# The Importance of Gram-Negative Rods in Chronic Rhinosinusitis
## 4 Discussion
coli_, were also isolated from patients with asthma and those who had previously used antibiotics. Guidelines differ for the use of antibiotics in the treatment of CRS patients [55; 65] According to the EPOS2020 steering group [37], there is insufficient evidence that the use of antibiotics in long-term and short-term therapy impacts treatment outcomes in adults with CRS compared with placebo. This group analyzed the results of studies using macrolides (mainly in long-term treatment) and amoxicillin, amoxicillin with clavulanic acid, cefaclor, cefuroxime, ciprofloxacin, and levofloxacin. It should be noted that Gram-negative rods are naturally resistant to macrolides. Given that the occurrence of Gram-negative rods is found in a significant number of patients with CRS, it is advisable to select an antibiotic based on the result of the drug susceptibility test. The Gram-negative rods isolated in our study were 100% sensitive to ciprofloxacin. However, significant percentages of strains were resistant to ampicillin and amoxicillin with clavulanic acid, which effectively precludes the use of these drugs in empirical therapy. In the case of ceftazidine and cefuroxime, resistant strains were isolated only from patients with primary CRS. [PERSON] et al. assessed the trends in drug susceptibility of bacteria isolated from patients with CRS and found high percentages of _Klebsiella_ spp. and _Enterobacter_ spp. strains sensitive to ciprofloxacin (one _Klebsiella_ spp. strain resistant), while the number of ESBL-producing strains increased in the analyzed periods from 0.4% to 7.4% in the case of Klebsiella spp. and from 0% to 3.7% in the case of _Enterobacter_ spp. [60]. In our studies, no ESBL-positive strains were recorded. In recent years, researchers have identified bacterial biofilm as a significant factor in the pathogenesis of CRS. Biofilms are highly organized, complex bacterial structures enclosed in an extracellular matrix composed of polysaccharides, nucleic acids, and proteins. The matrix provides bacteria with a mechanism to reduce metabolic activity, protecting them from both the host's defense mechanisms and antibiotics. It is believed that biofilms exacerbate inflammation by activating the immune system by releasing planktonic bacteria and possibly exotoxins [48; 53; 65]. Moreover, [PERSON] et al. described that _S. aureus_ biofilm is a predisposing factor for treatment failure and poorer postoperative outcomes [34]. The presence of bacterial biofilm in sinus mucosa has been observed in 44-92% of CRS patients, depending on the detection method used [12; 15; 48; 66] [PERSON] et al. reported that 76.67% (23/30) of CRS patients undergoing FESS had evidence of biofilms on SEM micrographs [32]. The occurrence of bacterial biofilms in CRS patients at a similar frequency has also been confirmed by other authors [28; 67; 68; 69]. The most commonly identified species in biofilms are _S. aureus_, coagulase-negative staphylococci (CNS), particularly _S. epidermidis_, _S. pneumoniae_, _P. aeruginosa_, _H. influenzae_, and, less frequently, bacteria from the genera _Acinetobacter_, _Proteus_, _Citrobacter_, _Klebisella_, and _Enterobacter_[12; 15; 67; 70; 71; 72]. The mechanisms associated with biofilm formation may contribute to microbiota imbalance. The Quorum Sensing (QS) system is used by bacteria residing in biofilms for communication influences, among other things, the spatial differentiation of biomass, antibiotic resistance, and the expression of virulence factors, which may impact disease pathogenesis and mediate the host's immune response [32; 47; 66]. Biofilms on the surface of the sinus mucosa may contribute to the persistence of inflammation observed in treatment-resistant CRS [53]. The Gram-negative rods examined in this study also demonstrated the ability to form biofilms under in vitro conditions. Seven out of the 27 tested isolates formed a strong biofilm. These included _P. mirabilis_ (n = 2), _E. aerogenes_ (n = 1), _E. cloace_ (n = 1), _M. morganii_ (n = 1), _S. marcescens_ (n = 1), and _K.