Survey of the Sensitivity of Microorganisms to Aflatoxin

Among the 329 microorganisms tested for aflatoxin sensitivity were 30 genera of bacteria, 34 genera of fungi, 4 genera of algae, and 1 protozoan. Twelve species of the genus Bacillus, a clostridium, and a streptomycete were inhibited when 30 mug/ml of crude aflatoxin (36% pure) was incorporated into the growth substrate. A strain of Bacillus brevis and two of B. megaterium were most sensitive to aflatoxin, being inhibited at 10 and 15 mug/ml, respectively.     

Antibiotic Sensitivity of Micrococcus radiodurans

A wild-type strain of Micrococcus radiodurans and its nonpigmented mutant W(1) were tested for sensitivity to 10 antibiotics selected from the standpoint of their mechanism of action. Representatives of groups of antibiotics inhibiting deoxyribonucleic acid (DNA) synthesis, DNA-dependent ribonucleic acid synthesis, protein synthesis, and cell wall synthesis were selected. M. radiodurans and its mutant exhibited full susceptibility to all antibiotics tested (mitomycin C, actinomycin D, chloramphenicol, dihydrostreptomycin, erythromycin, neomycin, kanamycin, benzylpenicillin, bacitracin, and vancomycin), the degree of susceptibility being of the same order as that of a standard strain of Staphylococcus aureus 209 P, with the exception of dihydrostreptomycin.     

Survey of the Sensitivity of Microorganisms to Rubratoxin B

Of the 133 microorganisms tested, Tetrahymena pyriformis and Volvox aureus were the most sensitive to rubratoxin B, being inhibited at 25 and 50 mug/ml, respectively.     

Device for Turbidity Standardizing of Cultures for Antibiotic Sensitivity Testing

A specially designed metal rack which is illuminated by a modified Rh-typing view box is described. This device facilitates the handling and reduces the time involved in standardizing cultures.     

Mechanical Method of Inoculating Plates for Antibiotic Sensitivity Testing

A mechanical method of inoculating culture plates for antibiotic sensitivity testing is described. This method, which involves the use of a modified laboratory centrifuge, is rapid and provides a homogeneous distribution of organisms.     

Detecting Surfactant-producing Microorganisms by the Drop-collapse Test

Summary A rapid method, ’drop-collapse’, was used for screening biosurfactant production by Pseudomonas aeruginosa, Bacillus subtilis, Candida albicans and Phanerochaete chrysosporium liquid cultures. Before measuring the total biosurfactant, the drop-collapse method was used in order to detect rhamnolipid presence in the culture broths. The method was performed in a microwell plate; the polystyrene platform with small wells. If the culture broth contained biosurfactant, the droplets of the broth in the oil-coated wells collapsed. If not, there was no change in the shape of the droplets. Pseudomonas aeruginosa and Bacillus subtilis culture supernatants showed spreading movement, meaning that they produced biosurfactants. However, Candida albicans and Phanerochaete chrysosporium supernatants remained beaded, meaning they did not produce any type of microbial surfactant.     

300 株鲍曼不动杆菌琼脂稀释法与纸片扩散法药敏检测结果比较

目的:比较琼脂稀释法和纸片扩散法对鲍曼不动杆菌的药敏试验结果。方法:随机挑选的300株鲍曼不动杆菌,检测其标本及科室的分布情况,并采用琼脂稀释法和纸片扩散法检测鲍曼不动杆菌对环丙沙星(CIP)、庆大霉素(CN)、阿米卡星(AK)、头孢他啶(CAZ)、头孢吡肟(FEP)、左氧氟沙星(LEV)、氨苄西林-舒巴坦(SAM)、妥布霉素(TOB)、美洛培南(MEN)、米诺环素(MH)、头孢哌酮-舒巴坦(SCF)11种抗菌药物的敏感性,比较两种检测结果的差异。结果:300株鲍曼不动杆菌主要分布在痰液标本中,共214株,占71.3%,主要来源于ICU 101株(33.7%)及脑外科59株(19.7%)。药敏检测结果显示,两种检测方法所得的SCF和MH的敏感性差异具有统计学意义(P0.05),其他9种抗菌药物的药敏检测结果差异没有统计学意义(P0.05)。结论:琼脂稀释法和纸片扩散法对鲍曼不动杆菌药敏试验结果并不完全一致,临床用药时尤其要注意SCF和MH这两种药物药敏结果的可靠性。     

魔芋试管苗批量生产过程中外植体消毒灭菌技术研究

采用熏气法,可较为彻底地杀死魔芋球茎或根状茎的内生菌,再配合酒精、HgCl2等进行表面灭菌,可使初次接种污染率控制在10%以下,继代培养污染率控制在5%以下,从而建立魔芋试管苗的无菌繁殖体系,为试管苗的批量化生产提供了前提和技术保障。     

Field Trial of a Microcolony Method for Testing the Antibiotic Sensitivity of Bacteria

The sensitivity of bacteria to antibiotics may be measured by a rapid method in which the criterion of sensitivity is inhibition of microcolony formation on agar which contains antibiotic. As this method allows a report on the antibiotic sensitivity of a pathogenic bacterium four hours after the test is set up, a trial of the method was carried out in a diagnostic laboratory. Two thousand five hundred and four strains of fast-growing bacteria were tested against 10 antibiotics. The overall correlation rate between the four-hour microscopic readings and the subsequent overnight readings on the same cultures was 98.1%. Seven per cent of the microscopical readings attempted gave indeterminate results, and reports on these tests were withheld until the following day.The time spent in making microscopical readings was considered fully justified by the fact that results of a high proportion of antibiotic sensitivity tests were available one day earlier than is usual with established methods.     

解脲脲原体药物敏感性变迁研究

目的:探讨上海地区2008与2012年泌尿生殖道解脲脲原体(Ureaplasma urealyticum,UU)耐药性变化,为临床合理用药提供参考。方法:采用自制UU药物敏感检测试剂对2008年450例和2012年459例患者的标本进行检测,观察UU阳性情况及UU对交沙霉素、氧氟沙星、阿奇霉素和强力霉素的药物敏感性。结果:2008年分离到150例UU阳性标本和2012年分离到134例UU阳性标本分别对交沙霉素、强力霉素、氧氟沙星和阿奇霉素等4种抗菌素的敏感率有显著性差异;2008年46例和2012年38例男性患者阳性标本中分离的UU分别对交沙霉素和阿奇霉素敏感率有显著性差异;对强力霉素和氧氟沙星敏感率无显著性差异。2008年104例和2012年96例女性患者阳性标本中分离的UU分别对交沙霉素、强力霉素、氧氟沙星和阿奇霉素等4中抗菌素的敏感率都有显著性差异。结论:5年间UU药物敏感性发生了变迁;临床医师应该关注本地区药物敏感性变迁,合理选用抗生素。     

Rapid Sulfonamide Disc Sensitivity Test for Meningococci

Minimal inhibitory concentrations (MIC) of 90 strains of Neisseria meningitidis were determined by a plate dilution technique that employed twofold changes in concentrations of sulfadiazine. The geometric mean of three MIC determinations on each strain was correlated with inhibition zones produced by a 300-mug sulfathiazole disc. The linear relationship between the logarithm of the geometric mean MIC values and the zone diameters was highly significant. Strains were separated into sensitive and resistant populations by both test procedures. Quantitative criteria for interpreting the sensitivity of a strain by the disc test were established.     

Interpretation of the Tube Coagulase Test for Identification of Staphylococcus aureus

The tube coagulase test is a valid means of identifying Staphylococcus auerus, provided that only a firm clot that does not move when the tube is tipped is considered a positive reaction. The widely promulgated interpretation that all degrees of clotting in coagulase plasma are a positive identification of S. auerus was disproved by the use of other tests such as anaerobic glucose fermentation, thermonuclease production, and lysostaphin sensitivity. It was found that the source of supply of the coagulase plasma is a factor in the occurrence of false-positive coagulase test results. The use of a mixture of pig and rabbit plasma in the tube coagulase test is also discussed.     

Effect of Paper on the Performance Assay in the Control of Antibiotic Sensitivity Discs

Antibiotic discs were prepared, using several several batches of papers meeting Food and Drug Administration specifications. The analysis of 1,152 zones of inhibition produced showed no performance differences among these batches. Other discs were prepared using papers of different grades. These produced large differences in performance. It is obvious, therefore, that the use of a specified disc paper is necessary for standardizing the performances of the products of various manufacturers and that reproducible results can be attained with the grade of paper specified.     

Mannitol Enhances Antibiotic Sensitivity of Persister Bacteria in Pseudomonas aeruginosa Biofilms

The failure of antibiotic therapies to clear Pseudomonas aeruginosa lung infection, the key mortality factor for cystic fibrosis (CF) patients, is partly attributed to the high tolerance of P. aeruginosa biofilms. Mannitol has previously been found to restore aminoglycoside sensitivity in Escherichia coli by generating a proton-motive force (PMF), suggesting a potential new strategy to improve antibiotic therapy and reduce disease progression in CF. Here, we used the commonly prescribed aminoglycoside tobramycin to select for P. aeruginosa persister cells during biofilm growth. Incubation with mannitol (10–40 mM) increased tobramycin sensitivity of persister cells up to 1,000-fold. Addition of mannitol to pre-grown biofilms was able to revert the persister phenotype and improve the efficacy of tobramycin. This effect was blocked by the addition of a PMF inhibitor or in a P. aeruginosa mutant strain unable to metabolise mannitol. Addition of glucose and NaCl at high osmolarity also improved the efficacy of tobramycin although to a lesser extent compared to mannitol. Therefore, the primary effect of mannitol in reverting biofilm associated persister cells appears to be an active, physiological response, associated with a minor contribution of osmotic stress. Mannitol was tested against clinically relevant strains, showing that biofilms containing a subpopulation of persister cells are better killed in the presence of mannitol, but a clinical strain with a high resistance to tobramycin was not affected by mannitol. Overall, these results suggest that in addition to improvements in lung function by facilitating mucus clearance in CF, mannitol also affects antibiotic sensitivity in biofilms and does so through an active, physiological response.     

Increased Antibiotic Sensitivity in Pseudomonas aeruginosa Following Passage in Carbenicillin-containing Media

Twelve dissimilar clinical isolates and 4 type cultures of Pseudomonas aeruginosa have been repeatedly passaged on agar containing 200 μg carbenicillin/ml. Passaged variants were compared with control organisms for their sensitivities to a range of antibiotics initially by a multodisk test and subsequently by serial dilution in agar. Two of the variants, both derived from clinical isolates, showed pronounced increases in sensitivity to several antibiotics, particularly kanamycin, neomycin, gentamicin and colistin sulphate. In some instances the minimum inhibitory concentration (MIC) for the passaged variants was 32–64 times lower than that for the control organisms. These potentiations contrast with previous results obtained by other workers for P. aeruginosa . In addition, several other of our passaged variants developed a more moderate degree of enhanced sensitivity to a limited number of antibiotics. Eight (67%) of the clinical isolates and one type culture did not become more sensitive to any of the antibiotics tested following carbenicillin passage. Onset of increased antibiotic-sensitivity varied with the strain, particular antibiotic and medium employed for passage. Although the addition of sucrose (0·5 M) and magnesium sulphate (0·01 M) to the passage medium appeared to delay development of antibiotic-sensitivity their presence eventually encouraged larger potentiations in antibiotic activity. The significance of the conversion of P. aeruginosa into forms with increased susceptibility to several antibiotics during chemotherapy with carbenicillin is discussed.     

Changes in Preservative Sensitivity for the USP Antimicrobial Agents Effectiveness Test Micro-organisms

Chemically defined and semi-defined media were designed for the preservative-efficacy testing micro-organisms designated by the United States Pharmacopoeia, in which the organisms went into the stationary phase of growth at an optical density (E₄₇₀) of 1.0, because of depletion of a single carbon, nitrogen or phosphate source. Aspergillus niger was grown on solid media containing concentrations of these nutrients which limited the rates of mycelial development and sporulation density. The ability of the micro-organisms to survive and grow in the presence of chlorhexidine diacetate, benzalkonium chloride and thiomersal varied markedly with the nutrient-depletion of the inocula. No universal pattern of sensitivity emerged among microorganisms. Only A. niger showed little overall change in preservative sensitivity. These results highlight the need to define more adequately growth media and conditions for the production of inocula for antimicrobial challenge tests.     

Specificity and Sensitivity of the Streptozyme Test for the Detection of Streptococcal Antibodies

A comparison between the results of the streptozyme hemagglutination test and serological titers for anti-streptolysin O (ASO), anti-hyaluronidase (AH), anti-deoxyribonuclease B (ADN-B), and anti-nicotinamide adenine dinucleotidase (ANAD) was made in two groups of human sera. In one group, serological titers for all the four antibodies were lower than the threshold of sensitization reported by the producing firm. In the second group, the titer of at least one of the four antibodies was equal to or higher than the threshold. False-positive and false-negative reactions occur with those sera when one or more antibody titer is at or near the threshold of the test as described by the manufacturer. The test was positive for all sera where either the ASO was greater than 166 or the ANAD was greater than 270, and for 98% of the sera with ADN-B greater than 360. It is, therefore, concluded that the streptozyme test can be used as an adjunct to the clinical diagnosis of streptococcal infections and their nonsuppurative sequelae. It is less useful to assess the levels of antibodies in sera from general population surveys. For such sera, the relative specificity and sensitivity of the test might yield misleading results. Until more experience is gained with the test, caution should be used in its application to infant and older adult age groups, where significant streptococcal antibody titers are frequently near the threshold of the test.