Enterobacter Aerogenes – Habitat and Pathogenicity
Among the genera in the Enterobacteriaceae family are Escherichia, Shigella, Salmonella, Enterobacter, Klebsiella, Serratia, and Proteus. These are gram-negative bacteria which can be found in soil, water, dairy products, and in the gastrointestinal tracts of both animals and humans. Enterobacter aerogenes is that species we shall dwell on.
Enterobacteriaceae come in a variety of sizes and are not spore forming, they are motile (with peritrichous flagella) or nonmotile, grow aerobically and anaerobically, are active biochemically, ferment (versus oxidize) D-glucose and other sugars, often with gas production, reduce nitrate to nitrite, contain the enterobacter common antigen, and have a 39-59% guanine-plus-cytosine.
The genus Enterobacter is a nosocomial opportunistic pathogen that is being investigated as one of the major causes of extraintestinal infections, alongside E. coli.
Infections caused by E. aerogenes include respiratory, gastrointestinal, and urinary tract infections, particularly cystitis, as well as wound, bloodstream, and central nervous system infections.
Furthermore, the species most commonly associated with adult cases of meningitis are E. cloacae and E. aerogenes. Enterobacter strain colonies may be slightly mucoid.
Enterobacter aerogenes and Enterobacter cloacae are the most commonly isolated bacteria in clinical samples from infected hospitalized patients.
The majority of infections are caused by the inadvertent transfer of bacteria during surgery or prolonged hospitalization in patients who use venous or urethral catheters.
In clinical microbiology laboratories, Enterobacteriaceae may account for 80% of clinically significant isolates of gram-negative bacilli and 50% of clinically significant bacteria.
Furthermore, they are responsible for nearly half of all septicemia cases and more than 70% of urinary and intestinal tract infections. Because of the severity of these infections, it is critical to target, isolate, identify, and test for susceptibility to the causes of these nosocomial infections.
What is Enterobacter Aerogenes?
Aerobacter aerogenes was renamed Enterobacter aerogenes after being included in the genus Enterobacter in 1960. Because of its peritrichous flagella motility and genetic similarity to the Klebsiella genus, this species was proposed to be renamed Klebsiella mobilis in 1971.
Enterobacter is a genus of Gram-negative, facultative anaerobic, rod-shaped, non-spore-forming bacteria in the Enterobacteriaceae family.
The most common bacterial isolates recovered from clinical specimens are Enterobacteriaceae. These bacteria have an outer membrane that contains lipopolysaccharides, one of which, lipid-A, is important in sepsis.
Endotoxin, also known as lipid-A, is the primary inducer of the release of cytokines, which are the mediators of systemic inflammation and its complications. Enterobacter aerogenes and Enterobacter cloacae, two well-known Enterobacter species, have gained clinical significance as opportunistic bacteria and emerged as hospital acquired (nosocomial) pathogens from intensive care patients, particularly those on mechanical ventilation.
How does Enterobacter Aerogenes infections spread?
Cross-contamination from surgery or consistent treatment in hospitals for patients who use catheters is a common way for Enterobacter aerogenes to spread.
Diseases/Infections caused by Enterobacter Aerogenes
Because of the ubiquitous nature of Enterobacter species, the source of infection can be endogenous (via colonization of the skin, gastrointestinal tract, or urinary tract) or exogenous.
Infections caused by Enterobacter aerogenes
Many nosocomial infections and, less frequently, community-acquired infections are caused by Enterobacter species.
Infections Caused by Enterobacter Include:
Bacteremia
Lower respiratory tract infections
Skin and soft-tissue infections
Urinary tract infections (UTIs)
Endocarditis
Intra-abdominal infections
Septic Arthritis
Osteomyelitis
Central Nervous System (CNS) infections
Ophthalmic infections.
Enterobacter infections can necessitate extended hospitalization, a plethora of imaging studies and laboratory tests, a variety of surgical and nonsurgical procedures, and powerful and costly antimicrobial agents.
How do you treat Enterobacter aerogenes infections?
Carbapenems have proven to be the most effective antibiotics for infections caused by ESBL-producing Enterobacteriaceae.
How To Prevent Infections From Enterobacter Aerogenes
Because Enterobacter aerogenes is antibiotic resistant, most antibiotics are ineffective in treating infections.
Proactive prevention practices are the most effective way to combat these bacteria. Active adherence to standard hand-hygiene regimens, environmental decontamination procedures, controlled antibiotic use, and aseptic insertion of catheters and implanted devices can all help to reduce bacteria transmission.
Where are Enterobacter Aerogenes Found Naturally?
Enterobacter aerogenes is a ubiquitous bacteria in the environment, found naturally in soil, fresh water, vegetables and human and animal faeces.
Enterobacter Aerogenes is an important nosocomial pathogen that often produces extended-spectrum b-lactamases (ESBL). It can cause infections of the respiratory tract, urinary tract, and other organs.
Identification of this bacteria by routine laboratory methods is usually fast and straightforward. However, it has been shown that genotypically unrelated E. aerogenes strains can be misidentified as K. pneumoniae by phenotypic tests such as ornithine decarboxylase and motility.
Macromolecular Makeup of Enterobacter Aerogenes
Enterobacter Aerogenes is a gram-negative bacteria belonging to the family of Enterobacteriaceae. This strain is facultatively anaerobic and can be found in soil, wastewater and human faeces. Its cells are rod-shaped and measure 1.5-1.9 mm x 0.6-0.8 mm. It can cause wound (Munez et al 2012), respiratory and urinary tract infections. It can also form ESBL-bacteremia and is resistant to many antibiotics (Edlin 2013).
This bacterium was isolated from a sample of whey permeate from the cheese production process and named as LU2. The strain is capable of producing succinate (SA), a valuable bio-based compound. The strain is capable of using different carbon sources during fermentation, such as lactose, sucrose, maltose, xylose, cellobiose and sorbitol.
The morphological characteristics of the strain were determined by electron microscopy. In addition, the growth curves of the strain were analysed under various fermentation conditions. The results showed that the strain LU2 could produce SA from whey permeate and reach the logarithmic phase within 72 h. Moreover, the optimal temperature for SA production was 37 degC.
The strain was infected with the phage phiEap-2 and subjected to titration for phage detection. A mid-exponential culture of the strain (3 ml) was inoculated with the phage at a multiplicity of infection of 0.1. The cells were incubated at 37 degC and sampled for phage titration every 10 min for 80 min. Cell debris from the culture was collected by centrifugation (8,500 x g, 20 min, 4 degC). The precipitated phage particles were resuspended in TM buffer for TEM studies.
Laboratory Examination of Enterobacter Aerogenes
The most important laboratory tests for patients with suspected Enterobacter infections include blood work (complete blood count, bile pigments, Bence Jones proteins), urinalysis (blood, reducing sugars, urea and creatinine) and a stool examination for ova and cysts of parasites. A faecal culture is usually done as well.
A faecal culture is done by collecting a sample of a person’s stool into a clean sterile container. It is then placed in the laboratory for culturing. It is important to note that it takes at least a few days for cultures to be ready. The specimen should be refrigerated before sending to the laboratory.
When collecting a stool sample, it is necessary to label the container with the patient’s name and the type of test being performed. It is also important to collect the first, last and middle of the stool.
The stool sample is cultured in a special medium that contains carbon, nitrogen and phosphates. The medium is then inoculated with a sample of the patient’s blood. The specimen should be stored in a sterile container with the lid closed and placed in a refrigerator. A syringe needle needs to be used and the rubber bung of the culture bottle needs to be cleaned with iodine before injection of blood. This is to prevent contamination of the culture medium and subsequent errors.
Identification of Enterobacter Aerogenes in Clinical Cultures
The bacterium Enterobacter aerogenes is a Gram-negative rod and is close in nature to E. coli and Klebsiella. These bacteria have similar characteristics such as a thin cell wall. Therefore, it is important to differentiate these bacteria in clinical culture by growing them on blood agar and McConkey agar. The presence of lactose fermenting colonies helps in identification. Molecular techniques such as PCR can be used to verify the identity of these bacteria.
This GDEPIH/GOSPIZ survey involved all Belgian hospitals and asked them to report their Enterobacter incidence figures (excluding non-hospitalized patients). Incidences per hospital were calculated using the Poisson regression model for differences in incidence and a Chi-square test for trends between years.
Molecular typing of the ESBL-producing colistin-resistant E. aerogenes isolate showed that it carried the IncN plasmid. It also had an altered porin protein whose decrease could have been the result of selection pressure following antibiotic treatment.
This study shows the importance of accurate identification of antibiotic resistant bacteria. Misidentification would lead to the wrong prescription of antibiotics which would contribute to the emergence of resistance mechanisms in these bacteria. Detailed sensitivity tests should be performed on all pathogenic bacteria including Enterobacter aerogenes as they have the potential to develop antibiotic resistance. This can be accomplished by determining whether the bacteria are susceptible to certain antibiotics in a specific medium.
Resistance of Enterobacter Aerogenes to Antibiotics
The gram-negative bacteria Klebsiella and Enterobacter are normal intestinal flora that rarely cause disease in healthy people. However, they can cause serious infections in patients with weakened immune systems. These include infections of the urinary tract, bacteremia, pneumonia and sepsis. They are also associated with severe urinary tract infection, septicemia and pneumonia in critically ill patients in intensive care units. They may also cause otitis media, cellulitis and neonatal sepsis.
Bacterial resistance to antibiotics has been one of the major causes of treatment failure in hospitalized patients. This is particularly true of Enterobacter, which can be resistant to many commonly used drugs. Plasmid-mediated extended-spectrum beta-lactamases (ESBLs) have contributed to this problem. These enzymes degrade the activity of cephalosporins, resulting in decreased efficacy of this class of antibiotics.
The use of phage is an important method for eliminating E. aerogenes. The phage phiEap-2, for example, was developed to target the bacteria by binding to its DNA. The phage has an isometric head, long non-contractile tails and a double-stranded genome that is similar to Salmonella phage FSL SP-031. Its genome does not contain phage lysogeny factors, toxins or antibiotic resistance genes. It is also stable, making it suitable for commercial application. The phage has been shown to be effective against ESBL-producing E. aerogenes and has been tested in patients with pneumonia caused by this pathogen.
