Abstract
Drug-resistance genes found in human bacterial pathogens are increasingly recognized in saprophytic Gram-negative bacteria (GNB) from environmental sources. The clinical implication of such environmental GNBs is unknown. We conducted a systematic review to determine how often such saprophytic GNBs cause human infections. We queried PubMed for articles published in English, Spanish, and French between January 2006 and July 2014 for 20 common environmental saprophytic GNB species, using search terms "infections," "human infections," "hospital infection." We analyzed 251 of 1,275 non-duplicate publications that satisfied our selection criteria. Saprophytes implicated in blood stream infection (BSI), urinary tract infection (UTI), skin and soft tissue infection (SSTI), post-surgical infection (PSI), osteomyelitis (Osteo), and pneumonia (PNA) were quantitatively assessed. Thirteen of the 20 queried GNB saprophytic species were implicated in 674 distinct infection episodes from 45 countries. The most common species included Enterobacter aerogenes, Pantoea agglomerans, and Pseudomonas putida. Of these infections, 443 (66%) had BSI, 48 (7%) had SSTI, 36 (5%) had UTI, 28 (4%) had PSI, 21 (3%) had PNA, 16 (3%) had Osteo, and 82 (12%) had other infections. Nearly all infections occurred in subjects with comorbidities. Resistant strains harbored extended-spectrum beta-lactamase (ESBL), carbapenemase, and metallo-β-lactamase genes recognized in human pathogens. These observations show that saprophytic GNB organisms that harbor recognized drug-resistance genes cause a wide spectrum of infections, especially as opportunistic pathogens. Such GNB saprophytes may become increasingly more common in healthcare settings, as has already been observed with other environmental GNBs such as Acinetobacter baumannii and Pseudomonas aeruginosa.
Highlights
In 2013, the Centers for Disease Control and Prevention released a report “Antibiotic Resistance in the United States, 2013” that classified groups of drug-resistant microorganisms into “urgent threat,” “serious threat,” and “concerning threat” pathogens [1]
A previous study identified 20 distinct saprophytic Gram-negative bacterial (GNB) species among 231 randomly selected colonies cultured on MacConkey agar plates from 25 batches of retail spinach rinsates [12]
E. aerogenes together with Pantoea agglomerans and Pseudomonas putida together comprised more than half of the reported cases of infection caused by these saprophytic GNBs
Summary
In 2013, the Centers for Disease Control and Prevention released a report “Antibiotic Resistance in the United States, 2013” that classified groups of drug-resistant microorganisms into “urgent threat,” “serious threat,” and “concerning threat” pathogens [1]. Two strains of Pseudomonas putida and one strain of Pseudomonas teessidea contained blaCTX-M-15, the most common ESBL gene distributed globally and carried frequently by the most common pandemic extraintestinal pathogenic E. coli (ExPEC) lineage ST131 [13,14,15,16,17]. They suggested that environmental saprophytes may serve as a reservoir for some of the common drug-resistance genes found in human GNB pathogens [12].
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