A multidisciplinary look at Stenotrophomonas maltophilia: an emerging multi-drug-resistant global opportunistic pathogen

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A multidisciplinary look at Stenotrophomonas maltophilia: an emerging multi-drug-resistant global opportunistic pathogen


Stenotrophomonas maltophilia relates to an aerobic, gram-negative, motile, as well as non-fermentative bacillus widely considered an opportunistic pathogen. In most cases, it leads to infection in persons with immunosuppression, malignancies, and organ transplantation. As an organism, Stenotrophomonas maltophilia is an opportunist acquired from the environment and has been found to have limited ability to cause infections or colonize patients. Nonetheless, contaminated water of medical instruments in hospital environments are the principal causes of infection. Indeed, Stenotrophomonas maltophilia has been demonstrated to cause blood stream infections as well as pneumonia with substantial morbidity immuno-suppressed patients. In turn, intrinsic resistance inhibits infection management to various antibiotic classes. Prevention is dependent upon the utilization of modern practices including an emphasis on the antibiotic control use as well as environmental reservoirs.


Stenotrophomonas maltophilia refers to an opportunist bacterium, which is acquired from the environment. It is part of the non-fluorescent cluster of pseudomonas cluster of bacteriae. In addition, it is considered a frequent colonizer of fluids found in hospital environments including water baths, nebulizers, intravenous fluids, as well as dialysis machines. In most cases, infections cause by this bacterium are usually seen in immuno-weakened individuals especially in instances of prolonged hospital stay, with administration of wide spectrum antibiotics as well as malignancies. In fact, the most widespread manifestations due to this bacterium involve the soft tissues and skin. Nevertheless, Stenotrophomonas maltophilia is the only type or species of this genus (Stenotrophomonas) known to cause infections (Lee et al 2014, p. 1143-1148). Initially isolated from pleural fluid in 1943, the organism was labeled bacterium brookeri. Later on, the organism was reclassified as Pseudomonas maltophilia and Swings et al (2000, p. 1749–60) reclassified it leading to the name Stenotrophomonas maltophilia. Altogether, the bacterium has several factors making it a cause for concern among professionals today. For instance, its rate of isolation leading to serious infection in immune-weakened individuals is on the rise. Yet in the clinical environment, differentiation between contamination or colonization as well as true infection with the bacterium is repeatedly challenging. As cited above, antibiotic treatment is largely inhibited by broad drug resistance, the absence of controlled clinical treatment experiments as well as uncertainties over the value of in-vitro vulnerability testing. In fact, a major challenge in choosing optimal agents emerges when the estabslihed drug choice, in particular co-trimoxazole, is not an option because of contraindications including resistance.

Nonetheless, minimal progress has been made regarding identification of risk factors for the contraction of severe Stenotrophomonas maltophilia infections including pneumonia, bacteraemia as well as the mortality risk. One of the breakthrough is that management of antibiotic use has been shown as key to prevention of infections in hospital settings. Altogether, Stenotrophomonas maltophilia has emerged as a human pathogen increasingly challenging microbiologists, clinicians as well as infection-management specialists by exhibiting difficult situations. Thus, the aim of this paper revolves around exploring the present knowledge about the bacterium including epidemiology, pathogenicity as well as clinical issues associated with this problematic opportunist.

Taxonomy, microbiology and identification

Stenotrophomonas maltophilia or bacterium booker, was initially isolated decades ago and later on placed in the genus pseudomonas. It would later use the name xanthomonas before resting in Stenotrophomonas on the onset of the new millennium. Nevertheless, the genus (Stenotrophomonas) presently is known to comprise of four species and maltophilia is the one the causes human infection. Much information on this species remains unknown, but genetic analysis has suggested that Stenotrophomonas maltophilia has adapted over the years to human colonization after losing certain plant pathogenic characteristics. Subsequently, it gained likely human virulence traits (Vidigal 2013, p. 651-654). In fact, the closest known sequenced relatives of this bacterium include the plant pathogenic xanthomonads. The bacterium isolates from clinical as well as environmental sources represent various genomic clusters – defined through DNA hybridization as well as DNA fingerprinting. In addition, a number of groups including A, B and C have been identified via 16S rRNA sequencing, with the former revealing the highest resemblance to the Stenotrophomonas maltophilia bacterium. Several analysis of a group of clinical isolates are under group A and B, with relatively high genetic heterogeneity in the later group. Nonetheless, it remains possible that the first group strains share a number of characteristics favoring the growth of infection. It has been put forward that isolates from specific genomic clusters might be highly adapted to colonizing the respiratory system of individuals suffering from cystic fibrosis.

Stenotrophomonas maltophilia has also been shown to form biofilms solely or together with various species. Worth noting is that once the bacterium is growing in biofilms it becomes more resistant to antibiotics and phagocytes and thus underlining the challenge it presents to clinicians. Even though Stenotrophomonas maltophilia is known to engage in quorum sensing or cell to cell signaling, it does not utilize the standard LuxIR systems associated with gram-negative bacteria. Rather, it utilizes the diffusible signaling factor molecule present in the xylella and xanthomonas signaling systems. Also worth noting is that diffusible signaling factor disruption contributes to reduced biofilm growth, minimized production of extracellular proteases, loss of motility as well as increased susceptibility to heavy metals and various antibiotics. In addition, Stenotrophomonas maltophilia is known to modify the biofilm configuration as well as polymixin tolerance of pseudomonas aeruginosa by diffusible signaling factor signaling. It can also develop small colony variants – a form adapted for survival during chronic infections – which can be challenging to identify in clinical specimens. In sum, culture out of generally sterile body sites is rather straightforward, and bacteraemia as well as sever sepsis may be detected using standard blood culture methods. Additionally, lecetive media can enhance culture sensitivity for specimens gotten from non-sterile settings including respiratory secretion out of individuals suffering from cystic fibrosis. Currently, PCR use for diagnostic purposes needs further evaluation (LiPuma et al 2007, p. 749–769).