Gram-Positive and Gram-Negative Cocci of Medical Importance

These flashcards cover the essential concepts regarding Gram-positive and Gram-negative cocci that are relevant to medical microbiology.

What are the general characteristics of Staphylococci?

Common inhabitants of the skin and mucous membranes, spherical cells arranged in irregular clusters, gram-positive, lack spores and flagella, may have capsules, with more than 40 species.

What is a defining feature of Staphylococcus aureus?

Produces many virulence factors and grows in large, round, opaque colonies at an optimum temperature of 37°C.

What are some virulence factors of Staphylococcus aureus?

Includes coagulase, hyaluronidase, staphylokinase, lipase, penicillinase, hemolysins, leukocidin, enterotoxins, exfoliative toxins, and toxic shock syndrome toxin.

How is Staphylococcus aureus commonly transmitted?

Present in most environments frequented by humans and readily isolated from fomites, with a carriage rate for healthy adults of 20-60%.

What types of cutaneous lesions does Staphylococcus aureus cause?

Localized cutaneous infections, folliculitis, furuncles, carbuncles, and impetigo.

What is the difference between coagulase-positive and coagulase-negative Staphylococci?

Coagulase-positive includes Staphylococcus aureus, while coagulase-negative includes S. epidermidis and S. saprophyticus.

What are some commonly used treatments for Staphylococcal infections?

Cephalexin, sulfa drugs, tetracyclines, or clindamycin for less resistant S. aureus; vancomycin for MRSA.

What is the significant characteristic of Streptococci?

Gram-positive spherical/ovoid cocci arranged in long chains or pairs, non-spore forming, and can form capsules.

What are Lancefield groups?

Groups of Streptococcus classified based on cell wall carbohydrates.

What is the most significant pathogenic species of beta-hemolytic streptococci?

Streptococcus pyogenes, which is known for causing throat infections and scarlet fever.

What is the pathogenicity of Streptococcus pneumoniae?

It causes 60-70% of all bacterial pneumonias and is characterized by its capsule, which is a major virulence factor.

What increases the risk of pneumococcal infections?

Young children, the elderly, immune-compromised individuals, and people living in close quarters.

What are the virulence factors of Neisseria gonorrhoeae?

Fimbriae for attachment, IgA protease which cleaves secretory IgA, and the ability to not survive long outside of the host.

How are gonococcal infections transmitted?

Strictly a human infection, primarily transmitted through sexual contact.

What is a serious complication of untreated gonorrhea?

Potential for disseminated infection leading to arthritis, meningitis, or endocarditis.

What are the key characteristics of Neisseria meningitidis?

Capsule, adhesive fimbriae, IgA protease, and endotoxins; known for causing meningitis.

What populations are at high risk for meningococcal disease?

Children 6 months to 3 years, children and young adults aged 10 to 20, and individuals living in close quarters.