Table 2.

Experiment A: Megasphaera elsdenii antibiotic resistance phenotypes from mother sow and offspring

Animala	Day after birth	No. of M. elsdenii isolates testedb	No. of M. elsdenii isolates with antibiotic resistance phenotypec:
			Sens	T	A	C	AT	CT	CA	CAT
Sow	NAd	69	2	4	15	6	23	1	5	13
Group 1 offspring (6 pigs)	11	Und
	18	2	2
	25	31	31
	32	59	59
	46	60	30	7	13					10
	70	60	19	9	3	2		17	2	8
Group 2 offspring (4 pigs)	70	40	6	6		19		3	6

^aAt weaning, group 1 pigs were housed in a separate pen in the same room as the mother sow. Group 2 pigs were moved to a separate room.

^bTen M. elsdenii colonies (or all colonies, if fewer than 10) were randomly selected for each animal at each sampling time. Sow isolates were obtained from fecal samples taken on six separate days before farrowing and from one sample after farrowing. Und, no M. elsdenii colonies were obtained.

^cSens, sensitive to all four antibiotics. T, tylosin resistant; C, chlortetracycline resistant; A, ampicillin resistant. Reference strains 14-14 (Ctc^r Amp^r Tyl^r Cou^s) and 24-50C (Ctc^s Amp^s Tyl^s Cou^r) were included as controls in every assay. No coumermycin-resistant isolates were detected.

^dNA, not applicable.