Sensitivity testing of the patient

Easir Abedin A culture test is evaluation of fluid, tissue or other products of the body to look for presence of abnormal cells indicating presence of viruses, bacteria or fungi. Such a test usually relies on small samples collected from the body either by the individual or by a medical practitioner. These samples are placed in secure dishes named culture dishes, which have nutrients on them that encourage growth of abnormal substances and these are then examined regularly to determine if growth of irregular cells, indicating infection, is occurring. No growth indicates that infectious agents are not present. Culture and sensitivity testing should be done all Diagnostic Laboratory to know which antibiotics will be effective against the particular pathogen (i.e., disease-causing agent) causing the problem. This means that (1) the species (and strain) of bacteria (or other pathogen) must be identified and (2) the drugs most effective at inhibiting their growth must be determined. The only reliable way this can be done is a culture and sensitivity test. After confirming the culture and sensitivity test the Doctor should select the appropriate antibiotics for the patient. In modern laboratories, bacteria are usually identified by characterization of the genome: identifying the characteristics of the DNA and RNA of a sample species. This type of testing is generally considered more reliable (and soon, less expensive) than actually growing bacterial cultures and exposing them to various types of antibiotics to see which drugs kill or inhibit the bacterial growth Type of Culture * Blood culture * Urine Culture * Stool Culture * Skin Culture *Biopsy Culture * Throat Culture * Nose Culture * Any other suitable source Determine the bacterial populations sensitivity to a range of antibiotics. This can be done by placing small disks of filter paper or agar impregnated with various types of antibiotics onto the bacterial lawn. The bacteria are allowed to incubate for a day or two, and then the plate is examined to see whether the bacterial growth is inhibited (or not) by the antibiotics on each disk. SENSITIVE: In this case, a clear, circular "halo" (technically known as a "plaque," or zone of inhibition) will appear around the antibiotic disk, indicating an absence of bacteria. The antibiotic has inhibited their growth and/or killed them, meaning that this particular antibiotic should be effective against the infection your rabbit has. INTERMEDIATE: A somewhat cloudy plaque indicates that not all the bacteria in the area around the disk have been killed. This means that there are some members of the bacterial population that are sensitive to this particular antibiotic, but others that are genetically immune to its effects. If an antibiotic to which the bacteria show "intermediate" sensitivity is used, it is likely that the sensitive members of the bacterial population will be killed, and the resistant ones will survive, resulting in the selection of a population resistant to that particular antibiotic. RESISTANT: In this case, the filter paper will have no discernable plaque around it, meaning that the bacteria are growing normally, even in the presence of the antibiotic. An antibiotic producing no plaque will most likely be ineffective against the bacteria causing your bunny's infection. The Petri dish in the image above which includes a more detailed explanation of the appearance of the halos used in bacterial identification, shows bacteria being strongly and moderately inhibited by most of the antibiotics impregnated on circles of filter paper. Antibiotic Choices When to use and when not to use antibiotics Interpreting cultures Choosing appropriate empiric antibiotics Using antibiograms Appropriate Use of Antibiotics Employ empirically when there is a reasonable clinical suspicion of infection. Choose antibiotics active against the most likely organism(s). Choose antibiotics known to penetrate involved tissue. Use correct doses of antibiotics - don't underdose. Know when bacterostatic antibiotics are adequate or bacterocidal drugs are required. In serious, potentially life-threatening infections, start broad, then de-escalate after cultures back. Stop antibiotics when infection resolved or when evidence accumulates against existence of infection. Inappropriate Uses of Antibiotics Using wrong antibiotic for apparent infection. Using wrong dose of right drug. Using a 2nd or 3rd line drug when a first line drug could still be used. Using antibiotics in situations when antibiotics are not indicated - "just in case". Continuing antibiotics when infection is resolved or not likely. Keeping coverage broad when cultures reveal a single organism. Reacting to culture results by starting antibiotics without considering the significance of the culture. Results of Antibiotic Misuse Incomplete, delayed, or failed resolution of infection. Prolonged or unnecessary hospitalizations. Increased incidence of antibiotic side effects. Development of multi-drug resistant strains of bacteria. Increased cost of health care. All diagnostics Laboratories in Bangladesh should have qualified microbiologist (B.Sc Honors, M.Sc/MS in Microbiology) to perform their culture and sensitivity test though some renowned lab has qualified microbiologist. Government should take care regarding the microbiologist issue. (The writer is an Assiastant Manager, Quality Control at Beximco Pharmaceuticals Ltd)

19 May, 2013 Sunday

Sensitivity testing of the patient