Psychrophiles in Commercially Produced Sauces, Glazes, and Marinades

 These are plates from the 2nd dilution of 13 different sauces on week 4 of our study.  We plated on July 3rd and did the 2nd dilution so that we would not have a potential of too many to count after being incubated for 48 hrs at 37C.  The plates were pulled out on July 5th and placed into the refrigerator at 4C.  I did not view the plates until July 9th and observed yellow, bacterial colonies growing.  These photos were taken on July 10th.

The colonies are small, circular, opaque yellow, entire, raised to convex, and glistening.  Perhaps tomorrow I can stop by the lab to streak for singles and the next day do a Gram stain.  From there we will decide what metabolic media to use in identifying this organism.

What is interesting about this growth is that it did not occur the first two weeks of tests.  Those plates had 1 or 2 yeast colonies growing on a few of the sauces.  For the most part the plates have been clean.  After seeing this growth, we looked at the plates from week 1 and week 2.  Week one showed a single bacterial colony growing on one streak for 2 different sauces.  Week 2 showed these yellow colonies on ALL of our plates.  It appears this organism is a psychrophile.

In preparing for this long-term shelf-life study, we aliquoted 25 ml of 13 different sauces into 50 ml conical tubes.  One set remains in the refrigerator for future testing if we see a need to do so.  The other sets were stored at room temp at 30C and 2 sets were placed in the incubator at 37C for week 1 and week 2.  So for week 1 and week 2, we ran a set of tests of the sauces stored at 30C and at 37C.  Based on previous results of these same sauces in a similar study, we did not plan for additional weeks at 37C.  Last week we completed week 4, which was only for the sauces stored at 30C.


From Suite101.com:

Psychrophiles – Properties and Characteristics of Psychrophilic Bacteria

The best earliest review on psychrophiles is that of Ingraham and Stokes who describe these features of psychrophiles:

• are typically Gram-negative bacteria and include members of the genera Pseudomonas, Flavobacterium, Psychrobacter, Colwellia and others.
• often produce green, yellow, orange and purple-violet pigments at reduced temperatures
• can tolerate elevated levels of salt
• can grow well and sometimes optimally at temperatures up to about 20 degrees Centigrade
• can grow at temperatures as low as -3 to -7 degrees Centigrade
• produce extracellular enzymes that can degrade meats, milk, cheeses and other food products during cold conditions

I found a genus of bacteria that may fit but only testing will determine.  Chryseobacterium spp. (Flavobacterium) This genus is a Gram-negative, rod bacterium with yellow pigment.  It is non-motile.  C. indologenes tests positive for oxidase, negative for catalase, cannot ferment Mannitol or Urease, does not grow on MacConkey.  It weakly ferments glucose as seen on TSI slants.  They can grow at 4C but optimum growth is at 25C.  They are also heat stable and have a salt tolerance.  They are commonly found in soil, plants, foodstuffs, and water sources.


Like I said, we have to streak for singles and do a Gram stain first to determine next steps in identifying this organism.