The incidence of various human pathogenic bacteria in commercially available and home-made shrimp feeds used on some farms in India was analyzed. The Total Heterotrophic Bacteria in the commercial feed samples ranged between 103–105 cfu g-1 and those in the farm-made feeds between 106-107 cfu g-1. No bacteria of significance to human health were found to be associated with any of the commercial feed samples analyzed, while farm-made feeds analyzed during the study showed a high incidence of various human pathogens such as Vibrio parahaemolyticus, V. cholerae, Escherichia coli and Staphylococcus aureus. Possible modes of contamination in feeds and ways to prevent them are discussed

Raghavan, R.P.

Aquatic Commons

NAGA, WorldFish Center Quarterly  Vol. 26 No. 2 Apr-Jun 200322
articles
Incidence of human pathogenic bacteria 
in shrimp feeds - A study from India 
R.P. Raghavan
Abstract
The incidence of various human pathogenic bacteria in commercially available and home-made shrimp feeds 
used on some farms in India was analyzed. The Total Heterotrophic Bacteria in the commercial feed samples 
ranged between 103–105 cfu g-1 and those in the farm-made feeds between 106-107 cfu g-1. No bacteria of 
signifi cance to human health were found to be associated with any of the commercial feed samples analyzed, 
while farm-made feeds analyzed during the study showed a high incidence of various human pathogens such as 
Vibrio parahaemolyticus, V. cholerae, Escherichia coli and Staphylococcus aureus. Possible modes of contamination 
in feeds and ways to prevent them are discussed.
Introduction
Of the various hazards related to cultured 
aquatic products, the most important are 
the ones that are associated with human 
pathogenic bacteria. A number of 
pathogenic and potentially pathogenic 
bacteria belonging to the genus Vibrio, 
Staphylococcus, Escherichia and Salmonella 
have been isolated from cultured shrimps 
and their environments in India (Ahmed 
et al. 1995; Sugumar et al. 2001). In most 
instances, contamination has been 
attributed to the poor quality of source 
water used in the farms, pollution due to 
sewage and also the improper and 
unhygienic handling of shrimps by the 
farm workers. However, another possible 
reason for contamination could be due to 
the increased incidence of various human 
pathogenic bacteria in aquaculture feeds 
used in the culture systems. The use of 
wet or moist animal-based feeds has been 
identifi ed as one of the factors that could 
be responsible for the increasing 
incidence of food safety hazards in 
aquaculture (Reilly et al. 1998). However, 
this factor has been overlooked by many 
researchers and hence, not much 
information is available with respect to 
the Indian scenario. The present study is 
an attempt to analyze the incidence of 
human pathogenic bacteria in commercial 
and farm-made feeds used in the various 
shrimp culture systems of south India to 
ascertain the role of feeds as possible 
vectors of these bacteria into the culture 
systems.  
Bacteriological analysis
Samples of commercial and farm-made 
feeds used in the various shrimp culture 
systems of south India (Table 1) were 
obtained from the respective farm sites. 
Samples of commercial pelleted feed were 
taken from the feed bags, while farm-
made feed samples were collected after 
they were prepared at the farm site. They 
were then transferred to sterile polythene 
bags and taken to the laboratory where 
the bacteriological analyses were carried 
out as per the methods outlined in the 
USFDA (1995).  The Total Heterotrophic 
Bacteria (THB) in the feed samples was 
enumerated by the agar pour plate 
technique and results were obtained after 
48 hours of incubation at 37° C.  Specifi c 
agars were then used to isolate various 
pathogenic strains such as Thiosulphate 
Citrate Bile Sucrose (TCBS) agar for 
Vibrio, Tergitol-7 for Escherichia, Baird 
Parkers (BP) agar medium for 
Staphylococcus, Brilliant Green and/or 
Bismuth Sulphite agar medium for 
Salmonella and KF agar for Streptococcus. 
The plates were then inoculated and 
incubated at 37° C overnight and up to 
seven days. Specifi c colonies were then 
sub-cultured and the pure culture was 
used for further biochemical tests (Sneath 
and Holt 1986;  Alsina and Blanch 1994).  
Sample
Type /Nature of 
feed
Specifi cation Culture system/Location/Coast
A
B
C
D
E
F
Commercial
Commercial
Commercial
Commercial
Farm-made
Farm-made
Grower
Finisher
  
Starter
Grower
-
-
Semi-intensive-Andhra Pradesh -E. Coast
Semi-intensive- Andhra Pradesh - E. Coast
Semi-intensive- Andhra Pradesh - E. Coast
Semi-intensive- Tamil Nadu - E. Coast
Traditional – Kerala-W. Coast
Traditional – Kerala-W. Coast
Table 1. Details of different feed samples used for the study
Feed sample
THB
cfu g-1
A
B
C
D
E
F
4.18 X 103
4.01 X 105
5.22 X 103
4.68 X 103
3.78 X 106
5.01 X 107
Table 2. Total Heterotrophic Bacteria 
associated with the shrimp feed 
samples analyzed 
23NAGA, WorldFish Center Quarterly  Vol. 26 No. 2 Apr-Jun 2003
articles
Results
The THB in the commercial shrimp feeds 
ranged from 103 to 105 cfu g-1 (Table 2). 
No human bacterial pathogens were 
isolated from the commercial shrimp 
feeds. However, with regard to farm-made 
shrimp feeds, a higher bacterial load of 106 
to 107 cfu g-1 (Table 2) was observed 
together with the incidence of various 
pathogens such as Staphylococcus, Vibrio 
and Escherichia (Table 3).  
Discussion
Studies have shown that commercial 
fi sh feeds contain a mixed microfl ora, 
of which many are pathogenic or 
potentially pathogenic to fi sh and human 
(Trust 1971; Trust and Money 1972). 
The major bacterial genera associated 
with commercially available shrimp feeds 
were Flavobacterium, Bacillus, Micrococcus 
and Alcaligenes (Rajeev et al. Unpubl). 
Commercial feeds are considered 
unsatisfactory if they contain large 
bacterial populations even if the bacteria 
are non-pathogenic in nature and have 
not caused any changes to the pellet 
(Thatcher and Clarke 1968). Reports also 
indicate that the bacterial composition 
becomes evident in feeds containing 106 
to 108 microorganisms/g. In the present 
study, the THB in the commercial feed 
samples was in the range of 103 to 105 
cfu g-1 indicating that the bacterial counts 
were well within permissible limits. 
The farm-made feeds analyzed showed 
a higher bacterial load of 106 to 107 
cfu g-1 indicating the advent of bacterial 
contamination. It is known that 
aquaculture feeds that contain higher 
levels of moisture are prone to faster 
microbial spoilage due to the action of 
various bacterial enzymes (Jones 1987). 
Most of the farm-made feeds analyzed 
were wet feeds prepared from animal-
based raw materials such as prawn meal, 
shrimp-head meal, fi shmeal and clam meat 
which usually contain very high levels of 
moisture. This would have contributed to 
the higher bacterial loads as observed in 
these feed samples. 
Public health bacteria, including Escherichia 
coli (Niemi and Taipalinen 1982), 
Salmonella (Trust 1971) and Clostridium 
boutulinum  (Lalitha 1998; Sugita et 
al. 1989) have been reported in fi sh 
feeds. However, none of the samples 
of commercial shrimp feeds analyzed 
showed the presence of any such human 
bacterial pathogens. Modern and hygienic 
methods of feed processing and improved 
feed management practices at the farm 
sites have greatly reduced the incidence 
of such bacteria in shrimp feeds. 
Trust and Wood (1973) had suggested 
that the ingredients used in feed 
formulation partially determine the 
nature of its microfl ora. Farm-made 
feeds used in the traditional shrimp 
culture systems are generally made from 
marine animal ingredients such as prawn 
meal, fi shmeal and clam meat. These 
feed ingredients were mainly harvested 
and/or collected from contaminated 
coastal and estuarine waters and from 
unhygienic and poorly maintained 
landing centers and pre-processing units. 
Contamination by bacteria such as Vibrio 
cholerae, V. parahaemolyticus, E. coli and 
Staphylococcus aureus in one or more of 
these marine animal raw materials used 
for feed preparation would have led to 
the contamination in the fi nal products 
also. The presence of such pathogenic 
bacteria has been reported in the Cochin 
backwaters, which is the main water 
source for the culture farms, and also 
the principal area for harvesting the 
raw materials used in feed preparation  
(Pradeep and Lakshmanaperumalasamy 
1986a, b and Gore et al. 1979). In addition, 
the rather unhygienic handling practices 
followed by the workers at the farm site 
could also be a possible explanation for 
the contamination by indicator bacteria 
such as S. aureus and E. coli. 
There is little awareness of the 
importance of good feed management 
practices in shrimp culture among 
traditional farmers. This has resulted in 
the use of poor quality raw materials 
and unhygienic feed preparation, which 
ultimately have led to the increased 
incidence of many human bacterial 
pathogens in aquaculture feeds. 
From the results of the present 
investigation, it may be inferred that 
commercially available shrimp feeds used 
in the grow-out farms of south India are 
free from public health bacteria. However, 
farm-made feeds prepared from marine 
animal-based raw materials, especially 
those which are commonly used in 
traditional shrimp farms, are in most cases 
contaminated with various species of 
human pathogenic bacteria. Poor quality 
raw materials used for feed preparation 
and low personal hygiene at the farm sites 
have been found to be the main causes 
associated with the bacterial 
contamination in feeds.  The importance 
of using good quality raw materials, 
Table 3. Presence of human pathogenic bacteria in shrimp feed samples
Sample
Vibrio  
cholerae
Vibrio 
parahaemolyticus
Salmonella typhi
Staphylococcus 
aureus
Escherichia coli Streptococcus  faecalis
A
B
C
D
E
F
-
-
-
-
-
+
-
-
-
-
+
+
-
-
-
-
-
-
-
-
-
-
+
+
-
-
-
-
+
+
-
-
-
-
-
+
(+ present, - absent)
NAGA, WorldFish Center Quarterly  Vol. 26 No. 2 Apr-Jun 200324
articles
ensuring their hygienic storage and 
adoption of hygienic on-farm feed 
preparation techniques should be 
extended to traditional shrimp farmers to 
decrease the incidence of various 
pathogenic bacteria in shrimp feeds. These 
factors will reduce environmental pollution, 
enhance shrimp health and eliminate 
potential food safety hazards to humans.  
Acknowledgement
The author is grateful to Dr.  A. A. 
Mohamed Hatha, School of Environmental 
Sciences, Mahatma Gandhi University, 
Kottayam, India, and Dr. M. Harikrishnan, 
Department of Zoology and Aquaculture, 
St.  Albert’s College, Kochi, India, for their 
comments on an earlier draft of this 
manuscript. The encouragement and 
assistance provided by Ms Nirmala James 
during the preparation of this manuscript 
is much appreciated.  
References
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_________________________________
R.P. Raghavan is from the Unit of 
Aquaculture, PG and Research 
Department of Zoology, Government 
College-Nandanam, Chennai 600 035, 
Tamil Nadu, India.


Incidence of human pathogenic bacteria in shrimp feeds - a study from India

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Incidence of human pathogenic bacteria in shrimp feeds - a study from India

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