Thymine dependent strains of Escherichia coli selected by trimethoprim-sulphamethoxazole therapy

Beta-D-Glucuronidase activity among prototrophic and auxotrophic variants of Escherichia coli and other Enterobacteriaceae commonly implicated in urinary tract infections

Glucuronidase (GUD) activity of 102 prototrophic, 91 cysteine-requiring, and 19 thymidine-requiring strains of Escherichia coli was examined using growth from MacConkey, CLED, and enriched brain heart infusion (BHI) agars. After 24 h incubation, GUD activity was detected in 92%-96% of prototrophic strains and a similar proportion of thymidine-requiring strains with most reactions detectable in shorter incubation periods. GUD activity among strains requiring cysteine was significantly less than that found amongst prototrophic strains. The effects of different sources of inocula were evident in the shorter incubation periods. Other strains of the Enterobacteriaceae and oxidative strains frequently implicated in urinary tract infection were also tested. Here, positive reactions were detected among Citrobacter and Enterobacter spp. and a strain of Klebsiella oxytoca, but only after 24 h incubation. GUD activity was not detected among the oxidative strains tested under the same conditions. Although an incubation time of 24 h is necessary to detect activity in a small number of "slow hydrolyzing" E. coli, the increased sensitivity thus attained compromises the specificity of the test for this organism by simultaneously enhancing detection of the enzyme in other enterobacteria.

Assessment of conventional and commercial methods for identification of clinical isolates of cysteine-requiring strains of Escherichia coli and Klebsiella species

Cysteine-requiring strains of the family Enterobacteriaceae that are auxotrophic for this amino acid because of defects in the sulfur assimilatory pathway account for about 1.5% of urinary tract isolates of Escherichia coli and Klebsiella species. Forty Escherichia and eight Klebsiella cysteine-requiring strains were used to test the ease with which various test systems identified clinical isolates of cysteine auxotrophs. In a preliminary experiment, the growth yield of 10 cysteine-requiring E. coli in 10 solutions of commercially available peptones was in each instance less than that of prototrophic control and showed that these sources of nutrients were suboptimal for these strains. A significant proportion of the cysteine-requiring strains were not adequately identified by growth-dependent tests which used various peptones as a nutrient source. Problems were encountered with all test systems examined, which were as follows: conventional methods; the API 20E, Microbact, and Vitek systems; and two rapid methods for the identification of E. coli, the Rapidec coli and the beta-D-glucuronidase tests. The performance of the test systems was only partly improved when inocula were derived from appropriately supplemented media. However, the problems of the growth-dependent tests were resolved when a cysteine-supplemented suspension was used to inoculate each test system.

Septicemia caused by cysteine-dependent Escherichia coli

A case of septicemia and urinary tract infection caused by cysteine-dependent Escherichia coli in a 70-year-old woman with bilateral staghorn calculi is described. This is the second report of a cysteine-dependent E. coli bacteremia. The bacterium was falsely susceptible to ampicillin and co-trimoxazole when tested on a medium without cysteine supplement.

Cysteine requirements of naturally occurring cysteine auxotrophs of Escherichia coli

The requirements for cysteine of naturally occurring cysteine auxotrophs of Escherichia coli were determined in a defined liquid medium. Maximal growth was obtained in the presence of cysteine concentrations between 20 and 250 mg/l. At concentrations below 20 mg/l growth of the auxotrophs, but not the prototrophic control, was suboptimal in this system. In the presence of cysteine concentrations in excess of 250 mg/l, growth of both auxotrophic and prototrophic E. coli was inhibited with lower growth yields, a decreased specific growth rate and an extended lag phase being observed. These effects were minimised in the presence of 2 mM L-leucine, L-isoleucine and L-valine.

Infection caused by thymidine-requiring, trimethoprim-resistant bacteria

We first noted the appearance of thymidine-requiring, gram-negative bacilli in clinical specimens 2 years ago. Since then we have seen 10 patients colonized or infected with these organisms. These strains do not grow on Mueller-Hinton media, growth on MacConkey agar is variable, and growth in API 20E (Analytab Products) and Enterobacteriaceae-Plus Cards (AutoMicrobic system; Vitek Systems Inc.) is inadequate for reliable identifications. Thymidine-requiring organisms are routinely resistant to sulfonamides and trimethoprim. Infection or colonization is associated with previous sulfamethoxazole-trimethoprim therapy in most cases. Of 10 patients, 1 had septicemia of urinary tract origin, 5 had urinary tract colonization or infection, 2 had wound colonization, and two had colonization of respiratory secretions. Thymidine-requiring, gram-negative bacilli can be pathogens and present potential problems in diagnosis, identification, and susceptibility testing.

Pneumonia caused by a previously undescribed bacterium

A new and as yet unidentified bacterium was isolated from the lung tissue of a cancer patient with bilateral pneumonia. Clinically, the pneumonia was consistent with legionellosis; the organism cultured from the lung grew only on the charcoal-yeast extract agar routinely used for Legionella isolation. Subsequent testing, however, showed the organism to be quite distinct from the known Legionella species in its biochemical, antigenic, and growth characteristics.

Incidence of thymidine-dependent enterococci detected on Mueller-Hinton agar with low thymidine content

It was observed that 10% of urine culture isolates of enterococci tested for antimicrobial susceptibility failed to grow on commercially prepared Mueller-Hinton agar with low levels of thymidine and thymine. All strains could utilize exogenous thymidine and thymine and required only low levels (0.4-microgram disk) to support growth. All thymidine-thymine-requiring strains were resistant to trimethoprim-sulfamethoxazole.

The virulence of trimethoprim-resistant thymine-requiring strains of Salmonella

A thymine-requiring (thy-), trimethoprim-resistant (tmpr) mutant isolated from the faeces of chickens experimentally infected with salmonella typhimurium and treated with mixture of trimethoprim and sulphadiazine was less virulent for chickens than the parent strain and a thy+tmps revertant prepared in vitro from the mutant. The difference in chicken-virulence was more noticeable when the strains were administered orally than when they were administered subcutaneously. All tmpr mutants prepared in vitro from four other salmonella strains were also thy-; those tested were less virulent for chickens and mice than their parent strains. After oral infection, thy- salmonella organisms were found much less commonly in the alimentary tract of chickens then were thy+ organisms. This was especially so in the caeca, the principal site of colonization of both the thy+ and thy- organisms. Relatiely high concentrations of thymine or related compounds were found in the contents of all regions of the alimentary tract of chickens except the caeca; the caeca usually contained low or undetectable concentrations. The thy- salmonella strains would not grow on one brand of briliant green agar because of its deficiency in thymine; their colonial and appearance on other kinds of media used for isolating salmonellae from clinical material was often 'un-salmonella-like'.