In vitro activity of six beta-lactam antibiotics against non-beta-lactamase producing and producing enterobacteria and antibiotic resistance transfer.

beta-Lactamase production was evaluated by chromogenic cephalosporin 87/312 in 184 enterobacteria isolated from clinical sources. Minimal inhibitory concentrations (MICs) of six beta-lactam antibiotics (Ampicillin, Cephaloridine, Cephalexine, Cefazoline, Cefuroxime, Cefotaxime) were determined on 90 non beta-lactamase producing and 94 beta-lactamase producing strains by a miniaturized dilution method. beta-lactamase production transfer and antibiotic resistance transfer were observed in a receiving E. coli K12 C600 NA- after conjugation with 94 producing strains. Cefotaxime showed high antibacterial activity both against beta-lactamase producing and non producing bacteria. Cefuroxime, Cephalexine and Cefazoline were active only against high percentage of non beta-lactamase producing bacteria. Ampicillin and Cephaloridine showed low antibacterial activity both against producing and non producing bacteria. About 19% (18/94) of beta-lactamase producing bacteria transferred beta-lactamase producing capacity to E. coli K12 by conjugation and a significant increase of MICs of each antibiotic, except that of Cefotaxime, was observed in E. coli K12 that acquired capacity to produce beta-lactamase by conjugation. Resistant strains that produce beta-lactamase transfer antibiotic resistance by conjugation to E. coli in variable percentages to the antibiotics under examination. Antibiotic resistance to Ampicillin, Cephaloridine, Cephalexine and Cefazolin observed in receiving strains after conjugation is not only due to beta-lactamase transfer. All strains acquiring Cefuroxime and Cefotaxime resistance never acquire beta-lactamase producing capacity.

Comparative activity of ceftazidime and four other cephalosporins against gram-negative bacteria and their sensitivity to beta-lactamases.

The in vitro activity of ceftazidime compared with other beta-lactamase stable compounds was assessed against recent Gram-negative isolates. Three hundred forty-three bacterial strains were isolated from patients affected with UTI, identified by standard bacteriological methods and investigated for their production of beta-lactamases by the Nitrocefin test. MICs and MBCs (minimum inhibitory concentrations and minimum bactericidal concentration) of ceftazidime, cefamandole, cefoxitin, cefotaxime and cefuroxime were determined by a miniaturized dilution broth method against all beta-lactamase producing bacteria (129 out of 343). Sensitivity of the antibiotics to beta-lactamases isolated and semipurified by ultrasonic disruption and high-speed centrifugation was assessed by a spectrophotometric method. The in vitro antibacterial activity of each antibiotic was correlated to its sensitivity to isolated beta-lactamases. Ceftazidime showed lower MIC and MBC values and lower MBC/MIC ratios than the other compounds against all the bacteria including Pseudomonas spp. In addition, ceftazidime was not hydrolyzed significantly by any isolated beta-lactamases.

Comparative in vitro activity of norfloxacin and four other chemotherapeutics against urinary gram-negative isolates.

Three hundred seventy-five Gram-negative bacterial strains were isolated from urine specimens of as many patients affected by symptomatic or asymptomatic urinary tract infections. Susceptibility of bacteria to five chemotherapeutics (norfloxacin, oxolinic acid, pipemidic acid, nalidixic acid and nitrofurantoin) was studied determining minimum inhibitory concentrations (MICs) and minimum bactericidal concentrations (MBCs) of each compound by a miniaturized dilution broth method. Norfloxacin, a quinoline carboxylic acid compound structurally related to nalidixic acid, showed a much higher antibacterial activity against all bacterial strains under examination including Pseudomonas sp. The best activity of norfloxacin was expressed either by lower MICs and lower MBCs with respect to those of the other compounds, or by a low MBC/MIC ratio, which represents an important advantage in clinical practice.

[Sensitivity of 5 beta-lactam antibiotics to beta-lactamase isolated from E. coli and its respective transconjugates]. / Sensibilita' di 5 antibiotici beta-lattamici alle beta-lattamasi isolate da E. coli e dai rispettivi transconiuganti.

54 beta-lactamase producing E. coli were tested to observe their eventual capacity to transfer beta-lactamase production by conjugation to a receiving E. coli K12 C600 Na-. About 16% (9/54) of these strains transferred beta-lactamase producing capacity. MICs of five beta-lactam antibiotics (Ampicillin, Cephaloridine, Cephalexine, Cefuroxime, Cefotaxime) were performed against E. coli donors and E. coli K12 C600 transconjugates. It was observed a remarkable increase only of Ampicillin MICs against all transconjugates++. Beta-lactamases produced by donors and transconjugants were isolated and purified by sonication and high speed centrifugation. Sensitivity of the six antibiotics to these purified beta-lactamases was assessed by a spectrophotometric method that utilizes the velocity of cytochrome c reduction. beta-lactamases produced by transconjugants have identical substrate profile that beta-lactamases produced by donors.

[In vitro activity of beta-lactam antibiotics and their sensitivity to beta-lactamase]. / Attivita' in vitro di antibiotici beta-lattamici e loro sensibilita' alle beta-lattamasi.

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.

Rashes associated with intravenous administration of ampicillin.

532 patients under intravenous Ampicillin therapy have been included in the trial to evaluate the eventual onset of rashes. These patients have been divided into two groups: the first group comprised of patients affected with acute or chronic liver diseases, the second one with diseases of bacterial etiology. In the first group Ampicillin has been utilized either for its antiammoniaemic activity or to treat urinary or respiratory tract infections of bacterial origin. Ampicillin has been administered intravenously at the dosage of 1-6 g daily. Only 18 patients (3.4%) out of 532 under examination have shown skin reaction during treatment. It is suggestive that the low incidence of Ampicillin rashes observed is due to the way of administration of the drug.

Transferable drug resistance in Escherichia coli isolated from antibiotic-fed chickens.

The isolation and transferable drug resistance of Escherichia coli from the feces of chickens after oral administration of tetracylcine, chloramphenicol, rifampicin, and amoxicillin were studied. Each antibiotic was administered at two different dosages to four groups of 12 chickens. Treatment was carried out for 3 weeks. Feces were taken weekly and bacteriological examinations performed. E. coli biotypes were identified by fermentation and enzymatic reaction patterns. Antibiotic sensitivity tests were performed on all E. coli isolates. Rapid appearance of E. coli biotypes showing drug-resistance to each antibiotic was observed as soon as 1 week after treatment. Resistance was not detectable a few days after interruption of antibiotic administration. All E. coli strains showing drug resistance to the antibiotic under examination were studied to observe their capacity to transfer antibiotic resistance to E. coli K 12 E 711 F-strain. A high percentage of resistant E. coli strains transferred their antibiotic resistance to E. coli K 12. Transferable drug resistance was demonstrated mainly in tetracycline resistant E. coli.

[Antibiotic resistance and transfer in Enterobacteriaceae of avian origin]. / Antibiotico-resistenza e trasferimenti nelle enterobacteriaceae di provenienza avicola.

Thirty-six specimens of feces were taken from as many chicken farms, from which 118 different strains of Enterobacteriaceae were isolated. The resistances of the single isolated bacteria were studied, performing plate sensitivity tests by the Kirby-Bauer method. The capacity of the bacteria under examination to transfer their antibiotic resistances in vitro to a sensitive E. coli strain (E. coli K 12 E 711 F--) was observed. A very high percentage of strains has shown resistance to one or more antibiotics (91%). However a much lesser number of strains were capable of transferring their antibiotic resistances (12.9%). It is suggestive, then, that the animals under examination do not represent an important source of antibiotic resistance diffusion to man.