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Fig. 1

Multiple drug resistance of S. agalactiae shown as antibiotic phenotypic resistance and resistance gene prevalence data. 3 – resistance to 3 classes of antimicrobials; 4 – resistance to 4 classes of antimicrobials; 5 – resistance to 5 classes of antimicrobials; 6 – resistance to 6 classes of antimicrobials; 7 – resistance to 7 classes of antimicrobials; 9 – resistance to 9 classes of antimicrobials
Multiple drug resistance of S. agalactiae shown as antibiotic phenotypic resistance and resistance gene prevalence data. 3 – resistance to 3 classes of antimicrobials; 4 – resistance to 4 classes of antimicrobials; 5 – resistance to 5 classes of antimicrobials; 6 – resistance to 6 classes of antimicrobials; 7 – resistance to 7 classes of antimicrobials; 9 – resistance to 9 classes of antimicrobials

Fig. 2

Positive rate of S. agalactiae resistance genes
Positive rate of S. agalactiae resistance genes

Relationship between drug resistance phenotype and drug resistance genotype of S. agalactiae

Antibiotic type Resistance gene Genotype (%)
Phenotype resistance rate (%) Consistency rate (%)
Number of bacteria Positive rate
ermB 11/15 73.33 91.66
Macrolides ermA 10/15 66.67 80.00 83.33
ermC 5/15 33.33 41.66
Lincosamides lnuA 9/15 60.00 66.67 89.99
tetM 7/15 46.67 100.00
tetK 6/15 40.00 85.71
Tetracyclines tetS 6/15 40.00 46.67 85.71
tetO 5/15 33.33 71.42

The combined virulence gene profile of S. agalactiae

Virulence gene profile Distributiona (%)
glnA+hylB+bibA+iagA+fbsA+clyE 3 (20)
glnA+hylB+iagA+fbsA 2 (13.33)
bca+glnA+hylB+iagA+fbsA+clyE 1 (6.67)
bca+cfb+hylB+bibA+iagA+fbsA+clyE 1 (6.67)
bibA+iagA+fbsA+clyE 1 (6.67)
bca+hylB+bibA+iagA+fbsA 1 (6.67)
hylB+bibA+iagA+fbsA 1 (6.67)
bca+bibA+iagA+fbsA 1 (6.67)
hylB+bibA+iagA+fbsA+clyE 1 (6.67)
cfb+hylB+bibA+iagA+fbsA 1 (6.67)
cfb+hylB+bibA+fbsA+clyE 1 (6.67)

Primer sequence and reaction conditions of the drug resistance gene of S. agalactiae

Antimicrobial drug class Resistance gene Primer sequence (5′–3′) Annealing temperature (°C) PCR product size (bp) Reference
F: GGTGGCTGGGGGGTAGATGTATTAACTGG
Lincosamides lnuA R: GCTCTCTTTGAAATACATGGTATTTTTCGATC 56 323 (23)
F: AACTTAGGCATTCTGGCTCAC
tetO R: TCCCACTGTTCCATATCGTCA 50 515 (29)
F: TCGATAGGAACAGCAGTA
tetK R: CAGCAGATCCTACTCCTT 44 169 (33)
Tetracyclines
tetM F: GTGGACAAAGGTACAACGAG 50 406
R: CGGTAAAGTTCGTCACACAC
(39)
F: CATAGACAAGCCGTTGACC
tetS R: ATGTTTTTGGAACGCCAGAG 48 667
ermB F: CGAGTGAAAAAGTACTCAACC 48 652
R: AGTAACGGTACTTAAATTGTTTAC
F: ATCTTTGAAATCGGCTCAGG
Macrolides ermC R: CAAACCCGTATTCCACGATT 47 295 (32)
F: GTTCAAGAACAATCAATACAGAG
ermA R: GGATCAGGAAAAGGACATTTTAC 48 421

Minimum inhibitory concentration (MIC) values of, and resistance of S. agalactiae isolates to, β-lactams, sulfonamides and tetracyclines

Isolate no. MIC (μg/mL)
PEN A/C AMP CET OXA SMZ SXT TE DOX
SH07 ≤0.125 (S3) 1/0.5 (R) ≤0.125 (S) 32 (R) 1 (S) 4 (S) 0.5/9.5 (S) 4 (S) 4 (S)
SH07-2 4 (R) ≤0.25/0.12 (S) ≤0.125 (S) 0.5 (S) 16 (R) 256 (I) 0.25/4.8 (S) 16 (R) 2 (S)
SH12 ≤0.125 (S) ≤0.25/0.12 (S) 0.25 (I) 0.5 (S) 4 (R) 8 (S) 0.5/9.5 (S) 32 (R) 4 (S)
SH33 ≤0.125 (S) ≤0.25/0.12 (S) ≤0.125 (S) 0.5 (S) 16 (R) 64 (S) 0.5/9.5 (S) 32 (R) 0.5 (S)
SH45 ≤0.125 (S) ≤0.25/0.12 (S) ≤0.125 (S) 1 (S) 32 (R) 64 (S) 0.25/4.8 (S) 64 (R) 2 (S)
HLJ008 ≤0.125 (S) ≤0.25/0.12 (S) ≤0.125 (S) 32 (R) 32 (R) 128 (S) 0.25/4.8 (S) 32 (R) 2 (S)
HLJ048-2 2 (R) ≤0.25/0.12 (S) ≤0.125 (S) 1 (S) 4 (R) 2 (S) 0.5/9.5 (S) 16 (R) 8 (I)
HLJ030-3 ≤0.125 (S) ≤0.25/0.12 (S) ≤0.125 (S) 0.5 (S) 0.5 (S) 64 (S) 0.5/9.5 (S) 64 (R) 4 (S)
NM025 ≤0.125 (S) ≤0.25/0.12 (S) ≤0.125 (S) 1 (S) 1 (S) 64 (S) 0.25/4.8 (S) 32 (R) 16 (R)
HB016 ≤0.125 (S) ≤0.25/0.12 (S) ≤0.125 (S) 0.25 (S) 16 (R) 128 (S) 0.5/9.5 (S) 16 (R) 4 (S)
NM-2-72-4 8 (R) ≤0.25/0.12 (S) 2 (R) 1 (S) 16 (R) 128 (S) 0.25/4.8 (S) 32 (R) 32 (R)
NM-2-034-3 8 (R) 16/8 (R) 4 (R) 0.5 (S) 4 (R) 64 (S) 2/38 (I) 4 (S) 4 (S)
SH-2-46-1 ≤0.125 (S) ≤0.25/0.12 (S) ≤0.125 (S) 0.5 (S) 32 (R) 128 (S) 0.25/4.8 (S) 16 (R) 4 (S)
SH-2-14-2 2 (R) 4/2 (R) ≤0.125 (S) 1 (S) 16 (R) 128 (S) 0.25/4.8 (S) 32 (R) 8 (I)
SD-2-009-2 ≤0.125 (S) 16/8 (R) ≤0.125 (S) 0.5 (S) 4 (R) 128 (S) 0.25/4.8 (S) 8 (I) 4 (S)

Drug resistance rate (%) (/15)

S 66.67 (10) 73.33 (11) 80.00 (12) 86.67 (13) 20.00 (3) 93.33 (14) 93.33 (14) 13.33 (2) 73.33 (11)
I 0 (0) 0 (0) 6.67 (1) 0 (0) 0 (0) 6.67 (1) 6.67 (1) 6.67 (1) 13.33 (2)
R 33.33 (5) 26.67 (4) 13.33 (2) 13.33 (2) 80.00 (12) 0 (0) 0 (0) 80.00 (12) 13.33 (2)

Logistic regression analysis of the relationship between antibiotics and virulence genes

Virulence gene Penicillin Cefoxitin Oxacillin Doxycycline Gentamicin Clindamycin
B Exp(B) P B Exp(B) P B Exp(B) P B Exp(B) P B Exp(B) P B Exp(B) P
bca 40.537 4.028 0.999 1.099 3.000 1.000 −42.406 0.000 0.999 1.099 3.000 1.000 −41.307 0.000 0.999 −61.799 0.000 0.999
scpB −20.269 0.000 1.000 −60.718 0.000 0.999 62.916 2.108 0.999 19.699 3.590 1.000 62.105 9.369 0.999 −62.493 0.000 0.999
glnA 0.000 1.000 1.000 −19.411 0.000 0.999 −21.896 0.000 0.999 −19.411 0.000 0.999 −19.411 0.000 0.999 −0.693 0.500 0.744
cfb −0.934 0.393 1.000 42.406 2.610 0.999 −84.812 0.000 0.999 −38.011 0.000 1.000 −80.417 0.000 0.999 −81.880 0.000 0.999
hylB 42.406 2.610 0.999 −40.209 0.000 0.999 42.406 2.610 0.999 40.209 2.900 0.999 40.209 2.900 0.999 0.000 1.000 1.000
bibA 21.203 1.615 1.000 −19.411 0.000 1.000 −21.896 0.000 1.000 −19.411 0.000 1.000 −19.411 0.000 1.000 −42.412 0.000 0.999
iagA −41.472 0.000 1.000 −1.099 0.333 1.000 42.406 2.610 1.000 −1.099 0.333 1.000 41.307 8.699 1.000 −20.080 0.000 1.000
cylE 0.000 1.000 1.000 −1.099 0.333 1.000 42.406 2.610 0.999 −1.099 0.333 1.000 −1.099 0.333 1.000 21.203 1.615 1.000

16 kinds of antibacterial drugs and their classification

Drug category Antibacterial drugs
penicillin
ampicillin
β-lactams amoxicillin / clavulanic acid
oxacillin
cefoxitin
Macrolides erythromycin
Lincosamides clindamycin
Aminoglycosides gentamicin
Tetracyclines doxycycline tetracycline
Chloramphenicols florfenicol
Ansamycins rifampicin
Glycopeptides vancomycin
Quinolones ciprofloxacin
Sulfonamides sulfisoxazole
sulfamethoxazole

The drug resistance patterns and gene expression profiles of S. agalactiae

Isolate no. Drug resistance pattern Resistant gene Virulence gene
SH07 (A/C)/CET/ERY ermB+lnuA+tetM+tetO bca+hylB+bibA+iagA+fbsA
SH07-2 PEN/OXA/TE/ERY/CLI/FFC ermA+ermB+lnuA+tetM+tetK+tetS+tetO glnA+hylB+iagA+fbsA
SH12 OXA/TE/ERY/CLI/GM ermA+ermB+ermC+lnuA+tetS+tetO bca+glnA+hylB+iagA+fbsA+clyE
SH33 OXA/TE/ERY/CLI/GM ermA+ermB+ermC+lnuA+tetK+tetS+tetO bca+cfb+hylB+bibA+iagA+fbsA+clyE
SH45 OXA/TE/ERY/CLI ermA+ermB+lnuA+tetK+tetS hylB+bibA+iagA+fbsA
HLJ008 CET/OXA/TE/ERY/CLI ermB+ermA+ermC+lnuA+tetM+tetK glnA+hylB+bibA+iagA+fbsA+clyE
HLJ030-3 TE/CLI/FFC ermB+ermA+lnuA+tetM hylB+bibA+iagA+ fbsA+clyE
NM025 TE/DOX/ERY ermA+ermB+lnuA+tetK+tetO glnA+hylB+bibA+iagA+fbsA+clyE
HB016 OXA/TE/ERY/CLI/GM ermA+ermB+ermC+lnuA+tetM+tetK+tetS glnA+hylB+bibA+iagA+fbsA+clyE
SH-2-46-1 OXA/TE/ERY ermA+ermB+lnuA+tetO glnA+hylB+iagA+fbsA

Primer sequence and reaction conditions of the virulence gene of S. agalactiae (13, 22, 23)

Virulence factor Virulence gene Primer sequence (5′–3′) Annealing temperature (°C) PCR size product (bp)
F: CATTGCGTAGTCACCTCCC
β-haemolysin/cytolysis cylE R: GGGTTTCCACAGTTGCTTGA 54 399
F: TAACAGTTATGATACTTCACAGAC ⎕
αC protein Bca R: ACGACTTTCTTCCGTCCACTTAGG 51 535
F: CCAAGACTTCAGCCACAAGG
C5a peptidase scpB R: CAATTCCAGCCAATAGCAGC 57 591
F: ACCGTCTGAAATGATGTGG
Laminin binding protein lmb R: GATTGACGTTGTCTTCTGC 51 572
Glutamine synthetase glnA F: ACGTATGAACAGAGTTGGCTATAA 52 471
R: TCCTCTGATAATTGCATTCCAC
CAMP factor Cfb F: ATGGGATTTGGGATAACTAAGCTAG 52 193
R: AGCGTGTATTCCAGATTTCCTTAT
Hyaluronidase hylB F: ACAAATGGAACGACGTGACTAT 52 346
R: CACCAATTGGCAGAGCCT
F: AAGCAACTAGAAGAGGAAGC
βC protein bac R: TTCTGCTCTGGTGTTTTAGG 53 479
Bacterial immunogenic bibA F: AACCAGAAGCCAAGCCAGCAACC 58 127
adhesive R: AGTGGACTTGCGGCTTCACCC
F: CGGGATTGATCTAAGTCGCT
Invasion-associated gene iagA R: CCATCAACATCAGTCGCTAA 53 459
F: AGAGCCAAGTAGGTCAACTTATAG
Fibrin binding protein B fbsA R: TTCATTGCGTCTCAAACCG 54 290

Minimum inhibitory concentration (MIC) values of, and resistance of S. agalactiae isolates to, a macrolide, a lincosamide, an aminoglycoside, a quinolone, a chloramphenicol, an ansamycin, and a glycopeptide

Isolate no. MIC (μg/mL)
ERY CLI GM CIP FFC RIF VAN
SH07 16 (R) 0.25 (S) 4 (S) 0.5 (S) 2 (S) 0.5 (S) 0.5 (S)
SH07-2 16 (R) 4 (R) 4 (S) 0.5 (S) 16 (R) 0.125 (S) 0.5 (S)
SH12 32 (R) 8 (R) 16 (R) 0.5 (S) 4 (S) 0.5 (S) 0.5 (S)
SH33 16 (R) 8 (R) 16 (R) 0.5 (S) 8 (I) 0.5 (S) 0.5 (S)
SH45 64 (R) 8 (R) 2 (S) 2 (I) 8 (I) 0.5 (S) 0.5 (S)
HLJ008 16 (R) 4 (R) 4 (S) 0.5 (S) 4 (S) 0.5 (S) 0.5 (S)
HLJ048-2 16 (R) 16 (R) 8 (I) 0.5 (S) 4 (S) 1 (S) 0.5 (S)
HLJ030-3 0.5 (S) 16 (R) 2 (S) 0.5 (S) 16 (R) 0.5 (S) 0.5 (S)
NM025 16 (R) 0.5 (S) 1 (S) 0.5 (S) 8 (I) 0.5 (S) 0.5 (S)
HB016 16 (R) 4 (R) 16 (R) 0.5 (S) 4 (S) 0.5 (S) 0.5 (S)
NM-2-72-4 2 (I) 0.5 (S) 32 (R) 0.5 (S) 16 (R) 0.5 (S) 0.5 (S)
NM-2-034-3 0.5 (S) 16 (R) 4 (S) 4 (R) 16 (R) 0.5 (S) 0.5 (S)
SH-2-46-1 16 (R) 0.5 (S) 4 (S) 0.5 (S) 4 (S) 0.5 (S) 0.5 (S)
SH-2-14-2 16 (R) 16 (R) 4 (S) 4 (R) 8 (I) 0.5 (S) 0.5 (S)
SD-2-009-2 32 (R) 0.5 (S) 16 (R) 4 (R) 16 (R) 0.5 (S) 0.5 (S)

Drug resistance rate (%) (/15)

S 13.33 (2) 33.33 (5) 60.00 (9) 73.33 (11) 40.00 (6) 100 (15) 100 (15)
I 6.67 (1) 0 (0) 6.67 (1) 6.67 (1) 26.67 (4) 0 (0) 0 (0)
R 80.00 (12) 66.67 (10) 33.33 (5) 20.00 (3) 33.33 (5) 0 (0) 0 (0)
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Life Sciences, Molecular Biology, other, Microbiology and Virology, Medicine, Veterinary Medicine