A Systematic Review of Intracellular Microorganisms within Acanthamoeba to Understand Potential Impact for Infection

Abstract

Acanthamoeba, an opportunistic pathogen is known to cause an infection of the cornea, central nervous system, and skin. Acanthamoeba feeds different microorganisms, including potentially pathogenic prokaryotes; some of microbes have developed ways of surviving intracellularly and this may mean that Acanthamoeba acts as incubator of important pathogens. A systematic review of the literature was performed in order to capture a comprehensive picture of the variety of microbial species identified within Acanthamoeba following the Preferred Reporting Items for Systematic Reviews and Meta-Analysis (PRISMA) guidelines. Forty-three studies met the inclusion criteria, 26 studies (60.5%) examined environmental samples, eight (18.6%) studies examined clinical specimens, and another nine (20.9%) studies analysed both types of samples. Polymerase chain reaction (PCR) followed by gene sequencing was the most common technique used to identify the intracellular microorganisms. Important pathogenic bacteria, such as E. coli, Mycobacterium spp. and P. aeruginosa, were observed in clinical isolates of Acanthamoeba, whereas Legionella, adenovirus, mimivirus, and unidentified bacteria (Candidatus) were often identified in environmental Acanthamoeba. Increasing resistance of Acanthamoeba associated intracellular pathogens to antimicrobials is an increased risk to public health. Molecular-based future studies are needed in order to assess the microbiome residing in Acanthamoeba, as a research on the hypotheses that intracellular microbes can affect the pathogenicity of Acanthamoeba infections.

Survival of Campylobacter jejuni in Amoebae enhances subsequent invasion of mammalian cells

“…In our amoebae model, the greater survivability of C. jejuni within A. castellanii seems to be a host susceptibility factor rather than being bacterial induced. This phenomenon was also reported in other bacteria, where greater levels of invasion and intracellular survivability of Listeria monocytogenes was observed in A. castellanii [29] compared to other Acanthamoeba spp .. A recent review proposed that invasion and intracellular occurrences of microbes within amoebae is dependent on the genotype of the host [30]. Based on 18S RNA sequence studies, A. castellanii is from the T4 genotype [31] whilst A. polyphaga is from the T2 genotype [32], although how host genotype plays a role in intracellular survival remains unknown.…”

Transient internalization of Campylobacter jejuni in Amoebae enhances subsequent invasion of human cells

“…This phenomenon was also reported in other bacteria, where greater levels of invasion and intracellular survivability of Listeria monocytogenes was observed in A. castellanii [ 31 ] compared to other Acanthamoeba spp. A recent review proposed that invasion and intracellular occurrences of microbes within amoebae is dependent on the genotype of the host [ 32 ]. Based on 18S RNA sequence studies, A. castellanii is from the T4 genotype [ 33 ] whilst A. polyphaga is from the T2 genotype [ 34 ], although how host genotype plays a role in intracellular survival remains unknown.…”

The role of free-living amoebae in the persistence of viruses in the era of severe acute respiratory syndrome 2, should we be concerned?

“…In the environment, FLA feed on particulate organic material or prey on various microorganisms, such as protozoa, fungi, bacteria, and viruses. Some of these microorganisms escape the intracellular digestion route, survive, and multiply within the FLA (in many cases, leave and recolonize the extra-amoebic environment), which is why they are called amoeba-resistant microorganisms (ARM) 5 . ARM is phylogenetically diverse and includes the main taxa with microbial representatives, including bacteria, fungi, and viruses.…”