Cloning, Sequence Analyses, Expression, and Distribution of ampC-ampR from Morganella morganii Clinical Isolates

Abstract

Shotgun cloning experiments with restriction enzyme-digested genomic DNA from Morganella morganii 1, which expresses high levels of cephalosporinase, into the pBKCMV cloning vector gave a recombinant plasmid, pPON-1, which encoded four entire genes:ampC, ampR, an hybF family gene, and orf-1 of unknown function. The deduced AmpC β-lactamase of pI 7.6 shared structural and functional homologies with AmpC from Citrobacter freundii, Escherichia coli, Yersinia enterocolitica, Enterobacter cloacae, and Serratia marcescens. The overlapping promoter organization of ampC and ampR, although much shorter in M. morganii than in the other enterobacterial species, suggested similar AmpR regulatory properties. The MICs of β-lactams for E. coli MC4100 (ampC mutant) harboring recombinant plasmid pACYC184 containing either ampC and ampR (pAC-1) orampC (pAC-2) and induction experiments showed that theampC gene of M. morganii 1 was repressed in the presence of ampR and was activated when a β-lactam inducer was added. Moreover, transformation of M. morganii1 or of E. coli JRG582 (ΔampDE) harboringampC and ampR with a recombinant plasmid containing ampD from E. cloacae resulted in a decrease in the β-lactam MICs and an inducible phenotype for M. morganii 1, thus underlining the role of an AmpD-like protein in the regulation of the M. morganii cephalosporinase. Fifteen other M. morganii clinical isolates with phenotypes of either low-level inducible cephalosporinase expression or high-level constitutive cephalosporinase expression harbored the sameampC-ampR organization, with the hybF andorf-1 genes surrounding them; the organization of these genes thus differed from those of ampC-ampR genes inC. freundii and E. cloacae, which are located downstream from the fumarate operon. Finally, an identical AmpC β-lactamase (DHA-1) was recently identified as being plasmid encoded in Salmonella enteritidis, and this is confirmatory evidence of a chromosomal origin of the plasmid-mediated cephalosporinases.

Characterization of antimicrobial resistance patterns and class 1 integrons in Escherichia coli O26 isolated from humans and animals

“…Most E. coli O26 in this study were resistant to ampicillin (94%), and all ampicillin-resistant isolates carried ampC. This is consistent with observations made in E. coli and other Enterobacteriaceae [20]. After the introduction of ampicillin in the early 1960s, ampicillin-resistant E. coli emerged to the point that by the end of the decade 30-50% of hospital-acquired E. coli were resistant [31].…”

“…The presence of antimicrobial resistance genes encoding the tetracycline efflux pump (tetA, tetB, tetC, tetD, tetE and tetG), streptomycin phosphotransferases (strA and strB), aminoglycoside adenyltransferase (aadA), chloramphenicol transporter non-enzymatic chloramphenicol-resistance protein (cmlA), florfenicol export protein (floR), dihydropteroate synthetase type I (sulI), dihydropteroate synthetase type II (sulII) and ␤-lactamase/ampicillin resistance gene (ampC) was determined. Integrons and antimicrobial resistance gene primers were obtained from the published literature [15][16][17][18][19][20]. Primer sets were synthesised by Integrated DNA Technolo- …”

Resistance to ?-lactam antibiotics

“…Unlike most plasmid-borne AmpC enzymes, plasmid-encoded ACT-1 in K. pneumoniae isolates was shown to be inducible [191]. The C-4 family includes DHA-1 (found in Salmonella enteriditis and K. pneumoniae; [192]] and DHA-2 (found in K. pneumoniae; [19]) and appear to have originated from M. morganii [193,194]. The DHA enzymes, like some plasmid-borne ACT-1, are inducible [19,195].…”

Integron presence in a multiresistant Morganella morganii isolate

“…Nosocomial infections have also been reported. It is assumed that this species is intrinsically susceptible to most of the antibiotics active against Gram-negative bacilli, such as aminoglycosides, carbenicillin, chloramphenicol, ciprofloxacin and acid nalidixic, but is resistant to fosfomycin, colistin and some ␤-lactams, usually owing to a chromosomal cephalosporinase [9][10][11][12]. The role of salicylate in decreasing the production of ␤-lactamase has been documented [13].…”