Microbiology and Pathogenesis of Bacterial Infections

What are pyogenic cocci?

Spherical bacteria that cause various suppurative infections.

What is the normal microbiota habitat for Staphylococcus aureus?

Anterior nares, nasopharynx, perineal area, skin, and colonizer of mucosa.

How can Staphylococcus aureus be transmitted?

Through direct contact (person-to-person, fomites) and indirect contact (aerosolized).

What is the significance of Staphylococcus epidermidis?

It is part of the normal microbiota found on skin and mucous membranes.

What are the significant Gram-positive pyogenic cocci species?

Staphylococcus aureus, Streptococcus pyogenes, Streptococcus agalactiae, Streptococcus pneumoniae, and Viridans Streptococcus.

What are the significant Gram-negative pyogenic cocci species?

Neisseria gonorrhoeae, Neisseria meningitidis, and Moraxella catarrhalis.

What is the habitat of Staphylococcus saprophyticus?

Normal microbiota of skin, genitourinary tract, and mucosa.

What is the common mode of transmission for Staphylococcus saprophyticus?

Endogenous strain affecting the sterile urinary tract, particularly in young, sexually active females.

What does 'cocci' refer to in microbiology?

Spherical bacteria.

What does 'pyogenic' mean?

Producing pus.

What is the significance of Staphylococcus haemolyticus and Staphylococcus lugdunensis?

They are part of the normal microbiota found on skin and mucous membranes in low numbers.

What are the general characteristics of pyogenic cocci?

They are spherical and can cause pus-producing infections.

What is the role of Neisseria in human health?

Some species are pathogenic and can cause infections such as gonorrhea and meningitis.

What is the typical habitat for Neisseria species?

They are typically found in the mucous membranes.

What are the characteristics of Micrococcus spp.?

They are spherical bacteria that are part of the normal skin flora.

What is the significance of Kocuria spp. in microbiology?

They are considered part of the normal skin microbiota and can be opportunistic pathogens.

What is the role of Kytococcus spp. in human health?

They are skin commensals that can occasionally cause infections.

What does 'endogenous strain' refer to?

A strain that originates from the normal microbiota and can cause infections when introduced to sterile sites.

What are common conditions caused by pyogenic cocci?

Suppurative infections, such as abscesses and pneumonia.

What is the importance of understanding modes of transmission for pyogenic cocci?

It helps in preventing the spread of infections, especially in healthcare settings.

What are the normal microbiota locations in the human body?

Skin, mucosa, oropharynx.

What is the significance of endogenous strains in infections?

They are uncertain and rarely implicated in infections.

What infections are associated with immunocompromised hosts?

Brain abscess, meningitis, pneumonia, endocarditis.

What are the characteristics of Gram-positive, catalase-positive cocci?

They appear as spherical cells (0.5-1.5 μm), are aerobic or facultatively anaerobic, and some are obligate anaerobes.

What do colonies of these cocci look like after 18-24 hours of incubation?

They are medium-sized (1-8 mm), cream-colored, white, or rarely light gold, and have a buttery appearance.

What environmental conditions can these cocci tolerate?

They can grow in high salt concentrations and at temperatures ranging from 18°C to 40°C.

What factors determine the pathogenicity of staphylococci?

The ability to evade immune clearance, produce surface proteins for adherence, and elaborate specific toxins and hydrolytic enzymes.

What is the function of the capsule in staphylococci?

It inhibits phagocytosis and chemotaxis by leukocytes.

What is the role of the slime layer in staphylococci?

It facilitates adherence to foreign bodies and inhibits antibiotic penetration.

What are penicillin-binding proteins?

Enzymes that catalyze the constriction of the peptidoglycan layer and are targets of penicillin and other beta-lactam antibiotics.

What is the primary function of peptidoglycan in staphylococci?

It provides osmotic stability and has endotoxin-like activity.

What is the role of teichoic acids in staphylococci?

They bind to fibronectin and are involved in cell wall structure.

What is the function of protein A in staphylococci?

It binds to immunoglobulins, decreasing immune-mediated clearance from infection sites.

What are MSCRAMMs?

Microbial Adhesive Surface Matrix Components Recognizing Molecules, which are surface adhesion proteins in staphylococci.

What are some examples of surface adhesion proteins in staphylococci?

Staphylococcal protein A, fibronectin-binding proteins A and B, clumping factor proteins A and B.

What is the biological effect of the capsule in staphylococci?

It inhibits chemotaxis and phagocytosis, and inhibits mononuclear cell proliferation.

What is the significance of the cytoplasmic membrane in staphylococci?

It serves as an osmotic barrier and provides anchorage for biosynthetic and respiratory enzymes.

How does the peptidoglycan layer contribute to staphylococcal virulence?

It provides osmotic stability and stimulates the production of endogenous pyrogens.

What is the role of enzymes like coagulase in staphylococci?

Coagulase is mainly produced by Staphylococcus species and plays a role in pathogenicity.

What is the size range of staphylococci cells?

0.5-1.5 μm.

What color do staphylococcal colonies appear after incubation?

Cream-colored, white, or rarely light gold.

What is the temperature range for the growth of staphylococci?

18°C to 40°C.

What is the role of coagulase in Staphylococcus aureus?

Coagulase converts fibrinogen to fibrin, forming a clot that protects staphylococci from phagocytosis and localizes the infection.

What are the two types of coagulase produced by Staphylococcus aureus?

Bound coagulase directly converts fibrinogen to insoluble fibrin, while cell-free coagulase reacts with a plasma globulin factor to form Staphylothrombin.

What is the function of catalase in Staphylococci?

Catalase catalyzes the conversion of hydrogen peroxide to water and oxygen, protecting the organism from toxic H2O2 produced during metabolism and phagocytosis.

What is the function of hyaluronidase in Staphylococcus aureus?

Hyaluronidase hydrolyzes hyaluronic acid in connective tissues, promoting the spread of Staphylococci.

What is the role of fibrinolysin in Staphylococcus aureus?

Fibrinolysin dissolves fibrin clots, aiding in the spread of infection.

What do lipases do in Staphylococcus aureus?

Lipases hydrolyze lipids, contributing to the virulence of the bacteria.

What is the function of nucleases in Staphylococcus aureus?

Nucleases hydrolyze DNA, which can aid in the spread of infection.

What are cytotoxins and their effect on cells?

Cytotoxins are toxic to various cells, including erythrocytes, fibroblasts, leukocytes, macrophages, and platelets.

What is exfoliative toxin and its mechanism of action?

Exfoliative toxin, also known as epidermolytic toxin, splits intercellular bridges in the epidermis, leading to skin lesions.

What are the characteristics of delta toxin?

Delta toxin is a 30k Da polypeptide produced by most strains of S. aureus, acts as a surfactant, and disrupts cellular membranes.

What is gamma toxin and its components?

Gamma toxin is a bicomponent toxin composed of slow-eluting proteins (HlgA, HlgC, LuKS-PV) and fast-eluting proteins (HlgB, LuKf-PV).

What is Panton-Valentine Leukocidin (PVL)?

PVL is an endotoxin lethal to polymorphonuclear leukocytes, contributing to the virulence of certain strains of S. aureus.

What is the effect of enterotoxins produced by Staphylococcus aureus?

Enterotoxins stimulate the release of inflammatory mediators, leading to increased peristalsis, fluid loss, nausea, and vomiting.

What distinguishes enterotoxin A from other enterotoxins?

Enterotoxin A is most commonly associated with food poisoning.

What is the stability of enterotoxins at high temperatures?

Enterotoxins are heat-stable, remaining active at 100°C for 30 minutes.

What is the role of alpha hemolysin?

Alpha hemolysin disrupts smooth muscle in blood vessels and is toxic to erythrocytes, leukocytes, hepatocytes, and platelets.

How does alpha hemolysin affect cell membranes?

It binds to cell surfaces, aggregates into a heptamer, and forms pores that allow ion flux, leading to osmotic swelling and cell lysis.

What is the function of beta hemolysin?

Beta hemolysin is a 35k Da heat-labile protein produced by most strains of S. aureus, contributing to its virulence.

What are the effects of toxic shock syndrome toxin?

Toxic shock syndrome toxin causes leakage or destruction of endothelial cells.

What is the significance of exfoliative toxin A and B?

Exfoliative toxin A is heat-stable and phage-associated, while exfoliative toxin B is heat-labile and located on a plasmid.

What are the serologically distinct groups of enterotoxins?

There are 24 serologically distinct enterotoxins, primarily categorized into groups A through E and G through J.

What is the biological effect of lipases produced by Staphylococcus aureus?

Lipases hydrolyze lipids, aiding in the breakdown of host tissues and promoting infection.

What is Toxic Shock Syndrome Toxin-1 (TSST-1)?

A 22k Da, heat and proteolysis resistant chromosomal-mediated toxin responsible for most menstruating-associated TSS cases and approximately 50% of non-menstruating cases.

How does TSST-1 affect endothelial cells at different concentrations?

At low concentrations, it causes leakage by endothelial cells, and at higher concentrations, it is cytotoxic to these cells.

How is TSST-1 absorbed into the body?

It is absorbed through the vaginal mucosa, leading to systemic effects, often associated with prolonged tampon or napkin use.

What are the characteristics of cutaneous infections caused by Staphylococcus aureus?

They can extend to deeper subcutaneous tissue, present with multiple sinus tracts, chills, and fevers.

What are the symptoms of wound infections caused by Staphylococcus aureus?

Wound infections are characterized by edema, erythema, pain, and accumulation of purulent material.

What is Staphylococcal Scalded Skin Syndrome (SSSS)?

A bullous exfoliative dermatitis primarily affecting newborns and young children, characterized by abrupt onset of localized perioral erythema and large bullae.

What is the Nikolsky sign in relation to SSSS?

It is a sign where slight pressure displaces the skin, indicating the presence of bullous exfoliation.

What happens to the epithelium in SSSS after 7-10 days?

The epithelium becomes intact again when antibodies against the toxin appear, and scarring does not occur as only the top layer of the epidermis is affected.

What is the mortality rate of SSSS in neonates and young children?

Less than 5%, with deaths typically caused by secondary bacterial infections of denuded skin.

In what populations do SSSS infections occur in adults?

In immunocompromised hosts or patients with renal disease, with a mortality rate of 60%.

What is Bullous Impetigo?

A localized form of SSSS associated with specific strains of toxin-producing S. aureus, characterized by superficial skin blisters.

What distinguishes Bullous Impetigo from SSSS?

In Bullous Impetigo, S. aureus is present in the localized blisters, and erythema does not extend beyond the blister borders.

What are the characteristics of Toxic Shock Syndrome?

Typically involves abscesses filled with pus surrounded by necrotic tissues and damaged leukocytes, often following skin infections.

What is Folliculitis?

A mild inflammation of a hair follicle or oil gland, characterized by a raised and reddened base with small pus collections.

What are Furuncles?

Extensions of folliculitis that present as large, painful, raised nodules with underlying collections of dead and necrotic tissue.

What are Carbuncles?

A coalescence of furuncles, which can be rare but potentially fatal, characterized by fever and hypotension.

What is the initial fatality rate associated with Toxic Shock Syndrome?

The initial fatality rate is approximately 5%.

What is the risk of recurrent disease in Toxic Shock Syndrome?

The risk of recurrent disease can be as high as 65% unless treated with effective antibiotics.

What is Purpura fulminans?

A severe condition characterized by large purpuric skin lesions, fever, hypotension, and disseminated intravascular coagulation.

When was Toxic Shock Syndrome first described, and in which population?

It was first described in 1978, associated with women using highly absorbent tampons, but also appeared in men, children, and non-menstruating women.

What are the systemic effects of Toxic Shock Syndrome?

Involvement of multiple organ systems including CNS, GIT, liver, renal, and muscular systems.

What is the primary cause of food poisoning associated with Staphylococcus aureus?

Ingestion of a toxin formed outside the body, often from contaminated food such as salads with mayonnaise, meat products, and poultry.

What are the common symptoms of food poisoning caused by Staphylococcus aureus?

Nausea, vomiting, abdominal pain, and severe cramping.

What are the two types of pneumonia associated with Staphylococcus aureus?

Aspiration pneumonia and hematogenous pneumonia.

What is aspiration pneumonia and who is most at risk?

Aspiration pneumonia occurs when oral secretions are inhaled into the lungs, commonly seen in the young, elderly, and patients with conditions like cystic fibrosis and chronic obstructive pulmonary disease.

What is hematogenous pneumonia and in which patients is it commonly found?

Hematogenous pneumonia results from the spread of infection through the bloodstream, commonly found in patients with bacteremia or endocarditis.

What is necrotizing pneumonia and what is a common cause?

Necrotizing pneumonia is characterized by tissue death in the lungs and is often caused by community-acquired MRSA.

What is empyema and its prevalence in pneumonia patients?

Empyema is the presence of pus in the pleural space and occurs in about 10% of patients with pneumonia.

What is osteomyelitis and how does it typically occur?

Osteomyelitis is an infection of the bone that results from hematogenous dissemination or secondary infection from trauma.

What are the common causes of osteomyelitis in children?

In children, osteomyelitis often results from cutaneous infections and typically involves long bones.

What is bacteremia and its common origins?

Bacteremia is the presence of bacteria in the blood, most commonly originating from skin infections.

What percentage of bacteremia cases are nosocomial?

More than 50% of bacteremia cases are nosocomial.

What is the typical presentation of endocarditis?

Endocarditis presents with sudden onset of localized pain and high fever.

What are the risk factors for septic arthritis?

Septic arthritis occurs in individuals receiving intraarticular injections or those with mechanically abnormal joints, often seen in large joints.

What is the characteristic finding in a joint affected by septic arthritis?

A painful, erythematous joint with purulent material obtained on aspiration.

What is the mortality rate associated with untreated endocarditis?

The mortality rate is approximately 50% unless promptly diagnosed.