Therapeutic Activity of Lysostaphin in Experimental Staphylococcal Infections

Lysostaphin is an endopeptidase that cleaves the pentaglycine cross-bridges of the staphylococcal cell wall rapidly lysing the bacteria. Recently, lysostaphin has been examined for its potential to treat infections and to clear Staphylococcus aureus nasal colonization, requiring a reliable method for determining the lysostaphin susceptibility of strains of S. aureus. We compared four methods for determining the lysostaphin susceptibility of 57 strains of methicillin-sensitive S. aureus, methicillin-resistant S. aureus, vancomycin intermediately susceptible S. aureus (VISA), mupirocin-resistant S. aureus, and various defined genetic mutants of S. aureus. Three reference lysostaphin-resistant S. aureus variants were also included in the assays as negative controls. The assays examined included turbidity, MIC, minimum bactericidal concentration (MBC), and disk diffusion assays. All of the strains of S. aureus tested, including a VISA strain which had previously been reported to be lysostaphin resistant, were susceptible to lysostaphin by all four methods. The three reference lysostaphinresistant variants were resistant by all four methods. The disk diffusion assay was the simplest method to differentiate lysostaphin-susceptible S. aureus strains from lysostaphin-resistant variants, while the MBC assay could be used as a follow-up assay if required. In the disk diffusion assay, all strains of S. aureus tested revealed zones of inhibition of >11 mm using a 50-g lysostaphin disk, while the three reference lysostaphin-resistant S. aureus variants had no zones of inhibition. In MBC assays, concentrations of lysostaphin ranging from 0.16 g/ml to 2.5 g/ml were found to cause a 3 log or greater drop from the initial CFU of S. aureus within 30 min for all strains tested.

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confidence: 99%

Comparison of Four Methods for Determining Lysostaphin Susceptibility of Various Strains of Staphylococcus aureus

Kusuma¹,

Kokai‐Kun²

2005

“…The beneficial effect of lysostaphin has been demonstrated in numerous studies (13,16,17,31,38). Recently, it was shown to effectively eradicate oxacillin-resistant and vancomycin-intermediate-susceptible S. aureus strains in a rabbit model of endocarditis (8,28), and its ability to kill methicillin-resistant S. aureus (MRSA) has been demonstrated in rabbit models of both keratitis (9,11) and endophthalmitis (10,11).…”

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confidence: 99%

Pseudomonas aeruginosa LasA Protease in Treatment of Experimental Staphylococcal Keratitis

Barequet

Simon

Safrin

et al. 2004

LasA protease is a staphylolytic endopeptidase secreted by Pseudomonas aeruginosa. We have examined the effectiveness of LasA protease in the treatment of staphylococcal keratitis caused by methicillin-sensitive Staphylococcus aureus (MSSA) and methicillin-resistant S. aureus (MRSA) isolates in a rabbit model. Keratitis was induced by intrastromal injection of the bacteria. The eyes were treated topically, and the efficacy of LasA protease was compared to those of lysostaphin (a staphylolytic protease secreted by Staphylococcus simulans) and vancomycin. When treatment was initiated early (4 h) after infection, practically all of the MSSA-and MRSA-infected corneas were sterilized by LasA protease, and its efficacy in eradicating the bacteria was comparable to those of lysostaphin and vancomycin. By contrast, most of the control corneas were heavily infected, with median values of 4.5 ؋ 10 6 (MSSA) and 5 ؋ 10 5 (MRSA) CFU/cornea (P < 0.001). When treatment was initiated late (10 h) after infection, LasA protease reduced the numbers of CFU in both MSSAand MRSA-infected corneas by 3 to 4 orders of magnitude compared to the numbers of CFU for the controls (median values, 1,380 and 30 CFU/cornea, respectively, for the treated animals compared to 1.2 ؋ 10 6 and 5 ؋ 10 5 CFU/cornea for the respective controls [P ‫؍‬ 0.001]), and it was more effective than vancomycin in eradicating MRSA cells (P ‫؍‬ 0.02). In both the early-and the late-treatment protocols, the clinical scores for eyes treated with LasA protease were significantly lower than those for the eyes of the corresponding controls and comparable to those for the lysostaphin-and vancomycin-treated eyes. We conclude that LasA protease is effective in the treatment of experimental S. aureus keratitis in rabbits and may have potential for the treatment of disease in humans.Staphylococcus aureus is among the most frequent causes of bacterial keratitis (1, 3). S. aureus keratitis is potentially a sight-threatening ocular infection (24, 27); therefore, it requires intensive antibacterial therapy to eliminate rapidly the infecting organism, reduce the inflammatory response, and prevent structural damage to the cornea. Despite the availability of numerous efficient antibiotic agents, management of S. aureus infections remains a challenge due to the constantly increasing incidence of clinical isolates resistant to antibiotics (1,14,25,32). Moreover, the recent emergence of S. aureus strains resistant to vancomycin (34, 36), the drug of choice for the treatment of infections caused by antibiotic-resistant grampositive organisms, emphasizes the need for new broad-range and efficient antibacterial agents.An alternative approach to antibiotic treatment of S. aureus infections involves the use of lysostaphin, a 27-kDa staphylolytic endopeptidase that degrades the pentaglycine bridges of the peptidoglycan of S. aureus cells (33), as a therapeutic agent. The beneficial effect of lysostaphin has been demonstrated in numerous studies (13,16,17,31,38). Recently, it was shown to eff...

“…Earlier studies in animal models of oxacillin-susceptible S. aureus-induced infection indicated that lysostaphin was an effective treatment agent against intraperitoneal infection and renal abscess models in mice and against experimental aortic valve endocarditis in dogs caused by a penicillinase-producing S. aureus strain (3,10,14,15,16,19,(24)(25)(26)(27)32). Though there was evidence of efficacy, the impurity of lysostaphin preparations and wide availability of alternative antistaphylococcal antibiotics halted further development of lysostaphin as a therapeutic agent.…”

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confidence: 99%

Combinations of Lysostaphin with β-Lactams Are Synergistic against Oxacillin-Resistant Staphylococcus epidermidis

Kiri¹,

Archer

Climo

2002

Oxacillin-resistant Staphylococcus aureus is rapidly killed by the endopeptidase lysostaphin, and the addition of ␤-lactam antibiotics provides synergistic killing. We investigated the possibility that ␤-lactams given in combination with lysostaphin would improve the activity of lysostaphin against oxacillin-resistant Staphylococcus epidermidis (ORSE), which is normally less susceptible to lysostaphin. Checkerboard synergy testing was performed for lysostaphin given in combination with oxacillin against 10 ORSE isolates for which the lysostaphin MICs were > 8 g/ml. The fractional inhibitory concentration index ranged from 0.0234 to 0.2656, indicating synergy, which was confirmed in growth curve experiments. In the rabbit model of experimental aortic valve endocarditis using an ORSE strain, the combination of lysostaphin and nafcillin was as effective as vancomycin alone and significantly better than lysostaphin or nafcillin alone. We conclude that ␤-lactam antibiotics given in combination with lysostaphin are synergistic against many strains of ORSE.