Bacteriophage endolysin treatment for systemic infection of Streptococcus iniae in hybrid striped bass

Streptococcus iniae, a zoonotic Gram-positive pathogen, poses a threat to finfish aquaculture, causing streptococcosis with an annual economic impact exceeding $150 million globally. As aquaculture trends shift towards recirculating systems, the potential for horizontal transmission of S. iniae among fish intensifies. Current vaccine development provides only short-term protection, driving the widespread use of antibiotics like florfenicol. However, this practice raises environmental concerns and potentially contributes to antibiotic resistance. Thus, alternative strategies are urgently needed. Endolysin therapy, derived from bacteriophages, employs hydrolytic endolysin enzymes that target bacterial peptidoglycan cell walls. This study assesses three synthetic endolysins (PlyGBS 90-1, PlyGBS 90-8, and ClyX-2) alongside the antibiotic carbenicillin in treating S. iniae-infected hybrid striped bass (HSB). Results demonstrate that ClyX-2 exhibits remarkable bacteriolytic potency, with lytic activity detected at concentrations as low as ∼15 μg/mL, approximately 8-fold more potent than the PlyGBS derivatives. In therapeutic effectiveness assessments, both carbenicillin and ClyX-2 treatments achieved significantly higher survival rates (85 % and 95 %, respectively) compared to placebo and PlyGBS-based endolysin treatments. Importantly, no statistical differences were observed between ClyX-2 and carbenicillin treatments. This highlights ClyX-2 as a promising alternative for combating S. iniae infections in aquaculture, offering potent bacteriolytic activity and high survival rates.

Cheminformatics Study on Structural and Bactericidal Activity of Latest Generation β-Lactams on Widespread Pathogens

Raman spectra of oxacillin (OXN), carbenicillin (CBC), and azlocillin (AZL) are reported for the first time together with their full assignment of the normal modes, as calculated using Density Functional Theory (DFT) methods with the B3LYP exchange-correlation functional coupled to the 6-31G(d) and 6-311+G(2d,p) basis sets. Molecular docking studies were performed on five penicillins, including OXN, CBC, and AZL. Subsequently, their chemical reactivity and correlated efficiency towards specific pathogenic strains were revealed by combining frontier molecular orbital (FMO) data with molecular electrostatic potential (MEP) surfaces. Their bactericidal activity was tested and confirmed on a couple of species, both Gram-positive and Gram-negative, by using the disk diffusion method. Additionally, a surface-enhanced Raman spectroscopy (SERS)-principal component analysis (PCA)-based resistogram of A. hydrophila is proposed as a clinically relevant insight resulting from the synergistic cheminformatics and vibrational study on CBC and AZL.

Efficient embryogenic suspension culturing and rapid transformation of a range of elite genotypes of sweet potato (Ipomoea batatas [L.] Lam.)

Efficient Agrobacterium tumefaciens-mediated transformation was developed using embryogenic suspension cell cultures of elite sweet potato (Ipomoea batatas [L.] Lam.) cultivars, including Ayamurasaki, Sushu2, Sushu9, Sushu11, Wanshu1, Xushu18 and Xushu22. Embryogenic suspension cultures were established in LCP medium using embryogenic calli induced from apical or axillary buds on an induction medium containing 2 mg l(-1) 2,4-D. Suspension cultures were co-cultivated with A. tumefaciens strain LBA4404 harboring the binary plasmid pCAMBIA1301 with the hpt gene as a selectable marker and an intron-interrupted uidA gene as a visible marker. Several key steps of the sweet potato transformation system have been investigated and optimized, including the appropriate antibiotics and their concentrations for suppressing Agrobacterium growth and the optimal doses of hygromycin for transformant selection. A total of 485 putative transgenic plant lines were produced from the transformed calli via somatic embryogenesis and germination to plants under 10 mg l(-1) hygromycin and 200 mg l(-1) cefotaxime. PCR, GUS and Southern blot analyses of the regenerated plants showed that 92.35% of them were transgenic. The number of T-DNA insertions varied from one to three in most transgenic plant lines. Plants showed 100% survival when 308 transgenics were transferred to soil in the greenhouse and then to the field. Most of them were morphologically normal, with the production of storage roots after 3 months of cultivation in the greenhouse or fields. The development of such a robust transformation method suitable to a range of sweet potato genotypes not only provides a routine tool for genetic improvement via transgenesis but also allows us to conduct a functional verification of endogenous genes in sweet potato.

Interaction studies on proteins encoded by the phthiocerol dimycocerosate locus of Mycobacterium tuberculosis

Polyketide synthases (PKSs) of Mycobacterium tuberculosis are increasingly being seen as producers of virulence factors that are important for pathogenesis by the bacterium. Thus, the phenolphthiocerol synthase PKS cluster of M. tuberculosis is responsible, in part, for the synthesis of a virulence determinant called phthiocerol dimycocerosate (PDIM). Here, we provide evidence that the PpsE protein, which is part of that cluster, interacts with the type II thioesterase TesA of M. tuberculosis. The interaction was demonstrated by employing a two-hybrid system, and confirmed using a GST (glutathione S-transferase) pull-down' assay after both proteins had been purified to homogeneity. Based on the present findings, a revised model for the processing of polyketides during the synthesis of PDIM is presented.

Tn2610, a transposon involved in the spread of the carbenicillin-hydrolyzing beta-lactamase gene

We have found a new transposon, Tn2610, on pCS200 in clinical isolates of Escherichia coli, which encodes the carbenicillin-hydrolyzing beta-lactamase gene in combination with the resistance determinants to streptomycin and sulfonamide. Tn2610 has a molecular size of 24 kilobase pairs and is flanked by long inverted repeat sequences of 3 kilobase pairs in length. Genetical and physical analyses indicate that Tn2610 is a single transposable unit encoding the multiple resistance determinants and that is different from any previously described transposon. The characteristic DNA structure observed in various complex resistance transposons involved in the transposition of the carbenicillin-hydrolyzing beta-lactamase gene is discussed.

In vitro inactivation of gentamicin, tobramycin, and netilmicin by carbenicillin, azlocillin, or mezlocillin

The in vitro inactivation of gentamicin, tobramycin, and netilmicin, when combined with carbenicillin, azlocillin, and mezlocillin, was studied. Plasma samples containing the aminoglycosides at a concentration of 5-8 micrograms/ml in combination with the penicillins in concentrations of 500, 250, and 50 micrograms/ml were incubated at room temperature and 37 degrees C for 0.3, 1, 3, 6, and 9 days. The aminoglycoside concentration was determined by radioimmunoassay or enzyme immunoassay. The extent of inactivation was dependent on penicillin concentration, contact time, and temperature. Penicillin concentrations of 500 micrograms/ml caused the greatest loss of aminoglycoside, while little loss occurred at the 50-micrograms/ml penicillin level. Carbenicillin, in concentrations of 250 and 500 micrograms/ml, inactivated all three aminoglycosides to a greater extent than either azlocillin or mezlocillin. The initial rate of decline in aminoglycoside concentration was greater at 37 degrees C than at room temperature. The new acylureidopenicillins, azlocillin and mezlocillin, inactivate the aminoglycosides studied, in a similar manner to that previously described for carbenicillin.

Primary Klebsiella identification with MacConkey-inositol-carbenicillin agar

MacConkey-inositol-carbenicillin agar has successfully been used as a primary selective medium for Klebsiella enumeration. With pure cultures, nearly 100% recovery of Klebsiella was observed by membrane filtration. With environmental samples using membrane filtration, 95% of typical pink- to red-colored colonies were verified as Klebsiella, as opposed to only 1% of yellow background colonies. Recovery of Klebsiella on MacConkey-inositol-carbenicillin agar was as good or better than on mEndo agar LES (Difco Laboratories). Recovery and percent colony confirmation with MacConkey-inositol-carbenicillin agar were greater than for other proposed Klebsiella selective media.

Stability of carbenicillin and oxacillin frozen in syringes

The stability of carbenicillin disodium and oxacillin sodium following storage in syringes for three months at -20 C was studied. Employing a spectrophotometric assay, it was found that carbenicillin (2500 mg/ml) and oxacillin (200 mg/ml) remained stable in both glass and plastic syringes for three months when frozen at -20 C. Stability was not altered by storage in either glass or plastic, nor by the size of the syringe used. Although the results were favorable, additional evidence is necessary before the practice of freezing reconstituted carbenicillin and oxacillin in syringes is advocated.

Nocardicin A, a new monocyclic beta-lactam antibiotic V. In vivo evaluation

Nocardicin A is a new monocyclic beta-lactam antibiotic which provides a potent therapeutic effect in mice experimentally infected with gram-negative bacilli. When given subcutaneously to mice, the therapeutic effect of the drug was stronger than had been anticipated from in vitro studies. Nocardicin A was more potent in therapeutic effect than carbenicillin against infections due to Pseudomonas aeruginosa, Proteus mirabilis, Pr. vulgaris, Pr. rettgeri and Pr. inconstans, and was similar in effect to carbenicillin against infections due to Escherichia coli in mice. In addition, nocardicin A proved to be active against infections due to Serratia marcescens and other organisms resistant to beta-lactam antibiotics. When nocardicin A was given subcutaneously to mice, blood and hepatic levels of the drug were higher than those of carbenicillin.

Residues in antibiotic preparations, i: scanning electron microscopic studies of surface topography

The surface characteristics of residues obtained from several commercial antibiotic products were studied using scanning electron microscopy. The photomicrographs showed the presence of particulates possessing crystalline or amorphous properties with particle sizes ranging from 1 mum to several mum. Small, well-defined, granular crystalline particulates seemed to predominate in residues of products which were processed under optimum pH conditions. Coalescing or aggregating of small crystalline particles (1-10mum) to form larger masses was interpreted as a sign of instability of the antibiotic. Most of the penicillin and semisynthetic penicillins produced residues that were characterized as amorphous, flaky, bulky and of no distinct shape. Such structures were attributed to the drying of gelatinous particulates. The possible sources and causes of the occurrence of these particulates are discussed. It appears that in many of the products the particulates are product-related rather than process-related, and subtle degradation may be involved. Advice is given to practitioners regarding the preparation, storage and administration of these products.

Antimicrobial susceptibility testing

Considerable advances have been made in antimicrobial susceptibility testing. This review emphasizes the continued efforts toward standardization of methods for dilution and diffusion testing, particularly in the area of variation in medium performance, methods for detection of ampicillin resistant Haemophilus influenzae, and attempts to develop rapid automated systems for susceptibility testing. Susceptibility testing of anaerobes continues to be controversial from the standpoint of both the selection of methods and the application of susceptibility results to the clinical situation. It is expected that these and other problems in susceptibility testing will be solved by continued application of the investigative approaches that have brought us where we are today.

Isolation of mycobacteria from clinical specimens by use of selective 7H11 medium

7H11 agar containing carbenicillin, amphotericin B, polymyxin B and trimethoprim lactate (selective 7H11 or S7H11) was used for the selective isolation of mycobacteria from clinical specimens. This medium as previously described contained 100 mug. carbenicillin per ml. It was found that reducing the concentration of carbenicillin to 50 mug. per ml. made S7H11 less inhibitory to certain strains of mycobacteria. However, some strains of M. kansaii, M. intracellulare, and M. gordonae still do not grow well on S7H11. Of 3,134 clinical specimens (mostly sputum) received, processed, and plated on 7H11 agar and the S7H11 medium, 508 positive specimens were isolated. Of these, 402 were positive on both types of media, 30 were positive on 7H11 only, 19 were positive on S7H11 only, 52 were contaminated on 7H11 but positive on S7H11, while only 5 were contaminated on S7H11 and positive on the plain medium. Thus, the total positive specimens on 7H11 was 437 and total positive specimens on the selective medium was 473. Used in conjunction with nonselective media, S7H11 agar appears to be a valuable culture medium for used in diagnostic mycobacteriology laboratories.

Derivation and properties of F-prime factors in Escherichia coli carrying nitrogen fixation genes from Klebsiella pneumoniae

A His+ Nif+ Escherichia coli K12, Hfr strain (UNF43) was constructed by an intergeneric mating between a Klebsiella pneumoniae donor strain (HF3) and a his-HFR E. coli strain (SBI824) which transfers his as an early marker. An F-prime nif plasmid, FN39, carrying genes which correspond to the E. coli chromosomal region, metG gnd his shiA, but excluding purF and aroD, was isolated from UNF43. Translocation of carbenicillin resistance genes from a P-type R-factor, R68, to FN39 increased the stability of his and nif on the derivative F-prime, FN68. Sedimentation analysis of both F-primes in sucrose gradients revealed our covalently closed circular(CCC) DNA species of molecular weights 279 +/- 9, 136 +/- 3, 90 +/- 1 and 44 +/- 1 megadaltons. It is suggested that the two smallest CCC-DNA species are component replicons of the composite F-primes of molecular weight 136 +/- 3 megadaltons, and that the molecules of 279 +/- 9 megadaltons are CCC-dimers. FN68 was transferable in intergeneric matings to Klebsiella aerogenes, K. pneumoniae and Salmonella typhimurium but not to Proteus mirabilis; only carbenicillin resistance and sex factor activity were transferred to Erwinia herbicola. nif genes on FN68 were expressed in a Nif- mutant of K. pneumoniae and also in S. typhimurium, which in conventional tests is naturally non-nitrogen-fixing; expression of the his determinant of FN68 became temperature-sensitive in S. typhimurium.

Transformation of Pseudomonas putida and Escherichia coli with plasmid-linked drug-resistance factor DNA

Conditions optimal for the transformation of Pseudomonas putida and E. coli with a drug-resistance factor (RP 1) DNA, which specifies resistance to carbenicillin, tetracycline, kanamycin, and neomycin, are described. The transformants retain all the fertility, incompatibility, and drug-resistance characteristics present in the parent. Covalently-closed circular molecules of almost identical contour lengths have been isolated from the parent and the transformants. The frequency of transformation is drastically reduced by treatment of RP 1 DNA with DNase and by denaturation or sonication. Shearing of RP 1 DNA in vitro and their subsequent introduction in P. putida cells, by transformation, produces transformants that exhibit a wide range of drug-resistant phenotypes, including those which are resistant to neomycin but sensitive to kanamycin. Isolation of such neomycin-resistant but kanamycin-sensitive transformants indicates that there might be two separate mechanisms specified by RP 1 for resistance to the two antibiotics.

Susceptibility of Anaerobic bacteria to carbenicillin, cefoxitin, and related drugs

The agar dilution technique was used for determination of the bacteriostatic activity of carbenicillin, penicillin G, cefazolin, cephaloridine, cefoxitin, and cephalothin agaomst a variety of anaerobic bacteria. Carbenicillin showed a high level of activity at a concentration of smaller than or equal to 100 mug/ml; only five of 123 strains of Bacteroides fragilis, one strain of Bifidobacterium eriksonii, and one strain of Clostridium bifermentans were resistant to a concentration of larger than or equal to 100 mug/ml. Cefoxitin, a beta-lactamase-resistant drug, was highly active against B. fragilis and most other anaerobes at a concentration of smaller than or equal to 32 mug/ml; the exceptions were one strain of Bacteroides species and 13 of 28 strains of Clostridium species. The other cephalosporins were less active against B. fragilis but exhibited good activity against most of the other strains tested. Bactericidal concentrations of cefoxitin and cephalothin were determined for 51 selected strains by the broth dilution technique, and the activities of these drugs were compared with those of two other drugs (clindamycin and metronidazole) known to be very active against anaerobes. Metronidazole wasthe most consistently bactericidal of the four drugs tested for this activity.

A spectrophotometric assay of beta-lactamase action on penicillins

A new method for measuring the enzymic hydrolysis of the beta-lactam ring in penicillins is described. The change in extinction in the u.v. region is determined. The method is sensitive (50mum-benzylpenicillin can be used) and convenient.

Microbiological sterol conversions: utilization of selected mutants

Microbiological conversion of drugs and natural products, including sterols and steroids, is an important component of the commercial preparation of these agents. We have developed methodology which allows for the production and selection of mutant organisms capable of specific desirable transformations. This methodology is based upon mutation of wild-type strains which are capable of completely degrading certain sterols and selection of the mutants blocked at the desired conversion. This procedure should be equally useful for many if not all drug classes.

Selective media in the isolation of tubercle bacilli from tissues

Direct culture on Lowenstein-Jensen slopes and on three media made selective for tubercle bacilli by the addition of four antibacterial agents was compared with guinea-pig inoculation on 490 tissue specimens. Tubercle bacilli were obtained from 15 specimens by culture and 14 by guinea-pig inoculation; only one specimen was positive by guinea-pig and not by culture. The most efficient culture medium was a selective 7H11 slope. Routine guinea-pig inoculation has been replaced by a wider range of culture procedures.

A comparison of the amounts and the antigenicity of polymeric materials formed in aqueous solution by some beta-lactam antibiotics

Concentrated aqueous solutions of some β-lactam antibiotics were stored for 14 days. Samples were then subjected to gel filtration and fractions in the high molecular weight regions of the eluate were collected and lyophilized. The yields of materials from solutions of various β-lactam antibiotics were compared and the antigenicity of the materials was assessed by their ability to react with antibodies of benzylpenicilloyl specificity raised in rabbits and tested in guinea-pigs by passive cutaneous anaphylaxis.

L-forms of Pseudomonas aeruginosa

L-forms of a strain of Pseudomonas aeruginosa were produced by serial subculture of the bacterial form on agar medium containing sucrose as an osmotic stabilizer and carbenicillin. L-forms eventually became stable, i.e., would not revert in the absence of antibiotic, and were adapted to grow well in broth with the osmotic stabilizer. Gross morphology and light microscopic colony morphology were typical of an L-form. L-form cells were approximately spherical and bounded in part by a plasma membrane; they lacked the triple-layer cell wall structure and coarse, electron-dense nucleoidal granules of the parent bacterial form. The L-form, but not the bacterial form, contained cores, organelles previously reported only in group D streptococci. Antibiotic disc-sensitivity studies showed the stable L-form to be as sensitive as, or more sensitive than, the bacterial form to most antibiotics. Exceptions were polymyxin B, colimycin sulfate, and gentamicin, which were more active against the bacterial form. The remainder of the aminoglycosides and cell wall-active antibiotics showed no inhibition of either form. The L-form was more susceptible to cidal activity of normal human serum than the parent form. The L-form exhibited fewer biochemical activities than the parent bacteria or bacterial forms derived by reversion at a time when the L-form was still unstable. L-form colonies appeared colorless, and chemical analysis demonstrated that, if the L-form produces pigment at all, which was not demonstrated, it could not have been more than 3.6% of that produced by the bacterial form.

Antibiotic resistance in Pseudomonas aeruginosa from infections of the ear, nose and throat

1,000 strains of <i>Ps</i>. <i>aeruginosa</i> isolated from disease conditions of the ear, nose and throat, were examined for sensitivity to 9 antibiotics. Only 4.5 % of them were sensitive to all 9. The low incidence of strains resistant to polymixin B, colistin and carbenicillin makes them most suitable for the treatment of infections due to this organism, though the need for parenteral administration limits their systemic use to in-patients. A high level of cross-resistance exists between polymixin B and colistin, while there are various degrees of cross-resistance between the aminoglycoside antibiotics streptomycin, framycetin and neomycin. 63.9 % of strains resistant to oxytetracycline are cross-resistant to the chemically-unrelated chloramphenicol.