Salmonella enterica subsp.
enterica serovar 4,[5],12:i:- is considered to be a monophasic variant of
Salmonella Typhimurium and is increasing
ly associated with human infections. The use of PCR for the unequivoca
l identification of strains identified by conventiona
l serotyping as 4,[5],12:i:- has been recommended by the European Food Safety Authority (EFSA), in particu
lar the conventiona
l mu
ltip
lex PCR deve
loped by . An a
lternative protoco
l for the identification and differentiation of
S. Typhimurium and
S. Typhimurium-
like strains, inc
luding its monophasic variants, based on a mu
ltip
lex rea
l-time PCR assay was deve
loped in our
laboratory. A pane
l of 206
Salmonella strains was used to va
lidate our mu
ltip
lex rea
l-time PCR against the conventiona
l mu
ltip
lex PCR recommended by EFSA, i.e. 43
Salmonella strains of serovars other than Typhimurium and 163 routine iso
lates determined by s
lide agg
lutination serotyping to have an incomp
lete antigenic formu
la compatib
le with the
S. Typhimurium formu
la 4,[5],12:i:1,2. Both methods correct
ly identified the 43
Salmonella strains as non
S. Typhimurium. Among the 163 iso
lates of undetermined serovar by conventiona
l serotyping, both PCR protoco
ls identified 54 iso
lates as
S. Typhimurium, 101 as monophasic
S. Typhimurium and 8 as non-
S. Typhimurium.
Twenty isolates phenotypically lacking the phase-2 H antigen were positive for the fljB.1,2 gene. These strains have been recently described in the literature by other workers and have been referred to as ¡°inconsistent¡± variants of S. Typhimurium. Antimicrobial resistance and phage typing were also performed on the S. Typhimurium isolates, including monophasic variants, and approximately half of the isolates identified as monophasic S. Typhimurium by our multiplex real-time PCR protocol were DT193 with the resistance pattern ASSuT. There was 100 % concordance between the conventional PCR and the multiplex real-time PCR method developed in this study which proved that our protocol is equivalent to the one recommended by EFSA. In comparison to the conventional PCR, this new protocol is faster and is currently being applied routinely in our laboratory to all isolates that could potentially be S. Typhimurium.