Elizabethkingia anopheles is a gram-negative, rod-shaped bacterium which has resulted in a multistate outbreak of mainly bloodstream infections in the states of Wisconsin, Michigan and Illinois. Affecting primarily those individuals over 65 years of age with at least one serious underlying health condition, the states along with the Centers for Disease Control and Prevention are attempting to isolate the source(s) and contain the outbreak before further spread occurs.
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A multistate outbreak of infections caused by a bacterium called Elizabethkingia anopheles is being investigated by the Centers for Disease Control and Prevention (CDC), the Wisconsin Department of Health Services (WDHS), the Michigan Department of Health and Human Services (MDHHS) and the Illinois Department of Public Health (IDPH) (Table1).
|As of April 12, 2016||Wisconsin|
Number of Confirmed Cases (includes deaths)
|Deaths among Confirmed Cases||18||1||1|
|Cases under Investigation||2|
|Total Cases Reported to WDHS, MDHHS and IDPH respectively||63||1||1|
* These are cases that tested positive for Elizabethkingia, but will never be confirmed as the same strain of Elizabethkingia anophelis because the outbreak specimens are no longer available to test.
The majority of the patients who have had Elizabethkingia infections as part of this outbreak are over the age of 65 years and all have had serious underlying health conditions. The majority of the infections identified to date have been bloodstream infections but some patients have had Elizabethkingia isolated from other sites such as their respiratory systems or joints. It has not been determined whether the deaths associated with this outbreak were caused by the bacterial infection, the patients’ underlying health conditions or both. Most outbreaks associated with Elizabethkingia are healthcare-associated. There are few reports of community-acquired infections.
Elizabethkingia infections are often difficult to treat with antibiotics. These bacteria are resistant to many of the antibiotics healthcare providers use to treat infections. Early recognition of the bacteria is critical to ensure patients receive appropriate treatment and increase the probability of good outcomes. The signs and symptoms of illness that can result from exposure to the bacteria include fever, shortness of breath, chills or cellulitis. Confirmation of the illness requires a laboratory test.
The CDC is continuing to work with the WDHS, MDHHS and IDPH to identify the source of the bacteria and develop ways to prevent these infections. The CDC is assisting with testing samples from a variety of potential sources, including healthcare products, water sources and the environment. To date, none of these have been found to be a source of the bacteria.
The genus Elizabethkingia currently includes four species (Table 2):
E. endophyticaE. anopheles
E. anophelis has a circular genome of 4,369,828 base pairs and 4,141 predicted coding sequences. 16S rRNA gene sequence analysis revealed that E. anopheles showed 98.6% sequence similarity to that of E. meningoseptica and 98.2% similarity to that of E. miricola.
DNA-DNA hybridization experiments with E. meningoseptica and E. miricola gave relatedness values of 34.5 % (reciprocal 41.5 %) and 35.0 % (reciprocal 25.7 %), respectively. DNA-DNA hybridization results and some differentiating biochemical properties indicate that species R26(T) represents a novel species, for which the name E. anophelis was proposed.
The draft genomes were annotated using the National Center for Biotechology Information (NCBI) Prokaryotic Genome Automatic Annotation Pipeline (http://www.ncbi.nlm.nih.gov/genome/annotation_prok/), which predicted 3,687 protein-coding sequences (CDS) and 44 RNA genes in R26(T) and 3,648 CDS and 38 RNA genes in Ag1. Strikingly, 112 protein features were identified in the category “resistance to antibiotics and toxic compounds”. This included drug efflux/transport (36 features); resistance to β-lactam antibiotics, fluoroquinolones and heavy metals (28, 4 and 25 features, respectively) and 19 additional features involved in resistance to a diverse set of antibiotics. The large genetic capacity against various antibiotics is consistent with the observation that E. anophelis has natural antibiotic resistance to several antibiotics.
E. anophelis is a bacterial species in the family Flavobacteriaceae. The bacterium is a slightly yellow-pigmented, non-motile, non-spore-forming, gram-negative, rod-shaped cell. E. anophelis has two growth optima at 30 - 31 °C and 37 °C. It is a dominant resident in the mosquito gut of the malaria vector mosquito, Anopheles gambiae, and also a human pathogen. The possibility of a role for mosquitoes in the maintenance and transmission of E. anophelis remains unclear.
E. anophelis utilizes complex carbohydrates (glycans) in its metabolism with starch-utilization systems (Sus) including proteins:
SusD (glycan-binding protein)
SusC (Ton-B dependent transporter)
SusE/SusF (carbohydrate-binding proteins without enzyme activity)
SusA, SusB, SusG (enzymes for polysaccharide deconstruction)
SusR (an inner membrane-associated sensor-regulator system for transcriptional activation of Sus genes).
The major fatty acids of E. anophelis, strain R26(T) were iso-C(15 : 0), iso-C(17 : 0) 3-OH and summed feature 4 (iso-C(15 : 0) 2-OH and/or C(16 : 1)ω7c/t). Strain R26(T) contained only menaquinone MK-6 and showed a complex polar lipid profile consisting of diphosphatidylglycerol, phosphatidylinositol, an unknown phospholipid and unknown polar lipids and glycolipids.
The bacterium produces several hemolysins that may participate in the digestion of erythrocytes in the mosquito gut. Numerous TonB-dependent transporters (TBDTs) with various substrate specificities help the bacterium to utilize polymers. E. anophelis has well-developed systems for scavenging iron and stress response. The bacterial TBDTs are specialized elaborate machinery for active uptake of rare but essential nutrients and other substrates, such as iron complexes, vitamin B12, nickel, carbohydrates and colicin. To energize the transport process, TBDTs interact with the TonB complex, a cytoplasmic transmembrane assembly of the proteins ExbB and ExbD, which couples with the TonB in periplasm.
The cell also produces efflux pumps and β-lactamases that give the bacterium broad antibiotic resistance. RNA-sequencing-based transcriptome profiling indicates that expressions of genes involved in synthesis of a yersinibactin-like iron siderophore and heme utilization are highly induced as a protective mechanism toward oxidative stress caused by hydrogen peroxide stress. E. anophelis produces OxyR regulon and antioxidants that may provide defense against the oxidative stress that is associated with blood digestion in mosquitoes. One study showed that hemoglobin facilitates the growth, hydrogen peroxide tolerance, cell attachment and biofilm formation of E. anophelis and that siderophore production and heme uptake pathways might play essential roles in stress response and virulence.
E. anophelis is a dominant bacterial species in the gut ecosystem of the malaria vector mosquito, Anopheles gambiae. Like some Bacteroidetes, E. anophelis possesses polysaccharide utilization loci (PUL), which suggests the genetic capability to utilize various plant polysaccharides. This implies an intriguing ecological connection with the nectar and plant sap feeding behavior of mosquitoes in nature. The predominance of E. anophelis in the sugar fed gut of mosquitos and the possession of numerous Sus-like loci and GHs suggest that the bacterium may be capable of utilizing plant cellulose in the diet and could potentially be of benefit for the mosquito carbohydrate metabolism. The interactions among antibiotic-producing and resistant bacteria may be one of the determinants that shape and stabilize the community structure in the mosquito gut. The bacterium also displays hemolytic activity and encodes several hemolysins that may participate in the digestion of erythrocytes in the mosquito gut. At the same time, the OxyR regulon and antioxidant genes could provide defense against the oxidative stress that is associated with blood digestion. The genome annotation and comparative genomic analysis revealed functional characteristics associated with the symbiotic relationship with the mosquito host.
Little information exists about the pathogenesis of Elizabethkingia infections in general. Colonization of the respiratory tract with Elizabethkingia infections usually precedes invasive infection particularly in high risk populations such as neonates and adults in ICUs. Early and late onset neonatal meningitis is hypothesized to have been preceded by colonization of an infant at the time of delivery since this has been described for other common neonatal pathogens. However, this hypothesis has not been studied.
Elizabethkingia is a genus of bacteria commonly found in the environment and has been detected in soil, river water and reservoirs. They are not normally present in human microflora. It rarely causes infections. Elizabethkingia, though, are opportunistic pathogens preferentially affecting individuals with compromised immune systems or serious underlying health issues. These pathogens are associated with a high mortality rate.
Researchers do not know exactly how E. anophelis is transmitted. They suspect individuals get sick by coming into contact with the bacteria in hospitals or through contaminated water. They are also finding that the bacteria can be passed from mothers to babies.
Researchers in Wisconsin are reasonably certain that groundwater is not the source. The CDC is also assisting Wisconsin with testing of samples, including health care products, water sources and the environment. "To date, none of these have been found to be a source of the bacteria."
Risk factors which should raise suspicion for Elizabethkingia infections including E. meningisepticum and E. anophelis include:
General symptoms of E. anophelis are very non-specific and may mimic many other infections. Generalized symptoms may include:
The Wisconsin State Laboratory of Hygiene (WSLH) receives all isolates of Elizabethkingia species submitted by Wisconsin clinical microbiology laboratories. WSLH staff identify the species of the Elizabethkingia isolates, because clinical laboratories are not able to distinguish E. anophelis from E. meningoseptica. WSLH staff further characterize the E. anophelis isolates using pulsed field gel electrophoresis (PFGE).
Following characterization at the WSLH, all isolates of E. anophelis are shipped to the CDC for more extensive testing and confirmation that includes using optical gene mapping. The species of the outbreak strain has been identified at the CDC to be Elizabethkingia anophelis. The CDC laboratory is the only laboratory in the United States that can distinguish E. anophelis from E. meningoseptica.
Ideal antibiotic therapy is based on determination of the etiological agent and its relevant antibiotic sensitivity. Empiric treatment is often started before laboratory microbiological reports are available when treatment should not be delayed due to the seriousness of the disease. The effectiveness of individual antibiotics varies with the location of the infection, the ability of the antibiotic to reach the site of infection and the ability of the bacteria to resist or inactivate the antibiotic. Some antibiotics actually kill the bacteria (bactericidal), whereas others merely prevent the bacteria from multiplying (bacteriostatic) so that the host's immune system can overcome them.
Although Elizabethkingia are multidrug-resistant bacteria, antimicrobial susceptibility testing (AST) of recent isolates of Elizabethkingia conducted at Wisconsin clinical microbiology laboratories have demonstrated most of the isolates tested are susceptible to fluoroquinolones, rifampin and trimethoprim/sulfamethoxazole (TMP/SMX).
AST (MIC testing) and characterization of strains has been conducted at the CDC on 9 isolates of Elizabethkingiafrom blood specimens collected from Wisconsin residents (Table 3). These isolates include 5 Elizabethkingia anophelis with PFGE outbreak pattern 1, 3 isolates of E. anophelis with non-outbreak PFGE patterns and 1 isolate of Elizabethkingia species.
Elizabethkingia AST and Characterization Results
9 Isolates from Blood Indicated by Month and Year of Specimen Collection
Wisconsin, 3/2014 - 1/2016.
|Isolates||E. anophelis: 3 strains||E. anophelis: 5 strains||E. species: 1 strain|
Outbreak (pattern 1)
3/14, 10/15, 12/15
12/1/15 - 1/5/16
|Antimicrobic||MIC Range||MIC: Range||MIC: Mode||MIC|
2 - 8
1 - 4
4 - 16
|2 - 4|
1 - >16
≤0.25 - 0.5
≤0.5 - 1
32 - >32
|TMP/SMX°||0.5/9.5 - 2/38||≤0.5/9.5 - 2/38||1/19 - 2/38||1/19|
|Vancomycin||32 - >32||32 - >32||32||>3|
Broth MIC medium: Cation adjusted Mueller-Hinton broth (CAMHB).
Testing conducted at the Antimicrobial Resistance and Characterization Laboratory, CDC.
Characterized as Elizabethkingia species. Isolates 3/2014 and 10/2015 were from cultures of blood specimens collected prior to the outbreak interval.
If no interpretation is indicated, there are no approved breakpoints or they are under investigation.
Not all antimicrobics are appropriate for treatment of infections at all anatomic sites.
These MIC results demonstrate susceptibility to fluoroquinolones, minocycline, rifampin and trimethoprim/sulfamethoxazole (TMP/SMX). The medical literature suggests combination treatment with these agents may be more effective than monotherapy. Whenever possible, treatment should be guided by AST.
The optimal antimicrobial therapy for any Elizabethkingia infection is difficult to determine. Empiric therapy is based on the unusual susceptibility pattern, the availability of effective antimicrobials, the age of the patient, clinical presentation and reported experience.
Definitive therapy should rest upon the susceptibility results of the isolated organism. Important considerations to remember when managing these infections include:
Elizabethkingia infections are bacterial and treated with antibiotics. The problem is the bacteria often does not respond to the standard antibiotics. The antibiotics that work against Elizabethkingia infections are usually surprising and the last ones physicians would prescribe. Initial identification of the bacteria (as gram negative) would lead medical professionals to likely empirically treat with drugs that might not work.
Elizabethkingia infections are usually resistant to many antibiotics that commonly treat gram negative bacteria such as:
These are the antibiotics that are often thought to be the biggest "guns" against bacteria. However, Elizabethkingia infections are gram negative but seem to respond to some drugs used for gram-positive bacteria – like Vancomycin which is usually solely able to treat gram positive infections.
There is less experience with treating E. anophelis, but prior to this outbreak the bacteria was shown, without prior known antibiotic exposure, to be resistant to:
In the Wisconsin outbreak, E. anophelis appears susceptible to:
No vaccines are currently available to prevent any Elizabethkingia species.
Clinical studies have demonstrated the importance of rapid instigation of epidemiological investigation, while also ensuring that fundamental infection control procedures are in place during an outbreak and to prevent an outbreak.
Examples of infection control procedures that may be implemented include:
In conclusion, surveillance for the reservoir and maintenance of rigorous infection control measures are essential to control Elizabethkingia outbreaks in healthcare settings.
In all the cases in the United States, whether the bacteria caused or contributed to the deaths remains unclear. Any Elizabethkingia species can be deadly. The mortality rate from Elizabethkingia is usually around 20% although some outbreaks have resulted in the deaths of more than half of those infected.
Patients with Elizabethkingia infections who have high risk factors have an increased mortality. Several predictors of poor outcome include:
Healthcare facility response measures should include:
The past few years have seen an upsurge in the number of pathogens from primarily bacteria and viruses i.e., Elizabethkingia infections, Zika virus etc. which previously affected other countries populations. We have tended to focus our attention on “our own” diseases and less on other countries. Now, outbreaks arise and healthcare systems rush to stem the tide of the damage. E. anophelis should remind us that pathogens abide by no international boundaries…all pathogens are a risk to all peoples worldwide.
Baillon, R: "Elizabethkingia: It may be "weeks rather than days" before we know source of infection", WITI FOX6 News, Milwaukee, Wisc., posted 5:27 pm, March 9, 2016, updated at 05:56pm, March 9, 2016.
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