Acinetobacter species isolates from a range of environments: species survey and observations of antimicrobial resistance☆
Introduction
Acinetobacter species are aerobic, nonmotile, Gram-negative coccobacillary rods and are commonly classified as nonfermentative bacteria along with Pseudomonas aeruginosa and Stenotrophomonas maltophilia. They have been implicated in pneumonia, urinary tract infections, skin and soft tissue infections, and bloodstream infections (Lee and Ko, 2012). Although Acinetobacter species were viewed as colonizers and often ignored in clinical settings until the 1980s, they have emerged as major causal agents of healthcare-associated infections, particularly in immunocompromised patients and patients in intensive care units (Munoz-Price and Weinstein, 2008). Acinetobacter species are ubiquitous within the environment and are found in soil, water, and on the dry surfaces of diverse devices. The ability to persist in diverse environments makes Acinetobacter species one of the most common pathogens in hospitals (Espinal et al., 2012). In addition to nosocomial infections, recent reports suggest that Acinetobacter species cause community-acquired infections (Falagas et al., 2007, Kang et al., 2012). Thus, environmental exposure to Acinetobacter species should not be ignored as a potential agent of disease. Although the species distribution and antimicrobial resistance of Acinetobacter species isolates from hospitals are well studied, those of environmental Acinetobacter species isolates have not (Zeana et al., 2003).
In this study, we describe the isolation of Acinetobacter species from a range of environments, including soil. Species identification was performed via 16S rRNA and partial rpoB gene sequencing, and antimicrobial resistance was also investigated. Several isolates of A. baumannii, the most important nosocomial pathogen among the Acinetobacter species, were identified, and antimicrobial-resistant Acinetobacter species isolates, including imipenem-resistant or colistin-resistant isolates, were also found.
Section snippets
Bacterial isolation
To obtain microorganisms from soil, soils were sampled in 7 different locations in South Korea (Table 1). One gram of soil sample was suspended in 10 mL of distilled water and diluted 1:50. The diluted soil sample was spread on blood agar and incubated at 30 °C for 24 h. Microorganisms were also isolated from various life environments, which are defined in this study as artificial environments excluding soil, water, air, etc., near where the soil samples were obtained using sterilized cotton
Results
As a result of bacterial identification of 409 isolates using 16S rRNA gene sequencing, genus Bacillus was the most predominant (173 isolates). In addition to Bacillus, Arthrobacter, Psychrobacter, Acinetobacter, Aeromonas, and Pseudomonas were also frequently isolated. A total of 29 isolates were isolated from soil and life environment and identified to belong to the genus Acinetobacter based on 16S rRNA gene sequence analysis. While 20 of the 29 isolates showed ≥ 99% 16S rRNA gene sequence
Discussion
In this study, we observed the diversity of Acinetobacter species isolates obtained from a range of environments. Three previously described Acinetobacter species and 3 new species candidates were identified from soil, and 10 previously described Acinetobacter species and 3 genomic species were identified from life environment. One of the most important findings may be the identification of nosocomial human pathogens such as A. baumannii, A. nosocomialis, A. pittii, and Acinetobacter gen. sp.
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This study was partially supported by grants from the National Institute of Environment Research, South Korea.