Properties of plasmids responsible for production of extended-spectrum beta-lactamases

Abstract

The extended-spectrum P-lactamases are believed to arise by mutations which alter the configuration around the active site of TEM-and SHV-type enzymes so as to increase their efficiency with otherwise nonhydrolyzable cephalosporins and monobactams. This hypothesis predicts that the genes for these new enzymes should be found on the same wide variety of plasmids that encode TEM-1, TEM-2, and SHV-1 P-lactamases and that at least some of them should be mediated by transposons. Fifteen plasmids, each encoding an extended-spectrum 13-lactamase, were examined. Unlike the average TEM plasmid, all were large, ranging in size from 80 to 300 kb. All determined resistance to multiple antimicrobial agents, ranging from 5 to 11, and some conferred resistance to heavy metals and UY radiation as well. The plasmids belonged to a limited number of incompatibility (Inc) groups, including IncC, IncFI, IncHI2, and IncM. Because most of the mutations giving rise to extended-spectrum activity are G * C-*A T transitions and some of the mutant genes have as many as four base substitutions, a plasmid-determined mutator gene was searched for, but no such property was found.Several techniques were used to detect transposition of the extended-spectrum 13-lactamase genes, but a mobile genetic element could not be demonstrated even though eight of the plasmids hybridized with a DNA probe derived from the tnpR gene of Tn3. The genesis of extended-spectrum (-lactamases may not be as simple as has been supposed.Extended-spectrum 1-lactamases are enzymes that confer resistance to cefotaxime, ceftazidime, and other broadspectrum cephalosporins and to monobactams such as aztreonam (43). They appear to arise from genes for common plasmid-mediated SHV-1, TEM-1, and TEM-2 3-lactamases by mutations that alter the amino acid configuration around the active site of these enzymes so as to expand their spectrum of activity (19,30,42,49).TEM-1 and TEM-2 3-lactamases are determined by plasmids belonging to many different incompatibility (Inc) groups in enteric organisms (35) and are often carried on transposons (22). SHV-1 is also encoded by several plasmid types (36), but whether it is (40) or is not (33) transposon determined is in dispute.To explore the mutation hypothesis, we have characterized plasmids responsible for extended-spectrum P-lactamase production. The aims of this study were to establish whether the plasmids belonged to many or a few Inc groups, to determine whether they carried transposons encoding the extended-spectrum activity, and to investigate whether they possessed genes facilitating the mutational alterations observed.MATERIALS AND METHODS Bacterial strains, plasmids, and bacteriophages. line, 50; thiamine, 0.34; and L-threonine, 43. Antimicrobial agents were used at the indicated concentrations (in micrograms per milliliter): ampicillin, 50; gentamicin, 20; kanamycin, 25; nalidixic acid, 100; rifampin, 100; streptomycin, 25; tetracycline, 5 or 25; and tobramycin, 10.Antibiotic resistance was evaluated by disk or agar diffusion usin...

Extended-spectrum β-lactamase/AmpC-producing uropathogenic Escherichia coli from HIV patients: do they have a low virulence score?

“…In agreement with other Indian studies, the majority of our ESBL/AmpC-producing E. coli exhibited a high level of resistance towards quinolone (93.1 %) and FQ (75 %), which would have therapeutic implications (Baby Padmini et al, 2008). Several reports have documented a strong correlation between qnrA prevalence and ESBL positivity in E. coli isolates, especially the CTX-M type (Jacoby et al, 2003;Mammeri et al, 2005;Lavigne et al, 2006), which could frequently be due to the presence of these resistance determinants on mobile genetic elements (Jacoby & Sutton, 1991;Partridge et al, 2001;Preston et al, 2003;Villa et al, 2000;Wang et al, 2003 The virulence potential and multiple drug resistance observed among the E. coli of non-B2 phylogroups further strengthens the claim that horizontal gene transfer might play a major role in the emergence of drug resistance among these originally avirulent/less virulent strains which can no longer be called 'innocent bystanders'. Also, prior exposure to 3G cephalosporins/FQs probably serves as a driving force for the selection of multidrug-resistant isolates primarily of endogenous origin to establish UTI among HIV patients.…”

“…In agreement with other Indian studies, the majority of our ESBL/AmpC-producing E. coli exhibited a high level of resistance towards quinolone (93.1 %) and FQ (75 %), which would have therapeutic implications (Baby Padmini et al, 2008). Several reports have documented a strong correlation between qnrA prevalence and ESBL positivity in E. coli isolates, especially the CTX-M type (Jacoby et al, 2003;Mammeri et al, 2005;Lavigne et al, 2006), which could frequently be due to the presence of these resistance determinants on mobile genetic elements (Jacoby & Sutton, 1991;Partridge et al, 2001;Preston et al, 2003;Villa et al, 2000; Wang et al, 2003). In our study, of the 34 isolates that possessed bla CTX-M , 30 (88.2 %) were FQ …”

Clinical Significance of ESBL-Producing Escherichia coli Isolated from Urinary Tract Infections in Sylhet Bangladesh

“…Studies in the past have documented that isolates with ESBL phenotypes contained bla TEM , bla SHV , bla OXA , and bla CTX-M genes which were confirmed by polymerase chain reactions [4,[11][12][13][14][15][16][17][18][19].…”

“…Plasmids of high mol. wt are generally said to be transmissible between the organisms by the process of conjugation [4].…”

“…Recently ESBL-producing organisms have been reported from many parts of the world [4,5]. In Bangladesh a preliminary study showed that E. coli can be isolated from different sources such as urine, stool, etc.…”