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56 Cards in this Set
- Front
- Back
When microbes cause disease, the nature and extent of disease depend on:
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When microbes cause disease, the nature and extent of disease depend on:
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What must happen in order for infection to occur? |
For infection to occur, local defences have to be undermined, and/or the organisms have to develop strategies to overcome barriers |
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What is the innate immune response, and what are some examples of it? |
Innate immune response refers to the first line of defence, which does not adapt to repeated attacks, e.g. physical barriers, phagocytic cells, complement and inflammatory response |
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What is the adaptive immune response? |
Adaptive immune response refers to responses mediated by T and B cells, stimulated by each exposure to an antigen, and these response will improve which each successive contact |
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What are the various classes of human pathogens? |
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What is the structure of bacteria?
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Bacteria are prokaryotic cells with cell walls made up peptidoglycans (mixture of sugars and amino acids). Depending on whether the cell walls retain cyrstal violet stain, they are classified Gram negative or Gram positive. The main shapes are spherical (cocci) and rod-shaped (bacilli) |
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How does Gram staining differentiate between Gram positive and Gram negative bacteria? |
Gram positive bacteria are stained purple. Gram negative bacteria are stained red. |
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How does Gram staining work? |
Crystal violet is used to stain a fixed plate. Iodine is then applied to fix the stain. The excess dye is then washed off with ethanol. The plate is then counterstained with a counterstain such as safranin. |
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What is the principle behind Gram staining? |
Gram-positive bacteria have a thick mesh-like cell wall made of peptidoglycan (50–90% of cell envelope), and as a result are stained purple by crystal violet, whereas gram-negative bacteria have a thinner layer (10% of cell envelope), so do not retain the purple stain and are counter-stained pink by the safranin. |
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Viruses c____________ the host cell's b___________ and r__________ a__________ for their own p____________. They cannot be seen by light microscope, but often form characteristic ____________ ________ in infected cells. |
Viruses commandeer the host cell's biosynthetic and replicative apparatus for their own proliferation. They cannot be seen by light microscope, but often form characteristic inclusion bodies in infected cells. |
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Fungi have t_____ cell walls, and can grow as r________ y_____ cells or s______ f___________ h______ (______). In immunocompetent people, they usually only cause superficial infections involving the skin, hair and nails (dermatophytes, e.g. ringworm). |
Fungi have thick cell walls, and can grow as rounded yeast cells or slender filamentous hyphae (mould). In immunocompetent people, they usually only cause superficial infections involving the skin, hair and nails (dermatophytes, e.g. ringworm). |
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How do fungi cause disease? (3 ways) |
Fungi cause disease by
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Protozoa are s______ c______ e__________ that can survive within the human body (____________ and _____________). |
Protozoa are single celled eukaryotes that can survive within the human body (intracellular and extracellular). |
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How are protozoa infections transmitted? What are some examples of each category? |
Modes of transmission of protozoa:
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Helminths (p________ _______) are highly d______________ m____________ o___________. They often have c________ life cycles. |
Helminths (parasitic worms) are highly differentiated multicellular organisms. They often have complex life cycles. |
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What are the three classes of helminths? |
The three classes of helminths are:
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How do helminths cause disease? |
Helminths cause disease
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What are the common factors in parasitic infections? |
The common factors in parasitic infections are
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What are the various host barriers? |
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How does the skin function as a host barrier? |
The skin is a protective keratin layer. Its normal pH and fatty acids inhibit microbial growth, and it is constantly shed and renewed. Most micro-organisms penetrate through breaks in the skin. |
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How does the GI tract function as a host barrier? |
Gastric acid, viscous mucus secretions, pancreatic enzymes and bile, antimicrobial peptides, IgA antibodies and normal gut flora are all part of the GI host defence. |
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What are the methods used by microbes to penetrate through the GI barrier, and what are examples of each method? |
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How does the respiratory tract function as a host barrier? |
Large microbes are trapped in the nose and upper respiratory tract by mucus. They are then transported by ciliary action of the respiratory epithelium to the back of the throat, where they are swallowed. Smaller organisms which are inhaled are phagocytosed by alveolar macrophages. |
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What are the methods used by microbes to penetrate through the respiratory tract, and what are examples of each method? |
Virulent pathogens evade defences by
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How does the urogenital tract function as a host barrier? |
The urinary tract is usually sterile as it contains filtered fluid, and is flushed many times a day. The vagina is protected by low pH produced with the help of commensal lactobacilli |
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What factors are likely to lead to infection via the urogenital route? |
Obstruction and stasis in the urogenital tract increase the risk of infection. Pathogens can adhere to the epithelium (e.g. E. coli) |
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What are the various ways in which infections can be transmitted from one person to another? (Total: 7) |
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How does the infection spread after getting inside its host? (Total: 6 ways) |
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How do microorganisms evade the immune system? (Total: 6 ways) |
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What are the general mechanisms through which microorganisms cause disease? |
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How do bacteria in particular cause disease? |
Bacteria
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How do viruses in particular cause disease? |
Viruses
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How are bacterial infections diagnosed? |
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How are viral infections diagnosed? |
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What are the various inflammatory responses to infection? |
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What are some causes of immunosuppression? |
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What factors predispose hospital patients to getting infections? |
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What are some examples of viruses, and the mechanisms through which they cause disease? |
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What is the structure of influenza? |
Influenza virus consist of single-stranded RNA bound by nucleoprotein (A/B/C determines its type). The spherical surface of the virus is a lipid bilayer containing viral haemagglutinin and neuraminidase, which determines the subtype of the virus. |
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What type of influenza virus is the major cause of epidemics and pandemics? |
Type A influenza virus Example: Avian influenza is caused by certain type A strains of the virus |
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What is SARS, and what is the microorganism causes it? How is the infection transmitted? |
Severe acute respiratory syndrome (SARS) is caused by coronavirus (SARS-CoV). This coronavirus is able to cause severe pneumonia. Transmission is by close personal contact |
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What is MERS, and what is the microorganism causes it? What are the manifestations of infection? |
Middle East Respiratory Syndrome (MERS) is caused by the MERS-coronavirus (MERS-CoV). It causes severe pneumonia and renal failure |
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What is an example of a viral infection increasing the risk of cancer? How does it increase the risk of cancer? |
Human papilloma virus (HPV) is an oncogenic DNA virus. Viral infection affects normal growth-regulating proteins, resulting in transformed cells, which are capable of autonomous growth and are susceptible to acquisition of future mutations |
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What is an example of a chronic latent viral infection? How does it cause disease? |
Herpes zoster or varicellar zoster virus (VZV) is the virus that causes chickenpox during its primary infection. The virus then establishes latent infection in the neurons of the dorsal root ganglia. Reactivation in adults manifests as painful vesicular skin eruption in skin supplied by that nerve, a disease known as shingles |
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What is an example of a virus that can have different outcomes? What are the various outcomes it leads to? |
Hepatitis B virus (HBV) causes damage to virus-infected cells by CD8+ cytotoxic T cells. If the immune system is not properly calibrated to clear virus, it may cause widespread liver damage.
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What is the life cycle of the HIV? |
HIV requires CD4+ molecule to enter cell. Upon entering, its viral DNA integrates into the host genome. The virus mainly resides in the lymph nodes and spleen. It also infects macrophages and monocytes. The virus constantly varies the antigens on expressed proteins to evaded the immune system. Host proliferation eventually leads to cell death. When CD4+ counts become very low, there is a breakdown of host defenses and clinical disease ensues |
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What is Pneumocystis jirovecii? |
Pneumocystis jirovecci is a fungus that causes opportunistic infections. Pneuomnia due to this is the frequent presenting illness of AIDS, and is known as PCP. This is usually the result of a re-activation of previous infection |
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What are the various opportunistic infections seen in ADIS patients? |
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What are some neoplasms that HIV infected patients have a high risk of developing? |
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What is an example of a bacteria that causes pyogenic bacterial infections? |
Staphylococcus aureus induces large amounts of localized suppuration, i.e. pus, which consists of neutrophils, necrotic cells and edema fluid. S. aureus is a Gram+ bacterium that is found on the skin. Some strains are antibiotic resistant (known as MRSA). Some strains produce potent toxins which may food poisoning. Localized infection of the skin by toxin-producing bateria may cause bullous impetigo; septicemia may cause blistering at many sites |
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What are the diseases that Streptococcus pneumoniae causes? |
Strep pneumoniae is a Gram+ bacterium that colonizes the respiratory tract. It is a common cause of community-acquired pneumonia, and affects especially pts with congenital or acquired Ig defects, and those with decreased or absent splenic function. It can also cause acute otitis media and mengitis. Its virulence is due to its invasiveness and thick capsule |
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What are the effects of released cytokines in Gram- septicemia? |
May lead to septic shock and multiorgan failure |
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What is the microorganism causing meningococcal disease? How is it spread? |
Menigococcal disease is caused by Gram- coccus Neisseria meningitidis. It is spread by droplets. It causes meningitis and Gram- septicemia; pts will have a characteristic rash. |
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What are the symptoms of Clostridium difficile infection? |
Cytotoxin-producing strains of Clostridium difficile may overgrow after systemic antibiotic use, resulting in psuedomembranous colitis and severe diarrhea |
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What is malaria, and how does it develop? |
Malaria is caused by a protozoa (several types of Plasmodium), and leads to paroxysmal fevers and anemia. In humans, the parasite mainly resides in the liver and in RBC. Fever coincides with rupture of RBC and release of parasites. Anemia is caused by RBC destruction. Plasmodium falciparum may cause cerebral malaria - high levels of parasites causes the infected RBC to become sticky and occlude capillaries in the brain |
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What is amoebiasis, and how does it develop? |
Amoebiasis is caused by protozoan Entamoeba histolytica. The cysts are ingested, and 'hatch' into amoebae. They cause damage to the mucosa of the colon, resulting in abdominal pain and diarrhea. May spread to the liver, causing amoebic abscesses |