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Microbiology - Module 6
Microbiology
Angeles University Foundation
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ATYPICAL BACTERIA
- ^includes species identified in 16 s rRNA and rDNA and
metagenomics (field that studies diff genes in a particular
sample)
● Metagenomics
- Ex. You have a soil specimen and you want to identify the diff organisms so you extract the DNA and do 16 s rRNA gene amplification and you sequence then check the database for identity without having to culture/grow the organism ● Mycoplasma - no cell wall ● Chlamydia and Rickettsia - with cell wall; gram-negative ● Tenericutes
- Class Mollicutes don't have cell wall (phylum for Mycoplasma) ● Chlamydiae
- Phylum for Chlamydia ● Proteobacteria
- Gram-negative
- Phylum for Rickettsia, Enterobacteriaceae, Pseudomonas, Vibrio ● Firmicutes
- Have cell wall
- Phylum for Staphylococcus, Streptococcus, Lactobacillus Phylum Actinobacteria (Gram-positive) Mycoplasma
- Smallest organisms capable of autonomous growth (not obligate intracellular parasites) so they can grow outside the host cell ○ Autonomous growth - do not require to be inside a host cell, NOT obligate intracellular parasites in contrast to Chlamydia and Rickettsia
- Smallest are 125 - 250 nm in size
- Parasites in animals, insects, and plants
- With the smallest genomes (a total of about 500 - 1000 genes)
- Unit of measurement for bacteria: micrometer
- There's always a limit to the small size that a cell can have
- Limiting factor is that it should be able to carry the
different genes it requires
● Nutritionally fastidious
○ Even tho they are living outside the host cell, there
are many growth factors that cannot be synthesized
bc of the limit of the genes they can synthesize
● Comparison of genome sizes
- If double stranded - “base pair”, if single stranded - “base”
- Add 3 zeros to compute for the kbp so if 1660 , there are 1660000 base pairs ○ Borrelia burgdorferi - cause the lyme disease Gram-positive Phylum Actinobacteria Gram-positive Phylum Actinobacteria ALL TENERICUTES DONT HAVE CELL WALL!!
● Characteristics ○ Cell wall-less - All atypical bacteria are - Cell wall maintains the shape of the cell and protects them from plasmoptysis bc they are usually in hypotonic environment since they have so much solutes in the cytoplasm; they don't lyse because of the peptidoglycan - Consequence of no cell wall: ■ Pleomorphic - they can appear as coccoid and filamentous and assume various shapes ○ Phylogenetically more related to Gram + ○ Stable against plasmoptysis due to ■ Sterols in cell membrane or - Prokaryotic cells generally don't have sterols except for some mycoplasma ■ Lipoglycans ➢ Long chain heteropolysaccharides linked to membrane lipids, embedded in cell membrane ➢ Antigenic - Host can elicit antibody/immune response through B or T cells or both ➢ Enhances attachment to host cell surfaces - Virulence factor bc it enhances attachment to host cell surfaces ○ Low GC content ○ Obligate or facultative anaerobes, obligate anaerobes ○ Small genome so they don't have many genes ○ “Fried-egg” colonies - Cells embed themselves in the center ○ Fastidious: complex media + growth factors, fresh serum, ascitic fluid (sources of unsaturated FA and sterols) - If the organism if obligately intracellular then you have to have living cells to grow (tissue culture, lab animals, embryonated chicken eggs) - But to grow Mycoplasma, you don't need those - The red blood cells in blood agar plate are not metabolizing anymore so hindi pwede yun - Mycoplasma can be grown in culture media without living cells but bc they are fastidious bc of the gene limitation, you need to have complex media, growth factors, fresh serum, ascitic fluid - Those that have sterols in their membrane, you have to have sterols in the culture medium ● Major characteristics of Mycoplasmas ○ Usually pathogens are facultative anaerobes because it gives them more versatility to be in different locations in the host body BUT NOT ALWAYS ○ Require sterols - MASUE ■ Mycoplasma
- associated with disease in men and animals
- Mycobacterium tuberculosis is obligately anaerobic
- Many pathogenic; facultative aerobes ■ Anaeroplasma
- may or may not require sterols
- Obligate anaerobes
- not really associated with diseases in man
- Degrade starch
- Produce acetic, lactic, and formic acids plus ethanol and CO 2
- Inhibited by thallium acetate
- found in rumen of bovine and ovine ■ Spiroplasma
- Coccoid cells
- Occasional clusters and short chains
- not associated with pathogens in man
- no cell wall but namementain nila ung spiral shape
- infect plants and insects ■ Ureaplasma unless stated otherwise (like Rickettsia and Chlamydia)
○ What happens here: - Fusion of the lysosome with the endosome of the chlamydia does not take place - Phagolysosome is prevented so Chlamydia remains viable inside the endosome - Chlamydia grows in size until the elementary body transforms into the bigger reticulate body 3. Conversion of reticulate body
- Takes places about 6 - 8 hrs after it has been phagocytosed ○ Reticulate body
- Binary fission stage; multiplying form
- Fragile cell wall
- Non-infectious; found inside the host cell
- Multiplication of reticulate bodies
- Conversion of elementary bodies ( 24 - 48 hrs)
- Release of elementary bodies ( 72 hrs)
Cell undergoes lysis and releases infectious forms (elementary bodies) ➢ All atypical bacteria still possess the same features of bacteria that were discussed before (presence of cytoplasm, ribosome, fermentation, respiration, cell wall unless stated otherwise) ➢ Rickettsia, viruses, viroids - obligate intracellular ➢ Prions - not obligate intracellular ● Differential characteristics of Chlamydia and Chlamydophila ○ Chlamydia trachomatis
Common in the Philippines ■ Trachoma - eye infection, can lead to blindness if not treated ■ Otitis media - infection of middle ear ■ Nongonococcal urethritis
Symptoms similar to gonorrhea (purulent discharge, pain during urination, etc)
Gonorrhea is usually asymptomatic in females ■ Sexually transmitted
nongonococcal urethritis, urethral inflammation, lymphogranuloma venereum ■ Eye infections - some strains; can also be acquired via fomites (contaminated inanimate objects) ■ Cervicitis - inflammation of the cervix ○ Chlamydophila psittaci
Zoonotic infections (animals are the hosts) but can be transmitted to man (ex. Psittacosis - birds to humans) ○ Chlamidophila pneumoniae
Pneumoniae is human in nature; infection of the respiratory system ○ Mucus membranes - always the site of infection ○ DNA hybridization
Rendering the DNA of two different species into single stranded and allowing them to H bond with each other ● Parachlamydia acanthamoebae
Infects free-living amoebae, particularly Acanthamoeba
Can also infect humans although only weakly compared with Chlamydiae whose natural hosts are humans
Most species of Chlamydiae can multiply or survive within free-living amoebae, and these hosts may be important for the survival and dispersal of Chlamydiae in nature ■ Amoeba can also serve as a reservoir for the Chlamydia in the environment bc many species can multiply and survive ● Laboratory isolation and identification ○ Cultured in: ■ Tissue culture
Bc they are obligate intracellular parasites so they can be grown in lab eggs, animals, etc ○ Detection: ■ FAT or Giemsa stain of cytoplasmic inclusions in infected epithelial cells
Chlamydia are Gram-negative but the use of Giemsa stain can more easily facilitate the microscopic exam of the microorganism ■ Polymerase chain reaction Rickettsias
Belong to Phylum Proteobacteria
Not very common in the Philippines
Small Gram-negative coccoid or rod-shaped or pleomorphic
Better stained with the Giemsa, Gimenez stains and better visualized through the brightfield microscope ● Obligate intracellular ○ Exception: Rochalimea
Not inside the cell but in the periphery ● Arthropod-borne ○ Exception: Coxiella burnetii
Also arthropod-borne (via tick)
But can also be transmitted in the absence of a vector (aerosol) ● Metabolism ○ Cannot oxidize glucose or organic acids
Glucose and organic acids cannot serve as their hydrogen and electron donors ○ Oxidize only glutamate (amino acid), glutamine (derivative of amino acid) ○ With respiratory chain, NADH as electron donor ○ Obtain most nutrients from host cell (ex. NAD+)
Also have very limited metabolic pathways so they require nutrients from the host cell
NAD+ is from the host cell ● Laboratory isolation and identification ○ Cultured in: ■ Yolk sacs of embryonated chicken eggs ■ Tissue culture ○ Detection: ■ Direct FAT to detect organism’s antigen ■ Indirect FAT to detect antibodies (in the patient’s serum) ● Some characteristics of Rickettsias
Life cycle of SARS-CoV- 2 (Nice to know) ● S protein - Target of the prevention of the vital attachment (adsorption - first step to infection) to the host cell ● ACE 2 receptor - also present in the plasma membrane of our respiratory cells - Where the virus attaches to
- S protein binds to ACE 2 receptor
- Membranes of the host cell and virus fuse
- ENTIRE viral particle (capsid included) is taken into the cell via endocytosis
- Virion uncoats to release RNA (+ strand) ○ RNA is plus (+) strand - Has codons like the mRNA so when it enters the host cell, it can be translated using the host’s ribosomes ○ Minus (-) strand - Cannot be translated, does not serve as the mRNA - When it enters the host cell, it serves as the template to produce the + strand vis translation
- RNA translated; polypeptides synthesized
- Proteolysis
- Polypeptides are not functional yet so they undergo proteolysis (cut into shorter polypeptide chain
- Proteases can be inhibited by Lopinavir Darunavir
- Nonstructural proteins are formed
- “Nonstructural” - not component of capsid envelope (ex. RNA polymerase)
- RNA synthesis
- mRNA is now read by the RNA polymerase, producing the - strand RNA which serves as a template to produce + RNA 9. Translation - (-) strand translated into (+) strand 10. Structural proteins - Assemble the capsid, envelope, etc 11. Assembly Comparison of virus types Characteristics Novel Coronavirus (SARS-COV 2 ) Flu (A + B) Human Immunodeficien cy Virus (HIV) Family Coronavirus Influenza virus Retrovirus RNA strand 1 RNA strand (big genome) encodes 4 proteins 8 RNA strands encode between 8 - 11 proteins based on the reading frame 2 identical RNA strands encode 15 proteins Binds to the receptor of the host cell Spike protein Hemagglutinin Glycoprotein Integration in the patient’s genome No No Yes Envelope Present Present Present “Proof-reading” enzymes Present Absent Absent Reverse transcriptase enzyme Absent Absent Present (in all retroviruses) ➢ More often than not, viral genome DOES NOT integrate into the host chromosome but there are exceptions ➢ Attachment of the virus to the host cell has specificity between the viral particle and host receptor ● Flu virus - Does not integrate but very mutable that’s why different types of serotypes would appear from time to time - There can be a combination of different RNA molecules so different variations can occur, hence the different numbers in the names attaches to sialic acid attaches to CD attaches to ACE
Flu vaccine is yearly given because of mutations; the composition of vax varies so they consider what serotype and strain should be included in the vaccine ○ Lipid envelope ■ Hemagglutinin protein (HA) - Causes agglutination of RBC - Binds to the receptor ■ Neuraminidase protein (NA) - Enzyme: neuraminidase - Substrate: neuraminic acid (good component of the connective tissues) - Very important for the maturation, budding, exit of the flu virus from the host cell ● Human Immunodeficiency Virus (HIV)
Also has viral proteins on the envelope that are specific for the receptors of the host cell
For example, they are specific for CD 4 receptors, so only those cells with CD 4 receptors are infected (ex. T-helper cells, macrophage)
Epithelial cells are not targeted bc they dont have that receptor ○ Reverse transcriptase
Viral enzyme in the retroviruses
Present in all retroviruses
When it infects the host cell, it is already part of the infecting material
Unlike other viral enzymes (like SARS-CoV 2 ) na tinatranslate siya sa host cell palang using the host ribosome
When the uncoating occurs in the host cell, the reverse transcriptase will cause reverse transcription (RNA - > DNA)
Complementary DNA now integrates into the patient’s chromosomal DNA ● Human Papillomavirus (HPV)
Has 22 faces in the icosahedral symmetry
Causes genital warts
Some strains would have oncogenes (result in cancer like cervical, penile cancer) depending on the strain Influenza A (Flu) Infection ● Genome
8 single stranded RNA ● Segmented nature of genome
Allows for exchange of entire genes between different viral strains during cellular cohabitation
If there is one cell being infected with more than one strain, after uncoating, reproduction of viral RNA, and assembly, there might be exchange of genes between different strains that are infecting the same cell resulting in genetic variation (not only due to mutation but also due to the segmented nature of the genome) ● Components of the host cell ○ Glycoprotein - protein with sugar components (spherical structures) ○ Glycolipid - has sialic acid (N-acetylneuraminic acid; receptor of the host cell for the virus) ● Components of the virus ○ Hemagglutinin - attaches to the receptor Human Immunodeficiency Virus (HIV)
You cannot keep on subculturing if you are working on normal cells bc there is a tendency of chromosomal aberration to take place
Malignant cells are easily grown bc they dont have contact inhibition Viroids ● Circular, single-stranded RNA but no protein-encoding genes
- RNA is very unstable and easily degraded ● No protein coat
- No genes coding for proteins ● Smallest known pathogens
- Not the smallest organism but the smallest known pathogens
- Mycoplasma is the SMALLEST ORGANISM CAPABLE OF GROWING OUTSIDE THE CELL ● Obligate intracellular ● Cause plant diseases
- Coconut cadang cadang disease
- Potato spindle tuber disease
- Chrysanthemum stunt disease Prions
Infectious protein
No DNA or RNA
NOT INTRACELLULAR bc they are attached to the plasma membrane
But are made inside the cell (translated in the ribosomes attached to the RER)
Can arise spontaneously through mutation
- Can be passed along when an animal or human eats infected nervous system tissue
- Can't be destroyed by cooking
● Prpc (normal prion)
- “C” - cellular form
- Present in man and animals
- Coded for by the prnp gene ■ Chromosome 20 - human ■ Chromosome 2 - mouse
- 250 amino acids
- ~ 40 % alpha helix, two 3 - residue beta sheet (less beta form than Prp sc )
- Attach to the plasma membrane of the neuron
○ Glycosyl phosphatidylinositol (GPI)-anchored protein
in lipid rafts of neuron plasma membrane
- Lipid-anchored protein - covalently bonded to glycolipid
- Anchored to the plasma membrane of the nerve cell
- Prion is bound to lipid rafts ○ Probable functions: ■ Cell signaling ■ Homeostatic regulation ■ Influencing synaptic function ■ Protecting neurons against cell death Structure of lipid rafts (Nice to know)
Normal prion vs Diseased prion
- Diseased prion has ore beta sheet ( 40 - 50 %) than normal prion Transformation of Prpc to Prpsc
- Doesnt divide into two ● Sporadic nature ● Genetic mutation ● Acquisition/ingestion - ingesting infected meat
- When the Prp sc binds to Prp c , the Prp c is transformed and folded into the abnormal form
- Each one can cause the transformation to the abnormal form - Neuronal cells produce PrPc (normal prion) which carries out some normal functions in the cell - PrPsc (abnormally folded prion protein) can catalyze refolding of PrPc into PrPsc 1. Nerve cell makes normal PrP proteins 2. Prion version of PrP invades forcing normal PrP to refold into a prion form 3. Unlike normal PrP, prions aren’t naturally destroyed by the cell. They accumulate and eventually kill it 4. Prions move on to other cells and the cycle begins again ● PrP sc (diseased prion) - Protease resistant, insoluble, and forms aggregates in neural cells which eventually leads to destruction of neural tissues and neurological symptoms ○ Mad-cow disease - Starts when molecules in a nervous system protein (PrP) become abnormally folded - When an abnormal PrP touches normal PrP, they refold to match the abnormal ones, forming new prions - Eventually, brain cells become clogged with abnormal proteins
Microbiology - Module 6
Course: Microbiology
University: Angeles University Foundation
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- More from:MicrobiologyAngeles University Foundation152 Documents
