Characterization of Erythromycin and Tetracycline Resistance in Lactobacillus fermentum Strains

Table 2

Characterization of L. fermentum strains with antibiotic resistance for erythromycin and tetracycline.

L. fermentum strains	Source	Erythromycin			Tetracycline			Phenotype^d	Genotype^e
		Zone of inhibition (mm)^a	Characterization^b	MIC^c (μg/ml)	Zone of inhibition (mm)^a	Characterization^b	MIC^c (μg/ml)
HF-A1	Feces of healthy individuals	21.2 ± 2.9	S	0.25	15.7 ± 0.6	R	64	TET	tet(M)^p, tet(K)^p
HF-A4	Feces of healthy individuals	21.0 ± 1.4	S	0.25	15.5 ± 0.7	R	64	TET	tet(M)^p, tet(K)^p
HF-B1	Feces of healthy individuals	20.2 ± 3.4	MS	0.25	14.7 ± 0.6	R	64	TET	tet(M)^p, tet(K)^p
3-4	Sour-milk drink, “Tan,” “Chistaya Liniya,” Russia	21.0 ± 2.5	S	0.25	6.5 ± 2.1	R	16	TET	erm(C)^p, tet(M)^p, tet(K)^p
5-1	Fermented baked milk, ryazhenka, “Chistoe pole,” Russia	6.5 ± 2.1	R	1	20.3 ± 1.4	MS	8	—	erm(B)^c, tet(M)^p, tet(K)^p
5-2	Fermented baked milk, ryazhenka, “Nash product,” Russia	24.3 ± 2.5	S	0.25	14.5 ± 0.7	R	32	TET	tet(M)^p, tet(K)^p

^aDiameters of the zones of inhibition determined by the disc diffusion method (mean value ± standard deviation) (Figure S1A). ^bBased on standards mentioned in Materials and Methods, L. fermentum strains were characterized as either susceptible (S), moderately susceptible (MS), or resistant (R) to each antibiotic tested. ^cThe minimum inhibitory concentration (MIC) of antibiotics determined by the broth microdilution method as the lowest concentration of an antibiotic at which visible growth was inhibited. ^dBased on MIC values, L. fermentum strains were characterized as erythromycin resistant (ERM) or tetracycline resistant (TET). ^eAntibiotic resistance genes present in isolates of L. fermentum as detected using PCR: ^pplasmid-located gene; ^cchromosome-located gene (for details, see Figures S1B–S1D).