RESUMEN
ß-lactamases confer resistance to ß-lactam antibiotics, which are the most widely used family of antibiotics. It is, therefore, essential that one can identify the production of ß-lactamases by clinical isolates and have effective ways of distinguishing the different enzymes. This is necessary for epidemiologic surveys, predicting future resistance trends, and to ensure that patients receive the appropriate ß-lactam or alternative therapy.
RESUMEN
For the last 20 yr thin-layer polyacrylamide isoelectric focusing (IEF) has played a major role in the identification and characterization of ß-lactamases. IEF is able to distinguish enzymes that focus only 0.05 pI apart (1), but the exponential increase rin the numbers of ß-lactamases discovered over the last 10 yr has meant that this method no longer provides sufficient resolution to distinguish the majority of ß-lactamases. Today the pI of a ß-lactamase is still an essential determinant that must be used in combination with a variety of other data. Moreover, the IEF of ß-lactamases is now entering a new era as this technique can be adapted to provide important biochemical information on ß-lactamases other than simply their pI values. These approaches are discussed in Subheading 3.1.
RESUMEN
An in vitro microtest for assessing the susceptibility of Plasmodium falciparum to sulfadoxine-pyrimethamine (S-P) was developed following WHO guidelines. Paraaminobenzoic acid and folic acid were depleted in the culture medium used, the test wells were predosed with sulfadoxine and pyrimethamine at a constant ratio of 80:1, and the parasites were incubated for 48 hours. Optimum parasite multiplication was obtained with a 2% erythrocyte suspension in medium supplemented with 12% serum. During in vitro studies with laboratory-adapted isolates, response patterns were obtained which distinguished 3 isolates with documented in vivo sensitivity to S-P from 2 isolates with documented in vivo resistance to S-P. In addition, among the three S-P-sensitive isolates, one isolate that was pyrimethamine-resistant in vitro had a higher S-P inhibitory endpoint than 2 isolates that were pyrimethamine-sensitive in vitro. The S-P microtest was further evaluated in combined in vivo and in vitro studies in Port-au-Prince, Haiti. Twenty-six patients infected with P. falciparum were treated with standard doses of S-P, resulting in prompt clearance of parasitaemia, with no recurrence in the 24 patients who completed a 28-day follow-up period. Parallel in vitro tests with pyrimethamine alone showed 3 pyrimethamine-resistant isolates out of 22 successful tests on the patients' blood samples. In 23 successful S-P tests, the known in vivo S-P-sensitive parasites were inhibited at S-P concentrations that were generally lower for in vitro pyrimethamine-sensitive isolates than for in vitro pyrimethamine-resistant ones.