Ampicillin resistance (minimal inhibitory concentration >/=10 mug/ml) in the absence of beta-lactamase activity by Haemophilus influenzae was noted in tests performed with Mueller-Hinton agar containing one lot of supplement C. All strains, except five with known resistance due to beta-lactamase activity, were inhibited by 0.6 mug or less of ampicillin per ml of chocolatized blood agar.

Fecal samples from 200 consecutive patients admitted to a community hospital yielded 107 enterococci. High-level gentamicin resistance occurred in 10 (14%) of the Enterococcus faecalis isolates. Ampicillin resistance occurred in two (3%) of the E. faecalis isolates and six (23%) of the Enterococcus faecium isolates. There were no vancomycin-resistant enterococci. Risk factors for enterococci wi...

Enterococcus faecalis isolates were examined by an automated identification and susceptibility system. Almost all of the 97 isolates were ampicillin susceptible (n = 86) and tetracycline resistant (n = 89). All were nitrofurantoin susceptible. About a third of isolates showed high level resistance to the aminoglycosides streptomicin and gentamicin and this was usually associated with ciprofloxa...

Both ampicillin and cefuroxime therapy of neonates selected drug- and species-dependent beta-lactam resistance patterns in fecal strains of Escherichia coli and Klebsiella spp. This was in contrast to our previous findings that ampicillin, but not cefuroxime, contributed to the emergence of beta-lactam resistance also by the promotion of nosocomial spread of resistant strains.

We examined the antimicrobial resistance of 1,257 isolates of 30 serovars of Salmonella enterica subsp. enterica isolated from swine. Serovars Typhimurium and Typhimurium var. Copenhagen were widespread and were frequently multidrug resistant, with distinct resistance to ampicillin, kanamycin, streptomycin, sulfamethoxazole, and tetracycline and to ampicillin, chloramphenicol, streptomycin, sul...

A patient with Salmonella muenchen sepsis was unsuccessfully treated with ampicillin. During therapy, four strains that showed stepwise ampicillin resistance and affected other beta-lactams and unrelated antibiotics were isolated sequentially. Resistance was caused by decreased outer membrane permeability associated with diminished expression of porin OmpF. Furthermore, the most resistant isola...

Results: Epidemiological cut-off values of 19/20 mm for ampicillin (2 mg) and 11/12 mm for benzylpenicillin (1 U) accurately categorized 96% of the study strains, and outperformed cephalosporin-containing discs in the discrimination of mutational resistance in b-lactamase-non-producing isolates. Current EUCAST interpretative criteria for the categorization of clinical resistance showed concorda...

Compared with ampicillin, oxacillin, cefmetazole and imipenem, the combination of ampicillin and sulbactam at a constant ratio of 2:1 showed the greatest effect against 28 clinical isolates of methicillin-resistant Staphylococcus aureus (MRSA), but MICs of ampicillin/sulbactam were still above the resistance breakpoint. When ampicillin/sulbactam was further combined with epigallocatechin gallat...

The in vitro activity of cefixime was comparatively tested against 232 non-type b and 102 type b isolates of Haemophilus influenzae derived from clinical specimens of pediatric patients, including 10 non-type b strains that did not produce beta-lactamase and demonstrated resistance to ampicillin. Cefixime was active against the ampicillin-susceptible and ampicillin-resistant, beta-lactamase-pro...

Eriksson-Grennberg, Kerstin G. (University of Uppsala, Uppsala, Sweden), Hans G. Boman, J. A. Torbjörn Jansson, and Sone Thorén. Resistance of Escherichia coli to penicillins. I. Genetic study of some ampicillin-resistant mutants. J. Bacteriol. 90:54-62. 1965.-A number of ampicillin-resistant mutants have been isolated and characterized. Of these strains, two groups have been genetically invest...