Misao Tao's research while affiliated with Nagasaki University Hospital and other places

We prospectively surveyed gram-negative bacteria in patients and hospital environment in a room in the geriatric ward which was specifically under the infection control against MRSA once every two weeks between September and December 1996. We investigated the inpatients in an 8-bed room in the geriatric wards (190 beds) of AINO Memorial Hospital, affiliated with Nagasaki University. During the study period, we performed a total of 431 cultures. The number of specimens cultured was 116 from airways (nose, 42; pharynx, 42; sputum, 32), 24 from decubitus ulcer, 40 from urine, 42 from feces, a total of 125 from skin (head, 42; forearm, 42; inguinal region, 41), and 84 from the hospital environment (floor swab, 42; settled agar plate, 42), respectively. A total of 15 species were isolated from the hospital environment. Some species were the same as those which were recovered from the hospital environment were those observed on each body site. In the hospital environment, the isolation rates of Acinetobacter baumanii and Klebsiella pneumoniae were significantly high in the settled agar plate (A. baumanii, p < 0.01; K. pneumoniae, p < 0.05, respectively). Isolation rates of Pseudomonas aeruginosa, Citrobacter spp., and Enterobacter sakazakii were also high in the settled agar plate (p = 0.078, 0.078, 0.078, respectively). In conclusion, gram-negative bacteria in patients may be associated with the environmental bacteria in the room in the geriatric wards.

We investigated the efficacy of infection control measures against nosocomial pneumonia in geriatric wards. Cases with nosocomial pneumonia were retrospectively analyzed between January 1991 and March 1995. The study period was divided into four annual periods (periods 1, 2, 3 and 4). Period 1, January to December 1991, was applied as the cotrol. We investigated patients with nosocomial pneumonias in geriatric wards (190 beds) of AINO Memorial Hospital, affiliated with Nagasaki University. During the study period, nosocomial pneumonia significantly diminished. (period 1 vs periods 2, 3 and 4, p < 0.05, p < 0.05, p < 0.05, respectively). Major causative organisms of nosocomial pneumonia were MRSA and Pseudomonas aeruginosa. During the four periods, a significant reduction in cases with MRSA- and P. aeruginosa-induced nosocomial pneumonia was observed (MRSA: period 1 vs periods 2, 3 and 4, p < 0.05, p < 0.05, p < 0.01, respectively; P. aeruginosa: period 1 vs period 3, p < 0.01, period 2 vs periods 3 and 4, p < 0.01, p < 0.05, respectively). On the other hand, the improvement of decubitus ulcers was associated with a significant reduction in nosocomial pneumonia (period 1 vs. periods 2 and 3, p < 0.05 and p < 0.05, respectively). In conclusion, stringent infection control programs, including a cleaning in the upper airways by povidone iodine, are necessary in geriatric wards to reduce and prevent nosocomial pneumonia.

Active infection control measures began being taken in geriatric wards starting in October 1991. MICs of 148 strains (nasal cavity 72, pharynx 44, and sputum 32) of Staphylococcus aureus were determined for 14 antimicrobial agents, isolated from Aino Memorial Hospital patients between August 1995 and August 1996. The frequency of methicillin-resistant S. aureus (MRSA) was 62.5% in the nasal cavity, 79.5% in the pharynx, and 93.7% in the sputum, suggesting that most strains of S. aureus remain resistant to β-lactam agents such as cephems, penicillins, and carbapenems. The frequency of strains susceptible to minocycline (MIC≤6.25 μg/mL) was 61.1% in the nasal cavity, 54.5% in the pharynx, and 25.0% in the sputum. An increase in susceptible strains was brought by reinforcing infection control, including limiting the use of minocycline since 1987. No strains were highly intermediately or resistant to vancomycin. The frequency of strains with an MIC of 3.13 μg/mL to vancomycin was 19.4% in the nasal cavity and 20.5% in the pharynx. No such strains were isolated from the sputum. Most strains (90.6%) in the sputum revealed an MIC of 1.56 μg/mL, suggesting the need to follow up MICs of S. aureus to vancomycin carefully in the future.

A murine monoclonal antibody (MAb) specific for the Pseudomonas aeruginosa immunotype 1 (It-1) lipopolysaccharide (LPS) O-side chain was evaluated in terms of its in vitro bactericidal opsonophagocytic activity and in vivo bacterial killing in a mouse thigh infection model. An immunoglobulin (Ig) G2a MAb Ld3-2F2, specific for It-1 LPS, mediated in vitro complement-dependent opsonophagocytic killing at a concentration of 10 microg/ml. MAb-mediated, complement-dependent killing also occurred in the absence of neutrophils at serum concentrations in excess of 20%. A remarkable synergy was observed in opsonophagocytic assays between MAb Ld3-2F2 (0.5 microg/ml) and ceftazidime (1/4 MIC). The administration of MAb Ld3-2F2 at a level of 1 microg resulted in a significant decrease in the number of bacteria in the thigh muscles of normal mice, while 100 microg of the same MAb was required for one log of reduction in the number of bacteria at the same site in neutropenic mice. The combined therapy with MAb Ld3-2F2 and ceftazidime provided a significant reduction in the density of bacteria in the thigh muscle at 9 hr post-infection in normal and neutropenic mice as compared with those after treatment alone or with no treatment (P< 0.01). These favorable in vitro and in vivo interactions of an LPS-specific IgG MAb and ceftazidime strongly support their potential for use in therapy, combined with an LPS-reactive MAb and parenteral antipseudomonas beta-lactam antibiotics in the therapy of systemic Pseudomonas infections in normal and neutropenic hosts.

Twenty clinical isolates of Staphylococcus aureus were examined to elucidate the virulence factors which are directly related to lethality in a mouse septic model. Heat or formalin treatment of the organism abolished the lethal activity of the live organism during challenge intravenously administered via the tail vein. Nevertheless, injection of ten times concentrated culture supernatant fluid (SUP) showed lethal activity in the mouse. However, there was no lethality when SUP was heated at 60 degrees C for 15 min. To examine variations of SUP lethality among strains, we collected 20 strains of S. aureus from four different hospitals. Then, we compared several factors for SUP lethality, which were the extracellular toxins and enzymes, such as toxic shock syndrome toxin 1, enterotoxin A, B, D, and hemolysins (alpha,beta,gamma), and also cytotoxic activity to human polymorphonuclear leukocytes and Vero cells. No difference was found among these factors except cytotoxic activity to Vero cells. Furthermore, we compared two strains in a mouse septic model according to the grade of bacteremia and lethal events. We found that mortality was higher with challenge by the strain whose SUP was lethal in comparison to the strain whose SUP was not lethal, even though the viable bacteria counts in the septic blood in both strains were not significantly different. This strongly supports the possibility that extracellular products, not the cell wall components, of S. aureus play the key role in the lethal event in this mouse septic model. In addition, among the extracellular products, those which have cytotoxic activity to Vero cells may contribute to the lethality in sepsis caused by S. aureus in this murine model.

Respiratory infections are initiated by the attachment of bacteria to pharyngeal epithelial cells. We studied the attachment of Burkholderia pseudomallei to pharyngeal epithelial cells. After one, two, three, and four washes, there were 22.6+/-8.9, 15.7+/-7.0, 6.8+/-3.1, and 4.6+/-1.1 (mean+/-SD) attached bacteria/cell, respectively. If the bacterial concentration was maintained at 1 X 10(8) colony-forming units (cfu)/ml and three washes were done, at concentrations of 2.5 x 10(4), 5 X 10(4), and 1 x 10(5) cells/ml there were 9.9+/-3.6, 3.3+/-0.8, and 2.5+/-1.1 attached bacteria/cell, respectively. If the cell concentration was kept at 2.5 x 10(4) cells/ml and three washes were done, at bacterial concentrations of 1 x 10(5), 1 X 10(6), 1 X 10(7), 1 x 10(8), and 1 x 10(9) cfu/ml, there were 0.3+/-0.3, 0.6+/-0.6, 1.0+/-0.2, 5.1+/-2.3, and 9.6+/-1.9 attached bacteria/cell, respectively. There were 4.8+/-1.9, 5.5+/-2.5, 5.6+/-1.9, and 6.4+/-2.6 attached bacteria/cell at 0, 30, 120, and 240 min of incubation, respectively. Pharyngeal cells from 10 persons (seven men and three women, mean+/-SD age = 30.7+/-8.1 years, 12 experiments with a single isolate) showed that there were 7.8+/-4.3 attached bacteria/cell. It was found that the efficiency of attachment of this bacteria was very low (7.0+/-3.3 bacteria/cell). Electron microscopy revealed that there were no fimbriae but a thin capsular polysaccharide layer on the surface of B. pseudomallei. Attachment to pharyngeal epithelial cells appeared to be mediated by this structure.

Moraxella catarrhalis is an important organism causing respiratory infections. There have been several clinical failures to treat this infection using β-lactam antibiotics due to the wide prevalence of β-lactamase-producing strains. To determine trends in antibiotic susceptibility and suitable antibiotics for treatment, we determined the MICs of a panel of antibiotics againstM. catarrhalis, which were isolated from the sputum of patients with respiratory infections. These strains were randomly selected from stock isolates from 1984 to 1985 and from 1993 to 1994. It was found that over the 10-year period, the MIC90 increased against the β-lactam antibiotics. Satisfactory susceptibility was found with amoxicillin-clavulanic acid, third generation cephalosporins, carbapenems, tetracycline, erythromycin, aminoglycoside and new quinolones. High levels of β-lactamase-producing strains were found in both periods.

In the early 1980's methicillin-resistant Staphylococcus aureus (MRSA) was reported as a major pathogenic organism of geriatric hospital infection in Japan. At the same time in our geriatric wards, including 190 beds, MRSA infection was prevalent. In the early 1980's in our geriatric wards minocycline was one of the most sensitive antibiotics to MRSA isolated in our wards and used frequently against MRSA pneumonias and bacteremia. In the late 1980's resistant strains of MRSA to minocycline rapidly increased because vancomycin was not allowed to introduced for treatment of MRSA before 1991 in Japan. At the same period the predominant coagulase type changed from type II to type VII. To decrease minocycline-resistant strains to MRSA after 1987, use of minocycline was limited. Moreover since Oct. 1991 to decrease nosocomial infections some active preventive measures against hospital infection, including limited use of 2nd and 3rd cephems, were taken. In this study changing patterns of coagulase type of Staphylococcus aureus were discussed. At least 4 years was needed to find out that the predominant coagulase type changed from type VII to type II again in 1991. In this study about 22 antimicrobial agents MICs of 313 strains of Staphylococcus aureus isolated between March 1992 and June 1993 were determined and compared with the data of MICs before introduction of preventive measures. The pattern of susceptibility to MINO was in part improved. Thus the some sensitive strains of S. aureus were observed again in our geriatric wards. Interestingly indeed it took approximately 5 years to find out the emergence of sensitive strains to MINO since limitation of use of MINO in 1987.

In early 1980's methicillin-resistant Staphylococcus aureus (MRSA) was reported as a major pathogenic organism of geriatric hospital infection in Japan. At the same time in the geriatric hospital MRSA infection was prevalent. To decrease nosocomial infections some active preventive measures against hospital infection were taken since Oct. 1991. After introduction of preventive measures of hospital infection in the geriatric ward (190 beds) nosocomial bacteremia and pneumonia were markedly decreased in comparison of episode number before introduction of prevention. However several patients with MRSA colonization were observed every month. The aim of this clinical study was to clear how frequent MRSA was isolated from skin. Consequently 3 strains (3.4%) of MRSA were observed in 86 cultured skin. In conclusion we considered frequency of MRSA colonization frequency of MRSA colonization on skin was not so high but rather very low under the preventive measures.