Pulsed-field gel electrophoresis of restriction-digested genomic DNA and antimicrobial susceptibility of Xanthomonas maltophilia strains from Brazil, Switzerland and the USA

Comparison of pulsed-field gel electrophoresis and three rep-PCR methods for evaluating the genetic relatedness of Stenotrophomonas maltophilia isolates

AIMS

In this study, three facile repetitive-sequence PCR (rep-PCR) techniques have been compared with the pulsed-field gel electrophoresis (PFGE) method for differentiating the genetic relatedness of clinical Stenotrophomonas maltophilia isolates.

METHODS AND RESULTS

The dendrograms of 20 S. maltophilia isolates were constructed based on the data obtained from PFGE and three PCR-based methods, i.e. enterobacterial repetitive intergenic consensus-PCR (ERIC-PCR), BOX-PCR and repetitive extragenic palindromic-PCR (REP-PCR). When compared with PFGE, ERIC-PCR displayed a much lower discriminatory power, whereas BOX-PCR and REP-PCR had a comparable discriminatory power for close genetic-related isolates.

CONCLUSION

BOX-PCR and REP-PCR can be convenient and effective methods for evaluating the close genetic relatedness of clinical S. maltophilia isolates.

SIGNIFICANCE AND IMPACT OF THE STUDY

A rapid method for determining S. maltophilia's close genetic relatedness provides a convenient tool for understanding the epidemiology of S. maltophilia.

Antimicrobial therapy for Stenotrophomonas maltophilia infections

Stenotrophomonas maltophilia has emerged as an important nosocomial pathogen capable of causing respiratory, bloodstream, and urinary infections. The treatment of nosocomial infections by S. maltophilia is difficult, as this pathogen shows high levels of intrinsic or acquired resistance to different antimicrobial agents, drastically reducing the antibiotic options available for treatment. Intrinsic resistance may be due to reduced outer membrane permeability or to the multidrug efflux pumps. However, specific mechanisms of resistance such as aminoglycoside-modifying enzymes or the heterogeneous production of metallo-beta-lactamase have contributed to the multidrug-resistant phenotype displayed by this pathogen. Moreover, the lack of standardized susceptibility tests and their interpretative criteria hinder the choice of an adequate antibiotic treatment. Recommendations for the treatment of infections by S. maltophilia are based on in vitro studies, certain nonrandomized clinical trials, and anecdotal experience. Trimethoprim-sulfamethoxazole remains the drug of choice, although in vitro studies indicate that ticarcillin-clavulanic acid, minocycline, some of the new fluoroquinolones, and tigecycline may be useful agents. This review describes the main resistance mechanisms, the in vitro susceptibility profile, and treatment options for S. maltophilia infections.

High genetic diversity among Stenotrophomonas maltophilia strains despite their originating at a single hospital

The levels of genetic relatedness of 139 Stenotrophomonas maltophilia strains recovered from 105 hospitalized non-cystic fibrosis patients (51% from medical wards, 35% from intensive care units, and 14% from surgical wards) and 7 environmental sources in the same hospital setting during a 4-year period were typed by the pulsed-field gel electrophoresis (PFGE) technique. A total of 99 well-defined distinct XbaI PFGE patterns were identified (Simpson's discrimination index, 0.996). The dendrogram showed a Dice similarity coefficient ranging from 28 to 80%. Two major clusters (I and II), three minor clusters (III, IV, and V), and two independent branches were observed when using a 36% Dice coefficient, indicating a high diversity of genetic relatedness. It is of note that 84% of strains were grouped within two major clonal lineages. No special cluster gathering was found among strains belonging to the same sample type specimen, patients' infection or colonization status, and ward of precedence. Despite this fact, three different clones (A, B, and C) recovered from respiratory samples from six, three, and two patients, respectively, and two clones, D and E, in two bacteremic patients each, were identified. Isolation of an S. maltophilia strain belonging to the clone A profile in a bronchoscope demonstrated a common source from this clone. This study revealed a high genetic diversity of S. maltophilia isolates despite their origin from a single hospital, which may be related to the wide environmental distribution of this pathogen. However, few clones could be transmitted among different patients, yielding outbreak situations.

Use of random amplified polymorphic DNA PCR to examine epidemiology of Stenotrophomonas maltophilia and Achromobacter (Alcaligenes) xylosoxidans from patients with cystic fibrosis

Stenotrophomonas maltophilia and Achromobacter (Alcaligenes) xylosoxidans have been increasingly recognized as a cause of respiratory tract colonization in cystic fibrosis (CF). Although both organisms have been associated with progressive deterioration of pulmonary function, demonstration of causality is lacking. To examine the molecular epidemiology of S. maltophilia and A. xylosoxidans in CF, isolates from patients monitored for up to 2 years were fingerprinted using a PCR-based randomly amplified polymorphic DNA (RAPD-PCR) method. Sixty-one of 69 CF centers screened had 183 S. maltophilia culture-positive patients, and 46 centers had 92 A. xylosoxidans-positive patients. At least one isolate from each patient was genotyped, and patients with > or =10 positive cultures (12 S. maltophilia cultures, 15 A. xylosoxidans cultures) had serial isolates genotyped. In addition, centers with multiple culture-positive patients were examined for evidence of shared clones. There were no instances of shared genotypes among different CF centers. Some patients demonstrated isolates with a single genotype throughout the observation period, and others had intervening or sequential genotypes. At the six centers with multiple S. maltophilia culture-positive patients and the seven centers with multiple A. xylosoxidans-positive patients, there were three and five instances of shared genotypes, respectively. The majority of shared isolates were from pairs who were siblings or otherwise epidemiologically linked. These findings suggest RAPD-PCR typing can distinguish unique CF isolates of S. maltophilia and A. xylosoxidans, person-to-person transmission may occur, there are not a small number of clones infecting CF airways, and patients with long-term colonization may either have a persistent organism or may acquire additional organisms over time.

Molecular investigation of Stenotrophomonas maltophilia isolates exhibiting rapid emergence of ticarcillin-clavulanate resistance

The prevalence of Stenotrophomonas maltophilia resistance to ticarcillin-clavulanate has dramatically increased in our hospital over the past few years. Sixty-six clinical isolates, collected from 61 patients, were tested for antibiotic susceptibility and genotyped by two different enterobacterial repetitive intergenic consensus-PCR (ERIC-PCR) systems. Although two small outbreaks were identified in the medical intensive care unit, the remaining 58 strains generated 48 different PCR patterns. The rapid emergence of resistance in S. maltophilia occured in absence of an epidemic and was probably influenced by increasing-b-lactam use in our hospital.

Molecular epidemiology of Stenotrophomonas maltophilia isolated from clinical specimens from patients with cystic fibrosis and associated environmental samples

Stenotrophomonas maltophilia was isolated from the respiratory tracts of 41 (25%) of 163 children attending our pediatric cystic fibrosis unit between September 1993 and December 1995. The extents of S. maltophilia contamination of environmental sites frequented by these patients were investigated with a selective medium incorporating vancomycin, imipenem, and amphotericin B. Eighty-two isolates of S. maltophilia were cultured from 67 different environmental sites sampled between January and July 1996. The organism was widespread in the home environment, with 20 (36%) and 25 (42%) of sampled sites positive in the homes of colonized and noncolonized patients, respectively. In the nosocomial setting, it was isolated from 18 (32%) sites in the hospital ward and from 4 (17%) sites in the outpatient clinic area. The most common sites of contamination were sink drains, faucets, and other items frequently in contact with water. All environmental and clinical isolates were genotyped with enterobacterial repetitive intergenic consensus sequences as primers. A total of 33 of the 41 patients were colonized with unique strains, and four pairs of patients shared strains. Further characterization by pulsed-field gel electrophoresis after digestion with XbaI found that there was no evidence of patient-to-patient transmission; however, there was some evidence that a small number of patients may have acquired the organism from the hospital environment. Resampling of environmental sites in the hospital ward in January 1997 revealed evidence of genetic drift, complicating the accurate determination of environmental sources for clinical strains. The source of the majority of S. maltophilia strains colonizing the respiratory tracts of these patients with cystic fibrosis remained uncertain but may have represented multiple, independent acquisitions from a variety of environmental sites both within and outside the hospital.

Microbiological and clinical aspects of infection associated with Stenotrophomonas maltophilia

The gram-negative bacterium Stenotrophomonas maltophilia is increasingly recognized as an important cause of nosocomial infection. Infection occurs principally, but not exclusively, in debilitated and immunosuppressed individuals. Management of S. maltophilia-associated infection is problematic because many strains of the bacterium manifest resistance to multiple antibiotics. These difficulties are compounded by methodological problems in in vitro susceptibility testing for which there are, as yet, no formal guidelines. Despite its acknowledged importance as a nosocomial pathogen, little is known of the epidemiology of S. maltophilia, and although it is considered an environmental bacterium, its sources and reservoirs are often not readily apparent. Molecular typing systems may contribute to our knowledge of the epidemiology of S. maltophilia infection, thus allowing the development of strategies to interrupt the transmission of the bacterium in the hospital setting. Even less is known of pathogenic mechanisms and putative virulence factors involved in the natural history of S. maltophilia infection and this, coupled with difficulties in distinguishing colonization from true infection, has fostered the view that the bacterium is essentially nonpathogenic. This article aims to review the current taxonomic status of S. maltophilia, and it discusses the laboratory identification of the bacterium. The epidemiology of the organism is considered with particular reference to nosocomial outbreaks, several of which have been investigated by molecular typing techniques. Risk factors for acquisition of the bacterium are also reviewed, and the ever-expanding spectrum of clinical syndromes associated with S. maltophilia is surveyed. Antimicrobial resistance mechanisms, pitfalls in in vitro susceptibility testing, and therapy of S. maltophilia infections are also discussed.

Structure of the O20 antigen of Stenotrophomonas (Xanthomonas or Pseudomonas) maltophilia

The O-antigen polymer recovered from the reference strain for Stenotrophomonas (Xanthomonas or Pseudomonas) maltophilia serogroup O20, by mild acid hydrolysis of the lipopolysaccharide, was found to contain D-rhamnose and D-mannose. By means of chemical degradations and NMR studies, the repeating-unit of the polymer was deduced to be a linear tetrasaccharide with the structure shown. -->2)-alpha-D-Manp-(1-->3)-beta-D-Rhap-(1-->2)-alpha-D-Rh ap-(1-->2)-alpha-D- Rhap-(1-->.

Use of random amplified polymorphic DNA for epidemiological typing of Stenotrophomonas maltophilia

We used the technique of random amplification of polymorphic DNA (RAPD) to type 130 isolates of Stenotrophomonas (Xanthomonas) maltophilia, using four arbitrary short primers. Of the 130 isolates, 51 were from the hospital environment, 48 from clinical specimens and 31 were geographically diverse environmental isolates. DNA amplification with the four sets of primers generated 112 RAPD patterns that differed by two or more bands in one of the four primers. Sixteen pairs of isolates were of the same RAPD pattern and some of these pairs represented clinical strains obtained from patients hospitalized at the same time in the same ward. In three patients, two to three strains of S. maltophilia which gave different RAPD fingerprints were isolated on the same day from different specimens. RAPD fingerprinting demonstrated great genomic diversity within the species S. maltophilia and provided an effective method for the study of the epidemiology of both clinical and environmental strains.

Structure of the O6 antigen of Stenotrophomonas (Xanthomonas or Pseudomonas) maltophilia

A polysaccharide containing D-xylose, L-rhamnose, and N-acetyl-D-glucosamine was released on mild acid hydrolysis of the lipopolysaccharide extracted from defatted cell walls of Stenotrophomonas (Xanthomonas or Pseudomonas) maltophilia strain 557, the reference strain for serotype O6. By means of NMR spectroscopy and chemical degradations, the repeating unit of the polymer was identified as a branched trisaccharide with the structure shown. [formula: see text]

Molecular typing of Stenotrophomonas (Xanthomonas) maltophilia by DNA macrorestriction analysis and random amplified polymorphic DNA analysis

Stenotrophomonas (Xanthomonas) maltophilia is a multidrug-resistant, nosocomial pathogen for which optimal typing methods in epidemiologic investigations of nosocomial outbreaks have not been defined. We compared DNA macrorestriction analysis by pulsed-field gel electrophoresis (PFGE) with random amplified polymorphic DNA (RAPD) analysis by arbitrarily primed PCR for molecular typing of 109 multidrug-resistant strains of S. maltophilia from multiple outbreaks at our institution over a 10-month period in 1993. PFGE after digestion with restriction endonuclease DraI revealed 62 unique DNA restriction profiles among the 109 strains, with 23, 11, 6, 6, and 3 strains having concordant profiles in each of five types. There were four concordant profiles among 8 strains (2 strains with each profile), while unique profiles were present in each of the remaining 52 strains. Further RAPD analysis with a decanucleotide primer showed the same number of distinct strain types as PFGE but more subtype diversity within each clonal type. We concluded that DNA macrorestriction analysis and RAPD analysis are sufficiently discriminatory and useful for differentiation of S. maltophilia strains in epidemiologic investigations of nosocomial outbreaks. However, RAPD analysis by arbitrarily primed PCR is faster and less laborious method of molecular typing.

The emergence of epidemic, multiple-antibiotic-resistant Stenotrophomonas (Xanthomonas) maltophilia and Burkholderia (Pseudomonas) cepacia

Stenotrophomonas (Xanthomonas) maltophilia has recently emerged as an important nosocomial pathogen in immunocompromised cancer patients and transplant recipients. S. maltophilia has been documented as a cause of bacteraemia, infections of the respiratory and urinary tracts, meningitis, serious wound infections, mastoiditis, epididymitis, conjunctivitis and endocarditis. The reservoir of S. maltophilia and the mechanisms by which it is transmitted, remain largely unknown. Risk analysis has shown that mechanically ventilated intensive care unit patients, receiving antibiotics especially carbapenems, are at increased risk of colonization/infection. Because of the in vitro resistance to many commonly used agents, it is essential that S. maltophilia is isolated and identified correctly. Over the last decade Burkholderia (Pseudomonas) cepacia has become a major threat to the management of patients with cystic fibrosis (CF). The spread of B. cepacia through previously stable CF clinic populations, is an increasing cause for concern. Anxiety has arisen following the observation that some patients with previously mild disease, experience an accelerated and fatal deterioration in pulmonary function with fever, necrotizing pneumonia, and in some cases septicaemia. Early UK surveillance studies suggested a maximum prevalence of 7%, though this has risen in recent reports to approach the 40% described in the US. Mounting evidence of person-to-person transmission has led the Cystic Fibrosis Trust to issue guidelines for the management of colonized patients. In an attempt to monitor and understand the spread of B. cepacia, typing techniques such as ribotyping have been employed. Because of these problems, together with multiple-antibiotic resistance, there is an urgent need to identify the major routes of transmission, colonizing, pathophysiological and immunological factors.

Analysis of restriction fragment length polymorphism and ribotyping of multiresistant Stenotrophomonas maltophilia isolated from persisting lung infection in a cystic fibrosis patient

A cystic fibrosis patient was infected by Stenotrophomonas maltophilia over at least 15 months. The bacteria became increasingly resistant to antimicrobial agents. Determination of restriction fragment length polymorphism and ribotyping showed that resistance was due to changes in that S. maltophilia rather than to infection by another strain.