Extended-spectrum β-lactamase (ESBL)-producing bacteria constitute an emerging global health issue with food products being vehicles of transmission and the aquatic environments serving as potential reservoirs. This study aimed to characterize ESBLproducing Escherichia coli in Nile perch and water from Lake Victoria in Tanzania. A total of 180 samples of Nile perch and 60 water samples were screened for ESBL-producing E. coli on MacConkey agar supplemented with 2 µg/ml of cefotaxime and confirmed by bla CTX−M and bla TEM PCR. Antimicrobial resistance was determined by the disk diffusion method, and the ESBL-producing isolates were whole genome sequencing (WGS). ESBL-producing E. coli were detected in eight of the 180 analyzed Nile perch samples, and only one water sample was positive (1.7%, n = 60). Isolates were resistant to sulfamethoxazole-trimethoprim (100%), ampicillin/cloxacillin (100%), erythromycin 72.7% (8/11), tetracycline 90.9% (10/11), and nalidixic acid 63.6% (7/11). This mostly corroborates the resistance genes that they carried for sulfonamides (sul1 and sul2), trimethoprim (dfrA and dfrB), aminoglycosides [aac(3)-IId, strA, and strB], tetracycline [tet(B) and tet(D)], and fluoroquinolones (qepA4). They harbored plasmid replicon types IncF, IncX, IncQ, and Col and carried bla CTX−M−15 and bla TEM−1B genes generally found on the same contigs as the IncF plasmid replicon. Although epidemiologically unrelated, the strains formed three separate sequence type-phylogroup-serotypespecific clusters: C1, C2, and C3. Cluster C1 included five strains (3 to 13 SNPs) belonging to ST167, phylogroup A, and serotype O9:H21; the two C2 strains (11 SNPs) belong to ST156, phylogroup B1, and serotype ONT:H28; and C3 was made up of four strains (SNPs ranged from 4 to 17) of ST636, phylogroup B2, and serotype O45:H7. The common virulence gene gad was reported in all strains. In addition, strains in C2 and C3 possessed iss, lpfA, and nfaE virulence genes, and the vat gene was found only in C3. The present study reports the occurrence of multidrug-resistant ESBL-producing Frontiers in Microbiology | www.frontiersin.org February 2020 | Volume 11 | Article 108 Baniga et al.Genomics of ESBL-E. coli in Lake Victoria E. coli carrying plasmid-mediated ESBL genes in offshore water and Nile perch in Lake Victoria. Strains formed three clonal clusters of unknown origin. This study reveals that the Lake may serve as reservoir for ESBL-producing bacteria that can be transmitted by fish as a food chain hazard of One-Health concern.

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Non-enterica subspecies of Salmonella enterica are rarely associated with human infections. Paradoxically, food safety legislations consider the entire genus Salmonella as pathogenic to humans. Globally, large amounts of seafoods are rejected and wasted due to findings of Salmonella. To inform better food safety decisions, we investigated the pathogenicity of Salmonella Salamae 42:r- and Salmonella Waycross isolated from Nile perch from Lake Victoria. Genome-wide analysis revealed absence of significant virulence determinants including on key Salmonella pathogenicity islands in both serovars. In epithelial cells, S. Salamae showed a weak invasion ability that was lower than the invH mutant of S. Typhimiurium used as negative control. Similarly, S. Salamae could not replicate inside macrophages. Moreover, intracellular replication in S. Waycross strains was significantly lower compared to the wild type S. Typhimurium. Our findings suggest a low pathogenicity of S. Salamae reinforcing the existing literature that non-enterica subspecies are avirulent. We propose that food legislations and actions taken on findings of Salmonella are revisited to avoid wasting valuable sea- and other foods.

This study was conducted to investigate the microbial and physico-chemical qualities of salted sundried Nile perch (Lates niloticus) products and frozen fish from various storage facilities in Mwanza, Tanzania. The bacterial flora, moisture contents (MCs), and water activity (A w ) were investigated using standard methods. A total of 120 samples were collected for microbiological analysis with 90 of the samples additionally analysed for MC and A w . Findings showed that the mean total viable counts (TVCs) in salted sun-dried products sampled during rainy season was 4.5 log cfu/g in fish heads with MCs of 38.0% and A w of 0.682. This was significantly higher (P<0.05) than what was recorded during the dry season with mean TVCs of 3.0 log cfu/g at MCs of 24.6% and A w of 0.625. Fish chests had TVCs of 3.3 log cfu/g and MCs of 27.6% and A w of 0.659 in rainy season with no significant seasonal difference (P>0.05). Fish belly flaps had TVCs of 3.3 log cfu/g at 26.4% MCs and 0.669 A w in rainy season which were comparable (P>0.05) to those dried in the dry season. The microbial species recovered were Staphylococcus spp., Enterobacter spp., Psychrobacter spp., and Bacillus spp. Neither Escherichia coli nor extended-spectrum beta-lactamase producing Enterobacteriaceae were detected. Frozen Nile perch had TVCs of 5.7 log cfu/g on skin, 5.4 log cfu/g in gills and 2.9 log cfu/g in flesh and were within acceptable limit set by Tanzanian standards. These results reveal that dried Nile perch products are generally safe for human consumption; however, the recovered bacteria indicate a need of implementing hygienic procedures during processing of products for improved quality and safety.