Table 3.
Overview of the P. multocida (Pmu) and M. haemolytica (Mh) strains investigated in this study and their macrolide resistance profiles.
| Strains and species | Macrolide resistance genes | ICE-specific genes | MIC | |||||||||
|---|---|---|---|---|---|---|---|---|---|---|---|---|
| erm(42) | msr(E) | mph(E) | int1 | int2 | ICE-rel1 | parB | TIP | TUL | TIL | GAM | ||
| 3358 | Pmu* | + | + | + | + | + | + | + | 128 | >128 | 128 | 64 |
| 3361 | Pmu* | – | + | + | + | + | + | + | 2 | 64 | 32 | 32 |
| 3364 | Pmu | – | – | – | + | + | + | + | 1 | 32 | 16 | 0.5 |
| 4407 | Pmu* | – | – | – | – | – | – | – | 1 | 0.5 | 4 | 0.5 |
| 6052 | Pmu | + | – | – | + | + | + | + | >128 | 8 | >128 | 8 |
| 6053 | Pmu | + | – | – | + | + | + | + | 128 | 8 | 128 | 16 |
| 6054 | Pmu | + | – | – | + | + | + | + | >128 | 8 | >128 | 8 |
| 6055 | Mh* | + | + | + | + | + | + | + | 128 | >128 | 128 | 128 |
| 6056 | Mh | + | + | + | + | + | + | + | >128 | >128 | >128 | 128 |
| 11933 | Mh | + | – | – | + | + | + | + | 128 | 8 | 64 | 4 |
| 11934 | Mh | + | + | + | + | + | + | + | 128 | 64 | 128 | 64 |
| 11935 | Mh* | – | – | – | – | + | + | – | 0.5 | 2 | 4 | 0.25 |
| 11937 | Mh | – | – | – | – | + | + | – | 0.5 | 2 | 8 | 0.5 |
| 11938 | Mh | + | + | + | + | + | + | + | 128 | 128 | 64 | 128 |
| 11949 | Pmu | + | + | + | + | + | + | + | >128 | >128 | >128 | 64 |
| 11952 | Pmu | + | – | – | + | + | + | + | >128 | 8 | >128 | 8 |
| 11953 | Pmu | + | – | – | + | + | + | + | >128 | 4 | 128 | 4 |
| 11955 | Pmu | + | – | – | + | + | + | + | >128 | 4 | 128 | 4 |
| 11956 | Pmu | + | – | – | + | + | + | + | >128 | 4 | 128 | 4 |
| 11957 | Pmu | + | + | + | + | + | + | + | >128 | >128 | 128 | 128 |
| 12540 | Mh* | – | – | – | – | + | + | + | 1 | 2 | 32 | 0.5 |
| 12548 | Mh | – | + | + | + | + | + | + | 0.5 | 128 | 32 | 64 |
| 12553 | Mh | – | + | + | + | + | + | + | 1 | 128 | 32 | 128 |
| 12554 | Mh | – | + | + | + | + | + | + | 1 | 128 | 32 | 128 |
| 12557 | Mh | – | + | + | + | + | + | + | 1 | 128 | 32 | 128 |
| 12558 | Mh | – | + | + | + | + | + | + | 2 | >128 | 32 | 128 |
| 12565 | Mh* | – | – | – | – | + | + | + | 2 | 2 | 32 | 1 |
| 12568 | Mh | – | – | – | – | + | + | + | 2 | 2 | 32 | 1 |
| 12580 | Mh | + | – | – | + | + | + | + | >128 | 16 | 128 | 8 |
| 12581 | Mh | + | – | – | + | + | + | + | >128 | 16 | 128 | 8 |
| 12582 | Mh | + | – | – | + | + | + | + | >128 | 16 | 128 | 8 |
| 12583 | Mh | + | – | – | + | + | + | + | >128 | 16 | 128 | 8 |
| 12584 | Mh | + | + | + | + | + | + | + | >128 | 128 | 128 | 128 |
| 12585 | Mh | + | – | – | + | + | + | + | >128 | 16 | 128 | 8 |
| 12587 | Mh | + | + | + | + | + | + | + | >128 | >128 | >128 | 128 |
| 12591 | Pmu* | – | – | – | + | + | + | + | 1 | 0.5 | 32 | 0.5 |
| 12593 | Pmu | – | + | + | + | + | + | + | 2 | >128 | 32 | 64 |
| 12594 | Pmu | – | + | + | + | + | + | + | 2 | >128 | 32 | 64 |
| 12595 | Pmu | – | + | + | + | + | + | + | 4 | >128 | 32 | 64 |
| 12596 | Pmu | – | + | + | + | + | + | + | 4 | >128 | 32 | 64 |
| 12599 | Pmu | – | – | – | + | + | + | + | 1 | 1 | 32 | 0.5 |
| 12600 | Pmu | – | – | – | + | + | + | + | 1 | 1 | 32 | 0.5 |
| 12601 | Pmu* | – | – | – | + | + | + | + | 1 | 0.5 | 32 | 0.5 |
| 12602 | Pmu | – | + | + | + | + | + | + | 4 | >128 | 32 | 32 |
| 12604 | Pmu | – | – | – | + | + | + | + | 1 | 0.5 | 32 | 0.5 |
| 12606 | Pmu | + | + | + | + | + | + | + | >128 | >128 | >128 | 128 |
| 12608 | Pmu | + | – | – | + | + | + | + | >128 | 8 | >128 | 16 |
| 13030 | Pmu | – | – | – | – | – | – | – | 0.5 | 0.5 | 1 | 0.25 |
| 13031 | Mh | – | – | – | – | + | + | – | 0.25 | 1 | 2 | nd |
| 13065 | Mh | – | – | – | – | + | + | – | 0.25 | 1 | 2 | nd |
| 13069 | Mh | – | – | – | – | – | – | – | 0.5 | 1 | 4 | nd |
| 13082 | Pmu | – | – | – | – | – | – | – | 0.5 | nd | nd | nd |
| 13083 | Pmu | – | – | – | – | – | – | – | 0.25 | nd | nd | nd |
| 13085 | Pmu | – | – | – | – | – | – | – | 0.5 | nd | nd | nd |
| 13103 | Mh | – | – | – | – | + | + | – | 0.25 | 0.5 | 1 | 0.25 |
| 14499 | Pmu | – | – | – | – | – | – | – | 4 | 4 | 16 | 2 |
| 14500 | Pmu | – | – | – | – | – | – | – | 4 | 4 | 16 | 2 |
| 14501 | Pmu | – | – | – | – | – | – | – | 8 | 4 | 32 | 2 |
| 14502 | Pmu | – | – | – | – | – | – | – | 8 | 4 | 32 | 2 |
| 14503 | Pmu | – | – | – | – | – | – | – | 8 | 4 | 32 | 2 |
| 14504 | Pmu | – | – | – | – | – | – | – | 8 | 4 | 32 | 2 |
| 14582 | Pmu | – | – | – | – | – | – | – | 8 | 2 | 16 | 1 |
| 14583 | Pmu | – | – | – | – | – | – | – | 16 | 4 | 16 | 2 |
| 14625 | Pmu | – | – | – | – | – | – | – | 8 | 0.5 | 16 | 0.5 |
| 14626 | Pmu | – | – | – | – | – | – | – | 32 | 16 | 32 | 4 |
| 14627 | Pmu | – | – | – | – | – | – | – | 32 | 16 | 32 | 4 |
| 14421 | Pmu | – | – | – | – | – | – | – | >64 | >64 | >64 | >64 |
| 14424 | Pmu* | – | – | – | – | – | – | – | >64 | >64 | >64 | >64 |
| 14426 | Pmu | – | – | – | – | – | – | – | >64 | >64 | >64 | >64 |
| 14584 | Mh | – | – | – | – | + | + | – | 16 | 4 | 32 | 4 |
| 14628 | Mh | – | – | – | – | + | + | – | >64 | 32 | 64 | 16 |
| 14629 | Mh | – | – | – | – | + | + | – | >64 | 32 | 64 | 32 |
| 14668 | Mh | – | – | – | – | + | + | – | 16 | 64 | 8 | 32 |
| 14669 | Mh | – | – | – | – | + | + | – | 8 | 32 | 8 | 8 |
| 14717 | Mh | – | – | – | – | + | + | – | >64 | >64 | >64 | >64 |
Strains up to Pmu12608 were isolated in the USA from cattle suffering from respiratory infections (with the exception of Pmu4407, France); strains Pmu13030 to Mh14717 are from cases of bovine respiratory infection in Europe. The genomes of the strains marked with an asterisk were sequenced. All strains were screened using the multiplex PCR assay described here for ICE genes, and additionally with an independent multiplex assay to detect macrolide resistance genes (Rose et al., 2012). The presence (+) or absence (–) of the ICE-specific int1, int2, ICE-rel1, parB genes and the macrolide resistance genes erm(42), msr(E), and mph(E) is indicated. Some of the macrolide resistant strains, such as Pmu14421, Pmu14424, and Pmu14426 that lack ICE structures, have attained resistance via A2059G mutations in all six of their rrn operons; strain Mh14717 has the A2058G mutation in all six of its rrn operons (Olsen et al., 2015). The minimal inhibitory concentrations (MICs in μg/ml) of the macrolides tildipirosin (TIP), tulathromycin (TUL), tilmicosin (TIL), and gamithromycin (GAM), some of which have been reported previously (Rose et al., 2012; Olsen et al., 2015), are color coded to indicate whether the strains show susceptibility (green), intermediate resistance (orange), or resistance (red) according to CSLI breakpoints for these antibiotics: http://vet01s.edaptivedocs.info/GetDoc.aspx?doc=CLSI%20VET01S%20ED3:2015&scope=user. nd, not determined.