Question

5. Describe the role of biofilms in the establishment of infections. How do biofilms protect pathogens from the immune system or chemical or drug treatment?

7. Briefly describe the role that extracellular enzymes can play in the pathogenesis of microbes? Give an example.
8. Describe antigenic variation. Explain how pathogens like Trpanosoma and Plasmodium use antigenic variation to avoid the host immune system.
9. The Center for Disease Control (CDC) recommends that we receive an influenza vaccine each year. Why doesn’t the influenza vaccine provide long term protection?

Answer 1

5. Mechanisms of antibiotics and biocides resistance of biofilms are categorized into four classes which include (a) active molecule inactivation directly (b) altering body's sensitivity to target of action, (c) reduction of the drug concentration before reaching to the target site and (d) efflux systems (Figure 3). Biofilm antibiotic resistance level may vary among different settings and the key factors responsible for this resistance may also differ. Regarding resistance, the primary evidence shows that conventional mechanisms are unable to explain the high resistance to antibacterial agents associated with biofilms, although this evidence cannot be ignored in resistance in the growth of adherent cells. So it is suggested that the resistance posed by the adhered bacteria or biofilms may have some intrinsic mechanisms and are responsible for conventional antibiotic resistance. Several mechanisms have been explored that are considered to be key factors in high resistance nature of biofilms. These mechanisms are (a) limited diffusion, (b) enzyme causing neutralization, (c) heterogeneous functions, (d) slow growth rate, (e) presence of persistent (non-dividing) cells and (f) biofilm phenotype such adaptive mechanisms e.g. efflux pump and membrane alteration.

Low Penetration of Antibiotics

Diffusion of antibiotics can take place through the matrix of the biofilm. Diffusion or penetration of antibiotics to deeper layers of biofilm is affected by exopolysaccharide acting as a physical barrier. When molecules direct interact with this matrix, their movement to the interior of the biofilm is slow down, resulting in antibiotic resistance. This may also act as a hindrance for high molecular weight molecules such as complement system proteins and lysozyme, and in liquid culture, bacterial cells are readily exposed to antibiotics as compared to compact structure biofilm. Bacteria escape from biofilm that does not produce polysaccharide and are easily attack by immune system cells. Inactivation of antibiotic takes place when binding to biofilm matrix. P. aeruginosa has alginate exopolysaccharide, which is anionic in nature. Presence of this matrix explains slow penetration of fluoroquinolones and aminoglycosides. Low penetration of antibiotic is not sufficient to explain the biofilm resistance, other mechanisms have been assumed that must be involved. This is also suggested recently that slow diffusion of antibiotics permit plenty of time to establish a protective response to stress.

Neutralization by Enzymes

Antibiotics resistance in a biofilm may be due to the presence of neutralizing enzymes which degrade or inactivate antibiotics. These enzymes are proteins which confer resistance by mechanisms such as hydrolysis, modification of antimicrobials by different biochemical reactions. Accumulations of these enzymes occur in the glycocalyx from the biofilm surface by the action of antibiotics. Neutralization by enzymes is enhanced by slow penetration of antibiotics and also antibiotics degradation in the biofilm. In cystic fibrosis which is caused by P. aeruginosa, overproduction of cephalosporinase AmpC enzymes is responsible for resistance to different antibiotics. This enzyme confers resistance to ?-lactam in the presence of even much more concentration of carbapenems . During a study when filters impregnated with antibiotics was applied on K. pneumoniae biofilm (mutant cells ?-lactamases), in spite of good diffusion of antibiotic, growth was observed, suggesting that there would be another mechanism of resistance which need to be explored.

7. In bacteria and fungi, exoenzymes play an integral role in allowing the organisms to effectively interact with their environment. Many bacteria use digestive enzymes to break down nutrients in their surroundings. Once digested, these nutrients enter the bacterium, where they are used to power cellular pathways with help from endoenzymes.

Many exoenzymes are also used as virulence factors. Pathogens, both bacterial and fungal, can use exoenzymes as a primary mechanism with which to cause disease.The metabolic activity of the exoenzymes allows the bacterium to invade host organisms by breaking down the host cells' defensive outer layers or by necrotizing body tissues of larger organisms. Many gram-negative bacteria have injectisomes, or flagella-like projections, to directly deliver the virulent exoenzyme into the host cell using a type three secretion system.With either process, pathogens can attack the host cell's structure and function, as well as its nucleic DNA.

Similar to collagenase, hyaluronidase enables a pathogen to penetrate deep into tissues. Bacteria such as Clostridium do so by using the enzyme to dissolve collagen and hyaluronic acid, the protein and saccharides, respectively, that hold tissues together.

Hemolysins target erythrocytes, or red blood cells. Attacking and lysing these cells allows the pathogen to harm the host organism, and also provides it with a source of iron from the lysed hemoglobin, like the fungus Candida albicans.Organisms can either by alpha-hemolytic, beta-hemolytic, or gamma-hemolytic (non-hemolytic).

9. Influenza is a serious disease that can lead to hospitalization and sometimes even death. Every flu season is different, and influenza infection can affect people differently, but millions of people get the flu every year, hundreds of thousands of people are hospitalized and thousands or tens of thousands of people die from flu-related causes every year. Even healthy people can get very sick from the flu and spread it to others. CDC estimates that flu-related hospitalizations since 2010 ranged from 140,000 to 710,000, while flu-related deaths are estimated to have ranged from 12,000 to 56,000. During flu season, flu viruses circulate at higher levels in the U.S. population. (“Flu season” in the United States can begin as early as October and last as late as May.) An annual seasonal flu vaccine is the best way to reduce your risk of getting sick with seasonal flu and spreading it to others. When more people get vaccinated against the flu, less flu can spread through that community.

8. Trypanosoma brucei presents a large reservoir of sequences used to create mosaic genes of a single surface antigen family made up of about 1,000 genes located in subtelomeres as well as on minichromosomes . In the latter organism, pseudogenes provide segments to mosaic functional antigens . Plasmodium falciparum harbors one subtelomeric antigen family of ca. 60 members . These three organisms present a single gene family subject to mutually exclusive expression involving silencing in several cases. Thus, their populations are homogenous antigenically but may vary over time when the expressed gene is exchanged. Such a strategy might be imposed by sterile niches such as blood and the urinary tract.