Stellan Bengtsson

A new method to determine postantibiotic effect and effects of subinhibitory antibiotic concentrations.

It has been shown that bacteria in a postantibiotic (PA) phase exposed to subinhibitory concentrations (sub-MICs) of antibiotics show a long delay before regrowth. This effect has been named the PA sub-MIC effect (PA SME). In the present study, we have used a new method to demonstrate this phenomenon. A computerized incubator for bacteria, Bioscreen C (Lab Systems, Helsinki, Finland), which incubates the bacteria, measures growth continuously by vertical photometry, processes the data, and provides a printout of the results was used. With this method, one may easily test several antibiotics against different bacteria for PA effects (PAEs), PA SMEs, and SMEs. In this study, the effects of benzylpenicillin against beta-hemolytic streptococci and pneumococci were examined. The bacteria were exposed to 2, 10, or 50x MIC for 2 h, washed and diluted, incubated in the Bioscreen C incubator, and then exposed to 0.1 to 0.9x MIC. The regrowth was monitored for 20 h. The PAE was calculated as the difference in the time required for the exposed and unexposed bacteria to grow to a defined point (A50) on the absorbance curve. A50 was defined as 50% of the maximum absorbance for the control cultures. The PA SMEs were calculated as the difference in the time required for the reexposed cultures and the unexposed controls to reach A50. The PAEs ranged between 0.6 and 3.2 h and varied little with the concentration used for the induction of the PAEs. At 0.2x MIC, the PA SMEs were 2 to 3 h longer than the PAEs. Higher sub-MICs increased this delay before regrowth. Most cultures exposed to sub-MICs alone were only slightly affected compared with the controls.

Bacterial contamination in a modern operating suite. 3. Importance of floor contamination as a source of airborne bacteria.

The redispersal factor for bacteria-carrying particles from a contaminated floor was determined after mopping, blowing and walking activity. Walking gave the highest redispersal factor, 3.5 X 10(-3) m-1, which was three times higher than for blowing and 17 times higher than for mopping. The mean die-away rate for the bacteria-carrying particles used was 1.9/h without ventilation and 14.3/h with ventilation. It was calculated that in the operating rooms less than 15% of the bacteria found in the air were redispersed floor bacteria.

PURIFICATION AND CHEMICAL ANALYSIS OF THE ERYTHROCYTE RECEPTOR FOR HEMAGGLUTINATING ENTEROVIRUSES.

Abstract The receptor for hemagglutinating enteroviruses on human erythrocytes was solubilized by butanol extraction in the presence of high concentration of CaCl2. The soluble material was further purified by precipitation of lipids with polyanions, gel filtration on Sephadex G-200, and isodensity centrifugation in CsCl. The soluble receptor which was purified 100 times from the membrane suspension had a buoyant density of 1.18, a S20o,w of 14 Svedberg units, and contained approximately 31% lipid, 60% protein, and 9% carbohydrate. The greater part of the lipid is probably a neutral glycolipid, but phospholipids and cholesterol were also present. A deoxypolynucleotide material containing the bases adenine, thymine, cytosine, and guanine in the ratios 1:1:0.5:0.9 is firmly attached to the receptor structure. Eight hemagglutinating units of ECHO 7, ECHO 19, or Coxsackie B3 virus are inhibited by 0.1–0.3 μg of the purified receptor. The effect against myxoviruses is 1000 times lower. The infectivity of hemagglutinating enteroviruses is irreversibly inactivated by the purified receptor, which does not affect the infectivity of nonhemagglutinating enteroviruses.

Interaction of enteroviruses with receptors from erythrocytes and host cells

Abstract Receptors for ECHO viruses 7, 11, 19, and Coxsackie B3 were found only in the ghosts of human red cells, not in ghosts from other species. The receptor was destroyed by proteolytic enzymes, a fact suggesting that it may be a protein. The attachment of virus to receptor occurred in two stages: the first was a non-temperature-dependent attachment which was spontaneously reversible at 37° for ECHO 11 and ECHO 19 and reversible after different treatments for ECHO 7 and Coxsackie B3 virus. In some cases this was followed by a second stage in which the complex became increasingly resistant to attack by chymotrypsin. Intact monkey kidney and HeLa cells showed a similar two-step interaction between virus and cells. With inhibitory material from disintegrated cells and subcellular fractions, only the first attachment step could be demonstrated.

Countercurrent distribution of poliovirus type 1

Abstract Differences in the countercurrent distribution pattern in an aqueous polymer phase system are demonstrated for various strains of poliovirus type 1. The attenuated strains L Sc 2 ab and Baylor Att.-1 have partition coefficients of 0.2–0.4 whereas the CHAT strains and a virulent strain have partition coefficients of ≈4. Other strains tested were heterogeneous. The distribution pattern for homogeneous strains, which is genetically determined, is shown to be correlated to the m marker, since the strains with a low partition coefficient are m − and those with a high partition coefficient are m + . m + mutants from the m − strain L Sc 2 ab were shown to have a high partition co-efficient. The d character may also be correlated to the distribution pattern whereas other markers tested showed no evidence of correlation. The countercurrent fractionation can be used to eliminate m + mutants from virus pools.

THE BASIS FOR THE INTERACTION BETWEEN ATTENUATED POLIOVIRUS AND POLYIONS.

Abstract Thin-layer electrophoresis on Sephadex G-25 of m + and m − strains of poliovirus type 1 showed the isoelectric point of both strains to lie between pH 7.4 and 7.6. The interaction of these virus strains with polyions was studied by chromatography on the anion-exchanger DEAE-Sephadex and the cation-exchanger Sephadex-sulfate using different buffers as eluting agents. The m − strain adsorbed to the cation exchanger at a pH below, but not at or above, the isoelectric point and to the anion exchanger at a pH below and above, but less efficiently at, the isoelectric point. The reason for this effect may be that the positively charged DEAE-Sephadex attached anions, which, when complexed, adsorbed the positively charged virus at a pH below the isoelectric point. The m + strain did not adsorb to the ion exchangers except to DEAE-Sephadex in borate buffers above the isoelectric point. The salt concentration and the type of buffer used influenced the adsorption of the m − strains to the polyions. Both strains of poliovirus could also be quantitatively separated by ultracentrifugation in gradients of DEAE-dextran or Dextran sulfate. The m − strain had a lower rate of sedimentation than the m + strain under conditions favoring adsorption to the polyion. DEAE-dextran abolished the inhibitory effect of acid overlay on the plaque forming capacity of the m − variant in monkey kidney cells and inhibited the plaque formation of both m − and m + variants of the strain L Sc 2ab in HeLa cells, but not in monkey kidney cells. This effect may be due to the bicarbonate buffer.

Gel filtration of nucleic acids on pearl-condensed agarose

Abstract The use of gel filtration to separate molecules with molecular weights above 2 · 105 was made possible by the introduction of granulated agar gels by Polson (1961) . These gels might allow separation of high molecular nucleic acids according to size. An artificial mixture of T2 DNA and E. coli RNA has been separated on granulated 1,5% agarose gel ( Boman and Hjerten, 1962 ). The low flow rates in gels with agar concentrations less than 3% made them difficult to use but this was overcome by the introduction of pearl-condensed agar or agarose ( Bengtsson and Philipson, 1964 , Hjerten, 1964 ). The present study describes gel filtration of nucleic acids from KB cells and poliovirus RNA on pearl-condensed 2% agarose. It is also shown that the composition of the buffer influences the elution pattern of poliovirus RNA.

Genetic Markers Associated with Virulence of Foot-and-Mouth Disease Virus.∗

Summary Attenuated strains of FMDV types A4, C and O3 are more sensitive to heat and acid inactivation than virulent strains. The attenuated strains of FMDV type C and O3 are inhibited by dextran sulphate which does not affect the other strains.

In Vitro Aminoglycoside Resistance of Gram-negative Bacilli and Staphylococci Isolated from Blood in Sweden 1980–1984

The in vitro susceptibility to gentamicin, tobramycin, amikacin and netilmicin in septicaemia isolates was followed during 1980-1984 in 6-8 Swedish laboratories. The bacterial distribution was similar over the years and was dominated by Escherichia coli and staphylococci. Resistance to gentamicin was found in 2.3-3.6%, to tobramycin in 1.4-3.4%, to amikacin and netilmicin in 0.5-0.9%. Production of aminoglycoside modifying enzymes was observed among resistant strains.

Airborne contamination and postoperative infection after total hip replacement

The results of 163 hip replacements at the Uppsala University Hospital are presented. Deep infection occurred in ten cases and was caused by Staphylococcus aureus in four early or intermediate infections and by anaerobes in four late infections. The remaining two infections (both of which were late) were probably associated with Staphylococcus albus--in one case possibly also with alpha streptococci. Two superficial infections not affecting the operative result were caused by Staphylococcus aureus and betahaemolytic streptococci. The results of environmental analyses of staphylococci and the total number of bacteria in the air during 77 operations did not indicate that airborne infection is a major cause of postoperative infections--there was no difference between the number of bacteria found in the air during operations after which infection occurred and uninfected operations, and the use of special zonal ventilation with high rates of air exchange in the operating area had no effect on the infection frequency.