The intestinal microbiota play important roles in health of their host, contributing to maintaining the balance
and resilience against pathogen. To investigate effects of pathogen to intestinal microbiota, the bacterial
dynamics upon a shrimp pathogen, Vibrio harveyi, exposures were determined in two economically
important shrimp species; the black tiger shrimp (BT) and the Pacific white shrimp (PW). Both shrimp
species were reared under the same diet and environmental conditions. Shrimp survival rates after the
V. harveyi exposure revealed that the PW shrimp had a higher resistance to the pathogen than the BT
shrimp. The intestinal bacterial profiles were determined by denaturing gradient gel electrophoresis
(DGGE) and barcoded pyrosequencing of the 16S rRNA sequences under no pathogen challenge control
and under pathogenic V. harveyi challenge. The DGGE profiles showed that the presence of V. harveyi
altered the intestinal bacterial patterns in comparison to the control in BT and PW intestines. This implies
that bacterial balance in shrimp intestines was disrupted in the presence of V. harveyi. The barcoded
pyrosequencing analysis showed the similar bacterial community structures in intestines of BT and
PW shrimp under a normal condition. However, during the time course exposure to V. harveyi, the relative
abundance of bacteria belong to Vibrio genus was higher in the BT intestines at 12 h after the exposure,
whereas relative abundance of vibrios was more stable in PW intestines. The principle coordinates
analysis based on weighted-UniFrac analysis showed that intestinal bacterial population in the BT shrimp
lost their ability to restore their bacterial balance during the 72-h period of exposure to the pathogen,
while the PW shrimp were able to reestablish their bacterial population to resemble those seen in the
unexposed control group. This observation of bacterial disruption might correlate to different mortality
rates observed between the two shrimp species. Our findings provide evidence of intestinal bacterial population
altered by a presence of the pathogen in shrimp intestines and intestinal bacterial stability might
provide colonization resistance against the invading pathogen in the host shrimp. Hence, intestinal
microbial ecology management may potentially contribute to disease prevention in aquaculture.