Tag Archives: rapid identification of positive blood cultures

“Hot Chocolate”


We have been playing around for a while now, looking for the “best” way to rapidly identify isolates from positive blood cultures. 

First of all we had a look at FISH (Fluorescent In-Situ Hybridisation). This was accurate, and pretty quick, but for the volumes of positive blood cultures that we process, even in a fairly big lab, it was somewhat on the expensive side.

We then had a look at MALDI-ToF based “centrifugation” methods. We dabbled with the Bruker sepsityper, or at least “home brew” versions thereof… This was quickish, but quite labour intensive, and to be honest a bit tedious. Nevertheless pick-up rates were good, particularly for Gram negative organisms.

However now that we have the Kiestra TLA in place, I think we are going to settle for the “Hot Chocolate” method. This involves inoculating an aliquot from a positive blood culture on to a pre-warmed chocolate agar, incubating for a pre-programmed 6 hours on the Kiestra system, and then performing an immediate MALDI-ToF on the plate colonies.

OK, so it is not quite as quick as FISH or Sepsityper, but it is cost-effective, does not require a lot of manual input, and it is a service that we can provide 24 hours a day.

Realistic solutions always involve some degree of compromise…


“Spending money where it matters..”

                                     Foreign Banknotes 2.jpg

I suspect the next revolution in diagnostic bacteriology will be (routine) rapid identification of bacteria from blood cultures which have flagged positive on blood culture analysers.

Fluorescent In-Situ Hybridsation (FISH) technology along with Maldi-TOF sepsityper, now allows us to identify the causative bacterium accurately in the majority of cases within an hour of the blood culture becoming positive. This has obvious positive clinical implications, particularly if the identified bacterium is a beta-haemolytic streptococcus, a Pseudomonas aeruginosa or a Staphylococcus aureus. Even rapidly identifying coagulase negative staphylococci may avert the need for unnecssary anti-microbial therapy.

These technologies are NOT cost-prohibitive, and should be within the scope and skill level of most reasonably sized diagnostic laboratories.

I believe it will be only a matter of time before it becomes unacceptable to wait for the bacterium to grow on agar plates before identifying it.

I think these technologies also have implications for how the microbiology lab operates overnight. If we can identify the organism within one hour then is it really acceptable to leave a positive blood culture unattended to in an analyser for 8-12 hours overnight? (This definitely still happens in many diagnostic laboratories..)

With these new technologies becoming commonplace, maybe it is time to re-think how we use our budgets and how we roster the microbiology staff. Maybe we need to divert the money used to work-up bacteria from peri-anal abscesses and chronic venous ulcers towards rapid identification of bacteria from positive blood cultures, where it is going to make a real clinical difference and be potentially life-saving.

…and maybe the blood culture analyser needs to be staffed 24 hrs a day, 7 days a week, with blood cultures being processed and bacteria identified as soon as possible.

These sort of changes might cause a few grumbles but this is the sort of direction we need to be heading in, in order to have a clinical microbiology service that makes a genuine difference to the patient…


p.s. In future, any links from the articles will be highlighted in purple, to avoid confusion