SXT Resistance Research Articles

Evolution of Resistance against Ciprofloxacin, Tobramycin, and Trimethoprim/Sulfamethoxazole in the Environmental Opportunistic Pathogen Stenotrophomonas maltophilia.

Stenotrophomonas maltophilia is an opportunistic pathogen that produces respiratory infections in immunosuppressed and cystic fibrosis patients. The therapeutic options to treat S. maltophilia infections are limited since it exhibits resistance to a wide variety of antibiotics such as β-lactams, aminoglycosides, tetracyclines, cephalosporins, macrolides, fluoroquinolones, or carbapenems. The antibiotic combination trimethoprim/sulfamethoxazole (SXT) is the treatment of choice to combat infections caused by S. maltophilia, while ceftazidime, ciprofloxacin, or tobramycin are used in most SXT-resistant infections. In the current study, experimental evolution and whole-genome sequencing (WGS) were used to examine the evolutionary trajectories of S. maltophilia towards resistance against tobramycin, ciprofloxacin, and SXT. The genetic changes underlying antibiotic resistance, as well as the evolutionary trajectories toward that resistance, were determined. Our results determine that genomic changes in the efflux pump regulatory genes smeT and soxR are essential to confer resistance to ciprofloxacin, and the mutation in the rplA gene is significant in the resistance to tobramycin. We identified mutations in folP and the efflux pump regulator smeRV as the basis of SXT resistance. Detailed and reliable knowledge of ciprofloxacin, tobramycin, and SXT resistance is essential for safe and effective use in clinical settings. Herein, we were able to prove once again the extraordinary ability that S. maltophilia has to acquire resistance and the importance of looking for alternatives to combat this resistance.

The relationship between integrons, antibiotic resistance genes and SXT resistance in Shigella flexneri strains.

To investigate the correlation between sulfamethoxazole-trimethoprim (SXT) resistance in Shigella flexneri (S.flexneri) and the presence of integrons and relevant antibiotic resistance genes. We collected 115 strains of Shigella flexneri isolated from feces of children with diarrhea in Jinan from 2012 to 2020 and determined the minimum inhibitory concentration (MIC) of SXT by Etest method. The presence of class 1, class 2, and class 3 integron genes, variable region antibiotic resistance gene cassettes, and sul1, sul2, sul3, and SXT elements were detected using polymerase chain reaction (PCR). Positive results were further analyzed by DNA sequencing and BLAST comparison. In total, the resistance rate to SXT was 60.9% among the 115 S.flexneri strains. The prevalence of class 1 and class 2 integrons were 88.7% and 87.0%, respectively, with no class 3 integrons detected. Among the strains, 13.0% carried typical class 1 integrons with variable region antibiotic resistance gene cassettes dfrA17-aadA5 and dfrV, while 85.2% carried atypical class 1 integrons with variable region antibiotic resistance gene cassette blaoxa-30-aadA1. The variable region antibiotic resistance gene cassettes of class 2 integrons were all dfrA1+sat1+aadA1. There was a statistical difference between the presence of class 1 integrons and class 2 integrons between the SXT-sensitive and resistant S.flexneri strains (χ2=22.800, χ2=16.365, P<0.01, P<0.01). Integrons carrying dfrV and dfrA1 by integrons also showed a statistical difference in SXT resistance (χ2=9.422, χ2=16.365, P<0.01, P<0.01). PCR revealed the presence of sul1 and sul2 in 13.0% and 47.0% of strains, respectively, with neither sul3 nor SXT elements detected. There was a significant difference between the presence of sul1, sul2 between the SXT-sensitive and resistant S.flexneri strains (χ2=9.588, χ2=65.445, P<0.01, P<0.01). In summary, integrons are involved in SXT resistance of S.flexneri, and dfrV, dfrA1, sul1, sul2 are closely related to SXT resistance of S.flexneri.

Antibiotic profiles of Shigella and emergence of resistance: An editorial perspective

Between January 2008 and February 2009, the isolation rate of Shigella at St. Christopher’s Hospital for Children increased from 0.37% for a 6-month period (Jan - June 2008) to 7.3% for the month of February 2009. This has provided us with the rare opportunity to assess the antimicrobial characteristics of Shigella in our local area. Tabulation of antimicrobial profiles of all isolates revealed that most were resistant to ampicillin (90%) and some (26%) were resistant to trimethoprim-sulfamethoxazole (SXT). All remained susceptible to ciprofloxacin, which, unfortunately, is not always useful for treatment in pediatric patients. Studies in countries where Shigella is endemic reflect emerging resistance to SXT, mecillinam, azithromycin, ceftriaxone, and cefixime. Studies performed at a 10-year interval in an endemic area, showed an increase in SXT resistance of 20% and an increase in nalidixic acid resistance (as a marker for ciprofloxacin resistance) of 32%.1,2 Our new reporting scheme – SXT, ciprofloxacin (tested along with nalidixic acid as a screen for resistance), amoxicillin/clavulinate, and ceftriaxone - reflects the current trends, both locally and globally, in useful antimicrobial profiles for this organism.

Comparative genomics of trimethoprim-sulfamethoxazole-resistant Achromobacter xylosoxidans clinical isolates from Serbia reveals shortened variant of class 1 integron integrase gene.

Trimethoprim-sulfamethoxazole (SXT) is the preferable treatment option of the infections caused by Achromobacter spp. Our study aimed to analyze the SXT resistance of 98 Achromobacter spp. isolates from pediatric patients, among which 33 isolates were SXT-resistant. The presence of intI1 was screened by PCR and genome sequence analyses. The intI1 gene was detected in 10 of SXT-resistant isolates that had shorter intI1 PCR fragments named intI1S. Structural changes in intI1S were confirmed by genome sequencing and analyses which revealed 86 amino acids deletion in IntI1S protein compared to canonical IntI1 protein. All IntI1S isolates were of non-CF origin. Pan-genome analysis of intI1S bearing A. xylosoxidans isolates comprised 9052 genes, with the core genome consisting of 5455 protein-coding genes. Results in this study indicate that IntI1S isolates were derived from clinical settings and that cystic fibrosis (CF) patients were potential reservoirs for healthcare-associated infections that occurred in non-CF patients.

Whole-genome sequencing-based prediction and analysis of antimicrobial resistance in Yersinia enterocolitica from Ningxia, China.

Focusing on resistance trends and transmission patterns of pathogenic microorganisms is a major priority for national surveillance programs. The use of whole-genome sequencing for antimicrobial susceptibility testing (WGS-AST) is a powerful alternative to traditional microbiology laboratory methods. Yersinia enterocolitica antimicrobial resistance (AMR) in the Ningxia Hui Autonomous Region has yet to be described thoroughly in current studies. We assessed and monitored the development of Y. enterocolitica AMR in the Ningxia Hui Autonomous Region during 2007–2019 based on WGS-AST. Resistance genotypes were predicted based on WGS. Antimicrobial resistance testing using classical microbiology determined resistance to 13 antimicrobial agents in 189 Y. enterocolitica isolates from Ningxia. The highest resistance level was 97.88% for cefazolin, followed by ampicillin (AMP) (44.97%), ciprofloxacin (CIP) (25.40%), streptomycin (STR) (11.11%), and tetracycline (TET) (10.58%). Isolates emerged as chloramphenicol (CHL) and trimethoprim/sulfamethoxazole (SXT) resistant. The primary plasmid types were IncFII(Y) and ColRNAI. The TET, STR, and SXT resistance were mediated by the tetA, aph(6)-Id, aph(3″)-Ib, and sul2 genes located on the IncQ1 plasmid. The resistant strains were predominantly biotype 4/O:3/ST429 and the hosts were pigs and patients. The number of multidrug-resistant (MDR) strains was of concern, at 27.51%. At present, the prediction of antimicrobial resistance based on WGS requires a combination of phenotypes. From 2007 to 2019, Y. enterocolitica isolates from the Ningxia Hui Autonomous Region showed a relatively high rate of resistance to cefazolin (CZO) and some resistance to AMP, CIP, STR, and TET. CIP, SXT, and TET showed a relatively clear trend of increasing resistance. Plasmids carrying multiple drug resistance genes are an important mechanism for the spread of antimicrobial resistance. Isolates with low pathogenicity were more likely to present an AMR phenotype than non-pathogenic isolates.

Complete genome sequencing of transposon-mediated sulfamethoxazole resistance encoded by the Sul1 gene in multidrug-resistant Nocardia farcinica SZ 1509

The objective of this study is to explore the molecular basis of trimethoprim-sulfamethoxazole (SXT) resistance in Nocardia, an SXT-resistant N. farcinica strain, named SZ 1509, by whole-genome sequencing. Antimicrobial susceptibility testing of SZ 1509 was performed by broth microdilution, Etest, and disk diffusion arrays. Genome sequencing and analysis were performed to discover the SXT resistance determinant and its genetic context. Inverse PCR was conducted to confirm the circular form of the composite transposon. PCR for the sul1 gene was performed among SXT-susceptible isolates. SZ 1509 is resistant to many drugs, especially SXT, with a minimum inhibitory concentration (MIC) of up to 32/608 µg/mL (ratio of 1:19 for trimethoprim: sulfamethoxazole). Its assembled genome consists of one chromosome and four plasmids with a total size of 6 613 629 bp and 71.1% of GC content. The plasmid 2 was found to carry one IS6-composite transposon containing IS6100 carrying the sul1 gene, one tellurite resistance gene TerC, and several transcriptional regulators. Inverse PCR analyses showed its circular form. All 10 SXT-susceptible isolates do not contain sul1. In addition, mutations with strong associations to SXT resistance were not conclusive. This is the first study to elucidate the transposon-mediated sulfamethoxazole resistance in N. farcinica. Our results provide insights on acquired drug resistance of N. farcinica and further suggest that the prevalence and correlation of this resistance's determinants in clinical isolates should be continuously monitored to provide effective clinical management of its resultant diseases.

Phenotypic Detection of Hemin-Inducible Trimethoprim-Sulfamethoxazole Heteroresistance in Staphylococcus aureus.

ABSTRACTTrimethoprim-sulfamethoxazole (SXT) is a valuable second-line antimicrobial agent to treat methicillin-resistant Staphylococcus aureus infections. Discrepancies between various antibiotic susceptibility testing (AST) methods for SXT susceptibility in S. aureus have been described. Here, we describe a hemin-inducible heteroresistance phenotype in S. aureus. We compared the results of the Vitek 2 AST on a set of 95 S. aureus clinical isolates with broth microdilution, disk diffusion using standard Mueller-Hinton agar, and disk diffusion using Mueller-Hinton agar supplemented with 5% horse blood (MHF). To investigate the potential clinical relevance of SXT heteroresistance, an in vivo Galleria mellonella infection assay was performed. All Vitek 2 SXT-susceptible (n = 17) isolates were concordant with AST results by other methods applied in this study. In 32/78 (41%) of Vitek 2 SXT-resistant isolates, we observed a heteroresistant growth phenotype on MHF. The heteroresistance phenotype was associated with the presence of dfr genes, encoding trimethoprim resistance. The addition of a hemin-impregnated disk in a double disk diffusion method on standard Mueller-Hinton agar was able to induce growth in the SXT zone of inhibition. An in vivo infection assay with G. mellonella suggested that the SXT heteroresistance phenotype resulted in lethality similar to that of the SXT-resistant phenotype. In this study, we describe a novel hemin-inducible heteroresistance phenotype in S. aureus. This heteroresistance phenotype may be missed by standard AST methods but can be detected by performing disk diffusion using Mueller-Hinton agar supplemented with 5% horse blood, commonly used for AST of fastidious organisms. This phenomenon may partly explain the discrepancies of AST methods in determining SXT resistance in S. aureus.IMPORTANCE Staphylococcus aureus is one of most important pathogens in clinical medicine. Besides its virulence, the acquisition or emergence of resistance toward antibiotic agents, in particular to beta-lactam antibiotics (methicillin-resistant S. aureus [MRSA]), poses a major therapeutic challenge. Trimethoprim-sulfamethoxazole (SXT) is one of the effective antimicrobial agents of last resort to treat MRSA infections. Here, we report the detection of a SXT-heteroresistant phenotype which is inducible by hemin and can be detected using Mueller-Hinton agar supplemented with horse blood. Heteroresistance describes the presence or emergence of resistant subpopulations, which may potentially lead to inaccurate antibiotic susceptibility testing results and influence the success of antibiotic therapy.

Interplay between Phenotypic Resistance to Relevant Antibiotics in Gram-Negative Urinary Pathogens: A Data-Driven Analysis of 10 Years’ Worth of Antibiogram Data

The global emergence of antimicrobial resistance (AMR) has become a critical issue for clinicians, as it puts the decades of developments in the medical field in jeopardy, by severely limiting the useful therapeutic arsenal of drugs, both in nosocomial and community-acquired infections. In the present study, a secondary analysis of taxonomic and resistance data was performed, corresponding to urinary tract infections (UTIs) caused by Gram-negative bacteria, detected between 1 January 2008 to 31 December 2017 at the Albert Szent-Györgyi Health Center, University of Szeged. The following were identifiable from the data collected: year of isolation; outpatient (OP)/inpatient (IP) origin of the isolate; taxonomy; and susceptibility/resistance to selected indicator antibiotics. Principal component analysis (PCA) and a correlation matrix were used to determine the association between the presences of resistance against indicator antibiotics in each taxonomic group. Overall, data from n = 16,240 outpatient and n = 13,964 inpatient Gram-negative UTI isolates were included in the data analyses. In E. coli, strong positive correlations were seen between resistance to ciprofloxacin (CIP) and gentamicin (GEN) resistance (OP: r = 0.6342, p = 0.049; IP: r = 0.9602, p < 0.001), whereas strong negative correlations were shown for fosfomycin (FOS) and nitrofurantoin (NIT) resistance (OP: r = −0.7183, p = 0.019; IP: r = −0.7437; p = 0.014). For Klebsiella spp. isolates, CIP resistance showed strong positive correlation with resistance to third-generation cephalosporins (3GC) and GEN (r = 0.7976, p = 0.006 and r = 0.7428, p = 0.014, respectively) in OP isolates, and with resistance to trimethoprim-sulfamethoxazole (SXT) and FOS (r = 0.8144, p = 0.004 and r = 0.7758, p < 0.001, respectively) in IP isolates. For members of the Citrobacter-Enterobacter-Serratia group, the resistance among indicator antibiotics showed a strong positive correlation, with the exception of FOS resistance. In the Proteus-Providencia-Morganella group, the strongest association was noted between CIP and SXT resistance (OP: r = 0.9251, p < 0.001; IP: r = 0.8007; p = 0.005). In the case of OP Acinetobacter spp., CIP showed strong and significant positive correlations with most indicator antibiotics, whereas for IP isolates, strong negative correlations arose among imipenem (IMI) resistance and resistance to other drugs. For Pseudomonas spp., strong and positive correlations were noted among resistance to β-lactam antibiotics and aminoglycosides, with the exception of ceftazidime (CEFT), showing strong, but negative correlations. Though molecular tests and sequencing-based platforms are now considered as the gold-standard for AMR surveillance, standardized collection of phenotypic resistance data and the introduction of Big Data analytic methods may be a viable alternative for molecular surveillance, especially in low-resource settings.

Molecular characterization and improved diagnostics of Nocardia strains isolated over the last two decades at a German tertiary care center.

Nocardiosis is a rare but life-threatening infection caused by aerobic Actinomycetes of the genus Nocardia particularly affecting immunocompromised hosts. The identification of Nocardia ssp. and antibiotic susceptibility testing by standard microbiological methods are incomplete and molecular techniques may improve diagnostics. We studied 39 Nocardia strains isolated from 33 patients between 2000 and 2018. Twenty-four patients (72.7 %) were immunocompromised. Whole genome sequencing (WGS) revealed a broad taxonomic range of those isolates spanning 13 different species, including four strains that belonged to three novel species based on average nucleotide identity (ANI < 95 % with currently available genome sequences). 16S rRNA gene analyses mirrored WGS results. Conventional MALDI-TOF analysis correctly identified 29 isolates at the species level (74.4 %). Our advanced protocol with formic acid and acetonitrile treatment increased identification to 35 isolates (89.7 %). Antibiotic resistance was tested using both a microdilution method and MIC strip testing. Results were in good concordance with an overall trimethoprim-sulfamethoxazole (SXT) resistance rate of 13.5 %. WGS of a SXT resistant N. farcinica isolate showed a deletion of several amino acids in a homolog of dihydropteroate synthase (FolP2) that was not seen in sensitive members of this species. Diversity of Nocardia isolates was high and involved many different species, suggesting that this taxon has broadly distributed mechanisms for infecting individuals. Widely applicable diagnostic methods including MALDI-TOF and 16S rRNA gene analyses correctly identified most strains. WGS additionally revealed molecular insights into SXT resistance mechanisms of clinical Nocardia isolates highlighting the potential application of (meta)genomic-based diagnostics in the future.

Antimicrobial Resistance and Molecular Characterization of Class 1 Integron in Salmonella Isolates Recovered from Pig Farms in Chongqing, China.

Salmonella is considered one of the leading causes for foodborne diseases in humans. Pork and its products contaminated with Salmonella are increasingly recognized as an important source of human salmonellosis. The aim of this study was to investigate the antimicrobial resistance and prevalence of integrons in Salmonella isolates from pig farms. In total, 92 of 724 (12.7%) samples were Salmonella-positive, including 64 (15.0%) from fecal samples, 27 (12.6%) from floor samples, 1 (4.5%) from water samples, and 0 from feed and air samples. These isolates showed the highest resistance to tetracycline (85.9%), followed by trimethoprim (67.4%), ampicillin (60.9%), and chloramphenicol (51.1%). In addition, 51 isolates carried the complete class 1 integron, most of which (42/51) harbored antibiotic resistance cassettes. A total of six gene cassettes including orfF, est-X, dfrA1+aadA1, aadA1, dfrA12+aadA2, and sat were identified, in which the most prevalent one was orfF (29.4%). Furthermore, all 19 class 1 integron-positive isolates harboring dfr genes showed resistance to trimethoprim (SXT), suggesting that the trimethoprim resistance gene (dfr) may contribute to the emergence of SXT resistance phenotype. Therefore, considering the significance of integrons and related resistance genes for public health, special measures should be taken to control Salmonella spp. on the pig farms and to prevent spread of integrons and associated resistance genes.

Panton-Valentine leukocidin–positive Staphylococcus aureus in skin and soft tissue infections from primary care patients

ObjectivesTo characterize deep skin and soft tissue infections (dSSTI) caused by Panton-Valentine leukocidin (PVL)-positive versus PVL-negative Staphylococcus aureus isolates. MethodsWe performed a retrospective analysis of patients' records including S. aureus isolates from outpatients with dSSTI. Samples had been submitted by primary care physicians, i.e. general practitioners, surgeons, dermatologists and paediatricians, located in Berlin, Germany, in 2007–2017. Bacterial isolates were identified and tested for antimicrobial susceptibility by VITEK 2; PVL was detected by PCR. ResultsIn total, 1199 S. aureus isolates from 1074 patients with dSSTI were identified, and 613 (51.1%) of 1199 samples were PVL+. The median age of patients with PVL+S. aureus was lower than in patients with PVL− S. aureus (34 years, range 0–88 years, vs. 44 years, range 0–98 years; p < 0.0001). PVL was associated with repeated/multiple samples compared to single sample submission (69/92, 75% vs. 448/982, 45.6%, p < 0.0001; odds ratio (OR), 3.6; 95% confidence interval (CI), 2.2–5.8). Interestingly, the highest PVL positivity rate was found in isolates from gluteal (82/108, 75.9%; OR, 3.6; 95% CI, 2–5) or axillary (76/123, 61.8%; OR, 2; 95% CI, 1.1–3.3) localizations compared to isolates from the arm. The PVL positivity rate did not increase over time. Yet we noticed an increase in the trimethoprim/sulfamethoxazole (SXT) resistance rate in PVL+ isolates, mainly methicillin-sensitive S. aureus, when considering SXT resistance rates of 2007–2012 versus 2013–2017 (35/226, 15.5% vs. 74/289, 25.6%; p 0.01). ConclusionsIn outpatients, gluteal and axillary dSSTI are indicative of PVL+S. aureus. Providing SXT as a complementary treatment for dSSTI should be based on susceptibility testing.

Prediction of trimethoprim/sulfamethoxazole resistance in community-onset urinary tract infections

ObjectivesThis study aimed to predict trimethoprim/sulfamethoxazole (SXT) resistance in patients with community-onset urinary tract infection (UTI) due to Enterobacteriaceae based on patient-specific risk factors. MethodsThis was a retrospective case–control study in Prisma Health facilities in central South Carolina, USA, including three community hospitals, affiliated emergency departments and ambulatory clinics, including adult patients with community-onset UTI due to Enterobacteriaceae (1 April 2015 to 29 February 2016). Multivariate logistic regression was used to examine risk factors for SXT resistance. ResultsAmong 351 unique patients with community-onset UTI, 71 (20.2%) had SXT-resistant Enterobacteriaceae urinary isolates. Overall, median age was 64 years and 252 (71.8%) were female. A multivariate model identified prior urinary infection/colonisation with SXT-resistant Enterobacteriaceae (OR=8.58, 95% CI 3.92–18.81; P<0.001) and SXT use within past 12 months (OR=2.58, 95% CI 1.13–5.89; P=0.02) as predictors of SXT resistance among urinary isolates. Most patients with UTI (285; 81.2%) had no risk factors for SXT resistance. SXT resistance rates increased from 13% in the absence of risk factors to 31% in patients with prior SXT use, 66% in those with prior urinary infection/colonisation with SXT-resistant Enterobacteriaceae and 73% in the presence of both risk factors. ConclusionSXT resistance in Enterobacteriaceae urinary isolates may be predicted based on prior urine culture results and SXT use within the previous year. Utilisation of a patient-specific antibiogram may allow empirical SXT use in patients with community-onset UTI in the absence of risk factors for resistance.

1144. Modern Problem, Medieval Cure-Resistant Aeromonas in Medicinal Leeches

BackgroundMedicinal leeches are used primarily in plastic and reconstructive surgery when venous congestion threatens tissue viability. The associated infection risk ranges from 4.1 to 20%. Prophylactic antimicrobials such as fluoroquinolones (FQ) or trimethoprim-sulfamethoxazole (SXT) are recommended and target commonly isolated pathogen and gut symbiont, Aeromonas. However, resistance to these agents has been reported and detected in leeches, including at hospital systems across Canada that acquire their stock from the same supplier. Our objective was to describe the local epidemiology of leech-related Aeromonas resistant to one or more commonly used prophylactic agents, and determine if such resistance originates from the common supplier.MethodsSix hospital systems across Canada using leech therapy, purchased from the same supplier, were surveyed. A 5-year retrospective review of all antimicrobial resistant leech-related Aeromonas, derived from clinical, leech, and tank fluid specimens was performed. All Aeromonas resistant to either FQ or SXT were included, and retained frozen isolates from each system were analysed by pulse-field gel electrophoresis (PFGE) using a published Aeromonas protocol.ResultsAll six hospital systems reported leech-related Aeromonas resistant to one or more antimicrobials, totalling 15 isolates. Three systems only reported data from the last year. Four systems used FQ and two used SXT as prophylaxis. Fifteen of 15 were either FQ resistant or intermediate, and four of 15 were SXT resistant. Three of 10 isolates tested for ceftriaxone (CRO) susceptibility were resistant. Five of 15 of the isolates were resistant to two or more agents. Of the two leech quality control isolates, 2/2 were FQ resistant and 1/2 was FQ, SXT and CRO resistant. Only three isolates, each from a different, geographically distinct hospital system, had been retained. PFGE analysis indicated 2/3 are closely related (Figure 1).ConclusionOur preliminary investigation suggests that the presence of FQ and SXT resistance in leech-related Aeromonas might be more common than previously suspected, and that such resistance might originate from a common source. A broader study of the molecular epidemiology of leech-related Aeromonas is warranted. Disclosures All authors: No reported disclosures.

Risk factors and molecular mechanisms associated with trimethoprim-sulfamethoxazole resistance in Stenotrophomonas maltophilia in Mexico.

Stenotrophomonas maltophilia is a multidrug-resistant opportunistic pathogen causing an increasing number of nosocomial infections. Our aim was to evaluate the risk factors and mechanisms associated with trimethoprim-sulfamethoxazole (SXT) resistance in S. maltophilia infections in Mexico. Clinical isolates and patients' demographic and clinical data were collected from February 2007 to August 2015 in two tertiary-care hospitals in Mexico. Antimicrobial susceptibility and analysis of sul and SmeABC and SmeDEF efflux pump overexpression were performed in all isolates.Results/Key findings. In the 9-year period, 196 patients infected with S. maltophilia were identified. Most patients were male, and the mean age was 46.2 years. The mean Charlson score was 1.42, and the most frequent comorbidities were arterial hypertension (26.7 %), type 2 diabetes (21.2 %) and cerebral infarction (11.6 %). High drug resistance to meropenem (93.4 %), gentamicin (55.1 %), ceftazidime (52.3 %), cefotaxime (51.5 %), amikacin (42.3 %) and cefepime (32.1 %), and lower resistance to ciprofloxacin (26.0 %), SXT (25.0 %), chloramphenicol (14.3 %) and levofloxacin (2.6 %) were detected. SXT resistance was not associated with the sul genes. SmeABC overexpression was associated with gentamicin (P=0.001) and levofloxacin resistance (P=0.041), whereas SmeDEF overexpression was associated with ceftazidime resistance (P=0.003). Prolonged hospitalization (≥15 days) was an independent risk factor for SXT-resistant S. maltophilia infections (OR=3.05; 95 % CI=1.12-8.86; P=0.029). Given the high SXT resistance rate, SXT is not an effective first-line therapy for our patients; instead, levofloxacin could be used as an appropriate therapeutic option against S. maltophilia infections.

Stenotrophomonas maltophilia in a university hospital of traditional Chinese medicine: molecular epidemiology and antimicrobial resistance

Stenotrophomona maltophilia has emerged as an important opportunistic pathogen that is highly antibiotic resistant. Analysis of antibiotic susceptibilities, drug-resistant gene profiles and molecular typing of S. maltophilia was undertaken in a university hospital of traditional Chinese medicine in East China. Resistance to sulphamethoxazole (SXT) was found to be an indicator of multi-drug resistance. SXT resistance was mediated by sul and dfrA genes in integrons, especially class 1. Some evidence of clonal dissemination was found, indicating the occurrence of cross-transmission of antibiotic-resistant strains within the hospital. This underscores the need for effective control and prevention measures in hospitals.

Molecular Characterization of Trimethoprim Sulpha - Methoxazole Resistant Stenotrophomonas Maltophilia at Sohag University Hospital

Background: Stenotrophomonas maltophilia (S. maltophilia) is an opportunistic human pathogen that is intrinsically multidrug resistant causing serious infections in humans and its emerged resistance to trimethoprim-sulfamethoxazole (SXT) is worldwide reported. Objectives : This work aimed to determine the occurrence of SXT resistance among S. maltophilia isolated from Sohag University Hospitals and to assess the association of sul genes with SXT-resistant isolates. Methodology : This study carried during the period from December 2015 to November 2016 in the microbiology laboratory of Sohag University Hospital on 65 Stenotrophomonas maltophilia isolates collected from 380 inpatients samples admitted to the Intensive care units (ICUs) of Sohag university hospital through this period. Identification and antibiotic susceptibility of S. maltophilia was done by the Vitek- 2 colorimetric compact system (bioMerieux, France) then multiplex PCR was done to detect the presence of SUL1, SUL2, SUL3 genes in the isolates. Results : Among the 65 S. maltophilia isolates, 17(26.2%) were resistant to SXT. All SXT-resistant isolates were found to harbor sul1 gene (17/17, 100%), one of these isolates had sul2 gene (1/17,5.9%). Only 2 of the 48 SXT-susceptible isolates were found to yield positive PCR results for sul genes, one of them gave positive result for SUL1(1/48,2%) the other for SUL2 (1/48, 2%) genes. Meanwhile, sul3 gene was not detected in any of the isolates. Conclusions : Our study reported that S. maltophila is among the common causes of infections occurring in the ICUs of Sohag university hospital specially those of the respiratory tract. Presence of SXT resistance among clinical S. maltophilia isolates from Sohag University Hospital, in which sul1 gene was found to have a major role. Tigecycline and levofloxacin are the antimicrobials of choice for treatment of infections caused by S. maltophilia.

Increase in the Prevalence of Resistance Determinants to Trimethoprim/Sulfamethoxazole in Clinical Stenotrophomonas maltophilia Isolates in China.

AimsThis study was carried to reveal the genetic mechanisms of trimethoprim/sulfamethoxazole (SXT) resistance.MethodsAmong 300 clinical Stenotrophomonas maltophilia isolates from China, resistance determinants such as sul and dfrA genes, integrons and transposase were examined using PCR, DNA sequencing and thermal asymmetric interlaced PCR (TAIL-PCR). Data were analyzed using SPSS 20.0.ResultsOf the 300 isolates, 116 (38.7%) were resistant to SXT. An alarming trend of increased resistance to SXT were found over the 10-year period. The positive rates of sul and class 1 integrase (intI1) increased gradually with the development of SXT resistance over the 10-year period. Multiple logistic regression analyses indicated that the genes of qacEΔ1-sul1 (81% vs 46.2%, p = 0.000), sul2 (50.9% vs 9.8%, p = 0.000), intI1 (83.6% vs 65.8%, p = 0.000), dfrA12 (25% vs 3.3%, p = 0.000), dfrA17 (15.5% vs 3.8%, p = 0.000) and dfrA27 (4.3% vs 1.6%, p = 0.01) were more prevalent in SXT-resistant isolates than SXT-susceptible isolates except dfrA1(p = 0.83) and dfrA5(p = 0.18). Sequencing data revealed 12 types of resistance gene cassettes (aar-3-dfrA27, dfrA12–aadA2, dfrA17–aadA5, cmlA1, aacA4, aadA5, arr-3-aacA4, aadA1, aadB–aadA4, aacA4–catB8–aadA1, aadB–aac(6′)-II–blaCARB-8 and aac(6′)-II–blaCARB-8) located in the class 1 integron in 163 isolates (87% SXT-resistant vs 33.7% SXT-susceptible isolates, p = 0.000). A novel finding was the aar-3-dfrA27 (KC748137) gene cassette. The gene of sul2 linked to transposase in 50 SXT- resistant and 7 SXT- susceptible isolates was detected by TAIL-PCR.ConclusionsThe findings demonstrated a higher prevalence of sul, dfrA, intI1 and resistance gene cassettes in class 1 integron in SXT-resistant clinical S. maltophilia isolates in China. The sul1 and dfrA genes located in integrons and the sul2 linked to transposase may imply wide and rapid dissemination of resistance gene in bacteria.

Association of &lt;i&gt;sul&lt;/i&gt; genes and class 1 integron with trimethoprimsulfamethoxazole Resistance in &lt;i&gt;Stenotrophomonas maltophilia&lt;/i&gt; clinical isolates in Zagazig University, Egypt

Background : Stenotrophomonas maltophilia (S.maltophilia) is an intrinsically drug resistant opportunistic pathogen associated with serious infections in humans. Acquired resistance to trimethoprim-sulfamethoxazole (SXT,co-trimoxazole), the main stay of therapy against S. maltophilia ,has made its treatment more problematic. Objectives: This work aimed to determine the occurrence of SXT resistance among S. maltophilia isolated from Zagazig University Hospitals in Egypt and to assess the association of sul genes and integron1 with SXT-resistant isolates. Material and Methods : Thirty-two S.maltophilia isolates were identified in this study during the period from 2013 to 2015. Screening of SXT-resistant isolates was done by Kirby-Bauer method. Minimum inhibitory concentration(MIC) values for SXT were determined by agar dilution. S. maltophilia isolates were tested for the presence of sul1, sul2, sul3, and int 1 genes by multiplex polymerase chain reaction. Results : Amongst the 32 S. maltophilia isolates, 12(37.5%) were resistant to SXT. All SXT-resistant isolates were found to harbor sul1 gene and integron1. One of these isolates had sul2 gene (1/12,8.3%). Meanwhile, sul3 gene was not detected in any of the SXT-resistant isolates. Only 2 of the 20 SXT-susceptible isolates was found to yield positive PCR results for sul1 gene, one of them gave positive result for class 1 Integron. The association of sul genes and Integrin1 with resistance to SXT had a statistically significant difference( P<0.0001). Conclusion: Our study indicated a high frequency of SXT resistance among clinical S.maltophilia isolates from Zagazig University Hospitals, in which sul genes and class 1 integron were found to have a major role. Keywords : Stenotrophomonas maltophilia ; Sulphamethoxazole-trimethoprim-resistant; Multiplex PCR; sul genes; Integron 1

Analysis of Integron-associated Gene Cassettes in Clinical Acinetobacter Calcoaceticus-Baumannii Complex Isolates from Central Taiwan

Purpose: Acinetobacter calcoaceticus-baumannii complex (ABC) has become a major infectious pathogen in Taiwan, and mobile DNA such as integrons and transposons often contribute to its multiple antibiotic resistance characteristics. Methods: A clinical epidemiological study of the cassette contents of the class 1 integron of ABC isolates in two central Taiwan hospitals was performed. Results: It was found that 78% (39/50) of strains possessed the IntI1 integrase gene, while four major different sizes of class 1 integron cassette arrays were found: 3.0 kb (aacC1-ORF1-ORF2- ORF3-aadA1) (aacC1: aminoglycoside 3'-N-acetyltransferase; aadA1: aminoglycoside 3'-adenyltransferase), 2.5 kb (aacA4- catB8-aadA1) (aacA4: aminoglycoside 6'-N-acetyl-transferase), 2.0 kb (dhfrXII-ORF-aadA2) (dhfrXII: dihydrofolate reductase; aadA2: aminoacyl-adenyltransferase A) and 1.2 kb (dhfrAI-ORF) (dhfrAI: dihydrofolate reductase type AI). Six different combinations of cassette arrays were also noted. The co-relationships between antibiotic-resistant phenotypes and genotypic combinations of cassettes were analyzed. As the 2.5-kb cassette array was found to be the most common in this study, the flanking regions of the specific integron of ABC were also analyzed by inverse PCR. In addition to antibiotic resistance genes, such as aphA1 (kanamycin resistance gene) (AphA1: aminoglycosidephosphotransferase), the transposase gene (tnpIS15/tnpAIS26) was found in the 2.5-kb cassette array flanking regions. Furthermore, PCR-RFLP confirmed that these flanking regions were conserved in all of the examined isolates. Conclusion: The SXT and GM resistance phenotypes of ABC isolates could be used in clinical screening for the IntI1- associated genotype. ABC isolates that carry a 2.5-kb cassette array have become dominant in Central Taiwan, and dissemination of this specific type of integron may derive from the involvement of mobile DNA.

Biofilm formation in trimethoprim/sulfamethoxazole-susceptible and trimethoprim/sulfamethoxazole-resistant uropathogenic Escherichia coli

ObjectiveTo compare biofilm formation in trimethoprim/sulfamethoxazole (SXT)-susceptible Escherichia coli (E. coli) (SSEC) and SXT-resistant E. coli (SREC) isolated from patients with urinary tract infections, and study the motile ability and physical characteristics of the isolates. MethodsA total of 74 E. coli isolates were tested for antimicrobial susceptibility with the disc diffusion assay. Based on the SXT-susceptibility test, the E. coli isolates were divided into SSEC (N = 30) and SREC (N = 44) groups. All E. coli isolates were examined for motile ability by using a motility test medium, and for checking biofilm formation a scanning electron microscope was used. Bacterial colony size was measured with a vernier caliper and bacterial cell length was measured under a light microscope. The bacterial growth rate was studied by plotting the cell growth (absorbance) versus the incubation time. ResultsThe frequencies of non-motility and biofilm formation in the SREC group were significantly higher than that in the SSEC group (P < 0.01). The SREC bacterial cell length was shorter than that in the SSEC group [(1.35 ± 0.05) vs. (1.53 ± 0.05) μm, P < 0.05)], whereas the bacterial colony size and mid-log phase of the growth curve were not significantly different. ConclusionsThe present study indicated that biofilm formation and phenotypic change of uropathogenic E. coli can be attributed to the mechanism of E. coli SXT resistance.