Performance Of Antimicrobial Susceptibility Testing Research Articles

Helicobacter pylori therapy and clinical perspective.

Helicobacter pylori induces chronic gastritis and duodenal ulcer in a small fraction of the colonised population. Three decades after the discovery of H. pylori and disclosure of an urgent need for eliminating the bacterium in patients, it seems that we are still in the first steps of dealing with this mysterious organism. Treatment of H. pylori is a complex dilemma for clinicians, a repeating sentence by many scientists who spend years on this research topic. Apart from many modifications in initial first-line treatment of H. pylori, gastroenterologists are unable to overcome the problem of therapeutic failure. Choosing the best regimen in any region depends on many factors, which have been the focus of many randomised clinical trials. A potential increase in efficacy of future therapies may be influenced by adding the novel potassium-competitive acid blocker vonoprazan. Undeniably, in-depth analysis is necessary to propose more effective therapeutic regimens. Meanwhile, we recommend the performance of antimicrobial susceptibility testing before any antimicrobial prescription.

Emerging Resistance, New Antimicrobial Agents … but No Tests! The Challenge of Antimicrobial Susceptibility Testing in the Current US Regulatory Landscape.

Accurate and timely performance of antimicrobial susceptibility testing (AST) by the clinical laboratory is paramount to combating antimicrobial resistance. The ability of laboratories in the United States to effectively perform ASTs is challenged by several factors. Some, such as new resistance mechanisms and the associated evolution of testing recommendations and breakpoints, are inevitable. Others are entirely man-made. These include unnecessarily strict US Food and Drug Administration (FDA) limitations on how commercial AST systems can be used for diagnostic testing, the absence of up-to-date performance data on these systems, and the lack of commercially available FDA-cleared tests for newer antimicrobial agents or for older agents with updated breakpoints. This viewpoint will highlight contemporary AST challenges faced by the clinical laboratory, and propose some solutions.

Emerging Extended-Spectrum Cephalosporin Resistance in Neisseria gonorrhoeae

Over the last several decades, Neisseria gonorrhoeae has sequentially developed resistance to the agents recommended by the CDC and the Public Health Service for the treatment of gonorrhea. During the 1970s and through the 1990s, penicillin, tetracyclines, and the fluoroquinolones were recommended and subsequently removed as the therapy of choice for gonorrhea, leaving intramuscular ceftriaxone and the oral cephalosporin cefixime as the sole agents recommended for treatment of gonorrhea in 2010. In the late 1990s, treatment failures following oral cefixime therapy were recognized in Japan and the Far East, and subsequently, cefixime treatment failures were reported from the United Kingdom, Europe, and the United States. Gonococcal isolates from these cases showed diminished susceptibility to both cefixime and ceftriaxone, and molecular studies have shown that N. gonorrhoeae isolates with elevated cephalosporin MICs have genetic alterations primarily in the chromosomal penA gene, which encodes penicillin-binding protein 2. The altered proteins bind cephalosporins less efficiently, and isolates phenotypically demonstrate diminished cephalosporin susceptibility and elevated cefixime and ceftriaxone MICs. The penA alleles in these strains have a “mosaic” composition, as they contain nucleic acid sequences that were acquired from commensal Neisseria species. The strains also have genetic alterations in several other chromosomal loci that contribute to incremental cephalosporin resistance. With the utility of extended-spectrum cephalosporins for gonorrhea treatment being threatened, older agents (e.g., gentamicin and ertapenem) and newly developed antimicrobials (e.g., solithromycin) are now being evaluated as possible treatment options. The CDC has issued guidelines for the public health response to the emergence of cephalosporin-resistant N. gonorrhoeae. This plan includes improvements in gonococcal surveillance, identification by clinicians of “probable” and “suspected” treatment failures, the re-establishment of culture-based testing, and the timely performance of antimicrobial susceptibility testing on isolates obtained from treatment failures. Potential problems central to implementation of the response plan are also addressed.

Rarely seen infections

There are many rare cutaneous infections of the face. This phrase seems irrelevant, because rare infections in certain parts of the world are common in others. This is more apparent if applied to different sites of the body (eg, face). For instance, cutaneous leishmaniasis (CL) is common in Central and South America and uncommon in the United States. Because most medical practitioners in this country have never seen a case, it is easy for them to miss a diagnosis.Cutaneous leishmaniasis, a protozoan infection transmitted by phlebotomine sand flies, is typically divided into two forms: one found in the Middle East, Asia, Africa, and southern Europe, called Old World leishmaniasis, and one found in Latin and Central America, called New World leishmaniasis.Also atypical mycobacterial infection has been described in the medical literature since the mid-1950s. The development and introduction of a rapid radiometric mycobacterial detection system has advanced the field of mycobacteriology over the past 20 years. This method has allowed the distinction of Mycobacterium tuberculosis from other mycobacteria and enabled the performance of antimicrobial susceptibility testing of mycobacteria. The increased frequency of atypical mycobacterial infection stems from advances in the diagnostic procedures concerning the infection paired with the prevalence of mycobacterial disease in immunocompromised patients infected with HIV. Erysipelas and facial cellulitis are covered briefly in this paper.

Editorial: Assessing the antimicrobial susceptibility of bacteria obtained from animals

The accurate performance of antimicrobial susceptibility testing of bacteria from animal sources and the correct presentation of the results is a complex matter. A review of the published literature revealed a number of recurring errors with regard to methodology, quality control, appropriate interpretive criteria, and calculation of MIC(50) and MIC(90) values. Although more subjective, there is also no consensus regarding the definition of multiresistance. This Editorial is intended to provide guidance to authors on how to avoid these frequently detected shortcomings.

Antimicrobial Susceptibility Testing: A Review of General Principles and Contemporary Practices

An important task of the clinical microbiology laboratory is the performance of antimicrobial susceptibility testing of significant bacterial isolates. The goals of testing are to detect possible drug resistance in common pathogens and to assure susceptibility to drugs of choice for particular infections. The most widely used testing methods include broth microdilution or rapid automated instrument methods that use commercially marketed materials and devices. Manual methods that provide flexibility and possible cost savings include the disk diffusion and gradient diffusion methods. Each method has strengths and weaknesses, including organisms that may be accurately tested by the method. Some methods provide quantitative results (eg, minimum inhibitory concentration), and all provide qualitative assessments using the categories susceptible, intermediate, or resistant. In general, current testing methods provide accurate detection of common antimicrobial resistance mechanisms. However, newer or emerging mechanisms of resistance require constant vigilance regarding the ability of each test method to accurately detect resistance.

National hospital survey of anaerobic culture and susceptibility methods: III

To assess the current status of anaerobic bacteriology in the United States, we surveyed, by means of a questionnaire, 150 hospitals selected at random with bed capacities of 200–1000 and we received responses from 98 (65%). Ninety-eight percent processed anaerobic culture specimens with 21% sending them to reference laboratories. Almost all these hospitals processed blood and wound cultures for anaerobes and all used selective media for identification, including BBE (52%), LKV (77%), and PEA (53%) agars. All hospital laboratories attempted identification of blood culture isolates including 80% that attempted speciation. Wound cultures for anaerobic bacteria and sterile site cultures were also processed for anaerobes by almost all labs. Identification of B. fragilis group species to species level was performed only in 56% of labs always and 37% sometimes. Preformed enzyme kits were used by 66% of labs and 30% used special potency disks for identification. Susceptibility testing was performed in-house by 21% of hospital labs and sent out to reference labs an additional 20%. Susceptibility testing was attempted for all blood culture isolates by both hospital (21% of total labs) and reference laboratories, but only performed by 17% for sterile body site and 14% of the time for wound isolates. Etest was used most often followed by broth microdilution. No labs used the agar dilution or disk elution methods. The antimicrobials most often tested in hospital labs, predicated on the commercial panel used, were penicillin/ampicillin and clindamycin (15/18; 83%; 15% of total labs), metronidazole (16/18; 89%; 16% of total labs) and cefotetan and ampicillin/sulbactam (12/18; 67%; 12% of total labs), piperacillin/tazobactam (7/18; 39%; 7% of total labs), cefoxitin (9/18; 50%), imipenem (8/18; 44%), and chloramphenicol (6/18; 33%). Our current survey suggests that while many labs are processing anaerobic cultures, especially blood cultures, the identification of isolates and the performance of antimicrobial susceptibility testing of isolates are in disarray and in dire need of improvement.

Nontypeable Haemophilus influenzae susceptibility: Effect of inoculum size and β-lactamase production

The activities of cefixime, cefpodoxime, cefprozil, cefuroxime, loracarbef, and amoxicillin/clavulanate against 72 clinical isolates of nontypeable Haemophilus influenzae were determined by using an agar dilution method. The effects of β-lactamase production and bacterial inoculum size were investigated. All antimicrobials exhibited a significant inoculum effect, demonstrating the importance of accurately determining inoculum size in the performance of antimicrobial susceptibility testing of H. influenzae.

Clinically significant differences in antibiograms of morphologic variants of blood culture isolates.

The present environment of cost containment frequently forces laboratories to reassess various strategies for the diagnostic work-up of patient specimens. The necessity for the performance of antimicrobial susceptibility testing on all morphologic variants of blood culture isolates was examined in this study. Over a 4-year period, of 143 such organisms that were identified, 56 (39%) exhibited clinically significant differences in antibiogram profiles. Coagulase-negative Staphylococcus represented the largest proportion of isolates (n = 115), 39% of which demonstrated clinically significant differences in antibiograms. The authors conclude that these results justify the current practice in their laboratory of performing separate antimicrobial susceptibility testing on all morphologic variants of isolates.