Potentiation of the in vitro activity of some antimicrobial agents against selected gram-negative bacteria by EDTA-tromethamine

Lysis of cells of diverse bacteria by l,d-peptidases of Escherichia coli bacteriophages RB43, RB49 and T5

AIMS

The objective of this work was to study the antibacterial specificity and antibacterial effect of endolysins isolated from colibacteriophages RB43, RB49 and T5-as manifested on the exponential and stationary cell cultures of diverse bacteria depending on the growth stage, structure of peptidoglycan (PG) and antibiotic resistance.

METHODS AND RESULTS

Enzyme activity was assayed by the spectrophotometric method. Antimicrobial activity was estimated by the number of colony forming units (CFUs), with the results represented as logarithmic units. Morphological examination of bacterial cells was conducted using phase-contrast and scanning electron microscopy. The enzymes EndoT5, endolysin of bacteriophage T5, EndoRB43, endolysin of bacteriophage RB43 and EndoRB49, endolysin of bacteriophage RB49 turned out to be much less bacteriospecific than the corresponding Escherichia coli phages; they lysed bacteria of the genera Bacillus, Cellulomonas and Sporosarcina, whose PGs had different structures (A1γ, A4α and A4β) and chemical modifications (amidation). The specific lytic activity of phage enzymes was independent of the antibiotic resistance of bacterial cells and was higher when the cells were in the exponential, rather than stationary, growth phase. The analysis of morphological changes showed that the intermediate stage of the endolysin-induced lysis of bacterial cells was the formation of spheroplasts and protoplasts.

CONCLUSIONS

Endolysins of colibacteriophages RB49, RB43 and T5 have a wide spectrum of antibacterial action, which includes a number of diverse micro-organisms with different PG structures.

SIGNIFICANCE AND IMPACT OF THE STUDY

This is a study of the bacterial selectivity of enzymes degrading bacterial cell wall in relation to the chemical structure of PG. It is shown that endolysins of bacteriophages RB49 and RB43 efficiently lyse cell wall of Gram-positive bacteria of the genus Bacillus and Gram-negative bacteria of the genus Pseudomonas (including an antibiotic-resistant strain). The number of bacterial cells is reduced by 3-6 orders of magnitude, which indicates good prospects for using these enzymes in biotechnology.

Topical ear treatment - options, indications and limitations of current therapy

Topical otic products form an integral part of the overall management of otitis externa. With an ever increasing array of ear drops and cleaners to choose from, appropriate selection of therapy can be difficult. The investigation of all cases of otitis externa should consider primary and secondary causes and predisposing and perpetuating factors. This article considers topical therapy under these same broad headings and discusses, through literature review, the various properties of the components of the ear cleaning solutions and drops.

Advances in the diagnosis and treatment of chronic infectious and post-mating-induced endometritis in the mare

CONTENTS

Rapid physical uterine clearance is paramount for fertility. Mares that are unable to clear the by-products of insemination or foaling quickly may develop post-mating-induced or acute endometritis. If endometritis is not promptly resolved, the infection can become chronic. Endometritis can be difficult to identify because clinical signs, ultrasonographic and laboratory findings can vary between uterine pathogens. Some micro-organisms are associated with an influx of neutrophils and fluid into the uterine lumen while others are associated with only heavy debris on cytological specimens. Identifying the inciting cause may require more than swabbing the endometrium. Culturing endometrial biopsy tissue or uterine fluids are more sensitive methods for identifying Escherichia coli than culture swab while endometrial cytology identifies twice as many mares with acute inflammation than uterine culture swab. While post-mating-induced endometritis is classically treated with uterine irrigation and ecbolics and acute endometritis is treated with either systemic or intra-uterine antibiotics, these therapies are not always effective in resolving chronic uterine inflammation or infections. Mucolytics can be used to break up mucus produced by an irritated endometrium, steroids can modulate the inflammatory response associated with insemination and buffered chelating agents can remove biofilm, a protective mechanism used primarily by gram-negative organisms and yeast to evade the host immune response.

Clinical and subclinical endometritis in the mare: both threats to fertility

Endometritis, a major cause of mare infertility arising from failure to remove bacteria, spermatozoa and inflammatory exudate post-breeding, is often undiagnosed. Defects in genital anatomy, myometrial contractions, lymphatic drainage, mucociliary clearance, cervical function, plus vascular degeneration and inflamm-ageing underlie susceptibility to endometritis. Diagnosis is made through detecting uterine fluid, vaginitis, vaginal discharge, short inter-oestrous intervals, inflammatory uterine cytology and positive uterine culture. However, these signs may be absent in subclinical cases. Hypersecretion of an irritating, watery, neutrophilic exudate underlies classic, easy-to-detect streptococcal endometritis. In contrast, biofilm production, tenacious exudate and focal infection may characterize subclinical endometritis, commonly caused by Gram-negative organisms, fungi and staphylococci. Signs of subclinical endometritis include excessive oedema post-mating and a white line between endometrial folds on ultrasound. In addition, cultures of uterine biopsy tissue or of small volume uterine lavage are twice as sensitive as guarded swabs in detecting Gram-negative organisms, while uterine cytology is twice as sensitive as culture in detecting endometritis. Uterine biopsy may detect deep inflammatory and degenerative changes, such as disruption of the elastic fibres of uterine vessels (elastosis), while endoscopy reveals focal lesions invisible on ultrasound. Mares with subclinical endometritis require careful monitoring by ultrasound post-breeding. Treatments that may be added to traditional therapies, such as post-breeding uterine lavage, oxytocin and intrauterine antibiotics, include lavage 1-h before mating, carbetocin, cloprostenol, cervical dilators, systemic antibiotics, intrauterine chelators (EDTA-Tris), mucolytics (DMSO, kerosene, N-acetylcysteine), corticosteroids (prednisolone, dexamethasone) and immunomodulators (cell wall extracts of Mycobacterium phlei and Propionibacterium acnes).

In vitro activity of an ear rinse containing tromethamine, EDTA, and benzyl alcohol on bacterial pathogens from dogs with otitis

OBJECTIVE

To evaluate the in vitro activity of an ear rinse (ER) containing tromethamine, EDTA, and benzyl alcohol on bacterial pathogens from dogs with otitis.

SAMPLE POPULATION

Organisms were collected from ear swab specimens from the external and middle ear and included Staphylococcus spp (n = 11; Staphylococcus intermedius [7] and Staphylococcus spp [4]), Pseudomonas aeruginosa (5), Proteus spp (5), beta-hemolytic streptococcus (11), and 1 control strain of each organism.

PROCEDURES

3 test solutions were evaluated including EDTA, tromethamine, and benzyl alcohol (ER); EDTA and tromethamine (ER without benzyl alcohol [ER - BA]); and purified water. Ten-milliliter aliquots of each test solution were transferred into 36 tubes and inoculated with one of the organisms. Samples were retrieved from each tube at 0, 15, 30, 45, and 60 minutes, transferred to Petri dishes, mixed with soybean-casein digest agar, and incubated. After incubation, plates were examined for growth, and the number of colonies was expressed as CFU per milliliter.

RESULTS

ER significantly decreased bacterial growth in vitro of P aeruginosa and beta-hemolytic streptococcal organisms within 15 minutes, Proteus spp within 30 minutes, and Staphylococcus spp within 60 minutes. Comparatively, the presence of benzyl alcohol in ER significantly decreased bacterial growth of beta-hemolytic streptococcus and Proteus spp.

CONCLUSIONS AND CLINICAL RELEVANCE

On the basis of results of this study, future studies should be performed to evaluate the in vivo efficacy of ER alone as a treatment for otic infections caused by beta-hemolytic streptococcus, P aeruginosa, and Proteus spp and of ER combined with an antimicrobial agent for otic infections caused by Staphylococcus spp.

Use of potentiated antibiotics in wound management

Prevention or resolution of microbial colonization of wounds is critical to rapid and uneventful healing. The use and misuse of antimicrobial agents continues to support the evolution of multidrug resistant organisms that can cause severe or life-threatening infections. Chelating agents have been shown to potentiate the effects of antimicrobial compounds. The third generation chelating agent. Tricide has been shown to be effective against many multidrug resistant pathogens, prevents pathogens from development resistance to the antimicrobials with which it is mixed and substantially reduces the amount of antimicrobials needed to kill bacteria and fungi.

Potentiating effect of EDTA-Tris on the activity of antibiotics against resistant bacteria associated with otitis, dermatitis and cystitis

Possible synergistic effects of the combination of EDTA-tromethamine (EDTA-Tris) and three antimicrobial agents (cephaloridine, kanendomycin and enrofloxacin) against resistant Gram-positive and Gram-negative bacteria are reported. Bacteria were isolated from eight cases of chronic otitis externa, five cases of chronic dermatitis and four cases of recurrent cystitis in dogs which had previously been treated with one of the three antibiotics without success. Animals exposed to EDTA-tromethamine plus the antibiotic recovered completely within 10 days, and were controlled clinically and bacteriologically for 180 days. Local irrigation with EDTA-tromethamine solution was well tolerated and no side effects were recorded.

Antimicrobial effect of combinations of EDTA-Tris and amikacin or neomycin on the microorganisms associated with otitis externa in dogs

Combinations of EDTA-Tris and two aminoglycoside antibiotics (amikacin and neomycin) were tested for synergistic activities against the microorganisms associated with otitis externa in dogs and for the solutions' stability over time. Synergistic activity was observed when EDTA-Tris plus amikacin and EDTA-Tris plus neomycin were tested against Staphylococcus intermedius, Proteus mirabilis, Pseudomonas aeruginosa, and Escherichia coli, but not against Candida albicans. Stability studies over a 3-month period indicated that the test solutions were stable at room temperature and that their antimicrobial activity was maintained.

Potentiation of antibiotic activity by EDTA-tromethamine against three clinically isolated gram-positive resistant bacteria. An in vitro investigation

The in vitro synergistic effects of combinations of EDTA-tromethamine and five antimicrobial agents (ampicillin, cephalexin, oxytetracycline, streptomycin and sulphadimethoxine) on three clinically isolated Gram-positive bacteria (Staphylococcus aureus, Staphylococcus hominis and Streptococcus faecium) were investigated. The bacteria had been isolated from three cases of canine otitis resistant to beta-lactam antibiotic therapy. The antimicrobial activity was evaluated by measuring the minimal inhibitory concentration for the antibiotics alone or in combination with EDTA-tromethamine. EDTA-tromethamine potentiated the activity of cefalexin against S. aureus and S. hominis, of oxytetracycline against S. aureus and S. faecium and of streptomycin against S. faecium. No significant effects were noted on the activity of oxytetracycline against S. hominis. The remaining combinations gave a slight synergistic effect. As previously shown for Gram-negative resistant bacteria, these data suggest that the association of EDTA-tromethamine and appropriate antibiotic therapy may be useful to overcome persistent infections of soft tissues in domestic animals.