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P Gemski

Publications and source records attributed to P Gemski.

67 records · Page 4Linked to original sources
PubMed1972

Virulence of Shigella flexneri hybrids expressing Escherichia coli somatic antigens.

The genes controlling either Escherichia coli somatic antigen 8 or 25 were conjugally transferred to virulent Shigella flexneri 2a recipients to determine whether the aquisition of these antigens would affect the virulence of the resulting hybrid. A high proportion of such hybrids were found to be rough and hence were avirulent. Some smooth S. flexneri hybrids which replaced their native group antigens with E. coli factor 25 were still virulent in the animal models employed. All S. flexneri O-8 hybrids were uniformly avirulent. Our finding, that S. flexneri hybrids with the chemically divergent E. coli O-8 repeat unit are avirulent whereas some hybrids with the chemically related O-25 repeat unit retain virulence, suggests that the chemical composition and structure of the O side chain of somatic antigens may represent one determining factor for bacterial penetration of mucosal epithelial cells, the primary step in the pathogenesis of bacillary dysentery.

Animals↗
PubMed1972

Lytic replication of coliphage lambda in Salmonella typhosa hybrids.

Hybrids between Escherichia coli K-12 and Salmonella typhosa which conserved a continuous K-12 chromosomal diploid segment extending from pro through ara to the strA locus were sensitive to plaque formation by wild-type lambda. These partially diploid S. typhosa hybrids could be lysogenized with lambda and subsequently induced to produce infectious phage particles. When the K-12 genes were segregated from a lysogenic S. typhosa hybrid, phage-productive ability was no longer detectable due to loss of a genetic region necessary for vegetative replication of lambda. However, lambda prophage was shown to persist in a quiescent state in the S. typhosa hybrid segregant with phage-productive ability being reactivated after replacement of the essential K-12 lambda replication region. Low-frequency transduction and high-frequency transduction lysates containing the gal(+) genes of S. typhosa were prepared by induction of lambda-lysogenic S. typhosa hybrids indicating that the attlambda site is chromosomally located in S. typhosa in close proximity to the gal locus as in E. coli K-12. After propagation in S. typhosa hybrids, lambda was subject to restriction by E. coli K-12 recipients, thus establishing that S. typhosa does not perform the K-12 modification of lambda deoxyribonucleic acid. Hybrids of S. typhosa, however, did not restrict lambda grown previously on E. coli K-12. The K-12 genetic region required for lambda phage production in S. typhosa was located within min 66 to min 72 on the genetic map of the E. coli chromosome. Transfer of an F-merogenote encompassing the 66 to 72 min E. coli chromosomal region to lambda-insensitive S. typhosa hybrids enabled them to replicate wild-type lambda. The lambda-insensitive S. typhosa hybrid, WR4255, which blocks lambda replication, can be mutagenized to yield mutant strains sensitive to lambdavir and lambdaimm434. These WR4255 mutants remained insensitive to plaque formation by wild-type lambda.

Chromosome Mapping↗
PubMed1972

Behavior of coliphage lambda in Shigella flexneri 2a.

The insensitivity of wild-type Shigella flexneri 2a to coliphage lambda is a consequence of its native genetic defect in the malA gene cluster. The "smooth" S. flexneri 2a lipopolysaccharide layer affects the efficient adsorption of lambda. Derivatives, capable of serving as functional hosts for lambda, were obtained by repairing the malA lesion, enabling the expression of the malB-lambdarcp region of S. flexneri. Introduction of a mutation into S. flexneri causing a "rough" lipopolysaccharide character resulted in more efficient adsorption of lambda. Such S. flexneri hosts can be stably lysogenized and upon induction yield gal(+)-transducing lysates. Lambda propagated on a malA(+) rough S. flexneri host was restricted by Escherichia coli K-12 and E. coli B, but not by E. coli C. This S. flexneri host did not restrict lambda grown on these E. coli strains.

Adsorption↗
PubMed1971

A Chromosomal Locus Which Controls the Ability of Shigella flexneri to Evoke Keratoconjunctivitis.

The primary step in the pathogenesis of bacillary dysentery is the penetration of intestinal epithelial cells by shigellae. Lacking this capacity, Shigella flexneri becomes avirulent. By means of intergeneric conjugation between various Escherichia coli K-12 Hfr strains and S. flexneri 2a virulent recipients and by reciprocal transduction analysis with phage P1 vir, we established a locus on the genome of S. flexneri 2a which is necessary for the ability of this strain to penetrate epithelial cells as measured by the Sereney test for keratoconjunctivitis. This locus, termed kcpA (in reference to its involvement in provoking keratoconjunctivitis), has been positioned between the lac and gal chromosomal markers and is contransducible with the purE allele.

Journal Article↗
PubMed1970

Genetic Transfer of Shigella flexneri Antigens to Escherichia coli K-12.

The genes controlling synthesis of Shigella flexneri group- and type-specific antigens were transferred to Escherichia coli K-12 recipients by conjugation with an S. flexneri Hfr. After mating E. coli with an Hfr strain of S. flexneri 2a and selecting for his(+) recombinants, a high proportion of the E. coli hybrids agglutinated in S. flexneri grouping serum. None of these hybrids expressed S. flexneri type-specific antigen II. When an E. coli his(+) hybrid possessing the S. flexneri group antigen was remated with the same Hfr with selection for pro(+) hybrids, a high proportion now expressed the type-specific antigen as well as the previously inherited group antigen. If such crosses were performed in reverse order (i.e., pro(+) followed by his(+) selection), a different pattern of serological behavior was observed. None of the pro(+) hybrids showed the type-specific antigen. Subsequent mating for his(+) resulted in hybrids with both the group- and type-specific antigens. These results show that genes controlling the synthesis of S. flexneri group antigen (linked to the his locus) and type-specific antigen (linked to the pro locus) are widely separated on the chromosome. Expression of the type-specific antigen II depends on the presence of the group antigen.

Journal Article↗
PubMed1967

Transduction by bacteriophage P22 in nonsmooth mutants of Salmonella typhimurium.

The general transducing phage P22 attacks only smooth (S) Salmonella with O antigen 12, determined by the oligosaccharide repeating unit constituting the distal part of the somatic lipopolysaccharide (LPS) side chain; non-S mutants, whose LPS contain few or no O repeating units, appear to be resistant. Auxotrophic non-S mutants of Salmonella typhimurium LT2 were tested as transductional recipients. Some transductants (0.5 to 5% as many as from S recipients) were obtained from most semirough recipients, either of class D (presumed leaky rouA mutants) or of a class due to mutation near his (presumed leaky rouB mutants), and from recipients lacking uridine diphosphogalactose epimerase or phosphomannose isomerase. Transductants were not obtained from several rouA, rouB, "heptose-negative," and glucose-1-transferase mutants, nor from most semirough class C mutants, whose LPS side chains each bear a single O oligosaccharide unit. Most transductants evoked from non-S recipients by temperate (c(+)) phage P22 were nonlysogenic, and virulent P22.c2 phage was about as effective as P22.c(+) in transduction to non-S recipients; probably all P22 transducing particles neither lysogenize nor kill. The extended-host-range mutant P22h gave qualitatively similar results,but evoked 5- to 30-fold more transductants from some non-S recipients than did P22. Probably, the LPS of non-S mutants susceptible to transduction contains a few O-specific oligosaccharide units, conferring a slight ability to adsorb P22 and a greater ability to adsorb P22h.

Genetics↗
PubMedDate not supplied

Heterogeneity of lipid A.

In a previous study, lipid A from Shigella flexneri was separated into eight distinct fractions by thin-layer chromatography (TLC). In the present investigation, lipid A from different gram-negative bacteria was analyzed by thin-layer chromatography for its heterogeneity and compared with lipid A of S. flexneri. Purified lipid A preparations from six different enterobacterial species were heterogeneous, but based on Rf, comparable bands were found among all preparations. Changing the culture conditions by using two other culture media resulted in very minor changes in the TLC appearance. Different serotypes of Shigella grown under the same conditions also showed very minor differences. Two bands (5 and 8) in each preparation of lipid A comigrated with lysophosphatidylethanolamine and phosphatidylethanolamine, respectively, and both bands were stained with ninhydrin and molybdenum blue. Therefore, phosphatidylethanolamine, and probably lysophosphatidylethanolamine, are common constitutents of unfractioned lipid A preparations, and both phospholipids can occur even in highly purified unfractionated lipid A.

Chromatography, Thin Layer↗
PubMedDate not supplied

Genetic methods for the detection of microbial pathogens. Identification of enterotoxigenic Escherichia coli by DNA colony hybridization: collaborative study.

Enteropathogenic Escherichia coli strains may produce a cholera-like, heat-labile enterotoxin (LT) as a virulence factor. The gene that codes for LT can be purified by recombinant DNA techniques and used as a genetic probe for DNA hybridization. These probes detect enterotoxigenic strains as well as strains that may not manifest toxin production but carry the genetic information to do so. In this study, 13 laboratories tested 3 known and 25 unknown (10 positive and 15 negative) cultures of E. coli for the presence of the LT gene. The isolates had been tested and classified by the mouse Y-1 adrenal cell test and an enzyme-linked immunosorbent assay. Cultures were spotted on nitrocellulose filters on MacConkey agar and incubated. Colonies were lysed in situ and their DNA was hybridized to 32P-labeled, purified LT gene DNA (provided to the collaborators). Positive colonies were identified by autoradiography. Of 325 samples, 315 (96.9%) were identified correctly and 10 were misclassified; there were 6 false negative and 4 false positive identifications. Chi-square values indicated that the method agreed with the previous classification and was equally efficient in distinguishing positive and negative samples (95.7 and 98.1%, respectively). The method has been adopted official first action.

Autoradiography↗
PubMedDate not supplied

Investigation of a staphylococcal food poisoning outbreak in a centralized school lunch program.

The trend in many communities toward centralized school lunch preparation potentially increases the risk of foodborne illness. Foods often are prepared long before serving and may be distributed to satellite schools by persons with little formal training in safe techniques of food preparation or food service. In May 1990, an outbreak of staphylococcal food poisoning occurred in elementary schools in a Rhode Island community participating in such a program. In the investigation of the outbreak, students in schools that reported cases were interviewed. Food preparation, handling, and distribution were reviewed. At School E, 662 lunches were prepared and distributed to 4 additional schools (schools A-D). Schools A and B accounted for nearly all cases of the food poisoning, with rates of 47 percent and 18 percent. Eating ham increased the risk of illness (62 percent of those consuming ham and 3 percent of those who did not, relative risk = 18.0, 95 percent confidence interval = 4.0, 313.4). Large amounts of Staphylococcus aureus were cultured, and preformed enterotoxin A was identified in leftover ham. A food handler, who tested positive for the implicated enterotoxic strain S. aureus, reported having removed the casings from two of nine warm ham rolls 48 hours prior to service. Because of improper refrigeration, prolonged handling, and inadequate reheating, the ham was held at temperatures estimated at 10-49 degrees Celsius (50-120 degrees Fahrenheit) for a minimum of 15 hours. The potential for larger outbreaks prompted a statewide training program in safe food preparation for school lunch personnel, which may have applications for other communities.

Child↗