Emergence of Optochin Resistance among Streptococcus pneumoniae in Japan

Masaki Nagata, Osamu Ueda, Takeo Shobuike, Tetsuro Muratani, Yosuke Aoki, Hiroshi Miyamoto

Department of Clinical Laboratory, Kyurin Medical Laboratory, Fukuoka, Japan.
Division of Infection Control and Prevention, Saga University Hospital, Saga, Japan.
Division of Microbiology, Department of Pathology and Microbiology, Faculty of Medicine, Saga University, Saga, Japan.

DOI: 10.4236/ojmm.2012.21002                

Abstract

The optochin susceptibility test is a key method for differentiating Streptococcus pneumoniae from other α-hemolytic streptococci; however, optochin-resistant (Opt^r) S. pneumoniae have been reported in the last two decades. In this study, we investigated the isolation frequency of Opt^r S. pneumoniae in the North Kyushu area of Japan, and biochemically and genetically characterized Opt^r S. pneumoniae clinical isolates. Seven (0.68%) out of 1032 S. pneumoniae isolates collected by the North Fukuoka Infectious Diseases Working Group were found to be Opt^r S. pneumoniae. Resistant strains had MICs of optochin 2- to 64- fold higher than susceptible strains, possessed different antimicrobial resistance profiles, and belonged to different serotypes. All the seven Opt^r isolates had mutations in the nucleotide sequence code for subunit c of F₀F₁ ATPase. Three isolates had mutations in codon 48 (deduced amino acid substitution of valine with phenylalanine) and two isolates had mutations in codon 49 (substitution of alanine with threonine or serine). Of the remaining two isolates, one had mutation in codon 50 (substitution of phenylalanine with leucine) and the other had mutation in codon 44 (substitution of methionine with isoleucine, which was a novel mutation in this position). From these results, we identified the mutation in the H⁺-ATPase subunit c gene (atpC) of S. pneumoniae, which was not recognized earlier, and determined that Opt resistance among Japanese pneumococcal isolates is not related to a specific pneumococcal serotype or antimicrobial resistance profile. Furthermore, the results indicate that when α-hemolytic streptococci resistant to optochin are isolated from patients with invasive infectious diseases, such as meningitis and pneumonia, we should perform additional examinations such as bile solubility tests or PCR assays before confirming isolates as viridans streptococci. This is the first report of the characterization of Opt^r S. pneumoniae in Japan.

Keywords

Optochin; Streptococcus pneumoniae; H⁺-ATPase; MALDI-TOF MS; 16S rRNA

Conflicts of Interest

The authors declare no conflicts of interest.

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