Preferential Inhibition of Penicillinase Induction by Oxytetracycline and Its Effect on the Penicillin Susceptibility of Staphylococci

Exposure of penicillinase-producing staphylococci to a combination of penicillin and oxytetracycline resulted in a synergistic inhibitory activity of the antibiotics on the bacteria. Oxytetracycline was employed in concentrations having little or no effect on bacterial growth. It was found that the synergistic antibacterial effect was caused by the preferential inhibition of penicillinase induction by oxytetracycline, rendering the staphylococci more susceptible to penicillin.     

In Vivo Studies on Staphylococcal Penicillinase.

Eyckmans, Luc (Baylor University Medical Center, Dallas, Tex.), and Ralph Tompsett. In vivo studies on staphylococcal penicillinase. J. Bacteriol. 90:589-593. 1965.-The amounts of staphylococcal penicillinase present in tissue of mice with well-established infections due to penicillin-resistant staphylococci were determined. The data indicate that, in the presence of such infection, penicillinase can be found in amounts adequate to destroy large amounts of penicillin. These results are found in the absence of any conditions which are known to induce penicillinase. Although it has been generally assumed that penicillinase does account for the penicillin resistance of certain staphylococci in vivo, the data presented here document the quantitative aspects of this phenomenon, and indicate that the amounts of penicillinase produced are sufficient to account for the high degrees of resistance observed.     

青霉素酶基因异源表达及该酶分解牛奶中残留青霉素的研究

以获得大量青霉素酶并将其用于分解牛奶中残留青霉素为目的,通过PCR方法从蜡样芽孢杆菌ATCC10987基因组中获得了青霉素酶基因,将该基因克隆至表达载体pET28a( )中,并转化到E. coli BL21中;在IPTG诱导下对目的蛋白进行SDS-PAGE和酶活分析,结果显示最大酶活力可达到480.0 U/mL;利用Ni2 亲合层析柱纯化目的蛋白,纯化后的目的蛋白纯度超过90%;采用高碘酸钠氧化法制备固定化的青霉素酶,并利用该固定化酶将牛奶(含0.5 u青霉素G/mL)中的青霉素分解到浓度小于4 ppb程度.     

青霉素酶基因异源表达及该酶分解牛奶中残留青霉素的研究

以获得大量青霉素酶并将其用于分解牛奶中残留青霉素为目的, 通过PCR方法从蜡样芽孢杆菌ATCC10987基因组中获得了青霉素酶基因, 将该基因克隆至表达载体pET28a(+)中, 并转化到E. coli BL21中; 在IPTG诱导下对目的蛋白进行SDS-PAGE和酶活分析, 结果显示最大酶活力可达到480.0 U/mL; 利用Ni2+亲合层析柱纯化目的蛋白, 纯化后的目的蛋白纯度超过90%; 采用高碘酸钠氧化法制备固定化的青霉素酶, 并利用该固定化酶将牛奶(含0.5 U青霉素G/mL)中的青霉素分解到浓度小于4 ppb程度。     

Quantitative Nasal Culture: a Tool in Antibiotic Research

The use of the quantitative nasal culture was investigated as a means of evaluation of new antimicrobial drugs in man. Cyclacillin was somewhat more active in vitro than penicillin G against penicillin G-resistant organisms. Cyclacillin was highly effective in suppressing staphylococci susceptible to penicillin G in nasal carriers but did not suppress staphylococci resistant to penicillin G. Although in previous studies by others cyclacillin was effective in treating mice infected with penicillin G-resistant staphylococci, in the present studies cyclacillin was not effective in suppressing nasal penicillin G-resistant staphylococci in man at doses which markedly suppressed penicillin G-sensitive organisms.     

Cephalothin, a New Cephalosporin with a Broad Antibacterial Spectrum: I. In Vitro Studies Employing the Gradient Plate Technique

Cephalothin is 7-(thiophene-2-acetamido) cephalosporanic acid; it was prepared by N-acylation of the nucleus of cephalosporin C, 7-aminocephalosporanic acid. Cephalothin had a broad spectrum of antibiotic activity that was essentially unaffected by human serum or inoculum level, the activity of penicillinase, or pH variation of the growth medium. In vitro development of resistance by staphylococci could not be demonstrated, but the gram-negative organisms did develop a stepwise type of resistance to the antibiotic. Staphylococci made resistant in vitro to 5-methyl-3-phenyl-4-isoxazole penicillin were also resistant to cephalothin and to 6-(2,6-dimethoxybenzamido) penicillin; however, the mechanism of resistance to each antibiotic may have differed. Some complications involved in the laboratory evaluation methods currently in use in the field of antibiotics are examined.     

Trial of Phenoxymethylpenicillin,Phenethicillin, and Lincomycin in Treatment of Staphylococcal Sepsis in a Casualty Department

A comparative trial of phenoxymethylpenicillin (penicillin V), phenethicillin (Broxil), and lincomycin (Lincocin) against superficial staphylococcal infections seen in a casualty department showed no difference in the efficacy of the three agents, though half the staphylococci isolated were resistant to penicillin. Possible reasons include the fact that antibiotic treatment may not affect superficial staphylococcal infections, or that the organisms concerned may have been weak formers of penicillinase.Half the patients treated with lincomycin complained of diarrhoea and 5% of those treated with phenethicillin suffered from nausea.     

Characterization of mutations in the penicillinase operon of Staphylococcus aureus

Summary Mutant penicillinase plasmids, in which penicillinase synthesis is not inducible by penicillin or a penicillin analogue, were examined by biochemical and genetic analyses. In five of the six mutants tested, penicillinase synthesis could be induced by growth in the presence of 5-methyltryptophan. It is known that the tryptophan analogue 5-methyltryptophan is readily incorporated into protein by S. aureus and that staphylococcal penicillinase lacks tryptophan. 5-methyltryptophan seems to induce penicillinase synthesis in wild-type plasmids by becoming incorporated into the repressor and thereby inactivating the operator binding function of the penicillinase repressor. Therefore, induction of penicillinase synthesis in the mutant plasmids by 5-methyltryptophan strongly suggests that the noninducible phenotype of these five plasmids is due to a mutation that inactivates the effector binding site of the penicillinase repressor (i.e., the five mutant plasmids carry an i^s genotype for the penicillinase repressor). This conclusion was supported by heterodiploid analysis. The mutant plasmid that did not respond to 5-methyltryptophan either produces an exceedingly low basal level of penicillinase or does not produce active enzyme. This plasmid seems to carry a mutation in the penicillinase structural gene or in the promoter for the structural gene. Thus, a genetic characterization of many mutations in the penicillinase operon can be accomplished easily and rapidly by biochemical analysis.Journal Paper No. J-7994 of the Iowa Agriculture and Home Economics Experiment Station, Ames, Iowa. Project No. 2029     

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 (1 μg/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 4 μg/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.

     

Inactivation of cephalothin and cephaloridine by Staphylococcus aureus

Benner, Ernest J. (University of Washington School of Medicine, Seattle), John V. Bennett, Jean L. Brodie, and William M. M. Kirby. Inactivation of cephalothin and cephaloridine by Staphylococcus aureus. J. Bacteriol. 90:1599-1604. 1965.-Marked differences were observed in the susceptibility of penicillinase-producing staphylococci to cephalothin and cephaloridine. All of 100 strains of penicillin G-resistant Staphylococcus aureus, with the use of a large inoculum, were found to be susceptible to 2 mug/ml of cephalothin, whereas only 50% were susceptible to this concentration of cephaloridine, and 15% required 15 mug/ml or more for inhibition. In contrast, penicillin G-sensitive strains were more susceptible to cephaloridine and did not show the marked inoculum effect observed with the cephaloridine-resistant strains. These differences were due to a much greater destruction of cephaloridine than of cephalothin by staphylococcal penicillinase. Cephaloridine-resistant staphyloccoci were stronger penicillinase producers than were susceptible strains, and the resistant strains were found to inactivate cephaloridine by hydrolysis of the beta-lactam ring. In population studies, cephaloridine-resistant cells differed from methicillin-resistant cells in that they decreased in numbers as the drug concentration was increased, and the survivors in higher drug concentrations were no more resistant than was the parent strain. Treatment with acriflavine eliminated resistance of the cells to both penicillin G and cephaloridine. It was concluded that cephaloridine resistance was due to hydrolysis by penicillinase, and that this was related to the pyridine ring substitution in the cephalosporanic acid nucleus.     

Enumeration of sublethally heated staphylococci in some dried foods.

The effect of 45 substances to restore the salt tolerance of sublethally heat-injured Staphylococcus aureus was tested. Sodium pyruvate, yeast extract, L-histine, casitone (Difco), adenosine triphosphate, and acetylphosphate were effective. For enumeration a repair medium was first used, containing sodium pyruvate and penicillin in 1% skim milk. This step was followed by counting on Baird-Parker agar with penicillinase. This method was selective; fewer than 100 staphylococci/g food could be enumerated and it gave counts about 8 times higher than the method of Giolitti and Cantoni used as a five-tube most probable number technique. Heat injury sensitized S. aureus to polymyxin.     

Regulation of Staphylococcal Penicillinase Synthesis

5-Methyl tryptophan was found to be an efficient inducer of penicillinase synthesis in Staphylococcus aureus. Addition of actinomycin D or tryptophan to the culture medium shuts off the 5-methyl tryptophan-induced synthesis of penicillinase with an apparent half-life of approximately 1 to 2 min, respectively. Hence, in the induction of penicillinase synthesis, 5-methyl tryptophan seems to function as a structural analogue of penicillin rather than by becoming incorporated in proteins and thereby creating faulty penicillinase repressor or antirepressor. This conclusion is supported by similarities in the structures of the two compounds as revealed by solid atomic models. The fact that S. aureus exposed to (14)C-penicillin in the absence of protein synthesis failed to synthesize penicillinase at an increased level when cell growth was resumed strongly suggests that a protein involved in the regulation of penicillinase synthesis must be synthesized in the presence of the penicillinase inducer. In turn, this observation suggests that the penicillinase inducer promotes penicillinase synthesis by directing the penicillinase regulatory protein (i.e., the penicillinase antirepressor) to acquire a different conformation when it is synthesized in the presence of the penicillinase inducer. A working model for the regulation of penicillinase synthesis based on these and other data has been constructed and is presented.     

Penicillinase (β-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.     

The effect of membrane-bound beta-lactamase on linoleic acid sensitivity in Staphylococcus aureus

The presence of a plasmid conferring resistance to penicillin (PC plasmid, e.g. pI258blaI-) in Staphylococcus aureus NCTC 8325 increases the sensitivity of such a bacterium to the growth inhibitory effects of linoleic acid, whereas a plasmid conferring resistance to tetracycline does not affect linoleic acid sensitivity. The increased linoleic acid sensitivity of bacteria containing a PC plasmid may be related to the penicillinase protein itself since (i) strains having inducible penicillinase show increased sensitivity only after induction, (ii) strains in which penicillinase is directed from chromosomal or plasmid-borne genes show similar increased linoleic acid sensitivity and (iii) notwithstanding the above, the linoleic acid inhibitory effect is enhanced in a strain in which penicillinase activity is greatly reduced by a point mutation in the structural gene for penicillinase. The enhanced linoleic acid sensitivity seems to require the membrane-bound penicillinase since added extracellular penicillinase does not confer this sensitivity, and there appears to be a specific interaction between the membrane-bound penicillinase activity and linoleic acid.     

Sensitivity of Yersinia enterocolitica to antibiotics]

Sensitivity of 33 foreign and 10 native strains of Y. enterocolitica to tetracycline, aminoglycosides, penicillins, levomycetin and polymyxin was studied. All the strains proved to be resistant to penicillin, oxacillin and ampicillin: they produced penicillinase. The level of resistance to penicillin did not always correlate with penicillin activity. The ability of the native strains to acquire R-factor in vitro from Coli bacteria was shown.     

Effect of penicillin on the intensity of formation of penicillin-resistant staphylococcal populations in the suppurative foci of patients]

The dynamics of sensitivity to penicillin of staphylococcal populations in purulent inflammatory foci of patients treated and not treated with antibiotics was estimated according to 4 indices. No reliable differences in the dynamics of sensitivity to penicillin were found in 2 groups of the patients, when estimation was performed with respect to the frequency of the penicillin resistant or penicillin sensitive staphylococci and detection of the penicillin resistant staphylococci by direct inoculation of the focal excretion to the medium with penicillin. A reliable increase in the percentage of the penicillin resistant staphylococci in the microbial population was observed only in the patients treated with penicillin.     

青霉素酶在青霉素菌渣无害化处理中的应用

建立一种快速、有效的方法降解青霉素菌渣中青霉素残留。采用高效液相色谱（HPLC）方法检测湿菌渣,得到其平均青霉素效价残留为2179 U／g,即相对质量分数为1．3mg／g;将青霉素酶以相对于残留青霉素效价比为3：1的比例量混入菌渣中,37℃,1h后可以将残留青霉素完全降解,实现了菌渣的无害化处理,为青霉素菌渣的资源化利用奠定了基础。     

Semisynthetic Penicillin

The structure-activity in α-alkylthio-cinnamyl penicillins was studied. These penicillins were prepared by condensing 6-aminopenicillanic acid with α-alkylthio-cinnamic acids. α-Methylthxo-cinnamyl penicillin and its substituted analogues were highly inhibitory to Staphylococcus aureus 209P and some of them were also effective in vitro against benzyl-penicillin-resistant Staphylococcus. trans-α-Methylthio-2-bromo-cinnamyl penicillin, which showed a good in vitro activity, was resistant to penicillinase and was stable in acidic aqueous solution.     

Repressor and Antirepressor in the Regulation of Staphylococcal Penicillinase Synthesis

5-methyltryptophan (5MT) induces penicillinase synthesis in Staphylococcus aureus. The analog is incorporated into protein by both wild-type and tryptophan-starved cells. Since normal penicillinase repressor appears to contain tryptophan even though penicillinase itself does not, it is concluded that 5MT induces penicillinase synthesis by becoming incorporated into the penicillinase repressor and thereby inactivating the repressor. Thus biochemical data support the existence of a penicillinase repressor and indicate that penicillinase synthesis is regulated by negative control and not by positive control.-In the absence of exogenous tryptophan, staphylococcal penicillinase induction can be inhibited by 7-azatryptophan (7azaT). Because 7azaT is incorporated into protein by tryptophan-starved cells, it is concluded that 7azaT blocks penicillinase induction by inactivating a penicillinase regulatory protein into which the analog has been incorporated. Incorporation of 7azaT does not appear to inactivate the operator binding site or the effector binding site on the penicillinase repressor. Therefore, it appears that 7azaT blocks penicillinase induction by inactivating the penicillinase antirepressor, a protein required for inactivation of the penicillinase repressor and, hence, required for penicillinase induction.     

D-alanyl-D-alanine carboxypeptidase in the bacterial form and L-form of Proteus mirabilis.

Membranes of the bacterial form and the stable and unstable L-forms of Proteus mirabilis contain LD and DD-carboxypeptidase. The DD-carboxypeptidase is inhibited non-competitively by penicillin G. The enzyme of the bacterial form is highly penicillin-sensitive (Ki - 4 X 10(-9) M penicillin G). Inhibition is only partly reversible by treatment with penicillinase or by dialysis against buffer. In contrast, the DD-carboxypeptidase of the unstable L-form, grown in the presence of penicillin, is 175-fold less penicillin-sensitive (Ki = 7 X 10(7) M penicillin G). Inhibition is completely reversed by penicillinase or dialysis. After inhibition by penicillin and subsequent reactivation the penicillin sensitivity of the bacterial DD-carboxtpeptidase is similar to the sensitivity of the enzyme of the unstable L-form. The hypothesis is proposed that P. mirabilis contains two DD-carboxypeptidases of different penicillin sensitivity and with different mechanisms of penicillin binding. Peptidoglycan synthesis in the cell walls of the unstable L-form is probably carried out with the help of only one DD-carboxypeptidase, viz. the completely reactivatable enzyme with the lower penicillin sensitivity.