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Volume 6,
Issue 4,
1973
Volume 6, Issue 4, 1973
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The Zonation Phenomenon And Structure Of The Swarm Colony In Proteus Mirabilis
More LessSUMMARYZonation of the swarm colonies of six strains of Proteus mirabilis did not appear to be caused by an alternationof swarming and sessile phases. The margin was constantly composed of active swarmers; and, although a thickened ring could be caused by a check, it was more often due to the rapid advance of the edge, leaving a thinner area which permitted a new, interior edge to form behind it. Motility ceased when the bacteria became crowded; the change to the non-swarming phase took place later. The structure of the swarm colonies was lobate, and the zonation of the separate lobes was synchronised. Reduction of nutrients in the medium reduced the speed of advance of the swarm, but the timing of the zone formation was unaltered. Lobes, at the edges of old colonies, in which swarming had ceased, also showed synchronised zonation. These appearances are suggestive of genetic programming.
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An Immunodiffusion Analysis Of Myco-Bacterium Lepraemurium Marchoux And Sorel
More LessSUMMARYSix strains of Mycobacterium lepraemurium Marchoux and Sorel have been subjected to immunodiffusion analysis. They were found to be identical with each other and to possess 12 demonstrable antigenic constituents. Five of these were antigens common to all mycobacteria, two were shared only with slow-growing mycobacterial species, three were amongst those antigens hitherto considered specific to M. avium and two were specific to M. lepraemurium alone. Thus it was concluded that M. lepraemurium is a member of the slow-growing group of mycobacteria with an exceptionally close serological relationship to M. avium.
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Interactions Between Fusidic Acid And Penicillins
More LessSUMMARYInteractions were studied between fusidic acid and each of several penicillins in their effect on both penicillinase-positive and penicillinase-negative strains of Staphylococcus aureus. Estimation of the number of staphylococci that survived overnight exposure to the antibiotics, alone and in combination, showed three types of interaction.
In the commonest type, exhibited by more than half the penicillinase-positive and almost all the penicillinase-negative strains, there was two-way antagonism; more staphylococci survived overnight incubation in the presence of fusidic acid plus a penicillin than in the presence of either agent alone. Further evidence that penicillin antagonised the action of fusidic acid against these strains was provided by scanning electron microscopy, which revealed that the cell-wall collapse that followed the action of fusidic acid was inhibited by the presence of a penicillin.
In the second type of interaction there was one-way antagonism of penicillin by fusidic acid; least survivors were recovered after incubation with a penicillin alone, more from the mixture and most from fusidic acid alone.
The remaining strains showed “indifference”, in that the effect of the more bactericidal agent—which against some strains was fusidic acid—prevailed. Even when the effect of penicillin on the bulk of the bacterial population was antagonised, the presence of penicillin always prevented the emergence of fusidic acid-resistant mutants.
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R Factors In Enterobacteriaceae Causing Urinary-Tract Infection In General Practice In 1962–63 And 1968–69
More LessSUMMARYAntibiotic-resistance patterns of Escherichia coli causing urinary-tract infections contracted outside hospital were studied in 1962–63 and 1968–69. There was a slight but statistically significant increase in resistance over this period. The resistance was, in most instances, transferable.
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R Factors In Enterobacteriaceae Causing Asymptomatic Bacteriuria Of Pregnancy
More LessSUMMARYThe frequency of antibiotic resistance in coliform bacilli causing asymptomatic bacteriuria of pregnancy in two hospitals in West London was studied. Approximately one-fifth of the strains were resistant to at least one antibiotic. No increase in resistance was shown when these figures were compared with a previous study of symptomatic bacteriuria made in 1968–69, although both studies show an increase compared with figures obtained in 1962–63. In one-third of strains, resistance was shown to be mediated by R factors.
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Chemotherapy And Antibiotic-Resistance Transfer Between Enterobacteria In The Human Gastro-Intestinal Tract
More LessSUMMARYThe transfer of R factors in the human gastro-intestinal tract and the conditions under which it occurs was studied in healthy persons, who ingested derivatives of Escherichia coli containing chromosomal and R-factor-mediated resistance determinants that had been prepared from strains isolated from their own faeces. The experiments were designed to obtain presumptive evidence of survival and transfer of R factors by studying resistance-marker patterns of organisms isolated from the faeces. To prove conclusively that R-factor transfer had occurred and that the observed marker patterns were not fortuitous, studies of resistance-marker patterns in one of these subjects were supplemented by further detailed investigations including serological and molecular studies, which will be described in the succeeding paper.
An incidental finding was a significant positive correlation between the mean number of antibiotic-resistance determinants in resistant organisms and the age of an individual, although these studies were limited to a small and highly selected group of subjects.
No evidence of R-factor transfer was obtained in the absence of chemotherapy in four subjects, even though the plasmids concerned could be freely transferred in vitro from the potential donors to a wide range of faecal organisms, including the genetically marked ingested potential recipients. However, treatment of three subjects with a five-day course of a relevant antibiotic after ingestion of R factor bearing organisms led to the appearance in the faeces of large numbers of resistant coliform bacilli with antibiotic-resistance patterns consistent with transfer of the R factor either to an ingested potential recipient organism (one subject) or to endogenous strains of E. coli (two subjects).
Chemotherapy greatly prolonged the persistence of ingested R factors in the faecal flora long after the antibiotics were withdrawn and caused the number of R-factor bearing organisms in the faeces to increase. No evidence was obtained in limited studies of fragmentation or loss of R factors from ingested E. coli.
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Studies On The Nature Of Plasmids Arising From Conjugation In The Human Gastro-Intestinal Tract
More LessSUMMARYIn the studies described in the preceding paper, circumstantial evidence was found for transfer of antibiotic resistance from an ingested strain of Escherichia coli carrying an R factor, R-1, which determined resistance to ampicillin (A), chloramphenicol (C), kanamycin (K), streptomycin (S) and sulphonamide (Su). Resistant organisms isolated from the faeces of a single individual were examined in detail to prove conclusively that the DNA of the ingested plasmid had transferred to other organisms.
The O antigens of the resistant faecal isolates were the same as those of two organisms present before the beginning of the experiment, and these strains were resistant to all the determinants of R-1. The levels of resistance of the isolates to these antibiotics were quantitatively consistent with transfer of the plasmid R-1; and the β-lactamase conferring ampicillin resistance was of the same antigenic type.
The predominant resistant organism isolated from the faeces transferred resistance to ACKSSu to laboratory recipients, and plasmid DNA isolated from such strains had the same molecular weight as R-1 and gave 100 per cent. DNA hybridisation with DNA from R-1. Small populations of another strain were also isolated which transferred resistance to ACKSSu and to tetracycline, and this plasmid contained all of the DNA base sequence of R-1 plus additional DNA. The serotype of this strain was the same as that of a strain already resistant to tetracycline before the beginning of the experiment.
These results prove that R-factor transfer must have occurred during or after antibiotic therapy and illustrates possible dangers of chemotherapy.
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Growth Temperatures, Virulence, Survival, And Nutrition Of Leptospires *
More LessSUMMARYSome virulent and avirulent pathogenic leptospires and saprophytic leptospires grew continuously at 37°C, while others did not; variations amongst strains of the same serotype occurred and there was no correlation with virulence.
Each of 21 strains survived 24 months’ storage in semisolid polysorbate medium (P-80 medium) without intervening subculture and one strain tested after 52 months was still viable and fully virulent. Semisolid and liquid P-80 media had a shelf-life of at least 36 and 12 months respectively at 23–25°C.
One per cent. albumin was shown to favour the survival of leptospires.
In experiments with modified or incomplete semisolid P-80 medium, various leptospiral strains grew and survived when polysorbate, 60,40, or 20 were substituted for polysorbate 80, and when polysorbate, NH4Cl, thiamine, or vitamin B12 were omitted. However, the omission of any polysorbate orof vitamin B12 had a strikingly adverse effect on growth. These modified media were used to culture blood infected withpomona (HCE). Continuous subculture eventually failed to produce readily-detectable macroscopic growth in the absence of either polysorbate, NH4Cl or thiamine, but continuous subculture in the absence of vitamin B12 was successful. Nutrient-depleted P-80 media were still capable of maintaining viability and a low level of growth, probably because of the micro-nutrients in the one per cent. albumin component. Continuous subculture of pomona (MU) from hamster liver was successful regardless of the presence of vitamin B12 in the medium, but vitamin B12 was essential for similar subculture of the same organism isolated from kidney.
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Dialysis-Culture Production Of Vibrio Cholerae Exotoxin And Its Precipitation With Zinc Acetate
More LessSUMMARYMethods are described for the dialysis culture and subsequent concentration and purification of Vibrio cholerae enterotoxin, or its formolised toxoid (anatoxin), by precipitation with zinc acetate. The techniques are simple and rapid, and are likely to be suitable for research and large-scale production. An 11-fold increase in specific activity, a 67 per cent. yield, and a 40-fold concentration were achieved in a single precipitation step. Immuno-electrophoretic data indicate that the purified toxin may be a complex of two different antigenic components.
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INFANTILE ENTERITIS IN DUBLIN CAUSED BY ESCHERICHIA COLI O142
More LessSUMMARYFaeces or rectal swabs were taken from 460 patients under the age of 2 yr on admission to a Dublin paediatric hospital. Of the 460, 70 had diarrhoea and 390 were without diarrhoea on admission. The results of bacteriological examination of the specimens gave an indication of the range of enteropathogenic organisms causing disease in the community served by the hospital.
Of the 390 patients admitted without diarrhoea, 54 subsequently developed it; and of the 70 admitted with diarrhoea, 14 developed a second attack after recovering from the first. Examination of specimens from the 68 infants who developed diarrhoea after admission to hospital indicated the degree and pattern of cross-infection within the hospital. The importance of Escherichia coli 0142:K86:H6 as a cause of diarrhoea during the survey was clearly demonstrated.
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GENETIC ANALYSIS OF METHICILLIN-RESISTANT STRAINS OF STAPHYLOCOCCUS AUREUS; EVIDENCE FOR THEIR EVOLUTION FROM A SINGLE CLONE
More LessSUMMARYMethicillin-resistant staphylococci are characterised by: (a) chromosomal resistance to streptomycin, (b) tetracycline resistance determined by a stable plasmid, (c) production of orange pigment, (d) a similar degree of survival on glass. We consider that all or almost all isolates of methicillin-resistant staphylococci have evolved from a single clone. If so, plasmids determining a variety of antibiotic resistances (penicillinase, penicillinase/fusidic acid, erythromycin, erythromycin/lincomycin, neomycin and chloramphenicol) have probably been acquired in recent years by their transfer from other strains. One isolate (no. 11164) has probably acquired novobiocin resistance by mutation and lost the genes determining pigment and survival.
Strain no. 13136 contains a “penicillinase plasmid” with a molecular weight of about 20 million daltons and a plasmid specifying high-level resistance to tetracycline (MIC 200 μg per ml) of molecular weight about 2.9 million daltons. The latter plasmid was also present in other methicillin-resistant strains. After storage of strain no. 13136, some colonies were resistant to only low levels of tetracycline (MIC 2.5 μg per ml). In these derivatives, the “tetracycline plasmid” of molecular weight 2.9 million daltons was replaced by a plasmid of 2.2 million daltons.
Although methicillin resistance can be lost irreversibly from strains nos. 13136, 2273 and 9463, no discrete CCC-DNA component corresponding to a plasmid determining this resistance was resolved in any of them.
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STUDIES ON THE HISTAMINE SENSITISATION PRODUCED IN MICE BY CORYNEBACTERIUM PARVUM
More LessSUMMARYC. parvum resembled Bord. pertussis in being able to sensitise mice to histamine. Strains of mice that were strongly sensitised to histamine by Bord. pertussis were also strongly sensitised by C. parvum, whereas mouse strains that did not respond to Bord. pertussis were refractory to sensitisation by C. parvum. Other similarities between sensitisation produced by the two organisms included a dependence on mouse age and a tendency in some strains to produce a bimodal response to histamine following sensitisation. Both C. parvum and Bord. pertussis were capable of sensitising mice of one strain to serotonin, but sensitisation of another mouse strain to serotonin was produced only by Bord. pertussis and not by C. parvum.
Unlike Bord. pertussis, C. parvum did not augment anaphylaxis to heterologous antigens, nor did it produce leucocytosis and lymphocytosis in mice. Preliminary studies of the stability of the sensitising agent suggest that it is chemically different from the histamine-sensitising factor of Bord. pertussis.
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THE SEROLOGICAL RESPONSE TO ASPERGILLUS FUMI-GATUS IN EXPERIMENTAL MYCOTIC ABORTION IN SHEEP
More LessSUMMARYThe serological response to Aspergillus fumigatus in experimental mycotic abortion in sheep was examined. Infected ewes developed precipitins and complement-fixing antibodies to A. fumigatus mycelial antigens following the inoculation of spores. A gradual increase in complexity of the precipitation patterns given by immunodiffusion tests extended over several months and overlapped the times of abortion, but precipitins to individual A. fumigatus antigens could not be specifically associated with placentitis or abortion. Following abortion, the precipitation patterns decreased in complexity, although in most cases some activity persisted. Complement-fixing antibodies also developed before abortion and erratically declined in the post-abortion period.
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THE SENSITIVITY OF BRUCELLA ABORTUS TO CHEMOTHERAPEUTIC AGENTS
More LessSUMMARYThe sensitivity of 25 strains of Brucella abortus, comprising strains of the biotypes commonly encountered in the United Kingdom, was determined to six antibiotics and co-trimoxazole (a combination of sulphamethoxasole and trimethoprim) by means of four methods, including a modification of the ditchdiffusion method. The ditch method was shown to be satisfactory for routine sensitivity testing of brucellae. The strains were almost uniformly sensitive to tetracycline, and the MIC values were between four and eight times less than the expected peak plasma levels. The strains were not as sensitive to streptomycin as those previously reported by Spink (1956), and the MIC values to this antibiotic were distributed over a wider range of concentrations than those of gentamicin or kanamycin. A comparison of MIC, peak plasma levels and plasma half-lives suggest that gentamicin and kanamycin may be more effective than streptomycin in the treatment of brucellosis when used in combination with tetracycline.
The failure of ampicillin in the treatment of brucellosis accords with the finding that of 25 strains 17 had MIC values in excess of the peak plasma levels. An experiment with carbenicillin indicated that it was unlikely to be effective in the treatment of B. abortus infection.
Synergism between sulphamethoxazole and trimethoprim was demonstrated in vitro on all strains examined. The strains were less sensitive to trimethoprim than sulphamethoxazole, indicating that a high plasma value for trimethoprim should be maintained, but further clinical trials of co-trimoxazole are necessary.
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PYOCIN-SENSITIVITY TESTING AS A MEANS OF TYPING PSEUDOMONAS AERUGINOSA
More LessSUMMARYPyocin-sensitivity testing is a useful adjunct to a routine pyocin-typing scheme for Pseudomonas aeruginosa, permitting the subdivision of many groups of strains that belong to the same pyocin type, and also reducing the frequency of untypable strains.
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CYTOPATHIC FACTORS IN BACTERIA-FREE LYSATES OF ESCHERICHIA COLI
More LessSUMMARYA factor (CPFI) that caused a cytopathic effect on cultures of pig-thyroid cells was detected in bacteria-free lysates of K88-positive porcine enteropathogenic strains of Escherichia coli. CPFI was produced only by strains that synthesised heat-labile enterotoxin (LT) and was present in lysates that contained LT but was not associated with heat-stable enterotoxin, K88 antigens or haemolytic substances. CPFI was transmitted with LT from a donor to recipient strains; the factor was heat labile, non-dialysable, precipitated by ammonium sulphate and excluded from Sephadex G-200. CPFI was neutralised by some adult pig sera. Another factor (CPFII) that caused a morphologically different cytopathic effect on cultures of pig-thyroid cells was detected in bacteria-free lysates of six apparently non-pathogenic strains of E. coli isolated from pigs. CPFII was not related to the above products of E. coli and was not neutralised by pig sera. It is suggested that CPFI is similar to LT and that the cytopathic effect of CPFI could provide a simple, sensitive assay that may be of value in the characterisation of LT.
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