Microbiology Solo 3 Catalase Positive and Negative Gram-Positive Cocci

General Concepts

Organisms in this solo revolve around being catalase positive or negative

Catalase is the enzyme that releases water and oxygen from Hydrogen peroxide

Anaerobic and facultative anaerobic organisms produce hydrogen peroxide during normal metabolism

• Catalase enzymes are present to detoxify the hydrogen peroxide produced into non-harmful byproducts: water and oxygen

Staphylococcus species are primarily catalase positive

Streptococcus species are primarily catalase negative

Catalase Positive, Gram-Positive Cocci General Characteristics

Staphylococcus species now how 49 species in the genus

• 25 subspecies

This genera has a high frequency of being isolated in patient specimens

This genus is facultative anaerobic

One exception is Staphylococcus saccharolyticus that is strictly anaerobic (obligate anaerobe)

• Can be catalase negative

Non-motile

Non-sporing forming organisms

Coagulase is the primary serological test used to differentiate within the genus

Micrococcus species have been reclassified into new genera

• Kytococcus, Kocuria, Dermacoccus, and Nesternknoia

Staphylococcus Aureus: Epidemiology

Normal microbiota

• Anterior nares - nasal colonization

• - Can detect if a patient is a colonizer for a Methicillin Resistant Staphylococcus aureus (MRSA) before hospital admission

• Persistent carriers - Harbor a single strain for an extended period

• Intermittent carriers - Harbor different strains over time

• Noncarriers - DO not harbor any strains

Nasopharynx

Perineal area

Skin

Colonizer of mucosa

Mode of transmission

• Traumatic introduction into sterile sites

• Direct contact

• - Person to person

• Indirect constant

• - Aerosolized

• High among health care providers

Staphylococcus Aureus: V irulence Factors

Catalase - Enzyme that converts hydrogen peroxide into oxygen and water

Penicillinase - Beta lactamase; cleaves the beta-lactam ring of the penicillin molecule, rendering it ineffective

Coagulase - Binds plasma fibrinogen and activates a cascade of reactions causing plasma to clot;

• Clumping factor - The most important test for the virulence of Staphylococcus

Polysaccharide capsule - Inhibits Phagocytosis; also produces a slime layer or “biofilm” with impairs or inhibits the penetration of antibiotics

Peptidoglycan - Activates complement, Interleukin 1 (IL-1) and acts as a chemotactic factor for Polymorphonuclear cells (PMNs). This cascade can cause swelling and tissue damage

Protein A - Surface protein that has a high affinity to the Fc receptor on IgG molecules. Allows the organism to bind directly to the immunoglobulins, decreasing the immune-mediated response

Alpha toxin - Disrupts smooth muscle in blood vessels and is toxic erythrocytes, leukocytes, hepatocytes, and platelets

Beta toxin - Works in conjunction with Alpha toxin. Heat liable, sphingomyelinase that catalyzes the hydrolysis of membrane phospholipids resulting in cell lysis

Delta toxin - Cytolytic to erythrocytes and demonstrates nonspecific membrane toxicity to other mammalian cells

Gamma Toxin and Panton Valentine Leukocidin (PVL) - Responsible for the various skin, wound, and deep tissue infections. Gamma Toxin works with PVL

Heat Stable Enterotoxins A-E,G-I Resistant to hydrolysis by the gastric and intestinal enzymes. Associated with pseudomembranous enterocolitis and toxic shock syndrome

Toxic Shock Syndrome Toxin I - Also referred to as a pyrogenic exotoxin C has several systemic effects including fever, desquamation, and hypotension that can lead to shock and death

Hyaluronidase - Destroys the polysaccharide that holds animal cells together

Lipases - Assists in the biofilm formation

Nucleases - Digests single-stranded and double-stranded nucleic acids

DNase - Hydrolyzes DNA and uses it as a carbon source for energy and growth

Staphylococcus Aureus: Spectrum of Disease

Toxin mediated

• Scalded skin syndrome

• Toxic shock syndrome

• Food poisoning

Localized skin infections

• Folliculitis

• Furuncles

• Carbuncles

• Impetigo

Tissue and systemic infections

• Wounds

• Bacteremia

• Endocarditis

• Osteomyelitis

• Cerebritis

• Pyelonephritis

Staphylococcus Aureus: Staphylococcal Scaled Skin Syndrome

Ritter von Ritterschien disease (Ritter’s disease) in newborns

Varies from localized blisters to severe exfoliation affecting around 90% of the body

• Resembles a hot water burn

Caused by Toxins A and B

• Exfoliative toxin that splits the intracellular bridges of the epidermidis and is sloughed off

Most common in children and neonates

• 45.1 million cases in US infants annual aged less than 2

The effectiveness of these toxins that cause SSSS decrease after the age of five

• Immature renal function may contribute the impaired removal of these toxins

• Adults may have antibodies specific for this exotoxin and improved renal clearance

In children the mortality rate is very low (0.33-5%)

In adults the mortality rate is high (50-60%)

• Could be attributed to comorbidities

Cases have been reported with infants who have breastfed from mothers with Staphylococcus aureus breast abscess

Outbreaks have been reported in neonatal and newborn nurseries