**5. Antimicrobial resistance in UPEC**

Antimicrobial therapy is generally recommended for all symptomatic UTI cases including uncomplicated and complicated cases. The choice of an antibiotic should be led by spectrum and susceptibility patterns of the causative agent, its efficacy for the particular indication, tolerability and adverse events, costs and availability, etc. The most commonly used antimicrobials for treating uncomplicated cases include nitrofurantoin, cotrimoxazole (first line), fosfomycin and pivmecillinam (alternative), fluoroquinolones (second line). Ceftriaxone, cefepime, piperacillin-tazobactam, aminoglycosides and carbapenams are used for complicated cases [42]. The international guidelines recommend the use of nitrofurantoin, fosfomycin trometamol and trimethoprim-sulfamethoxazole for the treatment of uncomplicated UTI. Fluoroquinolones

*Uropathogenic* Escherichia coli *DOI: http://dx.doi.org/10.5772/intechopen.102525*

in such situations should be kept in reserved as they are used to treat complicated UTI and mild to moderate pyelonephritis [42].

UTIs and especially recurrent UTIs are associated with significant use of antibiotics that promotes resistance. Antimicrobial resistance in UPEC and the spreading of multidrug resistant (MDR) UPEC is a concerning clinical problem, particularly in women with recurrent UTIs. Increasing ineffectiveness of the antimicrobials has led to the emergence of MDR UPEC (resistance to at least one antibiotic in three or more classes) and XDR UPEC (resistance to at least one in all but at least two or fewer classes) [43].

The various mechanisms responsible for resistance include:

	- Target site inactivation
	- Presence of β-lactamases enzyme
	- Efflux pumps mechanism
	- Through mobile genetic elements such as transposons, gene cassettes, insertions sequences, integrons, etc.

## **5.1 Drug resistance mechanisms in different classes of antibiotics**

## *5.1.1 Beta lactam drugs*

They are cell wall synthesis inhibitors. One of the main mechanisms of resistance in UPEC is the production of the β-lactamase enzyme which is encoded by the *bla* genes, located on the plasmids. ESBL (extended-spectrum β-lactamase) is one of the types of β-lactamases and is responsible for conferring resistance to penicillin, cephalosporins and monobactams. ESBLs are susceptible to cephamycins, carbapenems and beta lactamase inhibitors; thus making carbapenems drug of choice in such cases. CTX-M, TEM and SHV are most common ESBLs observed among UPEC.
