## 4 Discussion  
The efflux pump system is the most important means of resistance encoded on the _P. aeruginosa_ chromosome [27]. Efflux pump systems, found in bacterial membrane trans  
Figure 5: Phylogenetic relationship of the bacteria harbouring _MexB_. \begin{table}
\begin{tabular}{c c} \hline \hline
**Operon** & **Number (\%)** \\ \hline _MexAB-OprM_ & 53 (93) \\ _MexCD-OprI_ & 34 (60) \\ _MexX-OprN_ & 28 (49) \\ \hline \hline \end{tabular}
\end{table} 
Table 5: The frequency of _P. aeruginosa_ MDR efflux pump genes arranged as operons. porters, are among the diverse mechanisms for multidrug resistance. Expression levels of the efflux system lead to antibiotic resistance when elevated [28]. This study investigated the resistance level and genotypic amplification of RND efflux pumps in all multidrug-resistant _P. aeruginosa_. The antibiotics investigated in this study are preferred substrates for RND efflux pumps. _P. aeruginosa_ isolated in this study were resistant to aminoglycos, fluoroquinolones, carbapenem, and the beta-lactam class of antibiotics with a phenotypic resistance rate of 76% for amikacin, ceftazidime (66%), gentamicin (60%) and levofloxacin (57%), meropenem (53%), ciprofloxacin (49%), aztreonam (30%), norfloxacin (15%), tobramycin (15%) and impenem (7%). All (100%) MDR _P. aeruginosa_ isolates resisted the aminoglycos antibiotics class, while 88% were simultaneously resistant to the beta-lactam and fluoroquinolones class. However, the lowest occurrence of MDR _P. aeruginosa_ isolates was detected in the carbapenem (75%) class of antibiotics. MDR was found in 70% of _P. aeruginosa_ isolates, with resistance to six antibiotic classes being the most common. The _MexAB-OprM_ is the earliest and most common MDR efflux pump with elevated expression levels in the RND family [29]. Generally, PCR amplification of the efflux pump genes revealed that all MDR _P. aeruginosa_ isolates harboured _MexB_ and _MexC_, while _MexA_ and _OprM_ had the same rate of 96.5%. Meanwhile, _MexX_, _MexD_, _OprM_ occurred in 89.6%, 74.1%, 63.7% and 51.7% of the _P. aeruginosa_ isolates, respectively. Similarly, a study detected _MexA_ and _MexB_ with prevalence rates of 88.2% and 70.5% in _P. aeruginosa_ isolated from patients suffering from healthcare-associated infections [30]. In contrast, a study on the roles and associations of efflux pumps of _P. aeruginosa_ in Iran found a lower occurrence of _MexA_, _MexB_, and _OprM_[18; 31]. _MexAB-OprM_ significantly extrudes quinolones, chloramphenicol, aminoglycos, tetracycline, novobiocin, and beta-lactams [32]. Based on possessing the three components of an efflux pump system, _MexAB-OprM_ is the most common in this study, with a frequency of 93%. Similarly, another study reported _MexAB-OprM_ as the most prevalent efflux pump [29]. In addition, the _P. aeruginosa_ isolates were also positive for _MexC-OprJ_ and _MexX-OprN_ operons in 60% and 49% of the MDR _P. aeruginosa_ isolates, respectively. Varying prevalence rates were observed for _MexA_ (96-98%), _OprM_ (95-96.5%), _MexD_ (74-76%), _OprJ_ (62-65%), _MexX_ (86-89.6%), and _OprN_ (51-52%) across beta-lactams, fluoroquinolones, carbapenem, and aminoglycos antibodies in MDR _P. aeruginosa_ isolates. However, _MexB_ and _MexC_ were present in all MDR _P. aeruginosa_ isolates across the abovementioned classes of antibiotics. The regulatory proteins of the efflux pumps in this study showed the highest occurrence of _NfxB_ (31.6%), followed closely by _NalC_ and _NalD_, with a prevalence rate of 15.8% and 12.2%, respectively, in the MDR _P. aeruginosa_ isolates. The exact incidence rate of 3.5% was found for _MexZ_ and _MexR_. The absence of regulatory genes in most of the MDR P. aeruginosa isolates in this study may have enabled the transcription of efflux pump operons, which is evident in the high occurrence of efflux pump genes and eventual increase in multidrug resistance. Antibiotic resistance has emerged due to alterations brought on by mutations [33].