Analysis of biofilm and bacterial communities in the towel environment with daily use.

Towels differ remarkably from other textile products in their fibre structure and usage, and microbial behaviours on towels remain underexplored. Thus, we evaluated biofilm formation on towels during use for 6 months in daily life and analysed its relationship with odour, dullness, and laundry habits. The towels exhibited odour and dullness after 2 months of use and biofilm structures were observed over the 6 months, especially in the ground warp part. Polysaccharides, proteins, nucleic acids, and viable counts on the towels increased over time. The microbiota was significantly different from that on human skin and clothing. Several species of Alphaproteobacteria were correlated with dullness intensity and the quantity of biofilm components. Therefore, bacterial species that specifically adapt to the towel fibre environment could form biofilms. Our results demonstrate bacterial diversity in textile products and suggest careful consideration of the textile fibre material, structure, and usage pattern to control bacterial communities.

Vancomycin loading dose is associated with increased early clinical response without attainment of initial target trough concentration at a steady state in patients with methicillin-resistant Staphylococcus aureus infections.

WHAT IS KNOWN AND OBJECTIVE: Vancomycin therapeutic guidelines suggest a loading dose of 25-30 mg/kg for seriously ill patients. However, high-quality data to guide the use of loading doses are lacking. We aimed to evaluate whether a loading dose (a) achieved a target trough concentration at steady state and (b) improved early clinical response. METHODS: Patients with an estimated glomerular filtration rate ≥ 90 mL/min/1.73 m2 were included. A loading dose of 25 mg/kg vancomycin followed by 15 mg/kg twice daily was compared with traditional dosing. A Cmin sample was obtained before the fifth dose. An early clinical response 48-72 hours after the start of therapy and clinical success at end of therapy (EOT) was evaluated in patients with methicillin-resistant Staphylococcus aureus (MRSA), methicillin-resistant coagulase-negative Staphylococci or Enterococcus faecium. RESULTS: There was no significant difference in Cmin between the regimen with and without a loading dose (median: 10.4 and 10.2 µg/mL, P = .54). Proportions of patients achieving 10-20 and 15-20 µg/mL were 56.9% and 5.6%, respectively, in patients with a loading dose. Although there was no significant difference in success rate at EOT between groups, a loading dose was associated with increased early clinical response for all infections (adjusted odds ratio [OR]: 4.588, 95% confidence interval [CI]: 1.373-15.330) and MRSA infections (OR: 12.065, 95% CI: 1.821-79.959). Study limitations included no Cmin measurements within 24 hours and the inclusion of less critically ill patients. WHAT IS NEW AND CONCLUSION: A loading dose of 25 mg/kg followed by 15 mg/kg twice daily did not achieve the optimal Cmin at steady state in patients with normal renal function. However, more early clinical responses were obtained with a loading dose compared with traditional dosing, possibly because of a prompt albeit temporary achievement of a more effective concentration.

Epidemiological and molecular characterization of invasive Streptococcus pneumoniae isolated following introduction of 7-valent conjugate vaccine in Kinki region, Japan, 2008-2013.

Streptococcus pneumoniae is one of the most common bacteria causing community-acquired pneumonia and meningitis. The use of 7-valent pneumococcal conjugate vaccine (PCV7) has reduced the incidence of pneumococcal disease while changing pneumococcal population through herd immunity and non-vaccine pneumococci replacement. This study investigated molecular epidemiologic characteristics of pneumococcal strains in the Kinki region of Japan from 2008 to 2013. A total of 159 invasive pneumococcal isolates were characterized by serotyping, antibiotic susceptibility testing, PCR analysis of penicillin-binding protein genes, multilocus sequence typing (MLST), and pulsed-field gel electrophoresis (PFGE). In adult populations, pediatric PCV7 introduction decreased isolates expressing PCV7 serotypes via herd immunity and increased isolates expressing non-PCV7 serotypes. The rate of penicillin resistance and isolates with alterations in all three pbp genes was higher in PCV7 type isolates than in non-PCV7 type isolates. In MLST analysis, all of serotype 19F isolates were of the same sequence type, ST236, which is the antimicrobial-resistant clone Taiwan19F-14, and the majority of serotypes 23F and 19A isolates were of ST1437 and ST3111 respectively, which are the predominant clones of antimicrobial-resistant pneumococci in Japan. In PFGE profiles, serotype 6B-ST2224, serotype 19F-ST236, serotype 19A-ST3111, and serotype 23F-ST1437 formed six separate clusters composed of genetically identical strains, and genetically identical serotype 22F-ST433 formed two different clusters between the pre- and post-PCV7 period. The results of molecular analysis suggest the spread and persistence of these identical antimicrobial resistant clones in the Kinki region and genetic changes of epidemic clone serotype 22F-ST433 before and after pediatric PCV7 introduction.

Antimicrobial susceptibility surveillance of obligate anaerobic bacteria in the Kinki area.

Obligate anaerobes exist as resident flora in various sites in humans, but they are also emphasized as endogenous causative microorganism of infections. We performed surveillance to understand the trend of drug susceptibility in obligate anaerobic bacteria in the Kinki area of Japan. In the experiment, we used 156 obligate anaerobe isolates collected from 13 institutions that participated in the Study of Bacterial Resistance Kinki Region of Japan. MALDI Biotyper was used to identify the collected strains, and among the 156 test strains, those that could be identified with an accuracy of Score Value 2.0 or more included 6 genera, 30 species, and 144 strains (Bacteroides spp. 77 strains, Parabacteroides sp. 2 strains, Prevotella spp. 29 strains, Fusobacterium spp. 14 strains, Porphyromonas spp. 2 strains, and Clostridioides difficile 20 strains), and they were assigned as subject strains for drug susceptibility testing. The drug susceptibility test was carried out by broth microdilution method using Kyokuto Opt Panel MP ANA (Kyokuto Pharmaceutical Industrial Co., Ltd., Tokyo, Japan) and judged according to CLSI criteria. As a result, Bacteroides and Parabacteroides species showed good sensitivities to tazobactam-piperacillin, imipenem, metronidazole and chloramphenicol, and low sensitivities to ampicillin, cefoperazone and vancomycin. Prevotella species showed good sensitivities to sulbactam-ampicillin, tazobactam-piperacillin, cefmetazole, imipenem, doripenem and metronidazole. Susceptibility rates to other drugs were slightly different depending on the bacterial species. Both Fusobacterium spp. and Porphyromonas spp. showed high sensitivities to many drugs. C. difficile was highly sensitive to vancomycin and metronidazole, having MIC90s of 0.5 µg/mL and ≤2 µg/mL, respectively.

Laboratory surveillance of antimicrobial resistance and multidrug resistance among Streptococcus pneumoniae isolated in the Kinki region of Japan, 2001-2015.

The 7-valent pneumococcal conjugate vaccine (PCV7) was introduced among children in Japan in 2010. There are no long-term multicenter surveillance studies of antimicrobial resistance in S. pneumoniae before and after the introduction of PCV7. Therefore, we examined chronological trends in antimicrobial resistance among 4534 strains of S. pneumoniae isolated from both children and adults in the Kinki region of Japan during 2001-2015. High-level penicillin and third-generation cephalosporin resistance in S. pneumoniae increased among both children and adults during the period before the introduction of PCV7 (2001-2010). Besides penicillin and cephalosporin, pneumococcal carbapenem and macrolide resistance increased among children. The rate of resistance to these antibiotics was higher among children than among adults. The introduction of PCV7 decreased the rate of non-susceptibility to ß-lactam antibiotics and the rate of multidrug resistant S. pneumoniae among children, but not among adults.

Evaluation of the modified carbapenem inactivation method for the detection of carbapenemase-producing Enterobacteriaceae.

Carbapenemase-producing Enterobacteriaceae (CPE) are increasing worldwide. Rapid and accurate detection of CPE is necessary for appropriate antimicrobial treatment and hospital infection control. However, CPE contains some strains that are difficult to detect depending on genotype and MIC value of carbapenem, and a detection method has not been established. The recently reported modified carbapenem inactivation method (mCIM) has been developed in CLSI M100-S27 as a phenotypic technique for detecting carbapenemase activity. In the present study, we examined mCIM as a new CPE detection method using 207 Enterobacteriaceae isolates in comparison with the three existing screening methods of modified Hodge test, Carba NP test and carbapenem inactivation method and evaluated its performance. Consequently, both the sensitivity and specificity of mCIM were 100%, indicating better results than the conventional screening methods. The mCIM is a useful tool for microbiology laboratories due to its simplicity, clear criteria, cost-effectiveness and availability at any laboratory.

Nosocomial spread of Klebsiella pneumoniae isolates producing blaGES-4 carbapenemase at a Japanese hospital.

Six Klebsiella pneumoniae clinical isolates resistant to various cephalosporins and cephamycins were identified in a Japanese general hospital, a tertiary care hospital, between November 2009 and April 2010. All K. pneumoniae isolates carried blaGES-4 and blaSHV-1, while 2 K. pneumoniae isolates also harbored blaCTX-M-15. The pulsed-field gel electrophoresis patterns revealed that these 6 K. pneumoniae isolates were almost identical, suggesting their clonal relatedness. Plasmid profiles and conjugation assays revealed that these blaGES-4 genes were located on similar conjugative plasmids. These data indicate that nosocomial spread caused by K. pneumoniae isolates producing blaGES-4 carbapenemase occurred at a Japanese general hospital. K. pneumoniae isolate harboring blaGES-4 is rarely reported in Japan, and, to the best of our knowledge, this is the second report of K. pneumoniae isolates harboring blaGES-4 that occurred nosocomial spread in Japan.

[The annual changes in antimicrobial susceptibility test results of Pseudomonas aeruginosa isolates from the Kinki district].

A study was conducted of the 1,225 Pseudomonas aeruginosa strains that were isolated at 20 medical institutions in the Kinki district between 2011 and 2013 to determine their antimicrobial susceptibility and to characterize the strains of multidrug-resistant Pseudomonas aeruginosa (MDRP) and the metallo-ß-lactamase (MBL) -producing strains. The MIC50/MIC90 values (µg/mL) of the various antimicrobial agents were as follows: imipenem, 2/>8; meropenem, 1/>8; doripenem, 0.5/8; biapenem, 1/>8; tazobactam/piperacillin, 8/>64; piperacillin, 8/>64; sulbactam/cefoperazone, 8/64; cefepime, 4/16; cefozopran, 2/>16; aztreonam, 8/>16; amikacin, 4/16; levofloxacin, 1/>4; and ciprofloxacin, 0.25/>2. From the viewpoint of the annual changes in the susceptibility rates (according to the CLSI guidelines [M100-S22]), the susceptibility to tazobactam/piperacillin, piperacillin, cefepime, cefozopran and aztreonam decreased in 2013. On the other hand, two antimicrobial agents showed high susceptibility rates each year; amikacin (94.0-95.6%) showed the highest rate, followed by doripenem (80.3-82.6%). With the exception of amikacin, there were substantial inter-institutional differences in antimicrobial susceptibility. In comparison to the previous CLSI guidelines (M100-S21), the new CLSI guidelines (M100-S22) on the use of carbapenems and penicillins show that the MIC80 has been affected. The MDRP detection rates in 2011, 2012 and 2013 were 1.8% (8 strains), 1.8% (8 strains), and 2.8% (10 strains), respectively. The MBL detection rates were as follows: bla(VIM-2), 0.2% (1 strain) in 2011; bla(IMP-1), 0.9% (4 strains) in 2012, and 1.7% (6 strains, including bla(IMP-1) [3 strains], bla(IMP-2) [2 strains] and bla(VIM-2) [1 strain]) in 2013.

Complete Nucleotide Sequence of pKOI-34, an IncL/M Plasmid Carrying blaIMP-34 in Klebsiella oxytoca Isolated in Japan.

We determined the complete nucleotide sequence of a self-transmissible IncL/M plasmid, pKOI-34, from a Klebsiella oxytoca isolate. pKOI-34 possessed the core structure of an IncL/M plasmid found in Erwinia amylovora, pEL60, with two mobile elements inserted, a transposon carrying the arsenic resistance operon and a Tn21-like core module (tnp and mer modules) piggybacking blaIMP-34 as a class 1 integron, In808, where blaIMP-34 confers a resistance to carbapenems in K. oxytoca and Klebsiella pneumoniae.

Complete nucleotide sequence of the IncN plasmid encoding IMP-6 and CTX-M-2 from emerging carbapenem-resistant Enterobacteriaceae in Japan.

We have determined the DNA sequence of Klebsiella pneumoniae multidrug resistance plasmid pKPI-6, which is a self-transmissible IncN-type plasmid. pKPI-6 harboring blaIMP-6 and blaCTX-M-2 confers a stealth-type carbapenem resistance phenotype on members of the family Enterobacteriaceae that is not detectable with imipenem. pKPI-6 is already epidemic in Japan, favoring the dissemination of IMP-6 and CTX-M-2 in members of the family Enterobacteriaceae.

High-dose regimen to achieve novel target trough concentration in teicoplanin.

In the treatment of severe MRSA infections such as endocarditis, more than 20 mg/L of plasma trough concentration (C(min)) is recommended for teicoplanin; however, in the treatment of common MRSA infections, recommended C(min) remains more than 10 mg/L. In this study, we set C(min) as 15-30 mg/L to obtain a favorable clinical outcome in the treatment of common MRSA infections, and investigated the optimal loading regimen that achieved the target C(min) in patients with normal renal function. Seventy-eight patients received the high-dose regimen A (6 mg/kg every 12-h for initial two days) and 60 patients received the high-dose regimen B (the first five loading doses of 10-12 mg/kg at 12-h intervals for initial three days, followed by 6 mg/kg once daily). The mean C(min) on the 4th day was 13.7 ± 5.3 mg/L in regimen A, and 20.0 ± 6.6 mg/L in regimen B (P < 0.001), and the proportion of patients achieving the 15-30 mg/L was 25.6% and 68.3% (P < 0.001). Clinical response at end-of treatment were 66.7% and 85.0% (P = 0.014). The patients of initial C(min) with ≥15 mg/L had tended to be higher clinical response than those with <15 mg/L (80.9% vs 68.6%, P = 0.084). There were no significant differences in the occurrence of adverse effects in regimen A and B (nephrotoxicity; 1.3% vs 3.3%, P = 0.413, hepatotoxicity; 5.1% vs 3.3%, P = 0.608). In conclusion, to obtain C(min) 15-30 mg/L, the first five loading doses of 10-12 mg/kg at 12-h intervals was required in patients with normal renal function.

Susceptibility of various oral antibacterial agents against extended spectrum ß-lactamase producing Escherichia coli and Klebsiella pneumoniae.

With the increase in extended spectrum ß-lactamase (ESBL)-producing bacteria in the community, cases are often seen in which treatment of infectious diseases with oral antimicrobial agents is difficult. Therefore, we measured the antimicrobial activities of 14 currently available oral antimicrobial agents against ESBL-producing Escherichia coli and Klebsiella pneumoniae. Based on the standard of the Clinical and Laboratory Standards Institute (CLSI), E. coli showed high susceptibility rates of 99.4% to faropenem (FRPM). In terms of fluoroquinolones, the susceptibility rate of E. coli to levofloxacin (LVFX) was low at 32.2%, whereas it showed a good susceptibility rate of 93.1% to sitafloxacin (STFX). With respect to other antimicrobial agents, susceptibility rates to fosfomycin (FOM) and colistin (CL) were more than 90% each, whereas rates of the two antimicrobial agents expected as therapeutic agents, minocycline (MINO) and sulfamethoxazole-trimethoprim (ST), were low at 62.4% and 44.3%, respectively. Based on the CLSI standard, K. pneumoniae showed high susceptibility rates to ceftibuten (CETB) (91.89%), LVFX (86.49%), and STFX (94.6%), indicating that K. pneumoniae showed higher rates than those of E. coli, particularly to fluoroquinolones. Comparison of susceptibility rates according to E. coli genotype showed that many antimicrobial agents existed to which the CTX-M-9 group showed high susceptibility rates. However, there were many agents to which the CTX-M-1 group showed low susceptibility rates, particularly to CETB (51.1%) and LVFX (17.0%). Although there was no significant difference by genotype between FRPM, STFX, and FOM, a significant difference was observed between LVFX, MINO, and ST. Antibiotic-resistant bacteria with highly pathogenic strains have spread in the community, appropriate use of oral antimicrobial agents is required.

[Laboratory-based surveillance of antibacterial drug-resistant bacteria in the Kinki region].

The study of bacterial resistance in the Kinki region of Japan (SBRK) was launched in 1997 for the purpose of monitoring antibacterial drug-resistant bacteria. In SBRK, laboratory-based surveillance, such as of Streptococcus pneumonia, Haemophillus influenzae, extended spectrum beta-lactamase-producing Enterobacteriaceae, carbapenemase producing Gram-negative rods, etc. has been carried out for over 10 years and the results have been reported through seminars and conference presentations. Technical seminars of detection methods for clinically important drug-resistant bacteria were also held in order to contribute to improving the quality of microbiology laboratories. To conduct appropriate infection control of drug-resistant bacteria, effective utilization of quality-assured microbiological data and information sharing of regional epidemiological data is very important. The construction of regional cooperation systems among microbiology laboratories and with public institutions is strongly required.

A novel metallo-ß-lactamase, IMP-34, in Klebsiella isolates with decreased resistance to imipenem.

We investigated 5 metallo-ß-lactamase (MBL)-positive Klebsiella isolates from Japan showing intermediate resistance to imipenem. Sequencing of the MBL gene identified a novel variant of IMP-1 with a single amino acid substitution, Glu87Gly. This variant is designated as IMP-34 where blaIMP-34 is located on a transmissible plasmid.

Epidemiology of Escherichia coli, Klebsiella species, and Proteus mirabilis strains producing extended-spectrum ß-lactamases from clinical samples in the Kinki Region of Japan.

In the present study, nonduplicate, clinical isolates of extended-spectrum ß-lactamase (ESBL)-producing Escherichia coli, Klebsiella spp, and Proteus mirabilis were collected during a 10-year period from 2000 to 2009 at several hospitals in the Kinki region, Japan. The detection rate of E coli markedly increased from 0.24% to 7.25%. The detection rate of Klebsiella pneumoniae increased from 0% to 2.44% and that of P mirabilis from 6.97% to 12.85%. The most frequently detected genotypes were the CTX-M9 group for E coli, the CTX-M2 group for K pneumoniae, and the CTX-M2 group for P mirabilis. E coli clone O25:H4-ST131 producing CTX-M-15, which is spreading worldwide, was first detected in 2007. The most common replicon type of E coli was the IncF type, particularly FIB, detected in 466 strains (69.7%). Of the K pneumoniae strains, 47 (55.3%) were of the IncN type; 77 P mirabilis strains (96.3%) were of the IncT type. In the future, the surveillance of various resistant bacteria, mainly ESBL-producing Enterobacteriaceae, should be expanded to prevent their spread.

Evaluation of teicoplanin dosing designs to achieve a new target trough concentration.

Minimum inhibitory concentration (MIC) creep in vancomycin has prompted guidelines that recommend a target trough concentration (C (min)) of 15-20 mg/L, and it is also considered necessary to set a C (min) of >15 mg/L for teicoplanin (TEIC), especially in patients with complicated methicillin-resistant Staphylococcus aureus (MRSA) infections. The aim of this study was to investigate the appropriate TEIC regimen for reaching the revised target C (min) (15-30 mg/L) in patients with normal renal function and those with renal dysfunction. We analyzed patients with MRSA infections who were treated with TEIC between July 2006 and December 2009. Two-day loading regimen was studied in patients with non-renal-dysfunction (group 1). The 1-day loading regimen was studied in patients with non-renal-dysfunction (group 2, control) and in patients with renal dysfunction (group 3). The 178 patients in the study consisted of 76, 28, and 74 patients in groups 1, 2, and 3, respectively. C (min) on day 4 was 14.6 ± 5.6, 11.9 ± 4.1, and 13.5 ± 4.2 mg/L, and the proportion of patients achieving the revised target range was 34.2%, 17.9%, and 20.3%, respectively. Only one patient in group 1 revealed C (min) of >30 mg/L. Treatment success rates, nephrotoxicity, and hepatotoxicity were similar among the three groups. It was difficult to achieve the revised target C (min) with the 2-day loading regimen in patients without renal dysfunction and with the standard TEIC regimen, even in patients with renal dysfunction. Further investigation of an even higher TEIC dosing regimen is considered necessary.

[Reference range of the auditory brainstem response for the patients in the NICU].

Since the auditory brainstem response (ABR) test is a test for the brainstem capacity and hearing function, it is recorded at the discharge from the neonatal intensive care unit (NICU) in our hospital. Although the reference range for the normal full-term newborn infants is well documented, that for the pre-term newborn and/or low birth weight infants is yet to be determined. The latency between wave-I peak and wave-V peak (I-V inter peak latency) on the ABR test was measured on the 254 infants (124 males and 130 females) of 36 to 45 corrected weeks old which was defined as the sum of the gestational weeks and weeks after birth at the test. The reference range for each corrected age group is set as mean +/- standard deviation. The mean value tends to be short as the corrected age increases, while it is not affected by the gestational weeks, body weight on birth, blood bilirubin level, neonatal asphyxia (defined as Apgar score at 1 minute after birth is less than 5), or intrauterine growth retardation. Eight out of 254 patients showed the abnormal values; among the 8 patients, 3 had brain diseases (intraventricular hemorrhage, intracranial hemorrhage, and microcephaly) and 1 with Down's syndrome. Thus the brain stem function testing at a discharge from NICU is important for the neurophysiological prognosis of the patients and the ABR test with the reference range defined here can be a useful tool.

Clinical characteristics of vancomycin minimum inhibitory concentration of 2 µg/ml methicillin-resistant Staphylococcus aureus strains isolated from patients with bacteremia.

Recent studies demonstrated that mortality associated with methicillin-resistant Staphylococcus aureus (MRSA) bacteremia was high when vancomycin was used to treat infections with strains that had a high vancomycin minimum inhibitory concentration (MIC). This study compared several characteristics of vancomycin MIC 2 µg/ml strains isolated from bacteremia with those isolated from infections other than bacteremia. A total of 128 episodes of MRSA bacteremia between 2005 and 2008 were followed-up, and compared with 631 MRSA infections other than bacteremia. The isolation of strains with a 2 µg/ml MIC accounted for 32.0% of isolates from MRSA bacteremia, whereas strains with a 2 µg/ml MIC comprised 9.0% of MRSA isolated from other sites (p < 0.001). The incidence of pneumonia as the source of infection was significantly higher in patients with bacteremia from strains with a 2 µg/ml MIC than in those with ≤1 µg/ml MIC. Prior vancomycin use did not correlate with the isolation of 2 µg/ml strains. The efficacy of glycopeptides as 1st line therapy in patients infected with 2 µg/ml strains was significantly lower than that for patients infected with ≤1 µg/ml strains (30.0 vs. 78.8%, p < 0.001) in bacteremia. In the analysis of infections other than bacteremia, efficacy did not reveal a significant difference according to MIC (69.0 vs. 79.6%, p = 0.109). In bacteremia, mortality was 65.8% in patients with 2 µg/ml strains and 19.5% in patients with ≤1 µg/ml strains (p < 0.001), whereas there was no significant difference in mortality from infections other than bacteremia (10.7 vs. 7.8%, p = 0.617). In multivariate analysis, bacteremia with 2 µg/ml strains, intensive care unit (ICU) stay, and liver cirrhosis were independent risk factors for death in patients with bacteremia, and initial appropriate therapy lowered the risk. Several characteristics such as a higher incidence than at other infection sites, a high incidence of pneumonia as a source of infection, a low success rate of vancomycin therapy, and poor prognosis were confirmed in 2 µg/ml MIC MRSA isolated from bacteremia; however, a low success rate of vancomycin and poor prognosis were not apparent in 2 µg/ml MIC MRSA strains isolated from infections other than bacteremia.

[Surveillance of antimicrobial activity of Pseudomonas aeruginosa isolated in the Kinki district].

The antimicrobial activity of 18 antimicrobial agents were measured for the 500 Pseudomonas aeruginosa strains that had been isolated from various clinical specimens in 17 medical institutions in the Kinki district from April to July of 2008. The antimicrobial activity was excellent in the order of tobramycin (TOB), arbekacin (ABK), doripenem (DRPM), gentamicin (GM) and amikacin (AMK). Susceptible rate that was interpreted by Clinical and Laboratory Standards Institute (CLSI) was high in the order of AMK, TOB, tazobactam/piperacillin (TAZ/PIPC), DRPM, ABK. Also, the difference in susceptible rate was observed between departments, materials and institutions. Multidrug resistant strains were only 12 (2.4%) but strains that had resistance to 2 agents were 48 (9.6%), therefore, implementation of further surveillance should be continued.

[Electrophysiological tests in a case of Hashimoto's encephalopathy].

Hashimoto's encephalopathy is regarded as an autoimmune disorder that appears in patients with anti thyroid antibodies. The thyroid function tests of the patients are not necessarily abnormal, which sometimes makes the diagnosis difficult. Since most of the patients show consciousness disturbance, psychiatric symptoms, and cognitive function decline, Hashimoto's encephalopathy must be distinguished from other disorders showing dementia. We performed the electrophysiological tests on a 38 year old woman with Hashimoto's encephalopathy. Event-related potentials showed impaired cognitive function, and somatosensory evoked potentials and motor evoked potentials showed abnormalities of central nervous system. Although the steroid pulse therapy with the following oral prednisolone treatment resulted in the remission of symptoms, results of electrophysiological tests remained unimproved. Thus the disease course of the patient should carefully be monitored, and the clinical importance of these tests in Hashimoto's encephalopathy may be further considered.