An investigation of horizontal transfer of feed introduced DNA to the aerobic microbiota of the gastrointestinal tract of rats

Table 2 CFUs obtained from the gastrointestinal tracts of rats, with a normal microbiota, consuming standard feed with added DNA over 4 days (100 μg/day)

Treatment	Total CFU/g faeces Range between animals^b	Resistant CFU/g faeces Range between animals	Resistant CFU Mean (total no.)	Detection limit^a
No DNA in feed (n = 2)
Stomach	1,4 × 10⁵ - 5,0 × 10⁵	0	0 (0)	-
Small	1,8 × 10⁵ - 1,8 × 10⁵	0	0 (0)	-
intestine
Cecum	< 10⁶	4-4	4 (8)	-
Colon	< 10⁶	4-5	4,5 (9)	-
With DNA in feed (n = 6)
Stomach	< 10³ - 6,0 × 10⁵	0-180	30 (181)	< 8,3 × 10^-7
Small	< 10³ - 1,5 × 10⁷	0-36	6 (36)	< 4,3 × 10^-8
intestine
Cecum	< 10⁶	0-84	24 (146)	< 1,0 × 10^-6
Colon	< 10⁶ - 3,8 × 10⁷	0-72	13 (78)	< 1,1 × 10^-8
Sum (6 rats)	1,1 × 10⁸	0-180	441	< 8,8 × 10^-9

^aAll the 441 colonies growing on selective-agar plates were tested by PCR for possible uptake of the plasmid DNA and none were found positive. The detection limit is therefore calculated as the reciprocal of the total CFU (summarized for each compartment for all 6 rats); and given as an absolute number. As seen from the range of total CFU obtainable per individual animal, the detection limit can vary 1000-fold. Specifically, the summarized CFU numbers for the compartments of the six DNA feed rats were 1,2 × 10⁶ (stomach), 2,3 × 10⁷ (small intestine), < 10⁶ (cecum) and 9,0 × 10⁷ (colon).
^bDespite preliminary studies to quantify the expected total CFUs, the number of CFU in the cecum and colon fell in several cases below the expected concentration/plate dilutions made. Hence the total CFU number could not be determined.

ISSN: 1756-0500