Comparison of disk diffusion,the E test,and detection ofmecA for determination of methicillin resistance in coagulase-negative staphylococci

The aim of this study was to find a reliable, fast, and simple alternative to the methicillin disk method for determination of methicillin resistance in coagulase-negative staphylococci, since results of this method are often difficult to read due to growth within the zone of inhibition. The sensitivity of 319 strains of coagulase-negative Staphylococci to a 5 g methicillin disk on Mueller-Hinton agar using an incubation period of 48 h was compared with that of 1 (1 g and 5 g oxacillin disks on Mueller-Hinton agar with or without 2% NaCl, using an incubation period of 24 h. The detection ofmecA (MecAgen) by the polymerase chain reaction was used as a standard. Minimum inhibitory concentrations were determined by means of the E test. Of the 225mecA-positive strains, 190, 215, and 193 were resistant to 5 g methicillin, 1 g oxacillin and 5 g oxacillin disks on Mueller-Hinton agar, respectively, and 216, 218, and 223 were resistant on Mueller-Hinton agar with 2% NaCl. Of the 94mecA-negative strains, 89, 93, and 94 were susceptible to 5 g methicillin, 1 g oxacillin, and 5 g oxacillin disks on Mueller-Hinton agar, respectively, and 92, 93, and 94 were susceptible on Mueller-Hinton agar with 2% NaCl. Using breakpoints of 2 g/ml for oxacillin resistance and 8 g/ml for methicillin resistance, the E test yielded sensitivities of 99.6 and 99.1% and specificities of 97.9 and 98.9% after 48 h of incubation. The 5 g oxacillin disk was faster and easier to read than the methicillin disk and correlated better with detection ofmecA than the methicillin disk or the 1 g oxacillin disk.     

Diversity of methicillin-resistantStaphylococcus aureus isolated in a Canadian hospital

Three neonates and three other patients located elsewhere in the hospital became infected withStaphylococcus aureus. Initial automated microdilution susceptibility testing with oxacillin and disk diffusion testing with amoxicillin-clavulanic acid indicated the isolates had borderline oxacillin resistance (MICs 4 µg/ml), presumably due to hyperproduction of -lactamase. Chromosomal DNA restriction fingerprinting and phage typing revealed the neonatal isolates to be identical; whereas, the other patients were infected with three different strains. Further analysis of the four strains by Southern hybridization with amecA specific oligoprobe and a quantitative -lactamase assay demonstrated that two strains carried themecA gene (coding for low affinity penicillin-binding protein 2a), and two strains were hyperproducers of -lactamase, including one which wasmecA gene positive. One strain neither carried themecA gene nor hyperproduced -lactamase. The twomecA gene positive strains displayed oxacillin MICs of 16 µg/ml on dilution susceptibility testing in 4% NaCl supplemented Mueller-Hinton agar. Hence, they were considered intrinsically methicillin-resistantStaphylococcus aureus. Both oxacillin and amoxicillin-clavulanic acid MICs were increased on NaCI supplementation. Results of amoxicillin-clavulanic acid disk diffusion susceptibility testing did not correlate with quantitative -lactamase production. It is recommended that clinical laboratories do not use amoxicillin-clavulanic acid disk diffusion assays to differentiate suspected borderline resistance due to -lactamase hyperproduction frommecA gene expression of PBP-2a since additional mechanisms may account for resistance.     

Beta-lactamase production and susceptibility of US and European anaerobic gram-negative bacilli to beta-lactams and other agents

The susceptibility of 1,476 US and European strains of anaerobic gram-negative bacilli to amoxicillin, amoxicillin/clavulanate, ticarcillin, ticarcillin/clavulanate, cefoxitin, imipenem and metronidazole was determined. All of theBacteroides fragilis group and 51 % of the non-Bacteroides fragilis group were -lactamase positive. Amongst the non-Bacteroides fragilis group, -lactamase positivity rates were higher for US strains (58 %) than for European strains (39 %). All strains were susceptible to imipenem and metronidazole. MIC90s of amoxicillin and ticarcillin for all -lactamase negative strains were 0.5 and 2 µg/ml, respectively. The addition of clavulanate reduced the MIC90s of amoxicillin ( 256 µg/ml) and ticarcillin ( 64 µg/ml) to 16 and 8 µg/ml, respectively, for theBacteroides fragilis group, and to 4 µg/ml for both agents for the non-Bacteroides fragilis -lactamase producing group. Twenty-nine cefoxitin-resistant strains were found, mainly in theBacteroides fragilis group, while 95 -lactamase producing strains (predominantlyBacteroides fragilis group and fusobacteria) did not show synergy between -lactams and clavulanate. Of the newer agents tested, meropenem and piperacillin-tazobactam were the most active (100 % of strains susceptible), followed by amoxicillin-BRL 42715 (99 % of strains susceptible); 94 to 98 % of the strains were susceptible to cefoperazone-sulbactam, tosufloxacin, tempafloxacin and clindamycin. Only 73 % of the strains were susceptible to cefotetan, compared to 91 % to cefoxitin; 88 % of the strains were susceptible to trospectomycin. Overall, all of the -lactam/-lactamase inhibitor combinations, imipenem, meropenem, cefoxitin, tosufloxacin, temafloxacin and clindamycin had good activity against -lactamase producing strains, while all agents tested had good activity against -lactamase negative strains.     

Survey of clinical isolates ofStaphylococcus aureus for borderline susceptibility to antistaphylococcal penicillins

On the basis of the MICs of methicillin and oxacillin, 975 clinical isolates ofStaphylococcus aureus were categorized as having resistance, borderline susceptibility or full susceptibility to penicillinase-resistant penicillins (PRPs). The borderline phenotype accounted for 122 isolates (12.5 %), whereas 562 isolates were fully susceptible and 290 resistant; one remaining isolate had resistance to methicillin and borderline susceptibility to oxacillin. Reductions in the MICs of methicillin and oxacillin in the presence of sulbactam were greater in strains with borderline PRP susceptibility than in fully susceptible or resistant isolates. Over 99 % of fully PRP-susceptible strains, 93 % with borderline susceptibility and 71 % of resistant strains were susceptible to ampicillin/sulbactam. The production of -lactamase, assayed in all strains using nitrocefin as substrate, could be detected without prior induction in 729 strains and after induction only in another 156 strains. With only two exceptions, the -lactamase negative strains were part of the fully PRP-susceptible group of organisms (88 of 562 isolates). Among the borderline isolates, strong -lactamase reactions were encountered with particular frequency, but not in all strains and not exclusively in borderline strains. Although associated with the majority of borderline strains, -lactamase hyperproduction thus did not appear to be an essential feature of the borderline phenotype. The results obtained may have implications for laboratory and clinical medicine, also in the light of recent findings suggesting that other mechanisms besides -lactamase hyperproduction may account for borderline susceptibility to PRPs.     

Selection and properties ofPseudomonas aeruginosa variants resistant to beta-lactam antibiotics

The relation between basal and inducible-lactamase production and resistance to-lactam compounds was studied in five clinicalPseudomonas aemginosa isolates and their corresponding resistant variants selected in the presence of either piperacillin, ceftazidime or aztreonam. In all wild-type strains enzyme levels were barely detectable in the uninduced state and most-lactams, including sulbactam and clavulanic acid, exhibited poor induction potency. Imipenem proved to be the most potent inducer in both these strains and their resistant variants. In the variants selected by either piperacillin or ceftazidime enzyme production amounted to 1.28 units/mg protein of the cell-free supernatants following the addition of-lactams as inducers. Additionally, these variants exhibited the phenomenon of non-specific induction, i.e. the increase of enzyme production by either a complex nutrient medium or by addition of vitamins. Enzyme production in the aztreonam-resistant variants was identical to that in the wild-type strains with a single exception, where the entire derepression of-lactamase production in one of the variants took place. Derepression of the chromosomally mediated enzyme affects the susceptibility to ureidopenicillins more than that to carboxy-penicillins and cephalosporins, whereas the-lactamase-independent resistance results in increased resistance to all-lactams with the single exception of imipenem.     

In vitro susceptibility ofHaemophilus influenzae to cefaclor,cefixime, cefetamet and loracarbef

The susceptibility of 2,212Haemophilus influenzae isolates cultured in UK clinical laboratories in 1991 was determined for four orally-administered -lactam drugs. These isolates included 1,893 ampicillin-susceptible, 191 -lactamase-positive and 128 ampicillin-resistant, -lactamase-negativeHaemophilus influenzae. While 150 (6.8 %) isolates were resistant to cefaclor (MIC 16 mg/l) and 85 (3.8 %) to loracarbef, all were inhibited by 2 mg/l cefetamet and 1 mg/l cefixime and were therefore susceptible to these agents. Ranges and modes of inhibition zone diameters and MICs indicated that the susceptibility of a variable proportion of the 191 -lactamase-positive isolates to cefaclor, loracarbef and cefetamet was reduced compared with the fully susceptible population. In contrast, a major reduction in susceptibility to all four antimicrobial agents was seen among the 128 ampicillin-resistant (MIC 1–64 mg/l) -lactamase-negative isolates such that these accounted for 53 % and 67 % of the total number of organisms resistant to cefaclor and loracarbef respectively. In addition, 23 of 25 isolates inhibited only by 1 mg/l cefetamet and all eight inhibited only by 0.5 mg/l cefixime showed this type of resistance to ampicillin. Results indicate the importance of detecting non--lactamase-mediated resistance to ampicillin and any concomitant diminished susceptibility to other -lactam drugs.     

Evaluation of a disk diffusion method with cefoxitin (30 μg) for detection of methicillin-resistant <Emphasis Type="Italic">Staphylococcus aureus</Emphasis>

The emergence of heterogeneous populations of methicillin-resistant Staphylococcus aureus (MRSA) causes major problems in routine screening for MRSA. In heterogeneous MRSA populations, a proportion of bacterial cells show low-level resistance to oxacillin, with minimal inhibitory concentrations (MICs) of oxacillin ranging between 1 and 100 mg/l, while in homogeneous MRSA populations, the MIC of oxacillin for all cells is >100 mg/l. Routine oxacillin disk diffusion tests often fail to detect heterogeneous MRSA populations. In the present study, a recently proposed disk diffusion method that employs a cephamycin antibiotic (cefoxitin 30 g; BD Sensi-disc, Becton Dickinson, Germany) was evaluated using 155 clinical isolates of S. aureus (73 mecA positive and 82 mecA negative). The results were compared with those of other MRSA screening techniques: a disk diffusion test with oxacillin 1 g and cefoxitin 30 g (BD Sensi-disc; Becton Dickinson), an MRSA latex agglutination test (Denka Seiken, Japan), and an oxacillin screen agar test (6 g/ml; Becton Dickinson). Detection of the mecA gene by polymerase chain reaction was considered the gold standard. The performances of the different methods were determined and compared. The results showed that the cefoxitin disk diffusion test is preferable to the oxacillin disk diffusion method for routine screening to detect MRSA.     

Characterization of interleukin-15 (IL-15) and the IL-15 receptor complex

IL-15 interacts with a heterotrimeric receptor that consists of the and subunits of the IL-2 receptor (IL-2R) as well as a specific, high-affinity IL-15-binding subunit, which is designated IL-15R. Since both the and the subunits of the IL-2R are required for signaling by either IL-2 or IL-15, it is not surprising that these cytokines share many activitiesin vitro. However, the differential expression of these cytokines and the chains of their receptors within various tissues and cell types suggests that IL-2 and IL-15 may perform at least partially distinct physiological functions. The production of IL-15 by macrophages, and possibly other cell types, in response to environmental stimuli and infectious agents suggests that IL-15 may play a role in protective immune responses, allograft rejection, and the pathogenesis of autoimmune diseases.     

Recognition by peptide mapping of three different structural groups of outer membrane protein YOP-1 of Yersinia enterocolitica and Yersinia pseudotuberculosis

The structural relation of YOP-1 of european and american Yersinia enterocolitica serotypes O3, O9, O5, 27, and O8 and O20, respectively, and Y. pseudotuberculosis serotypes I, II, and III was compared by sodium dodecyl sulfate polyacrylamide gel electrophoresis and peptide mapping using Staphylococcus aureus protease V8. Apparent molecular weights of YOP-1 ranged from 206,000 (O3) to approx. 180,000 (O8). According to their respective peptide maps YOP-1 of the european and american Y. enterocolitica serotypes and Y. pseudotuberculosis serotypes could be assigned to three different groups. Evaluation of several isolates of Y. enterocolitica serotypes O3, O9, and O8 by peptide mapping indicated that YOP-1 is conserved within a serotype. However, one serotype O8 isolate differed from the consensus peptide pattern of the other serotype O8 and O20 isolates. The similarity of the peptide patterns of Yersinia serotypes which predominate in certain geographical locations, i. e., european and american Y. enterocolitica serotypes, suggest common evolution of YOP-1 of these serotypes independent of the evolution of the other serotypes.     

Activity of beta-lactamase inhibitor combinations onEscherichia coli isolates exhibiting various patterns of resistance to beta-lactam agents

The efficacy of the clinically available -lactam/-lactamase inhibitor combinations (amoxicillin/clavulanic acid (CA), ticarcillin/CA, amoxicillin/sulbactam, and piperacillin/ tazobactam) was evaluated on 300 amoxicillin-resistantEscherichia coli isolates having the main patterns of -lactam resistance. The patterns, which reflect the production of various -lactamase enzymes, were analyzed by a principal component analysis of susceptibility to 11 -lactam antibiotics or -lactam/-lactamase inhibitor combinations. Sixty-two percent of strains were not very susceptible to penicillins, cephalothin, or any -lactam/-lactamase inhibitor combinations except for piperacillin/tazobactam; these strains may represent high-level broad-spectrum -lactamase (so-called penicillinase) production phenotype or inhibitor-resistant TEM-like enzyme production phenotype. Of the strains, 14.7 % were resistant to amoxicillin and ticarcillin compatible with low-level broad-spectrum -lactamase production phenotype; 5.7 % were cefoxitin resistant and were postulated to present a high-level cephalosporinase production phenotype; and 2.6 % were resistant to cephalothin only, attributable to a low-level cephalosporinase production phenotype. Three percent of strains were intermediate or resistant to cefotaxime and may produce an extended-spectrum -lactamase, and the remaining strains (12 %), resistant to all tested antibiotics except for cefotaxime and piperacillin/tazobactam, were hypothesized to produce both broad-spectrum -lactamase plus cephalosporinase. The minimal inhibitory concentration (MIC) for these phenotype patterns indicated that combinations of CA plus amoxicillin or ticarcillin, or sulbactam plus amoxicillin, restored the activity of penicillins against phenotype 1 strains, whereas these combinations remained inactive against the other phenotype strains. Piperacillin plus tazobactam showed the best in vitro effect against the strains of all resistance phenotypes.     

Application of the polymerase chain reaction to study the M protein(-like) gene family in beta-hemolytic streptococci

Evaluation of homologous regions of published M protein (emm) gene sequences from group A streptococci (GAS; Streptococcus pyogenes) was used to design three primer pairs for polymerase chain reaction (PCR) and three oligonucleotide probe sequences internal to the amplified products. One set of primers and corresponding probe should detect and lead to amplification of emm(-like) genes of virtually every type (all M), another (SOR^-M) should only amplify emm(-like) genes from GAS negative for serum opacity reaction (SOR) and the third (SOR⁺M) should expand only emm(-like) genes from SOR⁺ GAS. Using the all M primer pair for PCR on the genomic DNA from GAS of 29 different M types as well as from a group C and a group G streptococcal isolate, DNA fragments within the expected size range were amplified in every assay. All PCR products reacted with the all M probe. Related sequences were not detected in genomic DNA of an S. agalactiae and an Enterococcus faecalis isolate. Applying the SOR^-M and SOR⁺M primers to identical assays led to mutually exclusive amplification products. The SOR⁺M and SOR⁺M probes hybridized only to their corresponding products. Exceptions to this exclusivity were the SOR⁺ GAS of M types 3, 8, 27, 34, 42, 67, and 69, which consistently reacted only with the SOR⁺M primer/probe set. Analysis of sequence data from the amplified emm(-like) 2, 3, 18, and 19 genes revealed interesting specific features such as conserved gaps in the C-terminal sequence regions from SOR⁺ and the exceptional SOR^- GAS strains. These data indicate the existence of a subgroup of strains among SOR^- GAS and may advance our understanding of phylogenetic relationship between different serotypes of GAS.     

A simple method for measurement of inulin in nanoliter samples using glass capillaries

Summary A simple method using glass capillaries instead of microcuvettes for measurement of inulin in nanoliter samples is given. Inulin was determined with anthron reagent (5 or 10 nl samples +3 l anthron reagent). Glass capillary tubes (o.d.=1 mm, i.d.=0.68 mm, length=150 mm) in which the chemical reaction took place during incubation at 56°C were directly introduced into the optical system of a Zeiss spectrophotometer PMQ II with sphere attachment and objective.Extinction was measured vertically to the axis of the capillary. The changes of extinction of 20 different capillaries with the blank at different positions was only 1.13×10^–3. The exactness of measurement in the concentration range of 100 200 400 750 1500 3000 mg-% inulin was for 5nl/3 l: 19.8 11.0 6.7 4.7 3.0 2.2%. 10nl/3 l: 13.0 8.4 5.1 3.9%.This method of measurement may also be applicable for other colorimetric reactions with nanoliter samples.This work was supported by Fonds zur Förderung der wissenschaftlichen Forschung.     

Assessment of the oxacillin disk screening test for determining Penicillin resistance inStreptococcus pneumoniae

The 1 g oxacillin disk diffusion screening test was performed on 1516 recent clinical isolates ofStreptococcus pneumoniae obtained in a 1994–1995 U.S. surveillance study and the results compared to penicillin MICs determined using a standardized broth microdilution method. The oxacillin disk screening method failed to distinguish penicillin-resistant strains from those that were intermediately susceptible. Furthermore, a high percentage (11.1 %) of penicillin-susceptible strains, for which MICs of penicillin were usually 0.06 or 0.03 g/ml, yielded zone diameters of 19 mm with the oxacillin screen test and thus would have been falsely categorized as being resistant to penicillin.     

In vitro susceptibility of“Campylobacter upsaliensis” to twenty-four antimicrobial agents

The in vitro susceptibility of 41 strains ofCampylobacter upsaliensis to 24 antimicrobial agents was determined using a broth microdilution procedure. Most isolates were susceptible to the fluoroquinolones and -lactam antibiotics tested, but all strains were resistant to trimethoprim (MBCs 128 µg/ml) and teicoplanin (MBCs 32 µg/ml). These agents may be useful in a selective isolation medium forCampylobacter upsaliensis.     

Intrakranielle und intraspinale Blutungen unter Behandlung mit Cumarinderivaten

Summary From 1978–1986, 63 patients (48–79 years) under coumarin derivatives had to be hospitalized neurosurgically because of intrcranial or intraspinal bleedings. This corresponds to a twelvefold increased risk compared to the untreated people. The male/female ratio was 1.5. At the time of the bleeding there was no true indication for anticoagulation in at least 60% of the patients. 80% with coma on admission died. Only for 2/7 with an intraspinal hemorrhage the outcome was better than paraplegic. Women proved to have a better chance of survival. — There is a need for more concise indications for chronic anticoagulation.

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Abkürzungen CT Röntgen-Computertomographie - Cumarine für Cumarinderivate; hier zu 97% Phenprocoumon - ZNS-Blutung nur der Kürze wegen fürbegrifflich korrekt: intrakranielle und intraspinale Blutung Meinem Lehrer, Herrn Dr. med. Czeslaw Andrzejewski, zum 70. Geburtstag gewidmet!     

Antibodies to β2-Glycoprotein-I: Urea Resistance, Binding Specificity, and Association with Thrombosis

The aim of the present study was to evaluate the urea resistance and binding characteristics of anti-2-glycoprotein I (anti-2GPI) antibodies using standard anticardiolipin (aCL) and anti-2GPI enzyme immunosorbent assays (ELISAs). Sera from patients with antiphospholipid syndrome (APS) (n = 22) and non-APS (n = 24), positive in a standard aCL ELISA, were tested in an anti-2GPI ELISA performed in polystyrene-irradiated ELISA plates. Urea resistance aCL and anti-2GPI ELISAs were performed by measuring the ability of antibodies to recognize antigen in the presence of 2 M urea. The serum dilution after urea treatment (D) expressed as a percentage of the serum dilution without urea treatment (D _o) corresponding to the same optical density was defined as residual activity (RA = 100 D/D _o). The higher the RA, the higher the resistance of the antibodies to urea. APS compared to non-APS sera had higher aCL binding (absorbance values ranging between 0.180 and 1.400; median, 0.717 vs 0.120–1.273; median, 0.250, respectively; P < 0.004). Six APS patients' sera had low aCL levels but they expressed RA 30%. Anti-2GPI antibodies were detected in 15 of 22 APS vs 3 of 24 non-APS patients (P < 0.03); RA 30% was detected in 15 of 22 APS vs 1 of 23 non-APS patients (P < 0.004). Using a CL affinity column, antibodies were purified from three APS anti-2GPI negative and three non-APS anti-2GPI-positive patients and tested in a aCL ELISA, using highly purified bovine serum albumin (BSA) as a blocking agent (modified ELISA); reactivity was not detected in two APS and one non-APS sera. On the contrary, the reactivity of the purified antibodies was high when 2GPI was incubated with CL in the ELISA plates; thus some anti-2GPI negative sera from APS patients recognized the CL/2GPI complex, rather than CL or 2GPI alone. In conclusion, anti- 2GPI antibodies are common in the APS patients, but a number of such patients recognize the CL/2GPI complex and not CL or 2GPI. Antibodies to either 2GPI or the CL/2GPI complex derived from APS sera present a high resistance to urea. Anti-2GPI antibodies of low urea resistance exist in a minority of non-APS patients with autoimmune disease.     

Trennung der intestinalen β-Galactosidasen beim lactose-toleranten Erwachsenen durch Ultrazentrifugation im Dichtegradienten

Zusammenfassung Die intestinalen-Galactosidasen von 4 lactose-toleranten, erwachsenen Mitteleuropäern wurden im Saugbiopsie-Gewebe nach Solubilisierung mit Triton X-100 in einem linearen Mannitol-Gradienten (5–20%) auf der Ultrazentrifuge bei 4°C und 44000 U/min getrennt. Bei 12stündiger Zentrifugation fanden sich 3 Fraktionen, von denen die beiden schneller sedimenticrenden Lactose spalten. Alle 3 Fraktionen hydrolysieren p-Nitrophenyl--Galactosid. Die 3 isolierten-Galactosidasen entsprechen wahrscheinlich der neutralen Bürstensaum-Lactase, der sauren lysosomalen Lactase und einer cytoplasmatischen Hetero--Galactosidase.     

Morphologische Untersuchungen an pathogenen und potentiell pathogenen Amoeben der Typen „Entamoeba“ und „Hartmannella-Acanthamoeba“ aus Reptilien

Zusammenfassung Es wurden 114 Stämme von reptilpathogenen und potentiell reptilpathogenen Amoeben vom Typ Hartmannella-Acanthamoeba und der Gattung Entamoeba mit Hilfe der Single Linkage Cluster Analysis (SLCA) auf Grund von morphologischen Merkmalen in fünf Typen und einige Außenseiter aufgegliedert.Dabei zeigte sich, daß die Hartmannellen eine einzige Gruppe bilden, die einen sehr hohen Homogenitätsgrad besitzt. Innerhalb der heterogenen Gattung Entamoeba konnten 4 Typen (1, 2, 3 und 4) definiert werden, von denen Typ 1 und 2 Varianten der gleichen Art sein dürften, während Typ 3 und 4 wahrscheinlich unterschiedliche Arten sind. Der Unterschied zwischen den Untergruppen (1 und 2 und 3 und 4) ist größer als der zwischen den Typen 3 und 4.Eine eindeutige Zuordnung bestimmter Amoebentypen zu bestimmten Reptilgattungen war nicht möglich. Auch ließen sich krankheitserregende Formen nicht von solchen unterscheiden, die nur zu latenten Infektionen führten. Alle Typen konnten als pathogene oder auch als latente Erreger auftreten.

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Morphological study of pathogenic and potentially pathogenic amoebae of the types Entamoeba and Hartmannella-Acanthamoeba from reptiles

Summary A total of 114 strains of reptile pathogenic or potentially pathogenic amoebae of the genus Hartmannella-Acanthamoeba and Entamoeba was partitioned into five types and several outsiders by means of Single Linkage Cluster Analysis (SLCA) based on morphological items. The Hartmannella strains proved to be fairly homogenious whereas within the heterogenious group of Entamoeba strains four types (no. 1, 2, 3, and 4) could be defined.Types 1 and 2 are likely to be varieties of the same species whereas types 3 and 4 are probably distinct species. Difference between subgroups (1, 2) and (3, 4) is greater than that between types 3 and 4. A distinct association of specific amoebae types to specific reptile orders failed. Furthermore, pathogenic forms could not be distinguished from those causing only latent infections. Heavy amoebiasis and latent infections as well were due to all four types.

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Die Arbeit wurde mit Unterstützung der Deutschen Forschungsgemeinschaft durchgeführt.     

Evidence for a direct relationship between mitochondrial genome organization and regeneration ability in hexaploid wheat somatic tissue cultures

Summary Embryogenic and non-embryogenic long-term callus cultures of hexaploid wheat exhibit differences in the organization of their mitochondrial genome. Embryogenic and non-embryogenic fractions of callus cultures initiated from immature embryos of the wheat cultivar Chinese Spring have been isolated and subsequently subcultured. DNA-DNA hybridization experiments using labelled cloned wheat mitochondrial DNA fragments have shown that the mitochondrial DNA organization of embryogenic subcultures derived from embryogenic parts of Chinese Spring calli is closely related to that of the initial Chinese Spring calli, while non-embryogenic subcultures derived from non-embryogenic fragments of Chinese Spring calli exhibit a mitochondrial DNA organization similar to that found in non-embryogenic calli derived from cultivar Aquila. In addition, somatic tissue cultures initiated from three other non-embryogenic wheat cultivars (Talent, Thésée and Capitole) display mitochondrial DNA arrangements similar to those found in cultivar Aquila. These results strongly suggest that, in wheat callus cultures, a particular mitochondrial genome organization is correlated with the ability of cultured cells to regenerate whole plants.Abbreviations mtDNA mitochondrial DNA - ctDNA chloroplast DNA - rRNA ribosomal RNA - kb kilobase pair - cv cultivar - 2,4-D 2,4-dichlorophenoxyacetic acid     

Ampicillin-sulbactam susceptibility testing criteria

In vitro studies in five different medical centers documented the susceptibility of 2,440 consecutive isolates of theEnterobacteriaceae against ampicillin-sulbactam disks of different potencies. For determination of MICs, both 2:1 or 1:1 ratios were used as long as the concentrations of sulbactam at the breakpoints remained the same, i.e. MIC 16/8.0 µg/ml or 8.0/8.0 µg/ml for the susceptible category. Disks containing 10 µg of ampicillin and 10 µg of sulbactam are still to be preferred with interpretive criteria of 15 mm for susceptible and 11 mm for resistant (MIC 64/32 µg/ml or 32/32 µg/ml). The reliability of the disk test actually diminished when the amount of sulbactam in the disk was increased.