Multiple-Antibiotic Resistance Mediated by Structurally Related IncL/M Plasmids Carrying an Extended-Spectrum β-Lactamase Gene and a Class 1 Integron

Abstract

A conjugative IncL/M plasmid (pSEM) conferring resistance to gentamicin, amikacin, kanamycin, sulfonamides, and expanded-spectrum cephalosporins was found in pathogenic strains of Salmonella enterica serotype Typhimurium. Resistance to aminoglycosides was encoded by a sul1-type class 1 integron (In-t3). An extendedspectrum beta-lactamase gene, bla SHV-5 , was identified 3.5 kb downstream of the integrase (intI1) gene of In-t3. Nucleotide sequence analysis of the 5.3-kb bla SHV-5 -In-t3 region of pSEM highlighted striking similarities with IncL/M plasmids isolated from nosocomial gram-negative pathogens, conferring resistance to expandedspectrum cephalosporins and aminoglycosides.Although antibiotic resistance is becoming a major threat to human health worldwide, information concerning the dissemination and geographical distribution of antibiotic-resistant bacterial pathogens remains scattered (8,14,26). During the last decade many hospital outbreaks caused by extended-spectrum beta-lactamase (ESBL)-producing Enterobacteriaceae have been reported, and most of the ESBL-producing strains were found to carry the bla TEM-1 , bla TEM-2 , and bla SHV-1 gene derivatives (5,6,9,11,19,27). These genes are prevalently located on large conjugative plasmids of the incompatibility (Inc) groups IncC, IncFI, IncH12, and IncL/M (3,5,7,13,18,20,23,28).More recent reports have highlighted the emergence of ESBL-producing strains endowed with an extremely wide spectrum of antibiotic resistance, including resistance to sulfonamides, trimethoprim, streptomycin, kanamycin, gentamicin, and amikacin (17,21,23). However, the molecular mechanisms involved in the acquisition and/or transmission of ESBL-encoding genes are poorly understood.In previous work we identified an IncL/M plasmid, referred to as pSEM, in eight epidemiologically unrelated, multipledrug-resistant strains of Salmonella enterica serotype Typhimurium. This plasmid contains a sul1-type class 1 integron (In-t3) carrying the aacA4, aacC1, and aadA1 gene cassettes and conferring resistance to sulfonamides, kanamycin, gentamicin, and amikacin (29). The streptomycin and spectinomycin-resistance determinant, aadA1, is poorly expressed in In-t3 because it is located in a distal position relative to the main integron promoter P ant (29).The Salmonella strains harboring pSEM were analyzed in more detail with regard to their antibiotic resistance profile. Microdilution susceptibility tests demonstrated that all eight strains were resistant to ceftazidime (Ն16 g/ml), cefotaxime (Ն32 g/ml), ceftriaxone (Ն64 g/ml), cefamandole (Ն32 g/ ml), cefoxitin (Ն8 g/ml), and aztreonam (Ն16 g/ml) but sensitive to imipenem (Ͻ4 g/ml).To clone the gene responsible for resistance to expandedspectrum cephalosporins, an EcoRI genomic library was constructed in the pUC18 vector using total DNA extracted from the prototypic Salmonella 202 strain. The library was introduced by transformation in Escherichia coli DH5␣ competent cells, and selection was performed on Luria-Bertani agar plates containing ceftaz...

Prevalence of extended-spectrum β-lactamase-producing Gram-negative bacteria in septicaemic neonates in a tertiary care hospital

“…Such wide resistance spectra of ESBL producers, including resistance to drugs such as sulfonamides, trimethoprim and aminoglycosides, have been observed by many others (Jett et al, 1995;Villa et al, 2000;Subha et al, 2001). One study reported that ciprofloxacin resistance and ESBL production in Klebsiella pneumoniae are closely associated (Paterson et al, 2000).…”

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 …”

Antibiotic Resistance and the Prospects of Medicinal Plants in the Treatment of Salmonellosis

“…The pSEM plasmid was identified in 1997 in S. typhimurium strains isolated from children in Albania (Villa et al, 2000), while pACM1 was isolated from K. oxytoca strains responsible of a nosocomial outbreak in the USA (Preston et al, 1997;Preston et al, 1999). Both plasmids belonged to the same IncL/M group and conferred resistance to expanded-spectrum cephalosporins by the blaSHV-5 gene.…”

“…During the last decade, infections caused by S. enterica carrying ESBLs have been reported, and most of the ESBL-producing strains were found to carry plasmids encoding the blaTEM-1, and blaSHV-1 gene derivatives (Hammani et al, 1991;Morosini et al, 1995;Tassios et al, 1997;Villa et al, 2000;Mulvey et al, 2003).…”