Biology: Book and Lab Coat Essay

Biology: Book and Lab Coat Essay.

Guidelines for Biology Experiments 1. 0 Attendance 1. 1 Attendance to practical sessions is COMPULSORY. 1. 2 If you cannot come to the class due to ill health or emergency excuses, please inform the lecturer EARLIER, so that another practical session can be arranged for you ON THE SAME WEEK. 2. 0 Lab coat 2. 1 Wearing lab coat is COMPULSORY. 2. 2 Put on the lab coat throughout the class. 3. 0 Jotter 3. 1 Jotters should contain the summary on the PROCEDURES you are going to perform during the experiment. 3. 2 It can be in the form of short notes, flow charts, mind maps, diagrams or any other forms of summary.

3.

3 Jotter should also include observation whenever necessary. 3. 4 Complete jotters must be submitted in groups prior to the experiment. The lecturer will check, mark and return them before the class ends. 4. 0 Recording observations/results 4. 1 All observation should be done on blank A4 paper 4. 2 Drawings (a) Use blank A4 paper (b) Limit to only TWO diagrams on each page. (c) Each diagram should be enclosed by a border.

(d) As for scientific drawings, e. g. diagrams of cells, tissues or organelles, there shouldn’t be any discontinuous lines, overlapped lines and shades. (e) For each diagram, it must have : a.

Title of the diagram, if specimen’s name write down the common name and/or scientific name b. Magnification power (if using compound or dissecting microscope) c. Labels (minimum 3 labels) 1 4. 3 Numerical data (a) Record numerical data in the particular tables. 4. 4 Graphs (a) Use the graph paper to plot any graphs. (b) For each graph, it must have : a. Title of the graph b. Title of Y- axis and X-axis c. Label (if necessary) 5. 0 Report 5. 1 Front cover (a) The standard front cover will be given to students by the respective lecturer. (b) Make sure that all particulars on the cover are completed before submitting the report.

5. 2 Format and evaluation (a) The particulars should be in the following order: – Title (as in manual book) – Objective (as in manual book) – Observation/Result (draw in blank A4 paper following the format given) – Discussion/Exercises/Questions – Conclusion (at least 2 conclusions) – References (at least 3 references following the format given) (b) The marks will be awarded (only if the experiment is conducted, i. e. the student is present during the particular experiment) in the following areas: Criteria Manipulative skill Observation/Result Discussion/Exercise/Questions Conclusion Reference Marks 25% 40% 20% 10% 5%.

5. 3 Submission of report (a) Reports of an experiment should be submitted at least THREE (3) DAYS after the experiment is completed. (b) Marks for reports submitted after the date line will be deducted. 2 HOW TO WRITE A REFERENCE FORMAT : 1. Authors: Authors are listed in the same order as specified in the source, using surnames and initials. Commas separate all authors. When there are eight or more authors, list the first six authors followed by three ellipses (… ) and then the final author. If no author is identified, the title of the document begins the reference.

2. Year of Publication: In parentheses following authors, with a period following the closing parenthesis. If no publication date is identified, use “n. d. ” in parentheses following the authors. 3. Source Reference: Includes title, journal, volume, pages (for journal article) or title, city of publication, publisher (for book). Italicize titles of books, titles of periodicals, and periodical volume numbers. REFERENCE BOOK Format : Author. (Year of Publication). Book Title (periodical). (Page referred). Place. Publisher Eg : Campbell, N. A.

& Reece, J. B. (2007). Biology (8th ed. ). (pp. 80-94) Pearson, The Benjamin Cummings Publishing Company, Inc. JOURNAL Format : Author. (Year of Publication). Title of journal. Name of journal. (volume) :page referred. Eg : Keller, Margaret A. & E. Richard Stiehm (2000). Passive Immunity in Prevention and Treatment of Infectious Diseases. Clinical Microbiology Reviews. 13 (4): 602–614. INTERNET Format : Author. (Year of Publication). Website title. Website address. Eg : Wikipedia. (2012). Eukaryote. http://en. wikipedia. org/wiki/Eukaryote 3.

Biology: Book and Lab Coat Essay

Unknown Lab Report Microbiology Essay

Unknown Lab Report Microbiology Essay.

There are numerous reasons for identifying unknown bacteria. Some of these organisms have distinct qualities that set them apart from one another, such as the exposure to certain environments. Through out the semester in the laboratory, we are able to encounter some of the few microorganisms that we as humans have come into contact with. With the knowledge gained from the sessions in the laboratory, we can now integrate what we have learned to the process of finding out the unknowns given.

Materials and Methods

The professor gave out the unknown specimens. It contained one-­‐gram positive and one-­‐gram negative bacteria from the given list. I was assigned unknown A. The process of identification was achieved by utilizing procedures learnt during the semester. Procedures were followed as stated in the lab manual (1). Since the sample contained two unidentified bacteria, the first step was to isolate each bacterium using streak plate technique. Tryptic Soy Agar (TSA) plate, and differential media such as mannitol salt and Eosin methylene blue (EMB) were used for isolation streak technique.

This step is imperative because the bacteria need to be separated and isolated before they can be identified. Moreover, gram staining was used to understand the basic morphology of these bacteria. As these plates were incubated and grown, the presence of two separate bacteria colonies was visible. The colonies from the mannitol salt were used to incubate a TSB broth to grow the gram-­‐positive culture. The purity of this broth was tested using gram-­‐staining technique. A circular colony from the TSA plate was used to incubate a TSB broth for gram-­‐negative growth. Similarly, examining the morphology of the bacteria-­‐using gram staining technique tested the purity of the both.

After the isolation of gram-­‐positive and gram-­‐negative bacteria from unknown A, specific biochemical tests were performed. The results of the biochemical tests along with deductive reasoning and elimination led to the identification the unknown bacteria. The following tests were performed on the gram-­‐positive bacteria: 1. Mannitol salt streaking 2. Gram stating of the pure isolate 3. Oxidase test 4. Catalase test 5. Coagulase test The following tests were performed on the gram-­‐negative bacteria: 1. Gram staining of the pore isolate 2. Blood agar plate streaking 3. SIM (Sulfide, Motility, Indole) test 4. Catalase test Results

Table 1. Biochemical Tests for the Gram-­‐Positive Unknown TESTS PURPOSE REAGENTS/MEDIA OBSERVATION RESULTS Gram stain To determine the gram reaction and morphology �Crystal violet, Iodine, Alcohol, Safranin

Purple cocci, connected Gram positive purple cocci

Mannitol salt Selective growth media for Staphylococci and Micrococcaceae

Mannitol salt plate and gram positive isolate broth After incubation, media turned yellow

Bacteria is mannitol salt positive

Oxidase test To determine if bacterium produces cytochrome c oxidase

No color change Bacterium is oxidase negative Catalase test To identify if bacterium produces catalase

Hydrogen peroxide Bubbling is seen Bacterium is catalase positive Coagulase test Used to identify if bacterium produces coagulase (enzyme that clots blood plasma)

Citrated rabbit plasma Clouding and solidification of plasma is seen Bacterium is coagulase positive

Table 2. Biochemical Tests for the Gram-­‐Negative Unknown TESTS PURPOSE REAGENTS/MEDIA OBSERVATION RESULTS Gram stain To determine the gram reaction and morphology

Crystal violet, Iodine, Alcohol, Safranin

Small pink rods Gram negative pink rods Blood agar plateSelective growth media

Blood agar plate After incubation, media displayed beta hemolysis, metallic sheen, and blue-­‐green pigment growth (fig 1)

Non fermenting gram negative rods Oxidase test To determine if bacterium produces cytochrome c oxidase

Oxidase reagent (tetramethyl-­‐p-­‐phenyldiamine)

Color change to dark blue Bacterium is oxidase positive

Catalase test To identify if bacterium produces catalase Hydrogen peroxide Bubbling is seen Bacterium is catalase positive

SIM (Sulfide, Motility, Indole) test 1. To determine the ability of an organism to liberate hydrogen sulfide (H2S) from

SIM medium and indole reagent The medium showed no color change, motility, or color change when indole test was done.

-­‐/-­‐/-­‐ The bacterium is sulfide, motility, and indole negative.

sulphurbearing amino acids producing a visible, black colour reaction. 2. To determine the ability of an organism to split indole from the tryptophan molecule. 3. To determine if the organism is motile or non-­‐motile. Discussion and Conclusions:

The biochemical tests performed on the gram-­‐positive bacterium worked systematically to narrow down the possible species, and eventually eliminate every organism on the list except the correct one. The gram stain, that showed the gram positive cocci and the transformation of the mannitol media to yellow color left me with two choices that fit this profile-­‐ Micrococcus luteus and Staphylococcus aureus. Biochemical tests that differentiate these two were performed. These included, oxidase, catalase, and coagulase test. The results of

these tests (oxidase negative, catalase positive, coagulase positive), confirmed that the gram-­‐positive microorganism in unknown A is Staphylococcus aureus. After the Gram+ bacterium was identified as such, further tests were performed to narrow down which particular Gram- species this was. The first test done was blood agar plate. The results show that after incubation the blood agar media displayed beta hemolysis, metallic sheen, and blue-­‐green pigmentation.

Colonies of Pseudonomas aeruginosa often display similar result on this medium (2). To confirm the inference, oxidase, SIM, and catalase tests were performed on the gram-­‐negative isolate. The results showed that the bacterium was oxidase positive, SIM negative (-­‐/-­‐/-­‐), and catalase positive. Similar results are characteristic of P. aeruginosa. Hence, the gram-­‐negative microorganism in unknown A is Pseudonomas aeruginosa. Appendix:

Fig.1. Photograph of the blood agar medium (after incubation) streaked with the gram-­‐positive isolate of unknown A. References (1) Harley, J. P. (2014). Laboratory Exercises in Microbiology . University of Kentucky : McGraw Hill

(2) Buxton, R. (2010). Blood Agar Plates and Hemolysis: Non-­‐Fermenting Gram-­‐ Negative Rods (including Pseudomonas aeruginosa) .

Retrieved from http://www.microbelibrary.org/library/laboratory-­‐test/2862-­‐blood-­‐agar-­‐plates-­‐and-­‐hemolysis-­‐non-­‐fermenting-­‐gram-­‐negative-­‐rods-­‐including-­‐pseudomonas-­‐aeruginosa (3) Summary of Biochemical Tests. (n.d.). Retrieved from http://www.uwyo.edu/molb2210_lab/info/biochemical_tests.htm (4) Sigma Aldrich , J. S. (n.d.). Pseudomonas Media and Tests. Retrieved from http://www.sigmaaldrich.com/technical-­‐documents/articles/analytix/pseudomonas-­‐media.html

Unknown Lab Report Microbiology Essay

Cellular Components Essay

Cellular Components Essay.

1 What cellular components do some bacterial cells have that make them powerful pathogens? Explain your answer. Pili that allows the structure to attach onto other cells like a leech. The capsule which protects the cells from the white blood cells that attack foreign invaders. Endospores which allow them to survive rough conditions.

2 Why are penicillins often more effective against Gram positive bacteria than Gram negative bacteria? It is more effective against Gram positive because it has only one layer of the cytoplasmic membrane whereas the Gram negative bacteria has two layers of the member which makes it harder for the penicillin to synthesize.

3 Why is it important to understand the structure of a bacterial cell when developing an antibiotic? The cell structure provides an insight on what proteins and enzymes that create the cell wall. Which allows the scientist to develop the chemicals that can destroy the proteins and enzyme that create the cell wall, therefore killing the cells.

4 How do antibiotics work without harming the surrounding human cells? Antibiotics work by using a metabolic pathway necessary for bacterial life, but not for human life.

They also target cell walls, which eukaryotic cells don’t have which is what is in humans so our cells remain unharmed.

1. What class of antibiotics would you prescribe for Sue? Explain your answer. I would prescribe Sue sulfa drugs. The bacteria is a Gram negative so penicillin would be difficult to infiltrate the cell wall. The others are within the cells. So Sulfa drugs would be best.

2. Why are antibiotics NOT effective against viruses? (Think back to what you learned about viruses in PBS.) Antibiotics are drugs that are used to treat infections brought about by bacteria. They do not have effect on viruses as viruses are non-living and have different components compared to bacteria. They kill bacteria by disrupting the DNA as well as the cell wall bacteria.

Cellular Components Essay

Bacteria Lab Report Essay

Bacteria Lab Report Essay.

The most common way of alleviating the specific symptoms arrived from diseases is to ingest antimicrobial drugs. Chemotherapeutical antimicrobial agents are chemical compounds intended to inhibit or kill rapidly dividing microorganisms. In order to derive an antimicrobial drug, different chemical compounds must be synthetically formed. Among these specific chemical compounds is a compound famously known as the antibiotic. The antibiotic is classified as an antimicrobial drug because it’s a chemical that is produced by either a bacterium or fungus, which has the ability to regulate the growth of other microorganisms.

The validity of antibiotics as a category of antimicrobial drugs was determined by a method that was developed by Kirby and Bauer, and standardized by the World Health Organization in 1961 to ensure reliable results. The Bauer-Kirby method was highly suggested by the U.S. Food and Drug Administration to determine the antimicrobial disk susceptibility. (Liberman et al., 1966) Therefore, extreme care is required to meet to the standards. To begin meeting the standards, a Mueller-Hinton agar is used for the bacteria culture.

The standard Mueller-Hinton agar usually requires a pH between 7.2 and 7.4, which is then poured to a depth of 4mm in either 150 mm or 100mm Petri dishes. The petri dish is then heavily inoculated with a specific bacteria and different paper disks that contain different antibiotics to examine.

With the disks on the inoculated petri dish, the petri dish must be sealed and placed into an incubator at an exact temperature of 37°C for 24 hours and allow the bacteria to grow. Within 24 hours, the bacteria must be put into a refrigerator with an estimated temperature of 4.4°C to prevent overproduction of bacteria. By examining the results of the incubation of bacteria, the zone of inhibition, which is the area without bacterial growth that surrounds the antimicrobial disk, can determine how effective the antibiotics were against the bacteria. Depending on the length of the radius of the clear region around the paper disk, an estimated measure from the edge of the paper disk of 1-2 cm can determine how powerful the antibiotics were. Some of the bacteria may show small or no zones of inhibition if their growth was completely resistant to the antibiotic. Though this may be the case, the more sensitive cultures will be utilized efficiently to counter the different diseases that are brought on by specific bacterium.

With the experiment explained and discussed, a group of two students including I tested one antibiotic against three different pathogens. Erythromycin, a compound produced by a strain of Saccharopolyspora erythraea that is categorized as a macrolide group of antibiotics. This antibiotic is an extremely useful antibiotic often prescribed to patients who are allergic to penicillin. Erythromycin inhibits the synthesis of specific proteins that is essential to bacteria reproduction. (Weisblum, 1995) With the inhibition of protein synthesis, erythromycin does not necessarily kill the bacteria, but leaves them unable to replicate. The remaining bacteria are incapable of surviving and are destroyed by the immune system.

The three different pathogens, _Escherichia coli, Shigella flexneri, and Staphylococcus aureus_ were exposed by Erythromycin and the effects were examined.

_Escherichia coli (E. coli),_ a prokaryote with one circular chromosome composed of monocistronic (single genes) and polycistronic genes is a Gram-negative, rod shaped, bacterium that essentially lives in the intestine of warm-blooded organisms. The cell structure of an _E. coli_ possesses a cell wall that is constructed by lipopolysaccharides, a peptidoglycan layer, and a cytoplasmic membrane. _E. coli_ can cause severe infections to animals by ascending infections of the urethra and kidneys, which lead to bloody diarrhea or urinal tract infections. Though not a very dangerous bacterium, it can be prevented with amoxicillin, penicillin, and many other antibiotics. (Chan et al., 2006) _Shigella flexneri (S. flexneri),_ a physiologically similar prokaryote to _Escherichia coli,_ may very well have a common evolutionary basis.

This gram-negative rod shaped bacteria, is notoriously known to cause shigellosis, an acute bloody diarrhea. _S. flexneri_ can be treated with Beta-lactams antibiotics such as ampicillin and amoxicillin. (Chan et al., 2006) The last bacteria being tested, _Staphylococcus aureus (S. aureus),_ a Gram-positive, cocci-shaped bacterium, is the most common species among the entire Staphylococcus bacteria. Because it’s Gram-positive, _S. aureus_ is formed from a thick layer of peptidoglycan.

Out of the entire microbial species, _S. aureus_ is the most complete genome sequence. This bacterium causes mild skin infections, invasive diseases, and toxic mediated diseases by colonization. Though _S. aureus_ causes painful infections, they are becoming increasingly resistant to common antibiotics such as penicillin, erythromycin, tetracycline, and aminoglycosides. (Chan et al., 2006) Since Erythromycin is more effective towards Gram-positive bacteria, the radius of the zone of inhibition will most likely be longer for _Staphylococcus aureus_ than _Escherichia coli_ and _Shigella flexneri._

MATERIAL AND METHODS:

In our lab, with a team of three, each person distinguished the different areas of pathogens that were divided in fourths with a black permanent marker on either a 150 mm or 100 mm petri dish that is coated with a 4 mm deep Mueller-Hinton agar. In this case we used _Escherichia coli, Shigella flexneri, and Staphylococcus aureus_ as our pathogens. It is very important to label the pathogens where it was swabbed because all of the bacteria contained a transparent color, which were difficult to distinguish. After applying the bacteria onto the Mueller-Hinton agar petri dish, one McFarland standard disk that contained 15 μg of Erythromycin dosage was placed in the center of each sector.

It is important to take note that the stainless precision tweezers must be sterilized by flame or alcohol before placing the disk onto the center of the sector because there may be different bacteria on the tweezers before. When the McFarland disks were placed, the Mueller-Hinton agar petri dish were sealed and placed in an incubator that was set at a 37°C temperature for 24 hours. After 24 hours, the Mueller-Hinton agar petri dish was moved out of the incubator and placed into a refrigerator with an approximate temperature of 4.4°C to inhibit continuous bacterial growth. After incubation, the radiuses from the edge of the McFarland disks to the end of the clear zones were measured with a standard ruler to the nearest millimeter.

DISCUSSION AND CONCLUSION:

As a result from the experiment, _Escherichia coli_ was not very sensitive to Erythromycin. With a zone of inhibition of 2.6 mm, Erythromycin had a small effect on _Escherichia coli_. Erythromycin is not very effective against Gram-negative bacteria because they contain hydrophobic molecules and macrolides do not have the ability to penetrate both inner and outer membranes of Gram-negative bacteria. As a Gram-negative bacterium, the peptidoglycan layer is thinner, but contains a much more complex cell wall that contains polysaccharides, proteins, and lipids. Referencing back to the results, according to Figure 5 under oil-immersion objective at 1000x magnification, _Escherichia coli_ had a stained color of pink/red, which categorizes itself as a Gram-negative bacterium.

Similar to _Escherichia coli, Shigella flexneri_ is Gram-negative as well. Although these two bacteria are Gram-negative, _Shigella flexneri_ is less sensitive than _Escherichia coli._ The radius of the zone of inhibition resulted to be 0 mm when exposed to the Erythromycin antibiotic, which proved that _Shigella flexneri_ was completely resistant to Erythromycin. Since Erythromycin is categorized as macrolides, it is most likely that _Shigella flexneri_ is resistant to all the macrolides. In Figure 4, _Shigella flexneri_ had a stain color of red/orange, which is also a characteristic of a Gram-negative bacterium.

As for _Staphylococcus aureus,_ the radius of the zone of inhibition was 6.8 mm. This proved _Staphylococcus aureus_ to be Gram-positive when exposed by Erythromycin and would be expected to be very sensitive to the rest of the macrolide antibiotics. As a Gram-positive bacterium, _Staphylococcus aureus_ results with a blue/purple colored stain. (Figure 3)

The radiuses of the zone of inhibition could have been a lot more accurate because as I placed the McFarland disk with Erythromycin, it didn’t completely stick onto the bacteria. As I flipped the Mueller-Hinton agar petri dish over, the disk fell onto the cover of the petri dish. Without intelligently thinking, I quickly flipped the petri dish over back to its original position and the disks landed back onto the bacterial colonies. Luckily, my results still supported my hypothesis, which meant that as I flipped the petri dish over, all four of the Erythromycin disks spontaneously landed onto the correct sectors. Although the disks landed on the sector, they were not centered, which was difficult to determine the clear area radius since the disks were close to the constant. If they were centered, the results would have provided me a much more accurate measurement.

Ever since the discovery of penicillin in 1928, people have been utilizing this antibiotic to the utmost of their abilities. The rate of antibiotic discoveries has been phenomenal, but at the same time, different bacteria that undergo different mutations rapidly eclipse the rate of discovery for antibiotics. This puts pressure to find solutions to prevent the spread of renovating bacteria and continuing to ensure safety around the world with the utmost of our abilities.

REFERENCES:

Boyle, V.D., Fancher, E.M., Jr. Ross, W.R. (1973). Rapid, Modified Kirby-Bauer Susceptibility Test with Single, High-Concentration Antimicrobial Disks. _Antimicrobial Agents and Chemotherapy,_ 3(3): 418-424

Liberman, F.D., Robertson, G.R. (1975). Evaluation of a Rapid Bauer-Kirby Antibiotic Susceptibility Determination, _Antimicrobial Agents and Chemotherapy,_ 7(3): 250-255

Bauer, A.W., Kirby W.M., Sherris, J.C., Turck, M. (1966). Antibiotic susceptibility testing by a standardized single disk method, _Am J Clin Pathol,_ 45(4): 493-496

Boyle, V.J., Fancher M.E., Ross R.W., Jr Rapid. (1973) Modified Kirby-Bauer Susceptibility Test With Single, High-Concentration Antimicrobial Disks. _Antimicrobial Agents and Chemotherapy_, 3(3): 418-424.

Weisblum, Bernard (1995). Erythromycin Resistance by Ribosome Modification.

_Antimicrobial Agents and Chemotherapy_, Mar. 1995, 577-585.

Chan, V.L., Sherman M.P., Bourke, Billy (2006) Bacterial genomes and infectious diseases, _Humana Press._

Bacteria Lab Report Essay

Does Cerumen have a risk for transmission of diseases? Essay

Does Cerumen have a risk for transmission of diseases? Essay.

I learned in the A & P course that ear wax (or cerumen) is a waxy secretion by ceruminous gland (= modified sebaceous gland), mixed with sloughed epithelial cells, which inhibits the growth of certain bacteria due to its acidic pH. It also protects the skin of the external auditory canal by providing a waterproof layer, so, it’s something beneficial to us.

Sure enough, there appear to be a number of articles written to support this – “Bactericidal activity of cerumen”, Chai & Chai (ref 1), “Bactericidal activity of wet cerumen”, Stone & Fulghun (ref 2), etc.

(though this concept is refuted by a later study! (ref 3))On the other hand, I could find only very few articles that discuss the role that ear wax plays in disease transmission or as a portal of exist for pathogens. I started with an article by Kemp & Bankaitis (ref 4), in which it is stated that cerumen is not considered an infectious agent until it becomes contaminated with blood or mucus, and it can even be placed in the regular trash unless significant amount of blood or mucous is present.

So, it appears the danger is not in cerumen itself but in blood/mucous contaminant. CDC lists Hepatitis B, Hepatitis C, HIV and Viral Hemorrhagic Fever(VHF) as infectious diseases by bloodborne pathogens (ref 5).

On the topic of cerumen itself transmitting bloodborne viruses, I could find only two articles, both by the same group of researchers, Beyindir, Kalcioglu et al. First article is on the study of possible transmission of Hepatitis B (ref 6), in which the authors conclude that cerumen can be a potential source of transmission and further investigation for horizontal, nosocomial, and occupational transmission is necessary. The second article is on Hepatitis C, and it concludes that cerumen has no risk, even in patients with high HCV RNA serum levels. I could not find any articles to confirm/deny cerumen as a source of transmission for HIV or VHF.

I think our text book lists ear wax as a portal of exit for pathogens, because of more than minimal potential risk of contamination by blood, during treatment of otitis, removal of impacted ear wax etc. performed by otolaryngologists/audiologists on a regular basis.

Referrences

———–1: Antimicrobial Agents and Chemotherapy, 1980 Oct;18(4): 638-412: The Annals of otology, rhinology, and laryngology, 1984 Mar-Apr;93(2 Pt 1): 183-63: “Influence of human wet cerumen on the growth of common and pathogenic bacteria of the ear”, Campos, Betancor, et al., The Journal of laryngology and otology, 2000 Dec;114(12): 925-94: “Infection Control in Audiology”, http://web.clas.ufl.edu/users/sgriff/infectioncontrol.pdf5: http://www.cdc.gov/ncidod/hip/Blood/blood.htm6: “Does cerumen have a risk for transmission of hepatitis B?”, The Laryngoscope, 2004 Mar;114(3): 577-807: “Detection of HCV-RNA in cerumen of chronically HCV-infected patients”, The Laryngoscope, 2005 Mar;115(3): 508-11

Does Cerumen have a risk for transmission of diseases? Essay