MICROBIOLOGY - FUNGI, PARASITES

Question 1

How can fungi be classified

Answer 1

Yeasts, molds, dimorphic fungi

Question 2

Fungi cell wall components and which is most abundant

1 specific cell membrane component unique to fungi and targeted by medication

Answer 2

Glucan (60% and most abundant being beta-(1,3-) glucan), chitin (10%), 30% protein

ergosterol

Question 3

How do yeasts reproduce

Answer 3

Budding (spore forming)

Question 4

Candida epidemiology and the disease it causes? Name some risk factors (5)

Answer 4

Candida: commensals on skin, GI tract, female reproductive tract

Candidiasis

Risk factors: Immunocompromised, Broad spectrum antibiotics, transplants, steroids, ICU, IV

Question 5

Candidiasis in immunocompetent and immunocompromised hosts?

Answer 5

Immunocompetent: vaginal thrush

Immunocompromised: symptoms more refractory (do not respond to treatment), oral thrush, systemic candidiasis eg in liver/spleen

Question 6

Candidiasis diagnostic methods?

Answer 6

Culture using Sabouraud agar, Gram stain (gram +ve), detection of antigen (Beta-d-glucan antigen) in serum

Question 7

Treatment method for candidiasis?

Answer 7

Polyenes: Nystatin if topical (forms complex with ergosterol in cell membrane), amphotericin B when systemic infection

Azoles: eg Fluconazole to inhibit ergosterol synthesis

Echinocandins eg micafungin to inhibit cell wall synthesis

Question 8

Name 1 nucleoside analogue used to treat fungal infection

Answer 8

5-flucytosine

Question 9

Cryptococcus neoformans morphology under stain? What risk factors for C. neoformans?

Besides stain how can it be identified

Answer 9

WIth halo because of capsule when stained under India ink

Immunocompromised patients

Cultured or checked for capsular polysaccharide antigen

Question 10

Mould morphology?

Answer 10

multicellular, long filaments, reproduce by spores

Question 11

Aspergillus method of identification and disease? Risk factor?

Answer 11

Systemic infection, identified by galactomannan antigen, nucleic acid, culture

Risk factor: Immunocompromised (eg HIV/neutropenia/organ transplants/immunosuppressants/

Question 12

Dermatophyte species? What disease do dermatophytes cause

Answer 12

Trichophyton, Epidermophyton, Microsporum

Disease: tinea - aka ringworm (tinea pedis, tinea capitum, tinea unguium)

Question 13

Dimorphic fungi - name 1 example and its morphology at 37c and 25c

How can it be detected

Risk factors?

Symptoms?

Answer 13

Talaromyces marneffei - 37c yeast, 25c mold (mold has diffusible red pigment) on agar

Detected by patient antibodies

Immunocompromised patients

Multiple skin lesions with papules with central necrotic umbilication

Question 14

Fungi that cannot be cultured?

Answer 14

Pneumocystis jirovecii

Question 15

Define: Parasitism, parasite, host

Answer 15

Parasitism: any reciprocal association in which a species depends
upon another for its existence

parasite: the organism that derives all benefit from dependence upon another organism

host: the organism that harbors the parasite

Question 16

How can parasites be typified (in relation to host)

Answer 16

Level of dependence, time, physical relationship

Level of dependence: obligate (fully dependent) or facultative

time: temporary or permanent

physical relationship: endoparasite or ectoparasite

Question 17

Define definitive and intermediate host

Answer 17

Definitive host: Houses the parasite in active form
Intermediate host: houses intermediate form of parasite

Question 18

How to diagnose parasitic infection?

Answer 18

1)Demonstration of parasites in appropriate clinical specimens by direct microscopic examination, staining, or tissue sections.

2. Serology: detection of antigens or antibodies in blood or other body fluids.
3. Culture of parasites (extremely uncommon): applicable only to a small number of parasites, mainly protozoa.
4. Nucleic acid amplification (eg PCR)

Question 19

How to prevent parasite infection

Answer 19

Elimination: 1) of parasites in reservoir 2) of parasite vectors

Avoid exposure to parasite/vector

Chemoprophylaxis (eg antimalarial)

Vaccines (eg 2 vaccines available against malaria)

Question 20

Classify parasites based on physical relationship with hosts?

Answer 20

Endoparasites: Protozoa or helminth (trematode, cestode, nematode)

ectoparasite: arthropods

Question 21

Protozoa - how many cells? Classified into which 2 groups? For lumen dwelling further classify

GIVE EXAMPLES FOR ALL GROUPS

Answer 21

Unicellular

Lumen-dwelling or blood and tissue dwelling (extraluminal)

Lumen-dwelling:
in GI tract (eg Entamoeba histolytica) - Causes amoebic colitis/dysentery and amoebic liver abscess

in Genital tract: Trichomonas vaginalis (STI), Giardia lamblia

Extraluminal (blood/tissue): Toxoplasma gondii, Plasmodium

Question 22

Nematode morphology and classification? For each group give an example and properties of that example

Answer 22

Round worms

Classified into:
Intestinal nematodes, eg: Strongyloides stercoralis (asymptomatic in immunocompetent host, can lead to hyperinfection in immunocompromised host) (IF RUSH JUST REMEMBER THIS)

Blood and tissue nematodes, eg: Angiostrongylus cantonensis (associated with raw or undercooked snails/slugs/freshwater shrimp/land crabs - assoc. with meningitis)

Wuchereria bancrofti, Brugia malayi: Lymphatic filariasis

Enterobius vermicularis: perianal pruritusxz

Question 23

Trematode morphology? What hosts do they all need?

1 example of: Liver, Lung, Intestinal and Blood fluke, and what is it associated with

Answer 23

Flukes, leaf-shaped flatworms, freshwater snails

Clonorchis sinensis the liver fluke - associated with intake of undercooked freshwater fish, carcinogen associated with CHOLANGIOCARCINOMA

Lung fluke: Paragonimus, associated with eosinophilic pneumonia

Intestinal fluke; Fasciolopsis buski

Blood fluke: Schistostoma spp.

Question 24

Cestode - morphology? Which 2 groups? Examples for each group?

Answer 24

Segmented adults - Taenia solium/saginata

Intestinal cestode (adult stage) - Taenia solium (ingesting larvae)
Tissue cestode - (larval stage) - Taenia solium (cysticercosis) - ingesting eggs of Taenia solium

Question 25

Ectoparasite examples? Some vectors of parasites?

Answer 25

Fleas, scabies mite, maggots of flies Mosquitoes, tsetse flies, fleas, lice, sandflies, blackflies, triatomine bugs

Question 26

5 main plasmodium species and their distribution? Which is most fatal? Which 2 species cause majority of human malaria cases?

Answer 26

Most fatal: P. falciparum P. falciparum: tropics P. malariae: sporadic P. vivax: global P. ovale: West Africa, some South Pacific islands, also found in other parts of the world sporadically. P. knowlesi: Southeast Asia, esp Malaysia/Malaysian Borneo, simian malaria that sometimes causes human infection P. vivax and P. falciparum cause most malaria cases

Question 27

Malaria transmission methods? Its vector?

Answer 27

Vector: FEMALE Anopheles mosquito Blood transfusion and organ transplantation Contaminated needles/medical instruments and medications Vertical transmission: mother to unborn infant before or after delivery

Question 28

Plasmodium life cycle? In general

Answer 28

Infection Pre-erythrocytic cycle Erythrocytic cycle Transmission to Anopheles For P. vivax and ovale ONLY: Secondary schizogony in hepatocytes

Question 29

Each step in depth?

Answer 29

A) Infection: 1) Anopheles mosquito injects sporozoites into human bloodstream, 2) Sporozoites reach the hepatocytes within 30 min B) Pre-erythrocytic cycle: 1）sporozoites infect hepatocytes, 2）asexually reproduce to produce merozoites within a schizont, 3）schizont ruptures to release more merozoites 4） merozoites released invade circulating RBC C) Erythrocytic cycle: merozoites infect RBC, then: 1) Schizogony (make schizonts) - asexually reproduce to form more merozoites in schizont, schizont ruptures, releases merozoites to continue infecting OR 2) Gametogony (make gametocytes) - formation of gametocytes (male is microgametocyte, female is macrogametocyte) within RBC, gametocytes taken up when female Anopheles mosquito takes a blood meal D) Transmission by Anopheles: 1) Gametocytes mature, sexual reproduction to form zygote and oocyst 2) Sporogony: Sporozoite formation in oocyst, oocyst ruptures to release sporozoites, sporozoites migrate to salivary gland of mosquito B chronogically) Secondary schizogony (Vivax and ovale ONLY) Hypnozoite formation: Vivax and Ovale may stay in hepatocytes - sporozoite form hypnozoite, persists for many years (so can have 2nd infection)

Question 30

Pathogenesis of malaria? the 5 stages?

Answer 30

3 + 2: 3 related to RBC, 2 inflammatory 1) Increased RBC destruction as: RBCs lose deformability, become infected by parasites (especially P. falciparum), spleen becomes enlarged (splenomegaly) because of immune reaction to destroy more RBCs 2) Infected RBC cytoadherence to endothelium in P. falciparum infection - microvascular obstruction (think something like a clot) 3) RBC lysis - iron depletion, anemia, hemoglobinuria (blackwater fever - free hemoglobin excreted in urine, so urine becomes coca-cola colored) 4) Nephrotic syndrome - immune complexes deposit in kidneys during chronic P. malariae infection 5) Cytokine production during infection

Question 31

4 symptoms of malaria?

Answer 31

JUST KNOW THE BASICS FOR TIME! fevers, chills, nausea severe then end organ damage eg brain/lung/kidney 1) Paroxysms - Chills, rigor in the first 1-2 hours, then spiking fever in subsequent hours, then sweating and defervescence (body temperature decreases rapidly) - patients do not follow typical fever patterns Fever patterns for malaria: Vivax, Ovale, Falciparum: 48-hour cycle Malariae: 72-hour cycle Knowlesi: 24-hour cycle 2) Severe malaria - falciparum infection mostly, vivax occasionally - end organ damage, eg cerebral malaria, severe anemia, renal failure, circulatory shock, hypoglycaemia 3) Relapse - recurrence of symptoms after COMPLETE initial clearing of parasitaemia due to reinvasion of bloodstream by hypnozoite (P. vivax and P. ovale) 4) Recrudescence: recurrence of symptoms because of incomplete clearing to very low levels of parasitaemia (but not fully cleared)

Question 32

Malaria diagnosis?

Answer 32

1) take history (travel location, prophylaxis, fever patterns but not useful clinically, blood/blood product transfusion etc) 2) Take specimens - peripheral blood anticoagulated with EDTA 3) Make thick and thin blood films with Giemsa, Wright or Field's stains (1 single negative blood test DOES NOT rule out malaria) 4) Antigen testing or PCR

Question 33

Principles of malaria treatment? List some examples of medications as well

Answer 33

Suppressive therapy - chemoprophylaxis to prevent development of clinical syndromes, destroy asexual erythrocytic stages Clinical cure: eliminate asexual erythrocytic forms during acute attack Medication: Blood schizonticides, eg: Artemisinin based combination therapy (ACT), chloroquine, mefloquine, atovaquone-proguanil (many older drugs limited utility bc of drug resistance) Radical cure: kill gametocytes and hypnozoites Medication: tissue schizonticide, eg primaquine