CF patients produce thick, viscous mucus, which in their lungs is easily colonised by airborne bacterial and fungal species (Kreda et al., 2012). Infections are usually life-long and contribute significantly to morbidity and mortality. Many CF pathogens are opportunistic, able to cause infection in only susceptible, immuno-compromised individuals (Mahenthiralingam et al., 2008, Gomez and Prince, 2007). Pathogenic, biofilm forming bacteria such as P.

aeruginosa, S, aureus, B. cepacia, H. influenzae, Stenotrophomonas maltophilia and Mycobacterium absessus are frequently isolated from patient sputum samples (Coutinho et

al., 2013).

Research into CF pathogens is focused on two areas: treatments for the dispersal and killing of biofilm cells within the lungs, or discovery of the molecular mechanisms of pathogenesis and resistance. Some of the novel treatments developed will be discussed in more detail in Section 1.1.6, however a review of the extensive field of pathogenesis and resistance mechanism investigation is outside the scope of this work. Key research within the field is highlighted in reviews by Joo and Otto (2012) and Ciofu et al. (2014).

1.1.4.3 Biofilm formation in wounds

The formation of biofilms in wounds leads to chronic and persistent infections which can often only be cleared by debridement of the infection site (Cowan et al., 2013). Up to 90% of chronic wound infections contain biofilms (Attinger and Wolcott, 2012) and biofilm involvement has significant cost implications, recently estimated at $20 billion each year in the USA (Cowan et al., 2013). Although biofilm-associated wound infections have the potential to develop in any wound, they are frequently encountered in diabetic patients, following the development of ulcers on the feet and lower legs. Diabetic patients account for 80% of all non-traumatic lower extremities amputation around the world (Berlanga-Acosta et al., 2014), and biofilm associated infections negatively impact treatment outcomes (Zubair et al., 2012). Although infections are typically multispecies in nature (Dalton et al., 2011), they are often dominated by Gram positive bacteria such as Staphylococcus sp. (James et al., 2008).

Treatment of the wound infections focuses around debridement, draining, and packing with antimicrobial materials. Specialized dressings containing honey or antimicrobial metals such as silver are frequently used (discussed in more detail in Sections 1.1.6.2 and 1.1.6.4

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respectively). Debridement can be mechanical, although more recently insect larvae have been used with great success (Menon, 2012). Laval treatment, particularly using the maggots of the blow fly, is successful since it utilises four synergistic factors: the action of the maggots feeding stimulates wound drainage, the maggots destroy necrotic tissue and encourage formation of granulation tissue, and finally, the secretions of the maggots are antimicrobial, reducing the potential for further infection (Jaklic et al., 2008, Cazander et al., 2013). Studies have shown that maggot treatment was effective in over 80% of patients, and bacteria such as group G and C Streptococcus, Klebsiella sp., Serratia marcescens, S.

aureus and P. aeruginosa were susceptible to the antibiotic properties of the maggot

secretions (Jaklic et al., 2008).