In Escherichia coli wild-type cells, a mutation at the ,-glucoside regulatory gene (bglR+ to bglR-) leads to simultaneous expression of inducible phospho-,glucosidase B (bglB+) and a ,8-glucoside-specific species of enzyme II (,-glucoside transport I [bglC+]); an additional mutation (bglS+ to bglS4) allows these enzymes to be formed constitutively. The bgl alleles have been mapped in the following order: pyrE, bglA, bglB, bglS, bglR, bglC, ilvD. The back mutation in the regulatory allele (bglRto bglR+) caused the cessation of the expression of the bglB+, bglS+ or bglS4, bglC+ alleles. However, a mutation in a strain with bglB+, bglS4, bglR8, bglC+ alleles, at the ini site that lies between the bglS4 and the bglR8 allele, allowed the expression of the bglS4 and bglB+ alleles, but showed no affect on the expression of the bglC+ allele. It is suggested that the ini mutation possesses a promotor-type function that in the absence of regulatory allele function (bglR8) renews the functioning of only the bglS4 and bglB+ alleles. The complementation studies have shown that the bglB+, bglS+ or bglS4, bglC+ alleles are expressed only in cis to the bglR-allele. In the constitutive strain (bglB+, bglS4, bglR-, bglC+), the expressed bglS4 allele formed a soluble product that acts in trans over the bglB+ and bglC+ alleles and that appears effective only when the bglB+ and the bglC+ alleles are expressed in cis to the bglRallele. It thus showed that the constitutive biosynthesis of phospho-oglucosidase B and ,B-glucoside transport I is under positive control. Since the regulatory allele bglRlies between the bglS4 and the blgC+ alleles, and acts in

Wild-type Escherichia coli strains (8-gt) do not split f3-glucosides, but inducible mutants (fl-gl+) can be isolated which do so. This inducible system consists of a B-glucoside permease and an aryl ,B-glucoside splitting enzyme. Both can be induced by aryl and alkyl ,B-glucosides. In ,3-gt and noninduced (3-gl+ cells, C14labeled thioethyl,B-glucoside (TEG) is taken up by a constitutive permease, apparently identical with a glucose permease (GP). This permease has a high affinity for a-methyl glucoside and a low affinity for aryl ,B-glucosides. No accumulation of TEG occurs in a 3-gh strain lacking glucose permease (GP-). In induced 3-gl+ strains, there appears a second #-glucoside permease with low affinity for a-methyl

The incidence of amikacin resistance among gram-negative bacilli isolated at the New York V.A. Medical Center increased from 2.0% to greater than 7% during an 18-month period from January 1980 to July 1981. This increase coincided with a threefold increase in amikacin use at this institution. The amikacin-resistant (AKR) isolates most frequently recovered in 1981 were species of Klebsiella, Serratia, and Pseudomonas. These organisms were recovered from multiple sites, including urine, sputum, wounds, blood, peritoneal fluid, and pleural fluid. The amikacin-modifying enzyme 6'-N-acetyltransferase was detected in 27 (67.5%) of 40 randomly selected AKR isolates. These data indicate that resistance to amikacin in this hospital is enzymatically mediated in most strains of AKR Klebsiella and Serratia and in about one-third of AKR strains of P. aeruginosa. This finding supports the conclusion that amikacin resistance is enhanced by the pressure of increased amikacin use.

Two types of mutants obtained by treating ,B-gl+ cells with nitrosoguanidine are described. One type, ,3-gtc, is constitutive for the biosynthesis of the aryl ,B-glucoside splitting enzyme(s) and for the /3-glucoside permease; the other (/3-gl+ sat-) has lost the capacity to ferment salicin, but has retained the capacity to ferment arbutin and other aryl ,B-glucosides. By two successive mutational steps, 3-gl+ salc double mutants can be obtained. Determinations of the enzymatic splitting of salicin and p-nitrophenyl f-glucoside by ,B-gl+ salcells and extracts showed that these mutants have lost the capacity to split salicin but do split p-nitrophenyl (3-glucoside; they possess the (3-glucoside permease, and in them salicin is a gratuitous inducer for enzyme and permease biosynthesis. Studies on a #-gl+ strain, which splits salicin as well as p-nitrophenyl #-glucoside, have shown that the splitting of salicin is more temperature-sensitive than that of p-nitrophenyl ,B-glucoside and other 3-glucosides. Other properties of the two activities are similar. Interrupted mating experiments and cotransduction with Plkc phage showed that the genetic determinants of the f3-glucoside system map between the pyrE and ile loci. Three distinct mutational sites were found and are presumed to have the following functions: (3-glA, a structural gene for an aryl (3-glucoside splitting enzyme; B-giB, either the structural gene for the (3-glucoside-permease or a regulatory gene; and fl-glC, a regulatory gene (or site). Escherichia coli wild-type strains are of the genotype A+ B C+. The ,B-gl+ mutation determining the ability to ferment (3-glucosides is considered to be a permease or regulatory mutation, and the resulting genotype is A+ B+ C+. The #-gl+ sat-phenotype results from a mutation in the (3-glA gene (genotype A' B+ C+), and the constitutive phenotype results from a mutation in the ,B-glC gene, the genotypes A+ B+ C,, and A' B+ Ca corresponding to the phenotypes #-gl+c and ,B-gl+ salc. As described in the preceding paper (11), spontaneous,B-glucoside-fermenting mutants (,B-gl+) can be isolated from Escherichia coli K-12 wild type and several of its auxotrophic derivatives. Further studies on such mutants demonstrated the presence of an inducible system for the accumulation and utilization of ,B-glucosides. This system consists of one or more aryl ,B-glucoside-splitting enzymes and a ,B-glucoside permease. It was found that the induction of the enzyme and permease occurs simultaneously. These data indicate the existence of a regulon (9) consisting of at least two genes. It was shown in a