Abstract
Difficulties in accurately identifying serovar 4,[5],12:i:- as monophasic variants of Salmonella enterica serovar Typhimurium mean there is confusion in the reporting of serovars Typhimurium and 4,[5],12:i:-. To gain insight into the prevalence and diversity of these monophasic variants in England and Wales, screening for fljB, hin and the serovar 4,[5],12:i:- DT193-associated genomic island was conducted on 609 S. enterica isolates designated as definitive phage type (DT) 193, and 142 isolates serologically-defined as monophasic variants of serovar Typhimurium but belonging to phage types other than DT193. All latter 142 isolates were subtyped by multilocus variable-number tandem repeat analysis (MLVA). MLVA was also applied to 70 DT193 serologically-defined monophasic variant isolates. Results indicate that serovar 4,[5],12:i:- accounted for 108 of 209 (52%) of DT193 isolates with available serological data and 99 of 142 (70%) monophasic variant isolates belonging to other phage types. Of 609 DT193 isolates, 463 (76%) lacked fljB and hin. Moreover, genetically-related isolates of DTs 120, 191, 191a, 195, phage types U311 and U323, and reacts but does not conform (RDNC) and untypable (UT) strains were also lacking either hin and/or fljB. Of note, the serovar 4,[5],12:i:- DT193-associated genomic island was identified in not only 458 of 463 (99%) monophasic DT193 isolates, but also 25 of 139 (18%) biphasic DT193 isolates and 56 of 76 (74%) monophasic variants of other phage types. Accurate monitoring of the emergence of serovar 4,[5],12:i:- isolates is important to ascertain the public health impact of these strains; since 2012 the Health Protection Agency’s Salmonella Reference Unit has therefore begun determining full antigenic structures of all presumptive O:4 isolates in addition to routinely performing phage typing for identification of variants of serovar Typhimurium.
Highlights
Salmonella enterica serovar 4,[5],12:i:- strains failing to express the fljB-encoded phase-2 flagellar antigen have been increasingly isolated from food animals and humans in the European Union (EU) over the last two decades [1]
The study panel consisted of all S. enterica isolates (n=609) designated as phage type DT193 submitted to the Health Protection Agency (HPA) between January–December 2010 for which antigenic structures were readily available for 209 isolates
Serological detection of the phase-2 flagellar antigen largely agreed with detection of fljB by polymerase chain reaction (PCR), with only eight of 209 isolates where the phase-2 flagellar antigen was reportedly detected in isolates that were fljB-/ hin
Summary
Salmonella enterica serovar 4,[5],12:i:- strains failing to express the fljB-encoded phase-2 flagellar antigen have been increasingly isolated from food animals and humans in the European Union (EU) over the last two decades [1]. Such strains were rarely identified before the mid-1990s but according to Enter-Net data, serovar 4,[5],12:i:- was the fourth most common serovar isolated from humans in the EU in 2006 [2]. This process may be complicated by serovar Typhimurium strains in which serological detection of the phase-2 flagellar antigen is inconsistent [5]
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