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Questions and Answers
Which type of bacteria require the presence of oxygen to grow?
Which type of bacteria require the presence of oxygen to grow?
What is the primary purpose of the Gram stain in microbiology?
What is the primary purpose of the Gram stain in microbiology?
What is a characteristic of facultative anaerobic bacteria?
What is a characteristic of facultative anaerobic bacteria?
Which of the following bacteria do not stain well with Gram stain?
Which of the following bacteria do not stain well with Gram stain?
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What is included in the post-analytic phase of the microbiology process?
What is included in the post-analytic phase of the microbiology process?
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Which statement best describes sterilization in medical instruments?
Which statement best describes sterilization in medical instruments?
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What is a future trend expected in medical microbiology?
What is a future trend expected in medical microbiology?
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What is the correct sequence of the Gram stain process?
What is the correct sequence of the Gram stain process?
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Which of the following species accounts for the majority of Enterococcus infections?
Which of the following species accounts for the majority of Enterococcus infections?
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What characteristic is NOT associated with Enterococcus bacteria?
What characteristic is NOT associated with Enterococcus bacteria?
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Which of the following statements regarding the virulence of Enterococcus is correct?
Which of the following statements regarding the virulence of Enterococcus is correct?
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In which environment are Enterococcus bacteria predominantly found?
In which environment are Enterococcus bacteria predominantly found?
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What is the primary role of Enterococcus in food?
What is the primary role of Enterococcus in food?
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Which of the following best describes Enterococcus mobility?
Which of the following best describes Enterococcus mobility?
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What is a major factor that allows Enterococcus to survive in various extreme conditions?
What is a major factor that allows Enterococcus to survive in various extreme conditions?
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Which cell-surface proteins are considered virulence factors in Enterococcus?
Which cell-surface proteins are considered virulence factors in Enterococcus?
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Which statement is true regarding the virulence of S.constellatus?
Which statement is true regarding the virulence of S.constellatus?
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In immunocompetent individuals, which of the following is less likely to cause significant disease?
In immunocompetent individuals, which of the following is less likely to cause significant disease?
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What is the main clinical association when S.bovis is found in blood?
What is the main clinical association when S.bovis is found in blood?
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Which of the following types of infections is most commonly associated with S.mutans?
Which of the following types of infections is most commonly associated with S.mutans?
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What characteristic features do Group A streptococci (GAS) have?
What characteristic features do Group A streptococci (GAS) have?
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Which method is commonly used for the rapid identification of bacteria such as Streptococci?
Which method is commonly used for the rapid identification of bacteria such as Streptococci?
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What is a significant result of an infection caused by pyogenic streptococci?
What is a significant result of an infection caused by pyogenic streptococci?
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Which of the following statements is true regarding the natural habitat of Group A streptococci?
Which of the following statements is true regarding the natural habitat of Group A streptococci?
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What factors influence the likelihood of being a carrier of S.pneumoniae?
What factors influence the likelihood of being a carrier of S.pneumoniae?
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Which of the following infections is predominantly caused by S.pneumoniae?
Which of the following infections is predominantly caused by S.pneumoniae?
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In which age group is the prevalence of pneumococcal disease the highest?
In which age group is the prevalence of pneumococcal disease the highest?
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Which method is commonly used for rapid identification of bacteria such as S.pneumoniae?
Which method is commonly used for rapid identification of bacteria such as S.pneumoniae?
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Viridans-Group Streptococci (VGS) are categorized based on:
Viridans-Group Streptococci (VGS) are categorized based on:
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What is a key diagnostic method for detecting Candida infections?
What is a key diagnostic method for detecting Candida infections?
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What is a characteristic virulence factor of VGS?
What is a characteristic virulence factor of VGS?
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Which type of Candida infection management involves the use of Amphotericin?
Which type of Candida infection management involves the use of Amphotericin?
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What is the main risk factor associated with cryptococcosis?
What is the main risk factor associated with cryptococcosis?
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What defines the classification of viridans-group streptococci?
What defines the classification of viridans-group streptococci?
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Which of the following statements about S.pneumoniae is accurate?
Which of the following statements about S.pneumoniae is accurate?
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In which condition is dual therapy with azoles and echinocandins typically applied?
In which condition is dual therapy with azoles and echinocandins typically applied?
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Which pathogenic species of Cryptococcus is commonly found in pigeon droppings?
Which pathogenic species of Cryptococcus is commonly found in pigeon droppings?
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What symptom is associated with the development of a cryptococcoma?
What symptom is associated with the development of a cryptococcoma?
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What is the sensitivity and specificity of the serum cryptococcus Ag blood test?
What is the sensitivity and specificity of the serum cryptococcus Ag blood test?
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Which underlying condition can make individuals more susceptible to invasive cryptococcal infections?
Which underlying condition can make individuals more susceptible to invasive cryptococcal infections?
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Study Notes
Bacterial Morphology
- Cocci (round): streptococci (chains), diplococci (pairs), tetrad (groups of four), staphylococci (clusters), sarcina (cube-like packets)
- Bacilli (rod): chain of bacilli, flagellate rods (motile rods with flagella), spore formers (produce protective endospores)
- Others: vibrios (comma-shaped), spirilla (spiral-shaped, e.g. H. pylori), spirochaetes (long, helical, e.g. Treponema pallidum)
Oxygen Requirements for Bacterial Growth
- Aerobic: require oxygen for growth
- Obligate anaerobic: require absence of oxygen for growth
- Facultative anaerobic: can grow with or without oxygen
Gram Stain: Importance and Steps
- Provides initial guidance for bacterial identification and treatment
- Can stain other microorganisms, but not acid-fast bacteria (e.g., mycobacteria)
- May not stain bacteria lacking cell walls (e.g., chlamydia, mycoplasma)
- Steps:
- Fixation of organism
- Crystal violet dye (purple stain)
- Iodine treatment
- Decolorization (removes dye from gram-negative bacteria)
- Counter stain with safranin (pink stain for gram-negative bacteria)
Microbiology Laboratory Phases
- Pre-analytic: ordering tests, specimen collection and transportation, specimen processing
- Analytic: testing and interpreting results
- Post-analytic: reporting results
Infection Control Measures
- Hand Hygiene: hand washing with soap and water or using hand sanitizers
- Personal Protective Equipment (PPE): gloves, gown, mask, eye protection to create a barrier between healthcare workers and sources of infection
- Environmental Cleaning and Disinfection: cleaning and disinfecting equipment, surfaces, and the environment to eliminate pathogens
- Proper Waste Disposal: safe and regulated disposal of sharps, contaminated materials, etc., to prevent infection spread
- Sterilization of Medical Instruments: killing and removing all microorganisms from instruments and equipment to ensure safe use on patients
Future Trends in Medical Microbiology
- Advancements in genomic sequencing for rapid bacterial identification and characterization
- Personalized microbial therapeutics for tailoring probiotic or therapeutic treatments based on the patient's microbiome
- Antimicrobial resistance monitoring to track the spread of antibiotic-resistant pathogens
Streptococcus pneumoniae
- Leading cause of infections, particularly in the respiratory tract
- Causes non-invasive infections (e.g., acute otitis media, rhinosinusitis, pneumonia) and invasive infections (e.g., bacteremia, meningitis, endocarditis)
- Prevalence rates follow a U-shaped curve, increasing at age extremes (young children and older adults)
Viridans Group Streptococci (VGS)
- Gram-positive cocci in short or long chains
- Characterized by green discoloration on blood agar plates
- Diverse group with varying clinical presentations and antimicrobial susceptibility
- Mostly found in the GI tract (mouth, etc.)
- Typically cause more indolent infections, except for S. pneumoniae and S. anginosus
- Five major groups of VGS:
-
S. anginosus group: S. anginosus, S. constellatus, S. intermedius
- Non-spore forming
- Can cause abscess formation in various organs (lungs, GI tract, liver, brain, etc.)
- Unlikely to cause endocarditis
- More virulent than other VGS groups
- S. constellatus may be beta-hemolytic and produce a butterscotch smell
-
S. mitis group: S. mitis, S. infantis, S. pneumoniae, S. parapneumoniae
- Unlikely to cause disease in immunocompetent individuals (except S. pneumoniae)
- Can cause odontogenic infections, bacteremia, and infective endocarditis, mainly in immunocompromised individuals
-
S. bovis group: S. bovis, S. gallolyticus, S. infantarius
- Found in the GI tract and often benign, but can cause issues if propagated
- Association with bacteremia, colon malignancy (cancer), and infective endocarditis, particularly when found in the blood
-
S. mutans group: S. mutans, S. sobrinus
- Mostly cause local infections, rarely significant infections in immunocompetent individuals
- Linked to odontogenic infections, but rarely the primary cause
-
S. salivarius group: S. salivarius, S. thermophilus, S. vestibularis
- Cause local infections, rarely significant infections in immunocompetent individuals
- Association with odontogenic infections or infections in immunocompromised individuals
-
S. anginosus group: S. anginosus, S. constellatus, S. intermedius
Beta-Hemolytic Streptococci (BHS)
- Also known as pyogenic streptococci
- Focus on Lancefield groups A, B, C, and G
- Complete hemolysis of sheep blood agar
- Capable of causing mild to life-threatening diseases in various hosts
- Can cause acute and post-acute/post-infectious sequelae (post-infection complications)
- Each streptococcal species has unique surface antigens
- Groups A, B, C, and G refer to specific surface antigens
Streptococcus pyogenes (Group A Streptococci, GAS)
- Gram-positive cocci in chains
- Classified based on emm gene (encoding M-protein) with over 220 genotypes
- emm gene expresses surface markers for virulence factors
- Natural habitat: human skin and upper GI tract
- Virulence factors:
- Likelihood of carrier status and disease depends on age, immune status/vaccination, type of infection, and year
- Associated infections:
- Pharyngitis, scarlet fever, impetigo, cellulitis, necrotizing fasciitis, streptococcal toxic shock syndrome, post-streptococcal sequelae (rheumatic fever, glomerulonephritis)
Microbiological Identification
-
Sample Collection:
- Blood: morphology/hemolysis
- Tissue (abscess, biliary tract): rapid identification using MALDI-TOF
-
Identification:
-
Biochemical methods:
- Optochin susceptibility (for S. pneumoniae)
- Bile acid soluble GPC in chains (for S. pneumoniae)
- Rapid identification methods: MALDI-TOF (laser lysis and aerosolization, mass spectrometry for bacterial component analysis)
- PCR methods: multiplex PCR
- Antigen testing: not routinely used
-
Biochemical methods:
Enterococci
- Gram-positive cocci
- Historically part of the streptococci genus (group D streptococci)
- Over 40 diverse species, ubiquitous organism, exact number debatable
- 90% of infections caused by two species: E. faecalis (80-90%) and E. faecium (5-15%)
- E. gallinarium and E. casseliflavus are motile
- Most strains are non-virulent or low-virulent
- Mostly gamma-hemolytic (non-hemolytic)
- Virulent strains show alpha or beta hemolysis
- Common in the lower GI tract (10^5 - 10^7 cfu/gram of feces)
- Also found on skin and oral cavity (higher concentrations in the perineum)
- Found in animals, soil, water, food, sewage, and plants
- Easily transmissible to hands, clothing, environment, and inanimate objects
- Resistant to antiseptics and disinfectants
Enterococci: Role in the GI Tract
- Commensal organism
- Involved in meat and cheese fermentation, food preservation
- Stimulates the immune system and maintains intestinal homeostasis
- Used as probiotics
- Can cause food contamination
Enterococci: Role in the Body
- Part of the normal flora, but can become pathogenic
- Don't produce significant toxins
- Two main virulence factors:
- Cell-surface proteins: extracellular surface protein (Esp), aggregation (Agg) substances (Asa1, Asp1, Asc10)
- Intrinsic antibiotic resistance: acquired via chromosomal mutations
- Associated diseases: urinary tract infections (UTIs), bacteremia (bloodstream infections), endocarditis (inflammation of the heart lining), wound infections
- More commonly infect immunocompromised individuals with underlying health conditions
Candida spp.
- Gram-positive oval budding yeast cells with pseudohyphae
- Common cause of fungal infections (candidiasis)
- Usually a commensal organism
- Most common in women, but can affect anyone
- Risk factors:
- Immune deficiency (e.g., HIV, cancer, diabetes)
- Broad-spectrum antibiotic use
- Hospitalization, particularly in intensive care units
- Catheterization
- Prolonged use of corticosteroids
- Candidal colonization
- Associated infections:
- Oral candidiasis (thrush)
- Vaginal candidiasis (yeast infection)
- Esophageal candidiasis
- Cutaneous candidiasis
- Invasive candidiasis (serious bloodstream infections)
- Diagnosis:
- Gram stain: Gram-positive budding yeast cells with pseudohyphae
- Silver stains, KOH stains: visualizes fungi under the microscope
- Specimen and blood cultures: gold standard
- Immunodiagnosis: antibody/antigen detection against cell-wall mannan
- Management:
- Depends on the type of fungal infection
- Azoles (e.g., fluconazole): first-line therapy if susceptible
- Echinocandins (e.g., caspofungin): first choice for invasive infections
- Dual therapy with azoles and echinocandins: for endocarditis
- Amphotericin B: reserved for invasive infections unresponsive to first-line therapy
- Removal of catheters/foreign hardware: to prevent biofilm formation
Cryptococcus spp.
- Two major pathogenic species: Cryptococcus neoformans and Cryptococcus gattii
- C. neoformans: found in pigeon guano (droppings) and rotting trees
- C. gattii: found in eucalyptus and coniferous trees (Western Canada)
- May colonize humans without causing disease
- Causes more disease in immunodeficient individuals
- One million cases of cryptococcosis per year, over 600,000 deaths annually
- Requires low threshold for diagnosis and treatment
- Risk factors:
- AIDS
- Corticosteroid treatment
- Transplantation
- Cancer
- Sarcoidosis
- Lymphopenia
- Cirrhosis
- Major sites of infection:
- CNS (meningoencephalitis, cryptococcoma)
- Lungs (cavitary, nodular, interstitial pneumonia)
- Other sites: skin, prostate, peritoneum, eye
- Diagnosis:
- Serum C. neoformans antigen (blood test): sensitivity 99%, specificity 94%
- CSF C. neoformans antigen (cerebrospinal fluid): sensitivity 99%, specificity 99%
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Description
This quiz covers essential aspects of bacterial morphology, including various shapes and arrangements such as cocci, bacilli, and others. It also discusses oxygen requirements for bacterial growth and the importance of the Gram stain process in bacterial identification. Test your knowledge on these fundamental microbiological concepts!
