PVL expression correlates with decreased virulence in murine pneumonia. Weight loss data for BALB/cJ (A) and BALB/cAnNHsd (B) mice infected with either the LAC or LACΔpvl strains (4–6 × 10⁷ CFU per animal). Weights were recorded at the time of infection (day 0) and 2 days post-inoculation. C, Right lung colony forming unit recovery two days post-infection in BALB/cJ mice and (D) BALB/cAnNHsd mice inoculated with 4–6 × 10⁷ CFU S. aureus LAC or LACΔpvl. Statistical assessments were made for animal weights and CFU recovery data using the two-tailed Student’s t-test. E, Histopathologic appearance of representative thin lung sections from BALB/cJ mice infected with either LAC (upper panel) or LACΔpvl (lower panel). Tissue samples were derived from the left lungs of the animals described in B and C, and stained with hematoxylin and eosin prior to light microscopic evaluation. F, Acute lethal disease caused by the LAC and LACΔpvl strains when BALB/cJ mice were infected via intranasal route with 3–4 × 10⁸ S. aureus. Mortality was recorded daily for 3 days. Statistical significance was calculated using the Fisher’s exact test.

Virulence of LAC and LACΔpvl is comparable in BALB/cJ and BALB/cAnNHsd skin infection models. A, Weight loss and (B) abscess area for BALB/cJ mice infected with LAC and LACΔpvl. C, Weight loss and (D) abscess area for BALB/cAnNHsd mice infected with LAC and LACΔpvl. Results are the mean ± SE of 20 BALB/cJ or BALB/cAnNHsd mice infected with each S. aureus strain. *P < .05 versus LAC wild-type, unpaired t-test. E, Average skin abscess area per day. Each day is shown as a symbol and mice were monitored for 14 days (each symbol represents the average abscess size of 20 mice). F, Representative abscesses in BALB/cAnNHsd mice 4 days (day of largest abscess size) after infection with LAC (left panel) or LACΔpvl (right panel). G, Bacteria recovered from abscesses. Left panel, CFUs recovered from abscesses of 15 BALB/cJ or 14–15 BALB/cAnNHsd 4 days after infection with LAC or LACΔpvl as indicated. No bacteria were cultured from mice injected with DPBS (2 mice each of BALB/cJ and BALB/cAnNHsd, data not shown). Right panel, results are the abscess areas of the mice from which CFUs were recovered (see left panel). Statistics were performed using an unpaired t-test to compare wild-type LAC and LACΔpvl on identical days.