TABLE 4.
Mechanisms implicated in linezolid resistance in enterococci of animals, food of animal origin, and the environment
| Origin | Species | Sample | Year of isolation | Country | Number of linezolid resistant isolates (%) | Linezolid MIC (μg/ml) | Mechanism of linezolid resistance (genetic location, number of isolates)a | ST (number of isolates)b | Characteristics (number of isolates) | Reference |
|---|---|---|---|---|---|---|---|---|---|---|
| Food-producing animals | ||||||||||
| Cattle | E. faecalis | Feces | 2009 | China | 1 | 4 | cfr (P) | fexB-linked | 232 | |
| Pigs | E. faecalis | Feces | 2009 | China | 1 (0.3% of E. faecalis) | 4 | cfr (P) | ST21 | fexA (in a different plasmid) | 233 |
| Pigs | E. faecalis | Rectal swabs | 2013 | Brazil | 5 (2% of E. faecalis) | 8–>8 | cfr (5)Mutation in ribosomal L3 protein (V149I) (1) | ST591 (2); ST29, ST590, ST592 (1 each) | 234 | |
| Pigs | E. gallinarum (n = 1), E. casseliflavus (n = 24) | Rectal swabs | 2012 | China | 25 (31.5% of florfenicol-resistant enterococci) | 8–16 | cfr (25) (C,1; P, 8) | fexA-linked (5), fexA-fexB-linked (1) | 235 | |
| Poultry and pigs | E. faecalis | Feces | 2012–2013 | China | 20 (10% of E. faecalis of animal origin) | 2c–8 | optrA (C,8; P, 9; P/C, 3) | ST21 (2); ST27, ST59, ST74, ST93, ST116, ST256, ST330, ST403, ST475, ST476, ST480, ST593, ST618, ST619, ST620, ST621, ST622, ST623 (1 each) | fexA-linked (14), fexB-linked (2), fexA-fexB-linked (1)optrA amino acid changes: Y176D, T481P (2); K3E, Y176D, G393D (1); T112K, Y176D (2); Y176D, G393D (1) | 236, 237 |
| Poultry and pigs | E. faecium | Feces | 2005, 2009, 2012, 2014 | China | 5 (5.7% of E. faecium of animal origin) | 4d–8 | optrA (C, 1; P/C, 4) | ST957 (2); ST32, ST184, ST29 (1 each) | fexB-linked (4) | 236, 237 |
| Poultry and pigs | E. faecalis | Feces and carcass | 2008, 2012, 2014 | Korea | 12 (0.2% of E. faecalis) | 8–>16 | optrA (12) | ST21 (4); ST49 (2); ST16, ST32, ST256, ST403, ST728, ST729 (1 each) | fexA-linked (11) | 238 |
| Poultry and cattle | E. faecium | Feces and carcass | 2008, 2010, 2012–2014 | Korea | 27 (0.7% of E. faecium ) | 8–>16 | optrA (23)Mutation in ribosomal L4 protein (N130K) (7) | ST195 (6); ST32 (2); ST157 (2); ST1171 (2); ST1168 (2); ND (4); ST8, ST120, ST121, ST236, ST241, ST1166, ST1167, ST1169, ST1170 (1 each) | fexA-linked (19) | 238 |
| Pigs | E. faecalis (n = 5), E. gallinarum (n = 1) | China | 6 (17.14% of enterococci) | 8–16 | 23S rRNA mutation: G2576T | ST29, ST146, ST220, ST283, ST535 | 229 | |||
| Meat | ||||||||||
| Cattle | E. faecalis | Danish veal | 2015 | Denmark | 1 (<0.1% of E. faecalis) | 8 | optrA (P) | ST22 | fexA-linked | 239 |
| Poultry | E. faecium | Imported turkey and broiler meat | 2012, 2013 | Denmark | 2 (<0.1% of E. faecium) | 8 | optrA (P, 1) | ST22, ST873 | 239 | |
| Poultry | E. faecalis | Meat | 2010–2011 | Colombia | 3 (0.5% of enterococci) | 8 | optrA (P, 3) | ST59 (2), ST489 | fexA-linked | 240 |
| Environment | ||||||||||
| Wastewater | E. faecalis | Urban wastewater treatment plant | 2014 | Tunisia | 2 (1% of chloramphenicol-resistant enterococci) | 4 | optrA (P) | ST86 (2) | fexA-linked (2), optrA amino acid changes:M1L (2), K3E (1) and I622M (1) | 241 |
a
P, plasmid; C, chromosome.
b
ND, not determined.
c
Five optrA-positive E. faecalis isolates showed a linezolid MIC of 2 μg/ml, and five isolates showed an MIC of 4 μg/ml.
d
Two optrA-positive E. faecium isolates showed a linezolid MIC of 4 mcg/ml.