Week 12w This Week: Unknown Project Exp 45: Chemical Agents of Control: Disinfectants and Antiseptics Part B: Agar Plate-Sensitivity Method Last Week: Exp 43: Chemical Agents of Control: Chemotherapeutic Agents; Part A: Kirby Bauer Antibiotic Sensitivity Test Week 12w

Exp 43: Chemical Agents of Control: Chemotherapeutic Agents Some chemotherapeutic agents have a limited spectrum of activity being effective against only one group of microorganisms. Other chemotherapeutic agents exhibit broad spectrum activity against a range of microorganisms. Drug susceptibilities on many pathogenic microorganisms are known, but it is sometimes necessary to test several agents to determine the drug of choice.

Exp. 69: Species Identification of Unknown Bacterial Cultures Unknown project overview. Requisition Forms. Written report. Part 2: Gram Stain Differential Media Biochemical Tests

Exp 45: Chemical Agents of Control: Disinfectants and Antiseptics Disinfectants and antiseptics- chemicals used to prevent contamination and infection Efficacy is influenced by: Concentration Length of exposure Type of microbial population to be destroyed Environmental conditions Efficacy is influenced by: Concentration Higher conc prod more rapid death Toxicity of chemical must also be considered relative to conc. Length of exposure Sensitivity of microorg Toxicity of chemical also makes a diff Type of microbial population to be destroyed Spore more resistant than forms Capsulated bacteria more resistant than the noncapsulated Acid-fast more resistant than non-acid fast Older metabolically less active org are more resistant than young cells (metabolize more) Environmental conditions Temperature pH Type of material on which microorg exist If disinfectant combined w/ organic material such as pus, blood, or tissue fluid then antimicrobial activity will be reduced

Exp 45: Chemical Agents of Control: Disinfectants and Antiseptics Part B: Agar Plate-Sensitivity Method Media: 2 TSA plates, 2 swabs Culture: EC & SA Procedure: (refer to pg. 307) Label plate w/org. Label plate with test solution. Heavily inoculate entire surface of plate. Saturate disks with test solution. Use forceps to fix disks to agar. - mouth wash - peroxide - iodine - hand soap (lab) Incubate plates at 37oC for 24hrs in inverted position. PER TABLE Week 12W

In Kirby-Bauer testing, white wafers containing antibiotics are placed on a plate of bacteria. Circles of poor bacterial growth surround some wafers indicating susceptibility to the antibiotic. Antibiotic Sensitivity - The Kirby-Bauer Disk Diffusion Test The Kirby-Bauer disk diffusion test is a standardized protocol for determining antibiotic susceptibility. A pure culture of the test organism is inoculated on Mueller-Hinton agar. Paper disks impregnated with a standardized concentration of individual antibiotics are added to the plate which is then incubated at 35 degrees Celsius. Results are read and interpreted at 18 hours of incubation. If the growth of a test organism is inhibited by the antibiotic on a disc, a zone of inhibition will appear. The zone of inhibition is a circular area surrounding an antibiotic disk in which the test organism does not grow. The diameter of the zone of inhibition is calibrated in millimeters and compared with the Interpretive Zone Standards published by the National Committee for Clinical Laboratory Standards. Results are reported as S (sensitive), I (intermediate), or R (resistant). Results are affected by factors such as the antibiotic concentration, rate of diffusion of the antibiotic, pH and depth of the culture medium, inoculum density, incubation time and temperature. Thus it is essential that the Kirby-Bauer test is performed under standardized conditions: on Mueller-Hinton agar of pH 7.2 to 7.4, 4 mm. deep, inoculated with a pure culture of microbes matching the McFarland 0.5 standard for turbidity. Under these conditions, the results provide a guide for the potential effectiveness of a particular antibiotic. The plates shown here have been produced following the standardized procedure.

Epidemiology: the science of when and where diseases occur and how they are transmitted Descriptive (data on occurrence) Analytical (probable cause) Experimental (hypothesis, test) Epidemiology is the study of factors affecting the health and illness of populations, and serves as the foundation and logic of interventions made in the interest of public health and preventive medicine. It is considered a cornerstone methodology of public health research, and is highly regarded in evidence-based medicine for identifying risk factors for disease and determining optimal treatment approaches to clinical practice. In the study of communicable and non-communicable diseases, the work of epidemiologists ranges from outbreak investigation to study design, data collection and analysis including the development of statistical models to test hypotheses and the documentation of results for submission to peer-reviewed journals. Epidemiologists also study the interaction of diseases in a population, a condition known as a syndemic. Epidemiologists rely on a number of other scientific disciplines, such as biology (to better understand disease processes), Geographic Information Science (to store data and map disease patterns) and social science disciplines (to better understand proximate and distal risk factors). CDC, Center for Disease Control, US Public Health Service