Module 5: Chapter 15 Flashcards
tests that can be performed at the bedside, meaning samples do not have to be sent out and patient care can continue without delay
point-of-care testing/diagnosis
scans often used to diagnose peritonsillar abscesses
computerized tomography (CT) scans
scan used to find areas of deep tissue infection
magnetic resonance imaging (MRI) scan
position emission tomography (PET) scan
refers to the traits that an organism is expressing in the present
phenotype
method of microbial identification:
observation of microbe’s microscopic and macroscopic morphology, physiology, and biochemical properties; involves examining their appearance and behavior ( behavior = enzymatic activities they carry out, what kind of physical conditions they thrive in, what antibiotics it is susceptible to, and the chemical composition of its walls and/or membrane)
phenotypic methods
method of microbial identification:
the nature of the antibody response is exploited for diagnostic purposes when a patient sample is tested for the presence of specific antibodies to a suspected pathogen (antigen)
analysis of microbe using antibodies, or of patients’ antibodies using prepackaged antigens
alternatively, microbial antigens in the patient’s tissues can be tested with antibodies “off the shelf” (these methods can be easier than trying to isolate the microbes itself.
immunologic methods
methods of microbial identification:
analysis of microbe’s DNA or RNA
ie. numerous viable nonculturable (VNC) microbes are currently being identified in this manner through studies such as the Human Microbiome Project
genotypic methods
primary advantages of genotypic methods over phenotypic methods
culturing of the microorganisms is not always necessary
genotypic methods are increasingly automated, producing rapid results that are often more precise than with phenotypic methods
15.1 outcome
list the three major categories of microbial identification and a one sentence description for each
- Phenotypic methods: examining the appearance and behavior (enzymatic activities, physical conditions it thrives in, antibiotics its susceptible to, chemical comp of walls/membranes)
- Immunologic methods: examining the antibodies present in a patient’s sample, to see if the antibodies link to the suspected antigens; antigens in the patients tissues can be tested with antibodies “off the shelf”
- Genotypic methods: examining a microbes genetic material (RNA or DNA
15.2 First Steps: Specimen Collection
the success of identification and treatment depends on how specimens are:
collected, handles, stored, and cultured
in specimen collection it is important that general _______ procedures be used, including sterile sample containers and other tools to prevent contamination from the environment or patient.
aseptic
throat and nasopharyngeal swabs should not touch the cheeks, tongue, or _____.
saliva (saliva contains millions of bacteria per milliliter, most of which is normal biota)
mucus secretion that coats the lower resp surfaced, especially the lungs; is discharged by coughing or taken by a thin tube called a catheter to avoid contamination with saliva
sputum
saliva samples may be needed for dental diagnosis and are obtained how?
having the pt spit or drool into a container
the mucous lining of the urethra, vagina, or cervix can be sampled with a swab or _______
applicator
depending on the nature of a skin lesion, skin can be swabbed or scaped with a scalpel to expose deeper layers; wounds are sampled either by _______ or by using a __________
swabbing or a punch biopsy tool
fluids such as blood, cerebrospinal fluid, and tissue fluids must be taken by _______ _______ _______
; antisepsis of the puncture site is extremely important in these cases
sterile needle aspiration
name some additional sources of specimen besides urine, blood, CSF, mucous secretions, and sputum
eye, ear canal, synovial fluid (joint fluid), nasal cavity (all by swab), and diseased tissue that has been surgically removed (biopsied)
nonsterile samples such as urine, feces, and sputum, are especially prone to deterioration at
room temperature
nonnutritive maintenance media
a media used to maintain specimens in stable conditions for several hours, but will but grow them
before collecting a specimen, what should your analyze a patient for?
signs of microbial infection such as fever, wound exudate, mucus production, abnormal lesions
the time required for testing _______
ie. a few minutes for rapid strep testing to several weeks for tuberculosis testing
varies
- 2 outcomes
- identify factors that may affect the identification of an infectious agent from a sample
- compare the types of tests performed on microbial isolates versus those performed on patients themselves
1.
- improper collection technique
- collection, transport, storage, labeling
- Microbes: analysis involves
- Direct testing using microscope, immunologic or genetic methods that provide clues to identify the microbes.
- Cultivation, isolation, and identification of pathogens using a wide variety of general and specific tests.
Patients: tests on patient serum provide indirect evidence for specific pathogens though analysis of the antibody response. Skin testing can be used or some pathogens can be identified solely on the patient’s signs and symptoms
15.3 Phenotypic Methods
most used stains for bacterial identification
Gram stain and acid-fast stain
but as useful as these stains are they can identify only a few organisms on their own
direct microscopic observation of a fresh or stained specimen is one of the most ______ methods of determining presumptive and sometimes confirmatory microbial characteristics
rapid
in cases where the suspected pathogen is present in small amounts or is easily overgrown by normal biota, the specimen can be initially enriched with ____________ media.
specialized
nonsterile specimens containing a diversity of bacterial species, such as urine and feces, are cultured on _______ media to encourage the growth of only the suspected pathogen
selective
specimens are often inoculated into _________ media to identify definitive characteristics, such as reactions in blood (blood agar) and fermentation patters (mannitol salt and MacConkey agar)
differential media
dichotomous key
a graphic method that is essentially a flowchart leading to the identification of specimens
“di” refers to the fact that at each branch of the flowchart there are two (di) possible outcomes
a straightforward way to phenotypically identify specimens is to combine the results of tests such as gram staining (neg or pos?), growth on different media, and simple enzymatic tests —–> this can form the starting point for what
dichotomous key
cocci —>
gram + or gram - —>
gram + = Catalase + (irregular clusters, tetrads) or catalase - (pairs, chain arrangement) —>
catalase - = Streptococcus
catalase + = strictly aerobic or facultative anaerobic
strictly aerobic = micrococcus
facultative anaerobic = Staphylococcus/Planococcus
example of gram + dichotomous key
what technique in this chapter do most home pregnancy test kits utilize?
the lateral-flow test, which is an immunochromatographic method
Biochemical testing:
the physiological reactions of bacteria to nutrients and other substrates provide excellent evidence of the types of ______ systems present in a particular species;
knowing which ____ an isolate has can often leas to its identity
enzyme
enzymes
many biochemical testing are based on ________-mediated metabolic reactions that are visualized by a color change
enzyme
in enzyme-mediated biochemical testing the microbe is cultured in a medium with a special substrate and then tested for a particular end product.
microbial expression of the enzyme is made visible by a colored dye, no coloration means it ________ the enzyme for utilizing the substrate in that particular way
lacks
Mycobacterial Growth Indicator Tube (MGIT)
a type of phenotypic test used to detect the growth of slow-growing Mycobacterium tuberculosis
—> this system monitors oxygen levels in a tube that has been inoculated with a patient specimen (blood, sputum), tube contains medium that encourages growth of the tuberculosis bacterium; ***there is a silicon chip at the bottom of the tube that is impregnated with a fluorescent substance that is sensitive to oxygen
–> when first inoculated, there will be a lot of free oxygen in the medium because even if the bacteria are present, there will not be many of them
BUT, if the bacteria grow, they begin using the oxygen, and the decreased levels of O2 allow the silicon compound to fluoresce
antimicrobial susceptibility testing and phenotypic methods
most of the automated phenotypic systems incorporate a panel of commonly used antimicrobials for the particular infection site; and simultaneously test susceptibility while IDENTIFYING the pathogen;
*** commonly completed using an adaptation of the tube-dilation method (chapter 12)
–> these tests themselves can identify some species like Streptococcus, Clostridium, and Pseudomonas
