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Aminoglycosides are the most preferred choice of therapy against serious infections in humans. Therefore, its use in animal husbandry has been strictly regulated in the EU, UK, and USA to avoid the hazards of aminoglycoside resistance in gut microflora. Nevertheless, aminoglycosides are recommended for prophylaxis and therapeutics in food animals and agriculture owing to its bactericidal nature. In the recent past, the global surge in aminoglycoside-resistant lactic acid bacteria (LAB) from food sources has been noticed that might question its continued use in animal husbandry. Upon antibiotic administration, a selective pressure is created in the gut environment; in such instances, LAB could act as reservoirs of antibiotic resistance which may facilitate their transfer to pathogenic organisms contradicting its probiotic and industrial significance. This may be a risk to human health as the presence of one aminoglycoside resistance gene renders the bacteria tolerant to almost all antibiotics of the same class, thereby challenging its therapeutic efficacy. Low doses of aminoglycosides are recommended in farm animals due to its toxic nature and insolubility in blood. However, recent investigations indicate that use of aminoglycosides in sub-lethal concentrations can trigger the selection and conjugal transfer of aminoglycoside resistance in probiotic LAB. Resistance to erythromycin, tetracyclines, and fluoroquinolones in LAB were reported earlier to which immediate regulatory measures were adopted by some countries. Paradoxically, lack of regulations on antibiotic use in farms in most developing countries makes them a potential source of antibiotic resistance and its uncontrolled spread around the globe. The prevalence of aminoglycoside resistance was observed in enterococci from food origin earlier; however, its emergence in lactobacilli and pediococci suggests its spread in probiotic cultures which prompts immediate precautionary methods. This review highlights the emergence and hazards of aminoglycoside-resistant LAB which is in prime commercial demand both for preparing fermented food and also pharma-based therapeutics. It further focuses on the mode of aminoglycoside resistance and its occurrence in food-grade LAB, thus relating to its role in worldwide transfer via the food chain in spite of its limited use as compared to other antibiotics.

Inappropriate use of aminoglycosides in animal husbandry has led to the selection and emergence of high-level aminoglycoside resistance (HLAR) in lactic acid bacteria (LAB). The objective of this study was to assess the presence of aminoglycoside resistant LAB in farm animals and meat products. Gentamicin resistant LAB (n = 138) were selectively isolated from 50 different meat and farm animal sources. These native isolates of LAB were subsequently characterized for their minimum inhibitory concentration to seven different aminoglycoside antibiotics. HLAR to gentamicin, kanamycin and streptomycin was found to be 38 %, 45 % and 15 %, respectively. Selected cultures of LAB were identified by random amplified polymorphic DNA (RAPD)-PCR and 16S rDNA gene sequencing. Subsequent detection for the presence of nine aminoglycoside modifying genes [aac(6′)Ie-aph(2″)Ia, aph(3′)IIIa, aad6, ant(6)Ia, ant(9)Ia, ant(9)Ib, aph(2″)Ib, aph(2″)Ic and aph(2″)Id] was carried out by PCR. The Enterococcus spp. (n = 64) and Lactobacillus plantarum (n = 6) isolated from farm animals and chicken sausages, respectively, were positive for the bifunctional gene, aac(6′)Ie-aph(2″)Ia in PCR. In addition, Enterococcus sp. (n = 17), Lactobacillus plantarum (n = 3), and Pediococcus lolii (n = 2) possessed the kanamycin resistance gene, aph(3′)IIIa. Other LAB viz. Enterococcus faecalis (n = 2), E. faecium (n = 2) and L. plantarum (n = 1) harbored the streptomycin resistance gene, aad6. The integrase (int) gene, characteristic to Tn 916-Tn 1545 was detected in Enterococcus faecalis CS11+ and Enterococcus cecorum I40a suggesting its involvement in antibiotic resistant gene transfer. Besides, strains of L. plantarum, a species used as probiotic, isolated in this study showed the occurrence of aph(3′)IIIa as well as aac (6′)Ie-aph(2″)Ia genes that could be of concern in human health. The findings of the study highlight the spread and emergence of multi-resistance genes for aminoglycoside antibiotics among beneficial LAB.