Clinical innovations


NewsWounds update Infection update


Wounds International clinical updates present recent developments in the field of leg ulcers, pressure ulcers, skin integrity and diabetic foot, including the latest from associations, clinicians and industry. If you use an innovative technique in your practice that you would like us to feature in future issues, please email the editor at: scalne@woundsinternational.com


Methods for microbial identification in chronic wounds


I infection[1]


t is now well established that bacteria can use two different strategies for producing . The most widely


recognised is when bacteria propagate as single motile cells to invade host tissue. The bacteria is usually a single species and will upregulate virulence factors to kill the host cells. The bacteria will then


secrete bacterial-derived proteases to break down host tissue, which is used as nutrition for continued propagation. This planktonic strategy is most consistent with what is known clinically as an acute infection.


Wound biofilm A less recognised, almost paracystic strategy, is when bacteria attach to host cells and/or tissue to produce an infection. The act of attachment causes upregulation of biofilm genes, which produce a protective matrix and organise the bacteria into a polymicrobial community[2]


. To protect itself, the


community, through a variety of secretory systems, 'infects' the host cells with small effector proteins which render the host cells senescent[3]


appropriately). Using a variety of molecular mechanisms, the wound


biofilm blocks host cell apoptosis (programmed cell death),[4-7] shedding[8]


, migration[9] and manufacturing,[10] among other


functions. This produces a stable attachment to the host environment while also preventing the host from healing. These are the unique properties of a biofilm infection most consistent with the chronic infections seen clinically. Biofilm is present in chronic wounds[11]


(where the host cell ceases to function


possesses the genetic material necessary to either pursue a biofilm or planktonic mode of growth. This means that the bacteria present in any chronic wound can change from one mode of growth to the other. There is no question that a biofilm, with its colony


defences, is the more difficult phenotype to diagnose and treat. Therefore, the focus of diagnostic and treatment methods should be on biofilm, since any planktonic bacteria will also be adequately dealt with by the same process.


Accuracy of routine cultures Bacteria seem to play an important role in the non- healing of wounds. Therefore, it is important to choose diagnostic methods that can fully identify both planktonic (usually single species) and biofilm (usually polymicrobial) phenotypes present in the wound. Cultures have been shown to be wholly inadequate


in identifying bacteria in biofilm phenotypes and any polymicrobial infections[12]


. Cultures select against the large


numbers of species present in polymicrobial infections by growing only a few species favoured by the conditions. Therefore, cultures are not quantitative and the biochemical identification methods are inaccurate.


, yet much work


remains in order to establish the exact contribution a biofilm makes to the non-healing of an individual wound. It must be remembered that an individual bacterium


10 Wounds International Vol 3 | Issue 1 | ©Wounds International 2012


Recent findings A recent study which compared clinical cultures with molecular diagnostics uncovered several interesting findings. The clinical cultures were processed by a high-volume clinical lab, which routinely evaluated wound samples. The molecular methods included real-time polymerase chain reaction (PCR) — the use of a specific primer to identify an organism — combined with pyrosequencing — a method used to determine the DNA code (adenine, thymine,


Figure 1: Sequencing instruments in a dedicated analysis room.


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