Mathematical models are essentially needed to quantitatively predict microbial growth in food products during their production and distribution. Recently we developed a new logistic model for microbial growth. The model is an extended logistic model, which shows a sigmoid curve on a semi-log plot. The model could precisely describe and predict bacterial growth at constant and dynamic temperatures in broth, on nutrient agar plates, and in pouched food. Prediction results with our model were very similar to those with the Baranyi model, which is well known worldwide. The model also predicted the amount of metabolites (toxins) that would be produced by a microorganism. Namely, with the growth model and the kinetics of staphylococcal enterotoxin A production, the amount of the toxins produced by Staphylococcus aureus in milk was successfully predicted. Our model could be a tool in the alert system and the quantitative risk assessment of harmful microbes in food.
To investigate the bacterial contamination of preservative solutions for contact lenses, contact lens cases were swabbed and the swabs were cultured. Various bacteria were isolated from 26 of 100 samples (26.0%). By preservative solution, the bacterial presence was low (16.7%) in the 30 samples from cases using ReNu, which was the most frequently employed solution, and 27.3% in 11 samples from cases using Complete, which was the second most frequently employed solution. Of 34 strains isolated and identified, gram-negative bacilli-glucose non-fermenting bacteria were the most frequently isolated, accounting for 61.8% (21 strains); particularly, 10 isolates were Stenotrophomonas maltophilia, accounting for 29.4%. The biofilm-forming ability of these isolates was investigated by staining. The mean absorbance of the gram-negative rods was 0.369, which was about 3 times higher than that (0.107) of the Staphylococcus group, confirming marked biofilm-forming ability. In addition, the bactericidal effects of the preservative solutions on the isolates were investigated. The effect varied among the preservative solutions in the suspension experiment, but the highest disinfection rate, which was achieved by Complete, was 99.9->99.99%, showing a favorable bactericidal effect. In contrast, none of the 3 test preservative solutions showed any bactericidal effect in the adhesion experiment.
The distribution of filamentous fungi was studied in a production line for plastic caps for soft drinks. Of 52 samples from both the swab and air sampling tests, a total of 47 filamentous fungi were isolated. Of those 47 fungi, 32 (68.0%) were found in the swab test samples. As for the swab test results, the area where most of the filamentous fungi were isolated was the printing/inspection room followed by the resin storage room. The breakdown of the filamentous fungi showed Cladosporium: 14.9%; Penicillium: 10.6%; Acremonium: 8.5%; Trichoderma: 8.5%; Arthrinium: 6.4%; and Aureobasidium: 6.4%. The fungal count of raw material (MPN/100g) was zero for the base resin, 0.36 for the master batch and 4.3 for the liner material, respectively. Those fungal counts seemed to be very low and it was concluded that the hygienic conditions of the plastic cap production line were very good.
The VIDAS Listeria monocytogenes II (LMO2) method, which is an automated enzyme-linked fluorescent immunoassay (ELFA), was used for rapidly, specifically and sensitively detecting L. monocytogenes in food samples. All 31 L. monocytogenes strains examined gave positive results. The other bacterial species except Salmonella showed completely negative results, but it was suspected that Salmonella spp. had given a false-positive reaction to the assay. As the detectable limit of the assay was 106 cfu/ml in a food suspension, food samples were required to be enriched in order to increase the number of the bacteria to the detectable limit. However, the ELFA was reconfirmed to be applied satisfactorily as a rapid and precise method for the detection of L. monocytogenes in various food samples, even if the culture had to be enriched for 12 h prior to the assay.
Postoperative vision-threatening corneal edema sometimes occurs after eye surgery, and corneal endothelial damage may be caused or exacerbated by drug toxicity. A range of commercially available antibiotic and anti-inflammatory ophthalmic solutions used postoperatively, namely levofloxacin, moxifloxacin, gatifloxacin, cefmenoxime, diclofenac, bromfenac, pranoprofen, betamethasone, and fluoromethorone, were assessed by using human corneal endothelial cells (HCECs). Propylparaoxybenzoate and methylparaoxybenzoate were also examined. Cell survival after 48 h exposure to the drugs was evaluated using the WST assay. Cefmenoxime and betamethasone were the least toxic antibiotic and anti-inflammatory drug, respectively. Cell survival was concentration dependent and increased markedly to ≥80% with dilutions of 100-fold or more. Two preservatives seemed to cause minimal cytotoxicity among those tested. Antibiotic cytotoxicity to HCEC was ranked as cefmenoxime < levofloxacin = gatifloxacin < moxifloxacin, while the toxicity of anti-inflammatory drugs was dependent on benzalkonium chloride and polysorbate. These drugs are unlikely to cause HCEC damage at the concentrations used under the usual conditions. Preservatives are essential ingredients in ophthalmic solutions to control postoperative infection and inflammation and we should be aware of their toxicity as well as efficacy.
We monitored the quantity of airborne microorganisms at 11 points (points A to K) in a dental office on a routine day of use, and tested the bactericidal efficacy of chlorine dioxide (ClO2) gas in the dental operatory after consulting hours. Fallen airborne microorganisms were collected under air-conditioning (AC) in the dental office, and under four conditions in the operatory. Specimens of the microbes were cultivated on nutrient and Sabouraud agar media (NAM and SAM). Many colonies were observed at the entrance hall and on the cabinet in a disinfection room in the NAM and SAM tests, respectively, while no colony was observed at the foot position of the operating table and treatment bed, and above the head position of the operating room in the NAM and SAM tests, respectively. In the bactericidal efficacy test using ClO2 gas, the dental operatory could be kept clean by the use of 4 mg/L-ClO2 gas in addition to the use of an AC with a plasma filter and the HEPA filter.
The growth of four fungal species (four isolates) from bathrooms was examined under various environmental conditions. These fungi were found several times in bathrooms and washing machines, but not in other indoor environments such as house dust or windows. The four species (Ramichloridium strelitziae, Cyphellophora laciniata, Phoma fimeti, and Exophiala sp.) were identified using DNA and morphological analyses. These bathroom fungi were able to consume surfactants, soap and shampoo, but were unable to grow well in high-temperature or dry conditions. Soap and shampoo seem to affect fungal flora in the bathroom.
An ecological and molecular-epidemiological study of Vibrio cholerae in some aquatic environments of Okayama was carried out. The strains of non-O1/non-O139 were isolated frequently, and unconventional O1 strains were rarely observed. These non-O1/non-O139 strains did not have ctxA, the gene of choleratoxin, the major pathogenic factor of epidemic cholera, but possessed hlyA, a gene encoding hemolysin thought to be a pathogenic factor for sporadic diarrhea or food poisoning. Furthermore these strains also had toxR, a gene controlling the pathogenic island of the V. cholerae genome, suggesting the potentia of these strains for accepting the horizontal transfer of virulence factor genes. Thus, continuous survey of the vibrio is to ensure the food safety of fishery products.