Academic journal article The American Biology Teacher

Discovering Biofilms: Inquiry-Based Activities for the Classroom

Academic journal article The American Biology Teacher

Discovering Biofilms: Inquiry-Based Activities for the Classroom

Article excerpt

What do ear infections (Nistico et al., 2011), certain lung infections (Chmiel et al., 2002), infectious kidney stones (Parsek & Singh, 2003), bacterial endocarditis (Chuang-Smith et al., 2010), oral disease (Hirota et al., 2011), urinary tract infections (Anderson et al., 2003), intestinal disease (Durban et al., 2011), and chronic wounds (Ramage et al., 2010) have in common? They all involve the formation of bacterial biofilms. However, biofilms do not only lead to disease. Human commensal bacteria such as Staphylococcus epidermidis, Escherichia coli, Lactobacillus acidophilus, and Streptococcus salivarius, called "flora," exist as biofilms on the skin and inside certain organs in the human body (Klitgord & Segre, 2010). This natural microbial flora assists in metabolic functions and is involved in preventing disease (Stephani et al., 2011). Moreover, bacterial biofilms are important components of the environment, and they are found in symbiotic relationships with plant roots (Chang et al., 2011), on standing water (Chollet-Imbert et al., 2009), on submerged rocks (Ridal et al., 2007), and on many other surfaces. The aim of this review is to stimulate the introduction of biofilms into primary and secondary school curricula. We will review biofilms in general and discuss ways in which biofilms could be introduced to your students.

What Is a Biofilm?

Costerton et al. (1978) first demonstrated the significance and ubiquity of biofilms, and research in this area has exploded since then. Investigators have discovered that many infectious chronic disease states are caused by biofilm formation. In addition to revealing how biofilms develop, studies have shown that biofilm bacteria communicate with one another via the exchange of certain organic molecules, a process called "quorum sensing" (Morici et al., 2007). Further studies have established that biofilm formation is a common lifestyle for many bacteria, whether they are disease-causing or environmental biofilms (Hall-Stoodley et al., 2004).

Biofilms are communities of microorganisms. They can be composed of multiple species or a single species. For instance, dental biofilms (or "plaque") may be composed of > 700 different species, both bacteria and yeast (Jakubovics & Kolenbrander, 2010). On the other hand, some infections are caused by a single species. For example, E. coli causes urinary tract infections, and Pseudomonas aeruginosa causes lung infections of the cystic fibrosis airway--in each case, a single species of bacteria forms a chronic biofilm infection (Boucher, 2002; Anderson et al., 2003). These diseases are also examples of how biofilms form differently in the human body. Pseudomonas aeruginosa biofilms form outside the airway epithelia, within the thick mucus plugs secreted in the cystic fibrosis airway (Gibson et al., 2003). Escherichia coli form intracellular biofilms, termed "intracellular bacterial communities," around the urinary epithelial cell nucleus (Anderson et al., 2003).

Although biofilms differ from one another in many ways, including microbial composition, how and where they grow, and whether or not they cause disease, there are established qualities that all biofilms generally exhibit. Biofilms are traditionally defined as microorganisms, commonly bacteria, adhering irreversibly to a solid surface and undergoing global changes in gene expression that lead to polysaccharide secretion, innate antibiotic resistance, and other unique characteristics (Hall-Stoodley et al., 2004). Biofilm maturation occurs in three major stages: (1) initial attachment of planktonic, or free swimming, bacteria to a solid surface; (2) formation of microcolonies via aggregation of bacterial cells; and (3) formation of the mature biofilm (Figure 1).

Bacteria that constitute the mature biofilm undergo significant genetic regulatory changes (Stoodley et al., 2002). Phenotypically, mature biofilms may have either a mushroom-like or flat appearance, depending on nutrient availability and the bacterial species (Klausen et al. …

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