Assignment 2

docx

School

Athabasca University, Athabasca *

*We aren’t endorsed by this school

Course

325

Subject

Biology

Date

Jan 9, 2024

Type

docx

Pages

Uploaded by ElderHawk3269

March 12 th , 2023 Assignment 2 (covers Units 6-8; Chapters 10-12 of the textbook) Due: After Unit 8 Weight: 10% of course final grade This assignment is out of 100 marks. Your mark for this exercise will comprise 10% of your final grade for the course. 1. Write the binomial nomenclature for each of the following descriptions of microorganisms. (10 marks) a. a gram-positive bacterium that has a low G+C ratio and produces endospores Phylum Firmicutes Genera Clostridium and Bacillus i.e., Clostridium perfringens b. a  -proteobacterium that commonly inhabits the gastrointestinal tract Order Enterobacteriales Genera Escherichia, Salmonella, Shigella, Klebsiella, Serratia, Proteus, Yersinia, Erwinia, Enterobacter, and Cronobacter i.e., Escherichia coli c. a member of the Actinobacteria that can cause a disease of the lungs Genera Mycobacterium i.e., Mycobacterium tuberculosis d. a member of  -proteobacterium that causes crown gall and is used in biotechnology to transfer genes into plants Agrobacterium tumefaciens e. a β-proteobacterium that causes whooping cough Bordetella pertussis 2. A clinical microbiologist wishes to identify two bacterial species from a mixed bacterial skin infection. The microbiologist performed a Gram stain reaction of the sample, and noted by

microscopic observation that the sample contains gram-positive cocci in clustered or paired formation and randomly scattered gram-negative bacilli (rods). The Gram stain results are shown in Figure 1. Using A Photographic Atlas for the Microbiology Laboratory and your eText, describe the steps the microbiologist will use to a) separate the two organisms, and b) confirm their identity. For each step, explain the rationale for your choices. Hint : The microbiologist has access to selective and differential media as well as biochemical tests. (10 marks) FIGURE 1. Gram stain results of mixed infection. http://lib.jiangnan.edu.cn/ASM/030-2.jpg . Pfizer Inc., 2007. Creative commons. a) To isolate the gram-positive and gram-negative species the microbiologist could use either the streak plate method of isolation or selective media. The streak plate method of isolation involves the inoculation of a mixed culture on an agar plate. Streaking decreases the density of cell populations and leads to the formation of pure colonies on the agar that can distinguished via colony morphology and gram staining that can be manually extracted for further testing. This method is relatively easy and cost and time effective as a wide variety of agars can be utilized and the method can be repeatedly performed if necessary. Alternatively, selective media uses biochemical reactions to inhibit the growth of certain organisms while promoting the growth of others typically with indicators already present within the agar. This allows for isolation and some identification steps to occur simultaneously. For example, to separate the gram-positive cocci, a microbiologist could use a Columbia 2

CNA with 5% Sheep Blood Agar. The antibiotics colistin and nalidixic acid disturb the membrane of gram-negative cells suppressing DNA replication and the casein, yeast and beef extract, and sheep blood provide the nutrients for the growth of gram-positive microorganisms. To isolate the gram-negative bacilli, a microbiologist could use either a MacConkey (MAC) agar (with bile salts and crystal violet) or a xylose lysine deoxycholate (XLD) agar. The MAC and the XLD agar use bile salts to inhibit the growth of gram-positive bacteria. MAC agar indicates lactose fermenters by the pH indication turning the agar red when pH falls below 6.8 from the acid production. XLD agar indicates lactose and sucrose fermentation by turning yellow, sulfur reduction by turning black, and lysine decarboxylation by turning red. b) From cell morphology and gram staining results the microbiologist can narrow identification prior to selective and differential media and biochemical tests. As the sample contains gram-positive cocci in clustered and/or paired formation this narrows the identification to include species such as streptococci or enterococci. This can also be confirmed with a catalase reaction test by the addition of hydrogen peroxide to a small subsample of the microorganism. If bubbles are not formed, indicating the absence of the enzyme catalase (which catalyzes hydrogen peroxide and releases oxygen in the form of bubbles) the microbiologist can assume the organism to be an aerotolerant or obligate anaerobe such as streptococcus, enterococcus, or aerococcus. A Hemolysis test could then be performed using blood agar to narrow the identification further. These bacteria produce hemolysins, endotoxins that destroy red blood cells and hemoglobin, allowing for differentiation based on the type of hemolysis. α-Hemolysis is indicated by a green tinge due to the incomplete lysis of red blood cells. β-Hemolysis is indicated by a clearing around the cells due to the complete lysis of the red blood cells. Lastly, γ-Hemolysis is indicated by red colonies indicating no hemolysis. For the randomly scattered, singular, straight gram-negative bacilli (rods) with rounded edges, the microbiologist could use an EnteroPluri Test to draw 3

Your preview ends here

Eager to read complete document? Join bartleby learn and gain access to the full version

Access to all documents
Unlimited textbook solutions
24/7 expert homework help

conclusions on numerous biochemical characteristics concurrently, such as lactose and glucose utilization, indole production, and urase presence. Fermentation of sugars can be readily detected by the indication of end products of bacterial fermentation such as gas and/or acid. A pH indicator in the microbial growth medium changes colour with the lowering of pH when acid is produced. Within the EnteroPluri tube Glucose and Lactose utilization is typically indicated by a change in agar colour from red to yellow or the presence of gas within the specific compartment. Indole production is indicated by a change in colour in the agar from yellow to green after the external addition of Kovac’s reagent. Urease activity is as well detected by a pH indicator reacting with ammonia, the end product of the urea catabolism, turning the agar medium yellow to a bright pink. 3. As part of an investigation to identify the course of a respiratory infection among elderly patients at a nursing home, DNA fingerprints were obtained from bacterial isolates of sputum from affected patients and staff. All staff reported not having contracted the illness. Examine the results of the fingerprint below, and describe the conclusions that can be drawn from the results of the patients and the staff. Which staff members may have spread the illness to which patients? Do all of the patients have the same strain of bacteria? Why do strains of bacteria differ on a DNA fingerprint? Were all staff members tested responsible for infection in all of the patients tested? Why didn’t staff members become ill? What can be done to prevent the spread of infection from staff members to patients? (10 marks) Mrs. S. H. Mrs. J. M. Mr. A. D. Nurse 1 Nurse 2 Nurse 3 4

DNA fingerprinting is a quick way to determine the genetic similarity of bacteria in hospital-acquired infections to break an infection’s chain of transmission. DNA fingerprinting involves treating a sample of microorganisms with restriction enzymes. These restriction enzymes cut DNA anywhere a specific base sequence occurs, creating fragments called restriction fragments (RFLPs). These RFLPs are then separated by size through electrophoresis creating a specific DNA template from different organisms. Differences in these templates represent differences in the genetic make-up of the organisms sampled – more similarities, the more closely related the organism’s strains can be assumed to be. Given the results from the DNA fingerprints obtained, the bacteria from Mrs. S. H., Mr. A. D., Nurse 1, and Nurse 2 are identical. These results suggest that Nurse 1 and Nurse 2 likely took part in spreading the respiratory infection in the nursing home to or from patients Mrs. S. H. and Mr. A. D. Data from the DNA fingerprints also show that the bacteria of Nurse 3 and Mrs. J. M. are different from the others, suggesting that they did not play a role in the specific transmission of this strain (though they could be associated with mutated strains considering Mrs. J. M. was also ill from a respiratory infection). The hospital staff likely did not fall ill to the bacteria as their immune systems are not impaired and they are less likely to suffer from any high-risk comorbidities. An increase in aseptic practices is an easy way to reduce the spread of infection between hospital staff and patients. Correctly used personal protective equipment such as gloves, masks, and protective clothing that can be changed regularly. Frequent use of hand and surface cleaner alongside proper and frequent hand washing. 4. Answer the following questions on classification techniques: 5

a. An increase in the number of cases of necrotizing fasciitis was recently reported in hospitals. Explain how serotyping would have been used to identify the source of the infection. (5 marks) Serotypes are different types of microbial species, or different strains within a species that possess different antigens. Serotyping is a procedure that allows researchers to differentiate relatedness of serotypes based on these differences on microbial surfaces. The use of serotyping allows researchers to quickly pinpoint a common source of infection and diagnoses for diseases such as necrotizing fasciitis to prevent outbreaks. A widely used technique called the enzyme-linked immunosorbent assay (ELISA) uses known antibodies inserted into wells of microplates with unknown bacterium. The resulting reaction can then be read by a computer and provide insight into the identification of the bacteria. b. Discuss how DNA base composition can be used to determine relatedness between organisms. (5 marks) Closely related organisms will have similar amounts of the various base composition in their DNA as a species can be assumed to theoretically hold a fixed base composition. Base composition is typically described as the percentage of guanine plus cytosine (G + C). For example, if a known bacterium’s DNA contains 20% GC pairs and an unknown bacterium contains 60% GC pairs, researchers can conclude that these bacteria are probably not closely related – though further data is needed to make concrete conclusions as this is not an exact science but a means for estimation on genetic make-up. Comparing G + C content gives researchers a mechanism for comparing genetic relatedness without having to sequence the entire DNA. Adenine and thymine content can also be extrapolated from this data. 5. Answer the following questions on  ,  ,  ,  , and  -proteobacteria: (10 marks) a. Why is the genus Rickettsia an obligate intracellular parasite? Name one disease that is caused by a rickettsia. How is it transmitted? 6

Your preview ends here

Eager to read complete document? Join bartleby learn and gain access to the full version

Access to all documents
Unlimited textbook solutions
24/7 expert homework help

The genus Rickettsia is an obligate intracellular parasite as they can only reproduce within a mammalian cell. They are responsible for diseases that fall within the spotted fever group damaging the permeability of blood capillaries, creating a spotted rash. Specifically, Rickettsia rickettsii causes Rocky Mountain spotted fever which is transmitted by ticks. b. Burkholderia species are capable of degrading many organic molecules. What is the consequence of this ability, and how does this affect humans? The genus Burkholderia is able to degrade over 100 different organic molecules facilitating it to metabolize respiratory secretions and even grow in disinfectant solutions. This creates a unique problem for hospitals as these bacteria contaminate a wide variety of hospital equipment and drugs, as well as pose a great risk for those with cystic fibrosis, a genetic lung disease. c. Many of the  -proteobacteria are pathogenic. List two examples, including the genus and species name, and state the disease that they cause. Moraxella lacunata are aerobic coccobacilli that cause conjunctivitis, the inflammation of the membrane that covers the eye. Coxiella burnetii contaminates milk causing Q fever, resulting in headaches, muscle aches, chills/sweats, fatigue, nausea, vomiting, diarrhea, chest pain, and stomach pain. d. How does the genus Desulfovibrio contribute to the black colour that is present in many soil sediments? Desulfovibrio are sulfur-reducing bacteria present in anaerobic sediments that reduce sulfur (or sulfate) to H 2 S using organic compounds (e.g., lactate, ethanol, fatty acids). H 2 S in soil sediment reacts with free iron to form FeS, an insoluble form of iron, contributing to soil’s black colour. e. Name two genera of ε-proteobacteria, and indicate their relevance. Campylobacter, microaerophilic vibrios , can cause spontaneous abortion in animals and outbreaks in foodborne intestinal disease. Helicobacter , microaerophilic curved rods, are the most common cause of peptic ulcers and a cause of stomach cancer. 7

6. Answer the following questions on Nonproteobacteria, Gram-positive bacteria, other Gram- negative phyla, and the Archaea. (10 marks) a. Describe how cyanobacteria use water in photosynthesis and compare this process to the use of H 2 S by purple sulfur bacteria. Similar to eukaryotic plants and algae, Cyanobacteria produce oxygen from water through photosynthesis. 2 H 2 O + CO 2 →C H 2 O + H 2 O + O 2 Whereas purple sulfur bacteria use sulfur compounds, instead of water, to produce sulfur, instead of oxygen. 2 H 2 S + CO 2 →C H 2 O + H 2 O + 2 S 0 b. What growth characteristic does Staphylococcus aureus possess that contributes to it being a common food pathogen? What characteristic of this organism makes it a problem in hospitals? Staphylococci grows well in high osmotic pressures and low moisture environments. This enables species like Staphylococcus aureus to grow on cured meat or on low-moisture food that other bacteria are unable to inhabit. Due to these same characteristics, Staphylococci are also able to grow and survive in nasal secretions and on our skin causing a wide variety of airborne diseases, easily transmittable. Scientists also theorize that it’s yellow pigment may serve as protection from the antimicrobial effects of sunlight. c. State the morphology, habitat, and unique characteristic common to Bacillus species. Bacteria belonging to the genus Bacillus are gram-positive, rod-shaped, endospore-forming aerobic or facultative anaerobe. They are commonly found in soil and the environment. Several species are used to make antibiotics. Bacillus endospores are of particular significance as they are resistant to heat, radiation, disinfectants, and chemicals such as antibiotics making them of medical importance. Some species (e.g., Bacillus thuringiensis ) produce intracellular crystals when they sporulate creating a crystallin toxin (Bt) that is sold commercially as a microbial insect pathogen. d. Briefly describe the mechanism of motility in spirochetes. 8

Spirochetes use two or more axial filaments (endoflagella) embedded near each of the cell’s poles, between the body of the cell and an outer sheath. The cell rotates in a corkscrew like motion in the opposite direction by rotating this axial filament, effectively moving the organism through liquid medium at a rate about 100 times its body length in a second. e. What features distinguish Domain Archaea from other bacteria? Microbes from the Domain Archaea are prokaryotic and lack peptidoglycan in their cell walls, in contrast to bacteria which contain peptidoglycan. rRNA sequencing also shows differentiation of the genetic sequencing of the Domain Archaea with the Domain Bacteria and Domain Eukarya. 7. Column B lists terms related to fungi and yeasts. Column A provides descriptions of the terms or organisms. For each description in Column A, select the answer from Column B. (10 marks) Column A Column B _e_ sac containing asexual spores a. zygospore _h_ ability to become pathogenic b. hypha _b_ vegetative fungal structure c. mutualistic _g_ result of mating two different strains d. septum _J_ asexual spore e. sporangium _i_ reproductive process used by yeasts f. mycosis _c_ partnered growth between fungi and algae g. ascospore _a_ enclosed by a thick wall h. opportunistic _f_ fungal infection i. budding _d_ hyphal cross-wall j. conidium 8. Answer the following questions on fungi and algae: a. Certain fungi are known to have positive and negative effects in nature. Use two examples of fungi to outline such effects. (4 marks) Dermatophytes are fungi that secrete digestive enzyme keratinase, which is able to degrade keratin. Dermatophytes are prevalent in soil microbiota and assist in breaking down organic matter on decomposing organisms, aiding in 9

Your preview ends here

Eager to read complete document? Join bartleby learn and gain access to the full version

Access to all documents
Unlimited textbook solutions
24/7 expert homework help

recycling nutrients. They also cause dermatomycoses (cutaneous mycoses), infections in epidermis, hair, and nails that can be transmitted zoonotically. Aspergillus is an opportunistic pathogen that causes aspergillosis, a debilitating lung disease that can cause cancer. Aspergillus niger are used commercially to produce citric acid for foods and beverages. b. What is a lichen? What type of relationship does this demonstrate? How does each organism contribute? Give an example of the importance of lichens. (5 marks) Lichens are slow growing organisms formed by a symbiotic relationship between green algae (or cyanobacteria) and fungi (typically an ascomycete). These symbiotic relationships are mutualistic, benefiting both the algae and the fungus as they commonly grow in environments where neither would be able to survive alone. The alga supplies carbohydrates produced by photosynthesis to the fungus, while the fungus provides a valuable source of attachment through rhizomes and a means of protection from dehydration through a thick cortex. Through this mutualistic relationship, Lichens are able to occupy an important ecological niche as they are able to colonize newly exposed soil or rock. They secrete organic acids that are able to break down rock allowing for an accumulation of specific nutrients plants are able to use. Lichens also serve as an invaluable pollutant estimate as they are extremely sensitive to pollutants and can indicate poor air quality. 9. Define the term mycosis, and differentiate between systemic mycosis, subcutaneous mycosis, and superficial mycosis. If a person contracted a fungal disease that was caused by the group of fungi known as dermatophytes, what type of mycosis would this be? Why is this group of fungi able to cause this type of infection and how it is usually transmitted? (7 marks) Mycosis refers to any fungal infection and are classified into five groups according to their effected tissue and mode of entry (systemic, subcutaneous cutaneous, superficial, or opportunistic). Systemic mycoses are fungal infections that affect numerous tissues and organs deep within the body usually transmitted 10

through inhalation. These are not contagious. Subcutaneous mycoses are fungal infections caused by saprophytic fungi that live in soil and on vegetation and infect hosts by direct implantation of part of the fungus beneath the skin (usually by a puncture wound). Superficial mycoses are fungal infections that are localized to hair shafts and in epidermal cells on the surface of hosts. Cutaneous mycoses are fungal infections that infect only the epidermis, hair, and nails, and are caused by a group of fungi called the dermatophytes . Dermatophytes are able to secrete a digestive enzyme called keratinase that degrades the protein found in hair, skin and nails called keratin. These infections are typically spread by direct contact with the infected cells. 10. What is an opportunistic pathogen? Give an example of an opportunistic mycosis. (3 marks) Many microorganisms inhabit healthy human bodies, living symbiotically and are generally harmless. Opportunistic pathogens are microorganisms that are relatively harmless but can become pathogenic when a host’s immune system is debilitated by disease or drugs such as broad-spectrum antibiotics. For example, in AIDS patients, Pneumocystis causes the most common life-threatening infection due to their compromised immune systems. 11. What is an algal bloom? (3 marks) Algae are critical members of the aquatic food chain which normally convert atmospheric carbon dioxide into carbohydrates producing oxygen as a byproduct. Populations commonly fluctuate with changes in nutrients, light, and temperature with the season. This can result in a periodic increase in planktonic algae called algal blooms. Some specific bloom species can indicate high concentrations of organic material pollutants, such as sewage or industrial waste. When large 11

concentrations of algal die, their decomposition depletes water of dissolved oxygen causing a cascade of negative biological effects. 12. Briefly outline the life cycle of Plasmodium sp. What stage of the life cycle results in fever and chills in the infected host and why? (5 marks) An infected blood-feeding insect vector (definitive host) transmits Plasmodium sp. sporozoites into a vertebrate intermediate host during a blood meal. The sporozoites grow and undergo schizogony within the intermediate host (usually the liver) infecting red blood cells with merozoites that migrate through the bloodstream. Through asexual reproduction, merozoite develops into a ring stage and the intermediate host’s red blood cells rupture and release merozoites resulting in the infection of new red blood cells. This release of the merozoites and their waste products results in the intermediate host undergoing fever and chills. Through sexual reproduction, some merozoites develop into male and female gametocytes. When another vector bites the infected intermediate vertebrate host it ingests said gametocytes. In the vector’s digestive tract, the gametocytes union creating a zygote that forms more Plasmodium sp. sporozoites that can now be transferred to another vertebrate host. 13. What is a vector? Give an example of a vector-borne disease and name the vector responsible for transmission. (3 marks) Animals with segmented bodies, hard external skeletons, and jointed legs are called arthropods. Vectors are arthropods that have the ability to carry pathogenic microorganisms. Vector-borne diseases are those that result from an infected blood- feeding arthropod that infects its host. Malaria, a deadly infectious disease, is vector- borne and comes from the mosquito genus Anopheles. 12

Your preview ends here

Eager to read complete document? Join bartleby learn and gain access to the full version

Access to all documents
Unlimited textbook solutions
24/7 expert homework help

Assignment 2

Related Documents