We report the 5.1-Mb genome sequence of Xanthomonas citri pv. mangiferaeindicae strain LMG 941, the causal agent of bacterial black spot in mango. Apart from evolutionary studies, the draft genome will be a valuable resource for the epidemiological studies and quarantine of this phytopathogen.

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.

DNA primers corresponding to conserved motifs in bacterial repetitive (REP, ERIC, and BOX) elements and PCR were used to show that REP-, ERIC-, and BOX-like DNA sequences are widely distributed in phytopathogenic Xanthomonas and Pseudomonas strains. REP-, ERIC, and BOX-PCR (collectively known as rep-PCR) were used to generate genomic fingerprints of a variety of Xanthomonas and Pseudomonas isolates and to identify pathovars and strains that were previously not distinguishable by other classification methods. Analogous rep-PCR-derived genomic fingerprints were generated from purified genomic DNA, colonies on agar plates, liquid cultures, and directly from lesions on infected plants. REP, ERIC, and BOX-PCR-generated fingerprints of specific Xanthomonas and Pseudomonas strains were found to yield similar conclusions wtih regard to the identity of and relationship between these strains. This suggests that the distribution of REP-, ERIC, and BOX-like sequences in these strains is a reflection of their genomic structure. Thus, the rep-PCR technique appears to be a rapid, simple, and reproducible method to identify and classify Xanthomonas and Pseudomonas strains, and it may be a useful diagnostic tool for these important plant pathogens.

From December 1985 to May 1986, Xanthomonas maltophilia (formerly known as Pseudomonas maltophilia) was isolated at an increased rate at our institution; 52 isolates of X. maltophilia were obtained in cultures of clinical specimens from 38 patients during that time. The records of 35 of these patients form the basis of this study. Twelve (71%) of the 17 infected and nine (50%) of the 18 colonized patients had received or were receiving antimicrobial therapy. Eleven of 17 patients (three of seven with septicemia, three of five with pneumonia, three with urinary tract infection, and two with wound infection) responded to antimicrobial therapy. Microbiologic studies of the potential environmental sources revealed growth of X. maltophilia in two water faucets and in one water sample from the medical intensive care unit. X. maltophilia is emerging as an important nosocomial pathogen in immunocompromised patients, especially those receiving broad-spectrum antimicrobial therapy.

We reviewed 149 episodes of septicemia caused by X. maltophilia and Pseudomonas spp. occurring over a 15-year period. The incidence of septicemia caused by these organisms increased in recent years and was most frequently associated with central venous catheterization. These infections were occasionally complicated by pneumonia or endocarditis, which was often fatal. Although the survival rate was superior to that seen with septicemia caused by other gram-negative organisms, recurrence of infection was significantly more frequent. Removal of central venous catheters is an essential component of therapy of this infection.

DNA was isolated from phenol-digesting activated sludge, and partial fragments of the 16S ribosomal DNA (rDNA) and the gene encoding the largest subunit of multicomponent phenol hydroxylase (LmPH) were amplified by PCR. An analysis of the amplified fragments by temperature gradient gel electrophoresis (TGGE) demonstrated that two major 16S rDNA bands (bands R2 and R3) and two major LmPH gene bands (bands P2 and P3) appeared after the activated sludge became acclimated to phenol. The nucleotide sequences of these major bands were determined. In parallel, bacteria were isolated from the activated sludge by direct plating or by plating after enrichment either in batch cultures or in a chemostat culture. The bacteria isolated were classified into 27 distinct groups by a repetitive extragenic palindromic sequence PCR analysis. The partial nucleotide sequences of 16S rDNAs and LmPH genes of members of these 27 groups were then determined. A comparison of these nucleotide sequences with the sequences of the major TGGE bands indicated that the major bacterial populations, R2 and R3, possessed major LmPH genes P2 and P3, respectively. The dominant populations could be isolated either by direct plating or by chemostat culture enrichment but not by batch culture enrichment. One of the dominant strains (R3) which contained a novel type of LmPH (P3), was closely related to Valivorax paradoxus, and the result of a kinetic analysis of its phenol-oxygenating activity suggested that this strain was the principal phenol digester in the activated sludge.

We identified 91 cases of bacteremia due to Stenotrophomonas (Xanthomonas) maltophilia in a prospective, multicenter observational study. The patients were highly compromised; the majority had an underlying malignancy, had received immunosuppressive therapy, and had indwelling venous catheters. Although 94% of patients received an antimicrobial agent to which the blood isolate was susceptible, the mortality among these patients 14 days after the onset of bacteremia was 21%. Mortality was significantly correlated with the presence of a hematologic malignancy or neutropenia or transplantation, immunosuppressive therapy, and a severity-of-illness score of > 4. S. maltophilia infection is associated with substantial morbidity and mortality among highly compromised patients. The organism is typically resistant to expanded spectrum beta-lactam agents and aminoglycoside antibiotics. Trimethoprim-sulfamethoxazole should be administered if the isolate is susceptible to this combination; addition of another agent to which the isolate is susceptible should be considered in treating patients who are neutropenic, immunocompromised, or critically ill.

We studied the mineralization of pyrene, carbazole, and benzo[a]pyrene in soils obtained from three abandoned coal gasification plants in southern Illinois. The soils had different histories of past exposure to hydrocarbon contamination and different amounts of total organic carbon, microbial biomass, and microbial activity. Mineralization was measured by using serum bottle radiorespirometry. The levels of indigenous mineralization of 14C-labeled compounds ranged from 10 to 48% for pyrene, from undetectable to 46% for carbazole, and from undetectable to 25% for benzo[a]pyrene following long-term (greater than 180-day) incubations. Pyrene and carbazole were degraded with short or no lag periods in all soils, but benzo[a]pyrene mineralization occurred after a 28-day lag period. Mineralization was not dependent on high levels of microbial biomass and activity in the soils. Bacterial cultures that were capable of degrading pyrene and carbazole were isolated by enrichment, grown in pure culture, and reintroduced into soils. Reintroduction of a pyrene-degrading bacterium enhanced mineralization to a level of 55% within 2 days, compared with a level of 1% for the indigenous population. The carbazole degrader enhanced mineralization to a level of 45% after 7 days in a soil that showed little indigenous carbazole mineralization. The pyrene and carbazole degraders which we isolated were identified as a Mycobacterium sp. and a Xanthamonas sp., respectively. Our results indicated that mineralization of aromatic hydrocarbons can be significantly enhanced by reintroducing isolated polycyclic aromatic hydrocarbon-degrading bacteria.

Factors predisposing to clinically significant nosocomial infection with Xanthomonas maltophilia were examined in a matched case-control study using multivariate techniques. Sixteen cases occurred among cancer patients in a six-month period, including an apparent cluster of three cases in an intensive care unit. These infections were unusually serious; eight patients had disseminated infection caused by X maltophilia and six died as a result of their infections. Among the 64 factors that were examined, therapy with broad-spectrum antibiotics and central venous catheterization were found to significantly increase susceptibility to infection. Therapy with imipenem was more than ten times more frequent among cases than among controls (p less than .001). All fatal infections occurred in patients who had received imipenem, including two patients who died before the organism could be identified and appropriate therapy instituted. Infection with X maltophilia should be suspected in patients who develop superinfection while receiving imipenem, and prompt therapy should be instituted to improve chances of survival. Because a common environmental source of X maltophilia was not identified, further study is necessary to determine specific preventive measures.

Between April 1992 and December 1993, 80 Xanthomonas maltophilia isolates were collected from 63 patients in three acute-care hospitals in Calgary, Alberta, Canada. On the basis of Centers for Disease Control and Prevention definitions, 48 patients had nosocomial and 15 had community-acquired X. maltophilia. Thirty-eight of the patients were colonized and 25 were infected. Sixty-four percent of patients who acquired X. maltophilia in the intensive care unit (ICU) became infected, whereas 32% of patients in a non-ICU setting became infected. ICU patients tended to be hospitalized for a shorter period of time than non-ICU patients before the onset of X. maltophilia infection. Regardless of being colonized or infected, all patients had debilitating conditions, with respiratory disease being the most common underlying illness (35%). Forty-two patients (88%) with hospital-acquired X. maltophilia received prior antibiotic therapy which included gentamicin, tobramycin, ceftazidime, piperacillin, and imipenem. Agar dilution MICs showed that patient isolates were resistant to these antimicrobial agents that patients had received. Pulsed-field gel electrophoresis of SpeI-digested genomic DNA revealed that six epidemiologically linked patient isolates from the ICU of one acute-care hospital had identical DNA profiles. In contrast, isolates from patients from the other two hospitals had unique genotype profiles (n = 57) regardless of the presence or absence of an epidemiologic association. In these patients there was genetic evidence against the acquisition of a resident hospital clone. These results indicate that pulsed-field gel electrophoresis can resolve genotypically distinct strains of X. maltophilia and, consequently, is a useful tool for evaluating nosocomial infections caused by X. maltophilia.

This study was undertaken to examine quantitatively the risks to human health posed by heterotrophic plate count (HPC) bacteria found naturally in ambient and potable waters. There is no clear-cut evidence that the HPC bacteria as a whole pose a public health risk. Only certain members are opportunistic pathogens. Using the four-tiered approach for risk assessment from the National Academy of Sciences, hazard identification, dose-response modeling, and exposure through ingestion of drinking water were evaluated to develop a risk characterization, which estimates the probability of infection for individuals consuming various levels of specific HPC bacteria. HPC bacteria in drinking water often include isolates from the following genera: Pseudomonas, Acinetobacter, Moraxella, Aeromonas, and Xanthomonas. Other bacteria that are commonly found are Legionella and Mycobacterium. All these genera contain species that are opportunistic pathogens which may cause serious diseases. For example, the three nonfermentative gram-negative rods most frequently isolated in the clinical laboratory are (1) Pseudomonas aeruginosa,(2) Acinetobacter, and (3) Xanthomonas maltophilia. P. aeruginosa is a major cause of hospital-acquired infections with a high mortality rate. Aeromonas is sometimes associated with wound infections and suspected to be a causative agent of diarrhea. Legionella pneumophila causes 4%-20% of cases of community-acquired pneumonia and has been ranked as the second or third most frequent cause of pneumonia requiring hospitalization. The number of cases of pulmonary disease associated with Mycobacterium avian is rapidly increasing and is approaching the incidence of M. tuberculosis in some areas. Moraxella can cause infections of the eye and upper respiratory tract. The oral infectious doses are as follows in animal and human test subjects: P. aeruginosa, 10(8)-10(9); A, hydrophila,> 10(10); M. avium, 10(4)-10(7); and X. maltophilia, 10(6)-10(9). The infectious dose for an opportunistic pathogen is lower for immunocompromised subjects or those on antibiotic treatment. These bacteria have been found in drinking water at the following frequencies: P. aeruginosa,< 1%-24%; Acinetobacter, 5%-38%; X. maltophilia,< 1%-2%; Aeromonas, 1%-27%; Moraxella, 10%-80%; M. avium,< 1%-50%; and L. pneumophila, 3%-33%. These data suggest that drinking water could be a source of infection for some of these bacteria. The risk characterization showed that risks of infection from oral ingestion ranged from a low of 7.3 x 10(-9)(7.3/billion) for low exposures to Aeromonas to higher risks predicted at high levels of exposure to Pseudomonas of 9 x 10(-2)(98/100). This higher risk was only predicted for individuals on antibiotics. Overall, the evidence suggests that specific members of HPC bacteria found in drinking water may be causative agents of both hospital- and community-acquired infections. However, the case numbers may be very low and the risks represent levels generally less than 1/10,000 for a single exposure to the bacterial agent. Future research needs include (1) determining the seasonal concentrations of these bacteria in drinking water,(2) conducting adequate dose-response studies in animal subjects or human volunteers,(3) determining the health risks for an individual with multiple exposures to the opportunistic pathogens, and (4) evaluating the increase in host susceptibility conferred by antibiotic use or immunosuppression.