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This study reports about 126 children with an age ranging from 12 months to 12 years having RA to beta-lactamase. More children with an age ranging from 7-12 years (59.5%), and more male (65.9%) than female subjects were studied. 76 patients (60.3%) showed a familial anamnesis of allergic diseases or similar diseases and a personal anamnesis of allergic diseases (45.2%). Among the RA responsible substances the more frequent were semisynthetic penicillin (44.6%) followed by cephalosporin and penicillin. Most clinical manifestations (87.3%) were cutaneous reactions and in smaller number of cases it was possible to observe gastroenteric or respiratory reactions. In 121 patients cutaneous tests were undertaken (Prick tests and intradermoreactions), patch tests, employing: PPL, MDM, Penicillin, Ampicillin, Cephaloridine. 5.8% of the studied subjects showed an allergy. Particularly 2.4% showed a "early" positivity. RAST was carried out in 92 patients and 3 of them showed a positive result (3.2%). This study stresses the opportunity to carry out allergologic tests within 6 months since the beginning of RA. In fact especially in children this test result can soon become negative. Furthermore the reduced percentage of positive allergologic tests can be due to the inclusion in other studies of patients with "coincidental reactions". A certain number of RA can be caused by additive to "per os" products. Finally it will be possible to use "tests dose" even in selectioned cases. These tests can frequently exclude the etiopathogenetic responsibility of beta-lactamic substances.

After a short introduction on bacterial resistance to the antibiotics and on the importance of the problem of emergence of the resistant strains, the mechanisms responsible are discussed. There are three major ways by which bacteria resist beta-lactam antibiotics; these include: altered outer membrane permeability, production of beta-lactamase and diminished affinity of the PbPs. Production of beta-lactamase is by far the most frequently encountered; for this reason there has been a major effort in the past 20 year to design new beta-lactam antibiotics, but on the other side bacteria elaborate constantly new strategies against new antibiotics. Moreover the use of antibacterial agents over the past half century has elicited a widespread deployment of genes for resistance in population of bacteria throughout the world and is conditioning the evolution of microbes.

The role played by beta-lactamases and by permeability barrier in resistance to beta-lactam antibiotics was investigated in 250 clinical isolates of Enterobacteriaceae. The data obtained showed that in 73 strains (52.9%) was a significant correlation between the specific enzyme activity and resistance, however in 38 strains (27.5%) an essential role was played by permeability barrier because the addition of subinhibitory levels of EDTA produced markedly reduction in the MIC.

beta-lactamase production was evaluated by chromogenic cephalosporin 87/312 in 116 E. coli isolated from clinical sources. Such test revealed beta-lactamase production in 54 strains out of 116 (46%): MICs of eight beta-lactam antibiotics (Ampicillin, Piperacillin, Cefazoline, Cephaloridine, Cephalexine, Cefuroxime, Cefotaxime, Cefotaxime) were determined using a miniaturized dilution broth method. Cefotaxime and Ceftriaxome and Ceftriaxone showed the highest antibacterial activity. All beta-lactamases produced by E. coli strains under examination were isolated and purified by ultrasonic disruption and high speed centrifugation. Sensitivity of the eight antibiotics to purified beta-lactamases was assessed by a spectrophotometric method that utilizes the velocity of cytochrome c reduction. The sensitivity to beta-lactamases was reflected in the in vitro activity of the antibiotics as assessed by the determination of the MICs.