Chapter 14 & 18 Toxins/Staphylococcus

Staphylococcus; streptococcus

2 medically important genera that are non-motile and non-spore forming.

Osteomyelitis

Abscesses of the bone; can result from hematogenous infection or as secondary infection resulting from trauma or overlying staph infection. Symptoms include localized pain over the bone involved and fever. In adults intense back pain. Treatments are antibiotic therapy or surgery when indicated, leads to an excellent cure rate.

S. saprophyticus

Almost always community acquired. Primarily caused UTI infections in sexually active young women. Symptoms usually include dysuria, pyuria, and numerous organisms in the urine. Typically responds well to antibiotics with reinfection uncommon.

S. epidermidis

Almost always hospital acquired. Part of the normal flora but can cause infections of intravenous catheters and prosthetic implants, heart valves, vascular grafts, and joints. Produce slime layers that bind them to catheters and shunts. Persistent bacteremia and immune-complex complications occur in patients with long-standing disease. Hospital personnel are a major reservoir of antibiotic-resistant strains of S. epidermidis.

Staphylococcal Scalded Skin Syndrome (SSSS)

Also known as Ritter's disease. Symptoms include abrupt onset with localized perioral erythema that spread over entire body within 2 days. Skin could be displaced with slight pressure (positive Nikolysky sign). Large cutaneous blisters follow that do not contain the organism, then desquamation of the epithelium. Recovery of intact epithelium within 7-10 days. Scarring does not occur. It is a disease of neonates and young children.

Toxic Shock Syndrome (TSS)

First described in 1978, associated with a new form of hyper-absorbent tampon. Most commonly associated with menstruating women. Less than 150 cases annually in U.S. Mostly women, aged 15-44 years. Pathogenesis: genital mucosa colonized by S. aureus strains producing toxic shock syndrome toxin-1 (TSST). Toxic mechanism: TSST-1 acts as a superantigen.

-smears from base of lesions reveal gram-positives in grapelike clusters or single cells and small groups. - diagnosis is made by the clinical presentation with isolation of S. aureus in culture confirmatory.

How is staph diagnosed?

Staphylococcus aureus

It is found worldwide. Transiently present in warm, moist skin folds, mainly in the anterior nares. Can survive on dry surfaces for long periods of time. It is carried by approximately 30% of population at any given time. It is spread person to person or by contact with fomites.

Bullous impetigo

Localized form of SSSS. The disease is manifested as superficial skin blisters. The blisters contain the organism. Sloughing of the skin does not occur (Nikolsky -). Found in very young children, but also may occur in adults. It is highly communicable.

Staphylococcus aureus

Main pathogen. Found mainly on the mucous membranes of humans. (Coagulase positive)

S. aureus

Mannitol-salt agar for ____ screening.

Type II Toxins

Membrane-damaging toxins. The lyse host cells by damaging membrane. They have two roles which are to kill host cells (phagocytes) and escape phagosome into cytoplasm.

Staphylococcus aureus

There are two causes for this disease: result of toxin activity and proliferation of organisms leading to abscess formation and tissue destruction.

A Subunit

Toxin (enzymatic) unit.

TSST

Treatment of ____ involves correction of shock using fluids and pressor drugs; removal of tampon or debridement of the infected site.

Channel forming

Type of type II toxin (alpha-helix or beta-sheets) insert into the membrane leading to leakage of cellular components and influx or water, lysing the cell. Example is alpha toxin of Clostridium perfringens.

Membrane disrupting

Type of type II toxin (phospholipases) alter membrane phospholipids sometimes removing a head group. Example is phospholipase C of Bacillus cereus , Listeria monocytogenes, and Pseudomonas aeruginosa.

Staphylococcus epidermidis

Usually a harmless skin bacterium comprising the normal flora, 99% of the population carries this bacterium.

Necrotizing

Usually due to MRSA; massive hemoptysis (coughing up blood), septic shock, and high mortality rate.

Staphylococcus

Very hearty bacteria. Relatively heat resistant. Gram (+) which grow in grape-like clusters. They are facultative anaerobes. They are able to grow on medium containing 10% NaCl. Temperature range 18 to 40 C.

Fibrinolysin

Virulence factor of S. aureus. (Staphylokinase) it dissolves fibrin clots.

Cytotoxins

Virulence factor of S. aureus. An alpha, beta, delta, gamma, and Panton-Valentine (P-V) leukocidin. All have broad activity against various cell types. P-V specifically lyses neutrophils and macrophages (found in all cases of community acquired MRSA).

Enterotoxin

Virulence factor of S. aureus. Causes vomiting and watery, non-bloody diarrhea. A superantigen. Contains 6 types (A-F). Stable to heating at 100 C and resistant to GI enzymes. It leads to release of IL-1 and IL-2 from macs and T-cells.

Coagulase

Virulence factor of S. aureus. Converts fibrinogen to insoluble fibrin, causing staphylococci to clump together. Mechanism of action allows the bacterium to wall itself off into an abscess with the formation of fibrin layers. Localizes the infection and protects the organisms from phagocytosis. It is used as a marker to distinguish S. aureus from other negative species.

Nuclease

Virulence factor of S. aureus. It degrades nucleic acids. The mechanism in pathogenesis is not known. It is thermostable. It is a marker for S. aureus.

Hyaluronidase

Virulence factor of S. aureus. It hydrolyzes hyaluronic acids (acidic mucopolysaccharides present in connective tissue). It facilitates the spread of S. aureus in tissues. 90% of S. aureus strains produce it.

PBP2'

Virulence factor of S. aureus. It is a novel penicillin-binding protein that is not bound by penicillins. Many Staph are resistant to penicillin. (MRSA).

Toxin Shock Syndrome Toxin-1 (TSST-1)

Virulence factor of S. aureus. It is heat and proteolysis-resistant chromosomally mediated exotoxin. Superantigen leading to release of large amounts of IL-1, IL-2, and TNF-alpha. It is responsible for symptoms of disease which include fever, hypotension, rash, and desquamation, involvement of multiple organ systems.

Lipases

Virulence factor of S. aureus. It is produced by all S. aureus and > 30% of coagulase negative Staph. It hydrolyzes lipids, making it possible for the bacteria to survive in sebaceous areas of the body. It is probably necessary for invasion of Staph into cutaneous and subcutaneous tissues and the formation of superficial skin infections (furuncles, boils, carbuncles).

Catalase

Virulence factor of S. aureus. It is produced by all staphylococci; it catalyzes the conversion of H2O2 to water and oxygen. It protects the organism from toxic effects of H2O2 in phagocytosis.

Exfoliative toxin

Virulence factor of S. aureus. It is responsible for symptoms of SSSS. It is expressed in 5-10% of strains. It produces exfoliative dermatitis. Has serine proteases that separate intracellular bridges in the epidermis.

Enterotoxins, cytotoxins, exfoliative toxins, and toxic shock syndrome toxin-1

Virulence factors of S. aureus. Contain toxins that produce many types of toxins. Include these 4:

Pneumonia

Ways to get ____ include aspiration, hematogenous, and necrotizing.

- staphylococcus aureus - staphylococcus epidermidis - staphylococcus saprophyticus

What are the 3 important types of staphylococcus?

1. Structural component of the cell envelope of Gram - bacteria (LPS complex) 2. Released from cell only with destruction of the cell. 3. Heat stable (can withstanding autoclaving at 120 C for 1 h.) 4. Lethal dose is much larger than exotoxins. 5. Cannot be converted and are not easily neutralized by antitoxin.

What are the properties of Endotoxins?

1. Produced by Gram + and Gram - bacteria. 2. Metabolic products of growing cells which are released into surrounding medium. 3. Proteins or short peptides. 4. High level of toxicity. (1 g of tetanus, botulinum, or Shigella toxin is enough to kill about 10 million people) 5. Lethal dose is small. 6. Heat liable. Most can be destroyed at 60-80 C. 7. Can be converted to tokoids and neutralized by antitoxins. 8. Targeted to specific cell structures or functions.

What are the properties of Exotoxins?

Channel forming and membrane disrupting

What are the two types of Type II toxins?

Ribosomes Transport mechanisms Intracellular signaling

What do A-B toxins target?

LPS; TA; LTA

____ (endotoxin), ____, and ____ interact with TLRs and trigger excessive cytokine release.

LPS; LPS

____ + ____-binding protein binds to CD14 receptor to trigger inflammatory cytokines. Triggers activation of complement cascade, increased vascular permeability, and activation of coagulation cascade. Clots form in small vessels (disseminated intravascular coagulation) leads to decrease in blood pressure, organ failure, and acute respiratory distress syndrome (ARDS).

Aspiration

____ is seen primarily in the very young, elderly, cystic fibrosis, influenza, and COPD patients.

Toxins

____ were the first "virulent factors" identified and studied in detail. They directly harm or trigger destructive biologic activities.

Staphylococcus aureus

Patients at risk for this disease: - infants (SSSS) - Young children with - poor hygiene (cutaneous) - Menstruating women (TSS) - people with intravascular catheters (bacteremia and endocarditis) or shunts (meningitis) - people with compromised pulmonary function or preceding viral infection (pneumonia)

Type I toxins (Superantigens) Type II toxins (Membrane-disrupting toxins) Type III toxins (A-B toxins)

Protein endotoxins include:

Pyogenic skin infections

Pus forming

B Subunit

Receptor binding - translocation across membrane.

- presence of foreign body - previous surgical procedure - suppression of normal flora by antibiotics

Risk factors of S. aureus

-Staphylococcal scalded skin syndrome (SSSS) - staphylococcal food poisoning - toxic shock syndrome (TSS)

S. aureus Result of toxin activity:

Capsule, slime layer, protein A

S. aureus evasion of innate immunity produces ____, ____, and ____. This is why it is a prolific pathogen.

- Cutaneous infections - bacteremia and endocarditis - pneumonia and empyema - osteomyelitis and septic arthritis

S. aureus proliferation of organisms leading to abscess formation and tissue destruction:

Capsule

S. aureus. Polysaccharide capsule (11 serotypes). Prevents effective phagocytosis.

Protein A

S. aureus. The major protein in the cell wall. It binds to Fc portion of IgG at the complement binding site. It prevents activation of complement and opsonization with C3b.

Slime layer

S. aureus. Water soluble film of monosaccharides, proteins, and small peptides. Facilitates adherence.

Bacteremia

Septicemia or sepsis. Can originate from any localized lesion, such as wound infection or IV drug abuse. Often the initial focus of infection is unknown.

Hematogenous

Spread by blood in patients with bacteremia or endocarditis.

SSSS; TSS

Staph are seen in the nasopharynx of patients with ____ and in the vagina of patients with ____ but cannot be distinguished from organisms that normally colonize.

Endocarditis

A very serious disease with mortality rate of approximately 50%. Has nonspecific flu-like symptoms at first but conditions can deteriorate rapidly. It requires immediate medical and surgical intervention. Peripheral evidence of embolization (blood clots resulting from the bacteria).

Entercolitis

Caused by a certain S. aureus strain. Symptoms include watery diarrhea, abdominal cramps, and fever. Strains usually express Enterotoxin A and IP-V leukotoxin. Generally occurs in patients who have received broad spectrum antibiotics. Abundant staphylococci in stool of patients and lack of normal gram negative bacteria.

Staphylococcal Food Poisoning

One of the most common foodborne illness. It is caused by preformed Enterotoxin in food rather than direct effect of organism. It is common in processed meats, custard-filled pastries, potato salad, ice cream. Contamination by a human carrier rather than animal reservoir. Heating food will kill bacteria but not the heat-stable toxin (superantigen).

Staphylococcus saprophyticus

Colonizes the urinary tract.

Type III Toxins

Consist of two domain subunits: A subunits and B subunits. After binding to receptor by B subunit, toxin is taken up by receptor-mediated endocytosis. Subunit A dissociates from B and exerts its toxic function.

S. aureus

Cultures of ____ grow as golden or yellow colonies which are beta-hemolytic. Coagulase (-) are white colonies with no hemolysis.

Furuncles

Cutaneous infection (Boils). Folliculitis that has progressed to large raised nodules with underlying dead and necrotic tissue.

Wound infections

Cutaneous infection. Generally requires foreign material to be present. Signs and symptoms include edema, erythema, pain, and accumulation of purulent material.

Impetigo

Cutaneous infection. Primarily on the face and limbs; generally seen with young children. Small macule (red spot) becomes pus filled vehicle called pustule. Crusting occurs after rupture and multiple vesicles can develop.

Folliculitis

Cutaneous infection. Pyogenic infection of hair follicles (style if at base of eyelid).

Carbuncles

Cutaneous infection. When furuncles coalesce and extend to the deeper subcutaneous tissue. Signs and symptoms include chills and fevers indicate systematic spread of staphylococci.

Staph antibiotic treatments

Most strains possess B-lactamases. Oxacillin (or other penicillinase-resistant penicillin), vancomycin for oxacillin-resistant strains, MRSA strains include trimethoprim-sulfamethizole, clindamycin, linezolid, daptomycin, or quinupristin-dalfopristin.

LPS, Teichoic acids, lipoteichoic acids

Non-protein toxins include:

Coagulase (-)

Novobiocin screening for ____ species.

Type I Toxins

Superantigens. They do not enter cells but bind externally to MHC Class II. Lead to indiscriminate activation of T cells and excessive production of IL-2 leading to symptoms including nausea, vomiting, malaise, and fever. It is the cause of toxic shock syndrome (Staphylococcus aureus).

Toxic Shock Syndrome (TSS)

Symptoms include abrupt onset of fever, hypotension, diarrhea, vomiting. Diffuse, macular erythrematous rash peels, with desquamation of all affected skin surfaces. Eventual involvement of multiple organ systems, initial fatality rate was 5-10%, but improved understanding of the disease has decreased deaths. Without effective treatment, more than 65% of patients will have recurrent episodes.

Staphylococcal Food Poisoning

Symptoms include onset of disease is abrupt and rapid after ingesting contaminated food. Vomiting more common than diarrhea. Abdominal pain and swelling. Sweating and headache may occur but no fever.

Abscess

The focus of infection ____ must be found and drained. Proper cleansing of wounds and use of disinfectants. Thorough hand washing and covering of exposed skin of medical personnel.