We are growing bacteria from environmental sources, found a gram positive rod that appears encapsulated when we do a gram stain. Rods are long, not short. We have some fungal contamination as well, as you can see in the image. It's also hemolytic on blood agar. Any ideas what this could be?
Hi Robin!
Might need some more information first; does it grow on nutrient agar in air? What is the colonial morphology (eg: mucoid, colonies convex and irregular, 3 mm diameter after 24 hours incubation at 37C, etc). Link to page on describing colony morphology attached.
Thanks, Richard. They are convex, mucoid colonies that grew on blood agar (though there seems to be growth into the broth as well). We haven't tried to grow them on regular nutrient agar but we can certainly do that. They were grown at 37C overnight and grew rapidly, colonies are >1.5mm.
Hi Again,
A few more questions -
1) it looks like they might be branching in the Gram stain - are any of them branching (forking into Y shapes or similar)?
2) Where are the environmental samples from? Have you cultured them from many sites or from only from one site?
3) Do they grow evenly throughout the broth, or is it more cloudy on the top of the broth? Is there a sort of matt of clumped bacteria (called a pellicle) on the top of the broth?
4) Do the colonies smell like soil?
5) Can you upload a photograph of the colonies?
Hope to at least point you in a direction of genus after all that if at all possible!!
Richard
From your micrograph, the organism exhibits the typical box car morphology of Bacillus or Clostridium spp. It is more likely to be the former if grown aerobically. Many Bacillus spp. are encapsulated, Bacillus subtilis being the most common of these. You will have to do either biochemical confirmation or send for sequencing.
You could cultivate it on MYEP agar. If you have large pink colonies with halo that give strong haemolysis on blood agar, they are presumptive Bacillus cereus.
I agree taht it is most probablly a Bacillus species, but there are other possibilities. My concern is that the colonies are only 3 mm diameter and mucoid at 24 hours, this is not consistent with Bacillus cereus. Bacillus licheniformis is perhaps more probable, but I would prefer to see a photorgaph of colonies and know a little more to confirm.
I would guard against trying to speciate using microscopic and colonial morphology alone. They could be one of a number of species. Although Bacillus is the most likely candidate, it is not a given. The easiest would be to do an API or do a PCR and send for sequencing.
I agree Pamela, a confirmed speciation cannot be made without further testing, but a direction for further ID is possible, it really depends on how accurate Robin needs to be! I will leave it with you to follow up further, hope that my input thus far has been helpful.
We are doing a PCR to send for sequencing. I think we have an API 20E kit but only for gram negatives, so we can't rely on that to ID this. Here is a picture of the bacteria growing on blood agar. It grows very very fast. We even serially diluted it and put it on plates and at the lowest dilution it took over the plate overnight. Thanks for all the comments and help, everyone.
Bacillus represents a genus of ubiquitous gram-positive bacteria. The species are used in many medical, pharmaceutical, agricultural, and industrial processes, including those for making antibiotics and insecticides. Blood culture which you are showing may be a nonhemolytic, nonmotile gram-positive rods. B. anthracis. By using fluorescein-labeled monoclonal antibodies specific to the B. anthracis capsule you can go for final answer.
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