INDUCTION OF STAPHYLOCOCCAL PENICILLINASE BY BENZYLPENICILLIN: EFFECT OF pH, CONCENTRATION OF FERROUS ION AND INDUCER, AND DURATION OF EXPOSURE OF CELLS TO INDUCER

Kinetics of penicillinase induction and variation of penicillinase translation in Staphylococcus aureus

At neutral pH, the rate of penicillinase synthesis by staphylococci declines gradually after removal of free inducer, while at pH 5.4 enzyme formation is generally linear for an extended period. Linear synthesis of penicillinase was observed at neutral pH in nonsaturating concentrations (1mug/ml) of actinomycin D. The rate of enzyme synthesis, corrected for inhibition of growth caused by the antibiotic, was relatively independent of the time of actinomycin addition. The lag preceding linear enzyme formation increased with the interval between induction and the addition of actinomycin. The findings are consistent with the concept that, at neutral pH, "operons" activated by induction are rapidly repressed, while at pH 5.4, this process is delayed. At a concentration of 4mug/ml, actinomycin D blocked penicillinase messenger synthesis and also elicited a short-lived acceleration of the increase of penicillinase activity in uninduced and, late after induction, in induced cultures. This effect did not require a functional genomic repressor mechanism since it occurred also in a penicillinase-constitutive strain. It required protein synthesis and could not be attributed to a greater enzyme stability in the presence of actinomycin. The results suggest enhanced penicillinase translation after addition of actinomycin D.

DERMATOPHYTE LESIONS IN THE HEDGEHOG AS A RESERVOIR OF PENICILLIN-RESISTANT STAPHYLOCOCCI

An antibiotic substance biologically resembling penicillin G was produced by the growth ofTrichophyton mentagrophytesvar.erinacei, T. mentagrophytes var. granulareandT. mentagrophytesvar.interdigitalein Sabouraud's dextrose broth. An antibiotic concentration equivalent to 7 units/ml. penicillin G could be produced by var.erinaceiwhen grown in a suitable nutrient medium.Epidermophyton floccosumalso produced a substance which inhibited the growth of the Oxford staphylococcus. However, this substance was not completely inactivated by penicillinase. Noin vitroantibiotic production could be demonstrated withT. rubrum, T. concentricum, T. terrestreorMicrosporum canis.

Penicillin production could be demonstrated in rabbit skin infected with T. ment-agrophytes var. erinacei. Pathogenic staphylococci falling on a var. erinacei guinea-pig lesion increased rapidly in the ringworm tissue. The inhibiting concentration of penicillin G for such staphylococci was shown to increase from 5·0 µg./ml. to above 20·0 µg./ml. as the ringworm progressed.

The presence ofT. mentagrophytesvar.erinaceiin a high percentage of hedgehogs is considered the main reason why the skin is the primary site of staphylococcal multiplication in hedgehogs and why most of theStaphylococcias aureusstrains recoverable from these animals are penicillin resistant.

Rapid, inexpensive method for specific detection of microbial beta-lactamases by detection of fluorescent end products

A rapid method was developed for specific detection of microbial beta-lactamases which uses ampicillin and cephalexin as substrates. The end products (open beta-lactam ring forms) generated after separately incubating either substrate with beta-lactamase-producing organisms initially were separated from the unhydrolyzed substrates by high-voltage electrophoresis at pH 2.1. The end products of both antibiotics were highly fluorescent and could be analyzed visually and semiquantitatively under a long-wave UV lamp. Application of 5 microliters of the same incubation mixture onto filter paper without subsequent electrophoretic separation also resulted in development of fluorescence after brief heating at 120 degrees C for 5 min. This spot test differentiates penicillinase activity from cephalosporinase activity and distinguishes between beta-lactamase and acylase activities, since the end products of acylase [the common side chain, D(-)-alpha-aminophenylacetic acid, and the intact beta-lactam nuclei, 6-aminopenicillanic acid and 7-aminodeacetoxycephalosporanic acid] are not fluorescent. This method was relatively rapid, inexpensive, and more sensitive than the chromogenic cephalosporin (nitrocefin) method when 21 strains of 7 gram-positive species and 77 strains of 29 gram-negative species of bacteria were tested.

Regulation of penicillinase synthesis: a mutation in Staphylococcus aureus unlinked to the penicillinase plasmid that reduced penicillinase inducibility

A mutant of Staphylococcus aureus strain 655 was isolated that is restricted in penicillinase induction. Wild-type plasmids that bear penicillinase determinants could not be fully induced in this mutant, 655par-1; hence, the responsible mutation is not located on the plasmid. Mutant plasmid PI(258)penI443, which produces penicillinase constitutively in wild-type cells, was fully constitutive for penicillinase production when it was harbored by mutant 655par-1. Therefore, the bacterial mutation does not interfere directly with the transcription of the penZ gene or translation of the penicillinase messenger ribonucleic acid. Mutant plasmid PII(147)penI220 was fully inducible in the mutant bacterium, even though the wild-type plasmid PII(147) was only partially inducible in the par-1 mutant. Thus, in the presence of inducer, complementation appears to occur between the product of the par-1 gene and the product of the penI220 gene. These results suggest that the par-1 gene codes for a penicillinase antire-pressor.

Penicillinase (beta-lactamase) induction in Bacillus licheniformis under Pseudogratuitous conditions by 2-(2'-carboxyphenyl)-benzoyl-6-aminopenicillanic acid

Induction of penicillinase (beta-lactamase) in Bacillus licheniformis 749 by 2-(2'-carboxyphenyl)-benzoyl-6-aminopenicillanic acid (CBAP) was examined, since this compound was reported to be a gratuitous inducer of penicillinase in Staphylococcus aureus. The specific activity of enzyme optimally induced by CBAP is slightly more than that formed in response to cephalosporin C and threefold the level induced by benzylpenicillin. The optimal inducer concentration of CBAP was not inhibitory toward the growth of penicillinase-deficient mutants, unlike benzylpenicillin or cephalosporin C which showed marked toxicities. CBAP is hydrolyzed by the Bacillus penicillinase, but as indicated by its "physiological efficiency" (V(max)/K(m)), CBAP is a poor substrate at low concentrations. At very high concentrations, CBAP inhibited benzylpenicillin hydrolysis. The overall effectiveness of CBAP as an inducer can be attributed to its low "physiological efficiency" which enables the use of nontoxic levels of CBAP for induction without its rapid hydrolysis. Although CBAP is not a true gratuitous inducer, operationally it approaches gratuity for induction of B. licheniformis penicillinase better than other known inducers.

Gratuitous synthesis of beta-lactamase in Staphylococcus aureus

The synthesis of beta-lactamase in response to 2-(2'-carboxyphenyl)-benzoyl-6-aminopenicillanic acid as inducer was studied in Staphylococcus aureus. The inducer was not detectably hydrolyzed by beta-lactamase and had minimal antibacterial activity. The kinetics of induction showed a lag of 4 to 6 min in a nutrient broth medium and 8 to 12 min in a defined medium, followed by constant differential rates of synthesis of beta-lactamase. The differential rate of beta-lactamase synthesis in nutrient broth was unaltered by supplementing the medium with glucose, galactose, lactose, arabinose, glycerol, or sucrose. Variations in the partial pressure of oxygen did not alter the differential rate of synthesis of beta-lactamase over the range 18 to 50% oxygen in nitrogen. Even when the rate of growth was considerably reduced by high-oxygen tension, the differential rate of synthesis of the enzyme remained the same. The differential rate of beta-lactamase synthesis at low inducer concentration increased after a shift down in growth rate. The effect was observed with several inducers and under different nutritional conditions, but was always preceded by a change in growth rate. It is suggested that the change in growth rate itself causes the increase in differential rate of beta-lactamase synthesis.

Relation between iron uptake, pH of growth medium, and penicillinase formation in Staphylococcus aureus

The uptake of iron and the formation of penicillinase was examined in cultures of wild-type Staphylococcus aureus. Uptake of iron was about twice as great at pH 4.7 as at pH 7.4 At pH 4.7, increase in iron uptake in the range of 1.0 to 4.0 mug per mg of bacterial protein was associated with a progressive increase in the rate of penicillinase formation, but a direct correlation between cellular iron content and rate of enzyme formation was not demonstrated. Addition of iron to deferrated medium enhanced penicillinase formation at pH 6.5 to 7.4 two- to fourfold in cultures induced with benzylpenicillin and in uninduced cultures. To demonstrate an effect on the uninduced cells, it was necessary to increase iron uptake by preliminary incubation of cells with iron in buffer. Calcium and certain other ions depressed iron uptake at acidic and at neutral pH, and, presumably as a result of this action, depressed the formation of penicillinase. Iron did not enhance penicillinase formation at pH 4.7 by two penicillinase constitutive mutants nor by wild-type cells undergoing induction at pH 6.5 by cephalosporin C or methicillin. After removal of cephalosporin C or methicillin during an early phase of induction, residual synthesis of enzyme was increased by prior uptake of iron. The results are considered compatible with the concept that uptake of iron, especially at acidic pH, interferes with the formation or function of penicillinase repressor.

Induction of penicillinase by staphylococci in vitro and in vivo

Eyckmans, Luc (Cornell University Medical College, New York, N.Y.), and Edward W. Hook. Induction of penicillinase by staphylococci in vitro and in vivo. J. Bacteriol. 91:997-1003. 1966.-Staphylococci in mice with peritoneal infection showed no significant increase in penicillinase activity 6 hr after administration of penicillin G. In contrast, induction of penicillinase was readily demonstrated in leukopenic animals under similar conditions. Induction of penicillinase by staphylococci in vitro was inhibited by including leukocytes and immune serum in the mixtures. The role of leukocytes in inhibiting induction of penicillinase by staphylococci in response to penicillin was investigated.