TABLE 3.
Unusuala antimicrobial resistance phenotypes and resistance genes identified in USA300 isolates
| Resistance phenotype (drug or drug combination)b | No. of isolatesc | No. of isolates with the following genetic determinant detected by PCR: |
Source(s) of isolates | |||||
|---|---|---|---|---|---|---|---|---|
| ermC | mupA | aac2′-aph6" | dfrA | tetM | pSK41d | |||
| CC | 42 | 42 | 0 | 0 | 3 | 0 | 1 | CA, CT, GA, NY, OR, TN |
| MUP | 12 | 0 | 12 | 0 | 1 | 0 | 9 | CA, GA, NY, OR |
| CC + MUP | 5 | 5 | 5 | 0 | 0 | 0 | 5 | CA, GA, OR |
| GM | 1 | 0 | 0 | 1 | 1 | 0 | 0 | CA |
| GM + TMP-SMZ | 3 | 0 | 0 | 3 | 3 | 0 | 3 | CA, TN |
| GM + MUP | 4 | 0 | 4 | 4 | 1 | 0 | 4 | GA, PA, TN |
| MUP + TMP-SMZ | 1 | 0 | 1 | 0 | 0 | 0 | 1 | OR |
| CC + TMP-SMZ | 1 | 1 | 0 | 0 | 1 | 0 | 0 | OR |
| CC + DOX | 2 | 2 | 0 | 0 | 0 | 2 | 1 | GA, OR |
| CC + MUP + DOX | 1 | 1 | 1 | 0 | 0 | 1 | 1 | TN |
| Total | 72 | 51 | 23 | 8 | 10 | 3 | 25 | |
a
Likely plasmid-mediated resistance to clindamycin, mupirocin, gentamicin, trimethoprim-sulfamethoxazole, and/or doxycycline.
b
CC, clindamycin resistance (10 isolates had inducible resistance, and 41 had constitutive resistance); MUP, high-level mupirocin resistance; GM, gentamicin resistance; DOX, doxycycline resistance.
c
The total number of isolates was 72 (8.7% of the isolates in this study).
d
The presence of pSK41 was identified by positive PCR for traE, traI, and repA.