Staphylococcus Species Overview

Staphylococcus Species

• Staphylococcus and Micrococcus are gram-positive cocci arranged in clusters and tetrads.
• Staphylococcus aureus is a common coagulase-positive species, while other staphylococci can be coagulase-negative.
• Gram-positive cocci include Staphylococcus, Streptococcus, and Enterococcus.
• Staphylococcus is catalase-positive, while Streptococcus and Enterococcus are catalase-negative.

Overview of Staphylococci

• Staphylococci are gram-positive cocci arranged in pairs, tetrads, short chains, and irregular clusters.
• Often unencapsulated or have a limited capsule or slime layer(serotype specific).
• Staphylococci are catalase-positive and facultatively anaerobic.
• They are non-motile and non-sporulating.
• Some staphylococci are part of the human commensal flora.
• Differences in adhesion genes and toxins exist among species.
• Staphylococcus gets golden color from "Aureus", outer skin from "Epidermidis", putrid from "Saprophyticus".

Genus: Staphylococcus

• Staphylococcus is divided into Coagulase-Positive Staph (CoPS) and Coagulase-Negative Staph (CoNS).
• Staphylococcus aureus is a key CoPS species.
• Staphylococcus epidermidis, Staphylococcus saprophyticus, and Staphylococcus lugdunensis are CoNS species.
• Clinically significant Staphylococcus species include S. aureus, S. epidermidis, S. saprophyticus, S. lugdunensis, and S. haemolyticus.
• Staphylococcus aureus may be part of the normal flora, while the other listed species typically are.

Epidemiology of Staphylococci

• Staphylococci organisms are ubiquitous and considered normal flora on human skin and mucosal surfaces.
• They can be found on moist skin, the scalp, the perianal area of neonates, the axilla, the oropharynx, the nasopharynx and in the gastrointestinal and urogenital tracts.
• The presence in the nasopharynx carries a 10%-40% risk of MRSA.
• The organisms can survive on dry surfaces for extended periods.
• Transmission occurs through person-to-person spread via direct contact or contaminated fomites.
• Risk factors for infection: presence of foreign bodies, previous surgical procedures, and use of antibiotics that suppress normal microbial flora.
• Patients who are considered at higher risk: young children with poor hygiene, menstruating women, patients with intravascular/intrarenal catheters, and patients with compromised pulmonary function.

Virulence Factors

• Peptidoglycan leads to osmotic stability.
• Teichoic acid: binding to fibronectin and inducing immune response
• Capsule: inhibits chemotaxis, inhibits phagocytosis and proliferation of mononuclear cells
• Slime layer: adherence to foreign bodies is facilitated
• Protein A: inhibits antibody-mediated clearance
• Hydrolytic enzymes: coagulase, etc.
• Toxins
• Teichoic acid is a polymer of polyglycerol phosphate or polyribitol phosphate covalently anchored to peptidoglycan.
• Teichoic acid binds to fibronectin on epithelial and endothelial surfaces.

Enzymes and their functions:

• Coagulase: binds fibrinogen and converts it to insoluble fibrin, resulting in clumping or aggregation of staphylococci
• Staphylokinase/Fibrnolysin: Dissolves fibrin clots
• Hyaluronidase: Hydrolyzes hyaluronic acids in connective tissue, promoting the spread of staphylococci in tissue
• Lipases: ensures the survival of Staphylococci in the sebaceous area
• Nucleases (DNase): hydrolyzes DNA for nutrients, but unlikely to have a pathogenic effect

Exotoxins (Cytotoxins or Membrane-Damaging Toxins)

• cause lysis of cells resulting in the release of lysosomal enzymes

Alpha Toxin

• Produced by most human pathogenic S. aureus strains.
• Can form lytic pores, leading to osmotic swelling/cell lysis of erythrocytes, leukocytes, hepatocytes, and platelets.
• Disrupts smooth muscle in blood vessels.

Beta Toxin (Sphingomyelinase C)

• Toxic to erythrocytes, fibroblasts, leukocytes and macrophages.
• Has a specificity for sphingomyelin and lysophosphatidylcholine.
• Damages membranes by enzymatic alteration of lipid contents.

Delta Toxin

• Produced by almost all strains of S. aureus.
• Acts as a surfactant that disrupts cellular membranes (erythrocytes, mammalian cells, intracellular membrane structures).

Gamma Toxin

• Can also form lytic pores.
• Causes lysis of neutrophils and macrophages.

Panton-Valentine (P-V) Toxin

• Leukotoxic without hemolytic activity.
• Present in Community-Associated MRSA (CA MRSA).
• Associated with skin/soft tissue infections and severe pneumonia in young adults and children.

Exfoliative Toxins:

• Esterases and proteases that split the intercellular bridges in the stratum granulosum epidermis toxins (A and B).
• Lyse neutrophils, resulting in the release of the lysosomal enzymes that subsequently damage the surrounding tissues---Staphylococcal scalded skin syndrome (SSSS).

Toxic Shock Syndrome Toxin (TSST-1)

• Acts as a superantigen that stimulates release of cytokines, leading to leakage of endothelial cells at cytotooxic concentrations.

Effects of TSST-1 (Toxic Shock Syndrome Toxin-1)

• Causes generalized systemic inflammation.
• Leads to leakage or cellular destruction of endothelial cells.
• Increases intestinal peristalsis and fluid loss, resulting in nausea and vomiting.

Enterotoxins

• Enterotoxins A, B, and C are frequent.
• Cause vomiting and diarrhea.
• Can occur in contaminated milk products.
• They are heat stable and have a short incubation period
• Enterotoxin B can cause staphylococcal enterocolitis by traversing the intestinal mucosa and can act as a superantigen

Clinical Manifestations of Staphylococcus aureus Infections

• include cutaneous infections, Staphylococcal Scalded Skin Syndrome (SSSS), Toxic Shock Syndrome, Pneumonia and Empyema, Staphylococcal Food Poisoning, Bacteremia and Endocarditis, Osteomyelitis and Septic Arthritis

Cutaneous Infections

• Impetigo: superficial skin infection that most effects children, usually on the face and limbs.
• Folliculitis: pyogenic infection of hair follicles in the superficial dermis.
• Furuncles: are painful, large, raised extension of folliculitis with dead tissue that is in the deep dermis
• Carbuncles: occur when furuncles merge, extending into subcutaneous tissue, and is in the deep dermis
• Erysipelas is cellulitis, fascitis and pyomyositis

Impetigo

• Starts as a flattened red spot then turns into a then a pus-filled vsesicle on an erythematous base
• The bullous form is more common in infants/children up to 2 years old
• Nonbullous form is more common in children ages 2-6
• Multiple vesicles greater than 1cm are at separate development stages from the infection spreading to adjacent sites
• Crusting occurs at a later stage and is contagious
• Staphylococcal wound infections can occur following surgical procedures or trauma

Staphylococcal Scalded Skin Syndrome (SSSS)

• Occurs more in neonates
• An abrupt onset of localized perioral erythema spreads over the entire body within 2 days
• Causes exfoliation of skin and has a low mortality rate of less than 5%
• Bacteria is either present of not present in the infection
• Bullous impetigo is a localized form of SSSS

Toxic Shock Syndrome

• Caused by TSST-1 and enterotoxins
• Localized growth of toxin results from Staphylococcus aureus in a vagina or wound
• Manifestations starts and include a fever, hypotension, diffuse macular erythematous rash, multiorgan issues, or skin desquamates
• Purpura fulminans can occur because of DIC, fever, or hypotension

Erysipelas

• Superficial cellulitis with prominent lymphatic involvement
• Soreness can show with skin infection
• Well demarcated in cellulitis
• Affects the skin instead of the underlying tissue such as peau d'orange appearances and also clinical signs of sepsis and fever

Cellulitis:

• edematous and warm and ill-defined border with rapid expansion-
• Lymphangitis is erythema and regional lymphadenopathy

Fascitis:

• Aggressive skin or tissue infections that can cause morbidity, chills are expected, and even fever
• There are Aches

Gastroenteritis (Food Poisoning):

• S Aureus is tolerant to salt
• Onset has a 4-hour incubation period
• Faecal-oral transition

Bacteremia and Endocarditis

• Bacteremia: Intravenous devices, surgical treatment, complication
• Versus Nosocomial infection
• Endocarditis : Secondary to Bacteramia
• Fever, Chills, embolism
• 50% of cases are parenteral

Pneumonia

• S.aureus causes Pneumonia
• Causes necrosis
• Panton-Valentine lukocidin(PVL)

Osteomyelitis

• Vertebral osteomyelitis spreads from infections
• Inflammation with drainage
• Hematogenous -Metaphyseal

HA-MRSA versus CA-MRSA difference:

• At-risk groups: HA is for hospital patients and CA is for children in public
• HA is multi drug resistant whereas CA is Lactam alone
• PVL toxin: its common with CA and is rare with HA

Coagulase-Negative Staph Infections

• broad group of species that reside as commensals on human skin, mucous membranes (S. hominis, S. epidermidis), and the vaginal tract (S. saprophyticus).
• less virulent than coagulase-positive S. aureus.
• Infections have become more prominent due to the use of long-dwelling medical devices

Clinical Information for Staphylococcus lugdunensis

• Causes cardiovascular, osteomyelitis, soft & skin, and nervous infections

UTI Symptoms

• dysuria, bacyeriura, pyruia

Biofilm

• non specific
• dormant
• antibiotic resistant
• common with CoNs(Coagulase-Negative Staph)

Laboratory Diadnosis

• test: Gram stain, catalase, blood culture, nucleic adic

Blood Agar Culture:

• S. aureus and staphylococci produce hemolysis for media that includes mannitol-salt and isolates S.aureus selectivly
• Positive for Coagulase

LAB Diagnosis

• Need to determine bacteria colony
• Gram cluster stain
• blood agar
• Chapman Mannitol
• DNase

Slide And Coagulase Test

• Helps coagulse for Staphylococcus Aureus in incubation

Growth Results for species

Staph Aureus : Golden yellow colonies after 48hrs with incubation on blood agar S.epididmidis: white colonies after 24 hrs of incubation on blood agar S.aprophyticu after 24 hrs of ibcubation

Treatment

1. Staph has antibiotic resistant
2. Methicillin is resistant to penicillin
3. Intravenous vancomycin is the treatment pf choice
4. Isolates is low with high resistance

Suceptibility Testing for MRSA

• must have B-lactamase-resistant antibiotics
• MRSA Vancomycin

Prevent Staphylococcus :

Cleaning screening Infection control Limit Ha