Gram Positive Bacteria

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74 Terms

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Catalase-positive genera

Micrococcus, Rothia, Staphylococcus

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Catalase-negative genera

Streptococcus, Enterococcus

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Micrococcus and Rothia characteristics

GPC: tetrads and clusters

Micrococci = anaerobes

Rothia = facultative anaerobes

Both non-fastidious

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Micrococcus and Rothia Habitat/Epidemiology

Habitat: colonizes skin, mucosa, oropharynx

Epidemiology: Endogenous, low virulence

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Staphylococcus General Characteristics

GPC: clusters

Most are facultative anaerobes and non-fastidious

S.aureus are beta hemolytic and cream colored colonies

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Staphylococcus Habitat/Epidemiology

Habitat: colonizes the nares, axillae, vagina, pharynx; S.aureus colonizes 30-40% of pop.

Epidemiology: Spread of endogenous flora, person to person, has virulence factors

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Staphylococcus epidermidis

Most frequently encountered staphylococci colonizing moist body surfaces

Infections are predominantly healthcare acquired: catheterization, medical implantation/prosthetic, immunosuppression (foreign body introduction), can form biofilms

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Biofilms

Antibiotic resistant, sessile cells are more resistant to phagocytosis than planktonic cells

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Catheter-associated infection

Microbe moves from skin, into the catheter, to the catheter tip within the bloodstream, hematogenous spread, forms biofilms (S.epidermidis)

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S.lugdenensis

Colonizes lower body and axillae

Causes community and healthcare acquired infections

Endocarditis, bacteremia, prosthetic devices, skin and soft tissue

Virulence Factor: Biofilm

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S.saprophyticus

Colonizes the gastrointestinal tract

Associated with UTIs predominantly in young sexually active women

Virulence factor: adhere to epithelial cells lining the urogenital tract

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Other CoNS bacteria

S.hominis and S.haemolyticus colonize axillae and pubic areas

S.capitis colonize the forehead and scalp after puberty

S.haemolyticus is the most virulent of CoNS

Major virulence factors: biofilms and adhesion

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S.aureus Virulence Factors

Exotoxins: Enterotoxins, Cytolytic (membrane-damaging) toxins, Exfoliative toxins, Toxic shock syndrome toxin

Enzymes

Biofilms

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S.aureus structure

Protein A (binds IgG, inhibits antibody-mediated clearance)

Teichoic acid/lipoteichoic acid (binds to fibronectin; aids adhesion to human cells)

Peptidoglycan (resists phagocytosis)

Capsule (slime layer, resists chemotaxis/phagocytosis, adheres to foreign bodies)

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S.aureus exotoxins: enterotoxin

Superantigens (stimulate cytokine production), Heat stable toxins, cause of food poisoning

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S.aureus exotoxin: Cytolytic toxin

Causes cell lysis to human cells leading to severe tissue damage

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Superantigens (general)

Interfere with the adaptive immune system

Only bind briefly to T-cells causing a cytokine storm (~2-20% of T cells impacted)

Leads to fever and shock

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S.aureus exotoxins: exfoliative toxin

Epidermolytic toxin (causes skin cells to slough off)

In about 5-10% of S.aureus strains

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S.aureus exotoxins: toxic shock syndrome toxin

Superantigen!

penetrates mucosal layers locally, can lead to systemic effects

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S.aureus enzymes: Hyaluronidase

Digests hyaluronic acids in host tissues promoting spread of the microbe

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S.aureus enzymes: Staphylokinase (Fibrinolysin)

Dissolves fibrin clots leading to spread of microbe

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S.aureus enzymes: Lipases

Hydrolyzes lipids promoting survival in sebaceous environments on body, may promote the spread of the microbe.

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Infections caused by S.aureus: skin/wound infections

Impetigo, Folliculitis, Furuncles/Carbuncles, Cellulitis

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Infections caused by S.aureus: cardio/osteo/respiratory

Pneumonia, Endocarditis, Osteomyelitis

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Infections caused by S.aureus: Toxin-mediated

Scalded Skin Syndrome, Toxic Shock Syndrome, Food Poisoning

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Skin and Wound Infection: Impetigo

Vesicles in epidermis filled with exudate forming a crusting lesion

Highly contagious among children in exposed areas in moist, hot weather

Clears on its own ~2 weeks - antibiotics as needed

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Skin and Wound Infections: Folliculitis

Inflammation/infection of the hair follicles

Appear as small papules to form pustules with white/yellow centers

Occurs at high friction points on the body

Goes away on its own or with use of topical antibacterial

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Skin and Wound Infections: Furuncles (boils)

Infection spreads from hair follicle to surrounding tissue

Red, firm, painful bump with drainage occurring on neck, face, breasts, buttocks (High friction and sweat excretion)

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Skin and Wound Infections: Carbuncles (multiple boils)

Infection spreads into deeper subcutaneous tissue and may have multiple drainage sites

Fever and chills may be present

Rarely heal on their own - medical attention required (drainage or antibiotics)

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Skin and Wound Infections: Cellulitis

Acute inflammation of subcutaneous tissue

Redness, heat, and tenderness typically on lower extremities following skin disruption

Over 90% of cases caused by S.aureus

May develop from minor injury to severe septicemia with 24-48hrs - Quick onset

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Skin and Wound Infections: Scalded Skin Syndrome aka Ritter Disease

Localized redness and inflammation around the mouth that spreads around the entire body within 2 days followed by blister formation

Primarily in young children ~5% mortality

Many have spontaneous recoveries

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Toxin Mediated Disease: Toxic Shock Syndrome

Release of toxin into the blood from vagina or wound

Symptoms are acute: fever, chills, rash

Fatality rate: ~5% to ~65% if wrong antibiotic administered

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Toxin Mediated Diseases: Food Poisoning

Symptoms appear 1-6 hours after consuming contaminated food

Small quantities of heat stable toxin can cause illness (Enterotoxin)

From poor food handling and contamination by carrier

Symptoms: vomiting, nausea, cramps, diarrhea

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Antibiotic Resistance of S.aureus

MRSA- Methicillin Resistant S.aureus

VISA- Vancomycin intermediate S.aureus

VRSA- Vancomycin resistant S.aureus

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Community Acquired Methillicin Resistant S.aureus (CA-MRSA)

Acquired by people who have not been recently hospitalized or had a medical procedure done

Causes “spider bite”: red, swollen, painful, drainage

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CA-MRSA Factors causing infection

Skin-skin contact/crowded spaces, Open wounds/abscesses, contaminated items, drug injection/poor hygiene

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CA-MRSA vs HA-MRSA

HA-MRSA diagnosis made 48 hours after admission to hospital

No major medical histories in the past year, no permanent catheters or injected medical devices

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CA-MRSA Virulence Factors

Generally more susceptible to antibiotics than HA-MRSA

Exotoxin: Pantone-Valentine Leucocidin (PVL) leading to severe skin and soft tissue infections and possible necrotizing pneumonia; can also cause leukocyte destruction and tissue necrosis

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CA-MRSA Treatment and Prevention

Antibiotics against Staphylococcus infections

Removal and replacement of colonized devices

Good hygiene, food safety, and be mindful in healthcare settings

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Laboratory Tests Used to ID Catalase positive Gram positive bacteria

Microscopy (Gram Stain slides)

Chemical Tests:

Catalase, Coagulase/latex agglutination, Mannitol salt agar ( S.aureus is positive for mannitol), Novobiocin (S.saprophyticus is resistant to novobiocin)

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Laboratory Diagnosis via Instrumentation

MALDI-TOF: Laser energy absorbing matrix to create ions from larger molecules drifting to mass:charge ratio

Nucleic Acid based tests: Amplifies DNA

automated biochemical tests/AST: uses biochemicals and carbohydrates to ID

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Blood infection vs contamination

As more blood bottles are drawn and cultured the less contamination there is

Contaminants: normal flora, growth of multiple organisms from one of many cultures, organism causing infection at primary site is different from blood culture

Infection: Growth of same organism through all cultures collected at different times of locations of body,

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Consequences of Blood Culture Contamination

Allocation of more resources, cost of culture bottles, increased length of hospital stays,

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Lancefield Typing

For Gram Positive Catalase Negative microbes

Identifies microbes by looking for agglutination when a homologous antibody serum is used on the microbe to identify. Agglutination = positive reaction

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Catalase Negative Genera

Enterococcus, Streptococcus, Streptococcus-like bacteria: Leuconostoc and Pediococcus (found in various food products, resistant to vancomycin), Abiotrophia and Granulicatella (part of oral and gastrointestinal flora, pyridoxal/Vitamin B6 required for growth)

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Enterococcus Characteristics

GPC: short chains and pairs

Non-fastidious, facultative anaerobe

Can grow in extreme conditions (alkaline pH, high temps, high solute concentrations)

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Enterococcus Background

Habitat: normal flora of gastrointestinal tract

Epidemiology: Endogenous, person to person

Most species either E.faecalis (80-90%) or E.faecium (5-10%)

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Enterococcus Virulence Factors

Surface adhesions: colonizes heart valves and renal epithelial tissue

Enzymes: Cytolysin (inhibits growth of Gram positive bacteria), hyaluronidase (spreads microbe by breaking down hyaluronic acid)

Vancomycin Resistant

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Enterococcus Infections

Common cause of nosocomial infections (UTIs, Bacteremia)

Peritonitis following abdominal surgery or trauma

Endocarditis

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Endocarditis

Mostly caused by microbes streptococci, staphylococci, and enterococci

Can damage heart valves for life

Transient bacteremia is a common event, however, endothelial cells are resistant to bacterial infections, so bacteria travel on platelet and fibrin aggregates

Vegetation is formed, bacteremia stimulates cytokine release = tissue damage

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Streptococcus General Characteristics

GPC: short chains and pairs

  • S.pneumoniae is lancet-shaped

  • Streptococci grown in broth form long chains

  • Non-fastidious facultative anaerobe

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Streptococcus pyogenes Background

Colonizes skin and upper respiratory tract

Transmitted through respiratory droplets or through breaks in skin through direct contact

Causes pharyngitis, skin infections, and septic infections

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Streptococcus pyogenes Virulence factors

Capsule: made of hyaluronic acid; resists phagocytosis

M proteins: adhere to invade host cells; resists phagocytosis

Teichoic/Lipoteichoic Acid: adhere to invade host cells

Toxins: Pyrogenic exotoxins, Streptolysin S and O, Streptokinase

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Streptococcus pyogenes Exotoxins

Streptococcal pyrogenic exotoxin

  • Superantigen

  • Causes necrotizing fasciitis and streptococcal toxic shock syndrome

Streptolysin S and O (hemolysins)

  • Lyse erythrocytes, leukocytes, and platelets

  • Streptolysin S is responsible for hemolysis on SBA

Streptokinase

  • Lyse blood clots and fibrin deposits ; facilitates spread of microbe

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Streptococcus pyogenes - Pharyngitis

Develops 2-4 days after exposure

Abrupt onset of sore throat, fever, malaise, and headache

Scarlet fever

  • erythematous rash

  • Strawberry tongue

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Streptococcus pyogenes - Pyoderma infection

Impetigo

Cellulitis

Erysipelas

  • Acute spreading skin lesion thats red on face and lower extremities

  • Affects upper layer of skin

  • Seen mostly in elderly

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Streptococcus pyogenes - Necrotizing fasciitis

Occurs in the deep subcutaneous tissue

Extensive destruction of muscle and fat

Introduced to tissue through break in the skin

Treatment requires tissue debridement

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Streptococcus pyogenes - Streptococcal toxic syndrome

Initial infection progresses to organ shock and failure

Patients are often bacteremic and have necrotizing fasciitis

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Streptococcus pyogenes - Post strep sequelae

Causes rheumatic fever

  • Inflammatory disease affecting heart and joints that could permanently damage heart valves

Acute glomeruloneohritis

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Streptococcus agalactiae Background

Normal flora of female genital tract and lower gastrointestinal tract

Transmission: person to person, endogenous

Epidemiology: Neonatal/postpartum infections

Virulence factor: Capsule, adhesions

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Streptococcus agalactiae - Neonatal disease

Early onset

  • Caused by vertical transmission from the mother

  • Bacteremia, pneumonia, meningitis

Late Onset

  • Acquired from exogenous source (other babies)

  • Mostly meningitis

Pregnant women

  • Postpartum endometritis, UTIs

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Streptococcus agalactiae - Other infections in adults

Most at risk over 65 years with underlying health issues

Bacteremia, pneumonia, skin and soft tissue infections, bone and joint infections, UTIs

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Streptococcus agalactiae - Prevention

All pregnant women screened at 36-37 weeks

Chemoprophylaxis used for all women infected

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Streptococcus pneumoniae - Background

Normal flora in nasopharynx and oropharynx with colonization more common in children

Epidemiology: person to person through respiratory droplets, endogenous

Meningitis, pneumonia, otitis media, bacteremia

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Streptococcus pneumoniae - Virulence factors

Protein adhesions

  • Ability to colonize oropharynx

Pneumolysin

  • Creates pores in epithelial and phagocytic cells allowing for spread into sterile tissue

Capsule

  • Resists phagocytosis; loss of capsule makes the microbe avirulent

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Streptococcus pneumoniae - Pneumonia

Causes 25-60% of all pneumonia cases

Sudden onset of chills, fever, chest pain, and cough

May be complicated by pleural fluid effusion (empyema)

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Streptococcus pneumoniae - Otitis media

Inflammation of middle ear

75% of children experience by 3rd birthday

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Streptococcus pneumoniae - Prevention

Vaccine available

PCV15 and PCV 20 = pneumococcal conjugate vaccine against stereotypes 15 and 20

PPSV 23 = 23-Valent pneumococcal capsular polysaccharide vaccine for children older than 2 years and adults

PCV7 = first PCV vaccine

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Viridans streptococci - Background

Normal flora of oral cavity, gastrointestinal tract, and female genital tract

Epidemiology: endogenous

Clinical significance: more than 30 species, opportunistic infections

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Viridans - Subacute bacterial endocarditis

Esp. Prosthetic valves

Progression of disease is slow, symptoms may be present for weeks to months

S.sanguis and S.mitis

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Viridans - Dental caries and gingivitis

Caused by S.mutans

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Viridans - gastrointestinal carcinoma

Presence of S.gallolyticus in blood cultures

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Treatment and Prevention of Streptococcus/Enterococcus

Antibiotics available to fight Enterococcus and Streptococcus

  • Drain abscess or remove infected bone/tissue

Use good hygiene

  • Clean and care for wounds

Droplet/contact precaution in healthcare settings

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Laboratory Diagnosis for Streptococcus

Lab tests depend on the hemolysis on SBA

S.pyogenes and S.agalactiae are beta hemolytic; S.pneumoniae and Viridans are alpha; enterococci are mostly gamma

Antigen Detection

  • Urine/CSF for pneumococcal (S.pneumoniae) polysaccharide

  • Lancefield typing