Lab Equipment

Question

HI
I have a son with CF. We are trying to improve facilites etc in the regional CF Centre.

I have come across some info on a piece of lab equipment for detecting bacteria in sputum and blood samples. It seems the results are available within 24hrs. Have you come across the "MALDI TOFF"? Pseudomonas results etc can be picked up within 24hours, this information I feel for a CF patient would be of great benefit.
Would you have any idea as to the cost of such a piece of equipment.
Thanks

Answer

Hello

Sorry for the delay in the answer as it took a little time to put together.Treating bacterial infections effectively requires both identification of bacteria, and subsequently, determination of a suitable antibiotic treatment. Standard methods for bacterial identification are based on biochemical testing: these results can be difficult to interpret because they can be affected by conditions of culture, or other environmental changes. It can be difficult to detect bacteria that are slow growing or present in small numbers using standard tests, because they rely on detecting compounds produced as the organism grows. Many hospital laboratories have automated systems for routine identification, and usually antibiotic testing and identification can occur in parallel. However, even with automated sample processing, it still may take at least 48hrs to generate information which can be passed to the clinical team, and this time is increased if the bacteria are difficult to grow.

In recent years, faster and more effective ways of identifying bacteria have been developed. These include detection of bacterial specific genes using polymerase chain reaction (PCR), which can generate results in a very short space of time. However, often the information obtained is not sufficient to generate a precise identification, requires a high level of expertise and can be costly. As a result, it’s not always suitable for many routine diagnostic laboratories.

A new approach is currently by studied for rapid identification of bacterial proteins, called MALDI-TOF (matrix-assisted laser desorption ionization-time of flight mass spectrometry). This process uses a laser to vaporize a bacterial sample, splitting it into its component molecules. The size and charge of each separated molecule in that sample is then determined and a molecular “fingerprint” obtained. This fingerprint can then be compared to other bacterial fingerprints in the database(1).

The advantages of MALDI-TOF are that identification from pure culture can take minutes and is relatively cost-effective- other than the cost of the machine (approx. $200,000), relatively few reagents are required to process a sample. A recent paper investigating the use of MALDI-TOF to identify common CF pathogens, estimated that 71% of Pseudomonas aeruginosa isolates were identified by MALDI-TOF by day 2 of incubation, at which stage none had been identified by conventional culture (2). Similarly, with Staphylococcus aureus, 89% were identified using MALDI-TOF by day 1 of incubation, whereas only 68% had been identified by culture on day 2. It can also identify bacteria which are slow growing much more quickly than by using standard culture techniques. In addition, it can also be used to identify yeasts and fungi, which are commonly found in CF patients. It can also determine differences between species of bacteria, such as those in the Burkholderia cepacia complex, which prove problematic for conventional culture based tests and are significant disease causing organisms in CF. In contrast, some Streptococcus species are hard to distinguish from each other using MALDI-TOF, and it has proven difficult to distinguish methicillin resistant Staphylococcus aureus (MRSA) from Meticillin susceptible Staphylococcus aureus (MSSA).

However, so far most research using MALDI-TOF has been done identifying intact bacteria from pure culture, rather than directly from a clinical sample. The culture conditions, and treatment of the bacteria prior to MALDI-TOF processing can affect the fingerprint produced, so careful standardization within labs and between research centers is required. Some researchers have shown that bacteria can be identified directly from blood and urine samples, without the need for first culturing the bacteria, but encountered problems in separating the bacteria from the blood or urine sample, and in distinguishing bacteria in a sample where more than one bacterial species is likely to be found (polymicrobial infection) (3,4). In addition, it appeared problematic to identify bacteria unless they were in sufficiently high numbers in the sample. So far, there are no reports of direct identification of bacteria in sputum samples from people with CF.


MALDI-TOF identification provides no information regarding the potential resistance or susceptibility of the identified bacteria to antibiotics. Traditional culture based techniques are therefore still required in order to provide additional information about which antibiotics are likely to be effective in treating the infection. However, clinicians can make a reasonable prediction of which antibiotics are likely to be effective, based on the identification, and so appropriate antibiotic therapy can be started more quickly. Although more research is required to validate techniques and protocols for identification of bacteria from sputum of patients with CF, MALDI-TOF may in the future represent a potentially very useful additional tool in diagnosing and treating lung infections in patients with CF.

Best wishes
Deirdre Gilpin

23.07.2012