Tiêu đề [LBA-CLIN MICRO] - Introduction to Microbiology (Part A) (no recit answers).pdf ✅

I. CLINICAL MICROBIOLOGY A. BASIC ASPECTS OF CLINICAL MICROBIOLOGY ● To start, microbes can be subdivided into the following five general groups: viruses, bacteria, archaebacteria, fungi, and parasites, with each having its own level of complexity. o Archaebacteria ▪ Predominantly inhabitants of extreme terrestrial and aquatic environments ▪ Often referred to as Extremophiles ▪ Do not seem to directly cause disease ▪ Can be distinguished from eubacteria due to lack of a peptidoglycan cell wall, possession of isoprenoid diether or diglycerol tetraether lipids, and characteristic rRNA sequences o Viruses ▪ Smallest infectious particles, ranging in diameter from 18 to 600 nm ▪ True parasites, requiring host cells for replication. o Bacteria ▪ Prokaryotic organisms → Simple unicellular organisms with no nuclear membrane, mitochondria, Golgi bodies, or endoplasmic reticulum, that reproduce by asexual division. → Most bacteria have either a gram-positive cell wall with a thick peptidoglycan layer, or a gram-negative cell wall with a thin peptidoglycan layer and an overlying outer membrane → Complex cell wall → Some lack the cell walls − Mycobacterium tuberculosis o Fungi ▪ Eukaryotic organisms ▪ Can exist either in a unicellular form (yeast), which can replicate asexually, or in a filamentous form (mold), which can replicate asexually and sexually. ▪ Dimorphic fungi → Some fungi have a mold form in the environment and a spherical form in the body at 37° C. → Histoplasma, Blastomyces, and Coccidiodes II. BACTERIAL MORPHOLOGY ● Microscopic appearance: size, shape, and arrangement ● Size Range: o Length = 0.1 – 20μm o Diameter = 0.2 – 2.0μm ● Clearly visible under light microscope A. SIZE OF BACTERIA ● Average diameter of common bacteria = 0.5 – 2.0μm o RBC is 7.5 μm in diameter ● Bacteria needs food to survive, and for food to reach certain parts of its cell, it needs to pass through the surface area ● SA is ~12μm2 ● Volume is ~4μm ● Surface Area (SA) to Volume ratio is 3:1 o The wide SA:V allows for easy absorption of food ● Food enters through SA, quickly reaches all parts of the bacteria ● Eukaryotes need structure and organelles B. BACTERIAL FORMS ● Average diameter of common bacteria = 0.5 – 2.0μm Figure 1. Bacterial Forms COCCI ● Coccus - round (spherical) o Chain = Streptococcus o Cluster = Staphylococcus ● May occur in clusters, pairs, or in chains ● May be large, small, or oval shaped Arrangement of Cocci ● Coccus o Single ● Diplococcus o Double or in pairs ● Streptococcus o Grow in chains ● Tetrad o Staphylococcus ▪ Clusters or clumps ● Sarcina o Cubical bundles Figure 2. Arrangements of cocci MORPHOLOGY GRAM POSITIVE GRAM NEGATIVE Circular (Coccus) Streptococcus Enterococcus Staphylococcus Neisseria Moraxella BACILLI CLIN MICRO Introduction to Microbiology Part A 1 of 11


● The gram-positive cell wall (stained blue) is very thick and has extensive cross-linking of the amino acid side chains. In ● contrast, the gram-negative cell wall (stained red) is very thin with a fairly simple cross-linking pattern D. CAPSULE ● Well-defined mucoid, polysaccharide structures ● Closely surrounds the cell wall of some bacteria ● Antiphagocytic property ● Virulence factor for some bacteria o one of the reasons why some patients when infected with capsular bacteria manifest such adverse events and some serious manifestations ● Helps scientists to diagnose what kind of capsular pathogen it is, as it has been used as a marker for detection o there are other diagnostic test which makes use of capsule to aid doctors come up with a rapid diagnosis of certain bacteria ● Also used to develop vaccines against capsular pathogens o Examples: ▪ Pneumococcal conjugate vaccine ▪ Haemophilus influenzae type B vaccine ▪ Meningococcal vaccine → All of the said examples, it’s because of the capsule that scientists were able to develop a vaccine against these pathogens ROLE IN PATHOGENESIS OF SOME INFECTIONS ● Protects the cell from drying ● Serves as an extra source of nutrition ● Helps the cell stick or attach to things because of its sticky or mucoid nature and such is part of biofilms ● By sticking the cells to solid surfaces, this prevents them from being washed away and provide a protective environment for the cells ● Protects cells from being destroyed by white blood cells ● May be toxic to a host’s defense system ● Capsules enable bacteria to become more virulent o Macrophages and neutrophils are unable to phagocytize the encapsulated bacteria Figure 4. Bacteria capsule function IV. BACTERIAL CELL APPENDAGE A. FLAGELLA ● Long, slender protein structures which originates from the cytoplasmic membrane ● Most flagellated pathogens are surrounded by numerous flagella called peritrichous o Pag sinabing peritrichous, all around the bacterial cell ay meron silang flagella. ● Flagellin - single protein unit of the structure o The flagellins of different bacterial species presumably differ from one another in primary structure. o They are highly antigenic (H antigens), and some of the immune responses to infection are directed against these proteins. ● Responsible for bacterial motility and may enhance bacterial invasion ARRANGEMENT BASIS FOR CLASSIFICATION Table 1. Arrangement basis for classification of bacteria. Monotrichous 1 Flagellum Lophotrichous Tuft at one end Amphitrichous Both ends Peritrichous All around the bacteria Figure 5. Comparison of flagella in Vibrio, E. coli, and Shigella ● Bacteria can have a single polar flagellum as in the case of V. cholera, or many peritrichous as in E. coli and P. mirabilis ● Shigella does not have flagella B. PILI ● Hair-like or spike-like rigid structures originating in the cytoplasmic membrane ● Found predominantly in gram-negative organisms ● Pilin – protein subunit of the structure o Some pili contain a single type of pilin, others more than one. o Minor proteins termed adhesins are located at the tips of pili and are responsible for the attachment properties. ● Two classes can be distinguished: o Sex pili ▪ Responsible for attachment of donor and recipient cells in bacterial conjugation o Common pili ● Play a role in the adherence of symbiotic and pathogenic bacteria to host cells CLIN MICRO Introduction to Microbiology Part A 4 of 11