Investigation of the Presence of Class 1, 2, 3 Integrons and Their Relationships with Antibiotic Resistance in Clinical Stenotrophomonas maltophilia Isolates

Abstract

Stenotrophomonas maltophilia is an opportunistic emergent pathogen causing hospital-acquired infections. It is resistant to majority of the broad spectrum antibiotics due to several mechanisms which significantly limit the treatment options. Although the relationship between integrons, mobile genetic elements which play role in transferring resistance genes, and the antibiotic resistance in different gram-negative bacteria have been investigated, the data are limited in Turkey especially for S.maltophilia. The aims of this study were to detect the presence of different classes of integrons and plasmids in clinical isolates of S.maltophilia and to investigate the antibiotic resistance profiles of those isolates. One hundred S.maltophilia strains isolated from various clinical samples (32 sputum, 25 tracheal aspirates, 9 urine and blood, 7 exudates and catheters, 4 sterile body fluids and wounds, 2 CSF, 1 conjunctiva) in our microbiology laboratory during January 2011-September 2012, were included in the study. The isolates were identified by VITEK2 Compact (BioMerieux, France) or Phoenix 100 (BD, USA) automatized systems, and the susceptibilities of the strains to levofloxacin, chloramphenicol, ceftazidime and trimethoprim/sulfamethoxazol (SXT) were evaluated via broth microdilution method according to the CLSI recommendations. Class 1 (intl-1), class 2 (intl-2), class 3 (intl-3) integron gene cassettes and integron 5'-3' conserved gene regions (intl-5'-3'CS) were investigated by polymerase chain reaction (PCR) using specific primers in all of the strains. Nucleotide sequence analysis of PCR products was performed in case of positive result, and the presence and size of plasmids were further investigated. The susceptibility rates of S.maltophilia strains to ceftazidime, chloramphenicol, SXT and levofloxacin were found as 24%, 66%, 93% and 95%, respectively, while MIC50 and MIC90 values were 64-128 mu g/ml, 8-16 mu g/ml, 1/19-2/38 mu g/ml and 1-2 mu g/ml, respectively. In PCR amplification with intl-1, intl-2 and intl-3 primers, 12%, 2% and 10% of the isolates yielded expectative bands, respectively. DNA sequence analysis of the amplified products revealed five isolates to harbour intl-1 gene, while intl class 2 and class 3 genes were not detected in any of the strains. Furthermore in PCR amplification with intl-5'CS and 3'CS primers, 20% of the strains yielded expected bands. Sequence analysis of these amplicons revealed the presence of quaternary ammonium compound resistance protein genes (qacL) in two, aminoglycoside adenyltransferase gene (aadA) in one and integron-associated recombination site (attl1) genes in five strains. Additionally, the presence of plasmids have been detected in 9 (9%) of the strains, however all of them was integron-negative. The sizes of plasmids were 2340, 1350, 2760, 18600, 20000, 3570-2540, 2510 and 5000-2540 base pairs, respectively. When the antibiotic susceptibility patterns of strains were compared with the presence of intl gene regions, no statistically significant relationship was observed (p> 0.05). In conclusion, the demonstration of integron class 1 genes and plasmids among clinical S.maltophilia strains is regarded as a warning data to indicate the potential for spread of those resistant strains in our hospital.