Decreases in abundance of several bacterial taxa may be associated with increased risk for carbapenem-resistant Pseudomonas aeruginosa colonization-acquisition in intensive care unit (ICU) patients, according to a study published in Clinical Infectious Diseases.

The gastrointestinal (GI) microbiota provides colonization resistance by preventing pathogen colonization and/or inhibiting pathogen overgrowth. However, a significant subset of hospitalized patients experience a collapse of their GI microbiota that increases the risk for colonization and infection by antibiotic-resistant pathogens. In addition, antibiotics are major contributors to dysbiosis in the GI microbiota. Around 28% of ICU patients colonized with carbapenem-resistant P aeruginosa develop infection as a result of colonizing a strain of the bacteria during their ICU stay, suggesting prevention of carbapenem-resistant P aeruginosa colonization-acquisition represents an important target for interventions to reduce infection and the spread of carbapenem-resistant P aeruginosa in the hospital. Previous studies have not examined relationships among the microbiota, medications, and carbapenem-resistant P aeruginosa colonization-acquisition. Therefore, this study aimed to describe the GI microbiota of ICU patients, examine the effect of antibiotics and other medications on the GI microbiota, and identify taxonomic markers associated with carbapenem-resistant P aeruginosa colonization-acquisition in the GI tract.

At the University of Maryland Medical Center, data and 259 perirectal swabs were collected from 109 patients in the ICU. Patients were then classified into 3 groups by carbapenem-resistant P aeruginosa colonization-acquisition status and antimicrobial exposure, including patients with carbapenem-resistant P aeruginosa colonization-acquisition during their ICU stay (group 1), patients without carbapenem-resistant P aeruginosa colonization-acquisition (group 2), and patients who did not receive systemic antibiotics and did not have carbapenem-resistant P aeruginosa colonization-acquisition during their ICU stay (group 3). After 16S rRNA gene sequencing of at least 2 swabs, associations among patient characteristics, medications, carbapenem-resistant P aeruginosa colonization-acquisition, and the GI microbiota were evaluated. The 3 patient groups did not differ significantly by age, sex, race, or time between collection of swab 1 and swab 2.

Results demonstrated that the GI microbiota of patients in the ICU is characterized by high levels of pathobionts (Enterococcus, Escherichia, Staphylococcus, Enterobacteriaceae, and/or Pseudomonas) and low levels of bacterial diversity. In these patients, the effective number of species in their GI microbiota was low, ranging from 5 to 14 effective species per patient across all groups compared with the approximately 160 different taxa in healthy people. Further, 55.9% of patients were experiencing dominance by at least 1 of the 5 most frequent pathobionts at ICU admission. Piperacillin-tazobactam was prescribed more frequently to patients with carbapenem-resistant P aeruginosa colonization-acquisition compared with patients without colonization, and was associated with low abundance of potentially protective bacterial taxa and increased risk for Enterococcus domination (odds ratio [OR], 5.50; 95% CI, 2.03-14.92). Potentially protective bacterial taxa had higher abundance in patients who did not receive opioids. Between groups 1 and 2, the study examined the effect of combined use of 2 commonly prescribed and mutually exclusive antibiotic groups on carbapenem-resistant P aeruginosa colonization-acquisition: anti-anaerobic and anti-methicillin-resistant Staphylococcus aureus. Results suggested that the risk for carbapenem-resistant P aeruginosa colonization-acquisition was associated with prescription of both antibiotic groups when compared with prescription of no antibiotics (OR 3.06; 95% CI, 1.00-9.40).

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Overall, the study authors concluded that, “Greater understanding of these relationships will facilitate 1) the development microbiota disruption indices that could be used for monitoring patients for risk of [carbapenem-resistant P aeruginosa] colonization and infection, and 2) the development of strategies to minimize infection and spread of [carbapenem-resistant P aeruginosa] in the hospital.”


Pettigrew MM, Gent JF, Kong Y, Halpin AL, Pineles L, Harris AD, Johnson JK. Gastrointestinal microbiota disruption and risk of colonization with carbapenem-resistant Pseudomonas aeruginosa in ICU patients [published online Novemeber 1, 2018]. Clin Infect Dis. doi: 10.1093/cid/ciy936/5154869