DVC Microbiology 146 Fall 11 (Gard): Lab 36 Dental Caries

Dental caries= also called cavities or tooth decay

a. comprise one of the most common infectious diseases of humans worldwide

b. caries start as small erosions in tooth enamel

-if not treated, they can penetrate into the dentin and pulp cavity- causing pain, infection, and even tooth breakage when biting down

c. Bacteria and diet are important in the initiation and progression of dental caries
Initiation=

1. Bacteria=various oral streptococci (bacteria) establish a biofilm on the surface of the tooth

esp. Streptococcus mutans =cariogenic bacteria- forms dental caries

2. Sugar= a diet high in sucrose will encourage adherence of bacteria to the tooth surface

-bacteria use exoenzymes to break down the disaccharide, sucrose, into the monosaccharide subunits= glucose and fructose

-the energy released by this process, in conjunction with the enzyme, dextransucrase, is used to polymerize the glucose into the polysaccharide dextran

-Dextran= polysaccharide of glucose, forms sticky capsules around the bacteria which allow them to adhere to the tooth surface

-the remaining fructose is then fermented into lactic acid

Progression=

1. oral lactobacilli, including Lactobacillus acidophilus, and other bacteria also colonize the biofilm and produce lactic acid as a product of sugar fermentation

plaque= the multispecies biofilm, dextran capsules, and debris

2. the acids produced by plaque bacteria decalcify tooth enamel below pH of 5, creating erosions

-since the tooth surface does not slough cells like mucosa, plaque remains attached

-although the flushing action and antimicrobial chemicals of saliva do help keep plaque in check, plaque is not very permeable to acid neutralization by saliva

- the bacteria, meanwhile, thrive in highly acidic environment

In this lab, we grow oral bacteria from our saliva on popsicle sticks (which acts as tooth surface)

-one stick in sucrose broth= lots of colonies formed

cariogenic bacteria will adhere to the popsicle stick

-the number of S. mutans in saliva has been correlated with potential to form caries

-other stick in xylitol broth = no colonies formed

-xylitol= a sugar alcohol used to sweeten “sugar-free” stuff

-is non-cariogenic bc it cannot be converted to dextran

Xylitol broth= no growth on tooth pick (or very little growth)