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23S ribosomal ribonucleic acid of macrolide-producing streptomycetes contains methylated adenine.

Coresistance to macrolide, lincosamide, and streptogramin B-type (MLS) antibiotics by a common biochemical mechanism characterizes clinically resistant pathogens. Of 10 streptomycetes tested for resistance to macrolide, lincosamide, and streptogramin B-type antibiotics, only 1, Streptomyces erythreus, the organism used for production of erythromycin, was found resistant to all three classes; moreover, it was the only streptomycete in the series tested found to contain N6-dimethyladenine (m62A) in 23S ribosomal ribonucleic acid, the structural alteration of ribosomal ribonucleic acid associated with clinical resistance. Of the seven streptomycetes tested for the presence of m62A and N6-methyladenine (m6A), two, S. fradiae and S. cirratus, which produce the macrolide antibiotics tylosin and cirramycin, respectively, were found to contain m6A, but not m62A. The remaining strains tested, including strains which produce lincomycin and streptogramins, contained neither m6A nor m62A.

Adenine↗

Genetic transformation of Streptococcus pneumoniae by heterologous plasmid deoxyribonucleic acid.

A number of heterologous plasmid deoxyribonucleic acids (DNAs) coding for erythromycin, tylosin, lincomycin, tetracycline, or chloramphenicol resistance have been introduced into Streptococcus pneumoniae via genetic transformation with frequencies that varied between 10(-5) to as high as 5 x 10(-1) per colony-forming unit. Transformation with plasmid DNA required pneumococcal competence, was competed by chromosomal DNA, and showed a saturation at about 0.5 micrograms/ml (with a recipient population of 3 x 10(7) colony-forming units of competent cells per ml). Plasmid transformation did not occur with a recipient strain, 410, defective in endonuclease I activity and in chromosomal genetic transformation. All erythromycin-resistant transformants examined contained covalently closed circular DNA with the same electrophoretic mobility on agarose gels as the donor DNAs, and when examined in detail the plasmid reisolated from the transformants had the same restriction patterns and the same specific transforming activity as the donor DNA. In the cases of two plasmids examined in detail--pAM77 and pSA5700 Lc9--most of the transforming activity was associated with DNA monomers; DNA multimers present in pSA5700 Lc9 also had biological activity. An unexpected finding was the demonstration of transformation (2 x 10(-5) per colony-forming unit) with plasmid DNAs linearized by treatment with S1 nuclease or with restriction endonucleases.

Bacillus subtilis↗

A complex attenuator regulates inducible resistance to macrolides, lincosamides, and streptogramin type B antibiotics in Streptococcus sanguis.

Macrolide-lincosamide-streptogramin B resistance specified by Streptococcus sanguis plasmid pAM77 involves an adenine methylase, whose synthesis, demonstrable both phenotypically and by analysis of methionine-labeled proteins made in Bacillus subtilis minicells, is inducible by erythromycin, lincomycin, and streptogramin type B antibiotics. Localization of the methylase structural gene, including its control region in DNA fragments obtained with restriction endonucleases, has been deduced from DNA blot experiments with characterized target and probe DNAs from other streptococci, combined with DNA sequence analysis and comparison of the putative streptococcal methylase sequence with that of a cognate methylase in staphylococcal plasmid pE194. The streptococcal methylase migrates electrophoretically in polyacrylamide gels with the mobility of a 29,000-dalton protein. The sequence organization of the putative streptococcal methylase mRNA leader sequence partially resembles its staphylococcal counterpart and can support a similar mechanism of secondary structure rearrangement leading to methylase synthesis. The deduced 5' leader sequence preceding the pAM77 methylase structural gene sequence comprises approximately 155 nucleotides within which one can identify a putative control peptide 36 amino acid residues in length (in contrast to 19 in the pE194 peptide) and at least 14 possible classes of overlapping inverted complementary repeat sequences (in contrast to 3 in the pE194 control region), one of which can sequester the sequence AGGAG 7 nucleotides upstream from the putative (methionine) start codon of the streptococcal methylase. Comparison of the pAM77 and pE194 methylase amino acid sequences and their respective nucleotide sequences shows 51% conservation of amino acid residues (124 of 244) and 59% conservation of nucleotide residues (433 of 738), which suggests a common origin for the two methylase structural gene sequences. Differences in mRNA base composition associated with conserved amino acid residues occur mostly in the third nucleotide ("wobble") position of codons and may reflect adaptation of methylase genes to optimal expression in host cells with differing codon use patterns.

Amino Acid Sequence↗

Construction and application of a promoter-probe plasmid that allows chromogenic identification in Streptomyces lividans.

We cloned a Streptomyces coelicolor A3(2) DNA fragment which directed synthesis of a brown pigment, presumably a shunt product in the actinorhodin biosynthetic pathway, on the plasmid vector pIJ41 in Streptomyces lividans. The pigment production was observed only when the DNA fragment was inserted downstream from a functional promoter sequence. By subcloning the fragment together with in vitro manipulation, a promoter-probe plasmid vector (pARC1) with a unique BamHI cloning site was constructed that allows chromogenic identification of transcriptional control signals in Streptomyces lividans based on the expression of the cloned pigment gene(s). The Escherichia coli tac (trp-lac hybrid) promoter, consisting of 92 base pairs and a promoter region including the leader sequence of erythromycin resistance gene (ermC) on staphylococcal plasmid pE194, when ligated in the correct orientation in the BamHI site of pARC1, promoted expression of the cloned pigment gene(s) in Streptomyces lividans, whereas the Saccharomyces cerevisiae GAL7 promoter did not. In the case of the ermC, induction of the pigment production by the addition of either erythromycin or lincomycin, but not virginiamycin, was observed. The system was also shown to be useful and convenient in isolating transcriptional control signals of Streptomyces chromosomal DNA and estimating their activities.

Cloning, Molecular↗

Complementarity of Bacillus subtilis 16S rRNA with sites of antibiotic-dependent ribosome stalling in cat and erm leaders.

Inducible cat and erm genes are regulated by translational attenuation. In this regulatory model, gene activation results from chloramphenicol- or erythromycin-dependent stalling of a ribosome at a precise site in the leader region of cat or erm transcripts. The stalled ribosome is believed to destabilize a downstream region of RNA secondary structure that sequesters the ribosome-binding site for the cat or erm coding sequence. Here we show that the ribosome stall sites in cat and erm leader mRNAs, designated crb and erb, respectively, are largely complementary to an internal sequence in 16S rRNA of Bacillus subtilis. A tetracycline resistance gene that is likely regulated by translational attenuation also contains a sequence in its leader mRNA, trb, which is complementary to a sequence in 16S rRNA that overlaps with the crb and erb complements. An in vivo assay is described which is designed to test whether 16S rRNA of a translating ribosome can interact with the crb sequence in mRNA in an inducer-dependent reaction. The assay compares the growth rate of cells expressing crb-86 with the growth rate of cells lacking crb-86 in the presence of subinhibitory levels of inducers of cat-86, chloramphenicol, fluorothiamphenicol, amicetin, or erythromycin. Under these conditions, crb-86 retarded growth. Deletion of the crb-86 sequence, insertion of ochre mutations into crb-86, or synonymous codon changes in crb-86 that decreased its complementarity with 16S rRNA all eliminated from detection inducer-dependent growth retardation. Lincomycin, a ribosomally targeted antibiotic that is not an inducer of cat-86, failed to selectively retard the growth of cells expressing crb-86. We suggest that cat-86 inducers enable the crb-86 sequence in mRNA to base pair with 16S rRNA of translating ribosome. When the base pairing is extensive, as with crb-86, ribosomes become transiently trapped on crb and are temporarily withdrawn from protein synthesis to the extent that growth rate declines. Site-specific positioning of an antibiotic-stalled ribosome is a hallmark of the translational attenuation model. The proposed rRNA-mRNA interaction may precisely position the ribosome on the stall site and perhaps contributes to stabilizing the ribosome leader mRNA complex.

Bacillus subtilis↗

Altered lipopolysaccharide characteristic of the I69 phenotype in Haemophilus influenzae results from mutations in a novel gene, isn.

The 169 phenotype of Haemophilus influenzae results from a mutation leading to a lipopolysaccharide molecule consisting only of lipid A and a single phosphorylated 2-keto-3-deoxyoctulosonic acid residue. In this paper we describe the identification of a gene which, when mutated, results in the 169 phenotype. We have named the gene isn. The predicted amino acid sequence of Isn is homologous to the product of the lmbN gene involved in the biosynthesis of the sugar-containing antibiotic lincomycin by Streptomyces lincolnensis. lsn is situated between two loci that are homologous to the dpp and art periplasmic permease systems in Escherichia coli. Northern (RNA) blot and primer extension analyses reveal that isn is transcribed as a monocistronic mRNA. Potential functions of Isn protein are discussed.

Amino Acid Sequence↗

Transcriptional termination control of a novel ABC transporter gene involved in antibiotic resistance in Bacillus subtilis.

In members of one of the subfamilies of the bacterial ATP binding cassette (ABC) transporters, the two nucleotide binding domains are fused as a single peptide and the proteins have no membrane-spanning domain partners. Most of the ABC efflux transporters of this subfamily have been characterized in actinomycetes, producing macrolide, lincosamide, and streptogramin antibiotics. Among 40 ABC efflux transporters of Bacillus subtilis, five proteins belong to this subfamily. None of these proteins has been functionally characterized. We examined macrolide, lincosamide, and streptogramin antibiotic resistance in insertional disruptants of the genes that encode these proteins. It was found that only a disruptant of vmlR (formerly named expZ) showed hypersensitivity to virginiamycin M and lincomycin. Expression of the vmlR gene was induced by the addition of these antibiotics in growth medium. Primer extension analysis revealed that transcription of the vmlR gene initiates at an adenosine residue located 225 bp upstream of the initiation codon. From the analysis of the vmlR and lacZ fusion genes, a 52-bp deletion from +159 to +211 resulted in constitutive expression of the vmlR gene. In this region, a typical rho-independent transcriptional terminator was found. It was suggested that the majority of transcription ends at this termination signal in the absence of antibiotics, whereas under induced conditions, RNA polymerase reads through the terminator, and transcription continues to the downstream vmlR coding region, resulting in an increase in vmlR expression. No stabilization of vmlR mRNA occurred under the induced conditions.

ATP-Binding Cassette Transporters↗

SENSITIVITY OF COCCAL AND L FORMS OF STAPHYLOCOCCUS AUREUS TO FIVE ANTIBIOTICS.

Kagan, B. M. (Cedars of Lebanon Hospital, Los Angeles, Calif.), Susan Zolla, R. Busser, and Silvija Liepnieks. Sensitivity of coccal and L forms of Staphylococcus aureus to five antibiotics. J. Bacteriol. 88:630-632. 1964.-Antibiotics whose primary site of action is in the cell wall (penicillin and cephalothin) do not inhibit growth of L-phase organisms. In this study, kanamycin, neomycin, polymyxin B, lincomycin, and gentamycin were found to be more active against L-phase growth of Staphylococcus aureus in vitro than against the coccal forms. Therefore, their primary site of antimicrobial activity appears to be other than that involved in the synthesis or integrity of the cell wall.

Anti-Bacterial Agents↗

Antibacterial sensitivity of Bifidobacterium (Lactobacillus bifidus).

The antibacterial sensitivity patterns of gram-positive, nonsporeforming, anaerobic bacilli variously classed as Lactobacillus bifidus, Actinomyces bifidus, or Bifidobacterium were studied by the plate dilution method. A total of 34 strains, mostly from human feces, was studied. Three species, B. longum, B. adolescentis, and B. bifidum, were represented with 11, 11, and 6 strains, respectively. The other six strains fell into four other species. Most strains of all types resisted 100 mug/ml or more of neomycin, polymyxin B, and nalidixic acid. They were somewhat less resistant to kanamycin and still less so to streptomycin. All strains were inhibited by less than 1 mug/ml of penicillin G and erythromycin, by 3.1 units or less per ml of bacitracin, by 3.1 mug/ml or less of chloramphenicol, and by 6.2 mug/ml or less of tetracycline and lincomycin. Most strains were inhibited by 3.1 mug/ml of vancomycin. Results were very variable with cephalothin and nitrofurantoin, with some strains quite resistant. With half of the drugs tested, there were moderate differences in sensitivity between different species. These data are discussed in relation to the effect of antimicrobial agents on bifid bacilli in the normal human fecal flora, in relation to the implications thereof, and in relation to the usefulness of several agents (particularly neomycin, nalidixic acid, and polymyxin B) in selective media for Bifidobacterium.

Anti-Bacterial Agents↗

Neisseria gonorrhoeae strains inhibited by vancomycin in selective media and correlation with auxotype.

Strains of Neisseria gonorrhoeae that failed to grow on Thayer-Martin (T-M) and Martin-Lewis (M-L) media accounted for 2.0% of isolates at the University of Colorado Hospital and its Venereal Disease Clinic. A total of 31 inhibited and 31 control strains were compared by agar dilution testing for their susceptibilities to 13 antimicrobial agents used for treatment or in selective media. All 62 isolates were resistant to lincomycin, colistin, nystatin, amphotericin B, trimethoprim lactate, polymyxin B, and anisomycin. Vancomycin was the inhibitory antibiotic for N. gonorrhoeae in both T-M and M-L media. The vancomycin-inhibited strains were also significantly more sensitive to penicillin and ampicillin than were the control strains (P less than 0.001). The presence of the other antibiotics in selective media did not affect the minimum inhibitory concentrations of vancomycin for gonococci. All 31 inhibited strains were sensitive to 8.0 micrograms of vancomycin per ml, and 26 of these were sensitive to 2.0 microgram/ml. Decreasing the size of inoculum of gonococci results in greater inhibition by any given concentration of vancomycin. The vancomycin-sensitive strains contained significantly more arginine- hypoxanthine-, and uracil-requiring auxotypes (28 out of 31) than did the control strains (9 out of 31). As with T-M medium, some strains of gonococci will be missed when M-L medium with 4.0 micrograms of vancomycin per ml is the only medium used for the diagnosis of gonorrhea. This may be of particular importance in the confirmation of disseminated infection with Arg- Hyx- Ura- auxotypes of N. gonorrhoeae when cultures of blood, joint fluid, or skin lesions are negative.

Anti-Bacterial Agents↗

Dilution technique for isolation of Haemophilus from swine lungs collected at slaughter.

A total of 307 lungs obtained from a slaughterhouse were cultured by a dilution technique for the isolation of Haemophilus spp. The technique consisted of performing serial (10-fold) dilutions of the tissue samples to a dilution of 10(-5). Two selective media were used. L broth consisted of a basal brain heart infusion broth containing 5% horse serum, 5% yeast extract, and 100 micrograms of NAD and 0.5 microgram of lincomycin per ml. L-B broth was identical to L broth, except 1.5 microgram of bacitracin per ml was included. The broths were incubated overnight and then plated onto blood agar. A total of 83 (27%) isolates were obtained, and both media proved to be necessary, as a proportion of isolates grew in one of the media employed but not in the other. Of the isolates, 66.3% were urease positive and most of these (98%) were classified as "minor group" strains. Urease-negative strains (27.7%) were classified as Haemophilus parasuis.

Animals↗

Role of proteinase in the formation of inhibitory levels of hematin by group A streptococcus cultures on blood-containing media.

Group A streptococci were tested for proteinase production and for the possible relationship of this production to the generation of bacteriocinlike inhibitor activity. Of 126 strains tested, 83% were positive for proteinase, and a similar distribution was found among strains isolated in association with rheumatic fever (89%) and nephritis (94%) and from uncomplicated acute infections (78%). Although application of an inhibitor production (P) typing scheme demonstrated a variety of P types, all of the proteinase-positive strains produced inhibitory activity and over 65% of these strains were P type 204. It was shown that hematin was responsible for this P type 204 activity and that it was produced only by actively proteolytic strains when grown on a hemoglobin-containing medium. Conditions optimizing proteinase production (anaerobic incubation at 37 degrees C on a test medium prepared from Columbia agar base [GIBCO Laboratories, Grand Island, N.Y.]) increased P type 204 activity. Interference with proteinase activity either by growth of the cultures at an alkaline pH or by incorporation of sub-growth inhibitory concentrations of either iodoacetic acid or lincomycin into the medium prevented production of P type 204 activity. Whether significant conversion of hemoglobin to hematin occurs in vivo and the possible implications of this conversion with regard to the pathogenesis of group A streptococcal infections remain to be determined.

Blood↗

Effects of transport temperature and medium on recovery of Bordetella pertussis from nasopharyngeal swabs.

We compared relative recoveries of Bordetella pertussis from simulated nasopharyngeal (NP) specimens incubated in three separate transport media at different temperatures. Transport media included one-half-strength Regan-Lowe (RL.5), Regan-Lowe with one-half-strength agar (RL.5A), and buffered charcoal-yeast extract agar supplemented with alpha-ketoglutarate, lincomycin, and anisomycin (BCYE alpha LA). For each transport medium, recovery of B. pertussis was least efficient after storage at 25 degrees C. The highest recovery of B. pertussis from a mixed culture was achieved with RL.5 at 4 degrees C. Overall, RL.5 and RL.5A were comparable as transport media whether held at 4 or 25 degrees C, but fewer organisms were recovered from BCYE alpha LA. In addition, Regan-Lowe (RL), Bordet-Gengou, and cyclodextrin media were compared as primary isolation media for recovering B. pertussis from simulated NP swabs held at 4 and 35 degrees C in RL.5 medium. The highest recovery of B. pertussis was obtained on RL primary isolation medium. Bordet-Gengou medium recovered only 80% and cyclodextrin medium recovered less than 60% of the numbers recovered on RL medium. Based on these results, refrigeration (4 degrees C) of NP swabs shipped in RL.5 transport medium and using RL as the primary isolation medium are recommended for recovering B. pertussis from swab specimens.

Bordetella pertussis↗

Antimicrobial susceptibility of ileal symbiont intracellularis isolated from pigs with proliferative enteropathy.

Proliferative enteropathy is caused by the microaerophilic obligate intracellular bacterium ileal symbiont (IS) intracellularis. Treatment of this disease is problematic because of the lack of in vivo or in vitro data on the activities of antimicrobial agents. A new procedure for determining the susceptibility of IS intracellularis was developed by using a tissue culture system which promotes the in vitro multiplication of this organism. Nineteen antimicrobial agents were evaluated in triplicate cultures for their intracellular and extracellular activities against up to three IS intracellularis strains isolated from pigs with proliferative enteropathy. The MIC was defined as the lowest concentration which prevented multiplication of 99% of the IS intracellularis isolates. Penicillin, erythromycin, difloxacin, virginiamycin, and chlortetracycline were the most active compounds tested, all with MICs of < or = 1 microgram/ml. Tiamulin and tilmicosin were the next most active compounds, with MICs of < or = 4 micrograms/ml. The MICs of aminoglycosides were generally > 32 micrograms/ml. Both lincomycin and tylosin were relatively inactive against the IS intracellularis strains tested, with MICs of 32 and 64 micrograms/ml, respectively. These results indicate that some compounds capable of intracytoplasmic accumulation and blocking bacterial protein synthesis were active against IS intracellularis strains isolated from pigs with proliferative enteropathy. The in vitro cultivation system shows promise as a method for studying the interaction between IS intracellularis and antimicrobial agents and for screening new antibiotics for use in therapy.

Animals↗

Emergence and spread in French hospitals of methicillin-resistant Staphylococcus aureus with increasing susceptibility to gentamicin and other antibiotics.

Oxacillin (methicillin) resistance in methicillin-resistant Staphylococcus aureus (MRSA) is associated with an increased incidence of resistance to other antibiotics, which has increased since it was first reported in 1969. In 1992 a new phenotype of MRSA arose in France; this was characterized by a heterogeneous expression of resistance to oxacillin and susceptibility to various antibiotics, including gentamicin but also tetracycline, minocycline, lincomycin, pristinamycin, co-trimoxazole, rifampin, and fusidic acid. In French hospitals a longitudinal nationwide surveillance of antibiotic resistance in S. aureus has allowed for the detection of changes in antibiotic susceptibility profiles. Seven French clinical laboratories (six from the mainland and one from the West Indies) reported the results of susceptibility testing of 57,347 S. aureus strains isolated in their institutes between 1992 and 1998. Over a 7-year period the incidence of isolation of gentamicin-susceptible MRSA (GS-MRSA) strains has steadily increased to represent, in 1998, 46.8 to 94.4% of the MRSA strains, irrespective of the overall incidence of MRSA. Two predominant types recognized by pulsed-field gel electrophoresis (PFGE) accounted for the majority of the GS-MRSA in different mainland hospitals, both differing from the predominant type observed in the French West Indies. Some GS-MRSA and gentamicin-resistant MRSA (GR-MRSA) strains had closely related PFGE profiles, and hybridization studies confirmed the lack in GS-MRSA of the aac6'-aph2" gene, which confers resistance to all aminoglycosides, with conservation of the ant4' gene, which confers resistance to kanamycin, tobramycin, and amikacin. Thus, it is likely that certain GS-MRSA strains could have emerged from GR-MRSA strains by excision or deletion of the aac6'-aph2" gene.

Cross Infection↗

Processing of the precursor to a chloroplast ribosomal protein made in the cytosol occurs in two steps, one of which depends on a protein made in the chloroplast.

In pulse-chase experiments in which log-phase cells of Chlamydomonas reinhardtii were labeled in vivo for 5 min with H2(35)SO4, fluorographs of immunoprecipitates from whole cell extracts revealed that chloroplast ribosomal proteins L-2, L-6, L-21, and L-29, which are made in the cytosol and imported, appeared in their mature forms. However, in the case of chloroplast ribosomal protein L-18, which is also made in the cytoplasm and imported, a prominent precursor with an apparent molecular weight of 17,000 was found at the end of a 5-min pulse. This precursor was processed to its mature size (apparent molecular weight of 15,500) within the first 5 min of the subsequent chase. As determined by sodium dodecyl sulfate-polyacrylamide gel electrophoresis, the precursor to L-18 formed in vivo was 1.5 kilodaltons smaller than the primary product detected in translations of Chlamydomonas polyadenylated RNA in vitro. Upon a 10-min incubation with a postribosomal supernatant from Chlamydomonas, the 18,500-dalton precursor detected in vitro could be partially converted into a polypeptide that comigrated with the 17,000-dalton precursor detected in extracts of cells labeled in vivo. Under conditions in which the total amounts of chloroplast proteins had been reduced and cells were made to synthesize ribosomes rapidly, the apparent half-life of the 17,000-dalton precursor was extended over that seen in log-phase cells. When chloroplast protein synthesis was inhibited with lincomycin for 3 h before labeling under these conditions, the 17,000-dalton L-18 precursor but not the mature form was found, and the precursor was slowly degraded during a 60-min chase. When cells were placed in the dark for 3 h before labeling, processing of this precursor to the mature form appeared unaffected, but the chloroplast-synthesized ribosomal protein L-26 was detected, indicating that chloroplast protein synthesis was still occurring. We interpret these results to indicate that the maturation of protein L-18 in vivo involves at least two processing steps, one of which depends on a protein made on chloroplast ribosomes.

Chlamydomonas↗

Acute haematogenous osteitis.

During a 10-year period 217 cases of acute haematogenous osteitis were treated. In 131 patients the diagnosis was confirmed either radiologically or bacteriologically, but in the other 86 the diagnosis was based on clinical examination. Either cloxacillin or lincomycin proved to be effective if given before bacteriological diagnosis. Frequent clinical examination, assessing both local signs and the child's general state, will decide which child requires surgery (which should be reserved for the toxic child, the child with concomitant medical disorders lowering host resistance, and the child who does not respond to, or has a lesion which flares up after, initial conservative treatment). Constant vigilance is required by clinicians looking after children with this disease in order to reduce the disabling long-term sequelae.

Acute Disease↗