Development of a multi-locus sequence typing scheme for Laribacter hongkongensis, a novel bacterium associated with freshwater fish-borne gastroenteritis and traveler's diarrhea.
BACKGROUND
Laribacter hongkongensis is a newly discovered, facultative anaerobic, Gram-negative, motile, sea gull-shaped rod associated with freshwater fish borne gastroenteritis and traveler's diarrhea. A highly reproducible and discriminative typing system is essential for better understanding of the epidemiology of L. hongkongensis. In this study, a multilocus sequence typing (MLST) system was developed for L. hongkongensis. The system was used to characterize 146 L. hongkongensis isolates, including 39 from humans and 107 from fish.


RESULTS
Fragments (362 to 504 bp) of seven housekeeping genes were amplified and sequenced. Among the 3068 bp of the seven loci, 332 polymorphic sites were observed. The median number of alleles at each locus was 34 [range 22 (ilvC) to 45 (thiC)]. All seven genes showed very low d(n)/d(s) ratios of < 0.04, indicating that no strong positive selective pressure is present. A total of 97 different sequence types (STs) were assigned to the 146 isolates, with 80 STs identified only once. The overall discriminatory power was 0.9861. eBURST grouped the isolates into 12 lineages, with six groups containing only isolates from fish and three groups only isolates from humans. Standardized index of association (I(S)(A)) measurement showed significant linkage disequilibrium in isolates from both humans and fish. The I(S)(A) for the isolates from humans and fish were 0.270 and 0.636, indicating the isolates from fish were more clonal than the isolates from humans. Only one interconnected network (acnB) was detected in the split graphs. The P-value (P = 0) of sum of the squares of condensed fragments in Sawyer's test showed evidence of intragenic recombination in the rho, acnB and thiC loci, but the P-value (P = 1) of maximum condensed fragment in these gene loci did not show evidence of intragenic recombination. Congruence analysis showed that all the pairwise comparisons of the 7 MLST loci were incongruent, indicating that recombination played a substantial role in the evolution of L. hongkongensis. A website for L. hongkongensis MLST was set up and can be accessed at http://mlstdb.hku.hk:14206/MLST_index.html.


CONCLUSIONS
A highly reproducible and discriminative MLST system was developed for L. hongkongensis.
Woo
Patrick C Y
PC
State Key Laboratory of Emerging Infectious Diseases, The University of Hong Kong, Hong Kong, PR China. pcywoo@hkucc.hku.hk
Teng
Jade L L
JL
Tsang
Alan K L
AK
Tse
Herman
H
Tsang
Vivien Y M
VY
Chan
King-Man
KM
Lee
Edwin K Y
EK
Chan
Jim K H
JK
Ma
Shirley S L
SS
Tam
Dorothy M W
DM
Chung
Liliane M W
LM
Lau
Susanna K P
SK
Yuen
Kwok-Yung
KY
D000818:Animals; D001426:Bacterial Proteins / Q000235:genetics*; D015373:Bacterial Typing Techniques; D003967:Diarrhea / Q000382:microbiology*; D005393:Fish Diseases / Q000382:microbiology*; D005399:Fishes / Q000382:microbiology; D005618:Fresh Water; D005759:Gastroenteritis / Q000382:microbiology*; D016905:Gram-Negative Bacterial Infections / Q000382:microbiology; D006801:Humans; D009346:Neisseriaceae / Q000145:classification* / Q000235:genetics / Q000302:isolation & purification; D010802:Phylogeny; D017422:Sequence Analysis, DNA / Q000379:methods; D014195:Travel
D001426:Bacterial Proteins