Antimicrobial Resistance and Spread of Class 1 Integrons among Salmonella Serotypes

Abstract

The resistance profiles, for 15 antimicrobial agents, of 333 Salmonella strains representing the most frequent nontyphoidal serotypes, isolated between 1989 and 1998 in a Spanish region, and 9 reference strains were analyzed. All strains were susceptible to amikacin, ceftazidime, ciprofloxacin, and imipenem, and 31% were susceptible to all antimicrobials tested. The most frequent types of resistance were to sulfadiazine, tetracycline, streptomycin, spectinomycin, ampicillin, and chloramphenicol (ranging from 46 to 22%); 13% were resistant to these six drugs. This multidrug resistance pattern was found alone or together with other resistance types within serotypes Typhimurium (45%), Panama (23%), and Virchow (4%). Each isolate was also screened for the presence of class 1 integrons and selected resistance genes therein; seven variable regions which carried one (aadA1a, aadA2, or pse-1) or two (dfrA14-aadA1a, dfrA1-aadA1a, oxa1-aadA1a, or sat1-aadA1a) resistance genes were found in integrons.The worldwide use of antimicrobials in different fields, such as human and veterinary medicine and agriculture, and as food animal growth-promoting agents during the past decades has created enormous pressure for the selection of antimicrobial resistance among bacterial pathogens. Nowadays, there is increasing concern about the development of multiresistance in bacteria causing zoonosis and having an important animal reservoir, such as Salmonella strains (5, 6, 9); this multiresistance is of considerable importance in both human and veterinary medicine and is the subject of several surveillance programs (6, 9).An efficient route of acquisition and vertical and horizontal dissemination of resistance determinants is through mobile elements including plasmids, transposons, and gene cassettes in integrons (5,14,15,18,22). Four distinct classes of integrons encoding different integrases have been reported (13, 18), and class 1 integrons are the most frequent in clinical strains, being found in many different organisms. Class 1 integrons often contain sul1, which encodes resistance to sulfonamides (14,16,20). At the present time, about 60 different cassettes associated with resistance genes have been identified, and the same cassettes can be found in different classes of integrons (7,16).The aims of the present work were to (i) trace the frequencies and major changes throughout the last decade in susceptibility patterns of Salmonella enterica organisms representing the most frequent nontyphoidal serotypes causing human salmonellosis in the Principality of Asturias, Spain; (ii) ascertain the presence and spread of class 1 integrons among nontyphoidal serotypes; and (iii) characterize the different variable regions of the class 1 integrons found in order to identify the resistance genes located therein. MATERIALS AND METHODSBacterial strains. The study included 333 apparently epidemiologically unrelated nontyphoidal Salmonella strains collected in the Principality of Asturias, Spain, from 1989 to 1998 (Table 1), and 9 reference strain...

Diagnostic Accuracy of Class 1 Integron PCR Method in Detection of Antibiotic Resistance in Salmonella Isolates from Swine Production Systems

“…As described previously (10,16,17,26), a strong association of class 1 integrons (1,000, 1,000 and 1,200, and 1,600 bp) with identified resistance to specific antibiotics was demonstrated and attributed in part to the existence of resistance genes (aadA for streptomycin and spectinomycin, aadB for gentamicin and kanamycin, and ␤-lactamase for ampicillin) within these integrons. The gene sequencing and associated antibiotic resistance profiles of each integron group suggest that the 1,600-bp integron in part shares a common ancestor with the 1,000-bp integron plus additional genetic material containing the aadB gene.…”

“…Although the detection of class 1 integrons using PCR methods has become commonplace (5,9,10,14,19,25), the diagnostic accuracy (e.g., sensitivity and specificity) of integron PCR (Int-PCR) methods in detecting antibiotic resistance has not been investigated. An accurate PCR-based diagnostic tool for the detection of antibiotic resistance could be useful in epidemiological investigations due to time and cost savings compared to commonly used antibiotic resistance panels.…”

“…Class 1 integrons can capture genes from the environment and incorporate them by site-specific recombination. When they are part of the genome of pathogenic organisms such as Salmonella (10,8,9,17), Klebsiella (13,26), Yersinia (23), and Escherichia coli (16), integrons may be responsible for the horizontal transfer of antibiotic resistance among other pathogenic bacteria. The presence of genes within integrons coding for antibiotic resistance and the association of antibiotic resistance phenotypes with the presence of integrons have been well documented (10,16,17,25,26).…”

Prevalence of IncI1-Iγ and IncFIA-FIB type plasmids in extended-spectrum β-lactamase-producing Klebsiella pneumoniae strains isolated from the NICU of a North Indian hospital

“…Plasmids from ESBL-producing K. pneumoniae isolates were screened by PCR for the following b-lactamase genes -bla CTX-M , bla TEM , bla SHV , bla OXA-1 , bla KPC , bla NDM-1 , ampC and armA -using oligonucleotide specific primers as given in Table 2 (Pagani et al, 2003;Galimand et al, 2003;Versalovic et al, 1991;Guessennd et al, 2008 presence of integron was screened as described elsewhere (Guerra et al, 2000;Galimand et al, 2003). The amplified products were sequenced using an ABI 3130 genetic analyser (Applied Biosystems).…”

Integron content of Salmonella enterica serotype Typhimurium strains isolated in Hungary in the years 1997-1999

“…Reports published so far differ as regards the chromosomal (Threlfall et al, 1994;Casin et al, 1999;Martinez-Freijo et al, 1999;Markogiannikis et al, 2000) or plasmid (Tosini et al, 1998) location of integrons, as well as the number of IPs shown by S. Typhimurium strains and the size of integrons characterising the individual IPs Guerra et al, 2000;Markogiannikis et al, 2000).…”