Tohoku J. Exp. Med., 2009, 219(2)

Bactericidal Activity in Filtrated Supernatant of Streptococcus Sanguinis against Multidrug-Resistant Pseudomonas Aeruginosa

KIWAO WATANABE,¹ MASACHIKA SENBA,² AKITOYO ICHINOSE,³ TAKESHI YAMAMOTO,⁴ KOYA ARIYOSHI¹ and KEIZO MATSUMOTO⁵

¹Department of Clinical Medicine, Institute of Tropical Medicine, Nagasaki University, Nagasaki, Japan
²Department of Pathology, Institute of Tropical Medicine, Nagasaki University, Nagasaki, Japan
³Central Laboratory, Institute of Tropical Medicine, Nagasaki University, Nagasaki, Japan
⁴Department of Microbiology, Kyoto University Graduate of Medicine, Kyoto, Japan
⁵Professor emeritus, Nagasaki University, Nagasaki, Japan

In the past decade, multidrug-resistant Pseudomonas aeruginosa (MDRP) infection has become a serious clinical problem, due to the limitation of drug choices to fight against the bacteria. Here we explored the bactericidal activity in the filtrated supernatant of Streptococcus (S.) sanguinis against Pseudomonas (P.) aeruginosa. S. sanguinis is one of the α-hemolytic streptococci that commonly reside in the human oral cavity. A strain of S. sanguinis, isolated from the sputum of a pulmonary-disease patient, was cultured for overnight. The filtered supernatant was tested for bactericidal effect using the minimum bactericidal concentration method on 20 strains of P. aeruginosa, including two MDRP and five mucoid-type strains. The viable number of P. aeruginosa was decreased with time after exposing to the filtrated supernatant of S. sanguinis, and collapsed bacteria were detected with electron microscopy. Of the 20 strains, 19 (95%) strains of P. aeruginosa were affected by bactericidal effect. Among other species of bacteria examined, the filtrated supernatant of S. sanguinis showed remarkable bactericidal effect on 49% of indole-positive Proteus species (4/9 strains) and 60% of Acinetobacter (A.) baumannii (6/10 strains). We next investigated the property of bactericidal activity in filtrated supernatant by treating with proteinase K or autoclave. There was no change in the bactericidal activity of the filtrated supernatant after each treatment, excluding the involvement of protein and plasmid. Here, we identify the bactericidal activity in the filtrated supernatant of S. sanguinis against MDRP. This unexpected observation may contribute to the development of a novel therapeutic drug against P. aeruginosa.

keywords —— Bactericidal effect; Streptococcus sanguinis; Pseudomonas aeruginosa; Acinetobacter baumannii; multidrug-resistant Pseudomonas aeruginosa.

© 2009 Tohoku University Medical Press

===============================

Tohoku J. Exp. Med., 2009, 219, 79-84

Correspondence: Masachika Senba, Department of Pathology, Institute of Tropical Medicine, Nagasaki University, 1-12-4 Sakamoto, 852-8523 Nagasaki, Japan.

e-mail: mikiyo@net.nagasaki-u.ac.jp