The accurate identification of the infecting species and the determination of its susceptibility to antimicrobial agents, given the large number of strains with atypical patterns, are crucial if patients with nocardiosis are to be successfully treated.

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.

Acinetobacter baumannii is one of the major pathogens involved in nosocomial outbreaks. The clonal diversity of 729 epidemic strains isolated from 19 Spanish hospitals (mainly from intensive care units) was analyzed over an 11-year period. Pulsed-field gel electrophoresis (PFGE) identified 58 PFGE types that were subjected to susceptibility testing, rpoB gene sequencing, and multilocus sequence typing (MLST). All PFGE types were multidrug resistant; colistin was the only agent to which all pathogens were susceptible. The 58 PFGE types were grouped into 16 clones based on their genetic similarity (cutoff of 80%). These clones were distributed into one major cluster (cluster D), three medium clusters (clusters A, B, and C), and three minor clusters (clusters E, F, and G). Multidrug-resistant Acinetobacter baumannii is a bacterium frequently endemic in certain hospital wards and is responsible for numerous nosocomial outbreaks around the world (3,23,33). Its great capacity to survive in low-moisture environments and its ability to develop resistance to antimicrobial agents afford A. baumannii the possibility of spreading in hospitals. The skin, oropharynx, and digestive tract are the main body areas colonized in hospitalized patients. The risk of colonization and subsequent infection are associated with factors such as the presence of underlying severe illnesses, long-term hospitalization, stays in specific hospital wards, selective antimicrobial pressure, and invasive interventions such as the use of mechanical ventilation or catheters (4,12,14,18).Nosocomial outbreaks of A. baumannii can have their origin in a single reservoir or in multiple contaminated sites (37, 39), and infection can have serious repercussions for patient morbidity and mortality. Patients can acquire the bacterium from an environmental source or from other patients (6, 18).The clonal study of hospital strains is very important in terms of an understanding of the epidemiology of these outbreaks. The aim of the present work was therefore to analyze the genetic diversity and clonal distribution of epidemic strains of A. baumannii isolated from around Spain over a long period of time. Isolates collected during outbreaks at different hospitals were analyzed by pulsed-field gel electrophoresis (PFGE), sequencing of the RNA polymerase ␤ subunit (rpoB) gene, and multilocus sequence typing (MLST). The results were then compared. Antimicrobial susceptibility testing was also performed to determine the multidrug resistance phenotypes of these epidemic strains. MATERIALS AND METHODSBacterial strains. Over the 11-year period from 1997 to 2007, an initial 814 A. baumannii strains isolated from clinical settings and suspected of being involved in nosocomial outbreaks were sent to the Spanish National Center for Microbiology (CNM) for typing. Strains were isolated from 19 public hospitals in 17 Spanish provinces. Hospitals were coded H1 to H19, and provinces were coded P1 to P17. The type of clinical sample, the hospital ward of origin, and the isolation per...

Mutation frequencies were studied in 174 Stenotrophomonas maltophilia isolates from clinical and nonclinical environments by detecting spontaneous rifampin-resistant mutants in otherwise-susceptible populations. The distribution of mutation frequencies followed a pattern similar to that found for other bacterial species, with a modal value of 1 ؋ 10 ؊8 . Nevertheless, the proportion of isolates showing mutation frequencies below the modal value (hypomutators) was significantly higher for S. maltophilia than those so far reported in other organisms. Low mutation frequencies were particularly frequent among environmental S. maltophilia strains (58.3%), whereas strong mutators were found only among isolates with a clinical origin. These results indicate that clinical environments might select bacterial populations with high mutation frequencies, likely by secondorder selection processes. In several of the strong-mutator isolates, functional-complementation assays with a wild-type allele of the mutS gene demonstrated that the mutator phenotype was due to the impairment of MutS activity. In silico analysis of the amino acid changes present in the MutS proteins of these hypermutator strains in comparison with the normomutator isolates suggests that the cause of the defect in MutS might be a H683P amino acid change.

Susceptibility to 41 antimicrobials was studied with 99 Stenotrophomonas maltophilia strains, and different pulsed-field gel electrophoresis profiles were identified among 130 prospectively collected isolates. Moxalactam, doxycycline, minocycline, and clinafloxacin displayed the highest activity (>98% susceptibility). Ticarcillin resistance (75%) was reverted by clavulanate in 25% of strains. Trimethoprim-sulfamethoxazole resistance was 26.2% (>4 [trimethoprim]/76 [sulfamethoxazole] g/ml) and dropped to 11.1% when an 8/152-g/ml breakpoint was applied based on its bimodal MIC distribution. Resistance was lower when unique strains were considered, because clonal organisms contribute to resistance.

No abstract

No abstract

All the studied genes and their related ISs showed a clonal distribution. Imipenem resistance was probably provided by OXA-40 for the most part, while MBL- and OXA-23-encoding genes were absent in the studied population.