Wide host range and strong lytic activity of Staphylococcus aureus lytic phage Stau2

Abstract

In searching for an alternative antibacterial agent against multidrug-resistant Staphylococcus aureus, we have isolated and characterized a lytic staphylophage, Stau2. It possesses a double-stranded DNA genome estimated to be about 134.5 kb and a morphology resembling that of members of the family Myoviridae. With an estimated latency period of 25 min and a burst size of 100 PFU/infected cell, propagation of Stau2 in liquid culture gave a lysate of ca. 6 × 10(10) PFU/ml. It was stable at pH 5 to 13 in normal saline at room temperature for at least 4 weeks and at -85°C for more than 2 years, while 1 × 10(9) out of 2 × 10(12) PFU/ml retained infectivity after 36 months at 4°C. Stau2 could lyse 80% of the S. aureus isolates (164/205) obtained from hospitals in Taiwan, with complete lysis of most of the isolates tested within 3 h; however, it was an S. aureus-specific phage because no lytic infection could be found in the coagulase-negative staphylococci tested. Its host range among S. aureus isolates was wider than that of polyvalent phage K (47%), which can also lyse many other staphylococcal species. Experiments with mice demonstrated that Stau2 could provide 100% protection from lethal infection when a multiplicity of infection of 10 was administered immediately after a challenge with S. aureus S23. Considering these results, Stau2 could be considered at least as a candidate for topical phage therapy or an additive in the food industry.

FIG. 1.

Electron microscopy of Stau2. Arrows A and B indicate the knob-like appendage and the contracted tail sheath, respectively.

FIG. 2.

PFGE patterns of Stau2 genome. The phage genome was digested with ClaI (lane 1) and PstI (lane 2). Lane M contained the low-range PFGE marker. The values to the left and right are molecular sizes in kilodaltons.

FIG. 3.

Stau2 growth curve. (A) Time course of Stau2 adsorption to staphylococci. Experiments were performed using two Stau2-susceptible strains (S. aureus S23 and KS7) and three Stau2-resistant strains (S. aureus KS26 and W31 and S. epidermidis CoNS-1). (B) One-step growth of Stau2 on S. aureus S23. The symbols □ and ▪ represent numbers of PFU per infected cell in chloroform-treated and untreated cultures, respectively. Results are the means ± standard deviations from three independent experiments.

FIG. 4.

Time course of host cell lysis by Stau2. Cultures of S. aureus strains were infected with Stau2 at an MOI of 10, and OD₆₀₀s were measured following bacterial challenges. The results shown are means ± standard deviations from three independent experiments.