Vibrio spp. are among the most common opportunistic pathogens affecting shrimp aquaculture and can also pose zoonotic risks. The emergence and spread of antibiotic-resistant Vibrio strains threaten both shrimp production and public health. This study aimed to characterize the species diversity and antimicrobial susceptibility of Vibrio isolates from farmed Pacific white shrimp (Litopenaeus vannamei) in Southern Thailand and to establish provisional epidemiological cut-off values to help distinguish wild-type from non–wild-type (acquired-resistant) isolates.
Shrimp were collected from ten intensive farms in Southern Thailand that had histories of disease outbreaks. Vibrio spp. were isolated from the hepatopancreas of sampled shrimp. Species identification was performed using 16S rRNA sequencing. Isolates were tested for minimum inhibitory concentrations (MICs) against eight antibiotics to determine susceptibility profiles. The authors calculated epidemiological cut-offs (COWT) to separate fully susceptible (wild-type) populations from those with acquired resistance; florfenicol COWT was specifically reported.
A total of 27 different Vibrio spp. were recovered from the shrimp hepatopancreas samples. The most frequently recovered species among the selected isolates were Vibrio parahaemolyticus, followed by Vibrio alginolyticus and Vibrio harveyi. The report emphasizes broad species diversity across farms but does not provide isolate counts per species in the abstract.
Isolates were tested against eight antimicrobials; specific agent names reported in the abstract include oxytetracycline, doxycycline, ciprofloxacin, enrofloxacin, florfenicol, amoxicillin, ceftriaxone, and sulfadimethoxine.
Overall susceptibility:
The Vibrio isolates were generally susceptible to oxytetracycline, doxycycline, ciprofloxacin, enrofloxacin, and florfenicol. Reported MIC50 values for these susceptible agents ranged from ≤ 0.25 to 2 μg/mL.
Conversely, most isolates were resistant to amoxicillin, ceftriaxone, and sulfadimethoxine, with MIC50 values reported as at least 128 μg/mL. The authors note that, to their knowledge, this study provides the first evidence of high-level ceftriaxone resistance in Vibrio spp. isolated from farmed shrimp.
These results indicate a split susceptibility pattern in the sampled Vibrio population: retained susceptibility to several tetracyclines, fluoroquinolones, and florfenicol, but widespread high-level resistance to certain beta-lactams and sulfonamides tested.
To differentiate wild-type isolates from those with acquired resistance, the study calculated an epidemiological cut-off value (COWT) for florfenicol. The COWT was determined as ≤ 4 μg/mL. When this threshold was applied to the Vibrio spp. collection, 83.10% of isolates were classified as wild type for florfenicol susceptibility. The abstract does not present COWT values for the other antibiotics tested or full MIC distributions by species; those details would require consulting the full article.
Key conclusions drawn in the report include:
There is substantial species diversity of Vibrio associated with Pacific white shrimp farms in Southern Thailand, with 27 species identified and several species—V. parahaemolyticus, V. alginolyticus, V. harveyi—being most common.
The tested Vibrio isolates retained susceptibility to several commonly used agents including oxytetracycline, doxycycline, ciprofloxacin, enrofloxacin, and florfenicol, but exhibited high-level resistance to amoxicillin, ceftriaxone, and sulfadimethoxine.
The detection of high-level ceftriaxone resistance in Vibrio spp. from farmed shrimp is highlighted as a novel and concerning finding in this context.
Applying a provisional florfenicol COWT of ≤ 4 μg/mL classified the majority (83.10%) of isolates as wild type, supporting use of COWT methodology to monitor emergent resistance in aquaculture pathogens.
The authors underscore the need for strict regulation and stewardship of antibiotic use in shrimp aquaculture to reduce selection pressure and limit the emergence and spread of antibiotic-resistant bacteria.
The abstract provides key outcomes but omits several methodological and quantitative details that may be relevant for interpretation, including the total number of isolates tested, breakthrough rates per species, exact MIC distributions for each antibiotic by species, and the statistical methods used to calculate COWT beyond the florfenicol value reported. Those specifics are not reported in the abstract and would need to be obtained from the full text.
Overall, this study documents diverse Vibrio species in Pacific white shrimp farms in Southern Thailand and a concerning pattern of antibiotic susceptibility and resistance that supports tighter antimicrobial governance in shrimp aquaculture.