Unit 2 Flashcards
Colony morphology is defined as
Colony characteristics
Which of the following descriptions will directly facilitate ID of bacteria?
Physical characteristics of colony morphology
An upper respiratory specimen contains many indigenous organisms which may be time consuming, cost prohibitive and insurmountable. What should the microbiologist do?
Differentiate the potential pathogens from the “usual” inhabitants of the upper respiratory tract and direct the diagnostic work up only to potential pathogens
When microbiologists set up a biochemical ID using a commercial system on a suspected pathogen from a culture, they must
Correlate colony characteristics with the suspected ID of the organism
Generally, microbiologists observe the colonial morphology of organisms on primary culture after how many hours of incubation?
18-24 hours
Plate reading is
A comparative examination of bacteria growth on a variety of culture media
MacConkey (MAC) agar is used to
Differentiate between lactose fermenters and lactose nonfermenters
A microbiologist is reading stool culture plates. She is looking for enteric pathogens on the MAC plate. What do they look like?
Clear, colorless colonies
A microbiologist is reading still culture plates. She sees an organism that has dry, pink colony with a surrounding “halo” of pink on MAC. What is a good presumptive ID of this organism?
Escheriochia/citrobacter-like organism
The relative concentration of bacteria on culture plates in directly proportional to
The concentration in which they are present in the clinical specimen
Alpha Beta-hemolysis is
Partial lysing of erythrocytes in a BAP around and under the colony
Beta (beta)-hemolysis is
Complete clearing or erythrocytes in a BAP around and under the colony
Gamma (y)-hemolysis is
When organisms have no lytic effect on the erythrocytes in the BAP
Colonies growing on the SBA have discolored the media to a green color around and under the colonies. This is consistent with which type of hemolysis?
Delta
The colonies growing on the SBA have produced a wide, deep, clear zone around and under the colonies. This is consistent with which type of hemolysis?
Gamma (no hemolysis)
When differentiating colony size on the culture place, what organisms generally have the larger colonies by comparison?
Gram-negative rods
The edge of the colonies is described as all the following except
Glasslike
Colonies of Bacillus anthracite are described as
Medusa’s heads
Swarming is
A hazy blanket of growth on the surface of the agar that extends way beyond the streak lines
A microbiologist is a reading a vaginal culture. She sees the very white colonies that are non-hemolytic on a BAP but appear to have feet. What organism could this possibly be?
Yeast
The elevation of bacterial colonies is described by all of the following except
Pointed
A term used to describe colonies that resemble coins is
Umbilicate
The density of the bacterial colony can be described by all the following, except
Ground glass
The term used to describe colonies that are solid in color and that do not allow any light to pass through it
Opaque
All of the following terms are used to describe the consistency of a bacterial colony, except
Smooth
All of the following colors are commonly used to describe bacteria, except
Orange
What organism forms a small, fuzzy-edged colony with an umbonate center on blood or CHOC agar?
Eikenella corrodens
When looking at a tube of thioglycollate broth, streamers or vines and puffballs are visible. What organism grows like this is thioglycollate?
Streptococcus spp.
All of the following characteristics are used to describe bacterial colony characteristics except
Temperature
Nucleic Acid hybridization is
Coupling of complementary single-stranded nucleic acid molecule
The target nucleic acid strand is
The DNA or RNA sequence unique to the organism of interest
The probe is
Used to detect the target nucleic acid molecule
Common uses of probes include all of the following except
Abnormal WBC detection
The variables that affect the outcome of a given hybridization reaction include all of the following except
Organic acid concentration
How is the stability of a given hybrid calculated?
By determining the melting temperature of a probe
How do high probe concentrations affect a given by hybridization reaction?
Lower the reaction time
Many hybridization assay conditions are based on the expectation that a probe
Has exact complementarity to the target nucleic acid
In hybridization reaction, the pH affects
The stability of double-stranded nucleic acid molecules in solution
The function of the probe is to
Form a duplex with every complementary sequence available in the reaction
Which of the following compounds are used for labeling probes?
Fluorescein
The principle of solid support hybridization (often called blotting) is :
The target sequence is part of the solid support, and the probe, which is in isolation, hybridizes to the target
The southern blot test separates
DNA
The steps for performing the southern blot test include all the following except:
After the labeled probe is hybridized to specific target , the DNA is electrophoresed again, then dried and read
A northern blot is used to detect
RNA
The steps is separated the Northern blot test include all the following except
The membrane is then transferred to a gel so that the RNA can be immobilized in the gel
In situ hybridization, first described in 1969, is where
DNA or RNA can be detected directly in tissue with labeled probes
The principe of in-solubility hybridization is
The hybridization between a labeled probe and target nucleic acids in a liquid solution in tubes or in microtiter wells
The AccuProbe system uses the following technology prinicple
A single-stranded, chemiluminescent-labeled DNA probe is designed to hybridize to the target organisms ribosomal RNA (rRNA) forming a DNA:RNA duplex
PCR includes all of the following except
Gene expression
PCR requires all the of the following components, except
DNA helicase
This piece of instrumentation is a integral part of the PCR process
Thermal cycler
In a PCR, the target DNA is
Exponentially amplified over many cycles of PCR
During the denaturation step in PCR
The target double-stranded DNA is separated into single strands
The goal of the primer annealing step is to
Hybridize oligonucleotide primers to the denatured, single-stranded target DNA strands
What is the purpose of the primer extension?
To produce PCR products
The most commonly used polymerase is
Taq DNA polymerase
This cation is required for the proper function of the Taq DNA polymerase
Mg
One of the most significant drawbacks to PCR is:
The process is easily contaminated
What chemical has been very successful in reducing carryover from PCR assays?
Uracil-N-glycosylate
The most common nucleic acid stain used after separation by agarose gel electrophoresis is
Ethidium bromide
The advantages of real-time PCR over stranded PCR include all the following except
RT-PCR assay will contaminate equipment, reagents, and work spaces
What is the fluorescence resonance energy transfer (FRET) methodology?
The transfer of energy is made from a donor dye molecule to an acceptor dye
What is the principle of the 5’ nuclease assay (TaqMan)?
The Taq DNA polymerase extends from the primers and replicates the template to which the TaqMan probe is annealed. The reporter dye is released by 5’ nuclease activity of the polymerase first and then the probe is released, thus increasing the fluorescence
A Scorpion primer
Uses a single ogliocnucleotide to prime a specific sequence and to detect accumulated PCR product
The most sensitive technique available for detecting and quantifying messenger RNA is
Reverse-transcription PCR
Multiplex PCR is good for
Simutaneously detecting two or more different targets from one PCR tube
Nested PCR is very sensitive and specific because
The assay itself basically serves as a form on internal control and ensures specificity
NASBA stands for
Nucleic acid sequence-based amplification
Accurate epidemiological surveillance of specific organisms is needed for all the following reasons except
The increase in nosocomial infections
All of the following non amplified typing technique are used to differentiate strains of an organism except
Multilocus sequence typing
All of the following amplified typing techniques are used to differentiate strains for an organism, except
PFGE
What is the principle of restriction enzyme analysis of chromosomal DNA?
DNA is extracted and isolated, and digested with a restriction enzyme. The resulting RFLP pattern is analyzed by agarose gel electrophoresis and transferred to a membrane
This method is good for separating large DNA fragments is a low-percentage, low-melt agarose gel by an angled electrical field that periodically changes orientation
PFGE
This method analyzes gene expression polymorphism by analyzing proteins.
Multilocus enzyme electrophoresis
This technique is a popular method of DNA fingerprinting
Random amplified polymorphic DNA
When an organisms genome is sequenced, all of the following information can be obtained except
Disease causing mechanisms
The basis for this method is a microscopic grouping of DNA molecules attached to a solid support mechanism. Silicon chip, glass, or plastic have been used as he solid surfaces. What method is this?
DNA microarray
What is proteomics?
The study of proteins on a cellular level
Relatively nontoxic antimicrobial therapeutic agents include all of the following, except
Heavy metals
Antibiotics work by targeting all of the following except
Bacterial plasmid DNA
Which of the following public health issues in uniting scientists from across the world to develop strategies to address it?
Antibiotic resistance
Mechanism that mediate intrinsic antibiotic resistance include all of the following except
Alternate biosynthetic pathways
Antibiotic mechanism of action target all the following, except
Blocking the Embden-Meyerhof pathway
Both gram-positive and gram-negative bacteria have an inner cytoplasmic membrane that is composed of
Phospholipids and proteins
In gram-positive bacteria, this is substantially thicker and more multilayered than in gram-negative bacteria
Peptidoglycan
The outer membrane of gram-negative bacteria composed of
Lipopolysaccharides, phospholipids and porin proteins
All of the following are beta-lactate antibiotics except
Monoterpenes
Penicillins, cephalosporins, monobactams, and carbapenems all have this ring in their structure that is responsible for inhibiting the transpeptidation reaction, resulting in bacterial lysis and cell death
Beta-lactam
What is the mechanism of action of the glycopeptides (vancomycin and teicoplaninin)?
The glycopeptides bind to the substrate of the transpeptidation enzyme and disrupt the cell membrane construction
Which antibiotic inhibits folate synthesis, proving the essential precursor molecule, pyridine thymidylate, needed in DNA synthesis?
Sulfamethoxazole
This antibiotic affects the DNA replication by targeting topoisomerases II and IV, enzymes considered important in controlling DNA replication
Quinolone
This antibiotic interferes with DNA transcription by blocking of RNA chain elongation
Rifampin
All of the following antibiotics target the 50S ribosomal subunit to prevent mRNA translation in the bacteria, except
Quinolones
These antibiotics are cationic carbohydrate-containing molecules, and their positive charge provides the basis for the interaction with the 30S ribosomal subunit. What class of antibiotic are these?
Aminoglycosides
The members of the polyketide class of antibiotic include all the following except
Oxycycline
The members of the macrolide class of antibiotics include all the following except
Rifamycin
These two classes of antibiotics allow initiation and mRNA translation to begin, but they act by inhibiting peptide elongation
Macrolides and tetracyclines
All of the following are recently approved classes of antibiotics that target protein synthesis, except
Sixth generation cephalosporins
Intrinsic mechanisms of resistance are
Innate characteristics of the bacterium and transmitted to progeny
Acquired mechanims of resistance are those that
Result from acquisition of DNA by acquisition of extrachromosomal DNA
What is porin?
Outer membrane channels that permit the inflow of nutrients and the outflow of wastes
This type of pathogen may demonstrate decreased or loss of porin synthesis in combination with other resistance mechanisms, resulting in multi drug resistant pathogens
Nosocomial
Biofilms are groups of bacteria that are irreversibly attached to surfaces and are embedded in a matrix of extracellular polymeric substances. They are most commonly found on
Indwelling medical devices
Efflux pumps
Function as transported proteins involved in the removal of toxic substances from the interior of the cell to the external environment
The beta-lactam agents consist of all the following antibiotics, except
Vancomycin
Beta-lactamases hydrolyze Beta-lactam antibiotics using two distinct mechanisms: those having metallic-based mechanism of action and those with
A serine-based mechanism of action
How do the Beta-lactamase inhibitors work?
By acting as substrates for the Beta-lactamase and reducing their effect on the antibiotic
Acquired antibiotics resistance mechanisms include
All of the above
*efflux mechanisms
*acquisition of new targets
*modification of existing antibiotic targets
Streptococcus pneumoniae and streptococcus pyrogenes use efflux as an effective mechanism for acquired resistance to
Macrolides
The primary mechanism of resistance to this antimicrobial class is modification by mutations encoding single amino acid changes in these targets. What antimbiotic class is this?
Quinolones
This type of resistance mechanism modifies the antibiotic targets and results in reduced affinity of antibiotics for their microbial targets
Enzyme alteration
A young, healthy patient goes into the hospital for reconstructive knee surgery and spikes a fever the day after surgery. The doctor finds the patient has a nosocomial infection with methicillin-resistant staphylococcus aureus (MRSA). What antibiotic should the doctor use to treat this patient?
Vancomycin
A patient undergoes a colon resection. Because of the amount of bacteria present in the colon, the physician put the patient on broad-spectrum antibiotics after surgery. The patient develops a fever 2 days after surgery. He developed an infection with vancomycin-resistant enterococci (VRE). What antibiotics can be used to treat this organism?
Synercid
How does staphylococcus aureus acquire resistance to methicillin?
Mobile DNA element
This is one of the first resistance mechanisms identified and is a strategy that bacteria use successfully to survive the action of many classes of antibiotics
Acquisition of inactivating enzymes
Extdende beta-lactamase target all the following antibiotics except
Macrolides
Resistance to aminoglcosides is mediated by
All of the above
*efflux
*changes in the target site
*impermeability or by enzymatic modification of amino and hydroxy moieties appended to the cyclitol rings
Plasmids are
Circular structures present in bacteria that contain genes encoding proteins and DNA and have the capacity to self-replicate and portion into daughter cells during cellular division
Transposons are
DNA elements that encode transposition an excision function and can transpose from one place on the chromosome to another
Integrons are
Genetic elements capable of integrating resistance genes (cassettes) by an integrin-encoded, site specific recombinase
Insertion sequence are
DNA elements found in bacteria that carry genes only for the enzymes needed to promote their own transportation
When should antimicrobial susceptibility testing be performed on a bacterial isolate from a clinical specimen?
When the organism is part of the normal microbiota
A 12-year old girl goes to the doctor complaining of a sore throat, fever, headache, and general malaise. The doctor does a quick strep test that is positive for group A beta-hemolytic streptococcus. No antibiotic testing is needed because streptococcus is
Universally susceptible to penicillin
Important factors that must be considered when determining whether antimicrobial susceptibility testing is warranted include
All of the above
*the body site from which the organism was isolated
*the presence of other bacteria and the quality of the specimen from which the organism was grown
*the host’s status
Why should antimicrobial susceptibility testing or normal flora isolates or isolates likely to represent contamination or colonization not be performed?
This may encourage a physician to treat a normal condition
Why would normal flora isolating from immunosuppressed patients undergo antimicrobial susceptibility testing?
Species usually viewed as normal flora may be responsible for an infection in an immunosuppressant patient
How are antibiotics chosen for inclusions into laboratory antimicrobial testing protocols?
Both B and C
*the CLSI recommends the drugs that should be tested and reported for each type of specimen
*the institutional pharmacy and therapeutics committee sets the list of drugs that are used in their facility
Two antibiotics are contrainindicated in pediatric patients. They are
Tetracycline and fluoroquinolones
Because the identity of the bacterial isolate is often unknown at the time the susceptibility testing is performed, it’s may include drugs that are inappropriate for reporting. What does the microbiologist odor when this occurs?
A drug should not be indiscriminately reported because results may be misleading
A primary tenet of antimicrobial therapy is to use
All of the above
*the least toxic agents
*the most cost-effective agents
*the most clinically effective agents
Guidance for the development of a selective-reporting or cascade-reporting protocol for antibiotics is available from the
CLSI
As a general guideline, it is suggested that within a particular antimicrobial class, primary (ggroup A) agents should be reported first and secondary (group B) agents should be reported only if
The patient cannot tolerate the primary agents
Why are aminoglyecosides not an effective treatment for meningitis?
They do not cross the blood-brain barrier
When would it be appropriate for institution to routinely test group C agents?
If a particular institution routinely encounters large numbers of isolates resistant to group A and group B agents
What antibiotics should be reported for UTIs?
Urinary tract active agents
What is the most critical step in any susceptibility test?
Inoculum preparation
What is the most widely used method of inoculum standardization?
McFarlnad turbidity standards
What McFarland standard provides turbidity comparable to that of a bacterial suspension containing approximately 1.5 x 10^8 CFU/mL?
0.5
The minimal inhibitory concentration (MIC) is
The lowest antibiotic concentration to inhibit the growth of the an organism
What concentrations of antibiotics are typically tested in MICs ?
Serial twofold dilution concentration are tested
Note that for some antimicrobial agents, different MIC interpretive criteria exist for
Organisms or organism groups
What broth is recommended on the tube dilute MIC tests?
Mueller-Hinton
The broth microdilution MIC test uses these for the testing
Multi well microdilution trays
What is the approximate final concentration of organisms on each well of a microdilution tray?
5 x 10^5 CFU/mL
When reading broth microdilution MIC testing, the MIC for a particular drug is
The lowest concentration showing no obvious growth
What is the storage temperature for frozen panels?
-20 X to -70 C
What’s is a breakpoint panel?
An MIC panel with only one or a few concentration of each drug
On a breakpoint panel, when two concentrations aren tested and no growth is present in either well, isolate is
Susceptible
On a breakpoint panel, when there is growth in the low concentration but no growth in the high concentration, the isolate
Intermediate
One a breakpoint panel, when there is growth in both wells, the isolate is
Resistant
In terms of MIC microdilution trays, a skipped well occurs
When there is growth at higher concentrations and no growth at one or more of the lower concentration wells
In this method of antimicrobial susceptibility testing, specfic volumes of various concentrations of antimicrobial solutions are dispensed into premeasured volumes of molten and cooled agar, which is subsequently poured into standard Petri dishes. Organisms are inoculated onto the plate. What type of antimicrobial susceptibility testing is this?
Agar dilution
In this type of antimicrobial susceptibility test, a McFarland 0.5 standardized suspension of bacteria is swabbed over the surface of a Mueller-Hinton agar plate, and paper disks containing single concentrations of each antimicrobial agent are placed onto the inoculated surface. What is the name of this?`
Kirby-Bauer
A zone of inhibition is
The area around the antibiotic disk where the bacteria cannot grow
What agencies develop the zone interpretive Criteria?
FDA and CLSI
In the Kirby-Bauer test, what is used to grow streptococci that do not grow adequately on unsupplemented Mueller-Hinton agar?
Mueller-Hinton agar with 5% sheep blood
After the plate is incubated in the Kirby-Bauer test, what occurs?
The diameter of each inhibition zone for each antibiotic is measured using a ruler or caplier
Once zone measurements have been made, the mL reading for each antimicrobial agent is
Interpreted as susceptible, intermediate or resistant
Agar dilution and disk diffusion tests for streptococcus pneumonia and streptococcus spp. use
Mueller-Hinton agar supplemented with 5% sheep blood
A patient is admitted to the hospital with a diagnosis of endocarditis. Two separate blood cultures grow out of viridans streptococci. The penicillin MIC of the organism is 0.12 ug/mL. What antibiotic should the physician prescribe?
Penicillin
When performing disk diffusion testing with Haemophilus influenza and H. Parainfluenza what type of medium is used?
Mueller-Hinton with hematin and nicotinamide adenine dinucleotide (NAD)
Therapy of disseminated meningococcal infections and various types of Gonococcal (GC) infections are
Generally empiric based on recommendation of CDC
A man goes to his doctor because he has a cloudy substance dripping from his penis. A gram stain is performed and gonorrhea is isolated. What is the drug of choice to treat this infection?
Ceftriaxone
On what media is Kirby-Bauer testing performed for Neisseria gonorrhoeae?
GC agar base supplemented with various nutrients
What type of antimicrobial susceptibility testing method does CLSI recommend for anaerobes?
Agar dilution
How long are MIC panels for anaerobes incubated?
48 hours
The CLSI has published methods for susceptibility testing of several agents of potential bioterroism, including Brucella anthracis, yersinia pestis, burkholderia mallei, B. Pseudomallei, francisella tularensis and Brucella spp. How does CLSI suggest clinical laboratories perform antimicrobial susceptibility testing on these isolates/
Do not attempt to perform antimicrobial susceptibility on any these isolates; refer them t a Public health laboratory equipped to handle them
Oxacillin-resistant staphylococcus aureus is called
Methicillin-resistant S. Aureus (MRSA)
In vitro testing conditions that can be modified to enhance the expression of oxacillin resistance include all the following except
Use Mueller-Hinton media
Oxacillin-resistant staphylococci can appear susceptible in vitro to other B-Lactam agents such as
Cephalosporins
To obtain a bacterial effect in enterococci, ampicillin must be given in combination with
Aminoglycosides
Which enterococcus is/are the most common species demonstrating vancomycin resistance among clinical isolates?
Enterococcus faecium
Spontaneous mutations occur in the B-lactamase genes that results in extended-spectrum B-lactamases (ESBL). The ESBL inactivate
All of the above
* cephalosporins
* penicillins
* aztreonam
When testing E. Coli, Klebsiella spp., and proteus mirabilis, which drug is mostly likely to indicate the presence of an ESBL?
Cefpodoxime
What antibiotics are active against ESBL-producing strains of bacteria?
Carbapenems
What principle do most current automated antimicrobial susceptibility instruments use to read growth/?
Turbidimetric detection
The BD Phoenix system uses this principle to measure bacterial growth in the susceptibility test wells
Redox indicator system
How many hours of incubation are necessary for the antimicrobial susceptibility test run on the BD phoenix?
6-8 hours
What principle does the Microscan walk away SI use to determine antimicrobial susceptibility?
Turbidimetry
What principle does the TREK ARIS 2X system use to determine antimicrobial susceptibility?
Hydrolysis of a fluorogenic substrate
What automated system was originally designed for use in outer space?
VITEK
What principle does the VITEK series use to determine antimicrobial susceptibility?
Turbidimetry
What is the principle of the Etest?
Establishing an antimicrobial density gradient in agar
Who sets the criteria in the table of values that relate the diameter of the zone to a category of susceptibility in disk diffusion testing?
CLSI
The inhibition zone size and MIC interpretive criteria published by the CLSI are established by careful analysis of all of the following except
Pharmacodynamic data
If the MIC or zone size is interpreted as susceptible using the latest CLSI tables
The clinical interpretation of the result is the patients infecting organism should respond to therapy with that antimicrobial agent using the dosage normally recommended for that type of infection and that species
If the MIC or zone size is interpreted as resistant using the latest CLSI tables
The patients infecting organism in unlikely to be inhibited by the usually achievable concentration of the antimicrobial agent based on the dosages normally used with that drug
If the MIC or zone size is interpreted as intermediate using the latest CLSI tables
The patients infecting organism is likely to require the maximum amount of antimicrobial or more than can be achieved and for which of the clinical response is likely to be less than with susceptible strain
All of the following organisms often produce-B-lactamase, except
Neisseria Meningitis
What is the principle of the most commonly used test to detect B-lactamase production?
Chromogenic cephalosporin nitrocefin
A microbiology technologist is performing a B-lactamase test on a staphylcoccus isolated from a hospitalized patient. The test was negative, so the technologies reported out in vitro antimicrobial susceptibility tests results for B-lactam antibiotic. After 2 days, the patient was not improving and the physician changed the patients antibiotic to an Aminoglycoside. The patient showed improvement immediately. Why was the B-lactamase test on the staphylococci negative when the organism produced B-lactamase?
Staphylococci must be exposed to the B-lactam agent before it will produce a positive test results
Quality control of antimicrobial susceptibility tests involves
Testing standard reference strains that have defined antimicrobial susceptibility (or resistance) to the drugs tested
How should quality control testing occur?
Quality control testing should be included in all the patients tested and treated like a patient specimen
What is a mechanism for ensuring the testing personnel are proficient in their tasks?
All of the above
*supervisory review of reported results
*self-assessment checklists
*periodic competency testing through proficiency surveys
What is the most widely used supplementary quality control measure for antimicrobial susceptibility testing?
Use of antibiograms to verify results generated on patient isolates
All of the following steps are taken to verify the results from an atypical antibiogram, except
Calling around to other hospitals to see if they are encountering the same organism with the same antibiogram
What is generated by analysis of individual susceptibility results on isolates from a particular institution in a defined period and represents the percentage of isolates of a given species that is susceptible to the antimicrobial agents commonly tested against the species?
Cumulative antibiogram
Advantages of the commercial microdilution susceptibility test methods include all the following except
More accurate results than manual methods
A drug will generally inhibit multiplication of bacteria so that the patients immune defense mechanisms are no longer overwhelmed when
The drug concentration exceeds the MIC for the microbe
The minimum bactericidal concentration (MBC) test differs from the MIC test because the MIC test gives the concentration needed at the site of infection to Inhibit bacterial multiplications whereas the MBC gives
The amount of antimicrobial that must be achieved at the infection site to kill the organism
Goals of combination antimicrobial therapy include all of the following except
Ensure that at least one antimicrobial will obtain the MBC at the infection site
A combination of antimicrobias is said to show synergism if
It’s antibacterial activity is significantly greater than that of the single agents
When the activity of the combination of antimicrobial agents is less than that of the single agents, we say the agents are
Antagonistic
All of the following techniques are used to measure the amount of antimicrobial agent in the serum except
Bioluminescence assays
Staphylococci are catalase-positive, gram-positive cocci that resemble other bacteria and are members of this family
Staphylococcaceae
All of the following staphylococci are coagulate-positive, except
S. Saprophyticus
The two species of coagulate-negative staphylococci most often isolated in clinical laboratories are
S. Epidermidis and S. Saprophyticus
All of the following virulence factors are associated with staphylococcus aureus except
Endotoxins
What are the staphylococcal products that cause diarrhea and vomiting in humans?
Enterotoxins
Staphylococcal enterotoxin B is linked to
Staphylococcal psuedomembranous enterocolitis
What is the mechanism by which toxic shock syndrome toxin-1 (TSST-1) causes TSS?
The toxin is a superantigen that stimulates T-cell proliferation with production of large amounts of cytokines
What are the effects of the alpha-hemolysin produced by staphylococcus aureus?
It lyses RBCs, damage platelets and macrophages and can cause severe tissue damage
What are the effects of the a-hemolysin produced by staphylococcus aureus?
It acts on sphingomyelin in the plasma membrane of RBCs
What are the effects of the Panton-Valentine toxin produced by staphylococcus aureus?
It kills leukocytes
All of the following enzymes are produced by staphylococci, except
Amylase
Why do staphylococci spread so easily when infecting the skin?
They produce hyaluronidase, which hydrolyzes hyaluronic acid present in the intracellular ground substance that makes up connective tissue
What is the function of protein A in the cell wall of staphylococcus aureus?
To bind IgG and prevent phagocytosis
The primary reservoir for staphylococci is
Nares
The development of staphylococcal infection is determined by
All of the above
* virulence of the strain
*sizes of the inoculum
*status of the host’s immune system
Staphylococci resist the action of inflammatory cells by the production of toxins and enzymes, thereby establishing
A focal lesion
Infection caused by staphylcoccus aureus are suppurative, meaning
The infection is filled with pus and necrotic tissues
This disease is an extensive exfoliative dermatitis caused by staphylococcal exfoliative toxin
RItter’s disease
This is rare but potentially fatal multisystem disease characterized by high fever, hypotension, and shock, and it is associated with highly absorbent tampons
TSS
Staphylococcus aureus food poisoning is most commonly caused by these two enterotoxins
A and D
This infection occurs secondary to influenza A virus, has a high mortality rate, and occurs among the infants and immunocompromised patients
Staphylococcal pneumonia
Infection by this organism are predeominately hospital acquired. And some predisposing factors include catheterization, medical implantation, and immunosuppressive therapy
S. Epidermidis
This staphylococcal species is associated with UTI in young, sexually active females
S. Saprophyticus
Colony characteristics for staphylococcus aureus on blood agar after 18-24 hours incubation at 35 C include all the following except
Swarming
This staphylococcus products wide zones of beta hemolysis on 5% sheep blood agar
S. Aureus
All of the following is used to describe the colony morphology of staphylococcus Epidermidis, except
Beta-hemolytic
The presence of mecA indicates
Resistance to methicillin
How is staphylococcus Saprophyticus presumptively identified?
Novobiocin susceptibility
What antimicrobial agent is used for detection of methicillin resistance ?
Oxacillin
Automated antimicrobial to susceptibility testing methods are not reliable in detecting staphylococci resistant to this agent
Vancomycin
A 20 year old woman goes to her physician complaining of burning upon urination, frequency and general malaise. Her physician orders a urine culture, which grew 25,000 colony-forming units (CFU)/mL of a catalase-positive, coagulate-negative, novobiocin-resistant gram-positive occurs. What is the most likely pathogen?
S. Saprophyticus
A young man goes to his physican complaining of large, raised, suppurative abscesses on his neck. The man denies having a fever or the chills. What is the name of the lesions on his neck, and what organism causes this type of lesions?
S. Aureus and furuncles
a young, healthy woman was rushed to the hospital with a high fever, hypotension and shock. She has not been feeling well that day, but her conditions progressively worsened throughout the day. She was feeling fine until a couple of days after she started menstruating. What condition could this woman be exhibiting?
TSS
Later in the evening, after attending a family reunion, several family members went to the emergency department after experiencing nausea, vomiting, abdominal pain, and severe cramping. The menu included fried chicken, hot dogs, hamburgers, potato salad, deviled eggs, eclairs, and explanation for these symptoms?
Staphylococcal food poisoning
What is the most common causative agent of pyoderma?
Staphylococcus aureus
What test differentiates staphylococci from streptococci?
Catalase
The atmospheric conditions best suited to grow steptococci and enterococci are
Oxygen-free atmosphere
Which of the following is found in the cell wall made of streptococci and enterococci?
Teichoic acid and Peptidoglycan
Common schemes to classify streptococci include all the following except
Flagellar antigens
Physiologic classification of streptococci divide the species into all the following groups, except
Beta-hemolytic streptococci
Which of the following test can be used to presumptively identify streptococcus pyogenes?
Bacitracin
Which of the following test can be used to identify group B streptococci?
CAMP
What test can be used to differentiate streptococcus from other B-hemolytic streptococci?
Hippurate hydrolysis
What test presumptively differentiates B-hemolytic group A streptococci and non hemolytic group D enterococci from other streptococcal species?
PYR
Which two tests are often used in the ID of the non-hemolytic, catalase-negative, gram-positive cocci?
Bile esculin and salt tolerance
What test is used for the presumptive identification of streptococcus pneumonia?
Optochin
Most physicians offices use a rapid throat swab method to identify streptococcus pyogenes infections in children. If the test is positive, the physician treats the patient. What should happen if the test is negative?
The physician should perform a throat culture
Which of the following is the drug of choice in treating most streptococcal infections. However, penicillin is the drug of choice in treating and streptococcal infections?
Penicillin
What is the cellular structure that streptococcus pyogenes relies primarily on for its virulence?
M proteins
All of the following are virulence factors associated with group A streptococcus, except
Enterotoxins
What is the hemolysin responsible for hemolysis on SBA by Group A streptococci incubated anaerobically?
Streptolysin O
What causes the red spreading rash in scarlet fever?
Streptococcal pyrogenic exotoxins
Streptokinase is an enzyme produced by Group A streptococci that
Lyses fibrin clot
What is the most common disease caused by streptococci?
Pharyngitis
Skin infections of pyoderma caused by Group A streptococci results in all the following syndromes, except?
Bullous impetigo
What disease is produced by group A streptococci that are characterized by a rapidly progressing inflammation and necrosis of the skin, subcutaneous fat, and fascia?
Necrotizing fasciitis
Two serious complications of an infection with group A streptococci are
Acute glomerulonephritis and rheumatic fever
What is the drug of choice to treat group A streptococci when the patent cannot tolerate penicillin?
Erthyromyocin
What organism forms small, transparent colonies surrounded by a wide zone of B-hemolysis on SBA?
Streptococcus pyogenes
Streptococcus agalactiae is a significant cause of
Invasive disease of the newborn
What organism on SBA has grayish white colonies surrounded by a small zone of B-hemolysis?
Streptococcus agalactiae
What are two tests presumptively used to identify Group B streptococci?
Hippurate hydrolysis and CAMP
What two tests are presumptively used to identify enterococcus?
Bile esculin and 6.5% NaCl broth
What is VRE?
Vancomycin-resistant enterococcus
The major virulence factor for streptococcus pneumonia is
Capsular polysaccharide
Streptococcus pneumoniae causes all the following infections, except
Pharyngitis
A 57-year old male presents to the emergency department with a fever, productive cough, and complaining of chest pain. A STAT gram stain reveals gram-positive oval-shaped cocci in pairs. You should suspect
Streptococcus pneumonia
Why do streptococcus pneumonia colonies on SBA sometimes appear like a coin—raised edges and a depressed center?
The older growth at the center is killed due to autolysis
Where are the viridians strepococci constituents of the normal microbiota?
All of the above
*upper respiratory tract
*female genital tract
*GI tract
Streptococcus-like organisms that resemble enterococci and viridans streptococci include all the following except
Moraxella
A young girl goes to her physicians office with a fever, headache, and sore throat. The mother states the girl has a fever of 38.8 C (102 F) what test should be physician order?
Throat culture
A patient comes to the emergency department with a productive cough, shortness of breath, and 102 F fever. The patient is diagnosed with pneumonia. What organism commonly encountered in the microbiology laboratory can cause this disease?
Streptococcus pneumonia
A microbiologist is reading a sputum culture on the bench. There is growth on the BAP and CHOC plate, but no growth on the MAC plate. The colonies growing on the BAP have discolored the media to a green color around and under the colonies. What organism could this be?
Streptococcus pneumonia
A microbiologist is reading a sputum culture on the bench. There is growth on the SBA and chocolate (CHOC) plates, but no growth on the MacConkey (MAC) plate. The colonies growing on the SBA have produced a wide, deep, clear zone of B-hemolysis around and under the colonies. What organism could this be?
Streptococcus pyogenes
A microbiologist is reading a vaginal culture on the bench. There is growth on the SBA and CHOC plates but no growth on the MAC plate. The colonies growing on the SBA have produced a narrow, diffuse zone of B-hemolysis around and under the colonies. What organism could this be?
Streptococcus agalactiae
