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The induction and expression of tetracycline resistance in R(+) minicells from Escherichia coli is incomplete, suggesting that some chromosomally mediated function is necessary for the full expression of tetracycline resistance.
All 17 Salmonella typhi strains tested from the epidemic in Mexico carried R factors of compatibility group H, conferring resistance to chloramphenicol, streptomycin, tetracycline, and sulfonamides. Some S. typhi strains carried, in addition, non-conjugative, ampicillin resistance plasmids and R factors of the I or A-C complex. All 20 Shigella dysenteriae 1 strains tested of epidemic origin carried O-group R factors. Ampicillin resistance in S. dysenteriae 1 was not proved to be plasmid borne. R factors of group H were not identified in any of the tested Mexican isolates other than S. typhi, but R factors of group O were identified in Escherichia coli, Shigella flexneri, and one strain of S. typhi, as well as in the epidemic S. dysenteriae. An R factor was identified which seemed to have two compatibility specificities, groups Iomega and O.
Escherichia coli K-12 carrying the R-factor R1 is resistant to ampicillin, chloramphenicol, and streptomycin. This resistance is due to R-factor-coded enzymes that metabolize the drugs. The effects of these enzymes on the survival of cell populations were studied in the presence of high concentrations of antibiotics. For all three antibiotics there were considerable inoculum effects. For ampicillin and chloramphenicol, the inoculum effect was due to detoxification of the medium, whereas streptomycin was not significantly metabolized. The survival of the population in the presence of streptomycin was due to the presence of resistant mutants. At high concentrations of ampicillin or chloramphenicol, the surviving cells were not mutants. Survival in the presence of ampicillin is presumably due to variations in resistance during the cell division cycle. The rate of acetylation of chloramphenicol decreased with time and was zero after 1 to 2 h. Treatment with high concentrations of chloramphenicol did not cause lysis of the cells but partially opened the outer membrane, causing excretion of beta-lactamase.
Escherichia coli K-12 carrying the R-factor R1 or R6K is resistant to streptomycin. The resistance is due to R-factor-coded enzymes that metabolize the drug. Streptomycin can be inactivated in two ways, either by adenylylation or by phosphorylation; both reactions require adenosine 5'-triphosphate. In this work we show that the R-factor R1 codes for an enzyme that adenylylates streptomycin and that the enzyme activity is located in the periplasmic volume, whereas the R-factor R6K codes for a streptomycin phosphorylase, which is mainly cytoplasmic. From a strain without any R-factor or carrying different R-factors, mutants were isolated that are 10 times more resistant to streptomycin than the parent strains. This increased resistance is not due to increased amounts of metabolizing enzymes. The mutants have a decreased rate of uptake of streptomycin and an altered response to other antibacterial agents as well. The mutations are located on the chromosome and not on the plasmid. It is likely that the mutations cause changes in the outer layers of the cell envelope and that the increased resistance is due to the synergistic effect of an efficient penetration barrier and a low activity of inactivating enzyme.
A plasmid determining resistance to erythromycin, lincomycin, and vernamycin B(alpha) was isolated from a strain of Streptococcus pyogenes. The plasmid has a molecular weight of approximately 17 x 10(6) and is present to the extent of one to two copies per chromosomal genome equivalent.
An R factor carrying tetracycline resistance, the transfer of which was observed in mating cultures at 25 but not at 37 C, was demonstrated in strains of Salmonella typhimurium isolated from calves.
The plasmid RP1 was shown to contain a genetic region (the irp region) responsible for influencing the intrinsic resistance of Escherichia coli to penicillins but not to cephalosporins. Mutants in which the irp genes are inactive were isolated. RP1 carrying functional irp genes protected E. coli AS19 against lysozyme lysis and also enhanced resistance to actinomycin D, to nalidixic acid, and to rifampin. This plasmid also phenotypically repaired the hypersensitivity to penicillins of strain AS19, and also that of E. coli envA mutants. Similar regions were not detected on the plasmids R1 and R55.
A new R factor-mediated gentamicin acetyltransferase obtained from a clinical isolate of gentamicin-, tobramycin-, and kanamycin-resistant Klebsiella was characterized. R factor R 176 was transferred to Escherichia coli K-12 LA 290 from a Klebsiella. Resistance transfer, minimal inhibitory concentrations of various aminoglycoside antibiotics, enzymatic inactivation, and the isoelectric point of the enzyme obtained were determined. We found that R factor R 176 could govern the enzymatic 3-N acetylation of gentamicin, tobramycin, and kanamycin, and isoelectric point determinations suggested that the enzymes governed by R 176 and R 135 are different. The genes responsible for resistance to gentamicin, tobramycin, and kanamycin govern the synthesis of an isoenzyme of AAC(3)I, which we propose to call AAC(3)II.
A survey of clinical isolates from a hospital laboratory showed that Escherichia coli could be grouped into three classes of beta-lactam-antibiotic resistance by results of routine susceptibility testing to ampicillin, cephalothin, and carbenicillin. E. coli highly resistant to ampicillin and carbenicillin but not to cephalothin (class I) were found to have one of two levels of R factor-mediated, periplasmic-beta-lactamase which resembled R(TEM) and was located behind a permeability barrier to penicillins but not to cephalosporins. This permeability barrier appeared to act synergistically with the beta-lactamase in producing high levels of resistance to penicillins. E. coli highly resistant to ampicillin and cephalothin but not carbenicillin (class II) were found to have a beta-lactamase with predominantly cephalosporinase activity which was neither transferable nor releasable by osmotic shock. E. coli moderately resistant to one or to all three of these antibiotics (class III) were found to have low levels of different beta-lactamases including a transferable beta-lactamase which resembled R(1818). Thus, different mechanisms producing resistance to beta-lactam antibiotics could be deduced from the patterns of resistance to ampicillin, cephalothin, and carbenicillin found on routine susceptibility testing. E. coli of class I were much more prevalent than the other classes and the proportion of E. coli that were class I increased with duration of patient hospitalization. The incidence of class I E. coli rose only slightly over the past 7 years and that of class II E. coli remained constant despite increased usage of both cephalothin and ampicillin. These observations emphasize that the properties of the apparently limited number of individual resistance mechanisms that exist in a bacterial flora, such as their genetic mobility and linkages and the spectrum of their antibiotic inactivating enzymes and permeability barriers, may govern the effect that usage of an antibiotic has upon the prevalence of resistance to it and to other antibiotics.
Pseudomonas aeruginosa strain GN315, producing kanamycin acetyltransferase, can transmit a plasmid determining resistance to kanamycin, amikacin (BB-K8), butirosin, tobramycin, and sisomicin, but not gentamicin, to other pseudomonas strains. This plasmid, pMG5, belongs to the same incompatibility group as plasmids determining gentamicin resistance in P. aeruginosa via gentamicin acetyltransferase I. Like other members of this group, it also confers resistance to Hg(2+), organomercurials, and certain deoxyribonucleic acid phages. When pMG5 is introduced into a cell carrying a related R factor, some transconjugants can subsequently cotransfer new combinations of resistance determinants as though recombinant plasmids had been formed.
Genetic properties and host ranges of R factors derived from Bordetella bronchiseptica of pig origin were examined. All of 61 R factors tested could confer resistance to streptomycin, sulfonamide, and aminobenzyl penicillin on their host bacteria. All of them were identified as fi(-) (no fertility inhibition) type and were found to exhibit no restriction of phages lambda, phi80, P1, P2, T1, T3, T6, T7, W31, and BF-23. They could confer macarbomysin susceptibility on their host cells when infected. An Rte16, a representative R factor, was incompatible with both RP4 and R40a, which are classified as compatibility groups P and C, respectively. An Rte16 was conjugally transmissible to B. bronchiseptica, Escherichia coli, Citrobacter freundii, Salmonella typhimurium, and Yersinia enterocolitica, but not to Shigella flexneri, S. sonnei, Proteus mirabilis, P. vulgaris, P. rettgeri, Klebsiella pneumoniae, and Pseudomonas aeruginosa.
The Col Ib-P9 plasmid content of colicinogenic cells has been measured by both sedimentation analysis of cleared lysates and by deoxyribonucleic acid hybridization to purified Col Ib-P9 factor deoxyribonucleic acid. The results show an independence between mitomycin C-induced colicin synthesis and Col Ib-P9 replication. In addition, the ratio of the various molecular configurations (i.e., covalently closed circles or open circles) of the Col Ib-P9 plasmid does not change upon induction of colicin synthesis. Heat treatment of a colicinogenic strain carrying a thermosensitive dnaB mutation on the bacterial chromosome leads to complete inhibition of Col Ib-P9 plasmid replication and the simultaneous induction of colicin Ib synthesis in all cells of the colicinogenic population. These studies rule out mechanisms or regulation of colicin Ib synthesis based on the induced replication of the Col Ib-P9 plasmid. Our studies show that in a Col Ib-P9 colicinogenic population there is, on the average, one plasmid per cell.
A clinical isolate Pseudomonas aeruginosa GN315 resistant to amikacin (AK), a new semisynthetic antibiotic, inactivated AK by acetylation. The acetylating enzyme was purified approximately 146-fold from a crude extract of GN315 by affinity chromatography. Fractionated samples obtained by affinity chromatography showed almost the same inactivation curves toward 3',4'-dideoxykanamycin B (DKB) and AK. Partially purified AK-acetylating enzyme inactivated DKB and kanamycin A but could not inactivate gentamicin C(1). The optimal pH for their inactivation was 6.0 to 7.0, and the pH curves for the inactivation of both drugs were almost the same. These facts indicate that AK and DKB are inactivated by the same aminoglycoside-acetylating enzyme. Through elemental analysis, the inactivated AK was found to be a monoacetylated product of AK. A sample of inactivated AK was purified and compared with a synthetic 6'-N-acetyl AK by thin-layer chromatography, and the results indicated that AK was inactivated by acetylation of the 6'-NH(2) group. The ultraviolet, infrared, and nuclear magnetic resonance spectra of the inactivated AK showed that AK was inactivated by the enzyme through acetylation of the amino group of 6'-amino-6'-deoxy-d-glucose moiety of AK. This enzyme, mediated by R factor, is capable of conferring resistance to AK, DKB, kanamycin, gentamicin, and sulfanilamide.
R factors determining multiple resistance including both gentamicin and carbenicillin have been identified in high incidence among hospital isolates of Pseudomonas aeruginosa. The factors are readily transmitted to other P. aeruginosa but not to Escherichia coli strains K-12 or C, or to Proteus mirabilis. R factor-containing isolates are predominantly immunotype 7 isolated from urinary sources.
R factor RPL11 from Pseudomonas aeruginosa determines multiple drug resistance including resistance to gentamicin and carbenicillin. The host range and incompatibility properties of RPL11 are those of incompatibility group P-2. Strains harboring the factor are not altered with respect to the major immunotypes 1 through 7 of Parke-Davis, or with respect to pyocin type by using the 18 indicators of Jones and co-workers. Analytical ultracentrifugation of crude extracts of R factor-containing strains shows a band of satellite DNA with a buoyant density of 1.717 g/cm(3).
The mechanism of plasmid-mediated resistance to cadmium in Staphylococcus aureus was investigated. Protein synthesis in cell-free extracts from resistant or susceptible bacteria was equally susceptible to inhibition by Cd(2+), but spheroplasts from resistant bacteria retained their resistance. Resistant bacteria did not have a decreased affinity for cations in general, nor was active metabolism required for exclusion of Cd(2+). The kinetics of Cd(2+) uptake into susceptible and resistant bacteria suggested that the conformation of membrane proteins in resistant bacteria may be important in the exclusion of Cd(2+).
Rich media support the growth of bacteria in the presence of concentrations of sulfonamides and diaminopyrimidines that are highly inhibitory when the organisms are grown on minimal media. Many such rich media can be made more suitable for susceptibility testing by the incorporation of lysed horse blood. Harper and Cawston characterized the active substance, Harper-Cawston factor (HCF), and later studies indicated it to be a protein. It has now been identified as thymidine phosphorylase. The identification follows from the identical purification pattern of HCF and thymidine phosphorylase activities from horse blood to a high degree of purity. Blood of goats, sheep, oxen, geese, chickens, cows, dogs, rats, and humans had neither biological activity. The identification of HCF as thymidine phosphorylase is consistent with the earlier findings of Koch and Burchall (1971) that most of the interfering effects of rich media could be accounted for by their thymidine contents, and that thymidine is much more active in this respect than is thymine.
Ten strains of beta-hemolytic streptococci were tested for elimination of resistance to macrolide antibiotics, tetracycline, and chloramphenicol. Six of the strains lost resistance after cultivation at 41 C or addition of acriflavine (0.2 mug/ml). These results suggest that determinants governing resistance to these antibiotics are located on extrachromosomal genetic elements (plasmids) that are widely distributed in streptococci.