## 2 Results and Discussion
### Antimicrobial and Modulating Activities of Antibiotics  
The results showed that the minimum inhibitory concentration (MIC) values obtained for chalcones 1 and 2 was \(\geq\)1024 \(\mu\)g L\({}^{-1}\), meaning that the chalcones had no inhibitory action on bacterial growth at the highest concentration levels tested. Previous studies with chalcone derivatives have shown good antibacterial activity against Gram-positive and Gram-negative strains. However, these antibacterial activities are dependent on their pattern of structural replacement [10]Figure 8: Minimum inhibitory concentration (MICs) of the Ciprofloxacinacin (Cip) (**a**), Gentamicin (Gen) (**b**), and Cephalexin (Cep) (**c**) in the absence or presence of the chalcones 1 and 2 at sub-inhibitory concentrations (MIC 1/8) against multidrug-resistant _S. aureus_ SA10. Each result is the geometric mean of three simultaneous experiments. (***) Statistically significant values (\(p<0.0001\)); (*) (\(p<0.05\)).  
Previous studies have reported that compounds with a nitro group, depending on their molecular structure, are potential therapeutic agents due to their mode of action involving the biotransformation of the nitro group, releasing intermediates in the redox process and causing changes in the stability of the redox process. The results of the experiments presented in this paper are shown in Fig. 9.  
Figure 9: MICs of the Ciprofloxacin (**i**p) (**a**), Gentamicin (Gen) (**b**), and Cephalexin (Cep) (**c**) in the absence or presence of the chalcones 1 and 2 at sub-inhibitory concentrations (MIC 1/8) against multidrug-resistant _E. coli._ Each result is the geometric mean of three simultaneous experiments. (***) Statistically significant values (\(p<0.0001\)).  
membrane structures of several microorganisms and cells [17]. The computational chemical calculations showed that chalcone 2 has a greater electrophilic character than chalcone 1 due to the higher value of the electrophilicity index and the data obtained by the cyclic voltammetry of chalcones reveal that chalcone 2 undergoes the oxidation process before chalcone 1, which indicates a greater electrophilic character and greater chemical reactivity. The higher reactivity and electrophilicity of the synthetic chalcone 2, can be responsible for intermediated interactions between the nitro group and the bacterial cell wall and, when combined with the gentamicin drug, proved to be more efficient. It is worth adding that the sensitivity profile of Gram-positive and Gram-negative bacteria to antibiotics is different, and the bacteria tested in the present study already had an intrinsic resistance profile to these antibiotics.  
Chalcone 1 and 2 were able to modulate the resistance to EtBr in the strain SA1199B overexpressing the efflux pump NorA, indicating that both chalcones 1 and 2 could be efflux pump inhibitors (Figure 11(a,b)). However, when associated with Norfloxacin, an antagonism effect was observed. The results found for EtBr suggest that, although synthetic chalcones tested behave as efflux pump inhibitors, probably inhibiting other efflux pumps, they were not able to inhibit NorA and consequently were not recommended for use in association with Norfloxacin against _S. aureus_ strains overexpressing the _NorA_ gene.