Antibiotic resistance trends among
Vibrio vulnificus
and
Vibrio parahaemolyticus
isolated from the Chesapeake Bay, Maryland: a longitudinal study
Authors: Morgado Michele E. , Brumfield Kyle D. , Chattopadhyay Suhana , Malayil Leena , Alawode Taiwo , Amokeodo Ibiyinka , He Xin , Huq Anwar , Colwell Rita R. , Sapkota Amy R. 
Published: May 2024

Antibiotics are often used to treat severe
Vibrio
infections, with third-generation cephalosporins and tetracyclines combined or fluoroquinolones alone being recommended by the US Centers for Disease Control and Prevention. Increases in antibiotic resistance of both environmental and clinical vibrios are of concern; however, limited longitudinal data have been generated among environmental isolates to inform how resistance patterns may be changing over time. Hence, we evaluated long-term trends in antibiotic resistance of vibrios isolated from Chesapeake Bay waters (Maryland) across two 3-year sampling periods (2009–2012 and 2019–2022).
Vibrio parahaemolyticus
(
n
= 134) and
Vibrio vulnificus
(
n
= 94) t
ox
R-confirmed isolates were randomly selected from both sampling periods and tested for antimicrobial susceptibility against eight antibiotics using the Kirby-Bauer disk diffusion method. A high percentage (94%–96%) of
V. parahaemolyticus
isolates from both sampling periods were resistant to ampicillin and only 2%–6% of these isolates expressed intermediate resistance or resistance to third-generation cephalosporins, amikacin, tetracycline, and trimethoprim-sulfamethoxazole. Even lower percentages of resistant
V. vulnificus
isolates were observed and those were mostly recovered from 2009 to 2012, however, the presence of multiple virulence factors was observed. The frequency of multi-drug resistance was relatively low (6%–8%) but included resistance against antibiotics used to treat severe vibriosis in adults and children. All isolates were susceptible to ciprofloxacin, a fluoroquinolone, indicating its sustained efficacy as a first-line agent in the treatment of severe vibriosis. Overall, our data indicate that antibiotic resistance patterns among
V. parahaemolyticus
and
V. vulnificus
recovered from the lower Chesapeake Bay have remained relatively stable since 2009.

IMPORTANCE

Vibrio
spp. have historically been susceptible to most clinically relevant antibiotics; however, resistance and intermediate-resistance have been increasingly recorded in both environmental and clinical isolates. Our data showed that while the percentage of multi-drug resistance and resistance to antibiotics was relatively low and stable across time, some
Vibrio
isolates displayed resistance and intermediate resistance to antibiotics typically used to treat severe vibriosis (e.g., third-generation cephalosporins, tetracyclines, sulfamethoxazole-trimethoprim, and aminoglycosides). Also, given the high case fatality rates observed with
Vibrio vulnificus
infections, the presence of multiple virulence factors in the tested isolates is concerning. Nevertheless, the continued susceptibility of all tested isolates against ciprofloxacin, a fluoroquinolone, is indicative of its use as an effective first-line treatment of severe
Vibrio
spp. infections stemming from exposure to Chesapeake Bay waters or contaminated seafood ingestion.