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At least 973 records · Page 54Linked to original sources
PubMed1984

Differentiation of gram negative rods other than Enterobacteriaceae and Vibrionaceae by a micromethod for determination of carbon substrate assimilation.

The assimilation techniques described for taxonomic study are unsuitable for routine diagnosis because of the need for purification and standardization of substrates, the great quantity of medium consumed and difficulties in interpreting the results. A standardized micromethod (API Strip) for the study of carbon substrate assimilation by bacteria has recently been described (Zbl. Bakt. Hyg., I. Abt. Orig. A 255 (1983) 479-488). The prototype gallery used consisted of two strips of 32 microtubes each containing dehydrated carbon substrate. Each strip contained 30 tests plus positive and negative controls. The suspension medium was a synthetic semi-gel. A total of 1046 strains of Gram-negative rods representing 41 species belonging to the genera Pseudomonas, Alcaligenes, Moraxella, Acinetobacter, Flavobacterium and to the EF4 group were tested (Tables 1 to 6). Automatic reading was performed after incubation at 32 degrees C for one day, or two days for slow growing bacteria, using an ATB 1500 reader (API System) linked to a HP 85 microcomputer (Hewlett-Packard). Most species showed typical carbon substrate assimilation patterns allowing their differentiation from other species within each genus. The results obtained with the micromethod agreed in large measure with the nutritional patterns reported by other workers. It should be possible to use these results to construct a set of tests suitable for identifying species of Gram-negative rods other than Enterobacteriaceae and Vibrionaceae.

Acinetobacter↗
PubMed1987

Molecular relationship among Salmonella dublin isolates identified at the Center for Enterobacteriaceae of Palermo during the years 1971-85.

A molecular epidemiological study was carried out on 60 Salmonella dublin isolates identified at the Southern Italy Enterobacteriaceae Center between 1971 and 1985. These included 23 isolates from children with diarrhoea in Palermo obtained during 1984. All isolates from the outbreak of gastroenteritis in children were resistant to chloramphenicol and streptomycin and harboured two plasmids of 50 MDa and 3 MDa molecular weight, whereas the majority of the isolates identified before 1984 were susceptible to these antibiotics and carried only a 50 MDa molecular weight plasmid. Four S. dublin strains successively identified from cattle (Palermo, Foggia, Portici) and from a child (Palermo) were shown to possess similar antibiotic resistance patterns and plasmid profiles to S. dublin isolates from the outbreak of gastroenteritis in children. The 50 MDa plasmid was shown to be associated with virulence in mice, while it was not possible to assign any genetic function to the 3 MDa plasmid.

Ampicillin Resistance↗
PubMed2002

Xenorhabdus nematophila (enterobacteriacea) secretes a cation-selective calcium-independent porin which causes vacuolation of the rough endoplasmic reticulum and cell lysis.

Xenorhabdus nematophila and Photorhabdus luminescens are two related enterobacteriaceae studied for their use in biological control and for synthesis of original virulence factors and new kinds of antibiotics. X. nematophila broth growth exhibits different cytotoxic activities on insect (Spodoptera littoralis, lepidoptera) immunocytes (hemocytes). Here we report the purification of the flhDC-dependent cytotoxin, a 10,790-Da peptide we have called alpha-Xenorhabdolysin (alpha X). We show that plasma membrane of insect hemocytes and of mammal red blood cells is the first target of this toxin. Electrophysiological and pharmacological approaches indicate that the initial effect of alpha X on macrophage plasma membrane is an increase of monovalent cation permeability, sensitive to potassium channel blockers. As a consequence, several events can occur intracellularly, such as selective vacuolation of the endoplasmic reticulum, cell swelling, and cell death by colloid-osmotic lysis. These effects, inhibited by potassium channel blockers, are totally independent of Ca(2+). However, the size of the pores created by alpha X on macrophage or red blood cell plasma membrane increases with toxin concentration, which leads to a rapid cell lysis.

Animals↗
PubMed2006

Occurrence, prevalence and genetic environment of CTX-M beta-lactamases in Enterobacteriaceae from Indian hospitals.

OBJECTIVES: To determine occurrence, prevalence and CTX-M genotypes produced by Enterobacteriaceae from clinical samples from three geographically distant Indian hospitals and to detect linkage of IS26 with bla(CTX-M) and map its precise insertion position. METHODS: A total of 130, non-duplicate Escherichia coli and Klebsiella pneumoniae resistant to a third-generation cephalosporin (3GC) from three Indian centres were screened for extended-spectrum beta-lactamase (ESBL) production using phenotypic detection methods. All isolates were screened for bla(CTX-M) using multiplex PCR. Precise CTX-M genotype was identified using reverse-line hybridization. All CTX-M-producing isolates were screened for linkage of IS26 with bla(CTX-M). DNA sequencing was used to map the exact insertion position of this mobile element. RESULTS: Ninety-five of 130 3GC-resistant (73%) (73% of total E. coli, 72% of total K. pneumoniae) isolates were found to carry bla(CTX-M-15). No other CTX-M genotype was detected. IS26 linkage with bla(CTX-M-15) was detected in 31% of isolates carrying bla(CTX-M-15). DNA sequencing revealed variable insertion of this mobile element within tnpA of ISEcp1. RAPD-PCR typing demonstrated great diversity in isolates carrying bla(CTX-M-15); no predominant clone was identified. CONCLUSIONS: In contrast with other studies where greater diversity exists, CTX-M-15 was the only CTX-M ESBL produced in this Indian collection of unrelated E. coli and K. pneumoniae. This is the first systematic survey report from India detecting CTX-M-type beta-lactamases This is also the first report indicating such high mobility/diversity of insertion of IS26 in close association with bla(CTX-M) in a single bacterial collection.

Anti-Bacterial Agents↗
PubMed1977

Biochemical typing of urinary Escherichia coli strains by means of the API 20 E enterobacteriaceae system.

With the API 20 E Enterobacteriaceae system of biochemical testing, a biotype, coded numerically, was determined for each of 574 strains of Escherichia coli isolated from patients with urinary tract infection. The serotypes of the strains were also determined. Fifty-five different biotypes were identified, two accounting together for 42% of the strains examined and seven others each accounting for between 8.4 and 1.9%. There was little correlation between biotype and serotype. Fifty pairs of strains were isolated from patients before treatment. In 43 the biotype and serotype of both strains of each pair were the same. In six pairs the biotype, but not the serotypes, differed, the difference being limited to the results of the tests for lysine decarboxylase. The biotypes of the strains of the remaining pair differed widely although their serotypes were the same. It is suggested that this method of biotyping offers a simple but accurate way of discriminating between recrudescent urinary tract infection caused by E. coli and that due to reinfection.

Bacteriuria↗
PubMed2002

Diversity of CTX-M beta-lactamases and their promoter regions from Enterobacteriaceae isolated in three Parisian hospitals.

Nine clinical isolates of Enterobacteriaceae (six Escherichia coli and three Proteus mirabilis) isolated in three Parisian hospitals between 1989 and 2000 showed a particular extended-spectrum cephalosporin-resistance profile characterized by resistance to cefotaxime and aztreonam but not to ceftazidime. CTX-M-1, CTX-M-2, CTX-M-9, CTX-M-14 and two novel plasmid-mediated CTX-M beta-lactamases (CTX-M-20, and CTX-M-21) were identified by polymerase chain reaction and isoelectric focusing (pI>8) and were associated in eight cases with TEM-1 (pI=5.4) or TEM-2 (pI=5.6) beta-lactamases. We used internal ISEcp1 and IS26 forward primers and the CTX-M consensus reverse primer to characterize the CTX-M beta-lactamase promoter regions and showed their high degree of structure diversity. We found upstream of some bla(CTX-M) genes, a 266-bp sequence 100% identical to the sequence upstream of the Kluyvera ascorbata beta-lactamase gene, suggesting that this chromosomal enzyme is the progenitor of the CTX-M-2/5 cluster.

Base Sequence↗
PubMed1998

Ceftazidime-resistant Enterobacteriaceae isolates from three Polish hospitals: identification of three novel TEM- and SHV-5-type extended-spectrum beta-lactamases.

Twelve ceftazidime-resistant isolates of the family Enterobacteriaceae (11 Klebsiella pneumoniae isolates and 1 Escherichia coli isolate) were collected in 1995 from three Polish hospitals located in different cities. All were identified as producers of extended-spectrum beta-lactamases (ESBLs). Detailed analysis of their beta-lactamase contents revealed that six of them expressed SHV-5-like ESBLs. The remaining six were found to produce three different TEM enzymes, each characterized by a pI value of 6.0 and specified by new combinations of amino acid substitutions. The amino acid substitutions compared to the TEM-1 beta-lactamase sequence were Gly238Ser, Glu240Lys, and Thr265Met for TEM-47; Leu21Phe, Gly238Ser, Glu240Lys, and Thr265Met for TEM-48; and Leu21Phe, Gly238Ser, Glu240Lys, Thr265Met, and Ser268Gly for TEM-49. The new TEM beta-lactamases, TEM-47, TEM-48, and TEM-49, belong to a subfamily of TEM-2-related enzymes. Genes coding for TEM-47 and TEM-49 could have originated from the TEM-48-encoding sequence by various single genetic events. The new TEM derivatives probably document the already advanced microevolution of ESBLs ongoing in Polish hospitals, in a majority of which no monitoring of ESBL producers was performed before 1996.

Bacterial Proteins↗
PubMed2006

Clinical and economic impact of bacteremia with extended- spectrum-beta-lactamase-producing Enterobacteriaceae.

We studied outcomes of extended-spectrum beta-lactamase (ESBL) production in Enterobacteriaceae bacteremia. Inpatients with bacteremia caused by ESBL-producing Escherichia coli, Klebsiella spp., or Proteus spp. (cases) were compared with patients with bacteremia caused by non-ESBL producers (controls). Outcomes included mortality, mortality due to infection, length of stay (LOS), delay in appropriate therapy (DAT), discharge to a chronic care facility, and hospital cost. Ninety-nine cases and 99 controls were enrolled. Thirty-five percent of cases died, versus 18% of controls (odds ratio [OR], 2.5; 95% confidence interval [CI], 1.3 to 4.7; P=0.01). Thirty percent of cases died due to infection, versus 16% of controls (OR, 2.3; 95% CI, 1.1 to 4.5; P=0.03). The median LOS after bacteremia for cases was 11 days (interquartile range, 5 to 21), versus 5 days for controls (interquartile range, 3 to 9) (P<0.001). DAT occurred in 66% of cases, versus 7% of controls (OR, 25.1; 95% CI, 10.5 to 60.2; P<0.001). Cases were more likely than controls to be discharged to chronic care (52% versus 21%; OR, 4.0; 95% CI, 1.9 to 8.3; P<0.001). The average hospital cost for cases was 65,509 Israeli shekels, versus 23,538 shekels for controls (P<0.001). After adjusting for differences between groups by using multivariable analysis, ESBL production remained a significant predictor of mortality (OR, 3.6; 95% CI, 1.4 to 9.5; P=0.008), increased LOS (1.56-fold; P=0.001), DAT (OR, 25.1; 95% CI, 10.5 to 60.2; P<0.001), and increased cost (1.57-fold; P=0.003). The mean increase in equivalent cost attributable to ESBL production was $9,620. ESBL production was associated with severe adverse outcomes, including higher overall and infection-related mortality, increased LOS, DAT, discharge to chronic care, and higher costs.

Adult↗
PubMed2026

Dynamics and virulence of Enterobacteriaceae reservoirs harboring blaCTX-M group 1 in community wastewater.

UNLABELLED: Extended-spectrum beta-lactamase (ESBL)-producing bacteria are ubiquitous and can cause serious infections. Here, we examined untreated community wastewater influent as a reservoir for blaCTX-M group 1 organisms and their virulence potential. Raw influent samples (n = 268) were collected from four wastewater treatment plants (WWTPs) representing dense urban populations. We observed that blaCTX-M group 1 levels were high at all WWTPs and only ~1-2 log10 lower and not correlated to common human-specific microbiome fecal markers, Lachno3 and HF183, indicating a lack of connection to human fecal inputs. Concentrations of blaCTX-M group 1 genes and markers for presumptive host organisms Escherichia coli and Klebsiella pneumoniae were influenced by travel time and season. Amplicon sequencing revealed high diversity of blaCTX-M group 1-9 genes, with 63% belonging to group 1. Selective culture and 16S rRNA gene sequencing showed blaCTX-M group 1 isolates were 26% E. coli, 26% K. pneumoniae, 40% other Enterobacteriaceae, and 8% Aeromonas. Overall, E. coli averaged 3.6E7 cells/L, with 3% of all E. coli found to contain blaCTX-M group 1. Whole-genome sequencing of blaCTX-M group 1 E. coli from wastewater revealed resistance and virulence gene profiles similar to clinical isolates and distinct from other wastewater ESBL-resistant and non-resistant E. coli. Interpretation of wastewater data needs to consider both the existence of environmental reservoirs that contain potentially pathogenic organisms and the strong influence the dynamics of the conveyance system can have on final concentrations measured at the WWTP. IMPORTANCE: The CTX-M enzyme family is highly abundant in nosocomial, community, and environmental settings and is leading to treatment of infections with carbapenem antibiotics, a last-line therapeutic option. The progressive increase of the clinically relevant blaCTX-M group 1 resistance genes in the human population warrants investigation, particularly to understand the establishment and dynamics of environmental reservoirs. This study utilized molecular and culture methods to gain insight into the possible origin, abundance, and dynamics of blaCTX-M group 1 genes in untreated wastewater influent samples. We found extremely high levels of these genes, with Escherichia coli as a major host organism that closely resembled clinical strains, suggesting they are seeded and propagate in sewer pipe systems. The significance of our research is in developing approaches to monitor antimicrobial resistance reservoirs in community wastewater, which could shed light on global burdens and potential transmission cycles and indicate increasing inputs of clinically relevant strains originating from human populations.

E. coli↗
PubMed1976

Acetylene reduction (nitrogen fixation) by enterobacteriaceae isolated from paper mill process waters.

Using selective media containing galactitol, over 130 Enterobacteriaceae have been isolated from paper mill process waters collected from different localities. These bacteria were extensively characterized and tested for acetylene-reducing (nitrogen-fixing) activity under anaerobic conditions. High activity was found in representatives of Klebsiella pneumoniae, Enterobacter aerogenes, Enterobacter cloacae, Erwinia herbicola, Citrobacter freundii, Citrobacter intermedius, and Escherichia coli. Under argon, nitrogenase synthesis was generally not repressed by 5 mM l-glutamate, l-aspartate, l-leucine or Casamino Acids (0.5 g/liter). In many strains, both the specific activities (nanomoles of C(2)H(4) per minute per milligram of protein) and the activities (nanomoles of C(2)H(4) per minute) had considerably declined after 24 h. In three selected strains, activity in intact cells grown under nitrogen was unaffected by the presence during assay of 10 mM l-amino acids or ammonium acetate. All of the strains examined were tolerant towards inactivation of nitrogen-fixing activity by 1.8% (vol/vol) oxygen during assay, and inactivation by up to 10% oxygen was partly reversible. Representatives of the six taxa synthesized nitrogenase in stirred aerobic cultures, though the protein concentrations attained were lower than under anaerobic conditions. It seems reasonable to suggest that under natural conditions, nitrogen fixation is able to contribute significantly to the nitrogen economy of the cells.

Journal Article↗
PubMed1971

Two-tube test for the rapid identification of prompt lactose-fermenting genera within the family Enterobacteriaceae.

One hundred and fifty-nine prompt lactose-fermenting strains of Enterobacteriaceae were tested for H(2)S production, ornithine decarboxylase activity, motility, and citrate utilization by using two different sets of test media. It was shown that the three tests first mentioned could be carried out in a single tube, the results being as reliable as when each was done separately. Simmons medium was preferred for the detection of citrate utilization. Since these four tests require only two tubes, they are considered more convenient in routine diagnostics. A combined medium for the detection of H(2)S production and motility is described.

Bacteriological Techniques↗
PubMed1970

Relation of lipopolysaccharide and fatty acid ester release to the ethylenediaminetetraacetic acid alteration of permeability in enterobacteriaceae.

Escherichia coli subjected to cold osmotic shock released 30 to 40% of their fatty acid esters and 42% of their cellular hexosamine. In contrast, Enterobacter, although they released 40% of fatty acid esters, release only 25% of hexosamine. Proteus released less than 15% of either fatty acid esters or hexosamine. These differences are taken to explain the differences among the Enterobacteriaceae in releasing surface enzymes after osmotic shock. It is felt that the release of additional lipopolysaccharide after osmotic shock is necessary for the release of surface enzymes that are not freed by ethylenediaminetetraacetic acid-tris(hydroxymethyl)aminomethane exposure.

Buffers↗
PubMed1979

Fermentation of 1,2-propanediol with 1,2-ethanediol by some genera of Enterobacteriaceae, involving coenzyme B12-dependent diol dehydratase.

Klebsiella pneumoniae (Aerobacter aerogenes) ATCC 8724 was able to grow anaerobically on 1,2-propanediol and 1,2-ethanediol as carbon and energy sources. Whole cells of the bacterium grown anaerobically on 1,2-propanediol or on glycerol catalyzed conversion of 1,2-diols and aldehydes to the corresponding acids and alcohols. Glucose-grown cells also converted aldehydes, but not 1,2-diols, to acids and alcohols. The presence of activities of coenzyme B(12)-dependent diol dehydratase, alcohol dehydrogenase, coenzyme-A-dependent aldehyde dehydrogenase, phosphotransacetylase, and acetate kinase was demonstrated with crude extracts of 1,2-propanediol-grown cells. The dependence of the levels of these enzymes on growth substrates, together with cofactor requirements in in vitro conversion of these substrates, indicates that 1,2-diols are fermented to the corresponding acids and alcohols via aldehydes, acyl-coenzyme A, and acyl phosphates. This metabolic pathway for 1,2-diol fermentation was also suggested in some other genera of Enterobacteriaceae which were able to grow anaerobically on 1,2-propanediol. When the bacteria were cultivated in a 1,2-propanediol medium not supplemented with cobalt ion, the coenzyme B(12)-dependent conversion of 1,2-diols to aldehydes was the rate-limiting step in this fermentation. This was because the intracellular concentration of coenzyme B(12) was very low in the cells grown in cobalt-deficient medium, since the apoprotein of diol dehydratase was markedly induced in the cells grown in the 1,2-propanediol medium. Better cell yields were obtained when the bacteria were grown anaerobically on 1,2-propanediol. Evidence is presented that aerobically grown cells have a different metabolic pathway for utilizing 1,2-propanediol.

Aerobiosis↗
PubMed1966

Normal serum cytotoxicity for P32-labeled smooth Enterobacteriaceae. II. Fate of macromolecular and lipid phosphorus of damaged cells.

Spitznagel, John K. (University of North Carolina, Chapel Hill). Normal serum cytotoxicity for P(32)-labeled smooth Enterobacteriaceae. II. Fate of macromolecular and lipid phosphorus of damaged cells. J. Bacteriol. 91:148-152. 1966.-Fresh, normal adult guinea pig serum released micro- and macromolecular forms of metabolically incorporated P(32) from smooth Escherichia coli. A significant amount of P(32)-labeled phospholipid was also released. The overall acid solubility distribution of the P(32) label in bacterial suspensions was very little affected in fresh serum, although P(32)-labeled cytoplasmic contents and cell walls of E. coli lost some P(32) when they were suspended in fresh or heat-inactivated normal serum. These findings confirmed and extended earlier evidence that the peripheral wall and membrane structures of smooth E. coli are extensively damaged by factors in fresh normal serum.

Blood↗
PubMed1966

Normal serum cytotoxicity for P32-labeled smooth Enterobacteriaceae. 3. Isolation of a gammag normal antibody and characterization of other serum factors causing P32 loss.

Spitznagel, John K. (University of North Carolina School of Medicine, Chapel Hill). Normal serum cytotoxicity for P(32)-labeled smooth Enterobacteriaceae. III. Isolation of a gammaG normal antibody and characterization of other serum factors causing P(32) loss. J. Bacteriol. 91:401-408. 1966.-Gram-negative bacteria lost metabolically incorporated P(32) when suspended in serum only if the serum contained heat-labile in addition to heat-stable factors. Gram-positive bacteria labeled with P(32) and included for comparison lost P(32) in heat-inactivated as well as in fresh normal serum. Further investigation of gram-negative bacteria showed that a smooth Escherichia coli (O117:H27) lost P(32) only if suspended in serum containing complement fractions C'1, C'2, C'3, and C'4 "normal" antibody and lysozyme. The normal antibody was recovered by absorption on and subsequent elution from E. coli O117:H27 cell walls. Immunoelectrophoresis showed that it was a gammaG-globulin. Its P(32)-releasing activity was destroyed by 2-mercaptoethanol. Lysozyme was found to potentiate the P(32)-releasing action of normal antibody plus complement. Evidence was obtained suggesting that beta(1C) globulin was the component absorbed to zymosan during serum absorption at 15 C. Reduction of the beta(1C) level evidently upsets an important balance that exists in normal serum among complement, antibody, and lysozyme. This balance is essential for maximal P(32) release from labeled bacteria, or possibly for a maximal antibacterial effect from normal serum. The possible relationships of bactericidal, bacteriolytic, and opsonic action of normal serum are discussed.

Animals↗
PubMed1966

Episome-mediated transfer of drug resistance in Enterobacteriaceae. IX. Recombination of an R factor with F.

Watanabe, Tsutomu (Keio University, Tokyo, Japan), and Chizuko Ogata. Episome-mediated transfer of drug resistance in Enterobacteriaceae. IX. Recombination of an R factor with F. J. Bacteriol. 91:43-50. 1966.-R factors can be transduced in Salmonella typhimurium with phage P-22, and a majority of the drug-resistant transductants are unable to transfer their drug resistance by cell-to-cell contact, as we have previously reported. Several exceptional types of transductants of S. typhimurium, with the markers of resistance to sulfonamide, streptomycin, and chloramphenicol, were recently obtained by transduction with phage P-22 of a four-drug-resistance R factor carrying the markers of resistance to sulfonamide, streptomycin, chloramphenicol, and tetracycline. They were exceptional in that they had low conjugal transferability of their drug resistance. When one of these exceptional transductants (38R) was transferred to an F(+) strain of Escherichia coli K-12, 38R acquired high transferability in its further transfer. This high transferability was found to be due to the recombination of 38R with F. Transductant 38R was of the fi(+) (fi = fertility inhibition) type, and did not show superinfection immunity against fi(+) and fi(-) R factors. The recombinant 38R.F was genetically very stable and resistant to elimination with acridines. It did not show superinfection immunity against fi(+) and fi(-) R factors, but did show superinfection immunity against F. Further, 38R.F did not restrict a female-specific phage (W-31), unlike wild-type F. F(-) and R(-) segregants were isolated from this recombinant 38R.F, and these segregants exhibited genetic characteristics different from the original R, its transductant 38R, and wild-type F.

Coliphages↗
PubMed1966

Comparison of the tryptophan synthetase alpha-subunits of several species of Enterobacteriaceae.

Creighton, T. E. (Stanford University, Stanford), D. R. Helinski, R. L. Somerville, and C. Yanofsky. Comparison of the tryptophan synthetase alpha subunits of several species of Enterobacteriaceae. J. Bacteriol. 91:1819-1826. 1966.-The tryptophan synthetase alpha subunits of Escherichia coli K-12, E. coli B, Shigella dysenteriae, Salmonella typhimurium, and Aerobacter aerogenes have been purified and their structures compared. Each of these alpha subunits exhibits a sedimentation coefficient of about 2.7S. Peptide patterns of trypsin plus chymotrypsin digests of the alpha subunits have indicated that all of the alpha subunits have peptide regions in common. The patterns of E. coli K-12, E. coli B, and S. dysenteriae alpha subunits appear to be nearly identical, whereas the alpha subunits from S. typhimurium and A. aerogenes differ from those of E. coli and from each other. It has also been shown that the E. coli structural gene for the alpha subunit is translated identically in E. coli and S. typhimurium.

Amino Acids↗
PubMed1966

Delayed lactose fermentation by enterobacteriaceae.

Goodman, R. E. (University of California, Los Angeles), and M. J. Pickett. Delayed lactose fermentation by Enterobacteriaceae. J. Bacteriol. 92:318-327. 1966.-When 171 Citrobacter freundii strains and 14 Paracolobactrum arizonae strains examined, 51 of the C. freundii strains and 13 of the P. arizonae strains were found to be delayed or negative lactose fermenters. Of the slow fermenters, 65% yielded rapidly fermenting mutants in cultures undergoing delayed fermentation. Lactose fermentation could generally be hastened by increasing lactose concentrations. Many organisms which fermented lactose slowly grew readily on a medium containing lactose as the sole carbon source. Regardless of their ability to ferment lactose, all strains of C. freundii and P. arizonae investigated could be shown to possess beta-galactosidase. Delayed fermenters failed to take up lactose from the culture medium, whereas prompt fermenters did so readily. The beta-galactosidases of 12 strains of enteric bacteria were studied in crude cell extracts with respect to specific activity, stability, and activity at varying substrate (o-nitrophenyl-beta-d-galactopyranoside) concentrations, at varying pH, and in the presence of sodium, potassium, and magnesium. The widely varying specific activities and the approximate similarity of the Michaelis constants (about 2 x 10(-4)m) suggested that the strains investigated produced differing amounts of beta-galactosidase. Moreover, qualitative differences in the enzymes provided evidence that these strains synthesized different molecular forms of beta-galactosidase. The results suggested that organisms which ferment lactose only after a prolonged delay do so because they possess multiple defects in their lactose-metabolizing machinery.

Journal Article↗