Podcast
Questions and Answers
What indicates that a bacterial isolate should not be used on a patient?
What indicates that a bacterial isolate should not be used on a patient?
What type of resistance occurs when bacteria are resistant to an antibiotic before its introduction?
What type of resistance occurs when bacteria are resistant to an antibiotic before its introduction?
Which method determines the minimum amount of antibiotic that inhibits visible growth?
Which method determines the minimum amount of antibiotic that inhibits visible growth?
In the context of antibacterial susceptibility testing, which of the following tests can be categorized as quantitative methods?
In the context of antibacterial susceptibility testing, which of the following tests can be categorized as quantitative methods?
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What describes the highest dilution of a drug which can kill a specific bacterium?
What describes the highest dilution of a drug which can kill a specific bacterium?
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How can bacteria acquire antibiotic resistance?
How can bacteria acquire antibiotic resistance?
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Which of the following tests is NOT used to determine antibiotic susceptibility?
Which of the following tests is NOT used to determine antibiotic susceptibility?
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What is the significance of the sudden acquisition of antibiotic resistance in bacteria?
What is the significance of the sudden acquisition of antibiotic resistance in bacteria?
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What is the primary aim of the macrobroth dilution test?
What is the primary aim of the macrobroth dilution test?
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What inoculum concentration is determined using the 0.5 McFarland standard?
What inoculum concentration is determined using the 0.5 McFarland standard?
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What is the method used to categorize bacterial isolates as sensitive, intermediate, or resistant?
What is the method used to categorize bacterial isolates as sensitive, intermediate, or resistant?
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Which storage condition is recommended for E-test strips?
Which storage condition is recommended for E-test strips?
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In the macrobroth dilution test, what indicates that the antibiotic has completely inhibited bacterial growth?
In the macrobroth dilution test, what indicates that the antibiotic has completely inhibited bacterial growth?
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What does the zone of inhibition measure in the disk diffusion test?
What does the zone of inhibition measure in the disk diffusion test?
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What type of bacteria was tested using ciprofloxacin in the context of E-tests?
What type of bacteria was tested using ciprofloxacin in the context of E-tests?
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What is a common disadvantage of E-test strips?
What is a common disadvantage of E-test strips?
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What is the primary mode of transmission for Helicobacter pylori?
What is the primary mode of transmission for Helicobacter pylori?
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Which gastric diseases are commonly associated with Helicobacter pylori infections?
Which gastric diseases are commonly associated with Helicobacter pylori infections?
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What are characteristic clinical signs of Helicobacter infections in dogs and cats?
What are characteristic clinical signs of Helicobacter infections in dogs and cats?
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Which laboratory method is used for isolating Helicobacter species?
Which laboratory method is used for isolating Helicobacter species?
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In which condition can Helicobacter pylori survive due to its unique characteristics?
In which condition can Helicobacter pylori survive due to its unique characteristics?
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How can evidence of Helicobacter infections be identified in laboratory diagnostics?
How can evidence of Helicobacter infections be identified in laboratory diagnostics?
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What is a notable feature of Helicobacter pylori regarding its biochemical properties?
What is a notable feature of Helicobacter pylori regarding its biochemical properties?
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Which of the following non-pylori species can also cause gastric disease in humans?
Which of the following non-pylori species can also cause gastric disease in humans?
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What property of Campylobacter fetus contributes to its virulence?
What property of Campylobacter fetus contributes to its virulence?
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Which subspecies of Campylobacter fetus is primarily responsible for causing bovine genital campylobacteriosis?
Which subspecies of Campylobacter fetus is primarily responsible for causing bovine genital campylobacteriosis?
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How is Campylobacter fetus subspecies fetus typically transmitted to cattle?
How is Campylobacter fetus subspecies fetus typically transmitted to cattle?
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What characteristic of the placenta is commonly observed in cases of Campylobacter infections in ewes?
What characteristic of the placenta is commonly observed in cases of Campylobacter infections in ewes?
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Which of the following is a major public health implication of Campylobacter infections?
Which of the following is a major public health implication of Campylobacter infections?
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Which characteristic is NOT associated with Campylobacter bacteria?
Which characteristic is NOT associated with Campylobacter bacteria?
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Which of the following methods is primarily used for the presumptive identification of Campylobacter fetus in fetal stomach contents?
Which of the following methods is primarily used for the presumptive identification of Campylobacter fetus in fetal stomach contents?
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What is the mode of infection for Campylobacter fetus in cattle and sheep?
What is the mode of infection for Campylobacter fetus in cattle and sheep?
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What role does the serum C3b binding play in the pathogenicity of Campylobacter fetus?
What role does the serum C3b binding play in the pathogenicity of Campylobacter fetus?
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What atmosphere is optimal for incubating blood agar cultures of Campylobacter species?
What atmosphere is optimal for incubating blood agar cultures of Campylobacter species?
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Which Campylobacter species is commonly associated with human infections originating from pigs and poultry?
Which Campylobacter species is commonly associated with human infections originating from pigs and poultry?
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What type of infections can Campylobacter fetus subsp. fetus cause in humans?
What type of infections can Campylobacter fetus subsp. fetus cause in humans?
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Which of the following characteristics describes the morphology of Campylobacter species in culture?
Which of the following characteristics describes the morphology of Campylobacter species in culture?
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What is a common method used to identify isolates of Campylobacter species based on genetic material?
What is a common method used to identify isolates of Campylobacter species based on genetic material?
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Why is it critical for clinical materials collected for Campylobacter culture to be fresh?
Why is it critical for clinical materials collected for Campylobacter culture to be fresh?
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Which Campylobacter species is associated with infections following recovery only from humans?
Which Campylobacter species is associated with infections following recovery only from humans?
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Study Notes
Antibacterial Susceptibility Testing
- Antibacterial susceptibility testing allows for the identification of an appropriate antibiotic for treatment in clinical cases.
- Test results in vitro do not reflect the influence of varying factors during in vivo treatment.
- Quantitative tests determine the Minimum Inhibitory Concentration (MIC) of an antibiotic - the lowest amount of antibiotic that prevents the visible growth of an isolate.
- Qualitative tests categorize an isolate as sensitive, intermediate, or resistant to a particular antibiotic.
Quantitative Tests
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Broth dilution method:
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Macrobroth dilution MIC tests: involves a serial two-fold dilution of antibiotic in test tubes.
- The inoculum density is standardized to 5 x 10^5 cfu/ml, and 1ml of the bacterial suspension is added to each tube of antibiotic solution.
- The lowest concentration of antibiotic that completely inhibits growth is recorded as the MIC.
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Microbroth dilution MIC tests: performed on a polystyrene tray with 80 wells containing serial two-fold dilutions of different antibiotics.
- The inoculum suspension is standardized, and the bacterial inoculum is inoculated into each well.
- MIC is determined as in macrobroth dilution tests.
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Macrobroth dilution MIC tests: involves a serial two-fold dilution of antibiotic in test tubes.
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Agar dilution method (E-tests):
- Plastic strips containing a predefined gradient of a single antibiotic or antifungal are used.
- Each strip represents a single antibiotic, offering a wide range of antibiotics.
- Easy to use
- Stored at -20°C
- Short shelf life, expensive
Determining MIC and MBC
- MIC is the highest dilution of an antibacterial agent that inhibits growth of an isolate.
- MBC is the highest dilution of a drug that can kill a particular bacterium.
Qualitative Tests
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Disk diffusion test:
- A standardized bacterial isolate is spread on an agar plate.
- Paper discs containing specific concentrations of antibiotics are placed on the plate, followed by overnight incubation at 37°C.
- If the isolate is susceptible to the antibiotic, a zone of inhibition (where bacteria do not grow) forms around the disk.
- Strains resistant to an antibiotic grow up to the margin of the disk.
- The diameter of the zone of inhibition is measured and compared with standards to interpret results as sensitive, intermediate, or resistant.
Acquired Resistance
- Intrinsic resistance is inherent to the bacteria species.
- Acquired resistance arises from mutations or genetic material exchange among bacteria.
- Acquired resistance leads to difficulties in treating infections.
- Multidrug resistance (resistance to several antibiotics) poses an even greater challenge.
- Isolates showing reduced susceptibility or resistance should not be used for treatment.
Helicobacter Pylori
- Helicobacter pylori is a bacteria that infects the stomach
- The infection rate is about 50% of human population
- Helicobacter pylori lives beneath the mucous membrane of the stomach
- Infection can lead to gastritis and gastric ulcers
- Transmission is considered predominantly fecal-oral and oral-oral
- Helicobacter pylori survives by breaking down urea, raising the pH of the environment
Other Helicobacter species
- Helicobacter canis, Helicobacter felis, Helicobacter rappini, Helicobacter bills, and Helicobacter heilmannii (Helicobacter bizzozeronii) are also associated with gastric disease in humans
- These species can cause gastritis in dogs and cats
- Common clinical signs associated with infection include vomiting, regurgitation, abdominal pain, fever, diarrhea, anorexia, weight loss and poor condition
Campylobacter
- Campylobacter are S-shaped, spirally curved, Gram-negative and pleomorphic rods
- Motile with a single polar flagellum at one or both ends
- Microaerophilic (3%-5% CO2), aerobic or anaerobic, and oxidase-positive
- They do not use carbohydrates
- Two species, Campylobacter fetus and Campylobacter jejuni are pathogenic for animals
- The generally non-pathogenic species are found on the mucous membrane of the genital and intestinal tracts.
- Campylobacter fetus is comprised of two subspecies: C. fetus subsp.fetus and C. fetus subsp.Venerealis
- Both subspecies possess a surface protein capsule that is essential for virulence; the protein mediates resistance to serum killing and phagocytosis by preventing the binding of serum C3b.
Campylobacter fetus subspecies Venerealis
- Cause of bovine genital campylobacteriosis
- Found in the preputial cavity of asymptomatic bulls, and the genital tract of cows and heifers
- Infection mode is venereal, with organisms present in the semen of infected bulls
- Placenta and fetus can be invaded, resulting in abortion at 5-8 months
- If birth occurs, the newborn may only live for a few hours
- Infected placenta is usually hemorrhagic and edematous
- Uterine infection causes metritis, resulting in infertility and shedding of the organism from the uterus for various periods
Campylobacter fetus subspecies fetus
- Found in the intestine of cattle and sheep as well as the genital tract of infected sheep and cattle
- Transmission is via ingestion, directly or through fomites, but not venereally
- Infection spreads hematogenously, infecting the uterine mucosa
- May cause abortion in cows (sporadic) and sheep (multiple)
- Placenta and fetus can be infected, leading to late-term abortions, autolysis of fetuses, and stillbirths
- Ewes may develop metritis after expelling the fetus
- Placenta may be hemorrhagic and edematous
- Necrotic foci in the fetal liver is a common characteristic
Public Health Significance
- Campylobacter fetus subsp.fetus causes infrequent human infections, C.fetus subsp.venerealis does not
- Campylobacter infections in humans present as bacteremia, septic arthritis, endocarditis, septic abortions, peritonitis, salpingitis, meningitis, and thrombophlebitis
- Individuals with underlying disease, such as HIV infection, are particularly susceptible
INFREQUENTLY PATHOGENIC SPECIES
- Campylobacter coli: Found in pigs and poultry, can cause human infections
- Campylobacter concisus: Found in human infections
- Campylobacter heIveticus: Found in dogs and cats
- Campylobacter hyloileri: Found in pigs
- Campylobacter jejuni subsp.doylei: Found in human infections and recovered only from humans
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Description
This quiz covers the essential principles and methods of antibacterial susceptibility testing, an important aspect of clinical microbiology. Focus on both quantitative and qualitative tests, including the broth dilution method for determining Minimum Inhibitory Concentration (MIC). Understand the implications of test results for antibiotic treatment decisions.
