In two studies on the causative agents of bacteraemia in Malawi and Kenya, 33 Salmonella strains were isolated. Fourteen strains of Salmonella typhimurium and Salmonella enteritidis were found to exhibit resistance to amoxicillin, amoxicillinklavulanic acid and cotrimoxazole as well as decreased susceptibility to a range of aminoglycosides. The resistant strains were studied to establish their resistance mechanisms. Beta-lactamase co-focusing with TEM-1 was present in 12 strains. In two strains, both S. typhimurium from Kenya, an OXA-1 beta-lactamase was detected. The aminoglycoside-modifying enzyme ANT(2") was found in 10 strains. The presence of the encoding genes was confirmed by PCR. For comparison, susceptibility records of 73 Salmonella strains isolated during the past 14 years in our hospital were studied retrospectively. Only one of these strains was resistant to amoxicillin. This resistance was acquired during therapy.
The incorporation of beta-lactamases from crude, cell-free lysates incorporated into agar plates used for antibiotic sensitivity testing with sensitivity discs results in a characteristic decrease in the inhibition zones. The degree of zone reduction for a particular antibiotic depends on the substrate specificity of the enzyme involved and the concentration of the enzyme in the agar. By using this technique a distinction can be made between cephalosporinases, penicillinases and broad-spectrum enzymes. In a number of cases, the identification of the enzyme subclass is possible, provided that the relevant penicillin and cephalosporin discs are included in the test. For the elucidation of substrate profiles for routine and epidemiological purposes this method can replace other, more elaborate techniques, such as the iodometric, spectrophotometric and acidimetric methods. An analysis by this method is presented for 126, unrelated, consecutive clinical isolates.
Cefamandole therapy in a patient with suppurative thrombophlebitis failed due to selection of a resistant variant of the causative organism Klebsiella pneumoniae. Analysis of the resistance mechanism revealed that in the resistant variant one of the major outer membrane proteins, OmpF, was missing. Resistance of this type has implications for therapy with other antibiotics including non-beta-lactam antibiotics. This report demonstrates the role of outer membrane permeation in the emergence of bacterial resistance during antibiotic therapy.
Eight strains of Enterobacter cloacae with varying patterns of susceptibility to β-lactam antibiotics were studied to compare the inducibility and expression of their β-lactamase genes. These strains included two isolates from one patient, which differed in their susceptibility to cefamandole. A resistant strain constitutively produced large amounts of β-lactamase; a sensitive strain produced an inducible β-lactamase. Study of induction and growth characteristics of all strains revealed that the induction and the expression of inducible β-lactamase genes may vary considerably among strains of E. cloacae.
The susceptibility of ceftazidime, five other cephalosporins, moxalactam and cefoxitin to 13 different beta-lactamases was determined by means of the spectrophotometric method. None of the bacterial sonicates used as crude beta-lactamase solutions and which were prepared with cephalothin as an inducer, hydrolysed ceftazidime, cefoxitin or moxalactam. In comparative induction experiments one cephalosporinase (class I) was induced to some extent by cephalothin, cefuroxime, cefamandole and ceftazidime, but not by cefotaxime, cefoperazone and moxalactam. Both cephalosporinase-producing strains tested were strongly induced by cefoxitin. With the most potent inducer, cefoxitin, beta-lactamase activity against ceftazidime could not be detected with either of the two cephalosporinase preparations, or with any one of 11 other beta-lactamases. It is concluded that beta-lactamase induction as a result of therapy does not appear to be a factor which should be taken into account in therapy with ceftazidime.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.