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PubMed2006

Distribution of a transposon-like element carrying bla(CMY-2) among Salmonella and other Enterobacteriaceae.

OBJECTIVES: The dissemination of cephamycin resistance in Enterobacteriaceae and its correlation with a transposon-like DNA element consisting of a specific tnpA-bla(CMY-2)-blc-sugE structure were investigated. METHODS: A total of 140 enterobacterial isolates belonging to 17 species (10 genera) of Enterobacteriaceae phenotypically characterized as putative AmpC-producers were evaluated. The isolates were examined by PCR analysis, DNA-DNA hybridization and nucleotide sequencing. RESULTS: The bla(CMY-2)-carrying element was detected in 34 isolates from 10 species (9 genera), including all 14 Salmonella and 4 Shigella isolates as well as 7 of the 10 Escherichia coli isolates tested. The remaining 9 isolates were from 112 isolates of the other 14 species tested. The genetic structure of the bla(CMY-2)-carrying element was identical in 29 isolates, while in 3 E. coli and 2 Citrobacter isolates an additional insertion sequence IS1 was found inserted at various nucleotide positions close to the 3' end, either within or downstream, of tnpA. In 12 of the 14 representative isolates examined, the bla(CMY-2)-carrying element was found inserted in the finQ gene of various-sized plasmids with highly conserved 8 bp direct repeats flanking the junction regions. Among the other 106 non-CMY-2-producing isolates, plasmid-mediated ampC genes were found only in one isolate of Enterobacter aerogenes which carried a bla(DHA-1)-like gene. CONCLUSIONS: bla(CMY-2) is the most prevalent plasmid-mediated ampC gene among Enterobacteriaceae. All the bla(CMY-2) genes identified in the present study were associated with a specific transposon-like element that may be responsible for the spread of bla(CMY-2) among Enterobacteriaceae.

Cephalosporin Resistance↗

PubMed2006

Are laboratory-based antibiograms reliable to guide the selection of empirical antimicrobial treatment in patients with hospital-acquired infections?

OBJECTIVES: Antibiograms are often taken into account to define a rational selection of an empirical antimicrobial therapy for treating patients with hospital-acquired infections. In this study, we performed a paired comparison between the antibiogram constructed with laboratory-based data and that formed with data subjected to prior clinical validation. METHODS: Between 2003 and 2005, the laboratory of microbiology printed in duplicate every individual susceptibility report corresponding to hospitalized patients and the copy was sent to the department of infection control. Every individual report was assessed in real time at the bedside of the patient by a multidisciplinary team for clinical significance and appropriateness of the specimen, as well as for the type, source and origin of the infection. Cumulative resistance rates were estimated in parallel at the laboratory with the whole data, and at the infection control department with data subjected to prior clinical validation. These rates were designated as 'laboratory-based' and 'clinically based', respectively. RESULTS: A total of 2305 individual susceptibility reports were assessed. Only 1429 (62.0%) were considered as clinically significant by the multidisciplinary team. Escherichia coli, Enterobacter cloacae, Citrobacter freundii group, Klebsiella species and Proteus mirabilis resistant to broad-spectrum cephalosporins, as well as methicillin-resistant Staphylococcus aureus, were significantly more frequent in the clinically based rates (P < or = 0.03). CONCLUSIONS: Laboratory-based data underestimate the frequency of several major resistant organisms in patients with hospital-acquired infection. Previous clinical validation of the individual susceptibility reports seems to be a suitable strategy to get more reliable data.

Anti-Bacterial Agents↗

PubMed2007

Emergence of ArmA and RmtB aminoglycoside resistance 16S rRNA methylases in Belgium.

OBJECTIVES: 16S rRNA methylase-mediated high-level resistance to aminoglycosides has been reported recently in clinical isolates of Gram-negative bacilli only from a limited number of countries. This study was conducted to investigate the occurrence of this type of resistance in clinical isolates of Enterobacteriaceae from two Belgian hospitals and the characteristics of the strains. METHODS: We screened for high-level gentamicin, tobramycin and amikacin resistance in clinical isolates of Enterobacteriaceae consecutively collected between 2000 and 2005 at two laboratories by PCR for the armA, rmtA and rmtB 16S rRNA methylase genes. The beta-lactamase presence in the strains was also determined by phenotypic and genotypic methods. RESULTS: Overall armA genes were detected in 18 Klebsiella pneumoniae, Escherichia coli, Enterobacter aerogenes, Enterobacter cloacae and Citrobacter amalonaticus whereas rmtB was detected in a single E. coli isolate. The rmtA gene was not found. All 16S rRNA methylase-bearing strains produced extended-spectrum beta-lactamases (ESBLs), predominantly type CTX-M-3, as well as various types of beta-lactamases. In the majority of the strains, the armA gene was carried by conjugative plasmids of the IncL/M incompatibility group whereas rmtB was borne by an IncFI plasmid. CONCLUSIONS: This is the first report of the emergence of 16S rRNA methylases in Enterobacteriaceae in Belgium. The rapid spread of multidrug-resistant isolates producing both ESBLs and 16S rRNA methylases raises clinical concern and may become a major therapeutic threat in the future.

Aminoglycosides↗

PubMed2000

Comparison of the Escherichia coli K-12 genome with sampled genomes of a Klebsiella pneumoniae and three salmonella enterica serovars, Typhimurium, Typhi and Paratyphi.

The Escherichia coli K-12 genome (ECO) was compared with the sampled genomes of the sibling species Salmonella enterica serovars Typhimurium, Typhi and Paratyphi A (collectively referred to as SAL) and the genome of the close outgroup Klebsiella pneumoniae (KPN). There are at least 160 locations where sequences of >400 bp are absent from ECO but present in the genomes of all three SAL and 394 locations where sequences are present in ECO but close homologs are absent in all SAL genomes. The 394 sequences in ECO that do not occur in SAL contain 1350 (30.6%) of the 4405 ECO genes. Of these, 1165 are missing from both SAL and KPN. Most of the 1165 genes are concentrated within 28 regions of 10-40 kb, which consist almost exclusively of such genes. Among these regions were six that included previously identified cryptic phage. A hypothetical ancestral state of genomic regions that differ between ECO and SAL can be inferred in some cases by reference to the genome structure in KPN and the more distant relative Yersinia pestis. However, many changes between ECO and SAL are concentrated in regions where all four genera have a different structure. The rate of gene insertion and deletion is sufficiently high in these regions that the ancestral state of the ECO/SAL lineage cannot be inferred from the present data. The sequencing of other closely related genomes, such as S.bongori or Citrobacter, may help in this regard.

Databases as Topic↗

PubMed2001

Conserved regulatory elements of the promoter sequence of the gene rpoH of enteric bacteria.

The rpoH regulatory region of different members of the enteric bacteria family was sequenced or downloaded from GenBank and compared. In addition, the transcriptional start sites of rpoH of Yersinia frederiksenii and Proteus mirabilis, two distant members of this family, were determined. Sequences similar to the sigma(70) promoters P1, P4 and P5, to the sigma(E) promoter P3 and to boxes DnaA1, DnaA2, cAMP receptor protein (CRP) boxes CRP1, CRP2 and box CytR present in Escherichia coli K12, were identified in sequences of closely related bacteria such as: E.coli, Shigella flexneri, Salmonella enterica serovar Typhimurium, Citrobacter freundii, Enterobacter cloacae and Klebsiella pneumoniae. In more distant bacteria, Y.frederiksenii and P.mirabilis, the rpoH regulatory region has a distal P1-like sigma(70) promoter and two proximal promoters: a heat-induced sigma(E)-like promoter and a sigma(70) promoter. Sequences similar to the regulatory boxes were not identified in these bacteria. This study suggests that the general pattern of transcription of the rpoH gene in enteric bacteria includes a distal sigma(70) promoter, >200 nt upstream of the initiation codon, and two proximal promoters: a heat-induced sigma(E)-like promoter and a sigma(70) promoter. A second proximal sigma(70) promoter under catabolite-regulation is probably present only in bacteria closely related to E.coli.

Base Composition↗

PubMed1991

Cloning and nucleotide sequence of the gene (citA) encoding a citrate carrier from Salmonella typhimurium.

A cryptic citrate transport gene (citA) from Salmonella typhimurium chromosome was cloned and its nucleotide sequence was determined. The cloned plasmid conferred citrate-utilizing ability on wild-type Escherichia coli, which cannot grow on citrate as the sole source of carbon. The resultant E. coli transformant was able to transport citrate. A 1,302-base-pair open reading frame with a preceding ribosomal binding site was found in the cloned DNA fragment. The 434-amino-acid protein that could be translated from this open reading frame is highly hydrophobic (69% nonpolar amino acid residues), consistent with the fact that the transport protein is an intrinsic membrane protein. The molecular weight of this protein was calculated to be 47,188. The gene sequence determined is highly homologous to those of Cit+ plasmid-mediated citrate transport gene, citA, from E. coli, the chromosomal citA gene from Citrobacter amalonaticus and the chromosomal cit+ gene from Klebsiella pneumoniae. The hydropathy profile of the deduced amino acid sequence suggests that this carrier has 12 hydrophobic segments, which may span the membrane lipid bilayer.

Amino Acid Sequence↗

PubMed1988

The phylogenetic origin of the bifunctional tyrosine-pathway protein in the enteric lineage of bacteria.

Because bifunctional enzymes are distinctive and highly conserved products of relatively infrequent gene-fusion events, they are particularly useful markers to identify clusters of organisms at different hierarchical levels of a phylogenetic tree. Within the subdivision of gram-negative bacteria known as superfamily B, there are two distinctive types of tyrosine-pathway dehydrogenases: (1) a broad-specificity dehydrogenase (recently termed cyclohexadienyl dehydrogenase [CDH]) that can utilize either prephenate or L-arogenate as alternative substrates and (2) a bifunctional CDH that also posseses chorismate mutase activity. (T-proteins). The bifunctional T-protein, thought to be encoded by fused ancestral genes for chorismate mutase and CDH, was found to be present in enteric bacteria (Escherichia, Shigella, Salmonella, Citrobacter, Klebsiella, Erwinia, Serratia, Morganella, Cedecea, Kluyvera, Hafnia, Edwardsiella, Yersinia, and Proteus) and in Aeromonas and Alteromonas. Outside of the latter "enteric lineage," the T-protein is absent in other major superfamily-B genera, such as Pseudomonas (rRNA homology group I), Xanthomonas, Acinetobacter, and Oceanospirillum. Hence, the T-protein must have evolved after the divergence of the enteric and Oceanospirillum lineages. 3-Deoxy-D-arabino-heptulosonate 7-phosphate synthase-phe, an early-pathway isozyme sensitive to feedback inhibition by L-phenylalanine, has been found in each member of the enteric lineage examined. The absence of both the T-protein and DAHP synthase-phe elsewhere in superfamily B indicates the emergence of these character states at approximately the same evolutionary time.

Enterobacteriaceae↗

PubMed1993

Bacteriology of neonatal septicaemia in a rural referral hospital in south India.

Out of 640 suspected cases of neonatal septicaemia studied, bacteraemia was detected in 255 (40 per cent) of the infants. Gram negative organisms were predominant (56 per cent) with Pseudomonas, Citrobacter, and Klebsiella as the commonest pathogens. Among the Gram positive organisms both Staphylococcus aureus and Staphylococcus epidermidis were equally prevalent. Staphylococci were mainly responsible for early onset infections, whereas Salmonella typhimurium and Pseudomonas were the main organisms in late onset infections. Group B streptococcal infection was not encountered in this part of the country.

Age of Onset↗

PubMed1999

The bacteriology of neonatal septicaemia in Ile-Ife, Nigeria.

The incidence of septicaemia among neonates categorized as being at high risk was 55 per cent in Ile-Ife, Nigeria. Gram-positive organisms, specifically Staphylococcus aureus, were predominant (33.8 per cent) among bacteria cultured from proven cases of septicaemia. Other coagulase-negative staphylococci also contributed 21 per cent, with Staphylococcus epidermidis occurring in 5 per cent of the isolates. Listeria monocytogenes was cultured from 8.4 per cent of septic neonates. Pseudomonas aeruginosa was cultured from 3 per cent, Klebsiella pneumoniae from 14 per cent, and Escherichia coli from 7 per cent. Other Gram-negative bacilli cultured were Enterobacter aerogenes (5 per cent), Citrobacter freundii, Salmonella sp., and Proteus sp. (2 per cent each). The bacterial isolates were relatively resistant to antibiotics traditionally employed to treat cases of septicaemia. The study shows a high prevalence of neonatal bacterial sepsis at the centre and the emerging role of Listeria monocytogenes in the aetiology of neonatal sepsis. It highlights the preponderance of multiple antibiotic resistant organisms among these neonates early in life which is of epidemiological importance in the control of the infectious agents.

Bacteremia↗

PubMed2001

Risk factors for nosocomial pneumonia in critically ill trauma patients.

OBJECTIVE: To determine risk factors for nosocomial pneumonia in critically ill trauma patients. DESIGN: Prospective cohort study. SETTING: The trauma intensive care unit (ICU) of a 1500-bed tertiary-care hospital. PATIENTS: All critically ill trauma patients (n = 103) admitted consecutively between November 1995 and October 1996. INTERVENTIONS: A comparison of data recorded at the time of ICU admission and during the clinical evolution in patients with (n = 23) and without (n = 80) nosocomial pneumonia was made. Data referred mainly to possible risk factors were recorded; they also included factors related to pneumonia etiology and evolutive factors. Predictors of nosocomial pneumonia were assessed by logistic regression analysis. MEASUREMENTS AND MAIN RESULTS: The presence of significant growth on quantitative cultures of the protected specimen brush (> or = 103 colony forming units/mL) was required to accept pneumonia as microbiologically proven, as well as the concurrence of a cohort of clinical and radiologic signs. Twenty-three (22.3%) patients developed nosocomial pneumonia. The mean age of these patients was 41.7 yrs; 18 of them (78.3%) were men. The microorganisms isolated in significant concentrations were Acinetobacter baumanii (ten cases), Staphylococcus aureus (11 cases), Pseudomonas aeruginosa (five cases), Haemophilus influenzae (two cases), and Klebsiella pneumoniae, Citrobacter freundii, Serratia marcescens, Enterococcus spp., Enterobacter spp., coagulase-negative Staphylococcus, and Streptococcus intermedius (one case each one). Risk factors for pneumonia by univariate analysis included nasogastric tube; continuous enteral feeding; prolonged mechanical ventilation (>1 day); use of H2-receptor antagonist, sucralfate, muscle relaxants, corticosteroids, barbiturates, and inotropic agents; positive end-expiratory pressure; intense sedation; re-intubation; tracheotomy; urgent brain computed tomography (CT) scan; craniotomy; iatrogenic event; and hyperventilation. The mortality rate was 43.5% (10 of 23) in the nosocomial pneumonia group and 18.8% in patients without nosocomial pneumonia (p =.02). Also, the mean stay in the ICU, the therapeutic charge (measured with total and mean punctuation of the Therapeutic Intervention Scoring System) and the complications, infectious and noninfectious, of the clinical evolution were significantly more frequent in patients with nosocomial pneumonia than in those without pneumonia (p <.05). In the multivariate analysis, continuous enteral feeding, craniotomy, prolonged mechanical ventilation (>24 hrs), use of positive end-expiratory pressure, and corticotherapy were independent predictors of nosocomial pneumonia. CONCLUSIONS: It seems that factors related to the patient's clinical course, rather than variables registered on the first days of ICU admission, are those that would exert an influence on the development of nosocomial pneumonia in critically ill trauma patients. In this way, from our point of view, in our study the main risk factors are the use of prolonged mechanical ventilation (>4 hrs) and positive end-expiratory pressure. At the same time, we can conclude that the reduction of this infection incidence could decrease the mean stay in the ICU, the therapeutic charge, and the prognosis in terms of mortality and morbidity.

Adult↗

PubMed1987

In vitro activity of a new broad spectrum, beta-lactamase-stable oral cephalosporin, cefixime.

Cefixime is a new orally absorbed iminomethoxy, aminothiazolyl cephalosporin. It inhibits the majority, 90%, of Streptococcus pneumoniae, Streptococcus pyogenes, Branhamella catarrhalis, Haemophilus influenzae, Escherichia coli, Klebsiella pneumoniae, Proteus mirabilis and Neisseria gonorrhoeae at concentrations less than or equal to 0.25 micrograms/ml. It inhibits 90% of the other members of the Enterobacteriaceae at concentrations less than 1 microgram/ml, with the exception of some strains of Enterobacter spp., Citrobacter freundii and Morganella morganii, Cefixime does not inhibit enterococci, Listeria, Pseudomonas aeruginosa, Acinetobacter, Bacteroides spp. or staphylococci. In general, cefixime has in vitro activity superior to cephalexin, cephradine, cefadroxil and cefaclor against all bacteria with the exception of staphylococci. Cefixime is not destroyed by most of the common plasmid and chromosomal beta-lactamases and its activity is not reduced by serum, blood or urine. Cefixime overall has excellent in vitro activity against the commonly encountered respiratory and urinary tract pathogens.

Bacteria↗

PubMed1995

Third generation cephalosporin-resistant gram-negative bacilli in the feces of hospitalized children.

In view of the widespread use of third generation cephalosporins in hospitalized infants, we attempted to determine whether their use was associated with the emergence of resistance in fecal Gram-negative bacilli. Stools from infants hospitalized for varying durations were cultured on MacConkey agar containing 4 micrograms/ml of cefotaxime. All isolates growing on this medium were identified and their susceptibilities to 29 antimicrobial agents were determined. Sixty-five infants were studied of whom 44 were receiving a third generation cephalosporin, 7 another antibiotic and 14 no antibiotic. Thirty-one strains resistant to third generation cephalosporins (minimal inhibitory concentrations > or = 16 micrograms/ml) to cefotaxime, ceftriaxone or ceftazidine) were isolated from 26 infants. The proportions of infants with resistant strains were not significantly different whether they were: (1) receiving a third generation cephalosporin or not; (2) hospitalized for longer or shorter than 2 days or not; (3) older or younger than 3 months or not. Notably 8 infants harbored resistant strains within 24 hours of admission. The commonest resistant strains isolated belonged to the genera Enterobacter (10), Citrobacter (6), Serratia (3), Cedecea (3) and Chromobacterium (3). In conclusion hospitalized infants had a high incidence of fecal colonization with Gram-negative bacilli resistant to third generation cephalosporins. These bacteria were predominantly those known to produce broad spectrum beta-lactamases. This colonization was not necessarily associated with the infant receiving such antibiotics or with prolonged hospitalization.

Anti-Bacterial Agents↗

PubMed2001

Cefepime microbiologic profile and update.

BACKGROUND: The evolution of the cephalosporin class of antibiotics through modifications of the basic cephem structure has resulted in a new generation with improved antibacterial activity. Cefepime is a prototypic agent of this new class of fourth generation cephalosporins. OBJECTIVE: To review the microbiologic profile of cefepime. RESULTS: Cefepime, which is a zwitterion, has a net neutral charge that allows it to penetrate the outer membrane of Gram-negative bacteria faster than third generation cephalosporins. It is more stable against beta-lactamases because of the lower affinity of the enzymes for cefepime when compared with third generation cephalosporins. As a result of these structural attributes, cefepime has in vitro activity against pathogens that are prevalent in pediatric infections. This agent offers the advantage of Gram-positive coverage similar to that of cefotaxime and ceftriaxone, as well as good activity against Pseudomonas aeruginosa and many enteric bacilli that are resistant to third generation cephalosporins, including clinical isolates of Enterobacter spp. and Citrobacter freundii. CONCLUSIONS: Based on its spectrum of activity cefepime is an option for the treatment of pediatric infections caused by susceptible pathogens.

Cefepime↗

PubMed1989

Initial antibiotic therapy for alligator bites: characterization of the oral flora of Alligator mississippiensis.

An open thumb fracture resulting from an alligator bite became infected with Aeromonas hydrophila, Enterobacter agglomerans, and Citrobacter diversus. The patient was treated by surgical debridement and antibiotic therapy. We obtained cultures from the mouth of ten alligators to characterize their oral flora. Initial empiric therapy after alligator bites should be directed at gram-negative species, in particular, Aeromonas hydrophila and anaerobic species including Clostridium. Of the numerous fungi that were isolated, none has been reported to result in wound infection after alligator bites.

Adult↗

PubMed2003

Etiologic diagnosis of 204 pericardial effusions.

The etiologic evaluation of pericardial effusion is frequently unsuccessful when noninvasive methods are used. To determine the cause of the current episode, all patients with echographically identified pericardial effusion from May 1998 to December 2002 underwent noninvasive diagnostic testing of blood, throat, and stool samples. Patients with postpericardiotomy syndrome were excluded. To analyze the value of our tests, we tested randomly selected blood donors as negative controls. Among 204 included patients, 107 (52.4%) had a final etiologic diagnosis: the etiology of 52 was highly suspected at first examination and later confirmed (thyroid deficiency, 5 cases; systemic lupus erythematous, 7; rheumatoid arthritis, 7; scleroderma, 3; cancer, 25; and renal insufficiency, 5). A definite etiologic diagnosis was made in 11 patients from pericardial fluid analysis (cancer, 5 cases; tuberculosis, 3; Streptococcus pneumoniae, Citrobacter freundii, and Actinomyces, 1 case each). Among 141 patients considered to have idiopathic pericarditis, 44 (32.1%) gained an etiologic diagnosis by our systematic testing strategy. This included serologic evaluation of serum (Coxiella burnetii, 10 cases; Bartonella quintana, 1; Legionella pneumophila, 1; Mycoplasma pneumoniae, 4; influenza virus, 1), viral culture of throat swabs (enterovirus, 8 cases; and adenovirus, 1), high-level antinuclear antibodies (>1/400, 3 cases), and thyroid-stimulating hormone (15 abnormal results). Antibodies to Toxoplasma and cytomegalovirus, enterovirus recovered from rectal swabs, and low-level antinuclear antibodies were seen with equal frequency in patients and controls. Using our evaluation strategy, the number of pericardial effusions classified as idiopathic was less than in other series. Systematic testing for Q fever, Mycoplasma pneumoniae, thyroid abnormalities, and antinuclear antibodies, accompanied by viral throat cultures, frequently enabled us to diagnose diseases not initially suspected in patients with pericardial effusion.

Adolescent↗

PubMed2002

Evolution of the gyrB gene and the molecular phylogeny of Enterobacteriaceae: a model molecule for molecular systematic studies.

Phylogenetic trees showing the evolutionary relatedness of Enterobacteriaceae based upon gyrB and 16S rRNA genes were compared. Congruence among trees of these molecules indicates that the genomes of these species are not completely mosaic and that molecular systematic studies can be carried out. Phylogenetic trees based on gyrB sequences appeared to be more reliable at determining relationships among Serratia species than trees based on 16S rRNA gene sequences. gyrB sequences from Serratia species formed a monophyletic group validated by significant bootstrap values. Serratia fonticola had the most deeply branching gyrB sequence in the Serratia monophyletic group, which was consistent with its atypical phenotypic characteristics. Klebsiella and Enterobacter genera seemed to be polyphyletic, but the branching patterns of gyrB and 16S rRNA gene trees were not congruent. Enterobacter aerogenes was grouped with Klebsiella pneumoniae on the gyrB phylogenetic tree, which supports that this species could be transferred to the Klebsiella genus. Unfortunately, 16S rRNA and gyrB phylogenetic trees gave conflicting evolutionary relationships for Citrobacter freundii because of its unusual gyrB evolutionary process. gyrB lateral gene transfer was suspected for Hafnia alvei. Saturation of gyrB genes was observed by the pairwise comparison of Proteus spp., Providencia alcalifaciens and Morganella morganii sequences. Depending on their level of variability, 16S rRNA gene sequences were useful for describing phylogenetic relationships between distantly related Enterobacteriaceae, whereas gyrB sequence comparison was useful for inferring intra- and some intergeneric relationships.

DNA Gyrase↗

PubMed1979

The strategy of infection as a criterion for phylogenetic relationships of non-coli phages morphologically similar to phage T7.

Five phages which are morphologically similar to coliphage T7 but attack other host bacteria have been compared to T7 and to its relative, T3, by the following criteria: (a) cross-reactivity with antisera against T7 and T3, (b) DNA base sequence homologies, as determined by the C0t technique, (c) synthesis of two phage-coded enzymes: RNA polymerase and SAMase, (d) patterns of phage-directed protein synthesis, as determined by SDS-polyacrylamide gel electrophoresis of phage coat subunits. As judged by all these criteria, Pseudomonas phage PX3 is not related to T7; thus, morphological similarity was attributed to convergent evolution. The other phages, i.e. Serratia phage IV, Psuedomonas phage gh-1, Citrobacter phage ViIII and Klebsiella phage No. 11, were considered to be related to T7 on the basis of similarities in the patterns of phage-coded proteins and because, early after infection, these phages induced, as T7 does, an RNA polymerase which specifically transcribes the DNA of thehomologous phage. Phages IV and No. 11 also induced the early synthesis of SAMase (previously only known to occur upon T3 infection). With the exception of phage IV, however, DNA base sequence homologies with T7 or T3 seem to be poor or non-existent. The tested phages, again with the exception of phage IV, did not react with antiserum against T3 or T7. It is concluded that a particular pattern of phage-directed protein synthesis (as characterized by polyacrylamide gel electrophoresis and enzyme tests) may provide evidence for phylogenetic relationships between phages, even in cases where other criteria, such as genetic recombination, serological cross-reaction, and DNA base sequence homologies, fail to indicate relatedness.

Adenosylmethionine Decarboxylase↗

PubMed1978

Thermosensitive H1 plasmids determining citrate utilization.

Twelve thermosensitive H1 plasmids from strains of Salmonella typhi that had caused outbreaks of chloramphenicol-resistant typhoid fever in Vietnam, Thailand and India mediated citrate utilization (Cit+) in a prototrophic Escherichia coli K12 strain but not in the S. typhi strains from which they were derived. Four H1 plasmids from a similar outbreak in Mexico differed from the Far Eastern plasmids in not mediating citrate utlization but in mediating mercury resistance. H1 plasmids resembling the Far Eastern and the Mexican plasmids in regard to citrate utilization and mercury resistance were found in sewage in Britain. Citrate utilization was transferred to eight pathogenic strains of E. coli and to one strain each of Shigella flexneri and Shigella sonnei. Cultures of Cit+ bacteria grew more rapidly in citrate media at 28 degrees C than at 37 degrees C. Plasmid mutants that were more efficient at utilizing citrate were present in all such cultures--they grew equally well or better at 37 degrees C than at 28 degrees C. None of 222 strains of E. coli or Shigella that contained a variety of different plasmids were able to utilize citrate. This property was not transferred to the prototrophic E. coli K12 strain from Citrobacter (3 strains), Salmonella (39 strains), Proteus (44 strains), Klebsiella pneumoniae (33 strains) or Pseudomonas aeruginosa (44 strains).

Anti-Bacterial Agents↗