Quality Control & Antimicrobial Agent Mechanisms
Define analytic sensitivity and analytic specificity.
Analytic sensitivity - ability to detect a particular analyte or a small change in its concentration
Analytic specificity - ability of a test to avoid reacting to substances other than the analyte of interest
Define MIC
Lowest concentration of antimicrobial agent required to inhibit the growth of a bacterial isolate
What is the most common contaminate isolated from blood cultures?
Propionibacterium acnes
What type of staining is performed on mycobacteria organisms.
Acid fast stain
-Mycobacteria resist staining with gram stain and resist decolorization with acid-ethanol (alcohol) - need to be acid fast stained
What is the process of viral replication?
Attachment - Penetration - Replication - Cell lysis
Describe Pre-analytical, Analytical, and Post-analytical
Pre-analytical - the phase where the lab has no direct control on the process. (Ex. collection, phlebotomy, identification, contamination, etc.)
Analytical - Occur in lab (Ex. lab testing, quality control, etc.)
Post-analytical - Once testing is complete/reporting (Ex. evaluating results, release to test results in a timely manner, etc.)
What is the reference/gold method for susceptibility testing of anaerobes?
Agar dilution method
How is blood collected for anaerobic bacteriology studies?
-Aseptic inoculation of both anaerobic and aerobic blood culture bottles
-venipuncture site with bactericidal agent (not just alcohol) (Ex. iodine, iodophore)
What organism is positive for niacin accumulation and is heat-stable catalase negative?
Mycobacteria tuberculosis
What is Cytopathic Effect (CPE) on cell cultures?
Some viruses produce characteristics cytopathic effects which provide a presumptive ID. It is the way it may structurally effect the host's cell by viral invasion.
Name some examples of B-lactam antibiotics.
Penicillins, cephalosporins, carbapenems, methicillin, monobactams, etc.
Susceptibility testing of agents of bioterrorism must be performed in:
Biosafety level (BSL) 2 or by higher facilities by trained individuals
A patient recently had some dental work done. They noticed swelling developing on their submandibular region and decided to go to the doctor. Sulfur granules were drained from the site and was sent to the lab for examination. Under the microscope, branching thin bacilli were seen.
What organism is suspected?
Actinomyces spp.
Suppresses gram-positive bacterial growth
What syndrome does Parvovirus B19 cause?
Erythema infectiosum (5th disease)
Define acquired resistance and natural resistance.
What are some examples of each?
Acquired resistance: the new ability of bacteria to withstand the antibiotic that they were once sensitive to.
Ex. Acquired ability to produce new efflux pumps, modification of existing antibiotic targets, acquisition of new targets, acquired ability to produce enzymes that inactivate antibiotic, etc.
Natural resistance: Innate characteristics of a particular group, genus, or species of bacteria/naturally found in the bacteria
Ex. lack of affinity of a drug to a bacterial target, inaccessibility of a drug into the bacterial cell, extrusion of the drug by chromosomally encoded pumps, innate production of enzymes that inactivate the drug, etc.
What can be used to screen for penicillin susceptibility for Streptococci?
What is an alternative for penicillin-allergic patients?
- plate with an oxacillin disk
- macrolides (clindamycin, erythromycin)
What are the type of diseases the following types of Clostridium spp. cause:
C. perfringens
C. botulinum
C. tetani
C. difficile
C. perfringens - food poisoning (GI illness)
C. botulinum - food borne- (weakness, flaccid paralysis), infant- (sluggish eyes, difficulty breathing, poor feeding), and wound botulism (blurred vision, weakness, similar to foodborne)
C. tetani - tetanus (spastic paralysis, trismus, difficultly breathing)
C. difficile - antibiotic associated diarrhea & pseudomembranous colitis (bloody diarrhea, necrosis of colonic mucosa)
What nontuberculous mycobacteria organism causes cervical lymphadenitis in children and is scotochromogenic?
Mycobacteria scrofulaceum
A patient visits his doctor with complaints of slight yellowing of his skin and having tenderness in his top right abdomen. The lab work shows an elevated serum aminotransferase. During the collection of his medical history, it is discovered that he is a drug abuser, but has been clean for the past weeks.
What is the patient likely diagnosed with?
How is this virus normally transmitted?
Hepatitis B Virus
Transmission of blood and blood products, needles, and sexual contact
A patient comes into the hospital with a skin infection. He states that during his previous visit in regard to his infection, they had stated that he had a Staphylococcus aureus infection and prescribed him methicillin. His infection has persisted.
What do you suspect is going on?
How do you develop this?
What alternative treatment can you give the patient?
-Methicillin-resistant Staphylococcus aureus (MRSA) infection
-MecA gene - codes for a new PBP with reduced affinity for beta lactam antibiotics
-Vancomycin (good for skin infections), other options for MRSA in general: teicoplanin, oxazolidinones
What is the difference between MIC and MBC.
Why is MBC performed?
An MIC and MBC is performed on a patient experiencing an infection. The MIC of the drug used was 2.0 ug/dl. The MBC was performed and had a result of 8.0 ug/dl. What does this indicate?
MIC - Lowest concentration of antimicrobial agent required to inhibit the growth of a bacterial isolate
MBC - In-vitro determination of the amount of antibiotic required to inhibit and kill the isolate
MBC is performed for the following reasons:
-Inhibitory concentration of drug are not sufficient
-Obtaining bactericidal concentrations of antimicrobial agents is important for achieving a cure
-Patient’s immune defenses cannot eliminate the infecting bacteria
2.0 ug/dl is the minimum amount of the drug to inhibit the growth of the organism and 8.0 ug/dl is the minimum amount of the drug to inhibit AND kill the organism.
A patient comes into the urgent care unit complaining of an acute onset of severe abdominal pain, diarrhea, and cramps. On sheep blood agar, the organism seemed to show a double-zone of hemolysis. The organism was plated on egg yolk agar and showed a positive lecithinase reaction on this media. It was negative for lipase.
What organism is suspected?
What is the expected gram stain appearance of this organism?
Clostridium perfringens
Boxcar-shaped, gram positive spore forming bacillus bacteria
A patient is experiencing spreading skin lesions on his back and slight destruction of cartilage on parts of his face.
What is organism is likely suspected?
How does it grow on media?
How is detection of the organism made?
Mycobacterium leprae (lepromatous leprosy)
Does not grow on media (in vitro)
Detection of bacteria is made from skin scrapings or biopsies using acid fast stain method
An infant is brought to the E.R. with complaints of dehydration, vomiting, and fever, and some abdominal pain. After some lab work, no bacterial cause was found. The doctor suspects that he may have gotten infected through fecal/oral route.
What organism is suspected?
What complications can arise?
-Rotavirus
-Infant mortality and failure to thrive in children