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Antimicrobial Therapy
Published in John C Watkinson, Raymond W Clarke, Louise Jayne Clark, Adam J Donne, R James A England, Hisham M Mehanna, Gerald William McGarry, Sean Carrie, Basic Sciences Endocrine Surgery Rhinology, 2018
Ursula Altmeyer, Penelope Redding, Nitish Khanna
A third method, known as the E-test, uses plastic strips that are coated with the tested antimicrobial forming a concentration gradient along the strip. This is placed on a testing medium inoculated with the test organism and again read after a period of incubation. An elliptical zone of inhibition is visible around the test strip, which intersects it at the measured MIC (Figure 22.3).
Metronidazole
Published in M. Lindsay Grayson, Sara E. Cosgrove, Suzanne M. Crowe, M. Lindsay Grayson, William Hope, James S. McCarthy, John Mills, Johan W. Mouton, David L. Paterson, Kucers’ The Use of Antibiotics, 2017
With regard to the anaerobic activity of metronidazole, the laboratory methodology used has potentially important implications. For instance, the Clinical and Laboratory Standards Institute (CLSI) has standardized metronidazole susceptibility testing of anaerobic bacteria: anaerobic bacteria are classified as susceptible if the metronidazole minimum inhibitory concentration (MIC) ≤ 8 µg/ml; intermediate, if the MIC = 16 µg/ml; or resistant, if the MIC ≥ 32 µg/ml, using agar dilution methodology (CLSI, 2012; CLSI, 2015a). The broth microdilution methodology is only recommended for susceptibility testing in relation to the B. fragilis group (CLSI, 2012). In contrast, the European Committee on Antimicrobial Susceptibility Testing (EUCAST) breakpoints are significantly lower for Gram-negative and Gram-positive anaerobes (except C. difficile); organisms are susceptible if the MIC ≤ 4 µg/ml and resistant if the MIC > 4 µg/ml (EUCAST, 2015). The breakpoints used in each study must be taken into account in assessing the proportion of isolates that have been labelled susceptible or resistant. In addition many studies have used Etest methodology (bioMerieux) for susceptibility testing. In general, Etest MIC values correlate well with the reference procedure, although there may be significant discrepancies, including very major errors in relation to Clostridium spp. and the Bacteroides fragilis group (Rosenblatt and Gustafson, 1995; Rennie et al., 2012).
The Microbiology Laboratory
Published in Keith Struthers, Clinical Microbiology, 2017
The ingenious Etest employs a strip of material incorporating an exponential gradient of an antibiotic from one end to the other. The strip is placed on an agar plate inoculated with the organism (Figure 5.29a). As the organism multiplies, the antibiotic diffuses out of the strip. The rate of diffusion is proportional to the concentration at a particular point, and this will determine the zone of inhibition. The MIC can be read from the scale, as shown in Figure 5.29b. A photograph of an Etest is shown in Figure 5.30. While the test is more expensive and labour intensive than the disc method, it is useful for determining the MIC of selected organisms. For example, laboratories may monitor the MIC values of Streptococcus pneumoniae isolates in a region where the prevalence of isolates with reduced susceptibility to penicillin is increased. In the setting of infective endocarditis, this test is used to determine the MIC of streptococci and enterococci to a number of antibiotics, including penicillin and (synergistic) gentamicin.
Paracoccus yeei, a Novel Bacterial Cause of Endophthalmitis following Intravitreal Injection
Published in Ocular Immunology and Inflammation, 2022
Riyaz Bhikoo, Smathi Chong, Kevin McLeod, Peter Heyworth, Ian L McAllister
A 90-year-old female with neovascular Age-Related Macular Degeneration in her right eye, and baseline visual of 6/36, presented to her treating ophthalmologist 3 days after her most recent Aflibercept (Eylea; Bayer, Sydney, NSW) intravitreal injection with pain and loss of vision. Her visual acuity was reduced to 6/60 with a fibrinous panuveitis without hypopyon. A vitreous tap and injection of intravitreal Vancomycin 1 mg and Ceftazidime 2.25 mg were performed. Over the next 48 hours, despite an improvement in pain, her vision deteriorated to hand motions with a 2 mm hypopyon and complete loss of the red reflex (Figure 1A). Direct microscopy of the vitreous tap specimen showed no leukocytes but occasional Gram-negative Coccobacilli confirmed on culture after overnight incubation at 35°C in the aerobic atmosphere on horse blood and chocolate agar. The colonies tested oxidase and catalase positive and were further identified using Matrix-Assisted Laser Desorption/Ionization Time-of-Flight mass spectrometry (MALDI-TOF) and confirmed by 16s Ribosomal RNA sequencing, with Paracoccus yeei identified as the offending pathogen. Susceptibility testing was performed by E-test. There are no standardized interpretation criteria for P. yeei susceptibility; however, Amikacin (Mean Inhibitory Concentration [MIC]: 0.5 mg/L) and Ceftazidime (MIC: 1.5 mg/L) were both considered appropriate intravitreal treatment options.
In vitro activity of the ketolide cethromycin in multidrug-resistant clinical Neisseria gonorrhoeae isolates and international reference strains
Published in Journal of Chemotherapy, 2019
Susanne Jacobsson, Emilie Alirol, Magnus Unemo
The MICs (mg/L) of cethromycin (Advanced Life Sciences Inc., Woodridge, Illinois, USA) were determined by agar dilution technique, according to current CLSI guidelines (www.clsi.org). The MICs (mg/L) of ceftriaxone, cefixime, azithromycin, spectinomycin, ciprofloxacin, ampicillin and tetracycline were determined by the Etest method (AB bioMérieux, Marcy l'Etoile, France), which is highly comparable to agar dilution technique.13–15 With exception of azithromycin for which no clinical resistance breakpoint exists, all MICs were interpreted into susceptibility (S), intermediate susceptibility (I) and resistance (R) according to the EUCAST clinical breakpoints (http://www.eucast.org/fileadmin/src/media/PDFs/EUCAST_files/Breakpoint_tables/v_9.0_Breakpoint_Tables.pdf). EUCAST does not any longer state any clinical breakpoint for azithromycin. However, an ECOFF of 1 µg/mL is recommended for testing purposes to detect acquired azithromycin resistance mechanisms (http://www.eucast.org/fileadmin/src/media/PDFs/EUCAST_files/Breakpoint_tables/v_9.0_Breakpoint_Tables.pdf). This ECOFF was used to indicate resistance to azithromycin in the present study. No interpretative criteria exist for cethromycin. Only whole MIC dilutions are reported in the present manuscript.
Changes in the microbial flora in patients of a Greek intensive care unit over two decades
Published in Infectious Diseases, 2018
Paschalina Kontou, Maria Papaioannou, Anastasia Dimaki, Zoi Bosmou, Militsa Bitzani, Ioannis Kioumis
This is a retrospective study that took place in an 18-bed general ICU of ‘G. Papanikolaou’ Hospital, a tertiary hospital situated in Thessaloniki in Greece. We analysed the results of microbiology cultures of biological samples obtained at the years 1995 and 2016. Based on the availability of data, a distinction between infectious and colonization episodes could not be made. The samples submitted for culture were blood, lower respiratory tract samples (protected specimen brush, endotracheal aspirate, bronchoalveoral lavage, pleural fluid), central venous catheters’ (CVCs) tips, urine, cerebrospinal fluid (CSF), wound exudates and surgical drainages. When the same microbe was isolated from more than one samples of the same patient, it was recorded as a single event of infection or colonization. The microorganisms evaluated were staphylococci, enterococci, Enterobacteriaceae and non-fermenting Gram-negative bacilli. The antibiotics tested were oxacillin, vancomycin, trimethoprim-sulphamethoxazole, ampicillin, imipenem, ciprofloxacin, ceftazidime, cefoxitin, amikacin, gentamicin, ampicillin–sulbactam and only for the more recent isolates, meropenem, colistin and tigecycline. In order to determine the minimum inhibitory concentration (MIC) of the bacteria to the antibiotics, an automated antimicrobial susceptibility testing system was used (Vitek) and sometimes an E-test was performed.