Antibacterial susceptibility testing in the clinical laboratory (original) (raw)
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Clinical Infectious Diseases, 2000
Clinical microbiology laboratories are faced with the challenge of accurately detecting emerging antibiotic resistance among a number of bacterial pathogens. In recent years, vancomycin resistance among enterococci has become prevalent, as has penicillin resistance and multidrug resistance in pneumococci. More recently, strains of methicillin-resistant Staphylococcus aureus with reduced susceptibility to vancomycin have been encountered. In addition, molecular techniques have demonstrated that there are still problems detecting methicillin resistance in staphylococci, especially in coagulase-negative species. Among members of the family Enterobacteriaceae, mutated b-lactamase enzymes may confer difficult-to-detect resistance to later-generation penicillins and cephalosporins. Anaerobic bacteria are no longer entirely predictable in their susceptibility to agents that might be selected for empiric therapy. Therefore, clinical microbiology laboratories may not be able to rely on a single susceptibility testing method or system to detect all those emerging resistant or fastidious organisms. For reliable detection, laboratories may need to employ conventional, quantitative susceptibility testing methods or use specially developed, single concentration agar screening tests for some resistant species. Certain of these screening tests are highly specific, while others may require additional confirmatory testing for definitive results. Therefore, laboratories must retain the versatility to apply several different approaches to detect resistance in both common and infrequently encountered bacterial pathogens. Clinical microbiology laboratories are faced with the challenge of accurately detecting emerging antibiotic resistance among several important bacterial pathogens. Certain of these are fastidious organisms that require enriched media and modified growth conditions for reliable susceptibility testing (e.g., Streptococcus pneumoniae), whereas some other organisms have subtle or inducible resistance mechanisms that may require special screening tests for reliable recognition (e.g., vancomycinresistant enterococci, staphylococci with reduced susceptibility to vancomycin, methicillin-resistant staphylococci, and gramnegative bacilli that produce extended-spectrum b-lactamases [ESBLs]). Clinical laboratories may not be able to rely on a single susceptibility testing method or commercial system to detect all of these emerging resistant organisms. For reliable detection, it may be necessary to employ conventional broth or agar dilution MIC procedures, special fixed-drug-concentration screening tests, and modified antibiotic interpretive breakpoints that increase the opportunity for recognizing resistant strains. However, with several of the screening methods it is important to confirm presumptive resistance by performing
Antibiotic susceptibility testing: a review on current practices
2016
An increasing Antimicrobial resistance (AMR) has resulted in morbidity and mortality from treatment failures and increased health care costs. Appropriate antimicrobial drug use has unquestionable benefit, but physicians and the public frequently use these agents inappropriately hence, it became necessary to perform the antimicrobial susceptibility test as a routine. The aim of antimicrobial susceptibility testing is to determine the lowest concentration of existing or even new antimicrobial agents which inhibits the visible growth of the bacterium being investigated, under certain test conditions. The Disk diffusion, well diffusion, stokes and gradient diffusion methods are manual methods that provide flexibility and possible cost savings. The most commonly used testing methods include broth microdilution method using commercially available 96-well micro dilution panel. Broth dilution, tube dilution and E test provide quantitative results (e.g. Minimal Inhibitory Concentration) wher...
Evaluation of antibiotic susceptibility test results: how guilty a laboratory could be?
The Journal of the Egyptian Public Health Association, 2019
Background: The selection of an appropriate antimicrobial is a challenging task for clinicians. The Kirby-Bauer disk diffusion method is one of the most widely practiced antimicrobial susceptibility tests (AST). It is affected by many factors among which are the media used. Mueller-Hinton agar (MHA) is the standard medium recommended in guidelines. However, these guidelines are not strictly adhered to in some developing countries. Objectives: Validation of AST results on nutrient agar (NA) medium used as a substitute for MHA by some microbiology laboratories in Alexandria, Egypt. Methods: A total of 149 clinical bacterial isolates and 3 reference strains: Staphylococcus aureus (S. aureus) ATCC® 25923, Escherichia coli (E. coli) ATCC®25922, and Pseudomonas aeruginosa (P. aeruginosa) ATCC®27853 were comparatively challenged to antibiotics employing MHA and NA. Results: All antibiotics-reference bacterial strain challenges on NA compared to MHA were unacceptable (> 3 out of limit zones in 30 consecutive days). Considering clinical isolates, the frequency of very major, major, and minor errors on NA was highest in the case of P. aeruginosa (8.98%, 4.08%, and 14.7% respectively) followed by S. aureus (7.6%, 6%, and 8.8% respectively). On the other hand, the least frequency of errors was in the case of Enterobacteriaceae (0%, 0.4%, and 3.2% respectively). Conclusions and recommendations: Using NA in AST resulted in multiple errors and the high discrepancy in results compared to MHA making it unreliable for susceptibility testing. MHA should not be replaced by NA in AST. Following guidelines and QC measures for AST must be neither bypassed nor underestimated.
Antimicrobial susceptibility test: from bacterial population analysis to therapy
International Journal of Antimicrobial Agents, 2002
The statistical methods and parameters commonly used to define bacterial susceptibility to antibiotics in vitro such as MIC 50 , linear regression or others, usually lead to a considerable loss of information: they do not take into account the heterogeneity of the bacterial population. In contrast, multivariate data analyses are more adapted to the description of biological systems. In this way, a population of a given bacterial species can be separated into homogenous classes corresponding to the different sensitivity and resistance phenotypes. The applications of this mathematical approach include: (i) a new model for more relevant interpretation of antimicrobial susceptibility test results; (ii) numerical estimation of breakpoints having a known risk; (iii) calibration of a technique relative to a reference technique; (iv) detection of strains with new phenotypes; (v) in vitro evaluation of the activity of new compounds.
Journal of Hospital Infection, 2003
decrease in the susceptibility of E coli to nine of 15 drugs (60%) was detected, ranging from 0.7% to 2.7% annually. In K. pneumoniae a significant decrease in susceptibility of K. pneumoniae was detected with only two agents. Pseudomonas spp. isolates remained highly sensitive to all traditional antipseudomonal agents, without significant decay in sensitivity rates over time. Susceptibility of S. aureus to methicillin decreased significantly for several subsets of patients ðP , 0:001Þ: Marked differences in susceptibility rates between the departments were detected. Trend statistical analyses, when appropriately applied to multi-year databases of microbial susceptibilities, may yield susceptibility tables that are significantly more accurate than traditional semi-annual or annual tables.
The Professional Medical Journal, 2019
Background: The emergence and spread of antibiotic resistant bacteria causing infection is a great health issue for clinicians. The problem of multidrug resistant (i.e. resistant to at least three groups of antimicrobial) is becoming more and more threatening. The rate of resistance among Gram negative bacteria especially non fermenters are increasing to all available antibiotic groups. Objectives: The aim of study was to detect the pattern of antimicrobial susceptibility in non-fermenter Gram negative bacilli (NFGNB) in a tertiary care hospital (Postgraduate Medical Institute, Lahore). Study Design: Descriptive study. Settings: The study was conducted in Pathology Department, Postgraduate medical institute (PGMI), Lahore. Study Period: Six months from August 2014 to December 2014. Material and Methods: Non-fermenter Gram negative bacteria were collected from various clinical specimen including blood, pus, urine, fluid aspirates and respiratory tract in a period of six months in pat...
Scientific Reports
Within healthcare settings, physicians use antibiograms, which offer information on local susceptibility rates, as an aid in selecting empirical antibiotic therapy and avoiding the prescription of potentially ineffective drugs. While antibiograms display susceptibility and resistance data at hospital, city, or region-specific levels and ultimately enable the initiation of antibiogram-based empirical antibiotic treatment, AST reports at the individual patient level and guides treatments away from broad-spectrum antibiotics towards narrower-spectrum antibiotics or the removal of antibiotics entirely. Despite these advantages, AST traditionally requires a 48- to 72-h turn-around; this window of time can be critical for some antimicrobial therapeutic interventions. Herein, we present a direct-from-specimen AST to reduce the time between patient sampling and receipt of lab AST results. The biggest challenge of performing AST directly from unprocessed clinical specimens with an unknown mi...
Cureus, 2023
Objectives: Breakpoints provided by European Committee on Antimicrobial Susceptibility Testing (EUCAST) are now being used in many countries. This study was planned to ascertain the agreement in antimicrobial susceptibility using the Clinical and Laboratory Standards Institute (CLSI) and EUCAST breakpoints during the Kirby-Bauer disk diffusion method. Methods: This was a prospective observational study. Clinical isolates belonging to the family Enterobacteriaceae recovered between January and December, 2022, were included in the analysis. The diameter of the zone of inhibition of the 14 antimicrobials (viz. amoxicillin/clavulanic acid, cefazolin, ceftriaxone, cefuroxime, cefixime, aztreonam, meropenem, gentamicin, amikacin, ciprofloxacin, levofloxacin, norfloxacin, trimethoprim/sulfamethoxazole and fosfomycin) was analysed. Antimicrobial susceptibility was interpreted using CLSI 2022 and EUCAST 2022 guidelines. Results: Susceptibility data from a total of 356 isolates showed a slight increase in the percentage of resistant isolates with most of the drugs using EUCAST guidelines. The level of agreement varied from almost perfect to slight. For two drugs, i.e., fosfomycin and cefazolin, the agreement was least among the drug analysed (kappa (κ) value < 0.5, p < 0.001). For Ceftriaxone and Aztreonam, with EUCAST, susceptible (S) isolates would have been categorised in the newly redefined "I" category. It would have indicated the use of higher dosages of drugs. Conclusion: Change in the breakpoints impacts the interpretation of the susceptibility. It can also lead to a change in the dosage of the drug used for treatment. Therefore, there is an urgent need to see the impact of recent modifications "I" category of EUCAST on the clinical outcome and usage of antimicrobials.
innovative publication, 2017
Background: The occurrence of bacterial infections is a major cause of morbidity and mortality in patients. Inappropriate and irrational use of antibiotics has led to increasing resistance in commonly isolated gram positive and gram negative organisms. Antimicrobial resistance is a matter of concern as its compromises the management of infectious diseases and increases the cost of health care as well. Aims and Objectives: This study was undertaken to document the common organisms isolated in patients in a variety of clinical conditions encountered and describe their antibiotic susceptibilities. Materials and Methods: This retrospective study was conducted in Department of Microbiology at Career Institute of Medical Sciences and Hospital. The records of bacteriology section were compiled for a period of 6 months from January 2016 to June 2016.The results were consolidated for types of clinical samples, organisms isolated and their susceptibility patterns. Results: Total 1121 samples were received in Department of Microbiology over a period of six months from January 2016 to June 2016 and 283(25.2%) were positive on culture. E coli, 38 (13.4%) was the predominant isolate followed by Staphylococcus aureus, 31(10.9%). The resistance pattern in E coli to Ceftazidime, Amoxicillin clavulanic acid and Imepenem was 30.3%, 22.9% and 14.7% respectively. Among S. aureus, 15.8%strains were Methicillin resistant. Conclusions: Gram negative bacteria still remain the predominant causes in most of the clinical infections in health care settings with E coli being the most common organism in most of the cases. Antimicrobial resistance is a major challenge and antibiotics need to be tested and prescribed according to standard guidelines. Local anti-biograms should be available periodically to help clinicians guide on antibiotic prescribing.