Resistance in Enteric Shigella and nontyphoidal Salmonella: emerging concepts

PURPOSE OF REVIEW: The emergence of globally resistant enteric Shigella and nontyphoidal Salmonella strains (NTS) has limited the selection of effective drugs, which has become a major challenge for the treatment of infections. The purpose of this review is to provide the current opinion on the antimicrobial-resistant enteric Shigella and nontyphoidal Salmonella. RECENT FINDINGS: Enteric Shigella and NTS are resistant to almost all classes of antimicrobials in recent years. Those with co-resistance to ciprofloxacin, azithromycin and ceftriaxone, the first-line antibiotics for the treatment of infectious diarrhoea have emerged worldwide. Some of them have caused interregional and international spread by travel, trade, MSM, and polluted water sources. Several strains have even developed resistance to colistin, the last-resort antibiotic used for treatment of multidrug-resistant Gram-negative bacteria infections. SUMMARY: The drug resistance of enteric Shigella and NTS is largely driven by the use of antibiotics and horizontal gene transfer of mobile genetic elements. These two species show various drug resistance patterns in different regions and serotypes. Hence treatment decisions for Shigella and Salmonella infections need to take into consideration prevalent antimicrobial drug resistance patterns. It is worth noting that the resistance genes such as bla(CTX,)mph, ermB, qnr and mcr, which can cause resistance to ciprofloxacin, cephalosporin, azithromycin and colistin are widespread because of transmission by IncFII, IncI1, IncI2 and IncB/O/K/Z plasmids. Therefore, continuous global monitoring of resistance in Shigella and Salmonella is imperative.