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PubMed1983

Polycations sensitize enteric bacteria to antibiotics.

Polymyxin B nonapeptide, a polymyxin B derivative which lacks the fatty acyl part and the bactericidal activity of polymyxin, was shown to sensitize smooth encapsulated Escherichia coli (O18:K1) and smooth Salmonella typhimurium to hydrophobic antibiotics (novobiocin, fusidic acid, erythromycin, clindamycin, nafcillin, and cloxacillin). The polymyxin B nonapeptide-treated bacteria were as sensitive to these antibiotics as are deep rough mutants. A lysine polymer with 20 lysine residues (lysine 20) had a largely similar effect. Larger lysine polymers and the protamine salmine were bactericidal but, at sublethal concentrations, sensitized the strains to the antibiotics mentioned above, whereas lysine4, streptomycin, cytochrome c, lysozyme, and the polyamines cadaverine, spermidine, and spermine had neither bactericidal nor sensitizing activity.

Anti-Bacterial Agents↗
PubMed1984

Susceptibility of gram-negative bacteria to polymyxin B nonapeptide.

Subinhibitory concentrations of polymyxin B nonapeptide sensitized all 21 polymyxin-susceptible gram-negative bacterial strains studied to hydrophobic antibiotics such as fusidic acid, novobiocin, and erythromycin. The susceptibility increases were usually 30- to 300-fold. The strains included representatives of Escherichia coli with different O- and K-antigens, Klebsiella pneumoniae, Klebsiella oxytoca, Enterobacter cloacae, Enterobacter agglomerans, Salmonella typhimurium, Acinetobacter calcoaceticus, Pseudomonas aeruginosa, and Pseudomonas maltophilia. In contrast, polymyxin-resistant strains (Proteus mirabilis, Proteus vulgaris, Morganella morganii, Providencia stuartii, and Serratia marcescens) were resistant to the action of polymyxin B nonapeptide.

Acinetobacter↗
PubMed1985

In vitro activities of rifapentine and rifampin, alone and in combination with six other antibiotics, against methicillin-susceptible and methicillin-resistant staphylococci of different species.

The antistaphylococcal activity of rifapentine, a new rifamycin SV derivative, was evaluated in vitro and compared with that of rifampin. A total of 313 staphylococcal strains freshly isolated from clinical material and including representatives of all currently recognized Staphylococcus species of human origin were used. The susceptibility to methicillin of all the test strains was determined preliminarily. Despite minor differences with some species, the MICs of rifapentine were found to be substantially similar to those of rifampin. Methicillin-resistant strains of all species were most resistant to rifapentine and rifampin than were their methicillin-susceptible counterparts. For most strains tested, the MBCs of both rifamycins exceeded by twofold the respective MICs. Both the checkerboard dilution and time-kill methods were used to determine the interactions of rifapentine or rifampin with six different antibiotics: cefamandole, vancomycin, teicoplanin, gentamicin, erythromycin, and fusidic acid. No significant differences between the two rifamycins in the combinations were observed against either methicillin-susceptible or methicillin-resistant strains. Minor differences were noted depending on the second antibiotic tested or the staphylococcal species examined. Antagonism was never observed, and indifference was the prevalent response. Cases of synergism were observed occasionally with the checkerboard method and slightly more often with the time-kill method.

Anti-Bacterial Agents↗
PubMed1985

Comparative in vitro activity of coumermycin against methicillin-resistant Staphylococcus aureus.

Coumermycin was the most active agent in vitro against methicillin-resistant Staphylococcus aureus when compared with fusidic acid, imipenem, rifampin, trimethoprim-sulfamethoxazole, and vancomycin. The MICs of coumermycin ranged from 0.002 to greater than 4 micrograms/ml and from 0.5 to greater than 4 micrograms/ml for inocula of 10(4) and 10(6) CFU/ml, respectively. The combination of coumermycin with either cephalothin or ciprofloxacin showed some synergy; antagonism was found with gentamicin.

Aminocoumarins↗
PubMed1987

Susceptibility of anaerobic bacteria to FCE 22101.

The activity of FCE 22101 against 675 strains of anaerobic bacteria was determined by an agar dilution method. Its activity was compared with those of benzylpenicillin, piperacillin, cefoxitin, imipenem, clindamycin, metronidazole, chloramphenicol, vancomycin, fusidic acid, and bacitracin. FCE 22101 and imipenem (MIC, less than or equal to 0.5 mg/liter) were the most active agents against the anaerobic strains tested, except against Clostridium difficile strains. On the basis of these results, FCE 22101 appears to be a promising antimicrobial agent for treatment of anaerobic infections, and further clinical investigations are indicated.

Anti-Bacterial Agents↗
PubMed1989

Activities of daptomycin and teicoplanin against Staphylococcus haemolyticus and Staphylococcus epidermidis, including evaluation of susceptibility testing recommendations.

The in vitro activities of daptomycin, teicoplanin, and three other antimicrobial agents were determined against 105 strains of Staphylococcus haemolyticus and 92 strains of Staphylococcus epidermidis. The MICs for 90% of strains tested (MIC90s) of fusidic acid and rifampin were less than or equal to 0.25 microgram/ml. The MIC90s of daptomycin and vancomycin were less than or equal to 4 micrograms/ml. Teicoplanin had a comparable MIC90 of less than or equal to 4 micrograms/ml for isolates of S. epidermidis. However, MIC90s were 8 and 16 micrograms/ml for oxacillin-susceptible and oxacillin-resistant S. haemolyticus, respectively. Disk diffusion tests were evaluated for daptomycin and teicoplanin. Disks with 30 micrograms of teicoplanin performed satisfactorily when S. epidermidis was tested, but when S. haemolyticus was tested, there was a very major error rate of 10% and a minor error rate of 38%.

Anti-Bacterial Agents↗
PubMed1990

Ciprofloxacin does not inhibit mitochondrial functions but other antibiotics do.

At clinical concentrations, ciprofloxacin did not inhibit mitochondrial DNA replication, oxidative phosphorylation, protein synthesis, or mitochondrial mass (transmembrane potential). No difference in supercoiled forms of DNA was observed. The tetracyclines and chloramphenicol inhibited protein synthesis at clinically achievable concentrations, while rifampin, fusidic acid, and clindamycin did not.

Animals↗
PubMed1990

In vitro activities of new antimicrobial agents against multiresistant Staphylococcus aureus isolated from septicemic patients during a Belgian national survey from 1983 to 1985.

The antimicrobial agents most active against bacteremic isolates of oxacillin-resistant Staphylococcus aureus isolated from 1983 to 1985 were new fluoroquinolones, including PD 117,596 and PD 127,391 (MIC for 90% of isolates [MIC90] in agar, in micrograms per milliliter, 0.1) and temafloxacin, pefloxacin, and ofloxacin (MIC90, 0.4). Other active antimicrobial agents included fusidic acid (MIC90, 0.2) and fosfomycin (MIC90, 12.5). Vancomycin was active against all isolates. Mupirocin was very active (MIC90, 0.4).

Anti-Bacterial Agents↗
PubMed1990

Mathematical modeling of antimicrobial susceptibility data of Staphylococcus haemolyticus for 11 antimicrobial agents, including three experimental glycopeptides and an experimental lipoglycopeptide.

Antimicrobial MIC data were obtained for 96 strains of Staphylococcus haemolyticus and the following 11 antimicrobial agents: methicillin, gentamicin, rifampin, fusidic acid, ciprofloxacin, vancomycin, teicoplanin; three experimental glycopeptides, MDL 62,873, MDL 62,208, and MDL 62,224; and an experimental lipoglycopeptide, ramoplanin. Resistance to methicillin and gentamicin was present in over 50% of the strains, although resistance to the other agents was present in less than 10%. It is shown how application of mathematical modeling techniques can add to the understanding of such MIC data. MICs of methicillin and gentamicin were highly correlated, suggesting that evolutionary pressures for development of resistance to these agents were similar. The structural relationships among the glycopeptides were accurately reflected in their spatial relationships within the model. MICs of ramoplanin were negatively correlated with MICs of some other antimicrobial agents, particularly gentamicin, suggesting that this agent is more active against gentamicin-resistant strains. Methicillin-resistant strains were more tightly clustered than were methicillin-susceptible strains, suggesting that methicillin-resistant strains were more closely related to each other than were methicillin-susceptible strains. Mathematical modeling techniques enable more detailed analysis of MIC data.

Anti-Bacterial Agents↗
PubMed1992

The lipid A biosynthesis mutation lpxA2 of Escherichia coli results in drastic antibiotic supersusceptibility.

The conditionally lethal lpxA2 mutant of Escherichia coli, which lacks detectable UDP-N-acetylglucosamine acyltransferase activity and which produces greatly reduced amounts of lipid A after a shift to 42 degrees C (S. Galloway and C. R. H. Raetz, J. Biol. Chem. 265:6394-6402, 1990), was found to be, at conditions which promote normal growth, remarkably susceptible to a number of antibiotics. The MICs of hydrophobic antibiotics, such as rifampin, erythromycin, clindamycin, and fusidic acid, were 32- to greater than 128-fold lower for the lpxA2 strain than for the parent type strain, and those of the peptide antibiotics vancomycin and bacitracin were 32- and 256-fold lower, respectively. Futhermore, the lpxA2 strain was found to be sensitive to hypoosmotic conditions. Comparisons with the other characterized outer membrane permeability mutants, such as the heptose-deficient strains of E. coli and Salmonella typhimurium, the acrA and abs mutants of E. coli, and the ssc-1 and class SS-B mutants of S. typhimurium, indicated that the lpxA2 mutant had characteristically the most antibiotic-supersusceptible phenotype. These findings advocate the possible use of the lpxA2 strain as a tool in various fields of basic and applied bacterial research in which the impermeability of the outer membrane currently poses problems.

Drug Resistance, Microbial↗
PubMed1993

Outer membrane permeability barrier to azithromycin, clarithromycin, and roxithromycin in gram-negative enteric bacteria.

Mutations which severely affect the function of the outer membrane of Escherichia coli and Salmonella typhimurium (lpxA and firA mutations of lipid A synthesis and rfaE mutation of the lipopolysaccharide inner-core synthesis) were found to decrease the MICs of erythromycin, roxithromycin, clarithromycin, and azithromycin by factors of 32 to 512, 32 to 1,024, 64 to 512, and 16 to 64, respectively. The sensitization factors for three other hydrophobic antibiotics (rifampin, fusidic acid, and mupirocin) ranged from 16 to 300. The outer membrane permeability-increasing agents polymyxin B nonapeptide (3 micrograms/ml) and deacylpolymyxin B (1 microgram/ml) sensitized wild-type E. coli to azithromycin by factors of 10 and 30, respectively. Quantitatively very similar sensitization to the other macrolides took place. Polymyxin-resistant pmrA mutants of S. typhimurium displayed no cross-resistance to azithromycin. Proteus mirabilis mutants which were sensitized to polymyxin by a factor of > or = 300 to > or = 1,000 had a maximal two- to fourfold increase in sensitivity to azithromycin. These results indicate that azithromycin and the other new macrolides use the hydrophobic pathway across the outer membrane and that the intact outer membrane is an effective barrier against them. Furthermore, the results indicate that azithromycin, in contrast to polymyxin, does not effectively diffuse through the outer membrane by interacting electrostatically with the lipopolysaccharide.

Azithromycin↗
PubMed1995

Antimicrobial susceptibilities of Corynebacterium species and other non-spore-forming gram-positive bacilli to 18 antimicrobial agents.

The susceptibilities of 265 strains of Corynebacterium species and other non-spore-forming gram-positive bacilli to 18 antimicrobial agents were tested. Most strains were susceptible to vancomycin, doxycycline, and fusidic acid. Corynebacterium jeikeium and Corynebacterium urealyticum were the most resistant organisms tested. Resistance to beta-lactams, clindamycin, erythromycin, azythromycin, ciprofloxacin and gentamicin was common among strains of Corynebacterium xerosis and Corynebacterium minutissimum. Ampicillin resistance among Listeria monocytogenes was more prevalent than previously reported. Optochin, fosfomycin, and nitrofurantoin showed very little activity against most organisms tested, but the use of nitrofurantoin as a selective agent in culture medium may prevent the recovery of some isolates. Except for the unvarying activity of vancomycin against Corynebacterium species, the antimicrobial susceptibilities of the latter to other antibiotics are usually unpredictable, such that susceptibility tests are necessary for selecting the best antimicrobial treatment.

Anti-Bacterial Agents↗
PubMed2001

Natural antibiotic susceptibilities of Edwardsiella tarda, E. ictaluri, and E. hoshinae.

The natural antibiotic susceptibilities to 71 antibiotics of 102 Edwardsiella strains belonging to E. tarda (n = 42), E. ictaluri (n = 41), and E. hoshinae (n = 19) were investigated. MICs were determined using a microdilution procedure according to NCCLS criteria and German standards. All edwardsiellae were naturally sensitive to tetracyclines, aminoglycosides, most beta-lactams, quinolones, antifolates, chloramphenicol, nitrofurantoin, and fosfomycin. Edwardsiella species were naturally resistant to macrolides, lincosamides, streptogramins, glycopeptides, rifampin, fusidic acid, and oxacillin. Although slight species-dependent differences in natural susceptibilities to some antibiotics (e.g., macrolides and cefaclor) were seen, differences in natural susceptibility affecting clinical assessment criteria were only seen with benzylpenicillin. Whereas E. tarda was naturally resistant to benzylpenicillin, E. hoshinae was naturally sensitive. Natural sensitivity and resistance to this penicillin were found among the strains of E. ictaluri. The observed oxacillin sensitivity of E. ictaluri was attributed to the failure of the species to grow at higher salt concentrations found in oxacillin-containing microtiter plates. The present study describes a database concerning the natural susceptibility of Edwardsiella species to a wide range of antibiotics, which can be applied to validate forthcoming antibiotic susceptibility tests of these microorganisms.

Anti-Bacterial Agents↗
PubMed2004

In vitro activities of 28 antimicrobial agents against Staphylococcus aureus isolates from tertiary-care hospitals in Korea: a nationwide survey.

Staphylococcus aureus, one of the most frequently isolated pathogens in both hospitals and the community, has been particularly efficient at developing resistance to antimicrobial agents. As methicillin-resistant S. aureus (MRSA) has prevailed and, furthermore, as S. aureus with reduced susceptibility to vancomycin has emerged, the therapeutic options for the treatment of S. aureus infections have become limited. To update the current status of antibiotic resistance, clinical S. aureus isolates were collected from eight university-affiliated hospitals from June 1999 to January 2001. Susceptibility tests with 28 antibiotics were performed by the disk diffusion method. Among a total of 682 isolates, the methicillin resistance rate was 64% (439 of 682), and most of the MRSA isolates were resistant to multiple classes of antibiotics. Although a constitutive macrolide-lincosamide-streptogramin B resistance phenotype was common, no isolates were resistant to quinupristin-dalfopristin or linezolid. Rifampin, fusidic acid, trimethoprim-sulfamethoxazole, and arbekacin showed superior in vitro activity compared with the other antibiotics against the MRSA isolates. No isolates showed reduced susceptibility to vancomycin.

Anti-Bacterial Agents↗
PubMed2005

Antistaphylococcal activity of ceftobiprole, a new broad-spectrum cephalosporin.

Ceftobiprole (formerly BAL9141), the active component of the prodrug BAL5788 (ceftobiprole medocaril), is a novel cephalosporin with expanded activity against gram-positive bacteria. Among 152 Staphylococcus aureus isolates, including 5 vancomycin-intermediate and 2 vancomycin-resistant strains, MIC(50) and MIC(90) values for ceftobiprole were each 0.5 microg/ml against methicillin-susceptible strains and 2 mug/ml against methicillin-resistant strains. Against 151 coagulase-negative staphylococci (including 4 vancomycin-intermediate strains), MIC(50) and MIC(90) values were, respectively, 0.125 microg/ml and 1 microg/ml against methicillin-susceptible and 1 microg/ml and 2 microg/ml against methicillin-resistant strains. Teicoplanin was less active than vancomycin against coagulase-negative strains. Linezolid, quinupristin-dalfopristin, and daptomycin were active against all strains, whereas increased MICs for amoxicillin-clavulanate, cefazolin, minocycline, gentamicin, trimethoprim-sulfamethoxazole, levofloxacin, rifampin, mupirocin, fusidic acid, and fosfomycin were sometimes observed. At 2x MIC, ceftobiprole was bactericidal against 11 of 12 test strains by 24 h. Prolonged serial passage in the presence of subinhibitory concentrations of ceftobiprole failed to select for clones with MICs >4 times those of the parents; the maximum MIC achieved for ceftobiprole after 50 passages (in 1 of 10 strains) was 8 mug/ml. Single-passage selections showed very low frequencies of resistance to ceftobiprole irrespective of genotype or phenotype; the maximal ceftobiprole MIC of recovered clones was 8 mug/ml.

Anti-Bacterial Agents↗
PubMed2005

Sixteen homologs of the mex-type multidrug resistance efflux pump in Bacteroides fragilis.

Sixteen homologs of multidrug resistance efflux pump operons of the resistance-nodulation-cell division (RND) family were found in the Bacteroides fragilis genome sequence by homology searches. Disruption mutants were made to the mexB homologs of the four genes most similar to Pseudomonas aeruginosa mexB. Reverse transcription-PCR was conducted and indicated that the genes were transcribed in a polycistronic fashion and that the promoter was upstream of bmeA (the mexA homolog). One of these disruption mutants (in bmeB, the mexB homolog) was more susceptible than the parental strain to certain cephems, polypeptide antibiotics, fusidic acid, novobiocin, and puromycin. The gene for this homolog and the adjacent upstream gene, bmeA, were cloned in a hypersensitive Escherichia coli host. The resultant transformants carrying B. fragilis bmeAB were more resistant to certain agents; these agents also had lower MICs for the B. fragilis bmeB disruption mutants than for the parental strain. The putative efflux pump operon is composed of bmeA, bmeB, and bmeC (a putative outer membrane channel protein homologous with OprM). Addition of the efflux pump inhibitors, carbonyl cyanide m-chlorophenylhydrazone (a proton conductor that eliminates the energy source) and Phe-Arg beta-naphthylamide (MC-207,110) (the first specific inhibitor described for RND pumps in P. aeruginosa), resulted in lowered MICs in the parental strain but not in the bmeB disruption mutant, indicating that the bmeB pump is affected by these inhibitors. This is the first description of RND type pumps in the genus Bacteroides.

Amino Acid Sequence↗
PubMed2006

AsnB is involved in natural resistance of Mycobacterium smegmatis to multiple drugs.

Mycobacteria are naturally resistant to most common antibiotics and chemotherapeutic agents. The underlying molecular mechanisms are not fully understood. In this paper, we describe a hypersensitive mutant of Mycobacterium smegmatis, MS 2-39, which was isolated by screening for transposon insertion mutants of M. smegmatis mc2155 that exhibit increased sensitivity to rifampin, erythromycin, or novobiocin. The mutant MS 2-39 exhibited increased sensitivity to all three of the above mentioned antibiotics as well as fusidic acid, but its sensitivity to other antibiotics, including isoniazid, ethambutol, streptomycin, chloramphenicol, norfloxacin, tetracycline, and beta-lactams, remained unchanged. Uptake experiment with hydrophobic agents and cell wall lipid analysis suggest that the mutant cell wall is normal. The transposon insertion was localized within the asnB gene, which is predicted to encode a glutamine-dependent asparagine synthetase. Transformation of the mutant with wild-type asnB of mc2155 or asnB of Mycobacterium tuberculosis complemented the drug sensitivity phenotype. These results suggest that AsnB plays a role in the natural resistance of mycobacteria.

Anti-Bacterial Agents↗
PubMed1975

Inhibition of protein synthesis in intact HeLa cells.

Polysome analysis has proved to be a sensitive probe for the mode of action of inhibitors of protein synthesis in intact HeLa cells. To classify the active compounds as inhibitors of initiation, elongation, or termination, their effects on the cellular polyribosome pattern were compared under three conditions. These conditions tested (i) their direct effect on the polyribosome profile; (ii) their effect on ribosome run-off produced by hypertonicity; and (iii) their effects on recovery from hypertonicity. Using this technique, diacetoxyscirpenol, 2-(4-methyl-2,6-dinitroanilino)-N-methylpropionamide, and three alkaloids, harringtonine, isoharringtonine, and homoharringtonine, were found to be inhibitors of initiation. Polysome analysis indicated that in HeLa cells 7.8 x 10(-7) M pactamycin, which inhibited protein synthesis 94%, interfered with elongation as well as initiation under these conditions. Emetine, anisomycin, cycloheximide, and trichodermin each gave polysome patterns consistent with inhibition of elongation. Fusidic acid and aurintricarboxylic acid inhibited incorporation of [(14)C]leucine into intact HeLa cells, but polysome analysis did not localize any specific inhibitory effects to the initiation, elongation, or termination steps of protein synthesis. The use of specific inhibitors of initiation of protein synthesis has indicated that most, if not all, mammalian messenger ribonucleic acids contain a single initiation site.

Amino Acids↗