Tuesday, July 30, 2013

Rapid Test Allows for Earlier Diagnosis of Tuberculosis in Children

A new test for diagnosing tuberculosis (TB)  in children detects roughly two-thirds of cases identified by the current culture test, but in a fraction of the time, according to the results of a study in South Africa supported by the National Institutes of Health.

The test, known as Xpert MTB/RIF, also detected five times the number of cases identified by examining specimens under the microscope, a preliminary method for diagnosis that is often performed as an initial test, but which must be verified by the culture test.

Xpert MTB/RIF results from respiratory secretions were ready in 24 hours, on average, compared with an average of more than two weeks for the culture test used in the study, the researchers found. Previous studies have shown that Xpert MTB/RIF is effective for diagnosing TB in adults and in children with pronounced symptoms of TB who have been admitted to a hospital. Diagnosing TB in children is more difficult than diagnosing it in adults, because children tend to have much lower levels of the TB bacteria than do adults.

The results of the current study indicated that the ease and speed of diagnosis would be useful for children seen in clinics in resource-limited countries, which often lack the resources for traditional testing that are available in hospitals. The test also was able to identify children with drug resistant TB. In addition, the researchers found that Xpert can readily determine when treatment for tuberculosis is not appropriate. Among children who did not in fact have TB, the results of the Xpert test came back negative for TB with 99 percent accuracy.

Xpert MTB/RIF was developed with funding from the NIH’s National Institute of Allergy and Infectious Diseases NIH’s National Institute of Allergy and Infectious Diseases. Testing of Xpert MTB/RIF in children was funded by NICHD.

Preliminary diagnosis of TB is often made by collecting a sample of lung secretions and examining the sample under a microscope to see if it contains the bacteria that cause TB. A sample is also sent to a laboratory so the bacteria can be cultured and identified. It may take as long as six weeks for the culture test to show a positive result. Because, children have lower levels of infectious bacteria than do adults, it is more difficult to detectthe bacteria under a microscope and to grow it in a culture. For this reason, accurately diagnosing TB in children has been difficult.

“The availability of this test in primary care settings can help children get appropriate treatment faster,” said Lynne M. Mofenson, M.D., of the Maternal and Pediatric Infectious Disease Branch of the Eunice Kennedy Shriver National Institute of Child Health and Human Development (NICHD), the NIH institute that funded the study. “Looking at a specimen under the microscope, often used for initial diagnosis of TB in adults, is very inaccurate in children.”

The Xpert MTB/RIF test also detects TB strains that are resistant to the drug rifampicin, allowing physicians to more accurately prescribe an appropriate treatment, said Carol Worrell, M.D., also of the NICHD’s MPIDB. This is particularly important in areas where drug-resistant TB is common, such as South Africa.

The World Health Organization estimated that in 2011 there were 500,000 TB cases and 64,000 deaths among those younger than 15 years.

The study was led by first author Heather J. Zar, M.D., Ph.D., of the University of Cape Town and Red Cross War Memorial Children’s Hospital, also in Cape Town, South Africa; and Mark P. Nicol, Ph.D, also of the University of Cape Town and the South African National Health Laboratory Service at Groote Schuur Hospital, Cape Town.

The findings appear in The Lancet Global Health.

“There has been a perception amongst health care workers that rapid diagnosis of TB in children wouldn’t be possible in primary care, but this study disproves that view, Dr. Zar said. “Given our results, widespread adoption of rapid testing for TB and drug resistance in children may substantially improve public health without greatly increasing costs.”

Dr. Zar and her colleagues collected almost 1500 samples from nearly 400 children who went to a primary care clinic with symptoms of TB. Collecting the samples — secretions from the lungs, the nasal passages or both — requires special equipment and trained clinical staff. The researchers compared the results from the Xpert MTB/RIF test, examination of samples under a microscope, and from growing the tuberculosis bacteria in laboratory cultures. Bacterial culture is the most accurate method for diagnosing TB.

Of the 30 TB cases detected by culture, 19 (63 percent) were positive by the Xpert MTB/RIF test on lung or nasal samples, while examining the samples under the microscope turned up only four cases (13 percent). Adding a second test (of a second lung or nasal passage sample) improved the detection rate for both culture and Xpert MTB/RIF.

In some cases, researchers started TB treatment for children they suspected had TB based on their symptoms. Xpert MTB/RIF identified seven children who had clinical symptoms of tuberculosis and responded well to treatment for tuberculosis, but whose tuberculosis had not been detected by the tuberculosis culture test. This might occur when a child is sick with TB, but the bacteria are at especially low levels, or because a sample did not contain enough of the bacteria present in the child’s body to appear when cultured, Dr. Mofenson explained. The total number of cases detected by culture (30 cases) and by XpertMTB/RIF (26 cases) was similar.

“Because of the global burden of this disease among children, it’s vital to make rapid, accurate diagnostic tests available in primary care settings in order to identify the disease and start treatment before children end up in the hospital,” said Dr. Worrell. “NICHD recognizes the value of supporting research to improve the accuracy of TB diagnosis in children, reduce the number of samples required, and make diagnostic tools widely accessible.”

About the Eunice Kennedy Shriver National Institute of Child Health and Human Development (NICHD): The NICHD sponsors research on development, before and after birth; maternal, child, and family health; reproductive biology and population issues; and medical rehabilitation. For more information, visit the Institute’s website at http://www.nichd.nih.gov.

Source: HealthCanal

Thursday, July 18, 2013

Detecting Plague With Anti-Carbohydrate Antibodies Leads to Rapid Diagnosis

Even today, the lives of humans and animals are claimed by plague. A new antibody-based detection method can be used to reliably and sensitively identify plague in patient serum and other biological samples. The antibody specifically recognizes a particular carbohydrate structure found on the cell surfaces of the bacterium that causes plague, as reported by German researchers in the journal Angewandte Chemie.

“Black death” took the lives of over 200 million humans over the course of three pandemics in the last 1500 years. More recently, cases of plague have been detected in Africa and Asia. Because of the high danger of transmission and the severity of the infection, Yersinia pestis, the pathogen behind the plague, is classified as a category A biological weapon. When inhaled as an aerosol it causes pneumonic plague, which usually results in death if it is not treated fast. Rapid and reliable diagnosis is thus critical.

“Currently, Y. pestis is detected by polymerase chain reaction based assays or traditional phenotyping,” explains Peter Seeberger of the Max Planck Institute of Colloids and Interfaces in Potsdam. “These methods of detection are reliable, but they are also often complex, expensive, and slow.” The recognition of surface proteins by antibodies is a highly promising and less complicated alternative method for the detection of plague, but it has a high failure rate and low selectivity with regard to related strains of bacteria.

Seeberger and his team have now found a way around this problem: Gram-negative bacteria like Y. pestis have molecules called lipopolysaccharides (LPSs), made of fat and carbohydrate components, on their outer cell membranes. “The inner core of the Yersinia LPS has a unique structure that differs from that of other Gram-negative bacteria,” says Seeberger. “This could be a suitable region for detection by means of specific antibodies for rapid point-of-care diagnosis.”

Because isolation of Y. pestis LPS is a laborious undertaking, the researchers chose to synthetically produce one typical motif from the molecule, a segment consisting of three sugar molecules, each of which has a framework of seven carbon atoms. The researchers attached these segments, called triheptoses, to diphtherietoxoid CRM197, which acts as a carrier protein. This protein is a typical component of licensed vaccine formulations and triggers the formation of antibodies. The researchers immunized mice and isolated antibodies from their blood.

Various immunoassays demonstrated that the resulting antibodies detect the plague pathogen with high selectivity and sensitivity, and selectively differentiate between Y. pestis and other Gram-negative bacteria. The researchers hope to be able to use this to develop applications for patient diagnostics. The development of corresponding tests is the focus of their current research.


Plague Detection by Anti-carbohydrate Antibodies. Dr. Chakkumkal Anish, Dr. Xiaoqiang Guo, Annette Wahlbrink, Prof. Dr. Peter H. Seeberger. Angewandte Chemie. Article first published online: 10 JUL 2013. DOI: 10.1002/anie.201301633. 

Tuesday, July 16, 2013

Whole-Genome Sequencing Detects Outbreaks Faster

Bench-top whole-genome sequencing platforms provided accurate detection of gram-negative bacteria at speeds faster than traditional identification, researchers found.

Whole-gene sequencing accurately discriminated between outbreak and non-outbreak isolates of Enterococcus faecium and Enterobacter cloacae when compared with conventional gene typing, and the results took less than a day, according to Sharon Peacock, PhD, of the University of Cambridge in England.

The platform also showed it was able to determine whether resistance of the bacteria was attributable to the presence of carbapenemases or other resistance mechanisms, they wrote online in JAMA Internal Medicine.

Rapid detection and effective treatment of gram-negative bacteria are paramount in controlling the emergence and spread of such threats, though the data required to fight these bugs are usually collected retrospectively and can fail to impact disease control, they noted.

They added that the most recent generation of bench-top DNA sequencing platforms "can provide an accurate whole-genome sequence for a broad range of bacteria in less than a day."

The authors compared whole-genome sequencing with current standard clinical microbiology investigation practices for nosocomial outbreaks due to multidrug-resistant bacteria in one outbreak of vancomycin-resistant E. faecium and in one outbreak of carbapenem-resistant E. cloacae.

The researchers collected clinical specimens and tested them for antimicrobial susceptibility through disk diffusion techniques and received additional testing through a reference laboratory, where needed.

In the E. cloacae outbreak, three patients at Cambridge University Hospitals NHS Foundation Trust tested positive for the bug. Isolates were sequenced along with four carbapenem-susceptible E. cloacae samples from patients in other wards as a control.

A single-nucleotide polymorphism-generated phylogenetic tree showed isolates from the outbreak were more closely related to each other than those from the control samples. Further analysis showed that the first two patients in the outbreak likely spread the bug between each other or from a third patient. The third patient infected with the drug-resistant strain was shown to likely not have received the same bug as the first two patients.

The study of the E. faecium outbreak included three children with hematologic malignancies at the same hospital. The authors sequenced seven isolates from the three patients and another vancomycin-resistant isolate from a fourth, unrelated patient from 7 weeks prior to the outbreak.

The phylogenetic tree of these samples showed two of the samples were related, while one sample from the three children and the control sample were unrelated to the others, "despite an overlap in time and place" in the third child.

Additional sampling of the related cases showed "that these isolates represented sampling from a larger underlying population," which they noted "was not possible to determine whether the second episode of vancomycin-resistant E. faecium bacteremia in one patient was due to relapse by the same isolate, or re-infection from the other."

An accompanying editorial by Garth Ehrlich, PhD, and J. Christopher Post, MD, PhD, both from the Allegheny-Singer Research Institute in Pittsburgh, noted that current methods are inadequate and that use of genome sequencing platforms will "revolutionize data acquisition for theranostics and tracking of outbreaks."

"Whole genome sequencing is critical as a diagnostic tool because the vast majority of bacterial pathogens possess a supragenome that is much larger than the genome of any individual strain," they wrote, adding that whole-genome sequencing will improve understanding of "rates and breadth of horizontal gene flow within and between species, the evolution of new virulence trails, and the role of host genetics in host-pathogen interactions."

The authors also said that the adoption of this technology can provide an outlet for sequencing to regional and local laboratories that provides higher-quality output at a rate faster than current techniques.

They also cautioned that future prospective studies are needed to show a cost-benefit analysis of using these techniques for individual patients and in public health.

Reference: Peacock SJ, et al "Rapid bacterial whole-genome sequencing to enhance diagnostic and public health microbiology" JAMA Intern Med 2013; DOI: 10.1001/jamainternmed.2013.7734.

Source: medpagetoday.com

Monday, July 15, 2013

Study Shows High Sensitivity, Specificity for Abacus Diagnostica C. Diff Test

A new automated molecular diagnostic assay to detect toxigenic Clostridium difficile directly from stool samples was found to have comparable sensitivity and specificity to both the gold standard of culture-based testing and reference testing with a competing assay, Cepheid's GeneXpert C. difficile, according to recently published research.

The test — called GenomEra C. difficile from Finnish company Abacus Diagnostica — may also provide cost and ease-of-use benefits over competing molecular diagnostic assays due to the simplicity of its chip design.

In addition, Abacus is currently developing an even more streamlined version of the assay that it hopes to begin selling to European customers by the end of this month, and anticipates starting clinical evaluation of the test in the US near the end of this year, Mari Gylling, director of marketing and sales at Abacus, told PCR Insider.

The C. difficile assay received CE marking in November, joining the firm's commercially available GenomEra assays for detecting and differentiating Staphylococcus aureus and methicillin-resistant S. aureus from nasal swabs and blood culture.

All of Abacus' tests run on the GenomEra CDX system, a self-contained, fully integrated and automated testing platform designed for routine clinical use. The system requires little to no sample preparation and performs rapid PCR amplification and end-point detection using homogenous time-resolved fluorescence chelates as labels.

According to Gylling, GenomEra C. difficile it is the "first PCR assay that uses feces as sample material with so few sample preparation steps and yet with such good results and low inhibition rate" — characteristics that are due at least in part to the time-resolved fluorescence detection scheme, which essentially eliminates autofluorescence, a common problem when conducting PCR assays on stool samples.

Abacus was selling the GenomEra CDX system prior to the C. diff test, but since that assay launched late last year, the company has nearly doubled the number of installed systems, Gylling said, although she didn't provide exact figures.

The company had previously presented data from clinical evaluations of the assay at various scientific conferences, including the European Society of Clinical Microbiology and Infectious Diseases annual congress in April. However, a study published late last month in the Journal of Clinical Microbiology is the first peer-reviewed paper on the assay to be published.

In the study, clinical researchers from Vassa Central Hospital and the National Institute for Health and Welfare, both in Finland, evaluated the performance of GenomEra C. difficile using 310 diarrheal stool specimens and a collection of 33 known clostridia and non-clostridia isolates.

Specimens were collected between August and September 2012, and were tested by toxigenic culture immediately or refrigerated and tested within 24 hours of receipt. Aliquots of each sample were frozen for later testing with GenomEra C. difficile.

In the case of discrepant results from toxigenic culture and the GenomEra test, specimens were tested with Cepheid's GeneXpert C. difficile assay.

Of the 310 stool specimens examined, 80, or 25.8 percent, were positive for the toxin B gene, tcdB, using the GenomEra test. Meantime, culture-based methods isolated toxin-producing C. difficile from 77, or 25.2 percent, of specimens. Two of the three GenomEra-positive but culture-negative samples were confirmed as tcdB-positive by the Cepheid assay, while one was positive only with the GenomEra test. In addition, one specimen was toxin-positive by culture, and initially yielded an inconclusive result using GenomEra, then yielded a negative result in retesting.

Overall, the results indicated that GenomEra C. difficile had a sensitivity of 98.8 percent and a specificity of 99.6 percent when performed directly on fecal specimens. In addition, the test yielded no false positives or negatives when used on the culture isolate collection, correctly differentiating between a number of different toxigenic or non-toxic Clostridium and non-Clostridium species.

The researchers underscored the simplicity of GenomEra testing, noting that the test produced results in less than an hour with only five minutes of hands-on time. This is a huge improvement over culture-based methods, and comparable to that of Cepheid's test. However, Gylling noted that the Abacus test may provide some additional advantages over the GeneXpert assay.

"The amount of waste due to assay runs is very low, and permanently sealed chips makes the waste handling very easy and safe," she said. "Among tighter rules in laboratory practices, this is highly appreciated." In addition, she noted, "the closed system with sealed chips eliminates the risk of contamination problems in the laboratory and spares the user from cleaning activities." Finally, she added, the assay features "user-friendly reagents [that] do not contain any irritating components."

In terms of cost benefit, the "test chip design is simpler than Cepheid’s cartridge design," which may make GenomEra's cartridges cheaper in the long run, Gylling said, although she declined to quantify this potential cost differential or disclose a price range for the GenomEra CDX system.

And, "as test production volumes are rapidly increasing and bigger batches are produced, we are able to compete even better with the prices [of] other MDX platforms," she added.

The authors of the JCM paper did not provide a cost analysis, but wrote that "laboratories of any size can easily adopt the GenomEra CDX instrument," and "the capacity of the assay is adequate for laboratories performing up to approximately 8,000 to 11,000 C. difficile analyses per year," with 32 sample analyses able to be performed in one eight-hour workday.

"In laboratories with lower numbers of C. difficile samples per year the capacity of the instrument may be used to test additional microbiological targets in order to take full advantage" of the platform, they added.

Indeed, Abacus is planning to add new targets and tests to its portfolio. Besides the commercially available C. diff, MRSA, and SA tests, the company is working on Chlamydia trachomatis, vancomycin-resistant enterococci, and other pathogen-specific markers, Gylling said. "As seen in several market studies and customer feedbacks, HIV, tuberculosis, and norovirus tests are moving fast towards small, easy-to-use molecular diagnostic systems," she added. "The benefits of our system would fit very well to these tests and are naturally among our high research interests."

None of Abacus' tests are available yet in the US. Last August, after winning a key pair of US patents covering its technologies, Abacus told PCR Insider that it planned to seek regulatory approval in the US this year for its MRSA and SA assays, as well as the C. difficile test.

Gylling did not provide an update on the former tests, but noted that the company is set to release an even easier-to-use version of the C. diff test in Europe this month, and plans to begin clinical testing of that assay in the US by the end of this year.

"The increased interest and growth in Eastern Europe, Middle East, Asia, and emerging markets has been [a] high priority among our commercialization efforts and activities during [the] first half of 2013," she said. "However, we still anticipate starting clinical evaluations in [the US] towards [the] end of this year with the new C. difficile version.

Source: Genomeweb

Sunday, July 14, 2013

Rapid Characterization of Staphylococcus aureus by Infrared Light (FTIR)

Scientists at the University of Veterinary Medicine, Vienna (Vetmeduni Vienna) are hot on the trail of the bacterium Staphylococcus aureus. The researchers have developed a technique for the rapid and reliable distinction between strains that can cause chronic infections and those that cannot. Using infrared light and artificial intelligence, the scientists present a sophisticated method for the prediction of disease progression. Their results are now published in the Journal of Clinical Microbiology.

The bacterium Staphylococcus aureus (S. aureus) is commonly found in nature and frequently colonizes the skin and the upper respiratory tract of humans. A healthy immune system can fight the microorganism but once the immune system is weakened the pathogen can spread and lead to life-threatening diseases of the lungs, the heart and other organs. Moreover, S. aureus produces toxins in foods and can cause serious food poisoning. Its effects are not confined to humans:  in cattle, S. aureus frequently causes inflammation of the udders, so the bacterium is also of great interest in veterinary medicine.

S. aureus comes in many different forms, which helps it evade the immune system. Aggressive types of S. aureus form capsules and multiply rapidly but are also quickly recognized by the immune system. Capsule-free forms are better able to survive within cells and are less well recognized by the immune system. In other words, they “hide and seek” before they attack and so are more likely to cause chronic infections that are harder to treat. Recent studies suggest that in the course of adapting to its host (human or animal) S. aureus undergoes a form of microevolution, during which it loses its capsule. The capsule-free form evades the host immune system and can even survive antibiotic treatment.

S. aureus was previously detected – and the nature of its capsule checked – by means of specific antibodies that bind the capsule. The procedure is relatively complex, as the antibodies are not commercially available and thus have to be produced in animal experiments. Tom Grunert and colleagues have now developed a method by which the capsules can quickly and clearly be distinguished from one another without the use of antibodies. The technique relies on a physical procedure known as FTIR or Fourier Transform Infrared Spectroscopy. Infrared light is shone on the microorganisms to be tested and the resulting spectral data are input into a supervised self-learning system, a so called artificial neuronal network, which uses the data to work out the type of capsule. As Grunert says, "With the new method we can routinely test patient samples with a success rate of up to 99 percent."

The head of Grunert’s institute, Monika Ehling-Schulz, puts the work in a broader context. "In principle, germs have two choices when they infect a host: attack or hide – in technical terms virulence or persistence. If they attack, they risk destroying the host and consequently themselves, whereas if they hide, they may be outcompeted by others. A detailed knowledge of the mechanisms of virulence and persistence and the way bacteria switch between them will help us to develop novel and more effective therapies."

The publication "Rapid and Reliable Identification of Staphylococcus aureus Capsular serotype by Means of Artificial Neural Network-Assisted Fourier Transform Infrared Spectroscopy" by Tom Grunert, Mareike Wenning, Maria Sol Barbagelata Martina Fricker, Daniel O. Sordellii, Fernanda R. Buzzola and Monika Ehling-Schulz was published in the Journal of Clinical Microbiology. The research was conducted in collaboration with the University of Buenos Aires, Argentina and the Technical University of Munich.

Friday, July 5, 2013

PathSensors: Rapid Detection of Airborne Pathogens Using Jellyfish Bioluminescence Proteins

Pathsensors, Inc. is an environmental testing company housed at the University of Maryland Biopark in Baltimore. The company specializes in developing tests to quickly find pathogens in the infectious disease and biodefense sectors.

Using genetically engineered cells made from jellyfish that glow in the ocean, a new system can identify dangerous substances in aerosols.

Since 2007, the company has developed products for the U.S. Department of Defense and companies specializing in defense contracting. Pathsensors' other markets include building protection, mail room screenings, first responders, and food processing.

The BioFlash-E® system is based on the CANARY® (Cellular Analysis and Notification of Antigen Risks and Yields) technology, a revolutionary diagnostic technology developed by the scientists at Massachusetts Institute of Technology and published in Science. BioFlash® delivers extremely rapid detection of pathogens at previously unseen levels of sensitivity and specificity. A short video of the CANARY system is provided below:

The BioFlash-E® utilizes the BioDiscTM, a unique disposable integrated collection, reagent storage and test chamber. The operator simply inserts the BioDiscTM and the BioFlash-E® automatically collects and identifies up to 21 potentially hazardous biological agents. The simple and safe “remove and replace” procedure takes less than 2 minutes to complete, requiring minimal user training.

Monday, July 1, 2013

Rapid Detection of Bacterial Antibiotic Resistance by Nanocantilevers

Researchers at Ecole Polytechnique Federale de Lausanne (EPFL) in Switzerland, have built a matchbox-sized device claimed to test for the presence of bacteria in minutes instead of up to several weeks.

According to EPFL, a nano-lever vibrates in the presence of bacterial activity, while a laser reads the vibration and translates it into an electrical signal that can be read easily, with the absence of a signal signifying the absence of bacteria. Thanks to this method, it is quick and easy to determine if a bacteria has been effectively treated by an antibiotic, a crucial medical tool especially for resistant strains. The research is published in Nature Nanotechnology (see below).

‘This method is fast and accurate. And it can be a precious tool for both doctors looking for the right dosage of antibiotics and for researchers to determine which treatments are the most effective,’ said researcher Prof Giovanni Dietler in a statement.

It currently takes a long time to measure a bacterial infection’s response to antibiotic treatment as clinicians must culture the bacteria and then observe its growth to determine if the treatment has been effective.

Thanks to advances in laser and optical technology, the EPFL team of physicists has reduced this time to a couple of minutes. To do so, Giovanni Dietler, Sandor Kasas and Giovanni Longo have exploited the microscopic movements of a bacterium’s metabolism.

These vital signs are almost unperceivable. In order to test for them, the researchers place the bacteria on an extremely sensitive measuring device that vibrates a small lever in the presence of certain activity. The lever then vibrates under the metabolic activity of the germs. These infinitely small oscillations, on the order of one millionth of a millimeter, determine the presence or absence of the bacteria.

To measure these vibrations, the researchers project a laser onto the lever. The light is then reflected back and the signal is converted into an electrical current to be interpreted by the clinician or researcher. When the electrical current is a flat line, the end-user knows that the bacteria are dead.

The researchers have miniaturised the tool, which is currently the size of a matchbox. ‘By joining our tool with a piezoelectric device instead of a laser, we could further reduce its size to the size of a microchip,’ said Dietler. They could then be combined together to test a series of antibiotics on one strain in only a couple of minutes.

The researchers are currently evaluating the tool’s potential in other fields, notably oncology. They are looking into measuring the metabolism of tumor cells that have been exposed to cancer treatment to evaluate the efficiency of the treatment.

‘If our method also works in this field, we really have a precious tool on our hands that can allow us to develop new treatments and also test both quickly and simply how the patient is reacting to the cancer treatment,’ said Kasas.

The researcher's abstract and full reference is as follows:

Rapid detection of bacterial resistance to antibiotics using AFM cantilevers as nanomechanical sensors. G. Longo, L. Alonso-Sarduy, L. Marques Rio, A. Bizzini, A. Trampuz, J. Notz, G. Dietler & S. Kasas. Nature Nanotechnology (2013). Advance online publication

The widespread misuse of drugs has increased the number of multiresistant bacteria1, and this means that tools that can rapidly detect and characterize bacterial response to antibiotics are much needed in the management of infections. Various techniques, such as the resazurin-reduction assays2, the mycobacterial growth indicator tube3 or polymerase chain reaction-based methods4, have been used to investigate bacterial metabolism and its response to drugs. However, many are relatively expensive or unable to distinguish between living and dead bacteria. Here we show that the fluctuations of highly sensitive atomic force microscope cantilevers can be used to detect low concentrations of bacteria, characterize their metabolism and quantitatively screen (within minutes) their response to antibiotics. We applied this methodology to Escherichia coli and Staphylococcus aureus, showing that live bacteria produced larger cantilever fluctuations than bacteria exposed to antibiotics. Our preliminary experiments suggest that the fluctuation is associated with bacterial metabolism.