Aerobic Gram-Positive Cocci: Identification, Pathogenicity, and Clinical Significance

What are Aerobic Gram-Positive Cocci commonly associated with?

They are members of the normal flora in most body sites covered with skin or lined with mucous membranes.

How are Aerobic Gram-Positive Cocci primarily acquired?

Mostly acquired by nosocomial infection (HAI).

What is the first step in identifying potential pathogens among Aerobic Gram-Positive Cocci?

Screening tests to group into possible genera.

What is the second step in identifying Aerobic Gram-Positive Cocci?

Specific tests to identify genus and species.

What is the catalase test result for Staphylococcus?

Catalase positive.

What are the general characteristics of Staphylococcus?

Usually aerobic or facultative anaerobe, nonmotile, and salt-tolerant.

What is the microscopic morphology of Staphylococcus?

Gram-positive cocci in pairs, tetrads, and grape-like clusters.

Which species of Staphylococcus is more virulent?

Staphylococcus aureus.

What is the normal microbiota of human skin?

Staphylococcus epidermidis.

How is Staphylococcus aureus primarily transmitted?

By direct contact or fomites.

What is the colony morphology of Staphylococcus aureus?

1 to 2 mm, opaque, round, butyrous, white to golden yellow, convex.

What does MSA stand for and what is its significance?

Mannitol Salt Agar; it allows only Staphylococcus to grow, with S. aureus turning the media golden yellow.

What are the three features that contribute to the pathogenicity of Staphylococcus aureus?

Structures that evade phagocytosis, production of enzymes, and production of toxins.

What is the function of Protein A in Staphylococcus aureus?

It binds to immunoglobulin G (IgG) and inhibits opsonization and the complement cascade.

What does hyaluronidase do?

It breaks down hyaluronic acid, enabling bacteria to spread between cells.

What is the role of β-lactamase in Staphylococcus aureus?

It breaks down penicillin, allowing bacteria to survive treatment with β-lactam antimicrobial drugs.

What type of diseases can Staphylococcus aureus cause?

Noninvasive diseases like food poisoning, cutaneous diseases, and systemic diseases like toxic-shock syndrome.

What is Toxic Shock Syndrome (TSS) caused by?

Some Staphylococcus strains produce TSS toxin, which is absorbed into the blood.

What is the treatment for methicillin-resistant S. aureus (MRSA) infections?

Vancomycin.

What is the significance of hand antisepsis in healthcare?

It is important to prevent healthcare-associated infections.

What is the colony morphology of Staphylococcus epidermidis?

1 to 2 mm gray-white, opaque, usually nonhemolytic.

What is the Gram stain result for Staphylococcus species?

Gram-positive.

Where are Staphylococcus species commonly found?

On the skin, in mucous membranes, and the oropharynx as normal flora.

What is the role of lipases produced by Staphylococcus?

They digest lipids, allowing Staphylococcus to grow on skin and in oil glands.

What is the appearance of colonies of Staphylococcus aureus on MSA?

Yellow colonies with zones on the agar.

What type of bacteria is Streptococcus?

Gram positive cocci in chains.

What is the optimal growth temperature for Streptococcus?

37°C on sheep blood agar (SBA).

How are Streptococcus species categorized?

Based on Lancefield classification into serotypes based on antigens.

What are the three types of hemolytic reactions in Streptococcus?

Alpha, beta, and gamma (nonhemolytic).

What is the main pathogen in Group A Streptococcus?

Streptococcus pyogenes.

What is a characteristic colony morphology of S. pyogenes?

Large, gray, transparent colony on SBA with a wide zone of beta-hemolysis.

What are the two hemolysins responsible for beta-hemolysis in S. pyogenes?

Streptolysin S (stable in oxygen) and Streptolysin O (labile in oxygen).

What structural component helps S. pyogenes evade phagocytosis?

Hyaluronic acid capsule.

What is the function of M protein in S. pyogenes?

Helps in adhesion to host cells.

What disease is commonly caused by S. pyogenes?

Pharyngitis (strep throat).

What is rheumatic fever?

A complication of untreated Streptococcal pharyngitis where the immune system attacks the body's own joints.

What is the significance of the pyrogenic toxin produced by S. pyogenes?

It can stimulate fever, rash, and shock.

What is the primary treatment for infections caused by S. pyogenes?

Penicillin.

What is the main pathogen in Group B Streptococcus?

Streptococcus agalactiae.

What is a characteristic colony morphology of S. agalactiae?

Large, flat, glossy, gray-white colonies with a narrow zone of beta-hemolysis.

What is a common disease associated with S. agalactiae in newborns?

Neonatal bacteremia, meningitis, and pneumonia.

What is the primary diagnostic test for Group B Streptococcus?

Enzyme-linked immunosorbent assay (ELISA).

What is the main pathogen in Streptococcus pneumoniae?

Streptococcus pneumoniae.

What is a key feature of S. pneumoniae's microscopic morphology?

Gram-positive diplococci, often described as lancet or football-shaped.

What is the most common disease caused by S. pneumoniae?

Pneumococcal pneumonia.

What is the gold standard for diagnosing S. pneumoniae infections?

Quellung reaction.

What is a significant characteristic of Group D Streptococcus?

Normal flora in the gastrointestinal system, can cause infections if spread.

What are the two species of Enterococcus that cause disease in humans?

E. faecalis and E. faecium.

What is a common challenge in treating enterococcal infections?

Enterococci are often resistant to antimicrobials.

What is the role of good hygiene in preventing enterococcal infections?

Minimizes transmission in healthcare settings.

Staphylococcus epidermis

Normal microbiota on human skin, Opportunistic infections

S. epidermis

ubiquitous to the skin

S. aureus

found only in moist skin folds

Bound Coagulase

Converts fibrinogen into fibrin molecules

Cell-free coagulase

triggers blood clotting

Staphylokinase

Dissolves fibrin threads in blood clots, allowing S. aureus to free itself from clots

Cytolytic toxins

Disrupt the cytoplasmic membrane of cells

Exfoliative toxins

Cause skin cells to separate and slough off

Noninvasive Disease: Food Poisoning

Due to ingestion of enterotoxin-contaminated food

Streptolysin S

stable in oxygen environment

Streptolysin O

liable in oxygen environment

Group B Streptococcus

Enzyme linked immunosorbent assay (ELISA) test used for

Scarlet fever

streptococcal pharyngitis infections, chest rash spreads

Pyrogenic toxin

causes fever, rash, and shock

Streptokinase

Break down blood clots, helps streptococcus spread through tissues