- Volume 6, Issue 1, 1973

Gram-negative bacteria, harbouring R factors that confer resistance to sulphonamides, mutate to trimethoprim resistance at an appreciable rate and are then able to grow in the presence of both trimethoprim and a sulphonamide.

All trimethoprim-resistant organisms isolated in this study were thymine requiring, and it is suggested that the frequency of isolation of organisms resistant to trimethoprim, or combinations of trimethoprim and a sulphonamide, may be increased if adequate thymine or thymidine is included in the media used for their isolation.

The virulence of influenza-virus strains for Swiss mice was compared with the amount of interferon induced by them in the lungs of the mice and with their sensitivity to inhibition by interferon. The virus strains examined, which included a number of temperature sensitive (ts) mutants, were graded for virulence by their ability to cause lung lesions and to kill mice after intranasal infection. The amount of interferon produced was found to be related to virus growth; the more virulent virus strains grew to higher titres and produced the most interferon. All the strains proved to be equally sensitive to interferon, by three different in-vitro techniques. It was concluded that the virulence of influenza viruses for the mouse is determined by factors other than interferon.

Observations by phase-contrast microscopy upon the swarm of Proteus mirabilis lead to the conclusion that its development is in two stages; at first, as an open mesh of bacterial strands, along which bodies of swarmers migrate in any direction; later, when these meshes have filled up to give a continuous film of bacteria, expansion continues by the growth of the whole body, in the manner of a Medusa-head colony. All parts are in motion, and masses of several hundred units move about within the swarm. The total effect is a general expansion, but the main motion of swarmers at the edges is at right-angles to the direction in which the swarm is extending.

Counts of antigen-reactive cells, obtained by means of the Jerne plaque and rosette techniques, in mice primed with sheep red cells, showed an initial fall after challenge with sheep red cells. To obtain this result, the challenge dose had to be relatively large and to be given at a sufficient interval of time after priming. The reduction in the numbers of antigen-reactive cells is mediated by a soluble substance released in consequence of the interaction of antigen and antigen-reactive cells. The activity of this substance is not restricted to the specific system that led to its formation, since a fall in the count of antigen-reactive cells of a different specificity could be demonstrated in mice primed with two antigens. Though not characterised, the substance responsible for this effect is probably a “lymphokine” possessing cytotoxic activity.

Extraction with 0.4 per cent. rivanol, at pH 9.0, provides a rapid and economical method of removing non-specific inhibitors of rubella virus HA from human serum without loss of specific antibody; natural agglutinins for pigeon erythrocytes are largely removed. Serum HI antibody titres are comparable to those obtained with the dextran sulphate-CaCl2 extraction method.

Possible sources of error in the HI test due to the method of serum extraction are discussed.

Ascending urinary-tract infection with Proteus vulgaris was established in rabbits. The bacteria were converted to L-phase organisms in vivo by treatment with penicillin. L-phase organisms were eliminated without further treatment from 9 per cent. In animals in which osmotic diuresis was established, L-phase organisms were eliminated from 59 per cent. In those treated with methacycline the elimination rate was 79 per cent. without and 90 per cent. with diuresis. A greater proportion of L-phase organisms survived in the kidney tissue than in the urine of animals treated by osmotic diuresis.

Eleven β-lactamases were tested for their ability to destroy the currently available β-lactam antibiotics. The biochemical activities of the enzymes against cephaloridine and benzylpenicillin were compared by iodometric assay. Their biological activity was tested by mixing various amounts of enzymes and of 13 different β-lactam antibiotic preparations and assaying the residual antibiotic by an agar-diffusion method, with Sarcina lutea as the test organism.

All the enzymes destroyed 500 µg per ml of benzylpenicillin and the more potent ones also destroyed “penicillinase-resistant” penicillins and cephalosporins. Crude enzyme extracts from a strain of Enterobacter aerogenes and of Klebsiella aerogenes compared favourably with the bacillus enzymes in their action on cephalosporins. Suitable β-lactamases can therefore be used to destroy all the available β-lactam antibiotics in specimens from patients, either in blood cultures or to allow the assay of other antibiotics in patients being treated concurrently with both.

Examination of bovine serum samples submitted from the field in connexion with the Brucellosis Eradication Scheme showed the value of immunodiffusion tests made with a diethyl ether-water extract of a smooth virulent strain of Brucella abortus.

Sera from cattle vaccinated with the killed strain-45/20 adjuvant vaccine frequently gave appreciable reactions when examined by standard tests, namely the serum agglutination, complement fixation and Rose Bengal plate tests. When these reactions were weak, the immunodiffusion test usually gave one or more precipitation lines, but these were formed only against sub-surface antigens. When these reactions were strong enough to suggest natural infection, a line against the smooth surface lipopolysaccharide antigen was present in addition. Infrequently, a similar line occurred in the absence of significant reactions to the standard tests.

Sera from cattle vaccinated with living strain 19 less frequently gave appreciable reactions in the standard tests. When the reactions were weak, immunoprecipitation lines were often formed against the sub-surface antigens but seldom against the lipopolysaccharide; when they were stronger, a line against the lipopolysaccharide was usually formed in addition.

Sera from unvaccinated cattle usually gave negative results in all tests, but several that gave marked reactions in the standard tests also gave precipitation lines with the sub-surface antigens and the lipopolysaccharide antigen. One sample gave two lines with sub-surface antigens, but was otherwise negative.

In immunodiffusion tests with sodium dodecyl sulphate extracts of the rough strain 45/20 a single precipitation arc was formed with some but not all of the sera that gave marked reactions in the standard tests.

The MIC of carbenicillin for 111 strains of Pseudomonas aeruginosa isolated from the sputum of patients with chronic respiratory infections was estimated. For 72 strains it corresponded to that reported for strains isolated from nonrespiratory sites (25−> 100 µg per ml), but for 39 strains it ranged from 6 µg per ml to <0.7 µg per ml.

About half of the strains were typed serologically, by bacteriophages and by pyocine production. No evidence for cross-infection between the patients was found, nor was there any correlation between sensitivity to carbenicillin and any particular type of organism.

There was no evidence that strains with an abnormally low MIC were more virulent in the respiratory tract than were strains with an “ordinary” MIC; nor did it appear that coexistence with enterobacteria in the respiratory tract affected the carbenicillin resistance of P. aeruginosa.

A large collection of group-A streptococci was examined for the production of opacity in horse serum and for the presence of M and T antigens. Opacity production is a constant character of certain M types and is consistently absent from the rest. Testing for opacity production is a valuable addition to the serological typing procedure especially if it is carried out first. It has proved useful in (1) reducing the number of tests with M antisera that have to be set up and (2) drawing attention to errors in M typing due to the presence of cross-reacting precipitins in typing sera.

The serological specificity of the opacity factor corresponds to that of the M antigen. Inhibition of opacity production therefore provides a useful alternative method of typing strains that form the opacity factor. M antisera for opacity-producing serotypes are often of poor quality and difficult to prepare. In these circumstances, the opacity inhibition test has proved useful for preliminary identification of new M types of streptococci.

We studied 148 strains of Pseudomonas aeruginosa isolated from nonbacteriaemic infections and healthy carriers (group I) and 50 strains isolated from patients with bacteriaemia (group II). More than 90 per cent. of the strains in both groups produced lipase, esterase, protease, and a haemolysin most active on ox and rabbit erythrocytes. Between 60 and 90 per cent. gave a positive egg-yolk reaction, produced nuclease (DNAase and RNAase), lecithinase, elastase, staphylolytic enzyme, and another haemolysin most active on sheep and horse erythrocytes. No significant difference between the two groups in the formation of any of these factors was found. The strains of the two groups showed more than 100 different phage-typing patterns when tested with a set of 22 phages; only a few strains were untypable and no phage-typing pattern predominated. About one-third of all the strains belonged to Habs′ serotype 6 and the rest of the strains were rather evenly distributed between the other serotypes without any difference between the two groups.

Epidemiological and clinical observations on streptococcal infections in 156 Egyptian school children aged 6 to 12 yr were obtained by prospective bacteriological, serological and clinical surveys from 1967 to 1970.

The yearly recovery rate of group-A streptococci from the throat varied from 13 per cent. to 24 per cent. The seasonal variations showed a peak during the late autumn and winter and a minimal rate in the summer months. The carrier rate in each of four school grades varied independently, an indication that the classroom, more than any other area of the school, is a primary locus of exposure and transmission.

The prevalence of the group-A streptococcal carrier state was assessed from the long-term observation of the study population. In 7 per cent. of the children, more than 25 per cent. of the monthly throat cultures were positive in a 3-yr period. Thirteen per cent. of the children had fewer than 5 per cent. of throat cultures positive. In most of the children, however, there were marked shifts in the percentage of positive monthly throat cultures from one year to the next.

The attack rate of streptococcal infections, defined as a throat culture positive for group-A streptococci with a concomitant rise of ASO, was 6 per 1000 per week.

Mucoid colonial forms of Pseudomonas aeruginosa were obtained by subculture from areas of “sliming” around zones of lysis on phage-typing plates. These mucoid forms were not spontaneous variants, but depended on the presence of phage in the lytic cycle for their initiation and continued existence. The properties of naturally occurring and phage-induced mucoid forms were similar. The mucoid colonial form was observed frequently only in patients with chronic disease of the respiratory tract.

Fifty-seven of 131 strains of Vibrio cholerae that were isolated in Calcutta durin an outbreak of cholera in April and May 1970 fermented lactose after overnight incubation in Andrade’s peptone water and in TSI medium. All the rapid fermenters of lactose belonged to the classical biotype, to serotype O-I, Inaba, and to phage-type 1.

V. cholerae strains are usually non-fermenters or late fermenters of lactose. A deviation from this previously accepted finding may cause error in identification. The inclusion of the lysine-decarboxylase and oxidase tests helps to overcome this difficulty.

Vibrio parahaemolyticus infection is generally believed to follow ingestion of heavily contaminated food, the commonest source being raw sea-fish. In the present communication we report a laboratory-acquired infection with this organism in which clinical disease probably followed the ingestion of only a small number of organisms.

Human embryonic tracheal organ cultures have been frozen to — 196°C and thawed without any apparent loss of ciliary activity or susceptibility to the growth of human influenza virus. Optimal preservation was obtained by freezing in the presence of 25 per cent. dimethylsulphoxide at a cooling rate of 0.3°C per min. This extremely simple technique facilitates the storage of tracheal organ cultures for experimental use.

A crude extract of the albumen gland of the edible snail, Helix pomatia, was used for the routine identification of group-C streptococci. The reaction is specific; all of the 338 group-C strains reacted with the extract but none of either 3560 group-A or 262 group-G strains. The test may be performed by slide-agglutination with trypsinised cells, or by capillary precipitation or agar-gel immunodiffusion tests with formamide extracts of streptococci.