# The Invisible Threat of Antibiotic Resistance in Food
## 2 Antibiotics and Their Effects on Bacterial Resistance
### Effect of Different Stressors on Antibiotic Resistance of Foodborne Bacteria  
During the production, distribution, and storage of food, as well as in the stomach and intestinal tract, microbial cells encounter several hurdles, such as suboptimal pH, suboptimal temperature or salt concentration, the impact of bile salts, and the presence of antimicrobial compounds such as bacteriocins and disinfectant residues [127; 128; 129].  
These stress factors can alter microbial cells, affecting cellular processes and resistance. The modification in resistance may result from a combination of stress response and molecular mechanisms of resistance to antibiotics [130].  
Various publications suggest a plausible correlation between stress adaptation in foodborne bacteria and the development of antibiotic resistance [131; 132]. Alternative sigma factor (\(\sigma\)B) may play a role in stress adaptation, which is a contributing factor in the expression of virulence and stress response genes. Additionally, two-component signaling systems (2 CSTS) were demonstrated to play a role in the innate cephalospor resistance of _L. monocytogenes_[133]. It was observed that the adaptive response in bacteria to various food-associated stresses provides cross-protection to antibiotics, which may accelerate the dissemination/spread of antibiotic resistance in the food chain.  
The stresses that arise in the food chain also affect the antibiotic resistance of starter cultures by inducing changes in gene expression [134]. Limited research exists concerning the effect of stress on the antibiotic resistance of lactic acid bacteria. [PERSON] and colleagues [135] conducted a study on the impact of acid and bile stresses on _Lactobacillus_. Their findings revealed that the effects of the stressors were varied; an increase in resistance was observed in some cases and a decrease in others depending on the type of stress, bacterial species or strain, and the type of antibiotic. The research of [PERSON] and [PERSON] [136] demonstrated that _Lactobacillus acidophilus_ cultures, which adapted to acidic stress conditions, exhibited higher resistance to antibiotics in comparison to their optimal pH counterparts. The strain selected for analysis was sensitive to all antibiotics used in the experiment, i.e., ampicillin, streptomycin, vancomycin, penicillin, chloramphenicol, and tetracycline, except erythromycin. The authors showed that after exposure to the stressor, the test strain showed higher resistance to all other antibiotics except tetracycline and chloramphenicol.  
[PERSON] et al. [137] observed an increase in the MIC of ampicillin, chloramphenicol, ciprofloxacin, and tetracycline in _Leuconostoc pseudomesenteroides_ and _Lactiplantiobacillus pentosus_ (formerly _Lactobacillus pentosus_) due to exposure to physicochemical stress, including antimicrobial agents, UV radiation, and chemicals such as isopropyl-b-D-thiogalactopyranoside, NaCl, and ethanol.  
In their examination of the impact of ionizing radiation in 2024, [PERSON] et al. [138] demonstrated that the genome of _S. aureus_, which is also a significant concern from the perspective of food safety, is modified by gamma radiation, resulting in the degradation of the _mecA_ gene that encodes \(\beta\)-lactamase resistance and the loss of its resistance to oxacillin.  
The induction of a heat shock response was also demonstrated to result in macrolide resistance in _Lactococcus lactis_[139]. The effect was explained by the fact that the observed changes in antibiotic resistance levels due to the stress factor may result from the triggering of the stress response. The phenomenon can be observed when antibiotic resistance genes and genes induced during a stress factor are located on the same operon and are simultaneously induced.