Table. Comparison between methicillin-sensitive and methicillin-resistant strains of Staphylococcus aureus

Strain and major resistance mechanism*

MSSA/penicillinase production

BORSA/novel methicillinase ± penicillinase hyperproduction

CA-MRSA/PBP alteration

HA-MRSA/PBP alteration

PBP2a detection (e.g., latex-agglutination method)

–

–

+

+

mecA gene detection (e.g., PCR method)

–

–

+ (SCCmec IVa)

+

PVL gene detection (PCR method)

Infrequent (<5%)

Data limited

Frequent (>66%–100%)

Infrequent (<5%)

Coresistance to non–β-lactam antimicrobial drugs

±

±

+

+++

Usual antimicrobial drugs to which MSSA is susceptible

PRP (e.g., cloxacillin), β-lactam/β-lactamase–inhibitor combinations (e.g., ampicillin /sulbactam); linezolid, vancomycin, erythromycin, clindamycin, trimethoprim-sulfamethoxazole, fluoroquinolones, rifampin, gentamicin, fusidic acid, tetracyclines

PRP (e.g., cloxacillin), β-lactam/β-lactamase–inhibitor combinations (e.g., ampicillin/sulbactam), other drugs to which MSSA is potentially susceptible

Vancomycin, linezolid, rifampin, gentamicin, trimethoprim-sulfamethoxazole, fusidic acid, tetracyclines, fluoroquinolone, clindamycin†

Vancomycin, linezolid; ± fusidic acid, rifampin, gentamicin, trimethoprim-sulfamethoxazole, fluoroquinolones‡

*MSSA, methicillin-susceptible Staphylococcus aureus; BORSA, borderline oxacillin-resistant S. aureus; MRSA, methicillin-resistant S. aureus; CA-MRSA, community-associated MRSA; HA-MRSA, hospital-associated MRSA; PBP, penicillin-binding protein; PCR, polymerase chain reaction; PVL, Panton-Valentine leukocidin; PRP, penicillinase-resistant penicillins; +, positive; –, negative. ±, occasionally present; +++, usually present.

†Concern over inducible clindamycin resistance; also, macrolide resistance is common.

‡Fluoroquinolone resistance increasing.