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59 terms

Staphylococci and related gram + cocci

What are the main genera of the Staphylococcaceae family?
What are the main genera of the Micrococcaceae family?
Micrococcus and staphylococcus are commonly recovered from where? Are tehy pathogenic?
Commonly recovered from environment or as commensals inhabiting skin and mucus membranes

Certain staphylococci are pathogenic for man
Micrococci are not associated with disease and not considered clinically significant when isolated from human specimens
Describe the structure of staphylococci
Are the motile? Do they form spores? Are they catalase negative or positive? Are they facultative or obligate? What part of the body do they infect? What specific sites are they associated with?
Gram-positive cocci arranged single cells, pairs, tetrads and short chains, but appear predominantly in grape-like clusters



Catalase positive

Facultative anaerobes, except S. aureus subsp. anaerobius and S. saccharolyticus (these two also catalase negative)

Found on skin and mucous membranes or humans and animals

In some cases associated with infections at specific sites
S. capitis subsp. capitis found on scalp, forehead, and neck
S. auricularis found in external auditory canal
What are the 4 staphylococci species are are accountable for?
1) S. aureus
2) S. epidermidis
3) S. lugdunensis
4) S. Saprophyticus
Where is S. aureus found? Where does it colonize humans? Is it pathogenic?
Found in external environment

Colonizes humans
Anterior nares - 20-40% of adults
Intertriginous skin folds

Significant opportunistic pathogen under appropriate conditions
What factors predispose someone with infection to S. aureus?
Defects in leukocyte chemotaxis

Congenital (Wiskott-Aldrich syndrome, Down's syndrome, Job's syndrome, Chediak-Higashi syndrome)

Acquired (Diabetes mellitus, rheumatoid arthritis)

Defects in opsonization by antibodies secondary to congenital or acquired hypogammaglobulinemias or complement component

Defects in intracellular killing of bacteria following phagocytosis due to inability to activate the membrane bound oxidase system (CGD, lymphoblastic leukemia, acute and chronic myelogenous leukemia)

Skin injuries (burns, surgical incisions, eczema, sports injuries)

Presence of foreign bodies (sutures, IV lines, prosthetic devices)

SERIOUS infection:
Infection with other agents, particularly viruses (e.g. influenza, measles)

Chronic underlying diseases e.g. malignancy, alcoholism, heart disease

Use of antibiotics to which the infecting S. aureus is not susceptible
What are considered usual sites of infection for S. aureus?
Usual sites of infection are those in which the organism is part of normal flora

Skin: folliculitis, impetigo, furuncles, carbuncles, postsurgical wound infections

Nose and throat: sinusitis, peritonsillar abscesses, mastoiditis, bronchitis and staphylococcal pneumonia

GI tract, urethra, vagina: enterocolitis, cystitis, prostatitis, cervicitis, salpingitis, pelvic abscess
What is pyoderma? What are causes?
Pyoderma means any skin disease that is pyogenic.

Causes may be infectious, such as Staphylococcal infections, or possibly autoimmune, such as pyoderma gangrenosum.
What is a furuncle?
Furuncle (or boil) skin disease caused by infection of hair follicles, resulting in localized accumulation of pus and dead tissue

Red, pus-filled lumps that are tender, warm, and extremely painful.

A yellow or white point at center of lump can be seen when boil is ready to drain
What is a carbuncle? Where do they develop?
A carbuncle is an abscess larger than a boil, usually with one or more openings draining pus onto the skin.

Carbuncles may develop anywhere, but they are most common on the back and the nape of the neck.
Give 2 examples of toxin-mediated infections
Scalded skin syndrome: neonates and children under age of four

Toxic-shock syndrome

Food poisoning
What factors predispose pts to serious infection with S. aureus? What are examples of serious infection?
1) Infection with other agents, particularly viruses (e.g. influenza, measles)
2) Chronic underlying diseases e.g. malignancy, alcoholism, heart disease
3) Use of antibiotics to which the infecting S. aureus is not susceptible

-toxin mediated (Scalded skin, toxic shock, food poisoning)
-Disseminated infections
How do disseminated infections happen? What do they result in?
Disseminated Infections: during localized infection metastasis via blood may result in:

Septic arthritis
Septic embolization
Metastatic infections
Give 4 examples of virulence factors of S. aureus
1) components interfering with phagocytosis: capsules, protein A, PVL, caogulase
2) Heomlysins (a,b,d,y)
3) Toxins (exofilates, epidermolytic toxins, endotoxin)
4) Enzymes (fibrinolysis, hyaluronase, phospholipase C)
What virulence factors of S. Aureus interfere with phagocytosis?
Capsules - prevent ingestion of organism by PMNs

Protein A - binds Fc region of IgG, interfering with opsonization and ingestion of organism by PMNs

Panton-Valentine Leukocidin (PVL) - an enzyme that alters cation permeability of rabbit and human leukocytes resulting in white cell destruction

Coagulase - binds to prothrombin catalyzing conversion of fibrinogen to fibrin, which in turn acts to coat bacterial cells with fibrin, rendering them more resistant to opsonization and phagocytosis
What is protein A and what does it do?
S. Aureus virulence factor: binds Fc region of IgG, interfering with opsonization and ingestion of organism by PMNs
What is PVL and what does it do?
Panton-Valentine Leukocidin (PVL) - an enzyme/virulence factor of S. Aureus that alters cation permeability of rabbit and human leukocytes resulting in white cell destruction
What is coagulase and what does it do?
enzyme/virulence factor of S. Aureus that binds to prothrombin catalyzing conversion of fibrinogen to fibrin, which in turn acts to coat bacterial cells with fibrin, rendering them more resistant to opsonization and phagocytosis
What are the four hemolysins?
What does alpha-hemolysin do? What happens upon subcutaneous injection?
Lyses RBCs of several animals

Dermonecrotic on subcutaneous injection

Leukocyte toxicity
what is another name for beta-hemolysin? what kind of lysis does it produce?
Sphingomyelinase, varying lysis of RBCs from different animals due to differences in membrane sphingomyelin content

Produces "hot-cold" lysis (hemolysis enhanced at low temperature after 35 C incubation)
What percentage of staph produce delta-hemolysin? What is its function? What can it cause in neonates?
Delta -hemolysin:
--Produced by 97% of S. aureus and 50-70% of coagulase negative Staph
--Acts as surfactant that disrupts the cell membrane, interacts with membrane to form channels that increase in size over time resulting in leakage of cellular contents

Some coagulase-negative staphylococci produce enough delta toxin to cause NEC (necrotizing endocolitis) in neonates
What does gamma-hemolysin cause?
gamma-hemolysin: found in some S. aureus strains, also causes lysis of variety of cells
What toxins does S. Aureus produce?
Exfoliatins or epidermolytic toxins - "staphylococcal scalded skin syndrome"

What toxins are responsible for staphylococcal scalded skin syndrome? How do they cause it? Is it normally found in adults or children?
Exfoliatins or epidermolytic toxins

Dissolves the mucopolysaccharide matrix of epidermis, causing separation of skin layers

More common in children, rare in adults
What are enterotoxins? How is it produced? What does it cause?
Heat-stable molecules responsible for clinical features of staphylococcal food poisoning, probably most common cause of food poisoning in U.S.

Toxin produced in contaminated food by toxigenic strains

Vomiting with or without diarrhea (2-8 hrs), quick recovery (24-48 hrs)
What do fibrinolysins do?
break down fibrin clots and facilitate spread of infection to contiguous tissues
What does hyaluronidase do?
Hydrolyzes intercellular matrix of acid mucopolysaccharides in tissue acting to spread organisms to adjacent tissue
What does phospholipase C do?
Described in patients with ARDS and DIC.

Tissues affected by this enzyme become more susceptible to damage and destruction by bioactive complement components and products during complement activation.
What enzyme virulence factors does S. Aureus contain?
fibrinolysins, hylauornidase, phospholipase C
What are superantigens? What 3 biologic characteristics do they possess? What do all 3 induce?
Group of toxins known as pyrogenic toxin superantigens, these include:

1) Toxic shock syndrome toxin-1 (TSST-1) of S. aureus
2) Streptococcal pyrogenic exotoxins (SPE)
3) Streptococcal superantigens

All posses three biologic characteristics
Enhance lethal effects of minute amounts of endotoxin

All induce polyclonal T-cell proliferation
What is tube coagulase? What does it react with? Is it possible for some
Free coagulase.

Reacts with substance in plasma called coagulase-reacting factor that converts fibrinogen to fibrin

Rare S. aureus may be coagulase-negative and some animal isolates (S. intermedius, S. hyicus, S. delphini, S. schleiferi subsp. coagulans) may be tube coagulase-positive
What is slide coagulase? What does coagulase react with in it?
Slide coagulase - bound coagulase or "clumping factor"

Reacts directly with fibrinogen in plasma causing rapid cell agglutination

Some human coagulase-negative species (S. lugdunensis and S. schleiferi subsp. schleiferi) produce clumping factor and may be positive with slide coagulase test
If a species of Staph is tube coagulase positive but slide coagulase negative, what might it be?
S. lugdunensis or S. schleiferi subsp. schleiferi
What is the alternative coagulation test? How does it work?
Latex Agglutination - uses latex beads coated with plasma.

Fibrinogen bound to latex detects clumping factor. In addition, Ig molecules also on beads detect Protein A (staphylococcal cell-wall protein that binds IgG by the Fc region)

Some strains of S. lugdunensis and S. schleiferi subsp. schleiferi produce clumping factor and may be positive with Latex Agglutination test
S. lugdunensis and S. schleiferi strains might show what unique pattern on the coagulase tests
tube coag -
slide coag +
latex agglutination +
What is the msot frequently isolated clinically significant coagulase-negative staphylococci?
Staphylococcus epidermidis
What is the most frequently associated bacteria with infections of indwelling devices?
Most associated with infections of indwelling devices
Is Staphylococcus epidermitidis coagulase positive or negative? What type of infections is it commonly associated with?
1) coagulase NEGATIVE
2) Indwelling devices
Virulence of Staphylococcus epidermatidis is related wo ath?
production of extracellular slime that promotes adherence of organism to surfaces of foreign bodies forming biofilm
What is the role of biofilm of Staph epidermitidis?
Promotes adherence
protects organisms from antimicrobial agents, therefore removal of foreign bodies often necessary for resolution of infection
Staph saprophyticus is a common cause of what? Identification is based on what?
Acute UTI in young women
2nd most common cause of uncomplciated cystitis (after E. coli) among women of college-bearing age

ID based on negative coagulase and resistance to novobiocin
How would one go about confirming Staph. saprophyticus?
Take a culture and place furozolidone disc. If it is resistant, it's micrococcus. If it's susceptible, it's more likley to be staphylococcus.

Then, take a culture and place a Novobiocin disc, if it is S. saprophyticus, it will be resistant, whereas all other staph will be susceptible.
What does Staph lugdunensis colonize? What is it unique about it as a species? What kind of diseases can it cause?
Human inguinal area

Only species that is both PYR and Ornithine positive

native-valve, prosthetic-valve, and pacemaker-associated endocarditis
skin and soft tissue abscesses
infected prostheses
vertebral diskitis
vascular line infection
oral infections
septic arthritis
Who gets staph infections most frequently? What are some examples of health-care associated MRSA infections?
Staph infections, including MRSA, occur most frequently among patients in hospitals and healthcare facilities (such as nursing homes and dialysis centers) who have weakened immune systems

Healthcare-associated MRSA (HA-MRSA) infections include:
Surgical wound infections
Urinary tract infections
Bloodstream infections
Central venous catheter line infections
What is the most important reservoir of MRSA in hospitals? What is the rol eof hospital personnel int ransmission?
In hospitals, the most important reservoirs of MRSA are colonized or infected patients

Hospital personnel can serve as a link for transmission between colonized or infected patients
What infections are considered CA-MRSA infections? What # of MRSA infections do they comprise?
MRSA infections that are acquired by individuals who have not been recently (within the past year) hospitalized or had an invasive medical procedure are known as CA-MRSA infections

12% of clinical MRSA infecitons
What are common settings in which MRSA breakouts occur?
Various settings
Sports participants: football, wrestlers, fencers - MPSM
Correctional facilities: prisons, jails
Military recruits
Daycare and other institutional centers
Newborn nurseries and other healthcare settings
Men who have sex with men - MSM
Is CA-MRSA susceptible to more or less abx than HA-MRSA? What Abx is it resistant to? What is the cause of methicilin resistance? What are the two pulsed field types of strains that cause CA-MRSA infections?
Susceptible to more antibiotics than HA-MRSA

Resistant only to methicillin with implied cross-resistance only to other ß-lactams

Methicillin resistance due to presence of mecA gene carried on a gene cassette called the "staphylococcal cassette chromosome mec" (SCCmec):
--SCCmec IV or V (rather than I-III)
--More mobile

MRSA strains that cause community acquired infections belong to two pulsed-field types, USA 300 and USA 400
Compare CA-MRSA SCCmec to HA-MRSA SSCec
Ca-MRSA SCCmec is:
--SCCmec IV or V (rather than I-III)
--More mobile
Many isolates of CA-MRSA express what two virulence factors? What are these properties associated with?
Many isolates express
1) Panton-Valentine Leukocidin (PVL): Potent toxin associated with furunculosis
2) Novel genetic region, designated the arginine catabolic mobile element (ACME)

Assoc. with syndromes usually caused by MSSA
Skin and soft tissue infection common, occasional necrotizing pneumonia
What gene in MRSA allows it to be resistant to methicillin? What does this gene encode for? What carries this gene?
MEC-A gene - Encodes for altered "penicillin-binding protein 2a" (PBP2a)
--Has decreased binding affinity for ß-lactam antibiotics and allows peptidoglycan synthesis even in the presence of B-lactam antibiotics

mecA is carried on a mobile genetic element called "staphylococcal cassette chromosome mec" (SCCmec)
MRSA belongs in the differential of what SSTIs? What more severe disease?
Abscesses, pustular lesions, "boils"
"Spider bites"

More severe disease:
Sepsis syndrome
Necrotizing pneumonia
Septic arthritis
Necrotizing fasciitis
How long can MRSA persist on a dry surface
Between 7 days and 7 months
What can be done to control MRSA?
Careful, compulsive hand hygiene for all patient interactions (behavioral change)

Standard and transmission based Contact/Droplet precautions:
Gowns Gloves Masks

Effective cleaning of the patient care environment

Clean shared/dedicated equipment:
Stethoscopes BP cuffs
Thermometer TV Remotes

Appropriate use of antibiotics
What is more likely to decrease MRSA trasmission: hand washing or screening all patients?
Screening all patients
What are 3 screening approaches for MRSA? What is the best one?
1) culture
2) tradtional real-time PCR
3) Cepheid GeneXpert real time PCR <-- this is the best one!
Running geneXpert tests in the excessive presence of what substances can generate errors or invalid results?
Whole blood
Nasal Spray