![]() Aminoglycoside Antibiotic-Inactivating Enzymes in Actinomycetes Similar to Those Present in Clinical Isolates of Antibiotic-Resistant Bacteria Proc. 2276-2280 Which of the following correctly describes individual actinomycetes according to their shape?Īdapted from Benveniste, R., Davies, J. ![]() The r-determinant genes responsible for this resistance may have originated from which of the following actinomycetes?Īdapted from Benveniste, R., Davies, J. 2276-2280 A meningitis-causing bacteria is resistant to streptomycin and gentamicin C1a. Table 1 Aminoglycoside acetylating, phosphorylating, and adenylylating enzymes in actinomycetes (+) means enzyme activity was detected, (-) means no enzyme activity was detected.Īdapted from Benveniste, R., Davies, J. However, careful examination of their cellular dimensions, their cytology, and their genetics place them among the bacteria. The actinomycetes are a group of rod-shaped organisms that were once thought to be intermediates between bacteria and fungi. The question is, where do the r-determinants originate?Ī search was initiated in the actinomycetes for aminoglycoside-modifying enzymes like those that have been characterized in strains carrying R-factors (R+) in the belief that this might represent the r-determinant gene pool. It has been hypothesized that r-determinants exist somewhere in nature as chromosomal genes and that they are "picked-up" by bacteria to form R-factors. These are the resistance transfer factor (RTF), and the r-determinants, genes that determine resistance to antibiotics. Molecular studies have shown that R-factors consist of two parts that are reversibly dissociable. Since these genes are not normal chromosomal components of the resistant strains, there has been considerable speculation as to their origin. The genetic loci coding for these enzymes are usually located on extrachromosomal elements, such as the R(antibiotic resistance)-factors in gram-negative bacteria. The β-lactamases hydrolyze the penicillins and cephalosporins, chloramphenicol acetyltransferase acetylates chloramphenicol, and nine enzymes acetylate, phosphorylate, or adenylylate the aminoglycoside antibiotics. Resistance to antibiotics in clinical isolates of gram-negative and gram-positive bacteria is usually mediated by the presence of various enzymes that modify the antibiotic so that it can no longer interact with its target in the cell. ![]() Feel free to jump into the MCAT sample questions below, then read on to learn more about what to expect from the actual exam! The good news is that these are all topics that will be incredibly useful in your future medical education. Just like medical school itself, the MCAT tests a wide variety of topics. Where to Find More MCAT Sample Questions.What kind of questions are on the MCAT?.In this post, you’ll find MCAT example questions for each section, plus a breakdown of what’s on real MCAT exams and where to find additional practice. If you’re planning on taking the Medical College Admission Test (MCAT), you need to know what you’re getting into! The best way to do this? Review MCAT sample questions at the start of your MCAT prep! As you do, you’ll be able to glean key information from test day, both in terms of what the exam tests and how the exam tests it! By Rachel Kapelke-Dale on Februin MCAT Practice Tests & Questions ![]()
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