Properties of novel beta-lactamase produced by Bacteroides fragilis

Bacteroides fragilis strains were isolated from clinical specimens. B. fragilis G-237 was highly resistant to beta-lactam antibiotics due to beta-lactamase production. The purified enzyme from this strain gave a single protein band on polyacrylamide gel electrophoresis. The isoelectric point was 4.8, and the molecular weight was estimated to be 26,000 by sodium dodecyl sulfate-polyacrylamide gel electrophoresis. The enzyme activity was inhibited by p-chloromercuribenzoate and iodine but not by clavulanic acid or sulbactam. The purified enzyme showed a unique substrate profile by hydrolyzing at a high rate most of the cephalosporins, including cephamycin derivatives, penicillins, and imipenem (formerly imipemide, N-formimidoyl thienamycin, or MK 0787).

In-vitro and in-vivo antibacterial activity of imipenem against clinical isolates of bacteria

Imipenem, a derivative of thienamycin, a carbapenem antibiotic, has a broad spectrum of activity against aerobic (Gram-positive and Gram-negative) and anaerobic bacteria. It is quite stable to all tested beta-lactamases produced by various species of bacteria isolated from clinical specimens, whether plasmid or chromosomally mediated. One exception is its hydrolysis by the beta-lactamase produced by Pseudomonas maltophilia which is thus usually resistant to imipenem. Imipenem was found to be hydrolysed by renal dehydropeptidase-I residing on the luminal surface of the renal tubular epithelium. A dehydropeptidase-I inhibitor, cilastatin (MK-0791) was developed with specific inhibitory activity toward the renal dehydropeptidase-I and showed detectable effects in humans.

Transferable resistance to cefotaxime, cefoxitin, cefamandole and cefuroxime in clinical isolates of Klebsiella pneumoniae and Serratia marcescens

In conjugational crosses, three Klebsiella pneumoniae strains and one Serratia marcescens strain have been demonstrated to transfer resistance determinants to newer types of cephalosporins. While Klebsiella strains donated cefotaxime, cefamandole and cefuroxime resistance to Escherichia coli K-12 recipients, the genetic analysis of exconjugants after the transfer of plasmids from Serratia strains to Proteus or Salmonella recipients showed that the cefoxitin resistance determinant was also co-transferred. In subsequent transfer cycles of this plasmid, cefotaxime and cefoxitin resistance determinants segregated in contrast to the relative stability of plasmids derived from Klebsiella strains in subsequent transfer cycles. From results obtained in this study, it may be concluded that in some strains of nosocomial Enterobacteriaceae, resistance to newer cephalosporins could be transmissible and thus plasmid-located.

Induction of cephalosporinase production by various penicillins in enterobacteriaceae

The inducer activity of seven penicillins for cephalosporinase (CSase) production and their antibacterial activity against CSase-producing strains were studied using clinical isolates of Proteus morganii, P. rettgeri, P. vulgaris, Enterobacter cloacae, and Serratia marcescens. Piperacillin, apalcillin, and methicillin showed rather low inducer activity for CSase production in all strains tested. On the other hand, ampicillin, carbenicillin, and sulbenicillin showed high inducer activity for CSase production. Piperacillin, apalcillin, and ampicillin were less stable to CSases than were carbenicillin, sulbenicillin, and methicillin, but much more stable than benzylpenicillin. In the growing culture of CSase-producing strains, piperacillin and apalcillin were rather stable. Against CSase-producing strains, piperacillin and apalcillin were more active than other penicillins tested.

Efficacy of BRL 25000 against Serratia marcescens, Enterobacter cloacae, and Citrobacter freundii in urinary tract infections

Synergism between amoxicillin and clavulanic acid was not expected against cephalosporinase-producing bacterial strains because clavulanic acid has little inhibitory action on cephalosporinases. However, in a clinical trial of BRL 25000 (amoxicillin-clavulanic acid), excellent results were obtained in complicated urinary tract infections caused by Serratia marcescens, Enterobacter cloacae, and Citrobacter freundii strains which produced cephalosporinase and were highly resistant to amoxicillin alone. The good clinical efficacy of BRL 25000 in such urinary tract infections was probably due to the fact that the urinary concentration of clavulanic acid was higher than its minimal inhibitory concentrations for these strains.

Mapping of the gene specifying aminoglycoside 3'-phosphotransferase II on the Pseudomonas aeruginosa chromosome

We examined the aminoglycoside inactivation enzymes in Pseudomonas aeruginosa strains, seven clinical isolates and seven laboratory strains without plasmids. All strains were found to possess the enzyme aminoglycoside 3'-phosphotransferase II [APH(3')-II]. We isolated an APH(3')-II-deficient mutant from a PAO strain by mutagenesis with N-methyl-N'-nitro-N-nitrosoguanidine. By plasmid (FP5 or R68.45)-mediated conjugation, we determined the locus of the gene specifying the APH(3')-II between trp-6 and pro-82 on the PAO chromosome and designated this gene aphA. It was concluded that the intrinsic resistance of P. aeruginosa to kanamycins, neomycins, paromomycins, ribostamycin, and butirosins was due to this newly determined gene.

Antibacterial activity of cefoperazone alone and in combination against cephalosporinase-producing Enterobacter cloacae

The activity of cefoperazone against a strain with an inducible cephalosporinase and a mutant that produces the enzyme constitutively indicates that the low inducer activity of this antibiotic plays an important role in its activity against Enterobacter cloacae.

In vitro and in vivo antibacterial activity of AT-2266

AT-2266 [1-ethyl-6-fluoro-1,4-dihydro-4-oxo-7-(1-piperazinyl)-1,8-naphthyridine-3-carbo xylic acid] showed a broad spectrum of antibacterial activity against gram-positive and gram-negative microorganisms, including Pseudomonas aeruginosa. The in vitro antibacterial activity of AT-2266 was in general comparable to that of norfloxacin, but much higher than that of pipemidic or nalidixic acid. The 90% minimal inhibitory concentrations (MIC90s) of AT-2266 for P. aeruginosa resistant to gentamicin (MIC range, 25 to greater than 200 microgram/ml) and Enterobacteriaceae resistant to nalidixic acid (25 to greater than 1,600 micrograms/ml) were 3.13 and 12.5 micrograms/ml, respectively. The to nalidixic acid (25 to 1,600 micrograms/ml) were 3.13 and 12.5 micrograms/ml, respectively. The MICs of AT-2266 were only slightly affected by the addition of horse serum or sodium cholate, by the pH of the medium, and by inoculum size. AT-2266 was sodium cholate, by the pH of the medium, and by inoculum size. AT-2266 was bactericidal at concentrations near its MIC value. The 50% effective doses of AT-2266 after oral administration against systemic infections in mice were about 1/2 those of norfloxacin, about 1/10 those of pipemidic acid, and between 1/20 and 1/40 those of nalidixic acid.

Drug resistance and R plasmids in Escherichia coli strains isolated from broilers

In 1978, 1,021 Escherichia coli strains were isolated from 105 field broilers (F) and 1,058 strains from 106 broilers in a zootechnical experiment station (Z), and their drug-resistance patterns and the presence of conjugative R plasmids were compared. The resistance markers examined were tetracycline (TC), chloramphenicol (CM), streptomycin (SM), sulfonamides (SA), kanamycin (KM), and ampicillin (APC). The populations of individuals that excreted resistant strains were 100% in F and 58% in Z. Frequencies of isolation of drug-resistant strains among the total isolates were 93% in F and 36% in Z, indicating that the resistant strains are a rather high proportion of the intestinal flora in F but are slightly less prevalent in Z. The resistance pattern to (TC.SM.SA.KM) was seen at the highest frequency in both groups. Conjugative R plasmids were demonstrated more frequently in field broilers (F). The results reflect the wide use of antibiotics in the livestock industry, resulting in the appearance of drug-resistant strains mostly due to the presence of R plasmids.

Conjugal transferability of multiple resistance in Shigella strains

Shigella strains isolated in Japan between 1971 and 1979 were surveyed for drug resistance and distribution of R plasmids. Of 2,510 strains, 89.3% were resistant to either one or various combinations of four drugs, tetracycline, chloramphenicol, streptomycin, and sulfanilamide. About 66% of the Shigella isolates were quadruply resistant. The frequency of isolation of R plasmids from quadruply resistant Shigella strains was the highest when compared with other strains resistant to various combinations of the four drugs. The conjugal transferability of 204 quadruply resistant strains isolated between 1977 and 1979 was tested by various mixed-culture methods. Among the total strains examined, 70.6% carried transferable resistance when tested by the conventional broth culture method, 90.2% transferred their resistance when, in addition the replica-plating method was used and 97.5% could transfer their resistance when the membrane filter method was also used. Although the remaining five strains could not transfer their resistance by any of the mixed culture methods, the drug resistance of four of the five strains was mobilized by the concomitant presence of F-tet or T-kan plasmid. These results indicate that almost all of the quadruple resistance in Shigella isolates was mediated by plasmid.

Tn2011, a new transposon encoding oxacillin-hydrolyzing beta-lactamase

The type II penicillinase (oxacillin-hydrolyzing beta-lactamase, OXA-1) gene on plasmid Rms213 was transposed to various plasmids or to the host chromosome. The transposon bearing this gene, designated Tn2011, conferred resistance to ampicillin, streptomycin, sulfonamide, and mercuric chloride. By restriction endonuclease digestion and agarose gel electrophoresis, the molecular weight of Tn2011 was estimated to be 12.5 X 10(6). The transposition frequency of Tn2011 was about 10(-4) to 10(-5). The activity of type II penicillinase is related to the copy number of the replicon bearing Tn2011.

[Study of cefotaxime on stability to beta-lactamases and affinity to penicillin-binding proteins]

Cefotaxime (CTX) was compared with other cephems concerning stability to beta-lactamases and affinity to penicillin-binding proteins of Escherichia coli JE1011. The results are summarized as follows. 1. CTX showed potent activity against bacteria whose resistance is mediated by plasmids on chromosomal genes. 2. The antibacterial activity of CTX was not influenced by the transfer of 25 different plasmids to E. coli ML1410. 3. CTX was stable to typical cephalosporinases (CSases). This compound was slightly hydrolyzed by cefuroximases (CXases). 4. There was no difference between CTX and other cephems in the affinity to beta-lactamases. 5. CTX showed high affinity to the 1A, 1Bs and 3 fractions of penicillin-binding proteins of E. coli JE1011.

pMS76, a plasmid capable of amplification by treatment with chloramphenicol

pMS76 is a nonconjugative, 5.54-megadalton plasmid. This plasmid is present in Escherichia coli K12 cells at about 20 copies per chromosome. In addition, the pMS76 plasmid can be mobilized by conjugative plasmids and it shares a number of other properties with the amplifiable ColE1 plasmid, including the ability to amplify copy number in the presence of chloramphenicol. However, pMS76 is compatible with ColE1-like replicons, pBR313, and with other multicopy plasmids, RSF1030 and pACYC184. Also the replication of pMS76 is rifampicin sensitive and requires DNA polymerase 1.

Incompatibility group K plasmids in bacteria isolated from a urinary tract infection

Citrobacter freundii and Klebsiella pneumoniae were concurrently isolated from a patient with a urinary tract infection. Transferable drug resistant plasmids were isolated from both strains, pMS434 and pMS435. These plasmids belonged to incompatibility group K and both carried genes governing resistance to various aminoglycoside antibiotics, i.e., kanamycin, gentamicin C complex, streptomycin, and 3',4'-dideoxykanamycin B, in addition to those governing resistance to sulfanilamide and ampicillin. They inactivated kanamycin, gentamicin C complex and 3',4'-dideoxykanamycin by adenylylation and kanamycin by phosphorylation. Electron microscopic observations disclosed that the molecular weights of the plasmids were about 67.8 megadaltons. These results indicated the similarity in genetic constitution of the two plasmids. This was the second isolation of incompatibility group K plasmids, following that reported by Hedges and Datta (Nature 234: 220-221, 1971).

Characterization of cephalosporinases from Bacteroides fragilis, Bacteroides thetaiotaomicron and Bacteroides vulgatus

The susceptibility of 80 Bacteroides fragilis group strains isolated from clinical specimens to beta-lactam antibiotics was investigated by agar dilution method. Twenty strains showed high resistance to the antibiotics. The resistance level of the isolates to cephaloridine was related to the amount of beta-lactamase activity (cephalosporinase; CSase) produced. B. fragilis GN-11477, B. thetaiotaomicron GN11478 and B. vulgatus GN11479 were selected from among the CSase producing strains, and the enzymes were purified about 300-fold by affinity chromatography employed ampicillin as ligand bound to activated CH Sepharose 4B. The enzyme preparations gave a single protein band on polyacrylamide gel electrophoresis. The molecular weights of the three enzymes were estimated to be approximately 32,000 and their isoelectric points were 5.2, 4.9 and 4.5, respectively. The optimal pH and the optimal temperature of the enzymes were 7.2 and 37 degrees C, respectively. The enzyme activities were inhibited by iodine, some divalent ions, p-chloromercuribenzoate, clavulanic acid, cephamycin derivatives and cloxacillin. The enzymes showed hydrolytic activity against cephaloridine, cephalothin, cefazolin, cefuroxime and also newly introduced cephalosporins such as cefotaxime, cefoperazone and cefmenoxime. Each mouse antisera obtained against the purified enzymes showed cross-reactions with its each enzyme and others in neutralization test.

In vitro and in vivo antibacterial activity of T-1982, a new semisynthetic cephamycin antibiotic

The activities of T-1982 (sodium 7 beta-[(2R, 3S)-2-(4-ethyl-2, 3-dioxo-1-piperazine-carboxamido)-3-hydroxybutanamido]-7 alpha-methoxy-3-[(1-methyl-1H-tetrazol-5-yl)thiomethyl]-3-cephem-4-carboxylate) against various gram-positive and gram-negative bacteria were compare with those of cefmetazole, cefoxitin, cefazolin, and cefoperazone. T-1982 was active against both gram-positive and gram-negative bacteria, including genera resistant to the other cephalosporins. T-1982 exhibited greater activity than did cefmetazole, cefoxitin, cefazolin, or cefoperazone against Escherichia coli, Klebsiella pneumoniae, Proteus mirabilis, and Serratia marcescens and was also highly active against Bacteroides fragilis. T-1982 was as stable to various beta-lactamases as were cefmetazole and cefoxitin. The therapeutic activities of T-1982 in mice experimentally infected with various gram-negative bacteria were superior to those of cefmetazole, cefoxitin, cefazolin, and cefoperazone.

Antibacterial activities of SM-1652 compared with those of other broad-spectrum cephalosporins

The in vitro and in vivo activities of Sm-1652 were compared with those of other cephalosporins. SM-1652 possessed a wide antibacterial spectrum which included activity against Pseudomonas aeruginosa. It also exhibited potent antibacterial activities against gram-positive cocci and clinical isolates of glucose nonfermentative bacteria. Most notably, its activity against glucose nonfermentative bacteria was the highest of all of the drugs tested. The bactericidal activity of SM-1652 was compared with that of cefoperazone. The difference between the minimum bactericidal concentration and the minimum inhibitory concentration of SM-1652 was actually smaller than that of cefoperazone for Escherichia coli and clinical isolates of indole-positive Proteus spp. SM-1652 was stable for most cephalosporinases but was hydrolyzed to some extent by penicillinases. The in vivo therapeutic effect of SM-1652 against infections in mice was better than those of cefazolin and cefoxitin. The in vivo antipseudomonal activity of SM-1652 was second to that of cefsulodin.

Isolation and characterization of a streptomycin resistance plasmid from Pseudomonas cepacia

A plasmid, Rms425, mediating resistance to streptomycin(Sm) and mercury(Hg) was isolated from Pseudomonas cepacia GN11131 of clinical origin. Rms425 was transferred to Pseudomonas cepacia, Pseudomonas aeruginosa and Escherichia coli strains by transformation with purified DNA and by conjugation between isogenic strains of P. aeruginosa or of E. coli by mixing on membrane filters. The molecular weight of Rms425 was estimated to be about 32 megadaltons by electron microscopy and it was classified as incompatibility group P. Examining the incorporation of [gamma-32P] or [8-14C] from isotope-labelled ATP into Sm using the cell-free extracts from P. cepacia or E. coli strains harboring Rms425, we found that the Sm resistance conferred by Rms425 was due to the phosphorylation of the drug.

Comparative stability of newly introduced beta-lactam antibiotics to renal dipeptidase

Renal dipeptidase purified from swine kidney hydrolyzed N-formimidoyl thienamycin, carpetimycins A and B, and Sch29482, but not azthreonam, penicillin G, or cephaloridine.

In vitro and in vivo activity of DL-8280, a new oxazine derivative

DL-8280, 9-fluoro-3-methyl-10-(4-methyl-1-piperazinyl)-7-oxo-2,3-dihydro-7H- pyrido-(1,2,3-de)1,4-benzoxazine-6-carboxylic acid, is a new nalidixic acid analog with a broad spectrum of antibacterial activity against gram-negative and gram-positive bacteria, including obligate anaerobes. The activity of DL-8280 against Enterobacteriaceae, Pseudomonas aeruginosa, Haemophilus influenzae, Neisseria gonorrhoeae, and Clostridium perfringens was roughly comparable to that of norfloxacin and far exceeded that of pipemidic acid and nalidixic acid. DL-8280 had greater activity against Staphylococcus spp., Streptococcus spp., Pseudomonas maltophilia, Acinetobacter spp., and Bacteroides fragilis than did norfloxacin, pipemidic acid, and nalidixic acid. Nalidixic acid-resistant Enterobacteriaceae, ampicillin-resistant gonococci, and clindamycin-resistant obligate anaerobes were also susceptible to DL-8280. The activity of DL-8280 was affected very little by inoculum size, and its action was bactericidal at two times the minimal inhibitory concentrations at most. Administered orally to mice experimentally infected with Staphylococcus aureus, Streptococcus pyogenes, Escherichia coli, Proteus mirabilis, Serratia marcescens, or P. aeruginosa, DL-8280 was 2 to 7 times more effective than norfloxacin and 7 to more than 50 times more active than pipemidic acid.

Purification and properties of inducible penicillin beta-lactamase isolated from Pseudomonas maltophilia

Two types of beta-lactamase were found in the cell-free extract from Pseudomonas maltophilia GN12873. One was an inducible penicillin beta-lactamase, and the other was an inducible cephalosporin beta-lactamase. The purified penicillin beta-lactamase gave a single protein band on polyacrylamide gel electrophoresis. The isoelectric point was 6.9, and the approximate molecular weight was 118,000 by gel filtration and 26,000 by sodium dodecyl sulfate-polyacrylamide gel electrophoresis, suggesting that this enzyme consisted of four subunits. For the hydrolysis of penicillin G, the optimal pH was 8.0 and the optimal temperature was 35 degrees C. The enzyme activity was inhibited by cephamycin derivatives, carpetimycins A and B, iodine, and HgCl2, but not by clavulanic acid. Furthermore, beta-lactamase activity was almost completely inhibited by EDTA but was recovered by the addition of zinc ion. The enzyme showed a unique substrate profile, hydrolyzing N-formimidoyl thienamycin at a significant rate.

Properties of a new penicillinase type produced by Bacteroides fragilis

A highly penicillin-resistant strain of Bacteroides fragilis, strain GN11499, was found among 80 clinical isolates of the B.fragilis group and appears to produce a new type of penicillinase. Penicillinase activity was detected in crude extracts and had a specific activity of 0.25 U/mg of protein. About 20% of the enzyme was released into the surrounding medium during growth. The enzyme hydrolyzed ampicillin and cloxacillin more rapidly than it did penicillin G, carbenicillin, and cephaloridine. Relative rates in a crude extract with penicillin G as 100 were ampicillin, 357; carbenicillin, 57; cloxacillin, 271; and cephaloridine, 71. Enzyme activity was inhibited by clavulanic acid, CP-45, 899, N-formimidoyl thienamycin, cefoxitin, moxalactam, and p-chloromercuribenzoate. The enzyme had a molecular weight of approximately 41,500 and an isoelectric point of 6.9. Penicillinase production and tetracycline resistance were transferred from B.fragilis GN11499 to two susceptible strains of B.fragilis and Bacteroides vulgatus by filter mating.

Plasmid-mediated gentamicin resistance of Pseudomonas aeruginosa and its lack of expression in Escherichia coli

We isolated 11 nonconjugative plasmids mediating resistance to aminoglycoside antibiotics, including gentamicin, from Pseudomonas aeruginosa strains. Their genetic properties were investigated in both P. aeruginosa and Escherichia coli transformants. The plasmid molecular weights ranged from 11 x 10(6) to 24 x 10(6). A low level or complete absence of gentamicin resistance was observed when these plasmids were introduced into E. coli, but gentamicin resistance was restored when the plasmids were transferred back to P. aeruginosa from E. coli. Aminoglycoside-modifying enzyme activity was detected in P. aeruginosa harboring these plasmids, but was absent or greatly reduced in E. coli strains. This lack of expression may explain the observed decrease in aminoglycoside resistance.