The isolation of Vibrio species from the environment is an indication that other human pathogenic microorganisms are present in the environment. This could be due to environmental contamination resulting from human activities or the discharge of untreated wastewater final effluent into the environment. In this study, PCR was used for the confirmation of Vibrio species. These confirmed Vibrio species were subjected to antibiotics susceptibility testing. The results observed show that Vibrio parahaemolyticus, Vibrio vulnificus and Vibrio fluvialis) expressed resistance against almost all the antibiotics tested in this study. Resistance against antibiotics is an important medical and public health issue of concern due to its direct link with disease management . Most of the Vibrio isolates were resistant against more than three antibiotics tested. Twenty-nine percent of the Vibrio isolates exhibited resistance against tetracycline, while 71 % of the isolates were susceptible against tetracycline. This report corroborates with the reports of Quilici et al. ; Raissy et al. ; Osuolale and Okoh, .
In contrast to this report, Mandal et al.  and Singh et al.  reported that Vibrio species exhibited a high resistance rate against tetracycline. Against nalidixic acid, 27 % of the Vibrio isolates were resistant, and 73 % were susceptible. This is in contrast to the findings of Srinivasan et al. , who reported that 73 % of Vibrio species were resistant against nalidixic acid. High rate of resistance against nalidixic acid is very concerning, as reports have stated that bacteria resistance to nalidixic acid is most likely to spread to other fluoroquinolones [20, 26]. No resistance pattern was observed in Vibrio parahaemolyticus and Vibrio fluvialis against imipenem and meropenem, while in Vibrio vulnificus, no resistance was observed against Trimethoprim-sulfamethoxazole. Baron et al.  reported increased Vibrio species' susceptibility to imipenem, ampicillin, amikacin and trimethoprim-sulfamethoxazole. This study is similar to that finding except for imipenem to which Vibrio vulnificus exhibited resistance. Okoh and Igbinosa,  also reported resistance to these antibiotics, including Imipenem and Vibrio vulnificus in this study exhibited resistance to imipenem, thereby corroborating with this report.
The multiple antibiotic resistance phenotype (MARP) evaluated in this study revealed that 38 MARP patterns were observed across all Vibrio species evaluated and most of the Vibrio isolates were resistant to three or more antibiotics, therefore, indicating that the isolates are resistant to almost all clinically important antibiotics used for treatment. The multiple antibiotic resistance index (MARI) index of 0.2 is the acceptable threshold values for differentiating low-risk and high-risk antibiotic usage regions. MAR index observed in this study ranged from 0.3 to 0.8 and this can be grouped under high-risk source of contamination. None of the isolates tested had MAR index value of ≤ 0.2. This therefore indicate inappropriate antibiotics usage in the environment. Increased MARI value like the one observed in this study could be as a result of various anthropogenic activities within the environment, thus suggesting that the environment is highly polluted with antimicrobial agents . The MARI value obtained also confirms the findings of Okoh and Igbinosa , whose findings also revealed ≥ 0.3 threshold value. Resistance to tetracycline and nalidixic acid were the most dominant antibiotics to which Vibrio parahaemolyticus (16 isolates) and Vibrio fluvialis (13 isolates) are resistant against. While tetracycline and imipenem were the most common antibiotics to which Vibrio vulnificus (16 isolates) are resistant. Hence, Minimum inhibitory concentration (MIC) and minimum bactericidal concentration (MBC) was carried out using two antibiotics to which highest rate of resistance was observed.
As shown in Table 3, against Vibrio parahaemolyticus, MIC concentration ranged from 16 µg/ml to 1024 µg/ml in nalidixic acid and 16 µg/ml to 128 µg/ml in tetracycline. At 128 µg/ml concentration, nalidixic acid had the highest number of bacteria inhibitions, where 4 (25 %) out of the 16 resistant Vibrio parahaemolyticus isolates tested were inhibited. Antibiotics concentration 1024 µg/ml recorded the lowest number of inhibitions where only 1 (6 %) of the 16 resistant isolates was inhibited. Tetracycline recorded the highest number of inhibitions at 32 µg/ml, where 7 (43.8 %) out of the 16 resistant Vibrio parahaemolyticus isolates were inhibited. MBC was further carried out and in Table 6, at 2048 µg/ml and 4096 µg/ml concentrations of tetracycline and nalidixic acid respectively, most of the isolates were completely eliminated. These concentrations were then taken as the MBC values for both antibiotics against Vibrio parahaemolyticus.
In Table 4, against Vibrio vulnificus, MIC concentration observed ranged from 8 µg/ml to 64 µg/ml for imipenem and 32 µg/ml to 256 µg/ml for tetracycline. Imipenem had the highest number of bacteria growth inhibition at 16 µg/ml concentration, where 6 (37.5 %) of the resistant isolates were inhibited. The highest number of bacteria inhibitions for tetracycline was observed at 64 µg/ml concentration, where 9 (56.3 %) of the 16 resistant isolates were inhibited. At concentration 8 µg/ml and 256 µg/ml for imipenem and tetracycline respectively, lowest number of bacteria inhibitions was observed. MBC was carried out against the resistant Vibrio vulnificus isolates. 128 µg/ml and 512 µg/ml concentration of imipenem exhibited highest rate of bactericidal activity, while 1024 µg/ml concentration of tetracycline exhibited highest number of bactericidal activities as shown in Table 7. These concentrations were taken as the MBC values for both antibiotics.
MIC concentration against Vibrio fluvialis ranged from 256 µg/ml to 2048 µg/ml for tetracycline and 32 µg/ml to 2048 µg/ml for nalidixic acid. Tetracycline and nalidixic acid had the highest number of bacteria growth inhibition at 256 µg/ml and 2048 µg/ml concentration respectively, where 5 (38.5 %) and 6 (46.2%) of the resistant isolates were inhibited by tetracycline and nalidixic acid respectively as shown in Table 5. MBC was carried out against the resistant Vibrio fluvialis isolates and at 8192 µg/ml concentration, tetracycline and nalidixic exhibited highest number of bactericidal activities. These concentrations were taken as the MBC values for both antibiotics. The MIC and MBC result in this study is in agreement with the result obtained from the disc diffusion susceptibility testing as resistance to tetracycline, nalidixic acid and imipenem were recorded in both tests. The report of Chandrakala et al.  is in contrast with findings from this present study as increased sensitivity of Vibrio species against tetracycline and nalidixic acid with low MIC values were observed.