Tiêu đề 3. STUDY OF BACTERIA, FUNGI, VIRUS, RICKETTSIAE, SPIROCHETES.pdf ✅

PHARMD GURU Page 1 BACTERIA:  Bacteria are unicellular, free-living small microorganisms which are visible under the light microscope.  They occur in water, food, soil, air and all natural environments.  They grow on artificial laboratory media and multiply by binary fission.  Bacteria show three basic shapes such as rod-shaped (bacilli), spherical (cocci), or helical (spirilla).  Bacteria may also be classified as Gram-positive or Gram-negative. Gram staining, bacterial culture with antibiotic sensitivity determination and other tests are used to identify bacterial strains and help to determine the appropriate course of treatment. STRUCTURE OF BACTERIAL CELL:  The structure of bacterial cell is shown in Fig. 2.5.  The outer layer or cell envelope consists of two components such as cell wall and a cytoplasmic or plasma membrane. STUDY OF BACTERIA, FUNGI, VIRUS, RICKETTSIAE, SPIROCHETES
PHARMD GURU Page 2  Inside the plasma membrane, there is protoplasm comprising the cytoplasm, cytoplasmic inclusions such as ribosomes, mesosomes, granules, vacuoles and nuclear body.  The cell may be enclosed in a viscid layer, which may be a loose slime layer or organised as a capsule.  Many bacteria have filamentous appendages called fimbriae or pili (organ of adhesion).  Many bacteria also possess flagella which are organs of locomotion. The cytoplasmic (plasma) membrane is a thin (5 to 10 nm) layer lining the inner surface of the cell wall and separating it from the cytoplasm. It is composed of phospholipids (20 to 30%) and proteins (60 to 70%). The phospholipids form a bilayer in which most of the proteins are tenaciously held and are called integral proteins. The bacterial cytoplasm is a suspension of organic, inorganic solutes in a viscous water solution. The cytoplasm of bacteria differs from that of higher eukaryotic microorganisms in not containing endoplasmic reticulum, Golgi apparatus, mitochondria and lysosomes. It contains the nucleus, ribosomes, proteins and other water soluble components and reserve material. In most bacteria, extrachromosomal DNA (plasmid DNA) is also present. Many bacterial species can cause diseases in plants, animals and human beings. Some species play an important role in the natural cycling of elements (soil fertility) and some others may be useful in industries for preparation of different compounds. The majority of bacteria are harmless to people and some strains are even beneficial. In the human gastrointestinal tract, good bacteria aid in digestion and produce vitamins. Many types of bacteria are classified as probiotics. Lactobacillus genera are the most common probiotic and find in yogurt and other fermented foods. Different strains can help with diarrhoea and may help with people who cannot digest lactose, the sugar in milk. Bifidobacterium genera can also find it in some dairy products. A bacterial infection is a proliferation of a harmful strain of bacteria on or inside the body. Bacteria can infect any area of the body. Pneumonia, meningitis, and food poisoning are just a few illnesses that may be caused by harmful bacteria.
PHARMD GURU Page 3 Antibiotics are medications that fight bacterial infections. They work by disrupting the processes necessary for bacterial cell growth and proliferation. Antibiotics do not treat viruses, but they are sometimes prescribed in viral illnesses to help to prevent a "secondary bacterial infection." Secondary infections occur when someone is in a weakened or compromised state due to an existing illness. FUNGI: Fungi are eukaryotic microorganisms which exist as saprophytes, parasites or commensals. Fungi may be simple oval cells (yeasts) or long tubular septate hyphae (moulds) showing true lateral branching. They are aerobic or facultatively anaerobic. They are cultivated in the laboratory like bacteria and reproduce by asexual and sexual processes. Fungi are important sources of antibiotics, enzymes, acids, foods, bakery and alcohol fermentations. Certain fungi also cause human diseases, such as athlete's foot and thrush. CANDIDA ALBICANS: Candida albicans is an ovoid or spherical budding cell 3 to 5 μm in diameter, which produces pseudohyphae. Gram-stained smears and KOH wet mounts from lesions, patches from the mucous membrane of the mouth, esophagus, vagina and skin shows budding Gram-positive yeast cells and pseudohyphae (Fig. 2.8 a). Candida species grow well on Sabourauds dextrose agar and on ordinary bacteriological culture media at 25 to 37oC. Cream-coloured, smooth, pasty colonies appear in 1 to 2 days.
PHARMD GURU Page 4 Candida albicans can be identified from other Candida species (C. tropicalis, C. pseudotropicalis, C. parapsilosis, C. stellatoidae, C. krusei) by growth characteristics and sugar assimilation and fermentation tests. Candida albicans alone forms chlamydospores on corn meal agar cultures at 20oC (Fig. 2.8 b). Candida albicans may be identified on its ability to form germ tubes within two hours when incubated in human serum at 37oC (Fig. 2.8 c). Candidosis is an opportunistic endogenous infection of the skin, mucosa and internal organs, caused by yeast like fungus Candida albicans. It is an acute or chronic, superficial or disseminated mycosis causing thrush (tongue), paronychia (subcutaneous tissues at the base of finger nails), vulvovaginitis (vagina), endocarditis (heart), meningitis (brain), septicemia (blood), bronchocandidiasis (chronic bronchitis) and pulmonary candidiasis. Nystatin and miconazole are useful for topical candidiasis. For systemic candidiasis amphotericin B, oral ketoconazole and 5-fluorocytosine are effective. PENICILLIUM (CLASS: DEUTEROMYCETES): There are more than 150 known species of the genus Penicillium. They occur as saprophytes in soil and decomposing organic debris. On Sabouraud's dextrose agar at 20oC for 1 to 4 days, the colonies become velvetty, white and later become blue green. Microscopic examination of these colonies show brush like arrangement of conidia, sterigmata and conidiophores (Fig. 2.9). Penicillium have septate vegetative mycelia which penetrate the substrate and then produce aerial hyphae on which develops conidiophores. Canidiophores may be branched and have brush like heads bearing spores. Clusters of sterigmata are usually in one place and form a chain of conidia. The colour of the mature plants is useful to identify species. They grow best at temperatures ranging from 15 to 30oC. Some species of Penicillum cause spoilage of fruits, vegetables, grains and grasses. Penicillium species causes different infections such as mycotic keratitis, penicilliosis, otomycosis, onychomycosis and deep infections. In otomycosis 5% aluminium acetate solution may be used to reduce edema and to remove epithelial debris. In mycocotic keratitis, tropical application of amphotericin B may be used.