Emergence of colistin resistance inEnterobacter aerogenesfrom Croatia

Abstract

A colistin-resistant Enterobacter aerogenes [study code 12264] was isolated from the tracheal aspirate of a 71-year-old male patient in the General Hospital [GH] in Pula, Croatia. The patient was previously treated in University Hospital Centre in Rijeka with colistin in order to eradicate Acinetobacter baumannii isolate, susceptible only to colistin and tigecycline. Genes encoding ESBLs [bla, bla, bla, bla] were screened by PCR. The strain was shown to possess bla and bla genes. To asses genes possibly involved in resistance to colistin the chromosomal enconding mgrB gene and the plasmid-mediated mcr-1 and mcr-2 genes were screened as described previously. Mcr-1 and mcr-2 genes were not detected and mgrB gene presented a wild-type sequence. PCR-based Replicon typing method [PBRT] conducted on an E. aerogenes isolate, showed that the strain carried an IncN plasmid. Adaptive mechanisms such as changes of the bacterial cell outer membrane that cause porin decrease or presence of an efflux pump, due to selection pressure exerted by the therapeutic administration of colistin, could be responsible for the development of colistin resistance in our strain, as recently reported in E. aerogenes from France. Due to effective infection control measures, the colistin-resistant strain did not spread to other patients or hospital wards. This is the first report of an ESBL-producing, colistin-resistant E. aerogenes in clinically relevant samples such as endotracheal aspirate and blood culture, showing the presence of this rare resistance profile among Gram-negative bacteria.

Enterobacter spp.: Update on Taxonomy, Clinical Aspects, and Emerging Antimicrobial Resistance

“…The genome of the colistin-resistant strain identified in 2005 has been sequenced and analyzed, and a mutation in pmrA has been identified as the cause of the alteration of LPS biosynthesis that had been previously observed (37,109). This type of chromosomal mutation that efficiently alters the OM structure and generates a noticeable decrease of polymyxin activity may be involved in the emergence of resistant strains devoid of mcr-1 and mcr-2 (247). Moreover, the dynamic of colistin resistance in E. cloacae during selective decontamination of the digestive tract in intensive care units has been recently reported, suggesting a possible clonal transmission (286).…”

“…Resistant isolates collected from patients who received antibiotherapy were extensively studied with regard to their levels of porin expression and pore activity (106,107,199,238,242). The loss of porins has been reported in many studies carried out on E. cloacae and E. aerogenes clinical isolates, and due to space limitations, only a limited part of the published studies are indicated here (10,200,219,(243)(244)(245)(246)(247)(248).…”

Treatment Options for Colistin Resistant Klebsiella pneumoniae: Present and Future

“…The emergence of a transmissible, plasmid-mediated colistin resistance is particularly alarming, because it may accelerate the spread of colistin resistance among different K. pneumoniae strains and among different bacteria [44,45].…”

Genetic Diversity of Virulent Polymyxin-Resistant Klebsiella aerogenes Isolated from Intensive Care Units

“…Researchers from Croatia have reported that polymyxin resistance in K. aerogenes occurred due to mgrB present in a wild-type sequence. However, they did not detect the presence of mcr -1 or mcr -2 plasmid genes [ 36 ].…”