## 4 Discussion  
The aim of our investigation was to determine the ESBL producer-relevant agents and to decrypt their genetic factors. The ubiquity of ESBLs produced by _Enterobacteriaceae_, particularly with _E. coli_ (ESBL-EC), has increased worldwide throughout the past two decades [25]. In our investigation, _E. coli_ isolates were collected from various samples. Several cefotaxime-resistant strains were detected. A total of 92.59% (25/27) strains were considered as being ESBL producers. However, 3.7% (1/27) of isolates produced AmpC \(\beta\)-lactamases. Indeed, this strain contained both ESBL and AmpC \(\beta\)-lactamase enzymes. This rate of ESBL-producer isolates was similar to those reported previously [7] from Al-Abha  
Figure 2: PFGE patterns for _E. coli_ isolates, with their corresponding pulsotypes. and Riyadh, KSA [26; 27]. The prevalence rates of ESBL-EC were 6.5% and 10.3% in 2002 and 2004, sequentially [8]. The preponderance rates were 15.4% and 4.5% for inpatients and outpatients, respectively [28; 29]  
The multidrug resistance (MDR) was described for all isolates, even for quinolones, aminosides, tetracycline, trimethoprim/sulfamethoxazole, fosfomicin, and chloramphenicol. MDR is frequent in _E. coli_; however, the high rates of resistance found for fosfomycin in this study are uncommon in such strains. Conversely, fosfomycin susceptibility tests are limited, since this agent is occasionally available in most clinical laboratories. Uncomplicated UTI is commonly treated in many countries with fosfomycin, whereas worldwide attention has been oriented to sparing carbapenems in ESBL-producing strains. Fosfomycin in combination with colistin was recommended for treating _Enterobacteriaceae_ that were resistant to carbapenems. A recent study from China [29] reported uropathogenic ESBL-producing _E. coli_ isolates that are resistant to fosfomycin. Indeed, fosfomycin resistance was encoded by the fosA3 gene carried by a 54.2 Kb transferable plasmid also co-harboring a _blaCTX-M_ gene. The genetic characterization of fosfomycin resistance mechanisms and its possible linkage to ESBL-encoding genes needs further investigation in KSA. The typical TEM and SHV variants of ESBLs have declined during the past two decades and were interchanged worldwide by the CTX-M group as the predominant ESBL group. Similarly, the ESBLs generated in our strains harbored CTX-M \(\beta\)-lactamases. The _blaCTX-M-15_ (21/27), _blaCTX-M-27_ (5/27), and _blaCTX-M-9_ (1/27) genes were identified. The _blaCTX-42_ gene was recorded in two strains; moreover, one isolate co-accommodated the _blaCTX-M-15_ gene. The concomitant occurrence of \(\beta\)-lactamase coded by the _blaSTV-1_ or _blaCTX-1_ genes was also common in these isolates, as reported previously [30]. Our findings support other studies from KSA showing the prevalence of a _blaCTX-M15_ type [26; 31]. However, the _blaCTX-M-9_ and _blaCTX-M-27_ genes are prevalent in KSA, and low rates were reported [7; 32]. It is also important to know the occurrence of the _blaCTX-42_ gene, a CMY-2 variant, which was present in two isolates of our collection. The _blaCTX-42_ was first described in _E. coli_[33], and was then rarely reported and mainly found to be associated with _blaNDM-S_, _blaN-12_, _blaCTX-M-14_, or _blaCTX-M-15_, as described in one isolate of our study. Presumably, we describe an early case of _blaCMTX-42_ harboring _E. coli_ isolates in KSA [34]. The prevalent plasmid replicon group was found in resistant _Enterobacteriaceae_ segregated from both animals and humans holding incompatibility (_Inc_) group F (including _FIA_, _FIB_, and _FII_ replicons), and A/C, L/M, I1, HI2, and N [35; 36]. Different _blaCTX-M_ genes are also combined with specific plasmid replicon types (_IncN_, _II_, _FII_, and L/M) [36]. The _blaCTX-M-15_ was primarily found on plasmids that involve FII and FIA replicons, and, to a lesser extent, to _IncI1_, _IncN_, and _IncA/C_, as well as being on pir-type plasmids.