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Abstract
Two hundred samples of Mugil cephalus, Tilapia niloticus, Bagrus bayad and Clarias lazera (50 of each) were collected randomly from different fish farms at Alexandria governorate. All collected samples were examined microbiologically for TBC, Enterobacteriacea count, isolation and identification of the members of Enterobacteriaceae, total coliform count, isolation of enteropathogenic E. Coli, Salmonella, V. parahaemolyticus, isolation of Y. enterocolitica, S.aureus count and total mould and yeast count contaminating such examined fish samples.
The obtained results revealed that the mean values of total bacterial counts of Mugil cephalus, Tilapia niloticus, and Bagrus bayad were 8.2x104 ± 2.1x 104 & 7.6x104 ± 1.2x 104& 6.3x104± 0.8x104 and 1.4x105±9.6x104 cfu /g respectively .
Also , the mean values of total Enterobacteriaceae and total coliform counts in the examined samples of farm fishes were 1.1 x 103 ± 6.2 x 102 & 5.2 x 103 ± 6.5 x 10 cfu/g for Mugil cephalus, 6.7 x 103 ± 1.1 x 103 & 1.1 x 103 ± 2.6 x 102 cfu/g for Tilapia niloticus, 2.8 x 103 ± 0.9 x 103 & 2.4 x 103 ± 1.6 x 102 cfu/g for Bagrus bayad and 1.48 x 104 ± 6.7 x 103 & 6.4 x 104 ± 7.1 x 102 cfu/g for Clarias lazera, respectively. Accordingly, the examined samples of Clarias lazera were more contaminated either with Enterobacteria or coliforms as compared with those of Tilapia niloticus, Bagrus bayad and Mugil cephalus.
The differences between the examined fresh water fish samples as a result of total enterobacteriaceae or total coliform counts were significant (P < 0.05).
Citrobacter diversus, Citrobacter freundii, Enterobacter aerogenes, Enterobacter agglomerans, Enterobacter cloacae, Enterobacter hafniae, Klebsiella ozaenae, Klebsiella pneumoniae, Proteus mirabilis, Proteus rettgerii, Proteus vulgaris, Serratia liquefaciens and Serratia marcescens were isolated from the examined samples of Mugi cephalus l, Tilapia niloticus, Bagrus bayad and Clarias lazera with varying percentages.
Furthermore, Enteropathogenic E.coli was isolated from 8%, 20%, 16% and 32% of the examined samples of Mugil cephalus, Tilapia niloticus, Bagrus bayad and Clarias lazera, respectively. Out of 8 strains of E.coli isolated from Clarias lazera, 3 strains were serologically identified as O124 : K72 (B17), 2 identified as O26 : K60 (B6), 2 were O128 : K67 (B12) and the last strain was O86 : K61(B7). However, O111: K58 (B9), O26 : K60 (B6), O124 : K72 (B17) and O128 : K67 (B12) strains were identified from Tilapia niloticus. Moreover, O26 : K60(B6), O111 : K58 (B9) and O128 : K67(B12) were recovered from 8%, 4% and 4% of Bagrus bayad samples, respectively. Concerning Mugil cephalus, out of 2 strains of E.coli, one could be identified as O86 : K61 (B7) and the other strain was O124 : K72(B17).
On the other hand, 8%, 12% and 20% of the examined samples of, Tilapia niloticus , Bagrus bayad and Clarias lazera were contaminated with Salmonella organisms, respectively. While, all examined samples of Mugil cephalus were free from such organism. Serotyping of the isolated Salmonellae indicated that S. enteritidis (4%, 4% & 8%) and S. typhimurium (8%, 4% & 8%) were serologically identified from the examined samples of Tilapia niloticus, Bagrus bayad and Clarias lazera , respectively. In contrast, only one strain (4%) isolated from Clarias lazera was serologically identified as S. haifa.
Therefore, Vibrio parahaemolyticus was detected in 16%, 4% and 28% of the examined, Tilapia niloticus , Bagrus bayad and Clarias lazera respectively. However, such organisms could not be isolated from the examined samples of Mugil cephalus.
In regard to Yersinia enterocolitica, 4% and 20% of the examined samples of Tilapia niloticus and Clarias lazera were contaminated with this pathogen, respectively. All examined samples of Bagrus bayad and Mugil cephalus were free from Yersinia enterocolitica.
Consequently, Clarias lazera was the most contaminated with all members of Enterobacteriaceae followed by Tilapia niloticus, Bagrus bayad and Mugil cephalus.
Regarding to the staphylococcus aureus count of the examined farm fishes revealed that the mean values of the staphylococcus aureus count were 1.3 x 103 ±9.2x102 & 1.4x103±8.4x102 & 2.3x103 ±7.6x102 and 9.2x103± 2.2x103 cfu / g for Mugil cephalus & Tilapia niloticus & Bagrus bayad and Clarias lazera respectively .
Regarding to mycological status of the examined farm fishes (Mugil cephalus & Tilapia niloticus & Bagrus bayad and Clarias lazer) the mean total mould counts were 8.2x102 ± 1.1x102 & 9.4x102±1.3x102 &8.9x102 ±1.2x102 and 8.2x103 ± 2.1x103 respectively Also the mean values of total yeast counts were 1.3 x103 ± 9.2x102 & 1.4x103 ± 8.4x102 & 2.3x103± 7.6x102 and 9.2x103±2.2x103 cfu / g respectively .
The public health significance of contaminants and the possible sources of contamination of farm fishes with these organisms as well as suggestive hygienic measures to improve the quality of such fishes were discussed.