Gram Positive Bacteria

Catalase-positive genera

Micrococcus, Rothia, Staphylococcus

Catalase-negative genera

Streptococcus, Enterococcus

Micrococcus and Rothia characteristics

GPC: tetrads and clusters

Micrococci = anaerobes

Rothia = facultative anaerobes

Both non-fastidious

Micrococcus and Rothia Habitat/Epidemiology

Habitat: colonizes skin, mucosa, oropharynx

Epidemiology: Endogenous, low virulence

Staphylococcus General Characteristics

GPC: clusters

Most are facultative anaerobes and non-fastidious

S.aureus are beta hemolytic and cream colored colonies

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

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

Biofilms

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

Catheter-associated infection

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

S.lugdenensis

Colonizes lower body and axillae

Causes community and healthcare acquired infections

Endocarditis, bacteremia, prosthetic devices, skin and soft tissue

Virulence Factor: Biofilm

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

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

S.aureus Virulence Factors

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

Enzymes

Biofilms

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)

S.aureus exotoxins: enterotoxin

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

S.aureus exotoxin: Cytolytic toxin

Causes cell lysis to human cells leading to severe tissue damage

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

S.aureus exotoxins: exfoliative toxin

Epidermolytic toxin (causes skin cells to slough off)

In about 5-10% of S.aureus strains

S.aureus exotoxins: toxic shock syndrome toxin

Superantigen!

penetrates mucosal layers locally, can lead to systemic effects

S.aureus enzymes: Hyaluronidase

Digests hyaluronic acids in host tissues promoting spread of the microbe

S.aureus enzymes: Staphylokinase (Fibrinolysin)

Dissolves fibrin clots leading to spread of microbe

S.aureus enzymes: Lipases

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

Infections caused by S.aureus: skin/wound infections

Impetigo, Folliculitis, Furuncles/Carbuncles, Cellulitis

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

Pneumonia, Endocarditis, Osteomyelitis

Infections caused by S.aureus: Toxin-mediated

Scalded Skin Syndrome, Toxic Shock Syndrome, Food Poisoning

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

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

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)

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)

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

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

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

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

Antibiotic Resistance of S.aureus

MRSA- Methicillin Resistant S.aureus

VISA- Vancomycin intermediate S.aureus

VRSA- Vancomycin resistant S.aureus

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

CA-MRSA Factors causing infection

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

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

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

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

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)

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

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,

Consequences of Blood Culture Contamination

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

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

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)

Enterococcus Characteristics

GPC: short chains and pairs

Non-fastidious, facultative anaerobe

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

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%)

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

Enterococcus Infections

Common cause of nosocomial infections (UTIs, Bacteremia)

Peritonitis following abdominal surgery or trauma

Endocarditis

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

Streptococcus General Characteristics

GPC: short chains and pairs

• S.pneumoniae is lancet-shaped

• Streptococci grown in broth form long chains

• Non-fastidious facultative anaerobe

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

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

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

Streptococcus pyogenes - Pharyngitis

Develops 2-4 days after exposure

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

Scarlet fever

• erythematous rash

• Strawberry tongue

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

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

Streptococcus pyogenes - Streptococcal toxic syndrome

Initial infection progresses to organ shock and failure

Patients are often bacteremic and have necrotizing fasciitis

Streptococcus pyogenes - Post strep sequelae

Causes rheumatic fever

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

Acute glomeruloneohritis

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

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

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

Streptococcus agalactiae - Prevention

All pregnant women screened at 36-37 weeks

Chemoprophylaxis used for all women infected

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

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

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)

Streptococcus pneumoniae - Otitis media

Inflammation of middle ear

75% of children experience by 3rd birthday

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

Viridans streptococci - Background

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

Epidemiology: endogenous

Clinical significance: more than 30 species, opportunistic infections

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

Viridans - Dental caries and gingivitis

Caused by S.mutans

Viridans - gastrointestinal carcinoma

Presence of S.gallolyticus in blood cultures

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

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