Antimicrobial resistance and virulence-associated genes of aer-omonads isolated from lake manzala water and wild nile tilapia: implications to public health and the lake microbial community

Abstract: This study was conducted to investigate the prevalence, antimicrobial susceptibility, and molecular characterization of Aeromonas spp. from wild Nile tilapia from Lake Manzala and the lake water. Swabs from the surface, gills, and internal organs of apparently healthy Nile tilapia (n =100) and lake water (n = 25) were collected and examined bacteriologically for the presence of Aeromonas spp. The isolates obtained were tested for their susceptibility to 11 antimicrobial agents using the disk diffusion method. The presence of antibiotic resistance genes (blaTEM, sul1, tetA(A), and aadA1) and virulence genes (enterotoxins) (alt, ast, and act) was determined using conventional polymerase chain reaction. Overall, Aeromonas spp. were recovered from 69% of Nile tilapia (Oreochromis niloticus) samples and 80% of water samples. Four types of aeromonads were detected in all the samples examined, namely, A. hydrophila, A. sobria, A. caviae, and A. schubertii, with A. hydrophila predominating in both the fish and the lake water samples. The antimicrobial resistance profiles of the isolates showed very high resistance to ampicillin, penicillin, sulfamethoxazole/trimethoprim, and oxytetracycline and considerable resistance to streptomycin. However, all isolates were sensitive to cefotaxime. Molecular characterization revealed the presence of the act (100%) and alt (37.5%) genes, but ast was not found in any of the isolates. Specific amplification bands of the antimicrobial resistance genes blaTEM, sul1, and tetA(A) were detected in all the tested isolates, whereas aadA1 (12.5%) was found only in one isolate of A. hydrophila from Nile tilapia. The presence of these enterotoxigenic and resistant Aeromonas spp. in the fish and water samples from Lake Manzala could pose a potential public health threat to human consumers and fish handlers in the study area; moreover, these species carry a risk for the transfer of resistance genes to other microbial communities in the lake. Key words: Aeromonas hydrophile complex; enterotoxin genes; antibiotic resistance genes; Oreochromis niloticus; Lake Manzala PROTIMIKROBNA ODPORNOST IN Z VIRULENCO POVEZANI GENI BAKTERIJE AEROMONAS IZOLIRANIH IZ JEZERA MANZALA IN DIVJE NILSKE TILAPIJE: VPLIVANJE NA JAVNO ZDRAVJE IN MIKROBNO ZDRUŽBO Izvleček: Namen te študije je bil raziskati razširjenost in protimikrobno občutljivost ter molekularno karakterizirati bakterijo Aeromonas spp., izolirane iz divje nilske talapije in vode iz jezera Manzala. Zbrali smo brise površine, škrg in notranjih organov navidezno zdrave nilske tilapije (n = 100) in vzorce vode (n = 25), ki smo jih bakteriološko pregledali na prisotnost bakterije Aeromonas spp. Pridobljene izolate smo testirali na občutljivost za 11 protimikrobnih sredstev z metodo difuzije diska. Prisotnost genov za odpornost proti antibiotikom (blaTEM, sul1, tetA(A) in aadA1) in genov za virulenco (enterotoksini; alt, ast in act) smo določili z običajno verižno reakcijo s polimerazo. Skupno smo Aeromonas spp. odkrili v 69% vzorcev nilske tilapije in 80% vzorcev vode. V vseh pregledanih vzorcih smo odkrili štiri vrste bakterij in sicer A. hydrophila, A. sobria, A. caviae, in A. schubertii, od katerih je A. hydrophila prevladovala v vzorcih rib in jezerske vode. Profili protimikrobne odpornosti izolatov so pokazali zelo visoko odpornost na ampicilin, penicilin, sulfametoksazol/trimetoprim in oksitetraciklin ter znatno odpornost na streptomicin. Izolati so bili občutljivi na cefotaksim. Molekularna karakterizacija je pokazala prisotnost genov act (100%) in alt (37.5%). Gena ast nismo našli v nobenem izolatu. Geni za protimikrobno odpornost blaTEM, sul1 in tetA(A) so bili prisotni pri vseh testiranih izolatih, medtem ko je bil gen aadA1 (12.5%) najden samo pri enem izolatu A. hydrophila iz nilske tilapije. Prisotnost enterotoksičnih in odpornih bakterij Aeromonas spp. v vzorcih rib in vode iz jezera Manzala bi lahko predstavljala nevarnost za javno zdravje potrošnikov in oseb, ki rokujejo z ribami na območju študije; poleg tega te vrste predstavljajo tveganje za prenos genov za odpornost na druge mikrobne skupnosti v jezeru. Ključne besede: Aeromonas hydrophile kompleks; geni za enterotoksin; geni za rezistenco na antibiotike; Oreochromis niloticus;, jezero Manzala