Acanthamoeba

There are around 22 species in the genus Acanthamoeba; a group of free-living protozoa that are widely dispersed in the environment. The Neff strain of Acanthamoeba castellani (recovered from Golden Gate Park in the 1960s) has been a significant contributor to the development of eukaryotic cell biology, since it has similarities to mammalian cells and can be grown easily in the laboratory.

There are several Acanthamoeba species that can cause human infection, including A. castellani, A.polyphaga, A. culbertsoni and A. astronyxis. The commonest infection is amoebic keratitis in contact lens wearers (video). Fortunately much less common is amoebic panencephalitis in which only a small percentage of patients respond to therapy. This generally occurs in patients with underlying co-morbidities such as diabetes, malignant disease, immunodeficiency or malnutrition.

Acanthamoebas can also act as a vehicle or potential vector for intracellular bacterial infections such as Legionnaires’ Disease ², melioidosis³ and even MRSA infection⁴. Evidence is lacking to prove their role as the principal means of exposure to infection, but amoebas can evidently provide an environmental reservoir to protect bacteria that are capable of human infection.

Acanthamoeba

Video: Acanthamoeba from contact lens keratitis. Amoebic trophozoites phagocytose bacteria (E.coli) grown on non-nutrient agar.

References

1. Wikipedia – Acanthamoeba.
2. Rowbotham TJ. Preliminary report on the pathogenicity of Legionella pneumophila for freshwater and soil amoebae. J Clin Pathol 1980; 33:1179-1183.
3. Inglis TJ, Rigby P, Robertson TA, Dutton NS, Henderson M, Chang BJ.  Interaction between Burkholderia pseudomallei and Acanthamoeba species results in coiling phagocytosis, endamebic bacterial survival, and escape. Infect Immun. 2000; 68: 1681-1686 [PMID Reference]
4. Huws SA, Smith AW, Enright MC, Wood PJ, Brown MR. Amoebae promote persistence of epidemic strains of MRSA. Environ Microbiol. 2006; 8: 1130-1133. [PMID Reference]

Author Credit: Dr Tim Inglis

Life in the Fast Lane Medical Blog - Emergency Medicine education blog

Thermus aquaticus

Despite the fact that Thermus aquaticus does not cause infection it is probably more important to microbiology than any other bacterial species. Yet few clinicians have heard of it. At least under its proper name. Many more will have mention of Taq, in ‘Taq polymerase’, the enzyme needed to run the polymerase chain reaction (PCR). This critical molecular biology reagent was first isolated from Thermus aquaticus in 1976.

Thermus aquaticus

T. aquaticus, for short, was first isolated from hot springs in the lower geyser basin of Yellowstone National Park during an investigation of heat-tolerant bacteria in 1969. Conventional wisdom insisted that bacteria could not survive at the high temperatures found in hot springs. And yet there were bacteria there, thriving at 70°C and tolerating conditions up to 80°C. Their ability to survive these extreme conditions depends on a heat-tolerant DNA polymerase; just what the molecular biologist needed.

These unusual bacteria belong to the Deinococcus-Thermus group of Archaea; ancient organisms that have features of both Gram positive (thick peptidoglycan cell wall) and Gram negative (double membrane) bacteria. They are chemotrophs, obtaining energy from inorganic chemicals in their environment. Their enzyme product Taq polymerase is used every day in clinical and research laboratories even if T. aquaticus can’t cause a single infection.

Author Credit: Dr Tim Inglis

Life in the Fast Lane Medical Blog - Emergency Medicine education blog

Escherichia blattae

A close relative of common-or-garden bacterium Escherichia coli (E.coli), first found in the hindgut of the oriental cockroach, Blatta orientalis. E.blattae is as rare as E.coli is common; an oddity still looking for a role in any kind of infectious disease.

Its main significance is that is was the second bacterial species added to the genus Escherichia (in 1973). In bacteriology, there are no awards for coming second.

It is now possible that this species will be assigned to another bacterial genus as Shimwellia blattae (No relation to the ‘Yale Kayaking E.coli‘)

At least the connection with cockroach faeces will be preserved for a while.

Escherichia blattae

Author Credit: Dr Tim Inglis

References

Gram-negative bacteria associated with brewery yeasts: reclassification of Obesumbacterium proteus biogroup 2 as Shimwellia pseudoproteus gen. nov., sp. nov. and transfer of Escherichia blattae to Shimwellia blattae comb. nov. Priest FG, Barker M. Int J Syst Evol Microbiol. 2009 Aug 6. [PMID 19661513]

Picture: Courtesy NIAID.

Life in the Fast Lane Medical Blog - Emergency Medicine education blog