MicroBio Chapter 12

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What is the key difference between yeast and mold?

Yeast is unicellular, while mold is multicellular.

You are given an unknown, pure sample of a eukaryotic organism. Which of the following tests would allow you to determine if the sample contains algae?

Place the sample in a clear container filled with media containing no sugars, and leave it in a sunny window. After a few weeks, look for growth of the organism.

Which of the following new chemicals would NOT be effective against Giardia?

a chemical that inhibits the formation of cell walls

Which phylum of protozoa contains organisms that are nonmotile obligate intracellular parasites? (Hint: They cause a well-known tropical disease.)

Apicomplexa

Apicomplexa contains many species that cause disease, including the Plasmodium species that cause Malaria.

Humans are the definitive host for __________, which is a type of __________.

Taenia saginata; tapeworm

Which of the following organisms requires an additional nonhuman host to complete its life cycle?

Plasmodium species

The life cycle of Plasmodium species requires two hosts, one of which is a mosquito.

The term dermatophyte is typically used for fungi that cause which of the following?

cutaneous mycoses

Dermatophytes (Greek for "skin plants") is a common label for a group of three types of fungi that cause skin disease in humans and other animals.

Helminthic diseases are usually transmitted to humans by

gastrointestinal route

All of the following are characteristic of the Platyhelminthes EXCEPT that they

have highly developed digestive and nervous systems.

The encysted larva of the beef tapeworm is called a

cysticercus.

A definitive host harbors which stage of a parasite?

adult

What do tapeworms eat?

intestinal contents

Seventeen patients in ten hospitals had cutaneous infections caused by Rhizopus. In all seventeen patients, Elastoplast bandages were placed over sterile gauze pads to cover wounds. Fourteen of the patients had surgical wounds, two had venous line insertion sites, and one had a bite wound. Lesions present when the bandages were removed ranged from vesiculopustular eruptions to ulcerations and skin necrosis requiring debridement. Fungi are more likely than bacteria to contaminate bandages because they

can tolerate low-moisture conditions.

In mid-December, a woman with insulin-dependent diabetes who had been on prednisone fell and received an abrasion on the dorsal side of her right hand. She was placed on penicillin. By the end of January, the ulcer had not healed, and she was referred to a plastic surgeon. On January 30, a swab of the wound was cultured at 35°C on blood agar. On the same day, a smear was made for Gram staining. The Gram stain showed large (10 µm) cells. Brownish, waxy colonies grew on the blood agar. Slide cultures set up on February 1 and incubated at 25°C showed septate hyphae and single conidia. The most likely cause of the infection is a

dimorphic fungus.

Ringworm is caused by a(n)

fungus.

Yeast infections are caused by

Candida albicans.

Which of the following is the most effective control for malaria?

eliminate Anopheles

You see acid-fast oocysts in a fecal sample from a patient who has diarrhea. What is the MOST likely cause?

Cryptosporidium

In the malaria parasite life cycle

humans are the intermediate host and mosquitoes are both the definitive host and the vector.

Which of the following arthropods does NOT transmit diseases by sucking blood from a human host?

houseflies

Which of the following pairs is mismatched?

mosquito - Pneumocystis

Based on the lab results, which organism is most likely causing Tori's new symptoms?

Candida albicans

Diagnosis of a yeast infection usually involves patient history, observation of yeast cells via microscopy, and growth of a culture on Sabouraud dextrose agar. Differentiation between yeasts and bacteria is reliant on biochemical characteristics. Differentiation between yeasts and molds is reliant on spore type and function.

Which of the following best explains why Tori developed a new series of symptoms?

The antibiotics that treated Tori's primary respiratory infection also removed some of her normal bacterial flora, resulting in an overgrowth of other organisms.

Tori had undergone treatment with a broad-spectrum antibiotic for her respiratory infection. Antibiotic treatment most likely affected the normal flora in the vagina, resulting in a preferential decrease in bacterial numbers. Yeasts are normal flora in the vagina, but with fewer bacteria present to antagonize their growth, the yeast cells were allowed to flourish beyond their normal levels. The increased numbers of yeast cells led to Tori's new symptoms. She had developed a yeast infection as a secondary infection to her primary respiratory infection. A secondary infection is defined as an infection caused by an opportunistic microbe after a primary infection has weakened the host's defenses. Yeast infections are common secondary infections after antibiotic treatment for a primary bacterial infection.

Which of the following could Tori's physician choose as a treatment for her yeast infection?

a topical over-the-counter ointment, such as clotrimazole or miconazole
a single oral dose of fluconazole

Treatment of a yeast infection includes the application of topical ointments and the use of oral antifungal agents. Nonprescription antifungal creams are among the most commonly purchased over-the-counter medications in the United States.

Which of the following infections are also caused by C. albicans?

oral thrush, fulminating disease

Candida albicans is also the causative agent of oral thrush and fulminating disease. Infants are prone to thrush because they come in contact with the yeast as part of mom's normal flora when nursing. Fulminating disease, which most often afflicts immunosuppressed individuals, results when the yeast enters the bloodstream and travels throughout the entire body, resulting in a systemic infection. Individuals suffering from AIDS are susceptible to this type of infection.

Which of the following statements best describes why the treatment for Tori's fungal infection may result in side effects to her own cells?

Fungal cells and human cells have a nucleus, multiple organelles, and 80S ribosomes for protein synthesis.

One of the key similarities between a fungus and its human host is that both are eukaryotic. This makes it difficult to develop antifungal drugs, because therapeutic agents that target certain properties of the fungus (e.g., ergosterol in the membrane, DNA replication, protein synthesis) also have the potential to target the host cells. One of the keys to antimicrobial therapy is selective toxicity, which means that the agent will hinder/kill the pathogen without doing much damage to the host. The more similar the agent is to its host, the harder it is to achieve selective toxicity.

How do blastoconidia and chlamydoconidia produced by yeast differ from bacterial endospores?

Blastoconidia and chlamydoconidia are spore structures produced by budding in yeasts, whereas bacterial endospores are produced by bacteria under extreme conditions.

Blastoconidia and chlamydoconidia are asexual spores used for reproduction. Blastoconidia and chlamydoconidia produce cells that are identical to the parent cells, whereas sexual spores produce offspring that have characteristics of both parents. Endospores are produced by bacteria during harsh conditions.

How do pseudohyphae in yeasts differ from vegetative hyphae in filamentous fungi?

Yeasts use pseudohyphae to produce new daughter cells, whereas filamentous fungi use their vegetative hyphae to distract immune cells in the human host.

Yeasts use the pseudohyphae as a virulence factor to better penetrate the host's tissues and also to evade phagocytosis. Filamentous fungi use their vegetative hyphae as a means to absorb nutrients from their environment. In optimal conditions, the vegetative hyphae will grow into a substrate to obtain food and will then support the growth of aerial hyphae, which project above the surface of the medium. These aerial hyphae are responsible for producing the reproductive spores of the fungus.

In humans, beef tapeworm infestations are acquired by ingesting

cystycerci of Taenia saginata in undercooked meat.

All of the following pertain to pinworm infections EXCEPT

it is most commonly transmitted by cysts in water.

Michael was excited when his boss sent him to work on a 6-month project with the Vice President of International Affairs at their corporation in Beijing, China. Before leaving the United States, he visited his family doctor for a complete physical and to receive his immunizations. The physician reviewed Michael's medical history and current lab results and declared that he was a healthy 32-year-old. Michael adjusted well to the move and made many new friends. They would often get together on the weekends to go swimming at a nearby lake, to play volleyball at the local park, or to watch movies and cook dinner. He quickly found that his favorite meal was a stir-fry containing a mixture of pork, fresh raw vegetables, and noodles. He would eat this combination of foods three to four times a week.
To his surprise, within 3 months of moving to China, Michael started losing weight. He was not trying to lose weight and when asked about his diet, Michael would say that he ate all the time. At first, he thought the weight loss was just a result of his metabolism adjusting to his new Asian diet and was not a cause for concern. However, after 2 months of continuous weight loss, the non-stop eating was replaced by nausea and slight abdominal pain. At this time, Michael began to think something might be wrong.

Michael scheduled an appointment with Dr. Clark at the local medical center. During his appointment, the two of them discussed where Michael had traveled since he had been in China, the types of foods he had eaten, the specifics of his exercise regimen, and his extracurricular activities. They also discussed the lack of symptoms other than the weight loss and recent bouts of nausea. After talking with Michael, Dr. Clark requested that multiple stool specimen be sent to the laboratory for examination. He also ordered serological testing of Michael's blood to determine his antibody titer levels. He was concerned that Michael may have an intestinal parasite infection, even though many are asymptomatic.

...

Why does Dr. Clark request stool samples for examination?

-He will have the laboratory prepare the samples for an ova and parasite (O&P) exam. Fresh or preserved stool samples can be observed microscopically for the presence of parasites or their eggs/cysts.
-Tapeworms are pathogens of the gastrointestinal tract; as a natural progression of digestion some of the tapeworm pieces will be expelled along with fecal matter.

Investigation of stool samples is an important diagnostic tool for physicians and other medical personnel. The stool is prepared in such a way that any parasite eggs or proglottids remain in the sample. After processing, the sample is placed on a microscope slide for observation. Staining can be performed, but is not always necessary. Morphological examination of any specimen found in the stool will help with identification.

Which of the following represents the MOST LIKELY route of transmission for Michael's infection?

Foodborne - Eating undercooked, unwashed, or otherwise contaminated food that contained parasitic propagules

Correct! The most likely mode of transmission in Michael's case was through the undercooked pork that he ate in his stir-fry. Humans are a definitive host for the pork tapeworm and are infected when they ingest larval cysts embedded in the muscle tissue of the pig. This transmission cycle is common in Africa, Asia, and Latin America. Interestingly, pigs in the United States are virtually parasite-free, and pork tapeworm infections are transmitted person-to-person via the fecal-oral route. Eggs from infected people with poor hygiene can be ingested by others, which allows the life cycle to continue without the pigs as an intermediate host.

Which of the following organisms is most likely the causative agent of Michael's tapeworm infection?

Taenia solium

Correct! T. solium is the tapeworm associated with eating undercooked pork. Eggs and proglottids from the adult tapeworm are released in the intestines and can be observed in fecal samples with a light microscope. Diagnosis is based on these findings.

Microscopic analysis of Michael's stool sample confirmed the presence of tapeworm eggs and proglottids in the genus, Taenia. Image A is the microscopic view of tapeworm eggs from a fecal sample. Image B is the microscopic view of a proglottid from a fecal sample. Dr. Clark informed Michael that given his diet history, he is most likely infected with the pork tapeworm, T. solium. A related species, T. saginata, is associated with eating raw beef and its scolex differs from that of T. solium. Image C is T. solium, the pork tapeworm. Notice how T. solium has a row of hooks. These structures are not found in T. saginata. Image D is Enterobius vermicularis, a roundworm.

Compare the anatomy of the tapeworm (Image C) to the anatomy of the roundworm (Image D). Given that both are parasitic worms, which of the following reasons best explains why the tapeworm is flat?

Tapeworms utilize diffusion to absorb nutrients from the host's digestive system.

Correct! The tapeworm's high surface-area-to-volume ratio is an adaptation to utilize diffusion in the nutrient-rich environment of the host's intestine. These worms lack digestive structures and must rely on the host to completely digest food before it is absorbed by the worm via its outer layer called a cuticle. Roundworms have a more complex digestive system and are capable of digesting food that has only been partially digested by the host. This decreases the need for a high surface-area-to-volume ratio because diffusion of nutrients is no longer an issue.

yeah pig tape worm

Correct! The adult worm produces thousands of eggs in the human host. These eggs leave the digestive tract via the feces. When pigs eat grass contaminated with, or fertilized by, human feces they become infected with T. solium. The tapeworm eggs mature into larvae that encyst themselves in the muscle tissue of the pig. When humans eat pork that has not been cooked to high enough temperatures, they become infected with the tapeworm.

Why do we see an increase in the levels of IgE antibody in Michael's serum?

IgE is the class of antibodies involved in hypersensitivities such as allergies and parasitic infections.

Correct! IgE is typically found in very low amounts in the blood serum. It increases in response to allergic reactions and parasitic infections. There is also a correlation with an increase in IgE amounts and the increase of eosinophils in a blood smear. Eosinophils are white blood cells that release peroxide ions to destroy the parasite from the outside.

What is the treatment that Dr. Clark will most likely recommend?

Praziquantel or albendazole, drugs that target eukaryotic parasites with minimal side effects in the host.

Correct! Praziquantel and albendazole are both anti-helminthic drugs. Praziquantel is effective against tapeworms because it changes the permeability of the cuticle and blocks nutrient uptake. During this process the drug also uncovers surface antigens that stimulate an immune response. Albendazole is a broad-spectrum anti-helminthic drug that also blocks nutrient uptake by inhibiting microtubule formation in the cytoplasm. It is used commonly to treat livestock as well.

Why was Dr. Clark worried about tapeworm infection in other body sites?

-When tapeworm larvae escape the stomach, they can travel to other parts of the body such as muscles, the liver, the eye, and even the brain to form cysticerci.
-The presence of T. solium in the brain can result in neurocysticercosis, a serious condition which has symptoms resembling those of brain tumors or epilepsy

Tapeworms in the intestinal tract are usually asymptomatic. Humans are the definitive host and support the growth of adult tapeworms. Pigs are intermediate hosts that continue the life cycle of T. solium. Occasionally, the human host can become an intermediate host. Larvae escape the stomach and migrate to other tissues in the body. Once in other tissues, the larvae form cysts called cysticerci. These cysts can cause problems, especially in the eye and in the brain.

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