Antimicrobial resistance of Streptococcus agalactiae isolates
| Antimicrobial | Phenotypic isolates (n = 21) | MIC (μg/mL) | ||||
|---|---|---|---|---|---|---|
| Susceptible | Intermediate | Resistant | Range | MIC50 | MIC90 | |
| penicillin | 21 (100%) | 0 | 0 | ≤0.13–>64.00 | 0.13 | 0.25 |
| ampicillin | 15 (71.4%) | 0 | 6 (28.6%) | ≤0.13–>64.00 | 0.25 | 1.00 |
| amoxicillin/clavulanic acid | 18 (85.7%) | 1 (4.8%) | 2 (9.5%) | ≤0.25/0.12–>128.00/64.00 | 0.25/0.12 | 0.50/0.25 |
| oxacillin | 19 (90.5%) | 0 | 2 (9.5%) | ≤0.25–>128.00 | 0.50 | 1.00 |
| cephalothin | 19 (90.5%) | 0 | 2 (9.5%) | ≤0.25–>128.00 | 0.25 | 2.00 |
| ceftiofur | 20 (95.2%) | 0 | 1 (4.8%) | ≤0.25~>128.00 | 0.25 | 0.50 |
| erythromycin | 8 (38.1%) | 3 (14.3%) | 10 (47.6%) | ≤0.25–>128.00 | 4.00 | 128.00 |
| clindamycin | 8 (38.1%) | 1 (4.8%) | 12 (52.1%) | ≤0.13–>64.00 | 32.00 | 64.00 |
| gentamicin | 20 (95.2%) | 0 | 1 (4.8%) | ≤0.25–>128.00 | 1.00 | 4.00 |
| doxycycline | 6 (28.6%) | 8 (38.1%) | 7 (33.3%) | ≤0.25–>128.00 | 8.00 | 16.00 |
| florfenicol | 20 (95.2%) | 0 | 1 (4.8%) | ≤0.25–>128.00 | 2.00 | 4.00 |
| tetracycline | 3 (14.3%) | 0 | 18 (85.7%) | ≤0.25–>128.00 | 64.00 | 128.00 |
| kanamycin | 14 (66.7%) | 4 (19.0%) | 3 (14.3%) | ≤0.50–>256.00 | 16.00 | 64.00 |
| ciprofloxacin | 14 (66.7%) | 3 (14.3%) | 4 (19.0%) | ≤0.13–>64.00 | 1.00 | 16.00 |
| sulfisoxazole | 15 (71.4%) | 0 | 6 (28.6%) | ≤2.00–>1024.00 | 4.00 | 1024.00 |
| sulfamethoxazole | 20 (95.2%) | 0 | 1 (4.8%) | ≤0.12/2.40–>64.00/1216.00 | 0.25/4.80 | 0.50/9.50 |
Primer sequence of drug resistance gene of Streptococcus agalactiae
| Resistance gene | Primer sequence (5-3’) | Annealing temperature (°C) | PCR product size (base pairs) | Reference |
|---|---|---|---|---|
| tet(M) | F: GTGGAGTACTACTACATTTACGAG | 55 | 359 | 31 |
| tet(O) | F: GCGGAACATTGCATTTGAGGG | 51 | 538 | |
| tet(L) | F: GGATCGATAGTAGCCATGGG | 53 | 516 | |
| tet(S) | F: CGCTACATTTGCGAGACTCAG | 55 | 569 | |
| erm(A) | F: TCTAAAAAGCATGTAAAAGAA | 52 | 645 | 27 |
| erm(B) | F: GAAAAGGTACTCAACCAAATA | 52 | 639 | |
| mef(A) | F: CGTAGCATTGGAACAGC | 50 | 316 | |
| lnu(B) | F: CCTACCTATTGTTTGTGGAA | 57 | 944 | 4 |
Serotyping and sequence types in 21 Streptococcus agalactiae strains
| ST | Allelic profile | Number of isolates in MLST (%) | Serotypes (Number of isolates) | ||||||
|---|---|---|---|---|---|---|---|---|---|
| adhP | pheS | atr | glnA | sdhA | glcK | tkt | |||
| 103 | 16 | 1 | 6 | 2 | 9 | 9 | 2 | 11 (52.4%) | Ia (10) NT (1) |
| 312 | 13 | 1 | 1 | 13 | 1 | 9 | 5 | 2 (9.5%) | II (2) |
| 67 | 13 | 1 | 1 | 13 | 1 | 1 | 5 | 1 (4.8%) | II (1) |
| 309 | 13 | 1 | 1 | 2 | 1 | 9 | 1 | 1 (4.8%) | III (1) |
| 1878 | 13 | 1 | 1 | 13 | 1 | 204 | 5 | 6 (28.6%) | II (6) |
The correlations between resistance phenotypes and drug resistance genes of Streptococcus agalactiae isolates
| Antimicrobial classes | Resistant gene | Number of strains with genotype | Number of phenotypes of resistance | Consistency rate (%) |
|---|---|---|---|---|
| tetracyclines | tet(M) | 10 | 18 | 55.6% |
| tet(O) | 7 | 38.9% | ||
| tet(L) | 0 | 0 | ||
| tet(S) | 2 | 11.1% | ||
| macrolides | erm(A) | 0 | 10 | 0 |
| erm(B) | 8 | 80.0% | ||
| mef(A) | 0 | 0 | ||
| lincosamides | lnu(B) | 0 | 12 | 0 |