Microbiology

1. How much growth there is- number of microbes
2. Time of exposure- length of time agent comes in contact with the bacteria
3. Microbial characteristics- presence of an outer membrane
4. Environmental influences- temperature (warm conditions increase action), pH

Susceptible- high likelyhood of therapeutic success
Intermediate- uncertain therapeutic effect
Resistant- high likelyhood of therapeutic failure

(supports the growth of whatever you’re growing) is used and the bacteria from the patient that you are concerned about is added so you get a nice consistent layer of bacteria across the surface of the plate. Overlay- mix it up and pour it on top and make sure it’s even or in some cases swab it with a sterile q-tip. Add little disks that have an antimicrobial drug in them and you place them on your newly inoculated plate. Let the plate grow because the bacteria need time to divide. The next day you will see clearing on the disk so bacteria are not able to grow with this drug. Measure the zones of inhibition and compare on a chart to determine the effectiveness of the drug against a microorganism. The farther the agent diffuses from the disk, the lower the concentration. The larger the zone, the more sensitive the microbe is to the antibiotic.

V strips with different types of antibiotics inside, there is more drug at one end of the strip than the other, the measurements are listed on the strip. Prepare a plate with bacteria, add one or more of the strips and give the bacteria a chance to grow, the next day you look and see where there is areas of growth. Allow you to determine the MIC (where the bottom of the tear drop is where it intersect the strip at the narrow side)

Determines MIC and MBC. The MIC is determined by making a sequence of decreasing concentrations of the drug in a broth, which is inoculated with the test bacteria. The wells that do not show growth can be cultured in brother or on agar plates free of the drug. If growth occurs in this broth the drug was not bactericidal and the MBC can be determined.

- The lowest antibiotic concentraion needed to prevent visable bacterial growth

O A few cells that are planktonic attach to a surface
o Bacteria switch into biofilm mode and they start changing, a more permanent association on the surface, if the bacteria started off with flagella those disappear, the bacterial start to produce a sticky gummy matrix material that is typical of biofilms (polysaccharides, protein, nucleic acids, ect.)
o As the biofilm matures the bacteria will be dividing and recruiting other bacteria and in a more mature biofilm they make a distinct structure that can be micro colonies and they start getting many layers of bacteria growing in the biofilm
o Some of the cells shut down most of their metabolism and the metabolism that is going on is directed towards making matrix and activities in the biofilm (not as much cell division in a biofilm as you would if you had bacteria living individually)
o Once the biofilm is mature if it ends up being deprived of nutrients there will be a dispersal of the biofilm (some of the cells leave and turn into planktonic type bacteria or whole clumps that break off and travel to attach to another surface)

O Biofilm formation is a carefully orchestrated process controlled by quorum sensing-the chemical signals that allow quorum sensing are essential to biofilm formation
o Bacteria use quorum sensing to coordinate certain behaviors based on the local density of the bacterial population
o Bacteria produce and secrete a signalling chemical (inducer) that diffuses into the surrounding medium> other bacterial cells move toward the source and begin producing the inducer. The conc of inducer increases, # of cells increases, attracts more cells and initiates synthesis of more inducer.
o Bacterial quorum sensing systems enhance access to nutrients and more favorable environmental niches, and they enhance action against competing bacteria and environmental stresses
o If enzymatic degradation of the signaling molecules happens, it will prevent biofilm formation or possibly weaken established biofilms

O Antimicrobial Neutralization- Materials in the matrix that can help neutralize certain drug
o Penetration failure- Matrix is difficult for a lot of chemicals to move through
o Nutrient limited physiology- Bacteria living in biofilms tend to be in dormant state- low levels of metabolic activity and drugs attack actively growing cells
o Bacteria are packed close together so genetic exchange can occur with horizontal gene transfer, therefore resistant agents can spread easily through a biofilm

O Cell-to-cell chemical communication that allows bacteria to coordinate their activity and group together into functional communities that provide benefits

A thin, slimy film of bacteria that adheres to a surface

1. Attachment of free floating microorganisms to a surface through van der Waals forces
2. Microbes anchor themselves to the matrix or directly to earlier colonists
3. During colonization cells are able to communicate via quorum sensing.
4. The biofilm begins to grow larger through a combination of cell division and recruitment.
5. The biofilm is developed and may only change in shape and size. These colonies in the biofilm are able to become resistant to antibiotics.

Pure cultures are controlled with nutrients.
In natural environments biofilms can become disrupted by chemicals.

Cultures grown in the lab are controlled by the amount of nutrients they have to grow with whereas in environments biofilms continulously grow and reproduce into more cells that seek more food and successfully become larger.

Dental plaqueis a biofilm, usually a pale yellow, that develops naturally on the teeth. Like any biofilm, dental plaque is formed by colonizing bacteria trying to attach themselves to a smooth surface (of a tooth).It has been speculated that plaque forms part of the defense systems of the host by helping to prevent colonizationby microorganismswhich may be pathogenic.