THE IN VITRO EFFECT OF LYSOSTAPHIN ON CLINICAL ISOLATES OF STAPHYLOCOCCUS AUREUS

Lysostaphin: Engineering and Potentiation toward Better Applications

Lysostaphin is a potent bacteriolytic enzyme with endopeptidase activity against the common pathogen Staphylococcus aureus. By digesting the pentaglycine crossbridge in the cell wall peptidoglycan of S. aureus including the methicillin-resistant strains, lysostaphin initiates rapid lysis of planktonic and sessile cells (biofilms) and has great potential for use in agriculture, food industries, and pharmaceutical industries. In the past few decades, there have been tremendous efforts in potentiating lysostaphin for better applications in these fields, including engineering of the enzyme for higher potency and lower immunogenicity with longer-lasting effects, formulation and immobilization of the enzyme for higher stability and better durability, and recombinant expression for low-cost industrial production and in situ biocontrol. These achievements are extensively reviewed in this article focusing on applications in disease control, food preservation, surface decontamination, and pathogen detection. In addition, some basic properties of lysostaphin that have been controversial and only elucidated recently are summarized, including the substrate-binding properties, the number of zinc-binding sites, the substrate range, and the cleavage site in the pentaglycine crossbridge. Resistance to lysostaphin is also highlighted with a focus on various mechanisms. This article is concluded with a discussion on the limitations and future perspectives for the actual applications of lysostaphin.

MICROBIOLOGICAL ACTIVITIES OF LYSOSTAPHIN AND PENICILLINS AGAINST BACTERIOPHAGE 80/81 STRAINS OF STAPHYLOCOCCUS AUREUS

Using 20 clinical isolates of S. aureus (all bacteriophage 80/81 type), we found that lysostaphin inhibits the growth of all cultures at concentrations significantly lower than those observed with any of eight penicillins, a penicillin-like compound (cephalothin), or fusidic acid (a steroid antibiotic). All test cultures were shown to be resistant to penicillin G, ampicillin, and propicillin. Of the remaining penicillins (all penicillinase-insensitive), oxacillin, nafcillin, cloxacillin, and cephalothin were approximately equal in antimicrobial activity. Ancillin was slightly less active, and methicillin was even lower in potency. Cultures varied more widely in susceptibility to fusidic acid. None of the clinical isolates tested was found to be resistant to lysostaphin.

Relationship between lysostaphin endopeptidase production and cell wall composition in Staphylococcus staphylolyticus

Mutants of Staphylococcus staphylolyticus incapable of producing an extracellular staphylolytic glycylglycine endopeptidase were isolated and found to have cells in the population susceptible to lysis by this enzyme, as did the wild-type organism under conditions in which the endopeptidase was not produced. These results suggest that cultures of this organism normally contain a heterogeneous population of cells with regard to cell wall composition and susceptibility to the enzyme. Production of the endopeptidase appears to act as a selective pressure which removes the susceptible cells in the population as the enzyme appears in the medium. A comparison of the peptidoglycan of the wild-type organism grown under conditions in which the endopeptidase was produced with that of this organism grown under nonproducing conditions and with those of endopeptidase-less mutants showed that in the presence of the endopeptidase the cell population had peptidoglycan with shorter peptide cross bridges and a greater percentage of serine in these cross bridges than was found in cells grown in the absence of the enzyme. The inability of the endopeptidase to hydrolyze glycylserine and serylglycine peptide bonds suggests that at least part of the resistance this organism has to the endopeptidase is due to relative amounts of serine found in the peptide cross bridges of some cells in the population.

Lysostaphin endopeptidase-catalysed transpeptidation reactions of the imino-transfer type

The glycylglycine endopeptidase in lysostaphin has been found capable of catalysing both hydrolysis and transpeptidation reactions when acting on glycyl peptides. The ability of the enzyme to utilize dansyldiglycine (5-dimethylaminoaphthalene-1-sulphonylglycylglycine) as an acceptor molecule in transpeptidation reactions, although it is incapable of hydrolysing the peptide bond in this compound, indicates the enzyme must be capable of forming the equivalent of an imino-enzyme intermediate during the catalytic process.

The identification of staphylococci in clinical and food microbiology laboratories

A comprehensive review of the methods which have been utilized for the identification of staphylococci is presented. Biochemical characteristics which have assisted in the primary isolation of staphylococci, such as pigmentation, hemolytic activity, the egg yolk phenomenon, and deoxyribonuclease and coagulase production, are also analyzed. The potential applicability of advanced techniques to identify staphylococci, such as the detection of enterotoxin production, base ratio analysis, cell wall analysis, phage typing, and serology, is discussed. The following procedures are recommended for routine use: Idnetification of Staphylococcus sp. (clinical laboratories): microscopic observation, catalase activity, coagulase production, lysostaphin sensitivity, and (optional) facultative growth in thioglycolate medium. Identification of Staphylococcus aureus (food laboratories): microscopic observation, catalase activity, coagulase production, thermonuclease production, and (optional) lysostaphin sensitivity.

Efficacy and safety of topical lysostaphin treatment of persistent nasal carriage of Staphylococcus aureus

The efficacy of lysostaphin nasal spray and Neosporin ointment (Burroughs Wellcome & Co.) in altering nasal carriage of Staphylococcus aureus was studied with persistent carriers in an institution for mentally retarded children and adults. Treatment for 5 days with either agent significantly reduced carriage rates. This effect persisted through the 5th day after therapy with lysostaphin but not with Neosporin. By the 11th day after therapy, carriage rates in the treatment and control groups were not significantly different. Except for a single immediate wheal and flair skin test reaction, no other evidence of adverse reactions to topical lysostaphin was detected. No consistent changes in hemagglutination-inhibition titers to lysostaphin were observed after therapy. Lysostaphin appears to be slightly more effective than conventional topical antimicrobial therapy in reducing nasal carriage of staphylococci in this rigorously defined population of persistent carriers.

Lysostaphin in experimental renal infections

By use of a renal staphylococcal infection model in mice, single intravenous doses of lysostaphin ranging from 1.56 to 50 mg/kg were effective in: (i) controlling the staphylococcal population of kidneys, (ii) reducing the mortality rate, and (iii) clearing high numbers of kidneys of infection. Semisynthetic penicillins and other antistaphylococcal antibiotics given in the same manner did not have significant activity. Only by the administration of a long-acting, depot form of penicillin (Bicillin) could results comparable to those seen with lysostaphin be obtained. The results of this study suggest that lysostaphin may be useful in staphylococcal septicemias in preventing the establishment of new foci of infection.

THERAPEUTIC ACTIVITY OF LYSOSTAPHIN IN EXPERIMENTAL STAPHYLOCOCCAL INFECTIONS

When tested in three experimental staphylococcal infections—acute peritonitis in mice, mouse leg edema produced by a localized infection, and dermal rabbit ear infections—lysostaphin demonstrated in vivo chemotherapeutic activity. Doses of less than 0.007 mg/kg (intraperitoneally) and 0.5 mg/kg (subcutaneously) of lysostaphin prevented death in 50% of the mice with acute staphylococcal peritonitis. A single intramuscular dose (0.15 mg/mouse) of lysostaphin suppressed the swelling produced by the injection of staphylococci into mouse legs to 50% of that produced in untreated animals. Lysostaphin (0.05% by weight) incorporated into gels and applied topically eradicated staphylococci from experimental skin lesions on the ears of rabbits. Lysostaphin was absorbed and transported by the body fluids from the point of injection to the site of the infection producing a desirable antistaphylococcal effect.

Comparative In Vitro Activities of Lysostaphin and Other Antistaphylococcal Antibiotics on Clinical Isolates of Staphylococcus aureus

The in vitro activity of lysostaphin against clinical isolates of Staphylococcus aureus was determined by conventional tube-dilution methods. For comparison, minimal inhibitory concentration (MIC) values were also determined for penicillin G, ampicillin, methicillin, ristocetin, vancomycin, and erythromycin. Phage type and penicillinase and coagulase production were determined for each isolate. The MIC values for lysostaphin ranged from <0.047 to 12.5 μg/ml; 96% of the penicillinase-positive strains were inhibited by 1.56 μg/ml of lysostaphin, whereas 3.12 μg/ml of vancomycin and methicillin were required to attain the same degree of inhibition.