Microbial Life PDF

Microbial life Viruses Very small: Diameter from 18 to 600 nanometers (most viruses are less than 200 nm and cannot be seen with a light microscope); Minimal content: usually only protein with DNA or RNA, or even proteins without DNA/RNA (prions); Parasitic: Requiring host ce...

Microbial life Viruses Very small: Diameter from 18 to 600 nanometers (most viruses are less than 200 nm and cannot be seen with a light microscope); Minimal content: usually only protein with DNA or RNA, or even proteins without DNA/RNA (prions); Parasitic: Requiring host cells for replication. Influenza Ebola H1N1 SARS www.huffingtonpost.com CDC CDC  Bacteria Prokaryotic organisms: simple unicellular organisms with no nuclear membrane, mitochondria, Golgi bodies, or endoplasmic reticulum—that reproduce by asexual division; Various phenotypic and genotypic properties: the size (1 to 20 µm or larger), shape (spheres, rods, spirals), and spacial arrangement (single cells, chains, clusters), cell wall components (two basic forms: gram-positive and gram-negative). Thousands of species co-exist with human. Staphylococcus aureus Bacillus cereus Streptococcus pneumoniae  Parasites Complex eukaryotic microbes: unicellular Plasmodium falciparum and or multicellular, range in size from tiny (1 to 2 µm similar to many bacteria) to up to 10 meters (tapeworms) and arthropods (bugs); Life cycles involve a complex relationship with animal hosts. Fungi Eukaryotic organisms that contain a well- Candida albicans defined nucleus, mitochondria, Golgi bodies, and endoplasmic reticulum; Unicellular form (yeast) or filamentous form (mold); Replicate asexually or sexually.  Archaea prokaryotes less morphological diversity than Bacteria mostly undifferentiated cells 1–10 μm long five well-described phyla historically associated with extreme environments, but not all extremophiles lack known parasites or pathogens of plants and animals Basic characters of bacteria Surface structures Pili, appendages involved in “conjugation” – transfer of genetic materials. Fimbriae, structures concerned with the adhesion of bacteria to various surfaces. Glycocalyx, polysaccharide and protein film that surround bacterial cells. Two types: capsules (well- defined outer layers) and S- layers (loosely organized network of materials). Bacterial cell walls Gram-negative Has an extra outer membrane containing lipopolysaccharide (LPS) - endotoxins that can cause diseases and are activators of immune response. Gram-positive Thick and compact peptidoglycan layer which helps to retain crystal violet dye.  Lipopolysaccharide (LPS) LPS (endotoxin) consists of three structural sections: Lipid A, core polysaccharide (rough core), and O antigen. Lipid A is a basic component of LPS and is essential for bacterial viability. Lipid A is responsible for the endotoxin activity of LPS. LPS structure is used to classify bacteria. The basic structure of lipid A is identical for related bacteria and is similar for all gram-negative Enterobacteriaceae. The core region is the same for a species of bacteria. The O antigen distinguishes serotypes (strains) of a bacterial species. For example, the O157:H7 (O antigen:flagellin) serotype identifies the E. coli agent of hemolytic-uremic syndrome. Inner structures of bacterial cells Cytoplasmic membrane Nucleoid, the site in the bacterial cytoplasm that contains DNA. Cytoplasmic inclusion bodies, storage places of various compounds e.g. carbohydrate, phosphate, nucleic acid, protein and lipid etc. Arrows: nucleoid in E. coli  Bacterial spores Under harsh environmental conditions, such as the loss of a nutritional requirement, bacteria can convert from a vegetative state to a dormant state, or spore. Some gram-positive, but never gram-negative, bacteria, such as members of the genera Bacillus and Clostridium (soil bacteria), are spore formers. The spore is a dehydrated, multishelled structure that protects and allows the bacteria to exist in “suspended animation”.  Biofilm Aggregation of growing bacterial cells occurs on a surface, forming a highly hydrated polysaccharide matrix in which the cells become enmeshed. The biofilm is a sturdy colony which is difficult to dislodge and provides the bacteria with protection against many environmental factors and also against antibiotics. TEM of biofilm formed by Prevotella intermedia. The gel matrix of the biofilm appears as a network of fine fibres interspersed between the cells. Biofilm of Staphylococcus aureus  Bacterial pathogenesis Bacterial Disease Production 1.Disease is caused by damage produced by the bacteria plus the consequences of innate and immune responses to the infection. 2.The signs and symptoms of a disease are determined by the function and importance of the affected tissue. 3.The length of the incubation period is the time required for the bacteria and/or the host response to cause sufficient damage to initiate discomfort or interfere with essential functions. Examples of bacterial diseases and disease symptoms Vibrio cholerae causing watery diarrhea and vomiting Pseudomonas infection of burn wound Concepts of sterilization, disinfection, and antisepsis Antisepsis: Use of chemical agents on skin or other living tissue to inhibit or eliminate microbes; no sporicidal action is implied. Disinfection: Use of physical procedures or chemical agents to destroy most microbial forms; bacterial spores and other relatively resistant organisms (e.g., mycobacteria, viruses, fungi) may remain viable. Sterilization: Use of physical procedures or chemical agents to destroy all microbial forms, including bacterial spores