Characterization of the invasiveness of monophasic and aphasic Salmonella Typhimurium strains in 1-day-old and point-of-lay chickens

Figures & data

Table 1. Serotype, phage type and antimicrobial resistance pattern of the strains included in the study.

Strain	Serotype	Phage type	Antimicrobial resistance
A	ST	DT8	Susceptible (to AHVLA panel^a)
B	4,12:i:-^b	DT193	ASSuT
C	4,5,12:i:-	DT193	Susceptible (to AHVLA panel^a)
D	4,5,12:i:-	DT193	ASSuT
E	4,5,12:i:-	DT193	ASSuT
F	4,5,12:-:-non-motile	DT104	Susceptible (to AHVLA panel^a)
G	SE	PT14b	Nalidixic acid resistant

ASSuT, ampicillin, streptomycin, sulphonamides and tetracyclines; PT, phage type. ^aAmikacin amoxicillin/clavulanic acid, ampicillin, apramycin, cefotaxime, ceftazidime, chloramphenicol, tetracycline, ciprofloxacin, furazolidone, gentamicin, nalidixic acid, neomycin, streptomycin, trimethoprim/sulphamethoxazole and sulphonamide compounds. ^bThe O1 antigen of ST and mST can only be determined after lysogeny of the culture with the corresponding phage so this is not normally carried out.

Table 2. Results of the strain passage trial, after direct plating and enrichment.

	n	Strain A (ST DT8)		Strain B (4,12:i:-)		Strain C (4,5,12:i:-)		Strain D (4,5,12:i:-)		Strain E (4,5,12:i:-)		Strain F (4,5,12:-:-)		Strain G (SE)
		DP	E	DP	E	DP	E	DP	E	DP	E	DP	E	DP	E
Cloacal swabs	3	0	0	0	2	0	2	0	3	0	2	0	3	0	3
Liver	3	0	0	0	3	0	0	0	1	0	1	1	1	0	1
Spleen	3	0	2	0	3	0	0	0	0	0	2	0	3	1	3
Heart blood	3	0	0	0	0	0	0	0	0	0	0	1	0	0	0
Caeca	3	0	3	0	3	0	3	0	3	0	3	0	3	0	3
Total	15	0	33.3%	0	78.3%	0	33.3%	0	46.6%	0	53.3%	13.3%	66.6%	6.6%	66.6%

DP, direct plating; E, enrichment. The isolates selected for use in the invasiveness trial in point-of-lay hens are shown in bold.

Table 3. Number of positive tissue samples (including post-enrichment data) at post-mortem examination 3, 7, 17 and 20 d.p.c.

			Positive samples
PM, d.p.c.		n	Strain A (ST DT8)	Strain B (4,12:i:-)	Strain C (4,5,12:i:-)	Strain D (4,5,12:i:-)	Strain E (4,5,12:i:-)	Strain F (4,5,12:-:-)	Strain G (SE)
PM1, 3 d.p.c.	Ovary	4	4 (4.6; n = 1)	4 (3.5; n = 2)	4 (4.1; n = 2)	4 (3.2; n = 2)	4	4 (3.0; n = 2)	4 (2.9; n = 3)
	Liver	4	4 (3; n = 4)	4 (3; n = 4)	4 (3.4; n = 4)	4 (3.3; n = 4)	4 (3.3; n = 4)	4 (3.3; n = 4)	4 (3.3; n = 4)
	Spleen	4	4 (2.7; n = 4)	4 (2.9; n = 4)	4 (3.4; n = 4)	4 (3.1; n = 4)	4 (3.1; n = 4)	4 (3.4; n = 4)	4 (3.2; n = 4)
	Caeca	4	4 (7.6; n = 4)	4 (7.7; n = 4)	4 (7.7; n = 4)	4 (7.9; n = 4)	4 (7.8; n = 4)	4 (7.6; n = 4)	4 (8.4; n = 4)
PM2, 7 d.p.c.	Ovary	4	2	4 (2.6; n = 2)	4 (3; n = 1)	4	4 (2.3; n = 2)	4 (2.7; n = 2)	4
	Liver	4	4 (3; n = 2)	4 (2.9; n = 2)	4 (3.1; n = 2)	4 (2.6; n = 1)	4 (2.8; n = 1)	4 (3.2; n = 2)	4 (3; n = 4)
	Spleen	4	4 (2.9; n = 3)	4 (3.1; n = 4)	4 (3.2; n = 3)	4 (2.7; n = 3)	4 (3.5; n = 4)	4 (3.4; n = 2)	4 (4.1; n = 2)
	Caeca	4	4	4 (5; n = 1)	4	4	4	4 (8.3; n = 2)	4 (5.6; n = 1)
PM3, 17 d.p.c.	Ovary	6	0	0	3	1	1	0	1
	Liver	6	0	3	0	2	2	0	5
	Spleen	6	4 (3.3; n = 3)	6 (3.2; n = 3)	6 (2.6; n = 1)	6 (3.1; n = 1)	6 (2.8; n = 3)	6 (3.3; n = 4)	4 (3; n = 4)
	Caeca	6	4	6	6	6	6	6	6
PM4, 20 d.p.c.	Ovary	6	0	0	0	1	0	4	2
	Liver	6	0	1	1	1	1	1	1
	Spleen	6	4 (2.7; n = 3)	4	2 (2.6; n = 1)	4 (2.6; n = 1)	5 (2.6; n = 3)	6 (3.8; n = 1)	5
	Caeca	6	0	6	6	6	5	4	6
Total		80	52.5%	72.5%	70%	73.7%	72.5%	73.7%	77.5%

PM, post-mortem. When Salmonella was isolated after direct plating, mean values of the log₁₀-transformed CFU/g counts for the positive samples are shown in parentheses.

Table 4. Number of Salmonella-positive cloacal swabs for each strain on all post challenge sampling occasions.

		Positive samples
	n	Strain A (ST DT8)	Strain B (4,12:i:-)	Strain C (4,5,12:i:-)	Strain D (4,5,12:i:-)	Strain E (4,5,12:i:-)	Strain F (4,5,12:-:-)	Strain G (SE)
2 d.p.c.	20	18 (2.6; n = 5)	19 (2.6; n = 5)	20 (4.1; n = 2)	20 (1.8; n = 3)	19 (2.7; n = 5)	20 (3; n = 6)	20 (2; n = 3)
6 d.p.c.	16	10 (2; n = 6)	16 (2.9; n = 3)	16 (2.3; n = 1)	16 (2.9; n = 2)	16 (2.9; n = 3)	16	15 (2.2; n = 4)
10 d.p.c.	12	0	11	12	0	11	7	12
13 d.p.c.	12	1	11	10	10	8	11	8
16 d.p.c.	12	0	10	8	7	12	9	11
Total	72	40.2%	93%	91.6%	73.6%	70.8%	63%	91.6%

When Salmonella was isolated after direct plating (2 and 6 d.p.c.), mean values of the log₁₀-transformed CFU/g counts for the positive swabs are shown in parentheses.