Questions and Answers
What is the most important coagulase positive Staphylococcus species?
Which Staphylococcus species is resistant to Novobiocin?
All coagulase negative Staphylococci are non-pathogenic.
False
What type of infections can S.aureus produce?
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What is VRSA?
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The main treatment for MRSA infections is _____.
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Match the following Staphylococcus species with their characteristics:
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List two diseases caused by S.aureus.
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What differentiates Group A streptococcus from other beta-hemolytic streptococci?
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Streptococcus agalactiae is a serious cause of disease in adults.
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What is the CAMP test used for?
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Which type of infection is primarily caused by Streptococcus pneumoniae?
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Study Notes
Introduction to Gram Positive Cocci
- Gram positive cocci measure 0.5-1.5 mm and cluster like grapes, reflecting their Greek origin: "staphyle" for bunch of grapes and "kokkus" for berry.
- Includes significant human pathogens and skin commensals like Micrococcus, Staphylococcus aureus, Staphylococcus epidermidis, and Staphylococcus saprophyticus.
Classification of Staphylococcus
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Based on Coagulase Production:
- Coagulase positive: Staphylococcus aureus (most important pathogen).
- Coagulase negative: Staphylococcus epidermidis, Staphylococcus saprophyticus, and Staphylococcus homonis (non-pathogen).
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Based on Pathogenicity:
- Common pathogens: S.aureus.
- Opportunistic pathogens: S.epidermidis, S.saprophyticus.
Culture Characteristics of Staphylococcus Aureus
- Nutrient agar: golden yellow pigment produced.
- MacConkey’s agar: appears pink.
- Blood agar: forms β-hemolytic colonies.
Toxins and Infections from S.aureus
- Produces enterotoxins, toxic shock syndrome toxin, and exfoliatin.
- Common infection sites include skin, nasopharynx, and perineum.
- Causes a variety of infections and intoxications including folliculitis, food poisoning, toxic shock syndrome, and staphylococcal scalded skin syndrome.
Structure and Virulence Factors
- Key virulence factors: Protein A, catalase, coagulase, hyaluronidase, lipases, B-lactamase, DNase, teichoic acids, polysaccharide capsule, and peptidoglycan.
- Catalase helps evade host defenses; coagulase serves as a virulence marker.
Pathogenicity and Transmission
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Source of Infection:
- Exogenous: from patients or carriers.
- Endogenous: from colonized body sites.
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Mode of Transmission:
- Direct or indirect contact (fomites) and inhalation of airborne droplets.
Treatment for S.aureus Infections
- Treatments include draining infected areas and using antibiotics such as semi-synthetic penicillins, cephalosporins, erythromycin, and clindamycin.
- Endocarditis may require a combination of semi-synthetic penicillin with an aminoglycoside.
Methicillin-Resistant Staphylococcus Aureus (MRSA)
- Initial symptoms: small red bumps advancing to painful abscesses.
- Vancomycin is the primary treatment; variants include VISA (intermediate susceptibility) and VRSA (resistant).
Staphylococcus Epidermidis and Saprophyticus
- S.epidermidis is adapted to grow on implanted foreign bodies, causing bacteraemia.
- S.saprophyticus primarily affects women, causing cystitis in those with urinary tract abnormalities.
Characteristics and Differences between S.epidermidis and S.saprophyticus
- Both are coagulase-negative and opportunistic.
- S.epidermidis is sensitive to novobiocin; S.saprophyticus is resistant.
- S.epidermidis is associated with skin/wound infections; S.saprophyticus with urinary tract infections.
Lab Diagnosis of Group A Streptococcus (GAS)
- Diagnostic steps include specimen collection, microscopic examination, inoculation on culture media, biochemical tests, agglutination test, and antimicrobial susceptibility tests.
- Bacitracin sensitivity can differentiate GAS; positive tests indicate inhibition by bacitracin.
Lab Diagnosis of Group B Streptococcus (GBS)
- GBS (Streptococcus agalactiae) is a Gram-positive bacterium that can cause severe disease in newborns.
- Key diagnostic features include beta hemolysis, catalase negativity, bacitracin resistance, and CAMP factor interaction.
Group D Streptococci
- Includes Enterococci (e.g., Enterococcus faecalis) and Nonenterococci (e.g., Streptococcus bovis).
- Enterococcus faecalis causes UTIs and endocarditis, especially post-surgery.
- Streptococcus bovis is also linked to endocarditis, particularly in cases of colon cancer.
Pneumococcus Infections
- Caused by Streptococcus pneumoniae, which can lead to pneumonia, meningitis, sepsis, and otitis media.
- Key treatments include penicillin G, erythromycin, and ceftriaxone, with a vaccine available against 23 common capsular antigens.
Lab Diagnosis of Pneumococcus
- Gram staining reveals Gram-positive cocci, often in pairs.
- Characteristics include alpha hemolysis on blood agar and susceptibility to optochin.
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Description
Explore the characteristics and classifications of Gram positive cocci, focusing on Staphylococcus species. This quiz covers important human pathogens such as Staphylococcus aureus, epidermidis, and saprophyticus, along with their identification and significance in microbiology.
