Microbiology

Budding

(1) asexual reproduction beginning as a protuberance from the parent cell that grows to become a daughter cell (2) release of an enveloped virus through the plasma membrane of an animal cell -Parent cell forms a protuberance (bud) on its outer surface - bud elongates - parent cell's nucleus divides and one nucleus migrates into the bud -Cell wall material laid down between the bud and parent cell - bud eventually breaks away -Produce up to 24 daughter cells by budding - some yeasts produce buds that fail to detach themselves -Buds form a short chain of cells - pseudohypha -Ex: Candida albicans - attaches to human epithelial cells as a yeast - requires pseudohyphae to invade deeper tissues

Mycosis

-Any fungal infection -Generally chronic (long-lasting) infections b/c fungi grow slowly -Classified into five groups according to the degree of tissue involvement and mode of entry 1. systemic 2. subcutaneous 3. cutaneous 4. superificial 5. opportunistic -Fungi - related to animals -Consequently - drugs that affect fungal cells may also affect animal cells -Makes fungal infections of humans and animals difficult to treat

Spore

A reproductive (sexual and asexual) structure formed by fungi and actinomycetes -Mold forms a spore - spore detaches from the parent and germinates into a new mold -True reproductive spore - second organism grows from the spore -Most do not exhibit the extreme tolerance and longevity of bacterial endospores

Coccidioides immitis

Another fungal pulmonary disease, also rather restricted geographically, is coccidioidomycosis. The causative agent is Coccidioides immitis, a dimorphic fungus. The arthroconidia are found in dry, alkaline soils of the American Southwest and in similar soils of South America and northern Mexico. Because of its frequent occurrence in the San Joaquin Valley of California, it is sometimes known as Valley fever or San Joaquin fever. In tissues, the organism forms a thick-walled body called a spherule filled with endospores. In soil, it forms filaments that reproduce by the formation of arthroconidia. The wind carries the arthroconidia to transmit the infection. Arthroconidia are often so abundant that simply driving through an endemic area can result in infection, especiallyduring a dust storm.

Thallus

Body of a mold or fleshy fungus

Meningococcal meningitis

Caused by Neisseria meningitidis (the meningococcus). This is an aerobic, gram-negative bacterium with a polysaccharide capsule that is important to its virulence. It is frequently present in the nose and throat of carriers without causing disease symptoms. These carriers, up to 40% of the population, are a reservoir of infection. Transmission is by droplet aerosols or direct contact with secretions.

Basidiomycota

Club fungi - possess septate hyphae -Includes fungi that produce mushrooms -Basidiospores - formed externally on a pedestal called a basidium -Usually four basidiospores per basidium -Some produce asexual conidiospores

Zygomycota

Conjugation fungi - saprophytic molds that have coenocytic hyphae -Ex: Rhizopus stolonifer - common black bread mold -Asexual spores are sporangiospores -When the sporangium breaks open - sporangiospores are dispersed -If they fall on a suitable medium - germinate into a new mold thallus -Sexual spores - zygospores - large spore enclosed in a thick wall -Forms when the nuclei of two cells that are morphologically similar to each other fuse

Septa

Cross-walls in hyphae which divide them into distinct, uninucleate (one-nucleus) cell-like units

Mycelium

Filamentous mass grown by hyphae when environmental conditions are suitable

Budding Yeasts

Following mitosis, a yeast cell that divides unevenly to produce a small cell (bud) from the parent cell Ex: Saccharomyces

Asexual Spore

Formed by the hyphae of one organism - when spores germinate, they both become organisms that are genetically identical to the parent **No fusion of the nuclei of cells

Sporangiophore

Formed within a sporangium - sac at the end of an aerial hypha called a sporangiophore -Sporangium - contains hundreds of sporangiospores

subcutaneous mycoses

Fungal infections beneath the skin caused by saprophytic fungi that live in soil and on vegetation -Ex: Sporotrichosis - subcutaneous infection acquired by gardeners and farmers -Infection - occurs by direct implantation of spores or mycelial fragments into a puncture wound in the skin

systemic mycoses

Fungal infections deep within the body - not restricted to any particular region of the body but can affect a number of tissues and organs -Caused by fungi that line in the soil -Spores are transmitted by inhalation - infections typically begin in the lungs and then spread to other body tissues -Not contagious from animal to human or from human to human -2 types: histoplasmosis and coccidioidomycosis

Tinea infections (any type)

Fungi that colonize the hair, nails, and the outer layer (stratum corneum) of the epidermis are called dermatophytes; they grow on the keratin present in those locations.

dermatophyte

Fungi that infect only the epidermis, hair, and nails -Infections are called dermatomycoses or cutaneous mycoses -Secrete keratinase - enzyme that degrades keratin - protein found in hair, skin, and nails -Infection transmitted from human to human or from animal to human by direct contact or by contact with infected hairs and epidermal cells -Ex: barber shop clippers or shower room floors

Septate Hypha

Hypha consisting of uninucleate cell-like units

Hyphae

Long filament of cells joined together of a fungus - can grow to immense proportions

Aspergillus species

Many other opportunistic fungi may cause respiratory disease, particularly in hosts who are immunosuppressed or have been exposed to massive numbers of spores. Aspergillosis is an important example; it is airborne by the conidia of Aspergillus fumigatus and other species of Aspergillus, which are widespread in decaying vegetation. Compost piles are ideal sites for growth, and farmers and gardeners are most often exposed to infective amounts of these conidia. Such diseases can be very dangerous, particularly invasive infections of pulmonary aspergillosis. Predisposing factors include an impaired immune system, cancer, and diabetes.

Pneumocystis jiroveci

Pneumocystis pneumonia is caused by Pneumocystis jirovecii, formerly P. carinii. There has been no universal agreement about whether it is a protozoan or a fungus. It has some characteristics of both groups. Analysis of RNA and certain other structural characteristics indicate that it's closely related to certain yeasts, and it's usually reported as a fungus. The pathogen is sometimes found in healthy human lungs. Immunocompetent adults have few or no symptoms, but newly infected infants occasionally show symptoms of a lung infection. Persons with compromised immunity are the most susceptible to symptomatic Pneumocystis pneumonia. This population may also be the reservoir of the organism, which is not found in the environment, animals, or very often in healthy humans. By 1993, it had become a primary indicator of AIDS. Other groups that are very susceptible to this disease are people whose immunity is depressed because of cancer or who are receiving immunosuppressive drugs to minimize rejection of transplanted tissue. In the human lung, the microbes are found mostly in the lining of the alveoli. Diagnosis is usually made from sputum samples in which cysts are detected. There, they form a thick walled cyst in which spherical intracystic bodies successively divide as part of a sexual cycle. The mature cyst contains eight such bodies. Eventually the cyst ruptures and releases them, and each body develops into a trophozoite. The trophozoite cells can reproduce asexually by fission, but they may also enter the encysted sexual stage.

Pneumococcal pneumonia

Pneumonia caused by S. pneumoniae is called pneumococcal pneumonia. S. pneumoniae is a gram-positive, ovoid bacterium. This microbe is also a common cause of otitis media, meningitis, and sepsis. The cell pairs are surrounded by a dense capsule, which makes the pathogen resistant to phagocytosis. These capsules are also the basis of serological differentiation of pneumococci into at least 90 serotypes. Most human infections are caused by only 23 variants, and these are the basis of current vaccines.

Vegatative

Referring to cells involved with obtaining nutrients, as opposed to reproduction; Fungal colonies - composed of cells involved in catabolism and growth

Ascomycota

Sac fungi - include molds ith septate hyphae and some yeasts -Asexual spores - usually conidia - produced in long chains from the conidiophore -Conidia means dust - spores freely detach from the chain at the slightest disturbance and float in the air like dust -Ascospore - forms when the nuclei of two cells that can be either morphologically similar or dissimilar fuse -Ascus - saclike structure where spores are produced -Members of this phylumm - sac fungi - b/c of the ascus

Histoplasmosis

Superficially resembles tuberculosis. It was first recognized as a widespread disease in the United States when X-ray surveys showed lung lesions in many people who were tuberculin-test-negative. Although the lungs are most likely to be initially infected, the pathogens may spread in the blood and lymph, causing lesions in almost all organs of the body. Symptoms are usually poorly defined and mostly subclinical, and the disease passes for a minor respiratory infection. In a few cases, perhaps fewer than 0.1%, histoplasmosis progresses, and it becomes a severe, generalized disease. This occurs with an unusually heavy inoculum or upon reactivation, when the infected person's immune system is compromised.

Candida albicans

The bacterial microbiota of the mucous membranes in the genitourinary tract and mouth usually suppress the growth of such fungi as Candida albicans. The morphology of these organisms is not always yeastlike but can exhibit the formation of pseudohyphae, long cells that resemble hyphae. In this form, Candida is resistant to phagocytosis, which may be a factor in its pathogenicity. Because antibacterial drugs do not affect the fungus, it sometimes overgrows mucosal tissue when antibiotics suppress the normal bacterial microbiota.

Histoplasma capsulatum

The causative organism, Histoplasma capsulatum, is a dimorphic fungus; that is, it has a yeastlike morphology in tissue growth, and, in soil or artificial media, it forms a filamentous mycelium carrying reproductive conidia. In the body, the yeastlike form is found intracellularly in macrophages, where it survives and multiplies. Although histoplasmosis is rather widespread throughout the world, it has a limited geographic range in the United States. In general, the disease is found in the states adjoining the Mississippi and Ohio rivers.

Cryptococcus neoformans

The disease Cryptococcus neoformans Meningitis (cryptococcosis) is caused by fungi of the genus Cryptococcus. They form spherical cells resembling yeasts, reproduce by budding, and produce extremely heavy polysaccharide capsules. These organisms are widely distributed, especially in areas contaminated by bird droppings most notably from pigeons, which excrete an estimated 25 pounds a year. The disease is transmitted mainly by the inhalation of dried, contaminated droppings. The inhaled fungi multiply in persons with compromised immune systems, such as AIDS patients, disseminate to the CNS, and cause meningitis that has a high mortality rate.

Dimorphic

Two forms of growth - can grow either as a mold or as a yeast -Moldlike forms - produce vegetative and aerial hyphae -Yeastlike forms - reproduce by budding **Temperature dependent - at 35ᵒC, the fungus is yeastlike, and at 25ᵒC, it is moldlike

Conidia

Unicellular or multicellular spore that is not enclosed in a sac -Produced in a chain at the end of a conidiophore -Species that produces such spores - Penicillim and Aspergillus

Microsporidia

Unusual eukaryotes - lack mitochondria -Do not have microtubules -Obligate intracellular parasites -Originally classified as fungi - reclassified as protists b/c they lack mitochondria - recent genome sequencing reveals that the microsporidians are fungi -Reported to be the cause of a number of human diseases - chronic diarrhea and keratoconjunctivitis (inflammation of the conjunctiva near the cornea)

Blastomyces dermatitidis

Usually called North American blastomycosis to differentiate it from a similar South American blastomycosis. It is caused by the fungus Blastomyces dermatitidis, a dimorphic fungus found most often in the Mississippi and Ohio River valleys, where it probably grows in soil. The infection begins in the lungs. It resembles bacterial pneumonia and can spread rapidly. Cutaneous ulcers commonly appear, and there can be extensive abscess formation and tissue destruction.