1. Pseudomonas pyocyanea N.C.T.C. 8203 produces a beta-lactamase that is inducible by high concentrations of benzylpenicillin or cephalosporin C. Methicillin appeared to be a relatively poor inducer, but this could be attributed in part to its ability to mask the enzyme produced. Much of the enzyme is normally cell-bound. 2. No evidence was obtained that the crude enzyme preparation consisted of more than one beta-lactamase and the preparation appeared to contain no significant amount of benzylpenicillin amidase or of an acetyl esterase. 3. The maximum rate of hydrolysis of cephalosporin C and several other derivatives of 7-aminocephalosporanic acid by the crude enzyme was more than five times that of benzylpenicillin. Methicillin, cloxacillin, 6-aminopenicillanic acid and 7-aminocephalosporanic acid were resistant to hydrolysis, and methicillin and cloxacillin were powerful competitive inhibitors of the action of the enzyme on easily hydrolysable substrates. 4. Cephalosporin C, cephalothin and cephaloridine yielded 2 equiv. of acid/mole on enzymic hydrolysis, and deacetylcephalorsporin C yielded 1 equiv./mole. Evidence was obtained that the opening of the beta-lactam ring of cephalosporin C and cephalothin is accompanied by the spontaneous expulsion of an acetoxy group and that of cephaloridine by the expulsion of pyridine. 5. A marked decrease in the minimum inhibitory concentration of benzylpenicillin and several hydrolysable derivatives of 7-aminocephalosporanic acid was observed when the size of the inoculum was decreased. This suggested that the production of a beta-lactamase contributed to the factors responsible for the very high resistance of Ps. pyocyanea to these substances. It was therefore concluded that the latter might show synergism with the enzyme inhibitors, methicillin and cloxacillin, against this organism.

Abraham & Newton (1956) showed that cephalosporin C was highly resistant to hydrolysis by purified penicillinase from BaciUu8 cereus (strain NRRL 569; see Pollock, 1959, 1960) but was a competitive inhibitor of the action of this penicillinase on benzylpenicillin. More recently, however, cephalosporin C was reported to have no significant inhibitory action on the hydrolysis of benzylpenicillin by penicillinase from a strain of Staphylococcus aureus (Abraham & Newton, 1961 a). Rolinson, Stevens, Batchelor, Wood & Chain (1960) reported that 2,6-dimethoxyphenylpenicillin was a competitive inhibitor of penicillinase from B. cereus, but not of penicillinase from Staph. aureus. These findings suggested that penicillinase from B. cereus and penicillinase from Staph. aureus differed with respect to structural features which influenced the combination of enzyme and substrate. They also drew attention to the fact that the affinity for penicillinase of a member of the cephalosporin C or penicillin family might partly determine the rate of enzymic hydrolysis of the substance in the concentration at which it was used as an antibacterial agent. The results of further experiments in this field are given here. The substances studied were N-acyl derivatives of 7-aminocephalosporanic acid which has structure (I; R = H, R' = CH3 Co00)

No abstract

The fitness effects of antibiotic resistance mutations are a major driver of resistance evolution. While the nutrient environment affects bacterial fitness, experimental studies of resistance typically measure fitness of mutants in a single environment only. We explored how the nutrient environment affected the fitness effects of rifampicin-resistant rpoB mutations in Escherichia coli under several conditions critical for the emergence and spread of resistance—the presence of primary or secondary antibiotic, or the absence of any antibiotic. Pervasive genotype-by-environment (GxE) interactions determined fitness in all experimental conditions, with rank order of fitness in the presence and absence of antibiotics being strongly dependent on the nutrient environment. GxE interactions also affected the magnitude and direction of collateral effects of secondary antibiotics, in some cases so drastically that a mutant that was highly sensitive in one nutrient environment exhibited cross-resistance to the same antibiotic in another. It is likely that the mutant-specific impact of rpoB mutations on the global transcriptome underpins the observed GxE interactions. The pervasive, mutant-specific GxE interactions highlight the importance of doing what is rarely done when studying the evolution and spread of resistance in experimental and clinical work: assessing fitness of antibiotic-resistant mutants across a range of relevant environments.

Some biological properties of cephalosporin C and of a pyridinium derivative, "cephalosporin CA (pyridine)," were examined. Staphylococci, both penicillinaseproducing and non-penicillinase-producing, and some other bacteria tested, were inhibited by 60 to 125 pg cephalosporin C/ml., and S to 20 pAg cephalosporin CA (pyridine)/ml. The ratio of the activity of the two antibiotics varied for different organisms. Resistance developed slowly on repeated subculture of penicillinaseproducing staphylococci in presence of either antibiotic. The minimum inhibitory concentration of cephalosporin CA (pyridine) upon penicillinase-producing staphylococci increased 4 to 8-fold with a 500-fold increase in inoculum size; with cephalosporin C there was a 2-fold increase. Their activity was not reduced by serum. Both substances were non-toxic. They were excreted quantitatively in the urine when given intravenously or subcutaneously to mice. After oral administration less than 5% of the dose was excreted. Cephalosporin CA (pyridine) was about 8 times more active than cephalosporin C in protecting mice from an experimental streptococcal infection, nine doses of 6.25 mg/kg affording complete protection.

The N-phenylacetyl derivative of 7-aminocephalosporanic acid (cephaloram) had roughly the same activity as benzylpenicillin against a number of Gram-positive organisms and about one-eighth of the activity of benzylpenicillin against penicillinsensitive strains of Staphylococcus aureus. This derivative and the N-a-phenoxypropionyl derivative of 7-aminocephalosporanic acid were 4 to 8 and 4 to 16 times as active as methicillin against penicillinase-and nonpenicillinase-producing staphylococcal strains, respectively. Neither the presence of horse serum nor changes in inoculum size appreciably affected the activities of any of the derivatives of 7-aminocephalosporanic acid which were tested. After forty-eight subcultures in the presence of antibiotic the increase in minimum inhibitory concentration against the staphylococcus was about four-times as -great for cephaloram as for cephalosporin C. The resistant penicillinase-producing strains remained stable after six subcultures in antibiotic-free medium, and all the strains retained coagulase activity. Some degree of cross-resistance was found between the derivatives of 7-aminocephalosporanic acid and those of 6-aminopenicillanic acid. Synergism was observed in vitro between certain derivatives of 7-aminocephalosporanic acid and 6-aminopenicillanic acid when they were tested together or with fusidic acid or cephalosporin Pi against a weak penicillinase-producing strain of Staphylococcus aureus. Cephalosporin C and cephalosporin C (pyridine), each in combination with benzylpenicillin, showed a significant degree of synergism in protection experiments in mice infected with a strong penicillinase-producing strain of Staphylococcus aureus.

Shennan (1944) in his analysis of 300 cases of dissecting aneurysm of the aorta (up to and including 1932) reported only six correctly diagnosed before death. Among 153 cases reported by Reich (1944), and 12 by Logue, (1943), 36 and 10 respectively were correctly diagnosed. Reviewing these and some other reports, about 49 correct ante-mortem diagnoses have been made among 512 instances of the disease.Differences in the carotid pulses were recorded by Nissim (1946) in one patient. The pulse was reduplicated on the right side and single on the left, without co-existing difference in the intensity of pulsation. He concluded that this was due to the difference in the rate of propogation of the pulse wave through the lumen of the artery and through its dissected coat, where the blood was probably partly clotted.The following case is described because the diagnosis was finally made on the diminished pulsation of-one carotid pulse. This was shown at necropsy to be due to pressure of the aortic aneurysm on the left carotid artery. Case ReportA man, aged 62, was admitted on 6/4/50. Eight days previously he had a sudden attack of cramp-like pain in the centre of the chest, radiating into the back and down the left arm. The pain was very severe for the first 24 hours, and then steadily diminished until his admission to hospital, when he had a feeling of slight constriction only in the centre of the chest and in the small of the back. Four days after the onset of his symptoms he complained of recurring cramps in the calves.In 1947, he had had a sudden attack of dizziness with amblyopia, lasting several days. He was told he had a high blood pressure. In 1948 his vision became blurred for a few days, but apart from these occurrences he had been well.On examination he was of plethoric appearance with a temperature of 99°F. The pulse rate was 90 per minute, with frequent extrasystoles; it was of high tension and equal on the two sides. The blood pressure was 270/160 but no pulsus alternans was detected. The heart was enlarged with a thrusting apex beat in the fifth space, 11 cm. from the mid-line. There was a generalized presystolic gallop rhythm with an apical systolic murmur; an aortic systolic murmur conducted into the neck was followed by a loud aortic second sound. The femoral and dorsalis pedis pulses were equal on palpation. Crepitations were heard at the bases of both lungs. No other abnormal physical signs were found.On 11/4/50 an electrocardiogram showed a left ventricular preponderance, but no evidence of myocardial infarction. An X-ray of the chest showed a large left ventricle and an unfolding aorta with clear lung fields. On 13/4/50, a barium swallow was normal and there was no change in the cardiac or aortic shadows. The Wassermann reaction was negative and the blood urea 84 mg. per cent. The urine contained al-bumen, but no red cells or casts.At this stage it was considered that this was probably a case of coronary thrombosis and he was treated with rest and sedatives only. 279