B1.3 OTHER Staphylococci Flashcards by 횐호 강

Other Staphylococci classifications

S. epidermidis
S. saprophyticus
S. lugdunensis
Other Coagulase-Negative Staphylococci
Methicillin-Resistant Staphylococci aureus (MRSA)
Vancomycin-Resistant Staphylococci
Macrolide Resistance

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indigenous microbiota of the skin
contaminant of medical instruments, catheters, CSF shunts and prosthetic heart valve implants (implanted medical devices), hip
prostheses

Staphylococcus epidermidis

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Staphylococcus epidermidis disease caused

: Stitch abcess,
Health care-acquired UTIs,
Endocarditis,
Bacteremia

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In charge for the adherence of S. epidermidis

Poly-γ-DL-Glutamic Acid (PGA)

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LABORATORY DIAGNOSIS used for detecting S. epidermidis

Blood agar plate
Biochemical Test
Susceptibility with 5-ug NOVOBIOCIN (16mm-27mm)

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Blood agar plate result for S. epidermidis

gray to white, opaque, small to medium-sized pinheads and non-hemolytic colonies

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Biochemical test results for S. epidermidis

Coagulase (-),
CNA (+),
DNase(-),
Mannitol Fermentation (-)

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present on the normal skin and in the periurethral and urethral flora
adheres effectively to the epithelial cells lining the urogenital tract

Staphylococcus saprophyticus

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Staphylococcus saprophyticus disease caused

common cause of UTI in young sexually active women

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significant result for urine culture in order to determine infection by S. saprophyticus

urine culture <10,000 CFU/ml

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LABORATORY DIAGNOSIS used to determine S. saprophyticus

Blood agar plate
Biochemical test
Resistance to NOVONIOCIN (5ug; 6mm-12mm) and NALIDIXIC ACID
Absence of Phosphatase production

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Blood agar plate result for S. saprophyticus

white, opaque, slightly larger than pin-heads, nonhemolytic colonies although some strains produce yellow pigments

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Biochemical Test results for S. saprophyticus

Coagulase (-),
Dnase (-)
Mannitol Fermentation (-)

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Staphylococcus lugdunensis results in coagulase test

clumping factor (+),
tube coagulase (-)

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contain mecA gene that encodes oxacillin resistance
more aggressive than other CoNS in inefectivity

Staphylococcus lugdunensis

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Staphylococcus lugdunensis disease caused

infective endocarditis,
septicemia,
meningitis,
skin and soft tissue infections,
UTIs, and
septic shock

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Other Coagulase-Negative Staphylococci that causes endocarditis, septicemia, and wound infections

S. warneri,
S. capitis,
S. simulans,
S. hominis, and
S. schleiferi

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Other Coagulase-Negative Staphylococci that causes wounds, bacteremia, endocarditis, and UTIs

medium-sized colonies, with moderate or weak hemolysis and variable pigment production

S. haemolyticus

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NOVOBIOCIN SUSCEPTIBLE CoNS

S. epidermidis
S. capitis
S. haemolyticus
S. hominis subsp. hominis
S. lugdunensis
S. saccharolyticus
S. warneri

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NOVOBIOCIN RESISTANT CoNS

S. saprophyticus
S. cohnii
S. kloosii
S. xylosus

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RESISTANT GENES PRODUCED BY STAPHYLOCOCCI

a. Erythromycin Ribosomal Methylase (ERM) Gene

b. Methionine Sulfoxide Reductase (MSR) A Gene

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Class of enzyme inactivating genes
Codes for the methylation of the 23s rRNA
Results in resistance to erythromycin
Inducible or constitutive resistance to clindamycin
May not be detected in routine susceptibility testing
Confer cross-resistance to macrolides (erythromycin) and streptogramins (quinupristin)

Erythromycin Ribosomal Methylase (ERM) Gene

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Codes for efflux mechanism

Methionine Sulfoxide Reductase (MSR) A Gene

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resistance to erythromycin but susceptibility to clindamycin

efflux mechanism

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type of S. aureus that is resistant to methicillin, nafcillin, and oxacillin  acquired after prolonged stay in the hospital, close contact with carriers, effects of broad spectrum antibiotic treatments and exposure to nasal secretions

Methicillin-Resistant Staphylococci aureus (MRSA)

treatment of choice for MRSA

VANCOMYCIN

Methicillin-Resistant Staphylococciaureus (MRSA) types

Community-Associated MRSA (CA-MRSA), Health Care–Associated Community-Onset (HACOMRSA), Hospital-Associated (HA-MRSA)

codes for altered Penicillin-Binding Protein (PBP) = PBP2a or PBP2′

mecA

LABORATORY DIAGNOSIS for identifying MRSA

a. OXACILLIN-SALT AGAR PLATE b. CHROMOGENIC TEST c. Latex Agglutination d. Molecular Nucleic Acid Probes or PCR Amplification

used to screen for MRSA in clinical samples differentiate MRSA from hyperproducers of β-lactamase, or Borderline Oxacillin-Resistant Staphylococcus aureus (BORSA)

OXACILLIN-SALT AGAR PLATE

Chromogenic Selective Differential Media:

MRSA Select, Spectra MRSA, CHROMagar MRSA

Substance used in chromogenic test that inhibits non-MRSA

CEFOXITIN

Results from CHROMOGENIC test for MRSA

Changes in color of MRSA colonies within 24 to 48 hours using CHROM Agar against colonies of non-MRSA

CHROM agar MRSA colonies color

Mauve-colored colonies

detect altered PBPs alternative method for testing and confirmation of oxacillin resistance  performed on both CoNS and S. aureus

Latex Agglutination

“gold standard” for MRSA detection

Molecular Nucleic Acid Probes or PCR Amplification

Vancomycin-Resistant Staphylococci screening used

Vancomycin Agar Plate

discrepant macrolide test results (erythromycin resistant and clindamycin susceptible)

MODIFIED DOUBLE DISK DIFFUSION TEST (D-zone test)

BETA-LACTAMASE TESTS types

Cephalosporinase Test Acidimetric Method Iodometric Method

uses cephalosporin or cefinase disk  Substrate: nitrocefin

Cephalosporinase Test

Cephalosporinase Test result for Staphylococci

 (+) result: deep pink or red color within 10 minutes (60 minutes for Staphylococci)

Acidimetric Method  Reagent:  pH indicator:  (+) result:

 Reagent: citrate-buffered penicillin  pH indicator: phenol red  (+) result: red  yellow (penicilloic acid = decrease pH)

Iodometric Method  Reagent:  (+) result:  (-) result:

 Reagent: citrate-buffered penicillin and starch iodine complex  (+) result: colorless solution- penicilloic acid reduces iodine and prevents it to combine with starch  (-) result: purple (no color change)8

ANTIMICROBIAL TESTING Treatment

methicillin, oxacillin, nafcillin, cloxacillin, and dicloxacillin (penicillinase-resistant penicllin drugs)

most commonly used treatment for Antimicrobial testing

Oxacillin

Cutaneous infections treatment used

oral oxaillin or dicloxacillin, if allergic, erythromycin may be substituted

Systemic infections treatment used

parenteral nafcilllin or oxacillin, if allergic, vancomycin or cephalosporin may be used

MRSA treatment used

vancomcin alone or in a combination with rifampicin

ANTIMICROBIAL TESTING types

A. Screening Test for MRSA: Oxacillin Screen Plate B. Cefoxitin Disk Diffusion (30 ug) C. Macro E Test D. Vancomycin Agar Screen Plate

A. Screening Test for MRSA: Oxacillin Screen Plate culture media used

MHA with 4% NaCl and 6 ug/mL oxacillin

Screening Test for MRSA: Oxacillin Screen Plate procedure

spot inoculated with cotton swab and incubated for 24 hours at 35°C

Microdilution Testing procedure for MRSA screening

oxacilin in cation-supplemented MH broth containing 2% NaCl

Result for Oxacillin Screen Plate for MRSA

Resistant- growth of more than one colony Susceptible- no growth on the agar plate

Result for Oxacillin Screen Plate for CoNS

 Resistant- 24 mm zone of inhibition  Susceptible- >25 mm zone of inhibition

Disadvantage of Oxacillin Screen Plate

Does not reliably detect oxacillin-resistant CoNS

preferred method for detection of oxacillin-resistance for both S. aureus and S. lugdunensis Improves detection of MRSA serves to induce greater PBP2a in mecA-containing strains Test reagent to detect resistance- both MIC and diffusion method

Cefoxitin Disk Diffusion (30 ug)

Cefoxitin Disk Diffusion (30 ug) interpretation

Resistant- < 21 mm Susceptible- > 22 mm

detection of heteroresistant VISA because the test uses a higher concentration of organisms (1 x 108 bacteria/ mL)

Macro E Test

best method for detection of either Vancomycin-resistant S. aureus (VRSA) or VISA

Vancomycin Agar Screen Plate

Vancomycin Agar Screen Plate S. aureus should be screened with

6-ug/mL vancomycin incorporated into BHIA

Confirmatory test for oxacillin resistance

Broth dilution and E-test

B1.3 OTHER Staphylococci Flashcards

S. epidermidis S. saprophyticus S. lugdunensis Other Coagulase-Negative Staphylococci Methicillin-Resistant Staphylococci aureus (MRSA) Vancomycin-Resistant Staphylococci Macrolide Resistance