Introduction to Microbiology & Infectious Diseases Flashcards
What is mycrobiology?
study of microscopic organisms
What are the 3 domains? What are the kingdoms and their role
bacteria, archaea, eukarya.
bacteria - many species are important in human health and disease
archaea - no known role in human disease, several species - “normal flora”
protista - includes protozoan (single celled) parasites
plantate
fungi - Important cause of human disease, especially in ICH (immune compromised host)
animalia - Includes multi cellular parasites – ‘worms’
Bacteria, protista, fungi, animalia are the four causing disease.
What are communicable diseases, zoonotic diseases, and opportunistic infections?
Communicable diseases – diseases passed between people through close proximity, social or intimate contact
Zoonotic diseases – diseases transmitted from animals to man
Opportunistic infections – infections caused by micro-organisms that require impaired host defenses to establish infection
How do you name all living things?
All living things have two names
Generic (genus name)
Specific (species name)
Staphylococcus aureus
S. aureus = proper abbreviated name (italicized)
Staph. aureus = common abbreviation ((italicized)
Proper scientific names are italicized.
Staphylococcus sp. = an unnamed species in the genus Staphylococcus
Stapylococcus spp. = multiple species of the genus (italicized) Staphylococcus
Staphylococci – generic term referring to the genus, not italicized
Why do names change for micro-organisms?
Molecular biology continues to challenge our understanding of the relationship between organisms – as new information becomes available, we discover that many organisms have been incorrectly assigned to a genus, thus requiring reassignment and renaming.
What classifies a bacteria?
Single celled organisms – prokaryotes
Contain both DNA and RNA
Usually have a cell wall
May have a capsule
Do NOT have:
A nucleus
Mitochondria
Other membrane bound organelles
What is an atypical bacteria?
Mycoplasma Lack a cell wall Chlamydia Lack peptidoglycan in cell wall Obligate intracellular parasite, require ATP from host Rickettsia Obligate intracellular parasites, require ATP from host Most transmitted by arthropods
What are the characteristics of fungi?
Possess both DNA and RNA
Have a defined nucleus and cell wall
Contain membrane bound organelles
All fungi are capable of asexual reproduction
Most fungi are also capable of sexual reproduction
Fungi capable of both asexual and sexual reproduction have different names for the asexual and sexual states.
What are the two major types of fungi?
Yeast – small, round, unicellular
Mold – grows in the form of filaments (hyphae) that form a tangled mass (mycelium). Often referred to as filamentous fungi - “fuzzies”
What classifies viruses?
Small organisms containing either DNA or RNA but not both
Capable of growth and reproduction ONLY when inside another cell
Lack systematic nomenclature
Viruses causing human disease are commonly named after the disease they cause OR the locality in which they were first isolated.
Measles virus, Mumps virus
West Nile virus, Ebola virus
Classification
DNA vs RNA
Single or double stranded or segmented nucleic acid
ss DNA viruses ds DNA viruses ss RNA viruses ds RNA viruses segmented RNA viruses
What are prions?
A non-living infectious agent, comprised only of protein
Transmit a misfolded protein state – abnormal protein induces normal proteins to covert to the misfolded state
Newly misfolded proteins convert more proteins into the prion state…and so on
Altered proteins are highly stable and accumulate causing tissue damage, dysfunction and cell death
What are parasites?
Organisms adapted to life in (endoparasites) or on (ectoparasites) higher organisms.
Includes single and multicellular (including macroscopic) organisms
Often have complex life cycles
Protozoans – single celled, eukaryotes
Helminths – multicellular organisms, micro or macroscopic (‘worms’)
Roundworms, tapeworms and flukes
How are bacteria organized?
How do we organize bacteria? Shape and organization Oxygen requirements Spore formation Staining patterns - these first ones are simple lab tests Metabolic processes Immunologic features Genetics these last ones are more complicated testing
What are the shapes?
coccus - round, diplococci are two round together, streptococci are multiple in a chain, staphylococci are triangle bunches of forms together.
bacilli - coccobacilus are oval, bacilus is oval and elongated like a rectangle with rounded edges,
vibrio - looks like a bean
what are the oxygen requirements?
Strict aerobes – require normal atmospheric levels of oxygen to grow
Facultative – grow in both aerobic and anaerobic environments. Use either aerobic or anaerobic metabolism (fermentation or anaerobic respiration) to generate energy. Anaerobic energy generation is less efficient than aerobic metabolism.
Aerotolerant – use only fermentative metabolism but are not killed in the presence of oxygen
Microaerophilic – require oxygen tensions to grow but at levels less than 21%; often require increased levels of CO2 (capnophilic).
Strict anaerobes – no growth in the presence of oxygen; some species are killed by oxygen.
Thioglycollate broth - test used, Tube1 – no growth at top – anaerobic
Tube 2 – only growth at top – aerobic
Tube 3 - Uniform growth throughout – aerotolerant
Tube 4 – growth throughout but best at top - facultative
Tube 5 – best growth near top of tube but not right at surface - Microaerophilic
What about spore formation? why do they do spores and what’s so bad about them?
The formation of spores is an important feature of some species of bacteria. Spore formation is typically a feature of gram positive bacilli.
Generalization: Spores are not formed by:
Medically important cocci
Medically important gram negatives
Aerobic spore forming bacilli
Bacillus spp: anthrax, food poisoning
Anerobic spore forming bacilli
Clostridium spp: tetanus, botulism, C. difficile
Spores help organisms survive times of adversity.
Lack of nutrients
Lack of moisture
Lack or excess of oxygen
Exposure to heat, radiation, toxic chemicals
Spores can survive for very long periods of time – perhaps thousands of years!
Responsible for disease transmission from food, environment, or other individuals.
Anthrax, Tetanus
Clostridum difficile infection
Responsible for disease relapse despite treatment.
Clostridium difficile relapses
What about bacterial staining?
Stains are chemical dyes that interact with molecules in the cell wall of the organism
Different types of bacteria take up stain differently (or not at all) based on structure.
Staining features help with rapid identification
General stains – general purpose: Identify presence and morphology of bacteria
Differential stains – different organisms take up stain differently: categorization of organisms based on staining characteristics
Special stains
Stains to identify specific bacterial features
Stains used for hard to visualize organisms
What are the general stains and differential stains?
General (Simple) stains – methylene blue
Differential stains
Gram stain: differentiates most bacteria into gram positive or gram negative based on cell wall structure
Acid Fast Stains: used for staining Mycobacteria and Nocardia - waxy material in cell walls repels gram stain
What is gram stain?
Differential stain – gram positive, gram negative, gram variable
Why is the gram stain so important in microbiology?
Crystal violet is retained by gram positive cell walls.
Crystal violet is NOT retained by gram negative cell walls. Safranin (pink) is used as a counterstain to visualize gram negatives.
You fix, then use crystal violet, the gram positive will retain this, you treat them with iodine and there will be decolorization with this, the negative will turn back clear and the gram positive will stay purple. Then you counter stain using sfranin (pink) which will then make the gram negative appear pink while the positive remains pruple.
Staining characteristics are based on major differences in cell wall structure – these characteristics correlate with other important features:
Ecology
Antibiotic susceptibility
Gram positive - have thick cell wall, no outer envelope
Gram negative have a thinner cell wall with outer envelope, that’s why the gram negative repels the dye, because it has that outer envelope.
How many organisms do you need to see gram stain?
In order to see organisms on a gram stain, there must be at least 104 to 105 organisms per ml.
Gram staining will also demonstrate human cells – this is critically important when staining specimens from NON STERILE sites where bacterial are expected to be present.
We can detect the presence of an inflammatory response (numerous pus cells – PMNs) which is indicative of true infection rather than contamination or colonization.
What’s a pathogen, infection, and disease?
A few more definitions
Pathogen: a micro-organism that has potential to cause disease
Infection: invasion and multiplication of pathogenic micro-organisms
Disease: infection causes damage to host tissues or function
NOTE: infection does not always = symptomatic disease
