# The Invisible Threat of Antibiotic Resistance in Food
## 3 Antibiotic Resistance in Traditional Foods
### Antibiotic Resistance in Dairy/Fermented Foods
Various literature [253; 254; 255] has demonstrated that probiotics such as _Lactobacillus_ (_Lacticasobacillus paracase_ (formerly _Lactobacillus paracase_), _Ligalactobacillus salivarius_ (formerly _Lactobacillus salivarius_), and _Lactiplantibacillus plantarum_ (formerly _Lactobacillus plantarum_)), _Enterococcus_, _Lactococcus lactis_, and _Bifidobacterium_ displayed complete intrinsic resistance to last- resort antibiotic colistin [1], as well as kanamycin, neomycin, ciprofloxacin, vancomycin, gentamicin, and streptomycin, with specific resistance patterns observed in various species retrieved from fermented milk products [233] and dairy environments [250; 256; 217]. Meanwhile, _Lactobacillus bulgaricus_, _L. acidophilus_, and _S. thermophilus_ showed different degrees of susceptibility to vancomycin, suggesting the inherent susceptibility of some LAB strains to this glycoptide antibiotic [257; 224]. Furthermore, a broad range of LAB displayed sensitivity to ampicillin, clindamycin, erythromycin, cef-sulodin, penicillin G, and rifampicin, reflecting that these antimicrobial agents are still effective for targeting lactobacilli [224]. Despite this, a concerning trend of acquired resistance to penicillin, erythromycin, clindamycin, and tetracycline was observed in multiple species of LAB from diverse sources, such as fermented milk [238; 258], probiotics or fermented foods [254; 259], and human intestine [219]. The emergence of such resistant strains outlines the dynamic nature of AR among LAB, posing potential risks for both food safety and public health. Many AR genes in _Bifidobacterium_, _Lactobacillus_, _Lactococcus_, _Leuconstoc_, _Pediococcus_, and _Streptococcus thermophilus_ were acquired through conjugative plasmids [260]. The characterization of AR genes in fermentative bacteria is often incomplete and represents a significant risk, as many of these genes may remain undetected or be novel. Fortunately,breakthroughs in genome sequencing and metagenomic analysis are helping to reveal this concealed realm, allowing us to better protect our food by uncovering the actual profile of AR genes in fermented products [261]. Almost 89% (8/9) of LAB strains derived from yogurt and cheese commercially available in Tianjin showed resistance to at least one antibiotic and were positive for _van_, _aph_, and _aadA2_ resistance genes [222]. Moreover, several resistance genes, including _tet(M)_, _strA_, _strB_, _sulI_, _sul2_, _aac(6\({}^{\prime}\))_, _aph(2\({}^{\prime\prime}\))_, _aph(3\({}^{\prime\prime}\))-II_, and _aph(3\({}^{\prime\prime}\))-III_, were detected by [PERSON] et al. [258] in 87 LAB strains isolated from fermented milk products in China. The results show that these bacteria do not transmit genes but pose a threat in spreading antibiotic resistance. However, [PERSON] and [PERSON] [230] declared that three strains of _Lactobacillus_ originally isolated from chicken meat showed the ability to transfer _erm(B)_ and _tet(M)_ AR genes to pathogenic bacteria in vivo (using rats), in vitro, and during the food fermentation process. Tetracycline resistance in lactobacillus involves 11 transferable AR genes, some of which, like _tet(K)_ and _tet(L)_, are plasmid-coded, while others, like _tet(M)_ and _tet(O)_, are both plasmid and chromosomally coded [1]. A recent analysis of 47 shotgun sequencing datasets from various probiotic samples reported over 70 AR genes, including those related to rifampicin, tetracycline, and extended-spectrum \(\beta\)-lactamase (ESBL) resistance. Alarmingly, many of these AR genes were associated with MGEs, plasmids, or phages, simplifying the transfer risk to human gut microbiota, and raising significant public health concerns [262]. In addition, [PERSON] et al. [263] analyzed 126 whole genomes of probiotic bacteria for AR genes. The results demonstrated that tetracycline (_tet_) and erythromycin (_erm_) resistance genes were prevalent, particularly in _Bifidobacterium_ and _Lactobacillus_.