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Role of fish in transmitting some zoonotic bacteria causing food poisoning to man


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ROLE OF FISH IN TRANSMITTING SOME ZOONOTIC BACTERIA CAUSING FOOD POISONING TO MAN

By


LOBNA, M.A. SALEM AND El-NEWISHY, A.A.

Department of Zoonoses, Faculty of Veterinary Medicine, Benha University



.

ABSTRACT
A total of seventy fish samples of Tilapia nilotica and cat fish (Clarias garipinus) (35 of each) were collected from different fish markets at Qalyobia Governorate. In addition to hand swabs of twenty fish handlers were examined bacteriologically to determine the role played by fish in transmitting some zoonotic bacteria causing food poisoning. Clarias fish samples had
a significantly higher bacterial isolates (62.9%) than tilapia fish samples (45.7%). Among the isolated bacteria, Staph-aureus was detectable at higher percentage (25.7%) followed by E.coli (18.9%), then Salmonella spp. (7.1%) and the lowest isolates were Shigella spp. (2.9%). The highest percentage of bacterial isolates was recovered from skin surface followed by intestine, whereas muscles showed the lowest percentage in both types of examined fish. Hand swabs of fish handlers demonstrated 20% and 10% positive results for Staph-aureus and E.coli respectively. The current research indicated that fish may represent a serious threat
to public health as a result of transmission of some food poisoning pathogens. The public health importance of the isolates and suggestive hygienic measures were discussed.

INTRODUCTION
Fish are one of the cheapest source of protein and considered as a good replacer of meat and poultry in the human diet for its high nutritive value, palatability and good digestibility.
On the other hand, fish have a significant role in possible transfer of pathogens between livestock and human, although some of them do not produce disease in fish (Edun et al., 2007). Fish act as carrier of some zoonotic bacteria either on the skin and gills or in the intestine. These include E.coli, Salmonella, Shigella, Proteus, staphylococcus and others which are incriminated in food poisoning, skin disorders, allergic conditions as well as other infections (Janssen, 1970). Fish can acquire pathogenic microorganisms from natural aquatic environment contaminated with sewage or from dirty hands of fish handlers, or contaminated utensils and equipments during harvesting, processing and preservation (National Academy of Science, 1985).

Nowadays, water pollution with domestic waste water is most common in River Nile and its tributaries, the greatest volume of wastes discharged in the water course is sewage, such pollution reduces the water quality and had been reported as a precursor to fish infection with some microorganisms that can infect both consumers and handlers (Omer et al., 2004).

Human infections caused by organisms transmitted from fish or the aquatic environment depending on the season, the patient's contact with fish and related environment, dietary habits and the immune system status of the exposed individual (Onyango et al., 2009). Human infections by fish pathogens are usually through contact with abraded skin with infected fish while handling or with water or other constituents of an aquatic environment (Acha and Szyfres, 2003). Moreover, people use some ways for preparation of fish to be eaten each as rapid frying, smoking and pickling and such methods have been proved to be insufficient to kill all harmful microorganisms which may be present in raw fish prior to preparation (Khalil et al., 1990 and Mansour et al., 1997). The consumption of contaminated fish gives rise to intestinal disorders ranging from diarrhea and vomiting to fever (Naglaa et al., 2002).

In Egypt, Salmonellae, E.coli and Staph. aureus are widely recognized as the principle causes of food poisoning outbreaks occurring as a result of consumption of contaminated fish and fish products (Eley, 1996 and Hassan & Fatin, 2003), so the present study was carried out to detect the role of fish in transmitting some zoonotic bacteria causing food poisoning to humans after handling or consumption of such fish in Qalyobia Governorate.



MATERIALS AND METHODS
1- Sampling:

1- a- Fish samples:

A total of seventy random fish samples of Tilapia nilotica and cat fish (Clarias garipinus) (35 of each) were collected from different fish markets at Qalyobia Governorate. The collected fish samples were packed separately in sterile plastic bags and transported to the laboratory in an ice box without delay to be examined.



1-b- Human samples:

Hand swabs were taken from twenty fish handlers working at the same markets from which fish samples were collected.



2- Preparation of samples:

2-a- Fish samples:

Surface swabs, pieces of muscles and intestinal contents were aseptically taken from each fish and were separately inoculated into separate sterile tubes containing nutrient broth, lauryl sulphate tryptose broth and selinite cystine broth as enrichment broth media, then incubated at 37°C for 18-24hrs.



2-b- Human samples:

From each fish handler, hand swabs were taken by rubbing swabs in the inter-digital spaces, nails, palms and on the back of the hands and were separately inoculated into separate sterile tubes containing the previously mentioned broth.



3- Bacteriological examination of samples:

3-a- Detection of staphylococcus:

For isolation of staphylococcus, plates of Baird Parker medium were streaked from previously inoculated nutrient broth with fish or human samples and incubated at 37°C for 24-48hrs. Suspected colonies were picked up and purified for further identification according to (Macfaddin, 1980 and Holt et al., 1994).



3-b- Detection of salmonellae and shigella:

It was done using the method recommended by A.P.H.A (1992) as: loopfuls from selenite cystine broth cultures were streaked onto MacConkey and salmonella shigella agar plates and incubated at 37°C for 24hrs. Suspected colonies were picked up and purified for further identification according to (Kaufmann, 1996; Andrews & Hammack, 1998 and Popoof & LeMinor, 2003).



3-C- Detection of E.coli: (according to A.P.H.A, 1992)

Loopfuls from each positive lauryl sulphate tryptose broth cultures were separately transferred into E.coli broth tubes and incubated at 45°C for 48hrs. From each positive E.coli broth tubes, loopfuls were streaked onto Levine Eosin methylene blue (EMB) agar plates and incubated at 37°C for 24hrs. The typical colonies were picked up and purified for further identification according to (Macfaddin, 1980 and Holt et al., 1994).



RESULTS
Table (1): Number and percentage of isolated microorganisms from examined fish.



Examined fish

Isolates

Tilapia nilotica (35)

Clarias garipinus (35)

Total (70)

No

%

No

%

No

%

Salmonella spp.

2

5.7

3

8.6

5

7.1

Shigella spp.

1

2.9

1

2.9

2

2.9

E.coli

5

14.3

8

22.9

13

18.9

Staphylococcus

8

22.9

10

28.6

18

25.7

Total

16

45.7

22

62.9

38

54.3

Table (2): Types of isolated microorganisms from examined fish.

Number

Types of isolates

Tilapia nilotica

Clarias garipinus

Salmonella typhimurium

1

2

Salmonella enteritidis

1

1

Shigella dysentery

1

1

E.coli







O55 : K59 (B5)

2

3

O111 : K58 (B9)

1

2

O86 : K61 (B7)

1

2

O128 : K67 (B12)

1

1

Staph. aureus

8

10

Table (3): Frequency distribution of isolated microorganisms in different parts of examined fish.

Examined fish parts

Isolates

Tilapia nilotica

Clarias garipinus

Total isolates

surface

muscle

intestine

Total isolates

surface

muscle

intestine

No

No

%

No

%

No

%

No

No

%

No

%

No

%

Salmonella spp.

2

2

100

0

0

0

0

3

2

66.7

0

0

1

33.3

Shigella spp.

1

1

100

0

0

0

0

1

1

100

0

0

0

0

E.coli

5

1

20

0

0

4

80

8

1

12.5

2

25

5

62.5

Staph. aureus

8

5

62.5

3

37.5

0

0

10

8

80

2

20

0

0

Total

16

9

56.3

3

18.8

4

25

22

12

54.5

4

18.2

6

27.3

Table (4): Results of bacteriological examination of hand swabs of fish handlers

Isolates

Fish

handlers

Staph. aureus

E.coli

No

%

No

%

20

4

20

2

10










The two strains were

O55 : K59 (B5)

O128 : K67 (B12)



DISCUSSION

It is evident from (Table 1) that total percentages of the isolated bacteria were 45.7 and 62.9 in tilapia fish and claries fish respectively. The higher bacterial isolation detected in claries fish than in tilapia fish may be due to feeding habits of claries fish as they are carnivorous fish and tend to eat more animal material than plant food (Abdel-Malak,1972 and Radwan, 1992). The presence of bacterial organisms in fish was attributed to contamination of such fish with polluted water, contact with dirty boats, cooking in fishing containers straight on the deck or direct contact with human carriers (Novotny et al., 2004). Moreover, the total percentages of isolation of different microorganisms from the examined fish were 7.1, 2.9, 18.9 and 25.7 for Salmonella spp., Shigella spp., E.coli and staphylococcus respectively. These organisms were frequently reported to be isolated by (Mekheal, 2003; Yagoub and Ahmed 2004 and Herrer et al., 2006). It is worth mentioning that isolation of these bacterial species is an indication of fecal and environmental pollution. In most instances, contamination results from the poor quality of water sources and sewage pollution. Furthermore, fish may get infected through improper and unhygienic handling, as fish take large number of bacteria into their gut from water, sediment and food which may become constituents of bacterial flora of digestive tract causing serious disease problems (Al-Harbi & Uddin 2005).

The most important fish-borne pathogens detected in this study was Staph. aureus which was detectable at a higher rate in both claries fish(28.6%) and in tilapia fish (22.9%). Similar results were obtained by Metawea & Abdel-Ghaffar 2007 (23.3%) but lower results were recorded by Simon & SanJeev 2007(17%) and Boari et al., 2008(10%). The higher percentage of isolated Staph. aureus may be due to higher prevalence of Staph. aureus in human being either on their skin or in their nose that create a great chance for contamination of fish upon improper handling through persons who are not observing the basic rules of personal hygiene. This substantiates the conclusion of Papadopoulou et al. (2007). Staphylococcal food poisoning is caused by ingestion of food containing enterotoxins secreted by Staph. aureus and characterized by nausea, voimition, abdominal pain and prostration often with diarrhea but without fever, food poisoning usually develops approximately 1-6hrs after ingestion of contaminated food (Eley, 1996).

It is clear from (Table 1) that Escherichia coli (E.coli) could be isolated at 18.9% from totally examined fish (14.3% from tilapia and 22.9% from clarias). These findings are nearly similar to those obtained by Onyango et al., 2009 (25.4%) and Yagoub, 2009 (23.2%) but they are slightly lower than those recorded by Hefnawy, 1989(30%) and Maysa & Abd-Elall, 2009 (30%). The presence of E.coli is a reliable indication of fecal contamination of water either from human and/or animal origin, faulty method of production and handling (WHO, 1998). Moreover, the increased prevalence of E.coli may be attributed to the municipal sewage disposal in the water course and persistence of bad habits (urination and defecation in surface water) as well as the misuse of organic fertilizers (El-Dahshan, 2004) and transportation of fish in dirty fishing boats or packing of fish in dirty baskets could also enhance post-harvesting contamination (Onyango et al., 2009). The identified serotypes of E.coli in examined fish samples were shown in (Table 2), the most predominant serotypes were O55: K59 (5 strains), O111: K58 (3 strains), O86: K61 (3 strains) and O128: K67 (2 strains), such serotypes have a great pathogenicity in the intestinal tract and cause gastroenteritis and implicated in food poisoning outbreaks (Bryan, 1980 and WHO, 1991).

In this study, Salmonellae were isolated from tilapia & clarias fish at percentages of 5.7 and 8.6 respectively (Table 1), the results showed that the most predominant serotypes were S. typhimurium and S. enteritidis (Table 2). Almost similar results were obtained by Mekhael 2003 (4%) and Metawea & Abd El-Ghaffar, 2007 (6.6%). On the other hand, other workers failed to detect this pathogen as (Shaaban et al., 2001, Boari et al., 2008 and Abou-Elez, 2010). Isolation of Salmonella confirms the fecal contamination of water where the fish are harvested, a finding which that has a public health concern (Morales et al., 2004). The risk of acquiring Salmonella infection is greater where hygienic standards are low and where people consume raw sea food harvested from water contaminated with sewage or feces (Rayan et al., 1989). In Egypt, Salmonellae are widely recognized as one of the principle causes of food poisoning outbreaks as a result of consumption of contaminated fish and fish products with clinical symptoms in man in the form of enteritis and systemic disease (Hassan & Faten, 2003). Shigella dysentery was the lowest isolated organisms from examined fish (2.9%). These results agree with Ibrahim et al., 2009(1.3%) and Yagoub, 2009(2.2%).The lower isolation rate might be due to persistence of Shigella in water is lower than other bacteria and it varies according to the geographic areas. This concept agrees with Tanios (1998). However, food including sea food has been the cause of outbreaks of Shigellosis as a result of contamination of raw or previously cooked food during preparation by infected or asymptomatic carrier with poor personal hygiene (Novotny et al., 2004).

The distribution of isolated bacteria (Table 3) showed that the highest number of bacterial isolates were recovered from skin surface, followed by intestine, whereas muscles showed lower number of isolates at percentages of 56.3, 25 and 18.8 for tilapia fish and 54.5, 27.3 and 18.2 for clarias fish respectively. This may be attributed to exposure of the surface to different sources of contamination. As regards to flesh of healthy fish, it is considered bacteriologically sterile (National Academy of Science, 1985), but the presence of bacterial isolates on the skin, muscles and intestine may reflect the effects of environmental contamination as water condition (Cesar et al., 1999), Moreover, the isolates from skin could be mainly accounted to the slime layer of skin and partially as a result of active bacterial multiplication and adaptation. Such bacteria may spread from gills to the vascular system and invade the fish flesh which are not in contact with the external aquatic environment (Shewan, 1971). This author also assumed that the bacterial count/gram in fish muscles ranges from zero to one thousand depending on the condition of the environment in which the fish live, degree of exhaustion, stress during catching and the health status of the fish. In addition to enteric bacteria, they do not seem to represent the normal flora of fish, but fish become contaminated with them when exposed to polluted water or contamination by workers as these organisms can be found in soil, water, sewage and intestinal tract of man and animals and these species have been implicated in acute and chronic diarrheal diseases (Twedt and Boutin, 1979).

Shifting to the results of bacteriological examination of fish handlers as shown in (Table 4)
, it was found that out of twenty hand swabs, 4 (20%) gave positive results for Staph. aureus, whereas 2 (10%) gave positive results for E.coli sero types as O55: K59 and O128: K67 (one strain each). These results are supported by (Mohamed, 2001, Aycicek et al., 2004, ShoJaei et al., 2006, Maysa & Abd-Ellal, 2009 and Abo-Elez, 2010) who isolated the same organisms from fish handlers at different percentages. It was previously emphasized by ShoJaei et al. (2006) that a significant number of food handlers might be nasal carriers of Staph. aureus and consequently contaminate their hands. Moreover, high proportion
(30-35%) of healthy humans have Staphylococci in the nasopharynx and on the skin (Pedro and Boris, 1994). Besides, about 20% of normal individuals harbor the organism in their intestinal tract (Stewart, 1973). It was clarified by Le-Loir et al (2003) that Staph. aureus is a main cause of gastroenteritis resulting from the consumption of contaminated food and information of outbreaks indicates that Staph. aureus was isolated from the implicated food, nose and hands of food handlers (Docarmo et al., 2004). So, it could be easily concluded that the fish handlers are still a potential hazard for Staphylococcal food contamination.

Regarding to the presence of E.coli in hand swab samples; it emphasized significant fecal contamination and indicates that food handlers were not taking enough care in hand hygiene (Landeiro et al., 2007). From the aforementioned results, it is evident that most of bacteria isolated from fish in this study are derived from natural aquatic environment contaminated with sewage or from dirty hands of fish handlers, so the fish handlers and water may act as dangerous sources of these pathogens to fish and consequently act as a vehicle of human infection constituting therefore a potential public health problem.



It can be concluded that fish may occasionally represent a serious threat to public health as a result of carrying several bacterial zoonoses, either in the skin, muscle or intestine. Therefore, strict hygienic measures should be carried out during the different steps from fishing to marketing, fish handling should be minimized and education programmes should be imposed for fisher men, fish handlers as well as consumers and households during preparation of fish for consumption, prevention of environmental pollution in the River Nile and its tributaries and periodical examination of water sources as well as fish handlers in markets to ensure fish safety.

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