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Questions and Answers
Which antimicrobial agent inhibits gram-positive bacteria when growing Neisseria gonorrhoeae on selective chocolate agar?
Which confirmatory test can be used to identify Neisseria gonorrhoeae?
What is the purpose of using cryoprotectants like 20% glycerol in storing Neisseria gonorrhoeae?
Which type of agar is commonly used for the isolation of Neisseria gonorrhoeae?
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Which sugar can Neisseria gonorrhoeae and Neisseria meningitidis ferment in the carbohydrate test?
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Which test is used to differentiate between Streptococcus and Staphylococcus?
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What is the cause of red man syndrome when overdosing on vancomycin?
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Which type of Staphylococcus aureus is resistant to methicillin?
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Which of the following antibiotics can be used to treat MRSA infections?
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What is indicated by a positive DNAse test result on DNAse agar?
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Impetigo, associated with Staphylococcus aureus infections, typically presents as which symptom?
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Which of the following conditions is NOT associated with Staphylococcus aureus?
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What is a major side effect associated with therapeutic drug monitoring (TDM) for vancomycin?
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What is the purpose of the CAMP test in relation to beta-hemolytic streptococci?
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What type of hemolytic activity is exhibited by viridans streptococci?
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Which factor is required by Haemophilus influenzae for growth?
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What is the significance of blackening in the Bile Esculin Hydrolysis Test?
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Which of the following is true regarding Haemophilus ducreyi?
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What differentiates Streptococcus pneumoniae from viridans streptococci?
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What is the role of sodium azide in the Bile Esculin Hydrolysis Test?
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What is a characteristic of Haemophilus spp. in terms of oxygen requirement?
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What characteristic distinguishes Rickettsia from typical bacteria?
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Which vector is responsible for the transmission of epidemic typhus caused by R. peowazekki?
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What is a common symptom associated with Rocky Mountain spotted fever caused by R. rickettsii?
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In what type of laboratory setting can Rickettsia be cultivated?
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Which risk factor is associated with the transmission of epidemic typhus?
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What type of organism is Rickettsia classified as?
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What is Brill-Zinsser disease a result of?
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What is one of the main vectors for murine or endemic typhus?
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What is the major virulence factor associated with group A streptococcus?
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Which condition is characterized by a severe sore throat, enlarged tonsils, and a mild fever due to strain of group A streptococcus?
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What is responsible for the severe sore throat and rash seen in scarlet fever?
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How does rheumatic fever occur following a streptococcal infection?
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Which bacterial species is primarily responsible for invasive lung infections?
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Study Notes
Staphylococcus aureus
-
Identification:
- Coagulase positive - forms a gel when mixed with rabbit plasma
- Catalase positive - produces bubbles when mixed with hydrogen peroxide
- DNAse positive - creates a clearing zone on DNAse agar
-
Types:
- MSSA (methicillin-sensitive Staphylococcus aureus) - sensitive to Methicillin
- MRSA (methicillin-resistant Staphylococcus aureus) - resistant to Methicillin
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MRSA:
- Resistance to Methicillin, a type of beta-lactam antibiotic
- Low incidence of MRSA in PH, treated with alternative antibiotics such as Vancomycin
-
Vancomycin:
- Overdose can lead to "red man syndrome"
- Requires therapeutic drug monitoring (TDM) to manage dosage
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Antibiotic Stewardship:
- Antibiotics should not be available over-the-counter (OTC)
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Diseases Associated with S.aureus
- Impetigo: skin infection causing yellow crusts
- Food poisoning: caused by toxins produced by S.aureus
- Toxic Shock Syndrome (TSS): associated with tampon use
- Septic Shock: bacterial toxins lead to dangerously low blood pressure
Streptococcus
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Hemolytic Properties:
- Beta-hemolytic: lyse red blood cells (RBCs)
- Group A (S. pyogenes) and Group B (S. agalactiae)
- CAMP test used to identify Group B beta-hemolytic streptococci (S. agalactiae)
- Alpha-hemolytic: partial lysis of RBCs
- Viridans streptococci and Streptococcus pneumoniae
- Optochin sensitivity used to differentiate S. pneumoniae (sensitive) from Viridans streptococci (resistant)
- Gamma-hemolytic: no hemolysis
- Group D (enterococci)
- Beta-hemolytic: lyse red blood cells (RBCs)
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Identification:
- Lancefield grouping: based on polysaccharide components of the bacteria
- Bile Esculin Hydrolysis Test: differentiates Group D enterococci from other streptococci - positive result indicated by blackening of the agar
Haemophilus spp.
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Characteristics:
- Gram-negative coccobacilli, microaerophilic
- Require growth factors: X factor (hemin) and V factor (NAD+)
- Grow on chocolate agar but not on blood agar
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Key Species:
-
- Haemophilus influenzae*:
- Cause of meningitis in neonates
- Capnophile (requires carbon dioxide for growth)
- Facultative anaerobe
- Haemophilus influenzae*:
-
- Haemophilus ducreyi*: cause of soft chancre
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- Haemophilus parainfluenzae*: low pathogenicity
-
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Specimen Collection and Identification:
- Gram stain for preliminary identification
- Culture on chocolate agar and selective chocolate agar (containing antimicrobials such as vancomycin, colistin, nystatin, anisomycin and trimethoprim sulfamethoxazole)
- Confirmatory tests: catalase, oxidase, and PCR
- Carbohydrate test (Cystine Trypticase Agar with 1% sugar) to determine sugar fermentation
- N. gonorrhoeae and N. meningitidis can ferment MALTOSE
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Storage:
- Frozen: Brain heart infusion broth with 20% glycerol
- Lyophilization: 2% skim milk, liquid nitrogen
Rickettsia
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Characteristics:
- Smaller than bacteria; similar in size to myxoviruses
- Non-motile
- Arthropod-borne (transmitted by insects)
- Small, gram-negative coccobacilli
- Difficult to cultivate on ordinary media. Requires monolayer cell culture or embryonated eggs
- Obligate intracellular parasites
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Groups:
- Typhus group
- Spotted fever group
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Typhus Group:
-
Rickettsia prowazekii
- Causes epidemic typhus (louse-borne)
- Reservoir hosts: humans and flying squirrels
- Vectors: human body louse (pediculus humanus humanus), squirrel louse or flea
- Brill-Zinsser disease: reactivation of louse-borne typhus
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Rickettsia typhi
- Causes murine or endemic typhus (rat-borne)
- Vectors: oriental rat flea
- Reservoir hosts: rats and cats
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Rickettsia prowazekii
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Spotted Fever Group:
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Rickettsia rickettsii
- Causes Rocky Mountain spotted fever (most common and severe)
- Transmitted by tick bites
- Sx: headache, high fever, hypotension, disseminated intravascular coagulation (DIC)
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Rickettsia rickettsii
Streptococcus pyogenes
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Characteristics:
- Group A streptococci (isolated from upper respiratory tract)
- Major virulence factor: M protein
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Diseases:
- Streptococcal pharyngitis (strep throat)
- Otitis media (middle ear infection)
- Mastitis (mammary gland infection)
- Impetigo (superficial skin infection)
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Exotoxins:
- Streptococcus pyrogenic exotoxins (SpeA, SpeB, SpeC, and SpeF): superantigens
- Cause scarlet fever (severe sore throat, fever, and rash)
- Necrotizing fasciitis (rapid and progressive destruction of soft tissues)
- Rheumatic fever (autoimmune disease affecting heart valves and joints)
- Streptococcus pyrogenic exotoxins (SpeA, SpeB, SpeC, and SpeF): superantigens
Streptococcus pneumoniae
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Characteristics:
- Invasive lung infection
- Encapsulated strains (S strain) are highly invasive
-
Disease:
- Can cause bacteremia (infection of the blood) and complications, such as bone, middle ear, and heart valve infections (endocarditis)
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Description
Test your knowledge on Staphylococcus aureus, including its identification methods, types, and associated diseases. This quiz covers important aspects such as methicillin resistance, treatment options, and antibiotic stewardship. Understand the clinical significance of this pathogen in healthcare settings.
