Micro1_QA3_highlighted.pptx

1. Which of the following technical terms and meanings are MISMATCHED: a. Sterilisation : Process by which all living cells including spores and viruses are either destroyed or removed from the habitat b. Disinfection : killing, inhibition or removal of microorganisms that may cause disease c. Antis...

1. Which of the following technical terms and meanings are MISMATCHED: a. Sterilisation : Process by which all living cells including spores and viruses are either destroyed or removed from the habitat b. Disinfection : killing, inhibition or removal of microorganisms that may cause disease c. Antisepsis : the prevention of infection 34.48% d. Bactericidal : antibacterial agent that kills bacteria 6.89% e. Bacteriostatic : antibacterial agent that allows bacterial populations to grow but to not infect a host 2. Which of the following is NOT a factor affecting effectiveness of antimicrobial activity: a. the number of microorganisms present 18.18% b. the concentration of the antimicrobial agent 6.81% c. the length of exposure 9.09% d. the temperature of the local environment e. all of the above are CORRECT 3. Which of the following is CORRECT with respect to employing radiation for sterilisation purposes: a. UV light, visible light and ionising radiation are used for sterilisation purposes 30.43% b. UV light penetrates glass c. UV light is used for water treatment 13.04% d. Ionising radiation penetrates very shallowly into objects 6.52% e. All of the above are CORRECT 1.Which of the following statements regarding fungi is INCORRECT: a.Filamentous fungi are also known as moulds b.Filamentous fungi possess hyphae c.Yeast has a characteristic form known as a mycelium d.Yeast reproduce by division or budding e.Some fungi can interconvert between the yeast and filamentous forms Classification of fungi May be divided into two groups: Filamentous fungi (moulds) Hyphae extend as a result of transverse divisions forming a mycelium Yeast Characteristic form is a single cell Reproduction by division or budding Bud attached to pseudohyphae 8 Filamentous fungi Filamentous fungi examples: Aspergillus Penicillium Trichophyton Consists of surface mycelium aerial hyphae Cells of hyphae often contain many nuclei Conidia (asexual spores) are found at the end of the hyphal branches Spores are numerous and spread easily through air They are common contaminants in laboratories and a source of allergies 9 Life cycle of filamentous fungi 10 Filamentous fungi On agar plates colonies have a dusty appearance Colonies are often brightly coloured Some species produce sexual spores These are resistant to drying, heating and freezing Not as resistant to heat as bacterial spores Some species produce fruiting bodies and mushrooms Mushrooms produce sexual spores (basidiospores) Can be dispersed through the air 11 Aspergillus spp. 12 Yeasts Yeasts Candida Saccharomyces Cryptococcus Unicellular Occur as spheres, ovals or cylinders Grow by Budding (S. cerevisiae) Fission (Schizosaccharomyces pombe) 13 Saccharomyces cerevisiae (bakers / budding yeast) 14 Dimorphic fungi Some fungi show both mycelial and yeast forms and are known as dimorphic fungi Dimorphic fungi: Form hyphae at environmental temperatures Occur as yeast cells in the body Switch being temperature-induced Some yeasts form a filamentous phase (opposite) Candida albicans This phase is involved in pathogenicity 15 1.Which of the following statements concerning fungal infections is INCORRECT: a.Cutaneous mycoses can be caused by Epidermophyton b.Tinea pedia is commonly referred to as Athlete’s foot c.Aspergillosis usually comes from an exogenous source d.Candida albicans appears as Gram-positive oval budding yeast following a Gram stain e.All of the above are CORRECT Cutaneous mycoses Caused by fungi that invade only superficial keratinised tissue: Skin Hair Nails Most important groups are the dermatophytes: Epidermophyton Microsporum Trichophyton 18 Morphology and identification Colonies can be cultured on: Sabouraud agar (pH 5.6) Agar containing cyclohexamide (inhibits saprophytes) Non-dermatophytes do not grow in the presence of cyclohexamide Conidia may be observed on slide cultures and aid in the identification Sources of dermatophytes are anthrophilic (human over other animals), zoophilic (animals over humans) and geophilic (prefer soil) 19 Identification of dermatophytes All have characteristic cultural and microscopic appearance used for identification Cause characteristic skin lesions called ‘ringworm’ (rash is circular with a ring-link appearance) or tinea Description of symptoms often includes part of the body Tinea pedis (foot) Tinea corporis (body), etc… Also cause brittle or thick nails 20 Trichophyton rubrum 21 Microsporum canis 22 Epidermophyton floccosum 23 Infections caused by dermatophytes Tinea pedia (athlete’s foot) Most prevalent of all dermatophytes Toe webs infected with Trichophyton spp. or E. floccosum Initially causes itching between toes and formation of vesicles which rupture and discharge fluid Skin becomes macerated and peels 24 T. mentagrophytes (Athlete’s foot) 25 Athlete’s foot Cracks prone to secondary bacterial infection Nail infection may follow Individual may become hypersensitive and develop dermatophytids (vesicles) elsewhere on the body: Especially the hands Athlete's foot is only found in people wearing shoes Infection is spread by communal showers and changing rooms Prevention by hygiene, especially keeping toes dry Treat with antifungal creams or powders e.g. Daktarin 26 Ringworm (Tinea corprois, Tinea cruris) Dermatophytosis of non-hairy skin gives rise to annular lesions of ringworm Varying degrees of inflammation may be found, the most common Isolates are E. floccosum T. rubrum T. mentagrophytes Treat with antifungal cream 27 M. canis ringworm (from feline) 28 Tinea capitis (ringworm of the scalp) Microsporum in childhood Trichophyton in adults Infection begins on skin of scalp and then down wall of hair follicle May appear as alopecia with scaling, black dot ringworm Trichophyton may also infect beard hair Treatment: Remove hairs Treat with Griseofulvin or shampoo with Miconazole 29 tinea capitis 30 Non-dermatophyte superficial infections Non-dermatophytes are often faster growing and grow on Sabouraud agar only (pH altered and without cyclohexamide) Cause problems for immunocompromised patients who have limited cellular immunity 31 Aspergillus Aspergillosis describes a group of mycoses caused by spp. of the filamentous fungus Aspergillus Infection comes from exogenous source Pulmonary aspergillosis may occur in distinct forms One, aspergilloma, is a fungus ball growing in a pre-existing cavity (e.g. tuberculosis) Often asymptomatic or patient has a cough 32 Aspergillus Invasive aspergillosis is caused by A. fumigatus in immunocompromised patients Widespread destruction of tissue as fungus grows Treat with Amphotericin B Allergic aspergillosis occurs in patients with elevated IgE levels 10-20% of asthmatics react to A. fumigatus Treatment is with corticosteroids Endocarditis may occur in immunosuppressed patients or those who have undergone open heart surgery Therapy depends on antifungals and surgical removal of infected tissue 33 Aspergillus fumigatus 34 Systemic mycoses Coccidioides immitis Grows as mould in soil Coccidioidomycosis is a lung infection caught after inhaling arthrospores Found in semi-arid regions, mainly southwest USA and Northern Mexico. Also called San Joaquin valley fever Usually asymptomatic or self-limiting lung infection, Mild cough Chest pains Headache 35 Coccidioides immitis Dissemination occurs in less than 0.5% of cases Often immunocompromised patients Chronic cases involve localised cavities in lungs filled with spherules (cylindrical bodies) of C. immitis Other tissues involved Bones Liver Meninges Brain Skin Heart Can be treated with Amphotericin B High death rate in disseminated cases 36 Coccidioides immitus 37 Histoplasma capsulatum Grows as mould in soil and in culture, and as a mould or yeast in animal tissues Intracellular parasite found in soil rich with droppings of birds and bats Occurs in USA, endemic in Ohio and Mississippi River valleys Histoplasmosis is usually asymptomatic or flu-like symptoms with fever and cough 250,000 new cases each year in USA 38 Histoplasma capsulatum Microconidia inhaled Symptoms of coughing, fever and joint pain Infections are mostly self-limiting but patient is often left with discrete calcified lesions in the lung Chronic form can develop in adults; large cavities develop in lung from new infection or by reactivation of old infection Sometimes dissemination occurs, most often in old age or infancy or with immunosupression Treatment with intravenous Amphotericin 39 Histoplasma capsulatum 40 Yeast infections Candida appears as Gram-positive, oval budding yeast, 2-3 mm x 4-6 mm Forms pseudohyphae in culture and tissues On Sabouraud agar it produces soft, cream coloured colonies with characteristic yeasty smell The submerged growth consists of pseudomycelia 41 Candida albicans 42 Which of the following is correct about the genera Plasmodium: a.Causes malaria in areas of the world where the mosquito vectors can breed b.Usually found between 60 degrees north and 40 degrees south (mainly in Africa, India, Far East and South America) c.Possesses a complex life cycle involving liver and blood cells and several different stages of parasites d.None of the above are correct e.All of the above are correct Plasmodium Causes malaria in areas of the world where the mosquito vectors can breed Tropics between 60 degrees north and 40 degrees south, mainly in: Africa India Far East South America Four species of plasmodium P. falciparum P. vivax P. malariae P. ovale Complex life cycle involving liver and blood cells and several different stages of parasites 45 Plasmodium life cycle 46 Plasmodium (malarial parasite) 47 Which of the following is NOT a distinguishing feature of viruses: a.Extremely small size (20-300nm) b.They can pass through bacteria-retaining filters c.They are invisible by light microscope d.They can be grown in standard culture medium e.They have a simple structure: nucleic acid + protein and some have a lipid outer membrane Distinguishing features of viruses Extremely small size 20-300nm (1nm = 10-3  m) Pass through bacteria-retaining filters Invisible by light microscope Impossible to grow on culture media Simple structure: nucleic acid + protein + some have lipid outer membrane 50 Distinguishing features of viruses Lack intracellular structures, e.g. ribosomes Some surrounded by envelope but no outer wall (peptidoglycan, etc…) Genetic information carried in nucleic acid Classified on the basis of the hosts they infect Animal viruses Plant viruses Bacterial viruses (bacteriophages) Also classified on structural characteristics 51 Distinguishing features of viruses Each type of virus has one type of nucleic acid Either RNA or DNA and provides a basis for classification RNA viruses are the only organisms to have their genome in this form sometimes the RNA genome consists of several segments 52 Distinguishing features of viruses Replication: Lack of protein synthesis, apparatus and energy producing systems makes them obligate intracellular parasites Incapable of binary fission Do not grow and divide as bacteria do Intracellular release of nucleic acid which directs viral protein production and its own replication 53 Distinguishing features of viruses Proteins and nucleic acid synthesised independently and ultimately assembled into identical mature virus particles which are then released from the cell Often aggregate and can be seen in infected cells as inclusion bodies Not affected by antibiotics and other chemotherapeutic drugs Inhibited by interferon 54 55 Which of the following antifungal drugs and mechanism of action is mismatched: a.Nystatin: binding of ergesterol in the cell membrane b.Azoles: inhibition of ergesterol synthesis c.Griseofulvn: interaction with fungal microtubules d.Flucytosine: conversion to fluorouracil e.Amphotericin B: inhibition of ergesterol synthesis Treatment of fungal infections The range of antifungals is poor compared to antibacterials Suggest a reason for this? There is interest in developing new drugs 58 ANTIFUNGAL DRUGS DRUG MECHANISM USES Amphotericin B Binds to ergesterol in cell membrane Broad spectrum, systemic Flucytosine Accumulated by permease Converted to fluorouracil Synergistic with amphotericin B Azoles (e.g. Fluconazole, Ketoconazole, Itraconozale) Inhibit ergesterol synthesis Systemic Griseofulvin Accumulates in keratinised tissue, interacts with fungal microtubules Dermatophytes Nystatin As amphotericin B Topical 59 Which of the following is INCORRECT concerning Histoplasma capsulatum: a.It grows as a mould in the soil and in culture but as a mould or yeast in animal tissues b.It is an intracellular parasite found in soil rich with droppings of birds and bats c.Histoplasmosis is usually asymptomatic or only with minor flue-like symptoms d.Infection can occur from microconidia being inhaled e.Treatment is often with beta-lactam antibiotics Histoplasma capsulatum Grows as mould in soil and in culture, and as a mould or yeast in animal tissues Intracellular parasite found in soil rich with droppings of birds and bats Occurs in USA, endemic in Ohio and Mississippi River valleys Histoplasmosis is usually asymptomatic or flu-like symptoms with fever and cough 250,000 new cases each year in USA 62 Histoplasma capsulatum Microconidia inhaled Symptoms of coughing, fever and joint pain Infections are mostly self-limiting but patient is often left with discrete calcified lesions in the lung Chronic form can develop in adults; large cavities develop in lung from new infection or by reactivation of old infection Sometimes dissemination occurs, most often in old age or infancy or with immunosupression Treatment with intravenous Amphotericin 63 Histoplasma capsulatum 64 Which of the following is INCORRECT concerning Coccidioides immitis: a.Dissemination occurs in the majority of cases b.Chronic cases involve localized cavitites in lungs filled spherules of C. immitis c.Can be treated with amphotericin B d.A very high death rate occurs in disseminated cases e.Other tissues may be involved including the bones, liver, meninges, brain, skin and heart Systemic mycoses Coccidioides immitis Grows as mould in soil Coccidioidomycosis is a lung infection caught after inhaling arthrospores Found in semi-arid regions, mainly southwest USA and Northern Mexico. Also called San Joaquin valley fever Usually asymptomatic or self-limiting lung infection, Mild cough Chest pains Headache 67 Coccidioides immitis Dissemination occurs in less than 0.5% of cases Often immunocompromised patients Chronic cases involve localised cavities in lungs filled with spherules (cylindrical bodies) of C. immitis Other tissues involved Bones Liver Meninges Brain Skin Heart Can be treated with Amphotericin B High death rate in disseminated cases 68 Coccidioides immitus 69