Comparison of the Virulence of Methicillin-Resistant and Methicillin-Sensitive Staphylococcus aureus

• Published in: MICROBIOLOGY and IMMUNOLOGY Vol. 38; no. 8; pp. 599 - 605
• Main Authors: Mizobuchi, Sadao, Minami, Junzaburo, Jin, Fu, Matsushita, Osamu, Okabe, Akinobu
• Format: Journal Article
• Language: English
• Published: Tokyo Blackwell Publishing Ltd 01.01.1994; Center For Academic Publications Japan; Center for Academic Publications Japan
• Subjects: Animals; Bacterial Toxins - analysis; Bacteriology; Biological and medical sciences; Colony Count, Microbial; Cyclophosphamide - pharmacology; Enterotoxins - analysis; Female; Fundamental and applied biological sciences. Psychology; Guinea Pigs; Hemolysin Proteins - analysis; Immunocompromised Host - drug effects; Lethal dose; Lethal Dose 50; Male; Methicillin - pharmacology; Methicillin Resistance; methicillin-resistant S. aureus (MRSA); Mice; Mice, Mutant Strains; Microbial Sensitivity Tests; Microbiology; Pathogenicity, virulence, toxins, bacteriocins, pyrogens, host-bacteria relations, miscellaneous strains; Staphylococcal Infections - microbiology; Staphylococcal Infections - mortality; Staphylococcus aureus; Staphylococcus aureus - drug effects; Staphylococcus aureus - pathogenicity; Staphylococcus aureus - physiology; Superantigens; Virulence; Staphylococcus aureus; Animal model; Virulence; Rodentia; Strain; Penicillin derivatives; Vertebrata; Antibiotic; Experimental disease; Mammalia; Guinea pig; Lethal dose 50; Sensitivity resistance; Mouse; Infectivity; Bacteria; Micrococcales; Micrococcaceae; Clinical isolate; Comparative study; Staphylococcus aureus
• ISSN: 0385-5600; 1348-0421
• DOI: 10.1111/j.1348-0421.1994.tb01829.x

The virulence of methicillin-resistant Staphylococcus aureus (MRSA) was compared with that of methicillin-sensitive S. aureus (MSSA), using 13 MRSA and 7 MSSA strains isolated from clinical specimens. The infectivity and lethality of the two groups were examined as to the inoculum required to infect 50% of guinea pigs (ID50) and to kill 50% of mice (LD50), respectively. The mean ID50 [log10 colony forming units (CFU)] for MRSA strains was 7.1±0.60 standard deviation, which was 1.5 higher than that for MSSA strains (P<0.001). The mean LD50 (log10 CFU) for MRSA strains was 9.0±0.42, being 1.1 higher than that for MSSA strains (P=0.001). Pretreatment of mice with cyclophosphamide decreased the mean LD50 for MRSA strains more than that for MSSA strains, resulting in the difference in the mean LD50 being insignificant (P=0.502). These results indicate that MRSA is less virulent than MSSA in normal hosts, but that they are equally virulent in immunocompromised hosts. The growth of MRSA strains was much slower than that of MSSA strains in the lag phase, although their growth rates were almost the same in the exponential growth phase, suggesting that the difference in virulence between them may be at least partly due to such a difference in growth.