Elizabethkingia meningoseptica
| Elizabethkingia meningoseptica | |
| |
| Wet raised colonies with clear margin and characteristic smell on Blood agar growth. Sometimes may not show yellow color. Vancomycin sensitivity (clearing around disk) and colistin resistance may lead to mistaking this organism as gram positive. | |
| Scientific classification | |
| Superdomain: | Phylogenetica |
| Kingdom: | Bacteria |
| Phylum: | Bacteroidetes |
| Class: | Flavobacteria |
| Order: | Flavobacteriales |
| Family: | Flavobacteriaceae |
| Genus: | Elizabethkingia |
| Species: | E. meningoseptica |
| Binomial name | |
| Elizabethkingia meningoseptica (King, 1959) Kim et al., 2005 | |
| Synonyms | |
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Elizabethkingia meningoseptica is a Gram negative rod shaped bacteria widely distributed in nature (e.g. fresh water, salt water, or soil). It may be normally present in fish and frogs but are not normally present in the human microflora.
In 1959 American bacteriologist Elizabeth O. King (who isolated Kingella in 1960) at CDC Atlanta, was studying unclassified bacteria associated with meningitis in infants, when she isolated an organism (CDC group IIa) that she named Flavobacterium meningosepticum (Flavobacterium means "the yellow bacillus"; meningosepticum means "associated with meningitis and sepsis", not septic meningitis).[1]
In 1994, it was reclassified in the genus Chryseobacterium and was named Chryseobacterium meningosepticum [2](chryseos = "golden" in Greek, so Chryseobacterium meaning again a golden/yellow rod similar to Flavobacterium).
In 2005, a 16S rRNA phylogenetic tree of Chrysobacteria showed that C. meningosepticum along with C. miricola (which was reported to have been isolated from Russian space station Mir in 2001 and placed in the genus Chrysobacterium in 2003[3]) were close to each other but outside the tree of the rest of the Chryseobacteria and were then placed in a new genus Elizabethkingia named after the original discoverer of F. meningosepticum. [4]
Microbiology
It is a species of gram-negative, obligate aerobic, non-fastidious, non-spore forming, nonfermentative; nonmotile; slender; slightly curved rod; and catalase positive, oxidase positive, and indole-positive, OF glucose ox+/F-, urease negative (contrast E. miricila which is urease positive), mannitol positive, non-nitrate-reducing (Some of the atypical strains may be nitrite reducing[5]) saprophytic bacilli. It is gelatinase, esculin, ONPG & DNAse positive. Chryseobacteria (Flavobacteria) are in general indole positive in contrast to most other nonfermenters, however the reaction may be weak. E. meningoseptica grows well in regular incubators on blood agar and chocolate agar. Colonies are very pale yellow and may not be easily evident at 24 hours. Elizabethkingia meningoseptica strains either are not pigmented or produce a weak yellow nondiffusible pigment (e.g., the type strain; Bruun and Ursing, 1987), in contrast members of all Chryseobacterium species produce a yellow to orange nondiffusible flexirubin type pigment. Strains growing better at 40oC are mostly associated with invasive meningitis.[6]. The greyish discoloration around the colonies on blood agar is due to the proteases & gelatinase. They grow poorly or not at all on MacConkey agar and are considered glucose oxidizers.[7] They do not grow on CNA (Colistin Nalidixic acid) agar because though they are resistant to colistin they are susceptible to quinolones line nalidixic acid.
E meningiseptica may show colistin resistant and vancomycin sensitive/intermediate growth which is paradoxic for a gram negative bacteria, but resembles Burkholderia cepacia which is also a nonfermenter, does not grow on MacConkey agar in less than 3 days (grows late) and colistin resistant and vancomycin sensitive. These two coluld be distinguished by Indole test or Pyr test both of which should be clearly negative for Burkholderia cepacia and positive for E meningoseptica. Automated bacterial identification system results should be observed with caution, especially when a patient with gram negative bacteremia does not improve with broad-spectrum antibiotic therapy, because several bacteria, including Aeromonas salmonicida (mistaken by ID32 GN [5]) and Sphingobacterium spp. (mistaken by Vitek 2 [8]), may be confused with this bacteria especially the atypical ones. However unlike many other Aeromonas species like Aeromonas hydrophilia, Aeromonas punctata, A. sulmonicida is indole negative which can help in distinguishing in case of doubt. An automated but so far relatively reliable Rapid NF plus system and API Zym systems use array of biochemical tests for a bettery of nonfermenters and other bacteria and can specifically identify E meningisepticum.
Infection
It has generally been reported to cause outbreaks of meningitis predominantly in premature newborns and infants in neonatal intensive care units of underdeveloped countries. Some of the outbreaks have been linked to sources like contaminated lipid stock bottles, contaminated venous catheter lines and nutritional solution, and tap water. It is also a rare cause of nosocomial pneumonia, endocarditis, postoperative bacteremia, and meningitis in immunocompromised adults. Only recently it has also been reported to cause soft tissue infection and sepsis in the immunocompetent[8] and a case report of a fatal necrotizing fasciitis in a diabetic patient.[9]
Antimicrobial susceptibility
This organism is usually multiresistant to antibiotics typically prescribed for treating gram-negative bacterial infections, including extended-spectrum ß-lactam agents (due to production by most starins of two betalactamases- one ESBL and one Class B Carbapenem-Hydrolyzing metallolactamase), aminoglycosides, tetracycline, and chloramphenicol. Though Vancomycin has been used in the past, high MIC (16 µg/ml) for vancomycin lead to search for alternatives especially for meningitis. Presently ciprofloxacin, minocycline, trimethoprim-sulfamethoxazole, rifampin and novobiocin are being considered good alternatives—most of which are classically drugs for gram positive bacteria and not routinely tested on gram negative bacteria).[10]