Global emergence of trimethoprim/sulfamethoxazole resistance in Stenotrophomonas maltophilia mediated by acquisition of sul genes

Comparative Genomics of Environmental and Clinical Stenotrophomonas maltophilia Strains with Different Antibiotic Resistance Profiles

Stenotrophomonas maltophilia, a ubiquitous Gram-negative γ-proteobacterium, has emerged as an important opportunistic pathogen responsible for nosocomial infections. A major characteristic of clinical isolates is their high intrinsic or acquired antibiotic resistance level. The aim of this study was to decipher the genetic determinism of antibiotic resistance among strains from different origins (i.e., natural environment and clinical origin) showing various antibiotic resistance profiles. To this purpose, we selected three strains isolated from soil collected in France or Burkina Faso that showed contrasting antibiotic resistance profiles. After whole-genome sequencing, the phylogenetic relationships of these 3 strains and 11 strains with available genome sequences were determined. Results showed that a strain's phylogeny did not match their origin or antibiotic resistance profiles. Numerous antibiotic resistance coding genes and efflux pump operons were revealed by the genome analysis, with 57% of the identified genes not previously described. No major variation in the antibiotic resistance gene content was observed between strains irrespective of their origin and antibiotic resistance profiles. Although environmental strains generally carry as many multidrug resistant (MDR) efflux pumps as clinical strains, the absence of resistance-nodulation-division (RND) pumps (i.e., SmeABC) previously described to be specific to S. maltophilia was revealed in two environmental strains (BurA1 and PierC1). Furthermore the genome analysis of the environmental MDR strain BurA1 showed the absence of SmeABC but the presence of another putative MDR RND efflux pump, named EbyCAB on a genomic island probably acquired through horizontal gene transfer.

Sulfonamide Resistance Genes (sul) M in Extended Spectrum Beta Lactamase (ESBL) and Non-ESBL Producing Escherichia coli Isolated From Iranian Hospitals

Background:

Extensive use of cotrimoxazole has been associated with increasing level of Escherichia coli resistance.

Objectives:

In the current study, we focused on assessing the prevalence of E. coli resistance to cotrimoxazole and frequency of its associated genes.

Materials and Methods:

One-hundred and forty-four E. coli isolates were identified during March 2007 to April 2012 at Ilam hospitals and Milad (Tehran) hospital. Antibiotic susceptibility for screening of resistance isolates was done by the Kirby-Bauer method. The sul1, sul2, sul3, dfrA1, dfrA5, int1, blaTEM, blaSHV and CTX-M genes were detected by polymerase chain reaction (PCR) amplification. Plasmid curing was done for identifying correlations between resistance genes and plasmids.

Results:

Amongst the 144 E. coli isolates, seventy-two (50%) Extended Spectrum Beta Lactamase (ESBL)-producing and seventy-two (50%) non-ESBL-producing E. coli isolates were identified; eighty-seven isolates (60.41%) were resistant to cotrimoxazole. Frequencies of sul1, sul2 and sul3, were 81% (116 isolates), 67% (96 isolates) and 2.29% (three isolates), respectively. Furthermore, 50.57% (72 isolates) had sul1 and sul2, 2.29% (3 isolates) contained sul2 and sul3, and 2.29% (three isolates) contained sul1, sul2 and sul3 genes, simultaneously. Thirty-four (39.1%) of the isolates had the dfrA1 gene. Five (5.7%) of the isolates had the dfrA5 gene. Sixty-eight (78.2%) strains contained the int1 gene. Furthermore, dfrA1 and dfrA5 were present in three (3.4%) of the isolates. The results showed that of the ESBL-producing isolates, 85.2% (n = 122), 53.2% (n = 76) and 26.1% (n = 37) were blaTEM, blaSHV and CTX-M harboring isolates, respectively.

Conclusions:

Our study indicated a high frequency of cotrimoxazole resistance gene in E. coli isolates from Ilam and Tehran (Milad) hospitals, and sul genes had a major role in cotrimoxazole resistance of these isolates.

Antibiotic resistance in the opportunistic pathogen Stenotrophomonas maltophilia

Stenotrophomonas maltophilia is an environmental bacterium found in the soil, associated with plants and animals, and in aquatic environments. It is also an opportunistic pathogen now causing an increasing number of nosocomial infections. The treatment of S. maltophilia is quite difficult given its intrinsic resistance to a number of antibiotics, and because it is able to acquire new resistances via horizontal gene transfer and mutations. Certainly, strains resistant to quinolones, cotrimoxale and/or cephalosporins-antibiotics commonly used to treat S. maltophilia infections-have emerged. The increasing number of available S. maltophilia genomes has allowed the identification and annotation of a large number of antimicrobial resistance genes. Most encode inactivating enzymes and efflux pumps, but information on their role in intrinsic and acquired resistance is limited. Non-typical antibiotic resistance mechanisms that also form part of the intrinsic resistome have been identified via mutant library screening. These include non-typical antibiotic resistance genes, such as bacterial metabolism genes, and non-inheritable resistant phenotypes, such as biofilm formation and persistence. Their relationships with resistance are complex and require further study.

Molecular Detection of Genomic Islands Associated With Class 1 and 2 Integron in Haemophilus influenzae Isolated in Iran

Background:

High levels of multidrug resistance are usually associated with mobile genetic elements that encode specific resistance genes. Integrons are important genetic elements involved in spreading antibiotic multi-resistance. In special cases, large exogenous segments in bacterial genomes form genomic islands, and one of the functions of these genomic islands is antibiotic resistance. Due to geographical heterogeneity in antibiotic resistance pattern, it is mandatory to determine resistance patterns that are region-specific rather than generalized.

Objectives:

The objective of this study was to detect class 1 and 2 integrons in clinical isolates of Haemophilus influenzae.

Patients and Methods:

Antibiogram tests were carried out for twenty clinical isolates collected from different patients admitted to the Milad hospital. The PCR reactions were performed using universal primers specified for Int1 and Int2 genes attributed to class 1 and 2 integrons. Also amplification of integrase genes related to genomic islands was investigated by designing specific primers.

Results:

Of the twenty isolates, all (100%) were resistant to clindamycin, chloramphenicol and tetracycline, 95% to amoxicillin, 50% to ceftriaxone, 45% to ciprofloxacin and 5% to azithromycin. Also, all isolates (100%) were sensitive to trimethoprim/sulfamethoxazole. Class 1 and 2 integrons were not detected in any of the isolates; however the integrase gene attributed to genomic islands was identified in twelve isolates.

Conclusions:

Antibiotic resistance gene cassettes may be carried on integron or other genetic elements. The purpose of this study was to detect integron or genomic islands involved in antibiotic resistance profile of the isolates of H. influenzae collected in this study.

The SmeYZ efflux pump of Stenotrophomonas maltophilia contributes to drug resistance, virulence-related characteristics, and virulence in mice

The resistance-nodulation-division (RND)-type efflux pump is one of the causes of the multidrug resistance of Stenotrophomonas maltophilia. The roles of the RND-type efflux pump in physiological functions and virulence, in addition to antibiotic extrusion, have attracted much attention. In this study, the contributions of the constitutively expressed SmeYZ efflux pump to drug resistance, virulence-related characteristics, and virulence were evaluated. S. maltophilia KJ is a clinical isolate of multidrug resistance. The smeYZ isogenic deletion mutant, KJΔYZ, was constructed by a gene replacement strategy. The antimicrobial susceptibility, virulence-related physiological characteristics, susceptibility to human serum and neutrophils, and in vivo virulence between KJ and KJΔYZ were comparatively assessed. The SmeYZ efflux pump contributed resistance to aminoglycosides and trimethoprim-sulfamethoxazole. Inactivation of smeYZ resulted in attenuation of oxidative stress susceptibility, swimming, flagella formation, biofilm formation, and secreted protease activity. Furthermore, loss of SmeYZ increased susceptibility to human serum and neutrophils and decreased in vivo virulence in a murine model. These findings suggest the possibility of attenuation of the resistance and virulence of S. maltophilia with inhibitors of the SmeYZ efflux pump.

The sul1 gene in Stenotrophomonas maltophilia with high-level resistance to trimethoprim/sulfamethoxazole

Emerging resistance to trimethoprim/sulfamethoxazole (SXT) poses a serious threat to the treatment of Stenotrophomonas maltophilia infections. We determined the prevalence and molecular characteristics of acquired SXT resistance in recent clinical S. maltophilia isolates obtained from Korea. A total of 252 clinical isolates of S. maltophilia were collected from 10 university hospitals in Korea between 2009 and 2010. Antimicrobial susceptibility was determined by using the CLSI agar dilution method. The sul1, sul2, and sul3 genes, integrons, insertion sequence common region (ISCR) elements, and dfrA genes were detected using PCR. The presence of the sul1 gene and integrons was confirmed through sequence analysis. Among the 32 SXT-resistant isolates, sul1 was detected in 23 isolates (72%), all of which demonstrated high-level resistance (≥64 mg/L) to SXT. The sul1 gene (varying in size and structure) was linked to class 1 integrons in 15 of the 23 isolates (65%) harboring this gene. None of the SXT-susceptible isolates or the SXT-resistant isolates with a minimum inhibitory concentration of 4 and 8 mg/L were positive for sul1. Moreover, the sul2, sul3, and dfrA genes or the ISCR elements were not detected. The sul1 gene may play an important role in the high-level SXT resistance observed in S. maltophilia.

Identification and characterization of a serious multidrug resistant Stenotrophomonas maltophilia strain in China

An S. maltophilia strain named WJ66 was isolated from a patient; WJ66 showed resistance to more antibiotics than the other S. maltophilia strains. This bacteraemia is resistant to sulphonamides, or fluoroquinolones, while the representative strain of S. maltophilia, K279a, is sensitive to both. To explore drug resistance determinants of this strain, the draft genome sequence of WJ66 was determined and compared to other S. maltophilia sequences. Genome sequencing and genome-wide evolutionary analysis revealed that WJ66 was highly homologous with the strain K279a, but strain WJ66 contained additional antibiotic resistance genes. Further analysis confirmed that strain WJ66 contained an amino acid substitution (Q83L) in fluoroquinolone target GyrA and carried a class 1 integron, with an aadA2 gene in the resistance gene cassette. Homology analysis from the pathogen-host interaction database showed that strain WJ66 lacks raxST and raxA, which is consistent with K279a. Comparative genomic analyses revealed that subtle nucleotide differences contribute to various significant phenotypes in close genetic relationship strains.

Infection and colonization by Stenotrophomonas maltophilia: antimicrobial susceptibility and clinical background of strains isolated at a tertiary care centre in Hungary

BACKGROUND

Stenotrophomonas maltophilia is an important opportunistic, mainly nosocomial pathogen that emerged in the last decades worldwide. Due to its inherent extended antibiotic resistance, therapeutic options are strongly limited. New resistance mechanisms in S. maltophilia make antibiotic therapy even more difficult. The aim of our study was to investigate the antimicrobial resistance of S. maltophilia isolates collected in our laboratory and to reveal related clinical background.

METHOD

Consecutive non-duplicate S. maltophilia isolates (n = 160) were collected in a three-year period. Conventional methods, automated identification system and MALDI-TOF MS was used for identification, ERIC-PCR for genetic relationship analysis and broth microdilution method to determine the susceptibility for trimethoprim/sulfamethoxazole (SXT), ciprofloxacin, levofloxacin, moxifloxacin, colistin, doxycycline and tigecycline. Clinical final reports were used retrospectively to collect clinical information.

RESULTS

ERIC-PCR revealed large heterogeneity. Trimethoprim/sulfamethoxazole, moxifloxacin and levofloxacin were found to be the most effective agents with MIC50/MIC90 0.5/1, 0.25/1, 1/2 mg/l, respectively. Seventy percent of patients with S. maltophilia infection were treated in intensive care units. All-cause mortality rate was 45%. Nearly 70% of the isolates were collected from polymicrobial infections/colonizations.

CONCLUSIONS

Trimethoprim/sulfamethoxazole is the most potent antibiotic agent against S. maltophilia. In case of SXT hypersensitivity, intolerance or resistance, fluoroquinolones are alternative therapeutic options. Missing clinical breakpoints, consensus antibiotic susceptibility testing guidelines and clinical trials make the interpretation of antibiotic susceptibility testing results difficult. The indirect pathogenicity of S. maltophilia in polymicrobial infections or colonizations has to be taken into consideration.

Antibiogram of Stenotrophomonas maltophilia Isolated From Nkonkobe Municipality, Eastern Cape Province, South Africa

Background:

Assessment of resistance genes is imperative, as they become disseminated to bacterial flora in plants and to the indigenous bacterial community, and thus ultimately contributes to the clinical problems of antibiotic resistant pathogens.

Objectives:

The research was to assess the antibiotic characteristics and incidence of sul3 genes of Stenotrophomonas maltophilia isolates recovered from rhizospheres plant in Nkonkobe Municipality.

Materials and Methods:

Identification and assessment of resistance genes (sul2 and sul3 genes) were carried out using polymerase chain reaction (PCR). Analytical profile index (API) was used for biochemical characterization for identification before the PCR. Antibiotic susceptibility test was carried out using the approved guidelines and standards of Clinical Laboratory Standard Institute (CLSI).

Results:

A total of 125 isolates were identified, composed of 120 (96%) from grass root rhizosphere and 5 (4%) from soil butternut root rhizosphere. In vitro antibiotic susceptibility tests showed varying resistances to meropenem (8.9%), cefuroxime (95.6 %), ampicillin-sulbactam (53.9%), ceftazidime (10.7%), cefepime (29.3 %), minocycline (2.2%), kanamycin (56.9%), ofloxacin (2.9%), levofloxacin (1.3%), moxifloxacin (2.8%), ciprofloxacin (24.3%), gatifloxacin (1.3%), polymyxin B (2.9 %), cotrimoxazole (26.1%), trimethoprim (98.6%) and aztreonam (58%). The isolates were susceptible to the fluoroquinolones (74.3-94.7%), polymycin (97.1%) and meropenem (88.1%). The newest sulphonamide resistance gene, sul3, was detected among the trimethoprim-sulfamethoxazole (cotrimoxazole)-resistant isolates, while the most frequent sulphonamide-resistant gene in animal source isolates, sul2, was not.

Conclusions:

The commensal S. maltophilia isolates in the Nkonkobe Municipality environment harbored the resistant gene sul3 as clinical counterparts, especially from the perspective of reservoirs of antibiotic resistance determinants.

Stenotrophomonas maltophilia in Lower Respiratory Tract Infections

BACKGROUND

Stenotrophomonas maltophilia infection is gaining importance as an important cause of nosocomial pneumonia due to its characteristic inherent resistance to many broad- spectrum antibiotics. In this study we evaluated the demographic, clinical and microbiological profile of patients with lower respiratory tract infection due to Stenotrophomonas maltophilia.

MATERIALS AND METHODS

A retrospective analysis of 33 patients diagnosed with Stenotrophomonas maltophilia lower respiratory tract infections during a period of two years from 2012 - 2013 was done.

RESULTS

The predominant predisposing factor observed was mechanical ventilation in 17(51.5%) cases. Fluoroquinolones were the most effective antibiotic (26;78.8%) followed by trimethoprim-sulfamethoxazole (24;72.7%). Among the 19 patients treated with proper antibiotic, 13(68.4%) showed clinical improvement. Among the 14 patients who did not receive appropriate antibiotic for Stenotrophomonas maltophilia infection, 8(57.1%) showed improvement. Two (6%) had blood culture positive for Stenotrophomonas maltophilia. Mortality rate was 21.2%.

CONCLUSION

Stenotrophomonas maltophilia is emerging as an important nosocomial pathogen with increased risk in patients on mechanical ventilation in ICU. Empiric therapy should include agents active against S.maltophilia such as newer flouroquinolones and trimethoprim-sulfamethoxazole.

Characterization of a genomic island in Stenotrophomonas maltophilia that carries a novel floR gene variant

OBJECTIVES

To characterize the chromosomally encoded novel floR gene variant floRv from Stenotrophomonas maltophilia of porcine origin and elucidate the gene order and content of the floRv-flanking regions in an MDR genomic island (GI).

METHODS

Whole genome sequencing was used to identify the unknown florfenicol resistance gene in S. maltophilia strain GZP-Sm1. The candidate gene was cloned into pMD19-T and Escherichia coli transformants carrying this vector were tested for phenicol MICs. Flanking sequences of the florfenicol resistance gene were identified by a de novo assembly and a primer walking strategy.

RESULTS

GZP-Sm1 carried a floR gene variant, designated floRv. E. coli clones carrying this gene were resistant to chloramphenicol and florfenicol. The deduced 404 amino acid FloRv protein showed 84.1%-91.8% amino acid identity to various FloR proteins. The gene floRv was located in an MDR region within a 40 226 bp GI region. Six resistance genes, including floRv (phenicol resistance), tetR-tetA(A) (tetracycline resistance), strA/strB (streptomycin resistance), sul1 (sulphonamide resistance) and aadA2 (streptomycin/spectinomycin resistance), were located in this MDR region. PCR analysis revealed that the GI was not stable and could be excised from the chromosome as a circular intermediate.

CONCLUSIONS

The floRv gene was identified in a porcine S. maltophilia isolate. Six resistance genes including floRv were located in a novel GI. As an opportunistic pathogen in animals and humans, S. maltophilia might act as a resistance gene reservoir in farm environments. Its contribution to the spread of resistance genes to other pathogens should be monitored.

The contribution of class 1 integron to antimicrobial resistance in Stenotrophomonas maltophilia

Two hundred clinical isolates of Stenotrophomonas maltophilia were examined for the presence of class 1 integron and for the susceptibility to 12 different antimicrobials and detergents. The prevalence of class 1 integron in S. maltophilia isolates was 11%. The class 1 integron-positive isolates exhibited a higher resistance to kanamycin, tobramycin, and trimethoprim-sulfamethoxazole (SXT) than the class 1 integron-negative ones. Polymerase chain reaction (PCR), amplifying the variable region of the class 1 integron, showed the existence of six different amplicon sizes, indicating that there are at least six different class 1 integrons distributed in the 23 class 1 integron-positive isolates. Sequence analysis of six representative PCR amplicons revealed that qacK, aac(6')-Ib', qacK-aac(6')-Ib, qacK-aac(6')-Ib-aac(6')-Ib, and qacL-aadB-cmlA-aadA2 were identified in the 550-, 800-, 1,200-, 1,800, and 3,600-bp amplicons, respectively. The sequence analysis of the 150-bp PCR amplicon demonstrated no additional resistance-associated genes except the basic genetic elements of class 1 integron. The impact of class 1 integron acquisition on the antimicrobials susceptibility was assayed by isogenic integron deletion mutant construction and the susceptibility test. The most significant contribution of the class 1 integron acquisition to S. maltophilia is the increased resistance to SXT.

Colistimethate sodium for the treatment of chronic pulmonary infection in cystic fibrosis: an evidence-based review of its place in therapy

Chronic bacterial respiratory-tract infections are a major driving force in the pathogenesis of cystic fibrosis (CF) lung disease and promote chronic lung-function decline, destruction, and progression to respiratory failure at a premature age. Gram-negative bacteria colonizing the airways in CF are a major problem in CF therapy due to their tendency to develop a high degree of resistance to antibiotic agents over time. Pseudomonas aeruginosa is the dominating bacterial strain infecting the CF lung from early childhood on, and multiresistant strains frequently develop after years of therapy. Colistin has been used for treating pulmonary bacterial infections in CF for decades due to its very good Gram-negative activity. However, drawbacks include concerns regarding toxicity when being applied systemically, and the lack of approval for application by inhalation in the USA for many years. Other antibiotic substances for systemic use are available with good to excellent Gram-negative and anti-Pseudomonas activity, while there are only three substances approved for inhalation use in the treatment of chronic pulmonary infection with proven benefit in CF. The emergence of multiresistant strains leaving nearly no antibiotic substance as a treatment option, the limited number of antibiotics with high activity against P. aeruginosa, the concerns about increasing the risk of antibiotic resistance by continuous antibiotic therapy, the development of new drug formulations and drug-delivery devices, and, finally, the differing treatment strategies used in CF centers call for defining the place of this "old" drug, colistimethate, in today's CF therapy. This article reviews the available evidence to reflect on the place of colistimethate sodium in the therapy of chronic pulmonary infection in CF.

Stenotrophomonas maltophilia in Mexico: antimicrobial resistance, biofilm formation and clonal diversity

Stenotrophomonas maltophilia is an important multidrug-resistant nosocomial pathogen associated with high mortality. Our aim was to examine antimicrobial susceptibility, biofilm production and clonal relatedness of clinical isolates of S. maltophilia. S. maltophilia isolates were collected between 2006 and 2013 from two tertiary care hospitals in Mexico. Antimicrobial susceptibility was evaluated by the broth microdilution method. PCR was used to determine the presence of β-lactamase genes L1 and L2. Biofilm formation was assessed with crystal violet staining. Clonal relatedness was determined by PFGE. Among the 119 collected S. maltophilia isolates, 73 (61.3%) were from the respiratory tract. Resistance levels exceeded 75% for imipenem, meropenem, ampicillin, aztreonam, gentamicin and tobramycin. Resistance to trimethoprim-sulfamethoxazole was 32.8%. L1 and L2 genes were detected in 77.1% (91/118) and 66.9% (79/118) of isolates, respectively. All S. maltophilia strains were able to produce biofilms. Strains were classified as weak (47.9%, 57/119), moderate (38.7%, 46/119), or strong (13.4%, 16/119) biofilm producers. A total of 89 distinct PFGE types were identified and 21.6% (22/102) of the isolates were distributed in nine clusters. This is the first study in Mexico to reveal characteristics of clinical isolates of S. maltophilia. Clonal diversity data indicate low cross-transmission of S. maltophilia in a hospital setting. The high antibiotic resistance underscores the need for continuous surveillance of S. maltophilia in hospital settings in Mexico.

Infections Caused by Stenotrophomonas maltophilia in Recipients of Hematopoietic Stem Cell Transplantation

Stenotrophomonas maltophilia (S. maltophilia) is a globally emerging Gram-negative bacillus that is widely spread in environment and hospital equipment. Recently, the incidence of infections caused by this organism has increased, particularly in patients with hematological malignancy and in recipients of hematopoietic stem cell transplantation (HSCT) having neutropenia, mucositis, diarrhea, central venous catheters or graft versus host disease and receiving intensive cytotoxic chemotherapy, immunosuppressive therapy, or broad-spectrum antibiotics. The spectrum of infections in HSCT recipients includes pneumonia, urinary tract and surgical site infection, peritonitis, bacteremia, septic shock, and infection of indwelling medical devices. The organism exhibits intrinsic resistance to many classes of antibiotics including carbapenems, aminoglycosides, most of the third-generation cephalosporins, and other β-lactams. Despite the increasingly reported drug resistance, trimethoprim-sulfamethoxazole is still the drug of choice. However, the organism is still susceptible to ticarcillin-clavulanic acid, tigecycline, fluoroquinolones, polymyxin-B, and rifampicin. Genetic factors play a significant role not only in evolution of drug resistance but also in virulence of the organism. The outcome of patients having S. maltophilia infections can be improved by: using various combinations of novel therapeutic agents and aerosolized aminoglycosides or colistin, prompt administration of in vitro active antibiotics, removal of possible sources of infection such as infected indwelling intravascular catheters, and application of strict infection control measures.

Comparisons between patients with trimethoprim-sulfamethoxazole-susceptible and trimethoprim-sulfamethoxazole-resistant Stenotrophomonas maltophilia monomicrobial bacteremia: A 10-year retrospective study

BACKGROUND/PURPOSE

The impact of bacteremia due to the resistance of Stenotrophomonas maltophilia to trimethoprim-sulfamethoxazole (TMP-SXT) is uncertain. This study compared the clinical characteristics and outcomes of patients with TMP-SXT-susceptible (TSSSM) and TMP-SXT-resistant S. maltophilia (TSRSM) monomicrobial bacteremia.

METHODS

The medical records of adult patients with TSSSM and TSRSM monomicrobial bacteremia from January 2004 to December 2013 were reviewed and classified into two groups, namely, TSSSM and TSRSM.

RESULTS

There were 184 patients with monomicrobial S. maltophilia bacteremia. The mean age was 68.3 years. Most patients were males (72.8%), had high Charlson Comorbidity Index scores, previously prescribed antimicrobial agents, and indwelling medical devices. The 14-day and in-hospital mortality rates were 23.9% and 47.2%, respectively. There were 128 patients (69.6%) with TSSSM and 56 (30.4%) with TSRSM. The incidence of TSSSM bacteremia increased during the study period. The TSSSM and TSRSM groups had similar demographic and clinical characteristics and no significant differences in 14-day and in-hospital mortality (24.2% vs. 23.2%, p = 0.833; 50.0% vs. 41.1%, p = 0.264, respectively). Patients with TSSSM bacteremia had an increased risk of septic shock (p = 0.044) and neutropenia (p = 0.028) at bacteremia onset. Logistic regression analysis indicated that acquisition of TMP-SXT resistance was an independent risk factor for prolonged hospitalization (p = 0.018) and catheter-related S. maltophilia bacteremia was inversely associated with prolonged hospitalization after bacteremia (p = 0.032).

CONCLUSION

There were no significant differences in mortality for patients with TSSSM and TSRSM bacteremia, but patients with TSRSM bacteremia were associated with prolonged hospitalization after bacteremia onset.

Clinical factors associated with acquisition of resistance to levofloxacin in Stenotrophomonas maltophilia

PURPOSE

Fluoroquinolones, rapidly gaining prominence in treatment of Stenotrophomonas maltophilia (SMP), are noted for their potency and tolerability. However, SMP may rapidly acquire resistance to fluoroquinolones. We evaluated associations of clinical factors with acquisition of levofloxacin resistance (LFr) in SMP.

MATERIALS AND METHODS

Our retrospective cohort study was based on patient data collected between January 2008 and June 2010. Through screening of 1275 patients, we identified 122 patients with data for SMP antibiotic susceptibility testing in ≥3 serial SMP isolates.

RESULTS

We assigned the 122 patients to either the SS group (n=54) in which levofloxacin susceptibility was maintained or the SR group (n=31) in which susceptible SMP acquired resistance. In multivariate regression analysis, exposure to levofloxacin for more than 3 weeks [odds ratio (OR) 15.39, 95% confidential interval (CI) 3.08-76.93, p=0.001] and co-infection or co-colonization with Klebsiella pneumoniae resistant to levofloxacin (OR 4.85, 95% CI 1.16-20.24, p=0.030) were independently associated with LFr acquisition in SMP.

CONCLUSION

Acquisition of LFr during serial sampling of SMP was related to the levofloxacin exposure.

Draft Genome Sequence of Stenotrophomonas maltophilia Strain M30, Isolated from a Chronic Pressure Ulcer in an Elderly Patient

Stenotrophomonas maltophilia is an emerging opportunistic pathogen with an increasing prevalence of multidrug-resistant strains. Here, we report the draft genome sequence of S. maltophilia strain M30, isolated from a pressure ulcer in an elderly patient.

Activity of colistin in combination with tigecycline or rifampicin against multidrug-resistant Stenotrophomonas maltophilia

The antimicrobial treatment of Stenotrophomonas maltophilia infections is complicated by intrinsic multidrug resistance and a lack of reliable susceptibility data. We assessed the activity of colistin (COL), rifampicin (RIF) and tigecycline (TGC) alone and in combination using a range of in vitro susceptibility testing methodologies and a simple invertebrate model of S. maltophilia infection (Galleria mellonella). Synergy [fractional inhibitory concentration indices (FICIs) ≤0.5] between COL and either RIF or TGC was observed against 92 % and 88 % of 25 S. maltophilia isolates, respectively, despite resistance to one or another of the single agents alone. In time-kill assays, COL combined with either RIF or TGC was superior to single agents, but only the COL/RIF regimen was reliably bactericidal. The in vitro findings correlated with treatment outcomes in G. mellonella, with heightened survival observed for larvae treated with COL/RIF or COL/TGC compared with COL, RIF or TGC alone. COL combined with RIF was the most effective combination overall in both in vitro and in vivo (p < 0.05) assays. Given the difficulty in selecting appropriate therapy for S. maltophilia infections, regimens consisting of COL combined with RIF or TGC could be considered for clinical use.

Interplay between intrinsic and acquired resistance to quinolones in Stenotrophomonas maltophilia

To analyse whether the mutation-driven resistance-acquisition potential of a given bacterium might be a function of its intrinsic resistome, quinolones were used as selective agents and Stenotrophomonas maltophilia was chosen as a bacterial model. S. maltophilia has two elements - SmQnr and SmeDEF - that are important in intrinsic resistance to quinolones. Using a battery of mutants in which either or both of these elements had been removed, the apparent mutation frequency for quinolone resistance and the phenotype of the selected mutants were found to be related to the intrinsic resistome and also depended on the concentration of the selector. Most mutants had phenotypes compatible with the overexpression of multidrug efflux pump(s); SmeDEF overexpression was the most common cause of quinolone resistance. Whole genome sequencing showed that mutations of the SmeRv regulator, which result in the overexpression of the efflux pump SmeVWX, are the cause of quinolone resistance in mutants not overexpressing SmeDEF. These results indicate that the development of mutation-driven antibiotic resistance is highly dependent on the intrinsic resistome, which, at least for synthetic antibiotics such as quinolones, did not develop as a response to the presence of antibiotics in the natural ecosystems in which S. maltophilia evolved.

Smqnr variants in clinical isolates of Stenotrophomonas maltophilia in Brazil

SUMMARY

Stenotrophomonas maltophilia contains a novel chromosomally-encoded qnr gene named Smqnr that contributes to low intrinsic resistance to quinolone. We described Smqnr in 13 clinical isolates of S. maltophilia from two Brazilian hospitals, over a 2-year period. The strains were identified by API 20 NE (bioMérieux, France). Susceptibility by microdilution method to trimetroprim/sulfamethoxazole, ciprofloxacin, levofloxacin, minocycline, ceftazidime, chloramphenicol and ticarcillin/clavulanate was performed according to CLSI. PCR detection of Smqnr gene was carried out. The sequence of Smqnr was compared with those deposited in GenBank. Pulsed-field gel electrophoresis (PFGE) of all strains was performed. Thirteen Smqnr positives isolates were sequenced and three novel variants of Smqnr were identified. All 13 Smqnr isolates had distinguishable patterns by PFGE. This is the first report of Smqnr in S. maltophilia isolated in Brazil.

Plasmid-mediated sulfamethoxazole resistance encoded by the sul2 gene in the multidrug-resistant Shigella flexneri 2a isolated from patients with acute diarrhea in Dhaka, Bangladesh

In this study, mechanisms of plasmid-mediated sulfamethoxazole resistances in the clinical strains of multi-drug resistant (MDR) Shigella flexneri 2a were elucidated for the first time in Bangladesh. From 2006 to 2011, a total of 200 S. flexneri 2a strains were randomly selected from the stock of the Enteric and Food Microbiology Laboratory of icddr,b. Antimicrobial susceptibility of the strains showed 73%, 98%, 93%, 58%, 98%, 64% and 4% resistance to trimethoprim-sulfamethoxazole, nalidixic acid, ampicillin, erythromycin, tetracycline, ciprofloxacin and ceftriaxone respectively. Plasmid profiling revealed heterogeneous patterns and interestingly, all the trimethoprim-sulfamethoxazole resistant (SXT(R)) strains yielded a distinct 4.3 MDa plasmid compared to that of the trimethoprim-sulfamethoxazole susceptible (SXT(S)) strains. Curing of this 4.3 MDa plasmid resulted in the susceptibility to sulfamethoxazole alone suggesting the involvement of this plasmid in the resistance of sulfamethoxazole. Moreover, PCR analysis showed the presence of sul2 gene in SXT(R) strains which is absent in SXT(S) strains as well as in the 4.3 MDa plasmid-cured derivatives, confirming the involvement of sul2 in the resistance of sulfamethoxazole. Furthermore, pulsed-field gel electrophoresis (PFGE) analysis revealed that both the SXT(R) and SXT(S) strains were clonal. This study will significantly contributes to the knowledge on acquired drug resistance of the mostly prevalent S. flexneri 2a and further warrants continuous monitoring of the prevalence and correlation of this resistance determinants amongst the clinical isolates of Shigella and other enteric pathogens around the world to provide effective clinical management of the disease.

Comparative in vitro activity of sulfametrole/trimethoprim and sulfamethoxazole/trimethoprim and other agents against multiresistant Gram-negative bacteria

OBJECTIVES

Sulfamethoxazole/trimethoprim is standard therapy for infections caused by opportunist non-fermenters except Pseudomonas aeruginosa and Acinetobacter. Sulfametrol(e)/trimethoprim is an alternative to sulfamethoxazole/trimethoprim available in some EU countries, with possible pharmacological advantages. We compared their activities against (i) non-fermenters, (ii) multiresistant Enterobacteriaceae and (iii) reference strains with sul1 and sul2.

METHODS

Test isolates were recent submissions to the reference laboratory, or were Escherichia coli previously shown to have sul1 or sul2. Identification was by MALDI-ToF, by 16S rRNA gene sequencing or with API20NE strips. MICs were determined by CLSI agar dilution. The Stenotrophomonas maltophilia and Burkholderia series were enhanced by inclusion of 25% sulfamethoxazole/trimethoprim-resistant isolates; other series were not enhanced.

RESULTS

MICs of sulfametrole/trimethoprim for non-fermenters tracked those of sulfamethoxazole/trimethoprim, being equal in 97/170 cases, 2-fold higher in 57/170 cases and 2-fold lower in 12/170 cases. Despite supplementing the Burkholderia and S. maltophilia collections with sulfamethoxazole/trimethoprim-resistant organisms, the antifolate combinations retained better activity against these and other non-fermenters than did piperacillin/tazobactam, moxifloxacin, ticarcillin/clavulanate, tigecycline, cefotaxime or imipenem. By contrast, few (5%-20%) of the extended-spectrum β-lactamase (ESBL)- and carbapenemase-producing Enterobacteriaceae were susceptible to the sulphonamides or their trimethoprim combinations, probably reflecting widespread co-carriage of sul1 and sul2, which both conferred resistance.

CONCLUSIONS

Antifolate combinations remain the most active antimicrobials against less common non-fermenters, importantly including S. maltophilia and Burkholderia spp., but resistance is prevalent among ESBL- and carbapenemase-producing Enterobacteriaceae. Sulfametrole/trimethoprim had similar activity to sulfamethoxazole/trimethoprim against non-fermenters.

Monotherapy with fluoroquinolone or trimethoprim-sulfamethoxazole for treatment of Stenotrophomonas maltophilia infections

The treatment of choice for Stenotrophomonas maltophilia is trimethoprim-sulfamethoxazole (SXT). Fluoroquinolones (FQs) have in vitro activity against S. maltophilia; however, there is limited published information on their effectiveness. The purpose of this study is to compare the effectiveness of FQs and SXT for the treatment of S. maltophilia. A retrospective review of 98 patients with S. maltophilia infections who received SXT or FQ monotherapy was conducted. Patients ≥18 years old with a positive culture for S. maltophilia and clinical signs of infection who received treatment for ≥48 h were included. Microbiological cure and clinical response were evaluated at the end of therapy (EOT). In-hospital mortality and isolation of nonsusceptible isolates were also evaluated. Thirty-five patients received SXT, and 63 patients received FQ; 48 patients received levofloxacin, and 15 patients received ciprofloxacin. The most common infection was pulmonary. The overall microbiological cure rate at EOT was 63%. Thirteen of 20 patients (65%) who received SXT and 23 of 37 patients (62%) who received FQ had microbiological cure at EOT (P = 0.832). The overall clinical success rate was 55%, 52% for those who received FQ and 61% for those who received SXT (P = 0.451). In-hospital mortality was 24%, with similar rates in the two groups (25% for FQ versus 22% for SXT; P = 0.546). Development of resistance on repeat culture was 30% for FQ and 20% for SXT (P = 0.426). Fluoroquinolone and SXT monotherapies may be equally effective for the treatment of S. maltophilia infections. Resistance was documented in subsequent isolates of S. maltophilia in both groups.

Involvement of mutation in ampD I, mrcA, and at least one additional gene in β-lactamase hyperproduction in Stenotrophomonas maltophilia

It has been reported that targeted disruption of ampD I or mrcA causes β-lactamase hyperproduction in Stenotrophomonas maltophilia. We show here that β-lactamase-hyperproducing laboratory selected mutants and clinical isolates can have wild-type ampD I and mrcA genes, implicating mutation of at least one additional gene in this phenotype. The involvement of mutations at multiple loci in the activation of β-lactamase production in S. maltophilia reveals that there are significant deviations from the enterobacterial paradigm of AmpR-mediated control of β-lactamase induction. We do show, however, that S. maltophilia ampD I can complement a mutation in Escherichia coli ampD. This suggests that an anhydromuropeptide degradation product of peptidoglycan is used to activate AmpR in S. maltophilia, as is also the case in enteric bacteria.

Abundance of the Quorum-Sensing Factor Ax21 in Four Strains of Stenotrophomonas maltophilia Correlates with Mortality Rate in a New Zebrafish Model of Infection

Stenotrophomonas maltophilia is a Gram-negative pathogen with emerging nosocomial incidence. Little is known about its pathogenesis and the genomic diversity exhibited by clinical isolates complicates the study of pathogenicity and virulence factors. Here, we present a strategy to identify such factors in new clinical isolates of S. maltophilia, incorporating an adult-zebrafish model of S. maltophilia infection to evaluate relative virulence coupled to 2D difference gel electrophoresis to explore underlying differences in protein expression. In this study we report upon three recent clinical isolates and use the collection strain ATCC13637 as a reference. The adult-zebrafish model shows discrimination capacity, i.e. from very low to very high mortality rates, with clinical symptoms very similar to those observed in natural S. maltophilia infections in fish. Strain virulence correlates with resistance to human serum, in agreement with previous studies in mouse and rat and therefore supporting zebrafish as a replacement model. Despite its clinical origin, the collection strain ATCC13637 showed obvious signs of attenuation in zebrafish, with null mortality. Multilocus-sequence-typing analysis revealed that the most virulent strains, UV74 and M30, exhibit the strongest genetic similitude. Differential proteomic analysis led to the identification of 38 proteins with significantly different abundance in the three clinical strains relative to the reference strain. Orthologs of several of these proteins have been already reported to have a role in pathogenesis, virulence or resistance mechanisms thus supporting our strategy. Proof of concept is further provided by protein Ax21, whose abundance is shown here to be directly proportional to mortality in the zebrafish infection model. Indeed, recent studies have demonstrated that this protein is a quorum-sensing-related virulence factor.

Distinct groups and antimicrobial resistance of clinical Stenotrophomonas maltophilia complex isolates from Korea

One hundred and twenty-one isolates of Stenotrophomonas maltophilia complex were collected from seven Korean hospitals. Species and groups were identified using partial gyrB gene sequences and antimicrobial susceptibility testing was performed using a broth microdilution method. Based on partial gyrB gene sequences, 118 isolates were identified as belonging to S. maltophilia complex, including S. maltophilia, S. pavanii, Pseudomonas beteli, P. geniculata and P. hibisciola. The S. maltophilia isolates were further divided into three groups, I to III. S. maltophilia groups II and III were clustered into clade A with S. pavanii and P. beteli; S. maltophilia group I was clustered into clade B with P. geniculata and P. hibisciola. For all S. maltophilia complex isolates, the resistance rate to trimethoprim/sulfamethoxazole (TMP/SMX) was very high (30.5%). Antimicrobial resistance rates varied among species or groups of S. maltophilia complex. Isolates of clade A showed significantly lower antimicrobial resistance rates than those of clade B; while 25% of clade A isolates were multidrug resistant, 46% of clade B isolates were multidrug resistant (P=0.001). The finding of high antimicrobial resistance rates, particularly to TMP/SMX, among S. maltophilia complex isolates from Korea, and the existence of distinct groups among the isolates, with differences in antimicrobial resistance rates, suggests consideration of alternative agents to TMP/SMX to treat S. maltophilia infections and indicates the importance of accurate identification for appropriate selection of treatment options.

Biofilm compared to conventional antimicrobial susceptibility of Stenotrophomonas maltophilia Isolates from cystic fibrosis patients

Stenotrophomonas maltophilia is a multidrug-resistant organism increasingly isolated from the lungs of cystic fibrosis (CF) patients. One hundred twenty-five S. maltophilia isolates from 85 CF patients underwent planktonic and biofilm susceptibility testing against 9 different antibiotics, alone and in double antibiotic combinations. When S. maltophilia isolates were grown as a biofilm, 4 of the 10 most effective antibiotic combinations included high-dose levofloxacin and 7 of the 10 combinations included colistin at doses achievable by aerosolization.

In vitro antibacterial and antibiofilm activities of chlorogenic acid against clinical isolates of Stenotrophomonas maltophilia including the trimethoprim/sulfamethoxazole resistant strain

The in vitro antibacterial and antibiofilm activity of chlorogenic acid against clinical isolates of Stenotrophomonas maltophilia was investigated through disk diffusion, minimum inhibitory concentration (MIC), minimum bactericidal concentration (MBC), time-kill and biofilm assays. A total of 9 clinical S. maltophilia isolates including one isolate resistant to trimethoprim/sulfamethoxazole (TMP/SMX) were tested. The inhibition zone sizes for the isolates ranged from 17 to 29 mm, while the MIC and MBC values ranged from 8 to 16  μg mL(-1) and 16 to 32  μg mL(-1). Chlorogenic acid appeared to be strongly bactericidal at 4x MIC, with a 2-log reduction in viable bacteria at 10 h. In vitro antibiofilm testing showed a 4-fold reduction in biofilm viability at 4x MIC compared to 1x MIC values (0.085 < 0.397 A 490 nm) of chlorogenic acid. The data from this study support the notion that the chlorogenic acid has promising in vitro antibacterial and antibiofilm activities against S. maltophilia.

Coordinate hyperproduction of SmeZ and SmeJK efflux pumps extends drug resistance in Stenotrophomonas maltophilia

A Stenotrophomonas maltophilia mutant that coordinately hyper-expresses three resistance nodulation division-type efflux pump genes, smeZ, smeJ, and smeK, has been identified. SmeZ is responsible for elevating aminoglycoside MICs; SmeJ and SmeK are jointly responsible for elevating tetracycline, minocycline, and ciprofloxacin MICs and conferring levofloxacin resistance. One clinical isolate with this same phenotype was identified from a sample of six, and the isolate also coordinately hyper-expresses smeZ and smeJK, confirming the clinical relevance of our findings.

Stenotrophomonas maltophilia in Malaysia: molecular epidemiology and trimethoprim-sulfamethoxazole resistance

OBJECTIVES

Stenotrophomonas maltophilia is a recently identified nosocomial pathogen in Malaysia. Despite limited pathogenicity, its rate of isolation has increased in recent years. The aim of this study was to investigate the antibiotic susceptibility patterns, antibiotic resistance determinants, and the epidemiology of S. maltophilia at the largest tertiary care hospital in Malaysia.

METHODS

This study was carried out from January to December 2008. Sixty-four S. maltophilia isolates were investigated for their antibiotic susceptibility patterns by disk diffusion test and E-test. The antibiotic resistance mechanism for trimethoprim-sulfamethoxazole (TMP-SMX) was assessed by PCR for sul1, sul2, qac/smr, and class 1 integrons in general. Epidemiological relatedness among isolates was determined by pulsed-field gel electrophoresis (PFGE).

RESULTS

The highest number of S. maltophilia infections was observed in the intensive care unit (ICU) (n=13; 20.3%), while the lowest number of infections was seen in the neurology, psychiatric, and dermatology wards (each n=1; 1.6%). All isolates were susceptible to minocycline. One isolate was resistant to TMP-SMX with a minimum inhibitory concentration (E-test) >32 mg/l. The strain carried the sul1 gene and class 1 integron. None of the isolates were positive for the qac/smr genes. Although the data suggest the potential for patient to patient transmission, most of the S. maltophilia strains showed unrelated PFGE patterns and were considered to be genetically diverse.

CONCLUSION

The increasing number of S. maltophilia isolates seen in the ICU, their resistance to mainstay antibiotics, their genetically diverse nature, and possible cross-transmission within the hospital, strongly underscores the need for continuous surveillance for S. maltophilia in the hospital setting.

Stenotrophomonas maltophilia infections in a general hospital: patient characteristics, antimicrobial susceptibility, and treatment outcome

Introduction

Stenotrophomonas maltophilia is acquiring increasing importance as a nosocomial pathogen.

Methods

We retrospectively studied the characteristics and outcome of patients with any type of S. maltophilia infection at the University Hospital of Heraklion, Crete, Greece, between 1/2005–12/2010. S. maltophilia antimicrobial susceptibility was tested with the agar dilution method. Prognostic factors for all-cause in-hospital mortality were assessed with multivariate logistic regression.

Results

Sixty-eight patients (median age: 70.5 years; 64.7% males) with S. maltophilia infection, not related to cystic fibrosis, were included. The 68 patients were hospitalized in medical (29.4%), surgical (26.5%), hematology/oncology departments (23.5%), or the intensive care units (ICU; 20.6%). The most frequent infection types were respiratory tract (54.4%), bloodstream (16.2%), skin/soft tissue (10.3%), and intra-abdominal (8.8%) infection. The S. maltophilia-associated infection was polymicrobial in 33.8% of the cases. In vitro susceptibility was higher to colistin (91.2%), trimethoprim/sulfamethoxazole and netilmicin (85.3% each), and ciprofloxacin (82.4%). The empirical and the targeted treatment regimens were microbiologically appropriate for 47.3% and 63.6% of the 55 patients with data available, respectively. Most patients received targeted therapy with a combination of agents other than trimethoprim/sulfamethoxazole. The crude mortality and the mortality and the S. maltophilia infection-related mortality were 14.7% and 4.4%, respectively. ICU hospitalization was the only independent prognostic factor for mortality.

Conclusion

S. maltophilia infection in a general hospital can be associated with a good prognosis, except for the patients hospitalized in the ICU. Combination reigmens with fluoroquinolones, colistin, or tigecycline could be alternative treatment options to trimethoprim/sulfamethoxazole.

Stenotrophomonas maltophilia: an emerging global opportunistic pathogen

Stenotrophomonas maltophilia is an emerging multidrug-resistant global opportunistic pathogen. The increasing incidence of nosocomial and community-acquired S. maltophilia infections is of particular concern for immunocompromised individuals, as this bacterial pathogen is associated with a significant fatality/case ratio. S. maltophilia is an environmental bacterium found in aqueous habitats, including plant rhizospheres, animals, foods, and water sources. Infections of S. maltophilia can occur in a range of organs and tissues; the organism is commonly found in respiratory tract infections. This review summarizes the current literature and presents S. maltophilia as an organism with various molecular mechanisms used for colonization and infection. S. maltophilia can be recovered from polymicrobial infections, most notably from the respiratory tract of cystic fibrosis patients, as a cocolonizer with Pseudomonas aeruginosa. Recent evidence of cell-cell communication between these pathogens has implications for the development of novel pharmacological therapies. Animal models of S. maltophilia infection have provided useful information about the type of host immune response induced by this opportunistic pathogen. Current and emerging treatments for patients infected with S. maltophilia are discussed.

A multicenter surveillance of antimicrobial resistance on Stenotrophomonas maltophilia in Taiwan

BACKGROUND

Stenotrophomonas maltophilia has emerged as an important opportunistic pathogen in debilitated hosts. Clinical management of S. maltophilia is challenging due to its intrinsic resistance to a variety of antibiotics. This study investigated the trend and prevalence of antimicrobial resistance in S. maltophilia from a nationwide surveillance study in Taiwan.

METHODS

S. maltophilia isolates were collected biennially between 1998 and 2008 as part of the Taiwan Surveillance of Antimicrobial Resistance (TSAR) program from medical centers and regional hospitals throughout Taiwan. Minimal inhibitory concentrations (MIC) were determined using the Clinical and Laboratory Standards Institute reference broth microdilution method.

RESULTS

A total of 377 non-duplicate S. maltophilia isolates were collected from 38 hospitals. The majority of the isolates were from the respiratory tract (256, 67.9%), followed by blood (48, 12.7%). Overall, 376 (99.7%) isolates were susceptible to minocycline, 362 (96%) to tigecycline, 311 (82.5%) to trimethoprim/sulfamethoxazole (TMP-SMX), 300 (79.6%) to levofloxacin, 92 (24.4%) to ceftazidime, and 70 (18.6%) to ticarcillin-clavulanic acid. The MIC(50)/MIC(90) of minocycline, tigecycline, TMP-SMX, levofloxacin, ceftazidime, and ticarcillin-clavulanic acid, were ≤0.5/1 μg/mL, 0.25/1 μg/mL, ≤0.25/8 μg/mL, 1/4 μg/mL, 32/128 μg/mL, and 64/128 μg/mL, respectively. A trend of increased non-susceptibility to levofloxacin (p=0.014) was observed over the 10-year study period. Compared to TMP-SMX-susceptible isolates, TMP-SMX-resistant isolates were less susceptible to levofloxacin (54.5% vs. 84.9%, p<0.001).

CONCLUSION

In this 10-year study, minocycline and TMP-SMX remained the two antimicrobials with better in vitro activities against S. maltophilia than ceftazidime, levofloxacin, and ticarcillin-clavulanic acid. The activity of levofloxacin against S. maltophilia in Taiwan declined during the past 10 years.

Stenotrophomonas maltophilia: emerging disease patterns and challenges for treatment

Stenotrophomonas maltophilia is a ubiquitous organism associated with opportunistic infections. In the immunocompromised host, increasing prevalence and severity of illness is observed, particularly opportunistic bloodstream infections and pneumonia syndromes. In this article, the classification and microbiology are outlined, together with clinical presentation, outcomes and management of infections due to S. maltophilia. Although virulence mechanisms and the genetic basis of antibiotic resistance have been identified, a role for standardized and uniform reporting of antibiotic sensitivity is not defined. Infections due to S. maltophilia have traditionally been treated with trimethoprim-sulfamethoxazole, ticarcillin-clavulanic acid, or fluoroquinolone agents. The use of combination therapies, newer fluoroquinolone agents and tetracycline derivatives is discussed. Finally, measures to prevent transmission of S. maltophilia within healthcare facilities are reported, especially in at-risk patient populations.

Antibiotic contamination and occurrence of antibiotic-resistant bacteria in aquatic environments of northern Vietnam

The ubiquitous application and release of antibiotics to the environment can result in bacterial antibiotic resistance, which in turn can be a serious risk to humans and other animals. Southeast Asian countries commonly apply an integrated recycling farm system called VAC (Vegetable, Aquaculture and Caged animal). In the VAC environment, antibiotics are released from animal and human origins, which would cause antibiotic-resistant bacteria (ARB). This study evaluated occurrence of ARB in the VAC environment in northern Vietnam, with quantitative analysis of antibiotic pollution. We found that sulfonamides were commonly detected at all sites. In dry season, while sulfamethazine was a major contaminant in pig farm pond (475-6662 ng/l) and less common in city canal and aquaculture sites, sulfamethoxazole was a major one in city canal (612-4330 ng/l). Erythromycin (154-2246 ng/l) and clarithromycin (2.8-778 ng/ml) were the common macrolides in city canal, but very low concentrations in pig farm pond and aquaculture sites. High frequencies of sulfamethoxazole-resistant bacteria (2.14-94.44%) were found whereas the occurrence rates of erythromycin-resistant bacteria were lower (<0.01-38.8%). A positive correlation was found between sulfamethoxazole concentration and occurrence of sulfamethoxazole-resistant bacteria in dry season. The sulfamethoxazole-resistant isolates were found to belong to 25 genera. Acinetobacter and Aeromonas were the major genera. Twenty three of 25 genera contained sul genes. This study showed specific contamination patterns in city and VAC environments and concluded that ARB occurred not only within contaminated sites but also those less contaminated. Various species can obtain resistance in VAC environment, which would be reservoir of drug resistance genes. Occurrence of ARB is suggested to relate with rainfall condition and horizontal gene transfer in diverse microbial community.

Pathogens resistant to antibacterial agents

Resistance to antimicrobial drugs is increasing at an alarming rate among both gram-positive and gram-negative bacteria. Traditionally, bacteria resistant to multiple antimicrobial agents have been restricted to the nosocomial environment. A disturbing trend has been the recent emergence and spread of resistant pathogens in nursing homes, in the community, and in the hospital. This article reviews the epidemiology, molecular mechanisms of resistance, and treatment options for pathogens resistant to antimicrobial drugs.

Class 1 and class 2 integrons in multidrug-resistant gram-negative bacteria isolated from the Salmon River, British Columbia

Using an enrichment protocol, we isolated 16 gram-negative, multidrug-resistant strains of known or opportunistic bacterial pathogens from the Salmon River in south-central British Columbia from 2005 to 2009, and investigated the genetic basis of their resistance to a variety of antibiotics. Of the 16 strains, 13 carried class 1 integrons and three carried class 2 integrons. Genes found in cassettes associated with the integrons included those for dihydrofolate reductases (dfrA1, dfrA12, dfrA17, and dfrB7), aminoglycoside adenyltransferases (aadA1, aadA2, aadA5, and aadB), streptothricin acetyltransferase (sat), and hypothetical proteins (orfF and orfC). A new gene cassette of unknown function, orf1, was discovered between dfrA1 and aadA5 in Escherichia sp. Other genes for resistance to tetracycline, chloramphenicol, streptomycin, and kanamycin (tetA, tetB, tetD; catA; strA-strB; and aphA1-Iab, respectively) were outside the integrons. Several of these resistance determinants were transferable by conjugation. The detection of organisms and resistance determinants normally associated with clinical settings attest to their widespread dispersal and suggest that regular monitoring of their presence in aquatic habitats should become a part of the overall effort to understand the epidemiology of antibiotic resistance genes in bacteria.

Antimicrobial resistance in the intensive care unit: mechanisms, epidemiology, and management of specific resistant pathogens

Infections caused by drug-resistant and multidrug-resistant microbial pathogens pose tremendous challenges to health care systems, including challenges related to the diagnosis, treatment, and containment of these infections. These challenges are amplified in the intensive care unit (ICU), where pressures for selection and emergence of resistance and risks of transmission of resistant pathogens are highest, and where the threat of resistance drives selection of empiric antimicrobial regimens. This article reviews basic concepts of resistance to antibacterial agents including mechanisms and modes of transmission, and discusses management issues for the important drug-resistant pathogens found in the ICU.

Pyrosequencing of antibiotic-contaminated river sediments reveals high levels of resistance and gene transfer elements

The high and sometimes inappropriate use of antibiotics has accelerated the development of antibiotic resistance, creating a major challenge for the sustainable treatment of infections world-wide. Bacterial communities often respond to antibiotic selection pressure by acquiring resistance genes, i.e. mobile genetic elements that can be shared horizontally between species. Environmental microbial communities maintain diverse collections of resistance genes, which can be mobilized into pathogenic bacteria. Recently, exceptional environmental releases of antibiotics have been documented, but the effects on the promotion of resistance genes and the potential for horizontal gene transfer have yet received limited attention. In this study, we have used culture-independent shotgun metagenomics to investigate microbial communities in river sediments exposed to waste water from the production of antibiotics in India. Our analysis identified very high levels of several classes of resistance genes as well as elements for horizontal gene transfer, including integrons, transposons and plasmids. In addition, two abundant previously uncharacterized resistance plasmids were identified. The results suggest that antibiotic contamination plays a role in the promotion of resistance genes and their mobilization from environmental microbes to other species and eventually to human pathogens. The entire life-cycle of antibiotic substances, both before, under and after usage, should therefore be considered to fully evaluate their role in the promotion of resistance.

Stenotrophomonas Maltophilia as a Causal Agent of Pyogranulomatous Hepatitis in a Buffalo (Bubalus Bubalis)

A 7-year-old female buffalo ( Bubalus bubalis) from a local herd in Serres, northern Greece, was presented to a private veterinary clinic with a chronic loss of appetite for 15 days. The clinical examination revealed high fever (41.5°C), lethargy, yellow discoloration of skin and mucous membranes, an abdomen that appeared to be empty, hyperactive rumen motility, and tachypnea. A biochemical profile revealed an elevated total bilirubin concentration and hepatic enzyme activities, whereas globulin, creatinine, and glucose concentrations were within the reference intervals. The animal received a 12-day course of treatment with intramuscular administration of ampicillin and corticosteroids. However, no significant clinical improvement was achieved, and the buffalo was euthanized. Gross necropsy lesions included serous atrophy of adipose tissue and hepatomegaly. Microscopic lesions included necrotizing pyogranulomatous hepatitis with thrombosis, hemorrhages, edema, and fibrosis. Small, nonpigmented, bacterial colonies were harvested in pure culture from the liver and were confirmed as Stenotrophomonas maltophilia by polymerase chain reaction. The bacterium was sensitive to ciprofloxacin, enrofloxacin, colistin, polymyxin, trimethoprim/sulfamethaxazole, and chloramphenicol. In contrast, resistance to ticarcillin, piperacillin, imipenem, ceftazidime, amikacin, gentamicin, tobramycin, and tetracycline was displayed. The bacterial strain carried the L1 metallo-β-lactamase (L1) and tet35 genes, which contribute to high-level resistance to β-lactams and tetracycline, respectively. Although S. maltophilia is widely believed to be a contaminant, the present report suggests that the isolation, identification, and susceptibility testing of this multidrug-resistant bacterium may be of clinical importance in diagnostic samples.

[Analysis of acquired resistance genes in Stenotrophomonas maltophilia]

BACKGROUND

Stenotrophomonas maltophilia is a gram-negative bacillus and a nosocomial pathogen in immunocompromised patients. Trimethoprim/sulfamethoxazole (TMP/SMX) is the drug of choice for treating S. maltophilia infection; however, resistance to TMP/SMX is increasing. In this study, we investigated the relationship between the incidence of TMP/SMX resistance and the presence of sul genes and mobile elements.

METHODS

A total of 120 S. maltophilia isolates were collected from 3 university hospitals between April 2007 and April 2009. Antimicrobial susceptibilities were determined using the disk diffusion method. PCR and DNA sequencing were conducted for the detection of sul1, sul2, class 1 integron, and ISCR2 element. Repetitive extragenic palindromic sequence-based PCR (REP-PCR) was carried out to evaluate the genetic relatedness.

RESULTS

The TMP/SMX-resistant (R) isolates harbored a significantly higher proportion of sul1 gene and class 1 integron than TMP/SMX-susceptible (S) isolates (P<0.001). Seventeen of 28 isolates with sul1 also had a class 1 integron, but none of the isolates without sul1 had a class 1 integron. The identified gene cassettes within class 1 integrons include aacA4, aadA1, aac6'-II, and qac. None of the 120 isolates carried sul2, glmM, or ISCR2 element. REP-PCR did not show any genetic relatedness among the isolates.

CONCLUSIONS

In Korea, the resistance of S. maltophilia isolates to TMP/SMX is due to sul1 within a class 1 integron rather than to sul2. The class 1 integron also harbors multiple antibiotic resistance genes in addition to sul1, and therefore it could mediate multidrug resistance in S. maltophilia.

Antimicrobial activity of the green tea polyphenol (-)-epigallocatechin-3-gallate (EGCG) against clinical isolates of Stenotrophomonas maltophilia

Stenotrophomonas maltophilia is increasingly recognised as an important nosocomial pathogen. Treatment options are limited due to intrinsic resistance to many antibiotics as well as concerns over toxicity of the mainstay of treatment, co-trimoxazole. Epigallocatechin-3-gallate (EGCG), the major catechin found in green tea, has been shown to have antimicrobial effects against a number of bacterial pathogens. We evaluated the in vitro activity of this compound against 40 clinical isolates of S. maltophilia. MIC(50/90) values (minimal inhibitory concentrations for 50% and 90% of the organisms, respectively) were 256 mg/L when determined by agar dilution and 512 mg/L by broth microdilution. MBC(50/90) values (minimal bactericidal concentrations for 50% and 90% of the organisms, respectively) were 512 mg/L. In time-kill assays, the bactericidal activity of EGCG was analysed by viable colony counts as well as a colorimetric assay for bacterial reduction of XTT. EGCG was slowly bactericidal at 4x MIC, with a 2.5 log reduction in viable bacteria at 24h. EGCG has promising in vitro antimicrobial activity against S. maltophilia. Although the mechanism of action is not yet clear, further studies to evaluate its clinical potential and role in combination with other antimicrobial agents are warranted.

Stenotrophomonas maltophilia: Significant contemporary hospital pathogen - review

Stenotrophomonas maltophilia (Sm) plays an important role as an opportunistic pathogen in immunocompromised individuals. The growing detection rates of this bacterium in hospitalized patients are associated with the invasiveness of therapeutic and diagnostic procedures and the selection pressure of antibiotic therapy. A broad range of infections that can be caused by Sm is frequently bound to biofilm. The high level of intrinsic resistance to many unrelated antibiotics and increasing acquired resistance to the drug of choice, trimethoprim-sulfamethoxazole pose a threat for the near future when our treatment options may become depleted. Prevention of colonization and infection consists in consequent implementation of the rules governing nosocomial infection control, rational use of antibiotics including the optimization of selection and testing of antimicrobial agents suitable for the treatment of stenotrophomonad infections.