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Answer on topics (Test 1 prep)
Terms in this set (17)
Define the following terms and give three examples of each: sterilization, disinfection, and antisepsis
There is not a uniform definition of sterilization and disinfection. In general sterilization represents the total destruction of all microbes including the more resilient forms such as bacterial spores, mycobacteria, nonenveloped viruses, and fungi. Examples of agents used for sterilization are ethylene oxide, formaldehyde gas, hydrogen peroxide, peracetic acid, and glutaraldehyde. Disinfection results in the destruction of most organisms, although the more resilient microbes can survive some disinfection procedures. Examples of disinfectants include moist heat, hydrogen peroxide, and phenolic compounds. Antisepsis is used to reduce the number of microbes on the skin surfaces. Examples of antiseptic agents include alcohols, iodophors, chlorhexidine, parachlorometaxylenol, and triclosan.
Name the three mechanisms bacteria use to become resistant to β-lactam antibiotics. What is the mechanism responsible for oxacillin resistance in Staphylococcus? Imipenem resistance in Pseudomonas? Penicillin resistance in S. pneumoniae?
Bacteria can become resistant to β-lactam antibiotics by (1) degrading the antibiotic with β-lactamases
(2) modifying the target (i.e., Penicilin binding protein - transpeptidase) so that either a new PBP is acquired by the organism or an existing PBP is altered, producing an enzymatically active PBP that is not recognized by the antibiotic
(3) preventing access to the target by creating a permeability barrier (e.g., change in porins in gram-negative cell wall).
Oxacillin resistance in Staphylococcus:
Staphylococcus aureus organisms become resistant to oxacillin and related β-lactams by acquiring a new PBP that is enzymatically active (e.g., can be used to build the peptidoglycan layer in the cell wall) but is not bound and inactivated by the antibiotic.
Imipenem resistance in Pseudomonas:
Pseudomonas aeruginosa can become resistant to imipenem by one of two mechanisms:
(1) acquisition of a β-lactamase that degrades the carbapenem antibiotic; or
(2) alteration in the outer membrane of the cell wall (i.e., porin mutation) that prevents entry of the antibiotic into the cell.
Penicillin resistance in S. pneumoniae:
Streptococcus pneumoniae organisms become resistant to penicillin when they acquire an altered PBP (through recombination)
List examples of direct microscopic examinations, differential stains, acid-fast stains, and fluorescent stains.
Direct microscopic examination:
Suspending the sample in water
(e.g., wet mount for fungi) or a contrasting dye (e.g., lactophenol cotton blue for fungi or iodine for parasites).
Differential stains are used commonly to detect
bacteria (e.g., Gram stain, acid-fast stain), parasites (e.g., iron hematoxylin and trichrome stains), and blood-borne pathogens
(e.g., Giemsa stain for Borrelia and Plasmodium).
A variety of acid-fast stain methods have been developed (e.g., Ziehl-Neelsen, Kinyoun, fluorochrome) that detect
(Mycobacterium, Nocardia, Rhodococcus) and
(Cryptosporidium, Cyclospora, Isospora).
Common fluorescent stains have been used to detect fungi (calcofluor white stain) or acid-fast organisms (auramine-rhodamine stain).
How do the differences between gram-positive and gram-negative cell walls influence the cells' clinical behavior, detection, and treatment?
The thickness of the Gram-positive membrane facilitates its identification by the Gram stain by trapping the stain, whereas the gram-negative peptidoglycan is only a single layer thick, and the stain washes away during the procedure, requiring use of a counterstain. The LPS present in the outer membrane is the most potent activator of innate and immune functions of any cell wall component and can induce fever and sepsis. Gram-negative bacteria are more likely to induce fever and sepsis due to their endotoxin in the membrane. The presence of the outer membrane of gram-negative bacteria provides a unique barrier to complement, to the permeability of large and hydrophobic molecules, and prevents access to peptidoglycan and other internal bacterial structures, including antibacterial drugs.
Describe the microscopic morphology (e.g., Gram-stain characteristic, shape of organism) of the following bacteria: Staphylococcus, Escherichia, Neisseria, Clostridium, Enterococcus, and Pseudomonas.
Staphylococcus: (Positive, golden pigment, cluster of spherical shaped bacteria)
Escherichia: (Negative, rod shaped)
Neisseria - (Negative, diplococci which resemble coffee beans)
Clostridium - (Positive, spore forming rod, resemble chicken drums/tennis rods)
Enterococcus - (Positive, spherical, alpha hemolytic)
Pseudomonas - (Negative, rod shaped, aerobic)
How are microbes able to resist immunologic clearance? Give at least one specific example of each mechanism.
Encapsulation. Example: antiphagocytic: Streptococcus pneumoniae
Intracellular growth. Example: Francisella tularensis
Anti-immunoglobulin proteases. Example: Neisseria gonorrhoeae
IgG binding proteins. Example: Staphylococcus protein A
Inhibition of phagolysosome fusion. Example: Legionella, Mycobacterium tuberculosis
Resistence to lysosomal enzymes. Example: Salmonella typhimurium.
What are the principal properties of a plasmid?
A plasmid is extrachromosomal, circular DNA with an origin of replication (allows replication) and often contains genes for antibiotic resistance, metabolism of unusual molecules (e.g., Pseudomonas) or virulence.
Give examples of strict pathogens and opportunistic pathogens.
Strict pathogens are organisms that are almost always found in the setting of disease. Some examples of strict pathogens are Mycobacterium tuberculosis, Clostridium tetani, Neisseria gonorrhoeae, Francisella tularensis, Plasmodium falciparum, and rabies viruses. Most human infections are caused by opportunistic pathogens; that is, organisms that can colonize humans without evidence of disease or cause disease when introduced into normally sterile tissues or into a patient with defective immunity. Some examples of opportunistic pathogens are Staphylococcus aureus, Escherichia coli, Pseudomonas aeruginosa, and Candida albicans.
Which organisms are important causes of bacterial pharyngitis?
Streptococcus pyogenes (group A Streptococcus) is the most common cause of bacterial pharyngitis. Other bacteria that can cause pharyngitis include Streptococcus dysgalactiae (group C or G Streptococcus), Arcanobacterium haemolyticum, Neisseria gonorrhoeae, Chlamydophila pneumoniae, and Mycoplasma pneumoniae. Corynebacterium diphtheriae and Bordetella pertussis can also cause pharyngitis but are uncommonly isolated in the United States.
The inactivated polio vaccine is administered intramuscularly, whereas the live polio vaccine is administered as an oral vaccine. How do the course of the immune response and the immunoglobulins produced in response to each vaccine differ? What step in poliovirus infection is blocked in a person vaccinated by each vaccine?
The inactivated polio vaccine elicits a predominantly antibody TH2 response. This antibody does not prevent infection but is sufficient to block the progression of a polio virus in the bloodstream from reaching its target tissue (muscle and brain) and hence prevents disease.
The oral vaccine infects the individual with attenuated mutants of the three types of poliovirus to initiate a natural response to each virus, including a secretory IgA response. The development of memory cells is stronger and more permanent.
Detection of group A streptococci and their distinction from other streptococci
Group A Streptococcus can be detected by ELISA techniques, including rapid methods (similar to the over-the-counter pregnancy tests) for detecting streptolysin A and S. Fancier techniques such as pulsed field gel electrophoresis of restriction fragments of the chromosome and PCR can be used to distinguish different strains.
Describe the diagnostic procedure or procedures (molecular or immunologic) that would be appropriate for Determination of the apparent molecular weights of the
to separate the proteins and
to identify the HIV proteins are appropriate.
Describe the diagnostic procedure or procedures (molecular or immunologic) that would be appropriate for Detection of human papillomavirus 16 (a nonreplicating virus) in a Papanicolaou (Pap) smear
Genome detection methods such as in situ hybridization on the Pap smear or a polymerase chain reaction of the cells obtained during the procedure can be used since virus proteins would be undetectable.
Describe the diagnostic procedure or procedures (molecular or immunologic) that would be appropriate for Detection of herpes simplex virus (a replicating virus) in a Pap smear
Cytopathologic effects such as syncytia or Cowdry type A inclusion bodies can be seen in Pap smears. Genome detection methods such as in situ hybridization on the Pap smear or a polymerase chain reaction of DNA obtained from the the cells or immunologic methods to detect virus antigen can be used to detect evidence of the virus.
Describe the diagnostic procedure or procedures (molecular or immunologic) that would be appropriate for
An Ouchterlony antibody diffusion or ELISA method can be used to detect fungal antigens.
Describe the diagnostic procedure or procedures (molecular or immunologic) that would be appropriate for Presence of Histoplasma fungal antigens in a patient's serum CD4 and CD8 T-cell concentrations in blood from a patient infected with HIV
Flow cytometry using immunofluorescence is probably the best method for identifying and quantitating CD4 and CD8 T cells.
How does each of the differences between prokaryotes and eukaryotes influence bacterial infection and treatment?
Size: The smaller size of prokaryotes allows them to enter smaller spaces. It also means that the cells have a smaller chromosome.
Nuclear structures: The lack of a nuclear membrane allows chromosome replication, transcription, and translation to be tied together. Inhibition of any one of them affects the others to a greater degree.
Chromosomes: The bacterial chromosome is a single, circular genome. As a circular chromosome, topoisomerases are very important to relieve stress on the structure and to maintain its function. As a result, these enzymes are excellent targets for antibacterial drugs e.g., quinolones. Having only one copy of each gene (haploid genome) instead of a diploid genome means that a single mutation will inactivate a function, because there is no "backup copy."
Cytoplasmic structures: Prokaryotes lack organelles, but this does not have a big effect on bacterial infection and treatment.
Ribosomes: The 70S (50S + 30S) provides an excellent target for antibacterial drugs because it differs so significantly from the 80S eukaryotic ribosome.
Cytoplasmic membrane: The prokaryotic membrane contains different phospholipids, which makes it susceptible to polymyxin action.
Cell wall: The bacterial cell wall is a complex structure containing protein, lipids, and peptidoglycan, which is unique to bacteria. The cell wall provides sufficient strength against osmotic shock to allow bacteria to exist in distilled water. It contains structures that promote interactions with tissues and target cells to promote and define the types of infections and diseases caused by bacteria; the enzymes which synthesize these structures are sufficiently unique to be excellent targets for antibacterial drugs (e.g., beta-lactams, vancomycin, bacitracin). Pili are very important for promoting adhesion which allows the bacteria to attach and maintain their location in the body (e.g., in the bladder).
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