256. Antimicrobial Susceptibility of Vancomycin Intermediate (VISA) and Vancomycin Resistant (VRSA) Staphylococcus aureusTo Thirteen Approved Agents
Session: Poster Abstract Session: Antimicrobial Susceptibility and Resistance
Friday, October 21, 2011
Room: Poster Hall B1
Background: VISA and VRSA strains present a challenge to the clinicians.  We evaluated the susceptibility of VISA and VRSA to approved antimicrobial agents that might be considered in the treatment of these pathogens as well as other characteristics including SCC mec typing and pulsed-field gel electrophoresis (PFGE)  to determine the number of unique strains tested.  

Methods:  

For 33 VISA and 13 VRSA isolates microdilution tests using Mueller-Hinton broth were used to determine minimal inhibitory concentrations (MIC) of 13 antimicrobial agents.  Minimal bactericidal concentrations (MBC) were also determined according to CLSI guidelines.   MICs to telavancin were determined using E-test strips.  Staphylococcal cassette chromosome (SCC) mec typing was determined by multiplex polymerase chain reaction (PCR).  Panton-Valentine leukocidan (PVL) genes were identified by PCR. PFGE was performed using SmaI restriction endonuclease on the VRSA isolates

Results: 

 

VISA (33)

 

VRSA (13)

 

 

MIC Range

MIC90/MBC90

% Susceptible

MIC Range

MIC90/MBC90

% Susceptible

Ceftaroline

0.25-2

2/2

85%

0.12-1

1/1

100%

Ceftriaxone

4->64

>64/>64

12%

16->64

>64/>64

0%

Telavancin

0.25-1

0.75/NA

100%

2-6

6/NA

0%

Daptomycin

1-8

4/8

30%

0.25-1

1/1

100%

Vancomycin

4-8

8/8

0%

32->64

>64/>64

0%

Linezolid

0.5-4

4/>8

100%

0.5-4

2/>8

100%

Clindamycin

0.06->64

>64/>64

30%

>64

>64/>64

0%

Gemifloxacin

0.06-32

8/8

12%

2-64

32/64

0%

Moxifloxacin

0.25-16

8/8

6%

2-32

32/32

0%

Minocycline

0.03-16

4/>16

94%

0.03-2

2/>16

100%

Tigecycline

0.03-1

0.25/>2

97%

<0.03-1

0.05/>2

92%

Rifampin

<0.004->4

>4/>4

51%

0.004->4

1/>4

92%

Sulfa/TMP

0.06/1.2->4/76

>4/76/>4/76

70%

0.06/1.2-2/38

2/38->4/76

100%

PVL was not detected. SCCmec typing for VRSA: II (9), IV (2), non typeable(2) and for VISA: I (3), II (21), III (3), IVd(2) and MSSA (4). Among VRSA strains there were 10 distinct PFGE patterns.

Conclusion: Telavancin, linezolid, minocycline and tigecycline  demonstrated activity against more than 90% of VISA while ceftaroline, daptomycin, linezolid ,minocyline tigecycline, rifampin and  sulfamethoxazole- trimethoprim demonstrated  activity against  more than 90% of VRSA. Clinical experience will be needed to determine the efficacy of antimicrobial agents against infections caused by VISA and VRSA.  


Subject Category: A. Antimicrobial agents and Resistance

Louis Saravolatz, MD, St. John Hospital and Medical Center, Grosse Pointe Woods, MI; Wayne State University, Grosse Pointe Woods, MI, Joan Pawlak, BS, St. John Hospital and Medical Center, Detroit, MI and Leonard Johnson, MD, Medicine, St. John Hospital and Medical Center, Grosse Pointe Woods, MI

Disclosures:

L. Saravolatz, Astellas: Grant Investigator and Speaker's Bureau, Research grant and Speaker honorarium
Forest Laboratories: Grant Investigator and Speaker's Bureau, Research grant and Speaker honorarium

J. Pawlak, None

L. Johnson, None

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