Drug Resistance in Staphylococcus aureus

Antibacterial and inducer activities concerning inducible macrolide resistance in Staphylococcus aureus were investigated using 32 erythromycin, oleandomycin and other macrolide antibiotic derivatives and analogues. The macrolides were classified into five groups from very high to none according to their inducer activity.     

Macrolide Resistance in Staphylococcus aureus

It was demonstrated that spiramycin (SP)-resistance could be related to the decrease in binding of ribosomes to SP and that the SP-binding to ribosomes was related with inhibition of polypeptide synthesis by SP in a cell-free system in staphylococcal strains. These facts were also observed in Mac (macrolide)-inducible strains, in which resistance to Mac antibiotics is enhanced by prior treatment with subinhibitory concentrations of erythromycin. From these results, it was concluded that the mechanism of resistance to Mac antibiotics is accounted for by alteration of ribosomes in staphylococcal strains and that this alteration of ribosomes is caused not only by mutation but also by induction.     

Macrolide Resistance in Staphylococcus aureus

A heat-inducible mutant, resistant to macrolide antibiotics (Mac), was isolated from Staphylococcus aureus MS537 in which Mac-resistance was induced by subinhibitory concentrations of erythromycin (EM). After induction at 42 C, this mutant acquired a high resistance to both Mac and lincomycin (LMC). Transduction and biochemical studies revealed that spiramycin (SP)-resistance in this mutant was induced by exposure to a high temperature (42 C) or by treatment with EM in broth but not in phosphate buffer. Induction did not take place when chloramphenicol (CM) was added to the induction mixture. Ribosomes from the mutant cultured at 42 C decreased their affinity for SP and consequently polypeptide synthesis on such ribosomes was not inhibited by SP, when compared with those cultured at 30 C. From these results, it was concluded that alteration of ribosomes took place after induction by exposure at high temperatures or by EM-treatment and that the mechanism of SP-resistance after induction was accounted for by a decrease in SP-binding to ribosomes.     

Complete Genome of Staphylococcus aureus Phage SA11

A novel lytic bacteriophage, SA11, infecting Staphylococcus aureus was isolated, and the whole genome was sequenced. It belongs to the siphoviridae based on electron microscopic observation. It has a linear double-stranded DNA genome of 136,326 bp. Genomic analysis showed that it is distantly related to Staphylococcus phages A5W, K, ISP, Sb-1, and G1.     

Phage release from biofilm and planktonic Staphylococcus aureus cells

The ability of pathogenic staphylococci to form biofilms facilitates colonization and the development of chronic infections. Therapy is hampered by the high tolerance of biofilms towards antibiotic treatment and the immune system. We found evidence that lysogenic Staphylococcus aureus cells in a biofilm and in planktonic cultures spontaneously release phages into their surroundings. Phages were detected over a much longer period in biofilm cultures than in planktonic supernatants because the latter were degraded by secreted proteases. Phage release in planktonic and biofilm cultures was artificially increased by adding mitomycin C. Two morphologically distinct phages in the S. aureus strain used in this work were observed by electron microscopy. We postulate that phage-release is a frequent event in biofilms. The resulting lysis of cells in a biofilm might promote the persistence and survival of the remaining cells, as they gain a nutrient reservoir from their dead and lysed neighboring cells. This might therefore be an early differentiation and apoptotic mechanism.     

Mutants of Staphylococcus aureus with Increased Sensitivity to Ultraviolet Radiation

Nitrosoguanidine (NG) mutagenesis of Staphylococcus aureus resulted in the isolation of eight mutants exhibiting 3 to 28 times greater sensitivity to ultraviolet (UV) radiation. These mutants were further characterized by their ability to repair UV-irradiated bacteriophage, to act as recipients in the transduction of antibiotic resistance, and their sensitivity to NG. Based on the available data, six of these mutants are reduced in their ability to perform host-cell reactivation. One of the remaining two mutants may be deficient in post-replication repair.     

Phage conversion of exfoliative toxin A production in Staphylococcus aureus

The staphylococcal exfoliative toxins (ETs) are extracellular proteins that cause splitting of human skin at the epidermal layer during infection in infants. Two antigenically distinct toxins possessing identical activity have been isolated from Staphylococcus aureus, ETA and ETB. The gene for ETA (eta) is located on the chromosome, whereas that for ETB is located on a large plasmid. The observation that relatively few clinical isolates produce ETA suggests that the eta gene is acquired by horizontal gene transfer. In this study, we isolated a temperate phage (phiETA) that encodes ETA and determined the complete nucleotide sequence of the phiETA genome. phiETA has a head with a hexagonal outline and a non-contractile and flexible tail. The genome of phiETA is a circularly permuted linear double-stranded DNA, and the genome size is 43 081 bp. Sixty-six open reading frames (ORFs) were identified on the phiETA genome, including eta, which was found to be located very close to a putative attachment site (attP). phiETA converted ETA non-producing strains into ETA producers. Southern blot analysis of chromosomal DNA from clinical isolates suggested that phiETA or related phages are responsible for the acquisition of eta genes in S. aureus.     

Resistance heterogeneity in methicillin-resistant Staphylococcus aureus

Abstract A striking feature of methicillin resistance in Staphylococcus aureus is the considerable heterogeneity of expression of resistance by cells in clonal populations: some are sensitive (or almost so), others are highly resistant, and others show intermediate resistance to the antibiotic. Subclones generally are also heterogeneous, suggesting variable inheritance or control of expression of resistance.
The degree of heterogeneity and mean resistance is influenced by environmental parameters: temperature, osmolality, pH, light, anaerobiosis, chelating agents and metal ions, and prior exposure to β-lactam antibiotics.     

A Cooling Modification to an Apparatus for Phage Typing of Staphylococcus aureus

Difficulty is experienced through overheating of the Tarr apparatus for phage typing. The provision of a cooling coil which overcomes this difficulty is described.     

Resistance of Spores of Clostridium botulinum 33A to Combinations of Ultraviolet and Gamma Rays

Spores of Clostridium botulinum 33A exhibit a sigmoidal survival curve if subjected to gamma radiation. The present investigation was concerned with two questions: (i) what is the form of an ultraviolet (UV)-survival curve and (ii) what is the combined effect of UV- and gamma radiation? The UV-survival curve was found to be of sigmoidal type with a "shoulder" width of 675 ergs/mm(2) and a D(10) (exp) of 2,950 ergs/mm(2). To test the combination effect, spores were subjected to UV doses of 225, 450, 675, and 900 ergs/mm(2) followed by a series of increasing doses of gamma rays from 200 to 2,000 krad in 200-krad steps. The gamma ray-survival curves showed that increasing UV pretreatment caused a gradual loss of the "Prodiginine" yielding straight line exponential survival curves after preirradiation with UV doses of 675 ergs/mm(2) and above. Simultaneously the D(10) value for gamma-ray irradiation was reduced, e.g. UV preirradiation with 900 ergs/mm(2) reduced the D(10) by 40%. This observation emphasizes the potential practical advantage of combining UV and gamma rays for sterilization of heat-sensitive commodities.     

Transfer of Antibiotic Resistance in Staphylococcus aureus

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Complete Genome Sequence of Wide-Host-Range Staphylococcus aureus Phage JD007

Methicillin-resistant Staphylococcus aureus-related infections have become a serious problem worldwide. Bacteriophage therapy is an alternative approach against this threat. S. aureus phage JD007, which belongs to the Myoviridae family according to transmission electron microscopic imaging, could lyse nearly 30% of the S. aureus strains from Ruijin Hospital, Shanghai, China, and was isolated from chicken feces in Shanghai, China. The complete genome showed that JD007 is a linear, double-stranded DNA phage 141,836 bp in length with a GC content of 30.4% encoding 217 open reading frames. A BLAST search of the JD007 genome revealed that it was very similar to that of phage GH15.     

Phage types of Staphylococcus aureus isolated in Poland in 1999-2004

The aim of study was to determine how population of Staphylococcus aureus strains from hospital environment forms itself with respect to phage types and frequency of their occurrence recently. 1157 S. aureus isolated from various clinical materials between 1999 and 2004 have been investigated. The basic set of phages and the three additional ones were used for typing strains according to Blair and Williams method. The results proved that population of S. aureus strains isolated from hospital environment differentiates with respect to phage types, like in the past. Strains belonging to phage group II dominates among them, but a considerable increase in number of phage group III have been remarked lately. A differential value of an individual phages from basic set remains on their usual level for years.     

Co-Transduction of Plasmids Mediating Resistance to Tetracycline and Chloramphenicol in Staphylococcus aureus

Independent plasmids mediating resistance either to tetracycline (Tc) or chloramphenicol (Cm) were transduced successively into Staphylococcus aureus strain 8325. From this doubly resistant donor strain, Tc was co-transduced with a frequency of 40 to 50% when Cm was selected. Co-transduction of Cm was 5 to 10% with Tc selection. Plasmid elimination was infrequent and restricted to the Cm plasmid. A variant, doubly resistant strain gave 100% co-transduction of Tc and Cm and a high rate of joint elimination of both plasmid markers. Co-transduction of the plasmids from recombination-deficient donor strains was much reduced if the plasmids had been introduced separately into the donor strain, but occurred at the normal high rate if they had been introduced jointly. The plasmids were co-transformed at relatively low rates with closed circular deoxyribonucleic acid (DNA) from doubly resistant donors, but not with DNA from a mixed lysate of singly resistant strains. Our evidence favored a hypothesis of recombination-dependent, reversible linkage between the two plasmids as the basis for their co-transduction. Examination of plasmid DNA from the doubly resistant strains by ultracentrifugal and electron microscopic methods did not disclose any physical differences between singly and doubly resistant strains that might account for the observed co-transduction.