Microbiology - Mechanisms of Diseases Past Paper PDF

Sbobinator: Roberta Fiorina Reviewer: Carlo Sirtori MICROBIOLOGY – MECHANISMS OF DISEASES – PROF. GARLANDA SOME QUESTIONS and PROKARYOTES True/false and multiple-choice questions 1. • All cell membranes contain phospholipids and a wide variety of proteins. Answer: FALSE, there are some microorganis...

Sbobinator: Roberta Fiorina Reviewer: Carlo Sirtori MICROBIOLOGY – MECHANISMS OF DISEASES – PROF. GARLANDA SOME QUESTIONS and PROKARYOTES True/false and multiple-choice questions 1. • All cell membranes contain phospholipids and a wide variety of proteins. Answer: FALSE, there are some microorganisms like Archaea which do not contain phospholipids in their membranes. • Lysosomes result from the endocytosis of food particles by eukaryotic cells. Answer: FALSE, because lysosomes are vesicles that contain hydrolytic enzymes. Vesicles that contain food particles are phagosomes. • Formation of a biofilm may contribute to bacteria's ability to cause disease. Answer: TRUE, microbes grown in biofilms cause diseases by acquiring pathogenic factors and exchanging resistance plasmids and are difficult to penetrate by drugs. • In a(n) (hypertonic/isotonic/hypotonic) animal cell can gain so much water that it may burst. Answer: HYPOTONIC solution, an • The presence of a cell (wall/membrane) enables bacterial and plant cells to resist the effects of hypotonic solutions. Answer: WALL 2. A higher concentration of solutes corresponds to a (higher/lower) concentration of water in a given solution. Answer: LOWER • • The molecule (LPS/NAM/Lipid A/NAG) is a part of the Gram-negative cell outer membrane that can produce fever, inflammation, and shock when it is released into the bloodstream. Answer: LIPID A, this ligand binds to a receptor and causes sepsis. 1 Sbobinator: Roberta Fiorina Reviewer: Carlo Sirtori • A (capsule/slime layer/matrix) is a type of glycocalyx that is firmly attached to the cell. Answer: CAPSULE, firmly attached to the cell is the capsule. All bacteria have a cell wall. Answer: FALSE, some bacteria do not have a cell wall and they are amorphic so may change their shape as it is the cell wall itself that gives them a certain shape. This means they are also able to change their diameter and are able to pass through filters. Before electron microscopy, these bacteria were classified as viruses because of their abilities. • 3. • Gram staining of bacteria provides all the physical characterization necessary to identify bacterial species. Answer: FALSE, after staining you may know if it is a Coccus or a Bacillus etc. or if it is Gram-positive or negative. To know ALL physical characteristics, you need other tests like, aside from sequencing, you can culture the bacteria and see which medium they grow avidly into, which sugars they use to grow. This means you are able to analyze the bacteria’s metabolism, which is quite specific between different species. • The Gram stain can be used to distinguish bacteria based on the structure of their cell walls. Answer: TRUE, Gram-positive bacteria have a thick peptidoglycan and Gramnegative have a thin one. These differences in cell wall modify the bacteria’s ability to retain the dye. • The endospore stain reveals internal structures within cells of the genera Bacillus and Clostridium. Answer: TRUE, these two genera of bacteria are the only ones which produce endospores. An endospore is a resistant structure which is produced by bacteria when the environmental conditions are harsh and help the bacteria survive. In the environment, viruses are found in metals, in the soil etc. Diseases like tetanus can spread, in countries with no compulsory vaccination, through metals dirty from the soil and this is because these bacteria live in the soil. • A (decolorizer/mordant/fixer) is a substance that binds to a dye and makes it less soluble. 2 Sbobinator: Roberta Fiorina Reviewer: Carlo Sirtori Answer: MORDANT, in Gram staining technique, after the first dye, you use one molecule that has the aim of fixing the dye and making it less soluble. • Coating a specimen with a heavy metal is a step in preparing it for (phase/fluorescent/electron) microscopy. Answer: ELECTRON, the sample is coated with a heavy metal, like gold, and in this way it is prepared for electron microscopy. For fluorescent microscopy you need a fluorescent dye, for phase microscopy you do not need to coat it with anything as it is a live cell. • A fluorescent molecule is one that absorbs invisible radiation and emits visible light. Answer: TRUE, we use a fluorescent laser which emits fluorescent light that we do not see, outside the visible wavelength, and this object will radiate back visible light. 4. • The total magnification using a 10x ocular and a 100x objective would be (110/1000/10000) X. Answer: 1000, 10 x 100 = 1000 • Bacterial viruses, called bacteriophages, can be used to help classify different groups of bacteria. Answer: TRUE, Bacteriophages are very specific for each family of bacteria. Bacteriophages bind to a specific receptor on the bacteria so they are specific, but more on this will be said in future lessons. • A serological test that involves the clumping of antigen and antibody is the (agglutination/antigen/ELISA) test. Answer: AGGLUTINATION, antigens are objects that are bound by antibodies forming clumping and aggregates, forming these visible agglutinates. • The system of taxonomy used today was originated by (Linnaeus/Darwin/Woese). Answer: LINNAEUS, he is the person who gave binomial nomenclature to anything. • A primary purpose for the use of stains in microscopy is to increase the (magnification/brightness/contrast) of a specimen. 3 Sbobinator: Roberta Fiorina Reviewer: Carlo Sirtori Answer: CONTRAST • The process of immobilizing organisms on a glass slide through the application of either heat or chemicals is (staining/mordant/fixation). Answer: FIXATION 5. • During glycolysis, glucose is converted to (pyruvic/acetic/lactic) acid, a molecule that can be used in either fermentation or respiration pathways. Answer: PYRUVIC. Yoghurt is made from lactic acid, generated from bacteria during fermentation. When you have an open wine bottle and you leave it open on a table for a month, for example, it becomes acetic acid. Bacteria generate the acetic acid. Acids are generated by bacteria through a process known as fermentation. If you produce beer, you generate alcohol. • Laboratory fermentation tests often include a pH indicator because many bacteria produce (CO2/bases/acids) as they ferment carbohydrates. Answer: ACIDS, as explained previously. • Obligate anaerobes have enzymes such as superoxide dismutase to protect them from the damaging effects of oxygen. Answer: FALSE. It is exactly the opposite because they do not have these enzymes and many others that would allow them to live in the presence of oxygen. They are obligate anaerobes so they cannot come into contact with oxygen. • Serial dilution can be used in combination with pour plates as a method for isolating pure cultures. Answer: Serial dilution is when you add, for example, 1ml of for example blood/bacterial culture to 9ml of water. Then you take 1ml of those 10ml and place it in other 9ml of water meaning that you have diluted by 10 again. In this way, you perform a logarithmic scale dilution which is very efficient and after 10 dilutions you will have a dilution of 1 million. When you will place your bacteria in culture, they will have been diluted by a lot. We could have a range of quantities: on one side you would have less diluted and on the other almost zero concentration. You want isolated colonies in order to collect single species, different in morphology and shape and an expert of microbiology will recognize Streptococcus pneumonia for example. 4 Sbobinator: Roberta Fiorina Reviewer: Carlo Sirtori • Quorum sensing is involved in the development and propagation of a biofilm. Answer: TRUE, from PubMed: “Quorum sensing is the regulation of gene expression in response to fluctuations in cell-population density. Quorum sensing bacteria produce and release chemical signal molecules called autoinducers that increase in concentration as a function of cell density.” It is essentially the ability to detect and react to cell population density thanks to gene regulation. For example, it helps inhibit the expression of certain genes at high cell densities to achieve phenotypes which will be beneficial. • Agar is a useful compound in the microbiology lab because it is an excellent nutrient for bacteria. Answer: FALSE, we add agar to have a solid medium base. When it is hot, it is liquid. At room temperature, it is solid. It is not a nutrient for the bacteria. The only reason we add agar is to have a solid base. • A(n) (culture/specimen/inoculum) is a sample of microorganisms introduced into a growth medium. Answer: INOCULUM, you take a small sample to put in a small medium and then you grow a culture as a final product. When you collect a sample from a patient, it is called a specimen. From the specimen, you take a small tip of the pipette to put it in the medium to culture it and that small tip is called the inoculum. • A (cytometer/spectrophotometer) can measure changes in the turbidity of a bacterial culture. Answer: SPECTROPHOTOMETER. Turbidity is known as the measure of how cloudy or opaque matter is. A spectrophotometer measures quantitatively the reflection or transmission of matter as a function of wavelength. A cytometer is used when you a solution containing cells and you want to count how many leukocytes a patient has in is blood, you put in a cytometer and it counts cell types you need. 6. • Transfer of DNA between bacterial cells by viruses is called (transformation/transduction/conjugation). Answer: TRANSDUCTION. Conjugation occurs through the pilus. Transformation is when a bacteria takes DNA from the external environment. The cell wall allows the cell to collect DNA fragments from the environment. • Reverse transcriptase synthesizes a DNA molecule from an RNA template. 5 Sbobinator: Roberta Fiorina Reviewer: Carlo Sirtori Answer: TRUE, we will study in a few lessons. • Nucleic acid molecules used to deliver new genes to cells are called (plasmids/vectors/clones). Answer: PLASMIDS. Plasmids can also be of viral (known as vectors, in this case) and bacterial origin. Clone is the colony of something you have transformed. Say a viral vector is introducing a piece of DNA into bacteria, all progeny from that is known as clones. • The ability to utilize different metabolites for cellular respiration is one method for identifying bacteria. Answer: TRUE. 7. • Some viruses are inactivated by the same chemical or physical agents that damage cytoplasmic membranes. Answer: TRUE. The membrane which envelopes viruses, including SARS-CoV 2, comes from the host so have eukaryotic origin. • Slow freezing is more damaging to microbial cells than quick freezing. Answer: TRUE, for food it is better to immediately freeze it to preserve it, but to damage bacteria more, it is better to have a more gradual freezing. • By themselves, soaps have only degerming activity, not antimicrobial activity. Answer: TRUE, you are just removing microbes, not killing them when you wash your hands. • The amount of time needed to sterilize materials using moist heart is (more/less) than the time needed to sterilize using dry heat. Answer: LESS • The deadliest, most contagious microbes are studied under conditions of (BSL-4/BSL-3/BSL-2/BSL-1) containment. Answer: BSL-4 • Ultraviolet light penetrates (more/less) effectively than gamma rays. Answer: LESS 8. 6 Sbobinator: Roberta Fiorina Reviewer: Carlo Sirtori • The (endospores/cysts/viruses) are the infectious agents most resistant to antimicrobial agents or processes. Answer: ENDOSPORES • A microbe resistant to a variety of different antimicrobials is said to have (cross/drug/multiple) resistance. Answer: MULTIPLE. Cross means that different microbes are resistant to the same principles in different antimicrobials. Multiple means that microbes are resistant to different principles on which antimicrobials are based. • Secondary infections that result from the killing of some of the normal microbiota are called (antagonism/superinfections/resistance). Answer: SUPERINFECTIONS. There are microorganisms that live within us, within us vagina and mouth for example. When we use a spectrum of antibiotics, we may damage our own microbiota in our body, thus creating instability in our organism causing overgrowth of the bacteria like with e.g. Candida and E.coli in Cystitis. We will also encounter Clostridium Difficile in hospitals which is very difficult to treat and leads to severe diarrhea and intestinal mucosal inflammation. • Drugs that slow down bacterial growth would be (competitive/synergistic/antagonistic) to penicillin. Answer: ANTAGONISTIC. Penicillin, the first antibiotic identified, acts through the Beta-lactam ring to damage the construction of a normal cell wall. The cell wall is built during cell growth and replication. To introduce something into the cell wall, we need to have a growing and replicating cell. If you use a drug that slows down bacterial cell growth, the cell will rest and not undergo growth and replication, which means it will not be able to incorporate penicillin in the cell wall. 7 Sbobinator: Roberta Fiorina Reviewer: Carlo Sirtori CHARACTERIZING AND CLASSIFYING PROKARYOTES PROKARYOTES • They are the most diverse group of cellular microbes • Thrive in various habitats, almost any • Only a few are capable of colonizing humans and cause diseases GENERAL CHARACTERISTICS: Three basic shapes: 1. COCCUS (Cocci): spherical, oval 2. BACILLUS (Bacilli): rod-shaped or spindle-shaped, thread-like, filamentous. 3. SPIRAL (spirillum/spirilla): stiff, spirochetes = flexible In addition: Vibrios = curved rods Coccobacillus Star-shaped, triangular Pleomorphic = vary in shape and size, pleomorphic can have any shape and size ENDOSPORES It confers a particular morphology to the microorganisms. The bacillus changes its shape thanks to the endospore. They are important because they exist in the environment for decades; they are produced by Gram-positive bacteria of genus Bacillus and Clostridium. Each vegetative cell transforms into one endospore. They are a defensive strategy in unfavorable conditions, and are not a reproductive structure. Resting stages with very low metabolism that will germinate in one single vegetative cell when conditions improve. Sporulation requires 8-10 h. Spores can be: Central, Subterminal or Terminal. They are a serious concern for food processors and health care professionals: they produce deadly toxins (tetanus, anthrax, gangrene). REPRODUCTION OF PROKARYOTIC CELLS 1. BINARY FISSION: Microbes replicate via binary fission. All prokaryotes reproduce asexually; they never have differential forms based on 8 Sbobinator: Roberta Fiorina Reviewer: Carlo Sirtori differential expression of different genes associated to sex. First, the nuclear material is distributed along the length of the cell which then elongates, producing 2 daughter molecules. Then, the cell wall and membrane invaginate, separating the cell and forming 2 daughter cells which may eventually separate or not. 2. SNAPPING DIVISION: Is a variation of binary fission occurring in some Grampositive bacteria: the inner portion of the cell wall remains attached to the two daughter cells and for this reason the cell may remain attached through this portion of cell wall. It is deposited across the dividing cell. As the cell grows, tension snaps the outer wall, leaving daughter cells connected by the remnants of old wall material. Actinomycetes produce reproductive spores (that undergo reproduction) at the end of their filamentous cells. They are not endospores, they are bacteria. The parental cell retains its identity. 3. BUDDING: This occurs when the two daughter cells are not identical in terms of morphology and dimensions. The DNA material is located in one portion of the elongated structure in the young bud so it is located there. DNA, attached to the cytoplasmic membrane, is replicated. Cell elongates to form a bud; the expanding cytoplasmic membrane carries one DNA molecule into the bud. 9 Sbobinator: Roberta Fiorina Reviewer: Carlo Sirtori ARRANGEMENTS OF PROKARYOTIC CELLS In prokaryotic cells, when they remain attached, they may have differential arrangements. You may have diplococci (two attached) or they may form chains (streptococci). If the plane of division is orthogonal, you may have tetrads. If you have three planes of division you may have Sarcina. If the planes of division are irregular, you may have Staphylococci. Bacilli divide only transversely, across the long axis. They may separate in singles cells or remain attached in pairs or chains. If they divide by snapping division, they remain attached to form Vshapes or a palisade. Take note of the particular morphology of Corynebacterium diptheriae which we will study in the upcoming lessons and has a very particular morphology compared to the others. You may perform a diagnosis of this disease thanks to its particular arrangement. NB: Streptococci or staphylococci or bacilli are words describing the shape. Streptococcus or Staphylococcus or Bacillus are genus names. MODERN PROKARYOTIC CLASSIFICATION 10 Sbobinator: Roberta Fiorina Reviewer: Carlo Sirtori In 99.5%of cases, which means millions of species, we have never cultured bacteria. We know them and we classify them thanks to their ribosomal RNA sequence. In the image on the right, you observe a taxonomic scheme. You observe the discs and their dimension and size show the number of species in that specific group of microbes. We subdivide Archaea and Bacteria. Among the Archaea, we observe different groups which have peculiar metabolic activities. In the bacteria group, we have a group called ‘Deeply branching bacteria’ or we have ‘Gram negative’ bacteria or even the ‘Gram positive’. They may also be divided based on their content of G+C. If they are close, they are similar. If they are far, they a larger difference in rRNA sequence. If the discs are large, they contain a large number of species. SURVEY OF ARCHEA They have a unique rRNA sequence. They do not have peptidoglycan in their cell wall. Cell membrane lipids have branched or ring-form hydrocarbon chains (not straight chains). Different shapes: cocci, bacilli, spirals or pleomorphic. They do not cause diseases, but they are important for the planet as they represent 1/3 of the prokaryotic biomass in sea water and are source of food for marine animals. They can live in extreme conditions. Some of them live in hot springs and others may survive in very high salt concentrations. Extremophiles: require and survive in extreme conditions of temperature, pH, salinity. E.g. Thermophiles(>45°C) and hyperthermophiles (>80°C). We use their enzymes for industrial applications or research. Halophiles: (>9% sodium chloride; 17-23%, some live in close to saturated saline solutions (35% NaCl) 11 Sbobinator: Roberta Fiorina Reviewer: Carlo Sirtori Methanogens: anaerobes, convert carbon dioxide, hydrogen gas and organic acids into methane gas. They are the major source of environmental methane. They convert organic wastes into methane and are important in sewage treatment. They have produced something like 10 trillion tons of methane that is buried in mud on ocean floor. Some of them live in the colon of animals. SURVEY OF BACTERIA 1. Deeply branching bacteria They are similar to the earliest bacteria: autotrophs (use carbon dioxide as source of carbon); live in extreme habitats, similar to those existing in the early Earth. First microbes on the planet and still live there. PHOTOTROPHIC BACTERIA: Pigments absorb light, so they are able to carry out photosynthesis which provides energy for metabolism and generates O2. E.g. Cyanobacteria are involved in the transformation of anaerobic atmosphere of the early Earth into oxygen-containing Earth. According to the endosymbiotic theory, chloroplasts derived from cyanobacteria. Cyanobacteria reduce nitrogen gas (N2) to ammonia (NH3) via nitrogen fixation, which is used by other organisms and then ammonia can be used by other organisms to convert nitrogen from an inorganic form to an organic form. 2. Low G + C Gram-Positive Bacteria (it is only a way of classifying them). Guanine + cytosine/adenine + thymine + guanine + cytosine <50% G+C. Phylum FIRMICUTES, three groups: Clostridia, Mycoplasma, Others. 2.1 CLOSTRIDIA: Rod-shaped, obligate anaerobes, most form endospores. Clostridium tetani: tetanus 12 Sbobinator: Roberta Fiorina Reviewer: Carlo Sirtori Clostridium perfringens: gangrene Clostridium botulinum: botulism Clostridium difficile: severe diarrhea 2.2 MYCOPLASMA Facultative or obligate anaerobes. Lack a cell wall and have cell membranes rich in sterols: they stain pink when Gram stained. They colonize osmotic protected habitats because they are unable to live in the environment because they are too fragile. They are pleomorphic (e.g. filamentous). 0.2-0.8 μm diameter: they are the smallest free-living cells. Require organic compound in culture or from host. Characteristic “fried egg” appearance colonies. In animals: they colonize mucous membranes of respiratory and urinary tracts and are cause of pneumonia and urinary tract infections. 2.3 Other low G + C Gram Positive Bacilli and Cocci Genus Bacillus Includes endospore-forming aerobes and facultative anaerobes. Peritrichous flagella. Numerous species live in the soil. Bacillus thuringiensis produces Bt toxin that kills caterpillars: used in agriculture and GMO plants (rice, corn). Bacillus polymixa: polymyxin Bacillus licheniformis: bacitracin. Bacillus anthracis: anthrax. Inhalation (100% fatal) or skin wounds (20% fatal). Genus Listeria Listeria monocytogenes: rod-shaped, contaminates milk and meat. Reproduce under refrigeration and survive inside phagocytes. Dangerous for the fetus or immunocompromised patients (meningitis, bacteremia), which is why pregnant women or immunocompromised people should not eat raw meat. Genus Lactobacillus Rod-shaped, components of useful microbiota: microbial antagonism with pathogens which is why they live in our stomach and intestinal tract and they are useful to maintain equilibrium in our GI tract. Used in food industry and as probiotics. 13 Sbobinator: Roberta Fiorina Reviewer: Carlo Sirtori Genera Streptococcus and Enterococcus: Cocci associated in pairs or chains. Cause of several diseases (pharyngitis, meningitis, wound infections...). Several multi-drug resistant streptococci strains have recently appeared. Genus Staphylococcus - Staphylococcus aureus: One of the most common inhabitants of humans, in the skin and nasal cavities. Specific strains produce toxins and enzymes allowing invasion: bacteremia, pneumonia, skin infections, food poisoning, toxic shock syndrome, joint and bone diseases. 3. High G + C Gram-Positive Bacteria Phylum Actinobacteria, rod-shaped or filamentous. >50% G+C. Many are pathogens. Genus Corynebacterium Pleomorphic or rod-shaped, aerobes and facultative anaerobes. Snapping division...V-shaped and palisade. It’s the only bacteria with this V-shape morphology. They are characterized by stores of phosphate in metachromatic granules (methylene blue). Corynebacterium diphtheriae: diphtheria. Genus Mycobacterium Aerobic rod shaped or filaments. Slow growth, waxy lipids in the cell wall (mycolic acid); resistant to desiccation. Acid-fast stain. Pathogenic species: M. tuberculosis (tuberculosis) and M. leprae (leprosy). Actinomycetes: Branching filaments resembling fungi and production of spores at the end of filaments. Cause of disease in immunocompromised patients. Genera include: - Actinomyces 14 Sbobinator: Roberta Fiorina Reviewer: Carlo Sirtori o Mucous membranes of oral cavity and throat. Actinomyces israelii: opportunistic pathogen causing abscesses which destroy tissues. - Nocardia o In soil and water, filaments. Able to degrade many pollutants. Some species are pathogens. - Streptomyces o They recycle nutrients in the soil by degrading complex carbohydrates (cellulose, lignin), proteins (keratin), aromatic chemicals. They produce antibiotics including chloramphenicol, erythromycin, tetracycline. 4. GRAM-NEGATIVE PROTEOBACTERIA Phylum Proteobacteria: the largest and most diverse group of bacteria. Five classes: alpha, beta, gamma, delta, epsilon. 1. ALPHAPROTEOBACTERIA These bacteria grow associated with the roots of plants, in particular with Leguminosae, which are essentially beans and peas and similar ones. You need proteins from your diet and you can get so many from legumes because they are so rich in these microbes in their roots, as they fix the nitrogen and turn it into ammonia and then there are other bacteria, always in the roots, that oxidize the nitrogenous compounds such as ammonia to nitrate that can be used in 15 Sbobinator: Roberta Fiorina Reviewer: Carlo Sirtori the plant. Plants are not able to use the inorganic form of nitrogen; they need a transformation from the nitrogenous gas to nitrate. Any shape, aerobes. Some produce extensions of the membrane and cell wall used for attachment called prosthecae. Nitrogen fixers: important in agriculture. They grow in association with roots of plants, they fix N2 and produce ammonia for the plant. Leguminosae and protein synthesis. Some produce hydrogen gas (biofuel). Nitrifying bacteria: they oxidize nitrogenous compounds (NH3) into nitrate (NO3) used by plants. Pathogenic alphaproteobacteria: o Rickettsia; live inside mammalian cells and are transmitted through the bite of arthropods. o Brucella (brucellosis): causes abortion and sterility. Survive phagocytosis. 2. BETAPROTEOBACTERIA Recycling N2 and sulfur in the environment, important in sewage treatment. o Neisseria: mucus membranes, cause of gonorrhea, meningitis… o Bordetella: pertussis (whooping cough) o Burkholderia: colonizes surfaces, medical equipment, respiratory tract of cystic fibrosis patients. 3. GAMMAPROTEOBACTERIA o The largest and more diverse class of proteobacteria. Every shape and arrangement, metabolic type, reproductive strategies. Pathogenic gammaproteobacterial, divided in subgroups: A. Intracellular pathogens: they avoid killing by leukocytes. Legionella: Legionnaires’ disease, Coxiella: Q fever. B. Glycolytic facultative anaerobes: many pathogens. C. Pseudomonads: Aerobic, flagellated, rod-shaped. Some are cause of diseases and food spoilage. D. Pseudomonas: urinary tract infections, lung infections in cystic fibrosis patients, external otitis. 16 Sbobinator: Roberta Fiorina Reviewer: Carlo Sirtori 4. DELTAPROTEOBACTERIA Is only involved in decaying materials, not involved in causing diseases. Found in the soil, needed to recycle sulfur, decay plant material and animal dung. 5. EPSILONPROTEOBACTERIA Pathogenic Epsilonproteobacteria: Campylobacter: enteritis Helicobacter: ucler 5. Other Gram-negative Bacteria Chlamydias: Small Gram-negative cocci that grow and reproduce only within the cells of mammals, birds and some invertebrate. They can be smaller (0.2 μm) than larger viruses. THEY LACK PEPTIDOGLYCAN. They cause severe infections in humans. Neonatal blindness, pneumonia, sexually transmitted lymphogranuloma venereum. Unique method of reproduction: invasion of a host cell by Elementary body, reticulate body formation, binary fission, and filling of the cell with reticulate bodies which change into elementary bodies with rigid outer boundaries. These are resistant to drying and an infective stage. We will see their life cycle in the future lessons. Spirochetes: helical bacteria, axial filament. o Treponema: syphilis o Borrelia: Lyme disease 17 Sbobinator: Roberta Fiorina Reviewer: Carlo Sirtori Bacteroids: o Are obligate anaerobes, rod-shaped; digestive tract: metabolize cellulose and complex carbohydrate. 30% of bacteria in human feces. The most common anaerobic human pathogen, cause of abdominal pain, diarrhea, fever. We can eat salad and vegetables without many problems because these microbes digest them for us and then we digest the common bricks and pieces deriving from these foods, thanks to the microbes that break them down for us. 18