Table 3.
Hypothesis for pleuromutilin resistance development in B. hyodysenteriae.
| Tiamulin resistance phenotype | Resistance genotype | Tiamulin inhibitory concentration (Single exposure) | Tiamulin sub-inhibitory concentration (Repeated exposure) | No antibiotic (Repeated exposure) | ||
|---|---|---|---|---|---|---|
| Category | MIC (mg/L) | Chromosomal SNPs | tva(A) | |||
| Susceptible | ≤0.25 | No | Noa | No change (remains susceptible) |
Becomes intermediate (not resistant) |
No change (remains susceptible) |
| Intermediate | >0.25 to ≤ 2 | No | Yesb | Can become resistant | Becomes resistant | No change (remains intermediate) |
| Resistant | >2 | Yesc | Yes | No change (remains resistant) |
No change (remains resistant) |
No change (remains resistant) |
Susceptible isolates have tiamulin MICs equal to or less than the ECOFF value (Pringle et al., 2012), resistant isolates exceed the proposed clinical breakpoint (Duinhof et al., 2008; Swedres-Svarm, 2015), and intermediate isolates reside in between.
a
Four susceptible isolates had an MIC of 0.25 mg/L and harboured tva(A).
b
One intermediate isolate had an MIC of 0.5 mg/L, did not carry tva(A) but did harbour chromosomal SNPs associated with resistance.
c
Two resistant isolates did not harbour known chromosomal SNPs associated with resistance.