Abstract: To investigate the antibiotic susceptibility, Vibrio parahaemolyticus were isolated and identified from the sample of shrimps collected from different shrimp processing plants located at Rupsha, Khulna. Among the 27 samples, 10 strains were identified as Vibrio parahaemolyticus. Susceptibility of these Vibrio parahaemolyticus was assayed by disc diffusion method against 11 antibiotics. All these strains were highly sensitive to Tetracycline, Norfloxacin, Gentamicin, Riphampicin and Neomycin, but were resistant to Erythromycin, Penicillin, Ampicillin and Kanamycin. Vibrio parahaemolyticus showed both resistant and susceptible character against Cephalexin and Streptomycin. 7 strains were resistant and 3 were sensitive to Cephalexin on the other hand 8 were resistant and 2 were sensitive to Streptomycin, among the 10 Vibrio parahaemolyticus strains. The antibiotics named Tetracycline, Norfloxacin, Gentamicin, Riphampicin and Neomycin should be the choice to control diseases due to Vibrio parahaemolyticus as well as enteric bacteria.
INTRODUCTION
Human infection follows either direct contact with aquatic environment or indirectly via contaminated food and water. Food-borne Vibrio infections tend to occur more frequently in developed countries while transmission of Vibrio infections in developing countries is, by and large, water-borne. Further, the magnitude of food-borne infections in developing countries is still incompletely understood for the want of robust scientific information. Members of the genus Vibrio are autochthonous bacterial flora in the aquatic ecosystem and quite a few of them are associated with infections in humans and aquatic animals.
Among V. cholerae, the toxigenic serogroups O1 and O139 are the etiologic serogroups that cause cholera, which are responsible for epidemics and pandemics mainly due to poor water supply and personal hygiene. The other important and most common seafood-borne halophilic Vibrio is Vibrio parahaemolyticus. Since its discovery in 1953, many aspects on this pathogen were explored and established through extensive research (Fujino et al., 1953).
However, there is a burgeoning problem of food-borne illness throughout the globe. The relation between strains isolated from the environment and, those isolated from seafood and human clinical isolates are poorly understood. Studies conducted in many countries have shown that Vibrio parahaemolyticus is common flora in many coastal areas, fresh water bodies, plankton and in fishes.
A massive intensification occurred in shrimp aquaculture throughout the world, where stocking density and the rate of application of aqua-drugs and chemicals have been hugely accelerated. Use of antimicrobials in aquaculture essentially started with the reserch of Gutsell (2006), who recognized the potential usefulness of sulphanamides for combating furunculosis. Following this, chloramphenicol, oxytetracycline, kanamycin, nifurprazine, oxolinic acid, sodium nifurstyrenate, flumequin, ciprofloxacin and others were introduced (Austin and Austin, 2005). Indiscriminate use of chemicals and drugs often lead to problems like drug resistance, tissue residues, adverse effect on species biodiversity, etc. which ultimately affect the shrimp culture, human and environment. Several of these aspects have been well documented (Spanggaard et al., 1993; Herwig and Gray, 1997; Anderson and Levin, 1999; Tendencia and Pena, 2001).
Antimicrobial agents have been widely used in aquaculture worldwide to treat infections caused by a variety of bacterial pathogens of fish including Aeromonas hydrophila, Aeromonas salmonicida, Edwardsiella tarda, Pasteurella piscicida, Vibrio anguillarum and Yersinia ruckeri. This memorandum summarizes evidence that use of antimicrobial agents in aquaculture, as with other uses, selects for antimicrobial resistance in the exposed bacterial flora. Because antimicrobial agents use in aquaculture are administered by mixing them with feed which is dispersed in the water, use of antimicrobial agents in aquaculture directly doses the environment, which results in selective pressures in the exposed ecosystem. The emergence of antimicrobial resistance following use of antimicrobial agents in aquaculture has been identified in fish pathogens (World Health Organization, 1999; Midtvedt and Lingaas, 1992). For example, in several countries Aeromonas salmonicida is frequently resistant to multiple drugs including sulphonamides, tetracycline, amoxicillin, trimethoprim-sulfadimethoxine and quinolones (Barnes et al., 1994; Inglis et al., 1991), antimicrobial agents which are commonly used in aquaculture. The first isolation of A. salmonicida resistant to a specific antimicrobial agent has often been reported shortly after the introduction of the agent into aquaculture (Dalsgaard et al., 1994). Similar correlations between antimicrobial agents used in aquaculture and antimicrobial resistance are also reported among other fish pathogens (DeGrandis and Stevenson, 1985; Takashima et al., 1987).
Antimicrobial-resistant bacteria which result from use of antimicrobial agents in aquaculture can transfer these resistance determinants to other bacteria and many antibiotic resistance determinants in fish pathogens are frequently carried on transferable R plasmids (Watanabe et al., 1977; Aoki, 1997). Horizontal spread of plasmids from fish pathogens may therefore transfer resistance genes to other bacteria including those that are pathogenic to humans. Horizontal transfer of resistance genes on plasmids has been demonstrated between bacteria in the water of fish ponds and in marine sediments (Stewart and Sinigalliano, 2005). Plasmids carrying resistance determinants have also been transferred in vitro from fish pathogens to human pathogens including Vibrio cholerae (Hayashi et al., 1982) Vibrio parahemolyticus (Nakjima et al., 1983) and potential human pathogens including Escherichia coli (Sandaa et al., 1992; Son et al., 1997). Furthermore, plasmids carrying multiple antimicrobial-resistance determinants have been transferred in simulated natural microenvironments between bacterial pathogens of fish, humans and other animals, demonstrating that resistance determinants on plasmids can spread from fish pathogens to human pathogens (Kruse and Sorum, 1994). These studies indicate that dissemination of antimicrobial resistance determinants may be facilitated by the horizontal transfer of plasmids between related and diverse bacteria.
Bacteria on fish may also be transmitted to humans when the aqua cultured fish are eaten, or when other foods, which have been cross-contaminated by bacteria from fish, are eaten. For example, Vibrio parahaemolyticus is a common food borne disease in Japan where infections have been linked to the consumption of aquaculture fin fish (Ministry of Health and Welfare, 1999).
The progressive increase in antimicrobial resistance among enteric pathogens in developing countries is becoming a critical area of concern. The acute diarrheal diseases for which antimicrobial therapy is clearly effective include shigellosis, cholera and campylobacteriosis. However, for campylobacteriosis, the diagnosis is usually too late for antimicrobial therapy to be effective (World Health Organization, 1999; Midtvedt and Lingaas, 1992). Among the bacteria causing diarrheal diseases, vibrio parahaemolyticus continue to be a major public health problem. So objectives of the present study are; (a) Isolation and identification of Vibrio parahaemolyticus from shrimp (b) Study of antibiotic susceptibility of Vibrio parahaemolyticus species.
MATERIALS AND METHODS
Isolation of Vibro Sp. From Shrimp
Shrimp samples were collected from different shrimp processing plant in
Khulna district. For the collection of samples some clean, dry and sterile polythene
bags were taken to the sampling site. Sufficient amount of fish was collected
from each site; kept in the polythene bag and tagged. Measures were taken to
avoid contamination as far as possible. Samples were processed immediately in
the laboratory. Samples were kept refrigerated (4°C) until culture. Aseptically
weigh a 25 g shrimp into a sterile stomacher bag. Cut large sample into smaller
pieces before stomaching. After stomach, add additional Alkaline Peptone Water
(APW) to bring the total amount added to 225 mL (10¯1 dilution).
Now APW was incubated for 24 h at 37°C.
Plating on Selective Agar Media
After incubation, a loop full of selective enrichment broth was transferred
to the surface of the selective TCBS agar plate. The plates were then incubated
at 37°C for 24 h and observed colonies of typical vibrio parahaemolyticus.
After 24 h typical vibrio sp. showed as green colonies on TCBS agar.
(Fig. 1A).
Maintenance and Preservation of the Selected Strains
Trypticase Soy Agar (TSA) slants were used for short-term preservation of
selected strains. The strains were inoculated in TSA slant using a sterile loop
and incubated at 37°C for 18-27 h. After growth, the slants were stored
at freeze for short-term storage and for uses.
Identification of Vibrio parahaemolyticus
We have done several biochemical tests e.g., Arginine Glucose Slant
(AGS), oxidase test, lysine decarboxylase test, arginine dihydrolase test, salt
tolerance test, voges-proskauer test, carbohydrate fermentation test, gelatin
hydrolysis test and urease test according to Berzes manual of microbiology for
identification of Vibrio parahaemolyticus from vibrio sp.
| Fig.1A: | Colonies plated out from enrichment culture of shrimp TCBS agars and incubated at 37°C for 24 h, spread plating. Green colonies on TCBS agar were identified as Vibrio parahaemolyticus |
Arginine Glucose Slant (AGS)
Each suspect T1N1 culture was inoculated to AGS by
streaking the slant and stabbing the butt and Incubated AGS with loose cap overnight
at 35±2°C. V. parahaemolyticus cultures showed an alkaline
(purple) slant and an acid (yellow) butt, as arginine is not hydrolyzed. No
gas or H2S is produced.
Oxidase Test
The overnight T1N1 cultures were transferred to a
filter paper that was saturated with oxidase reagent (1% N'-tetramethyl-p-phenylenediamine.
2 HCl) by using a platinum wire. A dark purple color developing within 10 sec
indicates a positive test growth. V. parahaemolyticus shows oxidase positive.
Lysine Decarboxylase Test
A Lysine Iron Agar (LIA) slant was used instead of lysine broth to test
for the production of lysine decarboxylase. Then the tubes were inoculated fresh
cultures by stabbing the butt and streaking the slant. Organisms that produce
lysine decaboxylase in LIA cause an alkaline reaction (purple color) throughout
the medium. Organisms without these enzymes typically produce an acid butt (yellow).
Vibrio parahaemolyticus gives a positive reaction in LIA.
Arginine Dihydrolase Test
An Arginine Glucose Slant (AGS) slant was used instead of arginine broth
to test for the production of arginine dihydrolase. The tubes were inoculated
fresh cultures by stabbing the butt and streaking the slant. Organisms that
produce arginine dihydrolase in AGS cause an alkaline reaction (purple color)
throughout the medium. Organisms without these enzymes typically produce an
acid butt (yellow). Vibrio parahaemolyticus gives a negative reaction.
Salt Tolerance Test
The 0, 3, 6 and 8% salt broths were inoculated very lightly from fresh growth.
T1N1 culture, lightly inoculate one tube each of T1N0;
T1N3; T1N6 and T1N8
broths. The broths were incubated at 35 to 37°C and read at 18 to
24 h. In the absence of growth, they were incubated for up to 7 days.
Voges-proskauer Test
one milliter of a 48 h culture grown in phosphate medium was taken in a
test tube. Then 10 drops of Barrits reagent A was added and culture was shaken.
Immediately 10 drops of Barrits reagent B was added and the culture was reshaken
every 3 to 4 times. The culture was observed after 15 min for the formation
of pink complex color as an indicative of positive VP test. Vibrio parahaemolyticus
gives a negative reaction.
Carbohydrate Fermentation Test
In the study, fermentation tests of sugars and sugar alcohol (lactose, arabinose
and D-mannitol) were carried out. Tryptone broth was used as a basal medium
for fermentation tests. 0.01% of phenol red was used as indicator. Fermentation
tubes with 9 mL of basal medium provided with indicator were made. The medium
was sterilized in autoclave at 121°C and 15 lb/inch 2 for 20
min. one milliter of filtered sterile 1% sugar was taken in each tube. One Durham
tube was introduced in each of the fermentation tube before sterilization of
the basal medium. The tubes were then inoculated in duplicate with fresh culture
of the bacterial isolate and allowed to incubate at 37°C for 72 h. The change
of color of the indicator to yellow indicated acid production and bubble in
the Durham’s tubes indicated gas production.
| Fig. 1B: | Urease test determine ammonia production A and C: Fresh medium color indicate negative result, B: Deep pink color indicates positive result, D: Negative control |
No change of color indicated negative fermentation. Vibrio parahaemolyticus gives a positive reaction.
Gelatin Hydrolysis Test
Nutrient gelatin deep tubes were inoculated with the test organisms and
kept at 37°C for 48 h. Following incubation the cultures were placed in
a refrigerator at 4°C for 30 min. culture that remained liquid produced
gelatinase and demonstrated gelatin hydrolysis. Culture that solidified on refrigeration
lacked gelatinase and gave negative reaction. Vibrio parahaemolyticus gives
a positive reaction.
Urease Test
Using sterile technique, each experimental isolate was inoculated into its
approximately labeled urea agar tube by means of loop inoculation. Then the
inoculated tubes were incubated at 37°C for 24 h. Deep pink color indicates
splitting of urea resulting production of ammonia. Ammonia is alkaline and turns
the indicator a bright pink color, which constitutes the positive result. (Fig.
1B).
Antibiotic Susceptibility of Isolated Vibrio parahaemolyticus
Antibiotic susceptibility testing was performed by the disk diffusion
method using guidelines established by Kirby-Bauer and Stokes' recommended by
the National Committee for Clinical Laboratory Standards (NCCLS) (National Committee
for Clinical Laboratory Standards, 1997). 11 antibiotic discs with Erythromycin
(15 μg) ; Penicillin (10 U) ; Streptomycin (10 μg) ; Tetracycline
(30 μg) ; Norfloxacin (10 μg) ; Cephalexin (30 μg) ; Ampicillin
(10 μg); Kanamycin(30 μg) Gentamicin (10 μg); Riphampicin (5
μg) ; Neomycin (30 μg) were used. We used commercially available antibiotics
discs. For quality control, E. coli ATCC 25922 was tested under the same
conditions and antimicrobial drugs.
Preparation of Müeller-Hinton Agar
Müeller-Hinton agar was prepared from a commercially available dehydrated
base according to the manufacturer's instructions. Immediately after autoclaving,
allowed it to cool in a 45 to 50°C water bath. The freshly prepared and
cooled medium was poured into glass petri dishes on a level of approximately
4 mm. A representative sample of each batch of plates was examined for sterility
by incubating at 30 to 35°C for 24 h or longer.
Turbidity Standard for Inoculum Preparation
To standardize the inoculum density for susceptibility test, a BaSO4
turbidity standard, equivalent to a 0.5 McFarland standard or its optical equivalent
(e.g., latex particle suspension), was used. A BaSO4 0.5 M McFarland
standards were prepared. A 0.5 mL aliquot of 0.048 mol L-1 BaCl2
(1.175% w/v BaCl2. 2H2O) was added to 99.5 mL of 0.18
mol L-1 H2SO4 (1% v/v) with constant stirring
to maintain a suspension. The correct density of the turbidity standard was
verified by using a spectrophotometer with a 1 cm light path and matched cuvette
to determine the absorbance. The absorbance at 625 nm was 0.008 to 0.10 for
the 0.5 McFarland standards. Then Barium Sulfate suspension was transferred
in 4 to 6 mL aliquots into screw-cap tubes of the same size as those were used
in growing or diluting the bacterial inoculums. These tubes were tightly sealed
and stored in the dark at room temperature. Then the barium sulfate turbidity
standard was vigorously agitated on a mechanical vortex mixer before each use
and inspected for a uniformly turbid appearance.
Preparation of Inoculum for Performing the Disc Diffusion Test
Three to five well-isolated colonies of the same morphological type were
selected from an agar plate culture. The top of each colony was touched with
a loop and the growth was transferred into a tube containing 4 to 5 mL of tryptic
soy broth. Then the broth culture was incubated at 35°C until it achieved
or exceeded the turbidity of the 0.5 McFarland standards (usually 2 to 6 h).
The turbidity of the actively growing broth culture was adjusted with sterile
saline or broth to obtain turbidity optically comparable to that of the 0.5
McFarland standards under adequate light to visually compare the inoculum tube
and the 0.5 McFarland standards against a card with a white background and contrasting
black lines.
Inoculation of Test Plates
After adjusting the turbidity of the inoculum suspension, a sterile cotton
swab was dipped into the adjusted suspension, within 15 min. The swab was rotated
several times and pressed firmly on the inside wall of the tube above the fluid
level to remove excess inoculum from the swab. The dried surface of a Müeller-Hinton
agar plate was inoculated by streaking the swab over the entire sterile agar
surface. The procedure was repeated by streaking two more times, rotating the
plate approximately 60° each time to ensure an even distribution of inoculum.
As a final step, the rim of the agar was swabbed. The lid was left ajar for
3 to 5 min, but no more than 15 min to allow for any excess surface moisture
to be absorbed before applying the drug impregnated disks.
Application of Discs to Inoculated Agar Plates
The predetermined battery of antimicrobial discs was dispensed onto the
surface of the inoculated agar plate. Each disc was pressed down to ensure complete
contact with the agar surface. The discs were placed individually or with a
dispensing apparatus, so that discs were distributed evenly and were no closer
than 24 mm from center to center. 5 discs (4 antibiotics discs and one blank
disc) were placed in each Petri dish. Then the plates were inverted and placed
in an incubator set to 35°C within 15 min after the discs were applied.
Reading Plates and Interpreting Results
After 16 to 18 h of incubation, each plate was examined. The diameters of
the zones of complete inhibition (as judged by the unaided eye) were measured,
including the diameter of the disc. Zones were measured to the nearest whole
millimeter, using a ruler, which was held on the back of the inverted petri
plate. The zone margin was taken as the area showing no obvious, visible growth
that can be detected with the unaided eye. Faint growth of tiny colonies, which
can be detected only with a magnifying lens at the edge of the zone of inhibited
growth, was ignored. However, discrete colonies growing within a clear zone
of inhibition were subcultured, re-identified and retested.
RESULTS AND DISCUSSION
In present study, total 27 samples were analyzed for isolation of Vibrio parahaemolyticus from locally available shrimp. After incubation of TCBS plates for 24 h at 37°C green colonies are screened out for biochemical identification. According to review of literature Vibrio parahaemolytics as well as Vibrio mimicus, Vibrio vulnificus and Vibrio shegeloides shows green colonies on TCBS after 24 h at 37°C. Among the samples only ten samples were positive for Vibrio parahaemolyticus suspected colony (Fig. 1A). To screen out Vibrio parahaemolyticus, several green colonies on TCBS agar was picked up and identified by a series of biochemical test.
To identify the Vibrio parahaemolytics isolates Arginine glucose slant, Oxidase, Lysine decarboxylase, Salt tolerance, Voges proskaur, fermentation (acid fermentation) test etc. were carried out. Typical Vibrio parahaemolyticus give positive Oxidase, Arginine glucose slant and Lysine decarbosylase test.
To differentiate the Vibrio parahaemolyticus from others, Salt tolerance and Acid from fermentation test was carried out. Typical Vibrio parahaemolyticus colonies do not grow in tryptone broth without any salt. But Vibrio mimicus and Vibrio shigeloides grew in tryptone broth without any salt. From Table 1 and 2, isolates only W1 P2, W2 P2, W5 P2, W8 P1, W8 P2, W14 P1, W15 P2, W18 P1, W18 P2, W23 P1 and W23 P2 can grow in tryptone broth but cannot grow in 6% and 8% salt in tryptone broth. Except these isolates others cannot grow in tryptone broth without salt but can grow in 3, 6 and 8% salt tryptone broth. Typical Vibrio parahaemolyticus also cannot grow in tryptone broth without salt but can grow in 3, 6 and 8% salt tryptone broth.
Fermentation test for acid production is one of the most important tests to differentiate between Vibrio parahaemolyticus and Vibrio vulnificus species. Typical Vibrio parahaemolyticus has shown positive reaction and form acid from arabinose and D- Mannital fermentation and shown negative reaction in lactose fermentation.
| Table 1: | Biochemical identification of Vibrio sp. isolated from shrimp |
| + = Positive result; - = Negative result; KA = Slant alkaline/ Butt acidic; V = Variable at different media; 1 = Oxidase; 2 = Argenine dihydrolase; 3 = Lycine decarboxylax and 4 = Vogas-Proskaur | |
| Table 2: | Biochemical identification of Vibrio sp. isolated from shrimp |
| + = positive result; - = negative result; KA = Slant alkaline/ Butt acidic; V = Variable at different media; 1 = Oxidase; 2 = Argenine dihydrolase; 3 = Lycine decarboxylax and 4 = Vogas-Proskaur | |
| Table 3: | Diameter of zone of inhibition (in mm) of identified Vibrio parahaemolyticus with antibiotic discs |
Among these isolates, W2 P1, W6 P1, W6 P2, W11P1, W13 P2, W15 P1, W22 P1, W22 P2, W26P1 and W27P1 showed positive reaction against Arabinose and D-Mannitol fermentation and also showed negative reaction in lactose fermentation. From the different biochemical test and according to Barge’s manual of bacteriology 10 isolates were identified as Vibrio parahaemolyticus. All isolates identified as Vibrio parahaemolyticus were carried out to antibiotic susceptibility test.
Antibiotic susceptibility testing has two major functions in both human and veterinary medicine. Primarily, it can be used to guide the choice of antimicrobial treatment for the patient. Secondarily, it may be used at a surveillance tool to monitor antimicrobial resistance.
Ten selected isolates were carried out to antibiotic susceptibility test against preselected antibiotics. Antibiotics used in this experiment were: Erythromycin, Penicillin, Streptomycin, Tetracycline, Norfloxacin, Cephalexin, Ampicillin, Kanamycin, Gentamicin, Riphampicin and Neomycin. The results were prepared according to the zone of inhibition produced on plates. The results were shown in Table 3.
In present study, we observed significant differences between different isolates in diameters of zones of growth inhibition against Erythromycin, Penicillin, Streptomycin, Tetracycline, Norfloxacin, Cephalexin, Ampicillin, Kanamycin, Gentamicin, Riphampicin and Neomycin. In Table 4, we show that all isolates were very sensitive to Tetracycline, Norfloxacin, Gentamicin, Riphampicin and Neomycin and all isolates were resistant to Erythromycin, Penicillin, Ampicillin and Kanamycin.
| Table 4: | Antibiotic susceptibility of identified Vibrio parahaemolyticus with antibiotic discs |
| R = Resistant; S = Susceptible | |
Several isolates show intermediate antibiotic susceptibility pattern. Among the isolates, W2P1, W6P1, W6P2, W11P1, W13P2, W22P2, W26P1 and W27P1, show resistant to streptomycin and W15P1, W22P1, isolates were sensitive. Similarly, W6P2, W11P1, W13P2, W22P1, W22P2, W26P1 and W27P1, show resistant to Cephalexin and W2P1, W6 P1, W15P1 isolates were sensitive.
The Kirby-Bauer agar disk diffusion places test results into the qualitative categories of sensitive, intermediate and resistant and may fail to detect subtle changes in antimicrobial resistance. As noted in the results from this study, most isolates tested, expressed antibiotic susceptibilities well within the 'sensitive' range.
If antibiotic use is the major selective pressure encouraging the development of antibiotic resistant, then reducing antibiotic use should result in decreased antibiotic resistance. A decrease in tetracycline resistance in Salmonella sp. isolated from man and pigs was observed after tetracycline was banned as a growth promoting in feed (Van Leeuwen et al., 1979). Similarly, when avoparcin was banned as a feed additive for poultry in Denmark in 1995, the prevalence of vancomycin resistant enterococci isolated from broilers has decreased from 80 to 5%, (Aarestrup et al., 1998). Enteropathogenic strains of Vibrio parahaemolyticus were isolated from shrimps, Penaeus monodon collected from the region of the Deltaic Sundarbans (West Bengal, India). About 63% of the isolated strains were resistant to ampicillin, cephalexin and kanamycin. However, all these strains were sensitive to nitrofurantoin, nalidixic acid, tetracycline and norfloxacin (Fig. 1C and D) Razvykh (1990). were studied sensitivity of 82 cultures of Vibrio parahaemolyticus to 8 antibiotics. It was shown that the majority of the strains were highly sensitive to levomycetin and gentamicin, sensitive to tetracycline, rifampicin, streptomycin, neomycin and kanamycin and resistant to ampicillin (Razvykh et al., 1990).
The disk diffusion method of determining antimicrobial sensitivity although widely used and economically attractive has its limitations. It is used mainly in a qualitative manner placing isolates in either a sensitive, intermediate, or resistant category. NCCLS, 1997 interpretative criteria for most antibiotics have been set using human pathogens and pharmokinetics. Only pirlimycin and penicillin-novobiocin have interpretive criteria that have been validated for bovine mastitis pathogens (Owens et al., 1997). Categorizing results for different Vibrio parahaemolyticus isolated from shrimp as simply sensitive, intermediate, or resistant may lead to erroneous conclusions (Fig. 1C and D). From Table 3, we chose to also compare results on the basis of zone diameter in millimeters for a more quantitative interpretation.
| Fig. 1C: | Results of the disk diffusion assay. This Vibrio parahaemolyticus isolate is sensitive to Gentamicin (GM), Riphampicin (RA), Neomycin (N) and Cephalexin (C) |
| Fig. 1D: | Results of the disk diffusion assay. This Vibrio parahaemolyticus isolate is sensitive to Tetracycline (ET), Norfloxacin (NOR) Gentamicin (GM) and Riphampicin (RA) |
In essence, this study design resulted in a cross-sectional evaluation of antibiotic susceptibility patterns at one point in time. A longitudinal follow-up between different isolate would be of value to understand the dynamics of developing antibiotic resistance or the return of antibiotic sensitivity in endemic bacteria.
CONCLUSIONS
Vibrio parahaemolyticus isolated in this study show good susceptibility to most of the antimicrobial agents that are commercially available for the treatment of causing disease. From this study, there was a significantly larger number of resistant isolates for Erythromycin, Penicillin, Ampicillin and Kanamycin suggesting that antibiotic use in these shrimp’s farms may be related to increased resistance.
To decrease antibiotic use and an increase in susceptibility; antibiotic use in our shrimp farm should be reevaluated. Guidelines for rational and limited antibiotic use should be set in place and communicated to both the veterinarian and shrimp producer so that development of antibiotic resistance can be prevented or reduced. Further studies are needed to examine the mechanisms of resistance.