1-Introduction to Medical Microbiology Flashcards
What are some characteristics of viruses?
Smallest infectious particles, ranging in diameter from 18-600 nm.
a. most are less than 200 nm and cannot be seen by a light microscope
more than 2,000 species of viruses have been described, and 650 are associated with infecting humans.
Consist of either DNA or RNA (but not both) and may contain proteins required for replication and pathogenesis.
True parasites, requiring host cells for replication.
Cells they infect and the host response to the infection dictate the nature of the clinical manifestation.
What are some general characteristics of bacteria?
Relatively simple in structure.
Prokaryotic organisms – simple unicellular organisms with no nuclear membrane, mitochondria, Golgi bodies, or endoplasmic reticulum – that reproduce by asexual division.
The cell wall is complex, consisting of two basic forms:
gram-positive cell wall with a thick peptidoglycan layer.
gram-negative cell wall with a thin peptidoglycan layer and an overlying outer membrane.
Some bacteria lack this cell wall structure and compensate by surviving only inside host cells or in a hypertonic environment.
The size (1-20 µm or larger), shape (spheres, rods, spirals), and spatial arrangement (single cells, chains, clusters) of the cells are used for the preliminary classification of bacteria, and the phenotypic and genotypic properties of the bacteria form the basis for the definitive classification.
Human body is inhabited by thousands of different bacterial species – some living transiently, others in a permanent parasitic relationship.
Also, our environment (air, water, food, etc.) is inhabited by bacteria, many of which are relatively avirulent and some of which are capable of producing life-threatening disease.
Disease can result from the toxic effects of bacterial products (toxins) or when bacteria inhabit normally sterile body site.
What are some general characteristics of fungi?
Cellular structure of fungi is more complex.
Eukaryotic organisms that contain a well-defined nucleus, mitochondria, Golgi bodies, and endoplasmic reticulum.
Can exist in two forms:
a unicellular form (yeast) that can replicate asexually.
A filamentous form (mold) that can replicate asexually and sexually.
Exist as either yeasts or mold; however, some fungi can assume either morphology.
What are some general characteristics about parasites?
Most complex microbes.
All classified as eukaryotic; however, some are unicellular and others are multicellular.
Range in size from tiny protozoa as small as 1-2 µm in diameter (size of many bacteria) to arthropods and tapeworms that can measure up to 10 meters in length.
Life cycles are complex, with some parasites establishing a permanent relationship with humans and others going through a series of developmental stages in a progression of animal hosts.
What are exogenous infections?
Some diseases arise when a person is exposed to organisms from external sources. These are known as exogenous infections.
Examples: diseases caused by influenza virus, Clostridium tetani, Neisseria gonorrhoeae, Coccidioides immitis, and Entamoeba histolytica.
What are endogenous infections?
Most human diseases, however, are produced by organisms in the person’s own microbial flora that spread to inappropriate body sites where disease can ensue (endogenous infections).
What are the 3 limitations for the lab to provide a definitive Dx of a bacterial infection?
- The quality of the specimen collected from the patient.
- The means by which it is transported from the patient to the laboratory.
- The techniques used to demonstrate the microbe in the sample.
