A critical review of 1113 isolates of non-fermentative Gram-negative rods isolated from 794 patients at a rural hospital

Authors:
Hugo Bonatti, Saron Araya, Yohana Araya, Pooja Ajith, Pathya Kunthy, Sridha Gona, Stephen Kavic, Aaron George

Body of Abstract:
Background: Non-fermentative Gram-negative rods derive their name from the inability to use glucose as energy substrate. This diverse group of organisms are found in various natural specimens such as soil; moist environments are their preferred habitat. Pseudomonas aeruginosa is the most common human pathogen in this group with Stenotrophomonas maltophilia, Acinetobacter spp, Alkaligines spp, Achromobacter spp and Moraxella spp amongst many others being important members. They may cause a variety of diseases including soft tissue, urinary tract, respiratory tract and blood stream infections, which may be difficult to treat due to natural antibiotic resistance and rapid development of resistance during treatment.

Methods: Our institutional database was searched for all surgical and blood stream infections caused by non-fermenters during a 4-year period and the most common pathogens were compared to each other.

Results: In total 1113 isolates in 792 patients were identified. Table 1 shows demographic, clinical and microbiology data for the most common pathogens. Pseudomonas aeruginosa (n=850) outnumbered all others; various non-aeruginosa Pseudomonas spp accounted for 35 isolates. More common pathogens were Acinetobacter spp (n=72), Stenotrophomonas maltophilia (n=57) and Alcaligines faecalis (n=40) followed by Moraxella spp (n=110, Achromobacter spp (n=11), Myroides spp (n=10) and Roseomonas spp (n=70. Shewanella spp, Brevundimonas spp, Kocuria spp, Comamonas spp, Delftia spp, Sphingomonas spp, Chryseobacterium spp , Aggregatibacter spp, Trueperella spp and Ochrobactrum anthropic were identified in <5 cases. Median patient age ranged from 60 to 66 years; approximately 55% were male. Median BMI was 32.5kg/m2 in non-aeruginosa Pseudomonas spp patients and 25.9kg/m2 Acinetobacter spp patients. 61% of patients with Alcaligines faecalis infections were active smokers as opposed to 23%-29% for all other pathogens resulting in highest rates of COPD and CAD in the Alcaligines group. Acinetobacter, Stenotrophomonas and Alcaligines infections were more commonly polymicrobial (approximately 70%) than Pseudomonas infections (approximately 50%); in all groups, staphylococci were the most common co-pathogens. Acinetobacter and non-aeruginosa Pseudomonas spp invaded the blood stream in 30% versus 10% (others); soft tissue infections of the lower extremity were in all groups the most common clinical manifestation whereas intraabdominal infections accounted only for 3% to 13% of cases. Survival after 2 years was 91% in patients with Acinetobacter spp infections but only 73% in the Alcaligines group. Conclusion: Pseudomonas aeruginosa remains the most common non-fermenter (almost 75% of cases). Significant differences between the various groups regarding demographics, clinical and microbiology parameters studied were found. The high rate of natural antibiotic resistance makes treatment challenging; for surgical infections source control is of utmost importance.