The genetic basis of antibiotic resistance in S. aureus: the importance of gene transfer in the evolution of this organism in the hospital environment.
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One hundred and four children undergoing strabismus surgery were randomised post-operatively to one of three treatment groups; 1) fucithalmic drops twice daily; 2) chloramphenicol (chlormycetin) ointment twice daily; 3) no treatment. Allocation to the 'no treatment' group had to be stopped after 3 of the first 8 patients in the group developed severe mucopurulent conjunctivitis. A parental questionnaire and clinical assessment, carried out in a single blind fashion revealed that nearly all parents were able to apply the prescribed treatment and that both treatments were effective in preventing bacterial conjunctivitis. Post-operative antibiotics seem to be necessary following squint surgery in children, and fucithalmic viscous drops are a useful alternative to chlormycetin ointment.
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Most types of antibiotic resistance impose a biological cost on bacterial fitness. These costs can be compensated, usually without loss of resistance, by second-site mutations during the evolution of the resistant bacteria in an experimental host or in a laboratory medium. Different fitness-compensating mutations were selected depending on whether the bacteria evolved through serial passage in mice or in a laboratory medium. This difference in mutation spectra was caused by either a growth condition-specific formation or selection of the compensated mutants. These results suggest that bacterial evolution to reduce the costs of antibiotic resistance can take different trajectories within and outside a host.
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The effect of 20 different antibiotics on chemotaxis by human neutrophils was studied. Human leukocytes incubated with chloramphenicol, rifampin, sodium fusidate, and tetracyclines in vitro showed markedly depressed migration. The mechanisms by which these antibiotics affect leukotaxis are discussed.
The microtiter broth dilution method was employed to determine the in vitro susceptibility of 525 recent clinical isolates of anaerobic bacteria to sodium fusidate. The minimal inhibitory concentrations of sodium fusidate ranged from </=0.06 to 1.0 mug/ml for 155 strains of anaerobic gram-positive rods and 130 strains of anaerobic gram-positive cocci. Minimal inhibitory concentrations ranging from </=0.06 to 32 mug/ml were observed for 240 strains of anaerobic gram-negative rods. Among the latter group a minimal inhibitory concentration of 16 mug/ml or greater was encountered with 16% of 45 Bacteroides fragilis strains, 19% of 32 Bacteroides thetaiotaomicron, and all 7 strains of Fusobacterium necrophorum. Minimal inhibitory concentrations for Veillonella parvula, the only gram-negative coccus tested, ranged from 0.5 to 8.0 mug/ml.
The effects of polymyxin B and polymyxin B nonapeptide (PMBN) on cell envelope integrity in Escherichia coli were compared. Both compounds caused loss of proteins from E. coli K-12 3300(pBR322), although PMBN released less protein than did polymyxin B. The origin of the released protein was determined both by polyacrylamide gel electrophoresis and by using specific enzyme markers (beta-lactamase in periplasm, beta-galactosidase in cytoplasm). The proteins released by both compounds were derived principally from the periplasm, accompanied in the case of polymyxin B by a low level of cytoplasmic proteins. Although polymyxin B and PMBN both caused release of periplasmic proteins, the individual proteins released by the compounds differed. The periplasmic fraction contained six principal polypeptides with molecular weights between 62,000 (polypeptide 1) and 29,000 (polypeptide 6). Polypeptide 6 was identified as the pBR322-encoded beta-lactamase, but the other proteins were not specifically identified. Polymyxin B caused considerable release of polypeptides 1, 2, and 5 with some release of polypeptides 4 and 6. PMBN released polypeptide 1 (trace), 3, 4, and 6 (trace). Scanning electron microscopy showed that polymyxin B and PMBN both caused surface damage in E. coli. However, polymyxin B produced greater morphological changes than PMBN.
In contrast to polymyxin B-susceptible gram-negative bacteria of human origin, the fish pathogen Aeromonas salmonicida was resistant to sensitization by polymyxin B nonapeptide (PMBN) to hydrophobic antibiotics. Similarly, sensitization of A. salmonicida strains by PMBN to the bactericidal action of brook trout (Salvelinus fontinalis) serum complement was less pronounced than the similar effect of PMBN against other gram-negative bacteria in certain mammalian sera. The surface array protein (A layer), overlying the outer membrane of virulent A. salmonicida strains, did not appear to cause resistance to PMBN sensitization since an A-layer-deficient mutant showed similar responses to PMBN as its parent strain. Electron micrographs of PMBN-treated A. salmonicida cells revealed very little visible outer membrane disruption when compared with the extensive blebbing on the outer membrane surface caused by PMBN in certain enteric bacteria, including Escherichia coli K-37. However, small extracellular vesiclelike components, which may have been derived from the outer membrane, were numerous around PMBN-treated A. salmonicida cells. In this connection, PMBN caused disruption of the A layer in the form of bulges, breaks, and detached fragments which appeared to be associated with the accumulation of these vesicles underneath the A layer of wild-type A. salmonicida strains.
Unlike the antibiotics erythromycin and penicillin G, sodium fusidate (fusidin) pretreatment (80 mg/kg of body weight) increased the survival rate of neonatal BALB/c mice challenged with Salmonella enteritidis lipopolysaccharide. Fusidin also significantly reduced the plasma tumor necrosis factor alpha levels. Hence, fusidin may prove useful in the management of bacterial sepsis in humans.
Tests for susceptibility of 29 group A, 4 group C, and 2 group G strains of beta-hemolytic streptococci to 63 antibiotics and to trimethoprim and sulfamethoxazole, singly and combined in a ratio of 1:16, were carried out in vitro. All strains tested were moderately or highly susceptible to all the antibiotics used except those belonging to the aminoglycoside and polymyxin groups. A few were also resistant to the tetracyclines and to sulfamethoxazole alone. Comparisons with results obtained in previous years indicate that, except for the tetracyclines and sulfonamides, there has been no change in the susceptibility of beta-hemolytic streptococci to the most important and useful antibiotics, particularly penicillin.
Butyrivibrio fibrisolvens strains resistant to tetracycline were isolated from the bovine rumen. Two of three Tcr B. fibrisolvens tested were able to donate tetracycline resistance at frequencies ranging from 10(-7) to 10(-1) per donor cell in anaerobic filter matings to a rifampin-resistant mutant of the type strain of B.fibrisolvens, 2221R. The recipient strain 2221R exhibited rapid autoaggregation, which might be a factor in the high transfer rates observed. Tcr transconjugants of B. fibrisolvens 2221R were also capable of further transferring tetracycline resistance to a fusidic acid-resistant mutant, 2221F. Comparison of genomic DNAs by pulsed-field gel electrophoresis demonstrated altered band profiles in transconjugants, consistent with the acquisition of a large mobile chromosomal element. The transferable elements from the two B. fibrisolvens donors 1.23 and 1.230 (TnB123 and TnB1230, respectively) showed the same preferred insertion site in the B. fibrisolvens 2221R chromosome and are likely to be similar, or identical, elements. Hybridization experiments showed no close relationship between TnB1230 and int-xis regions from Tn916 or Tn5253. Although DNA from the B. fibrisolvens donor strains hybridized with probes carrying tet(M) or tet(O) sequences, transconjugants were found to have acquired a distinct band that hybridized only weakly with these probes, suggesting that a second, distantly related Tcr determinant had been transferred.
After 5 days of treatment, sputa were analyzed from 40 patients treated with sodium fusidate and 20 patients treated with naficillin. There was a significant decrease in the number of staphylococci, but no significant change in the other flora. The quantitative bacteriological analysis of sputum specimens proved to be a useful laboratory procedure for providing information on the in vivo effectiveness of specific antibacterial therapy in respiratory infections.
Nonbullous impetigo is a common skin infection in children and is frequently caused by Staphylococcus aureus. Staphylococcal toxins and especially exfoliative toxin A are known mediators of bullous impetigo in children. It is not known whether this is also true for nonbullous impetigo. We set out to analyze clonality among clinical isolates of S. aureus from children with nonbullous impetigo living in a restricted geographical area in The Netherlands. We investigated whether staphylococcal nasal carriage and the nature of the staphylococcal strains were associated with the severity and course of impetigo. Bacterial isolates were obtained from the noses and wounds of children suffering from impetigo. Strains were genetically characterized by pulsed-field gel electrophoresis-mediated typing and binary typing, which was also used to assess toxin gene content. In addition, a detailed clinical questionnaire was filled in by each of the participating patients. Staphylococcal nasal carriage seems to predispose the patients to the development of impetigo, and 34% of infections diagnosed in the Rotterdam area are caused by one clonal type of S. aureus. The S. aureus strains harbor the exfoliative toxin B (ETB) gene as a specific virulence factor. In particular, the numbers (P = 0.002) and sizes (P < 0.001) of the lesions were increased in patients infected with an ETB-positive strain. Additional predictors of disease severity and development could be identified. The presence of a staphylococcal plasmid encoding multiple antibiotic resistance traits, as detected by binary typing, was associated with a reduction in the cure rate. Our results recognize that a combination of staphylococcal virulence and resistance genes rather than a single gene determines the development and course of nonbullous impetigo. The identification of these microbial genetic markers, which are predictive of the severity and the course of the disease, will facilitate guided individualized antimicrobial therapy in the future.
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One of 4 antibiotics with antistaphylococcal activity was given in a conventional oral dose for one day to each of 20 hospitalised patients with synovial effusion of a knee joint requiring aspiration. Serial synchronous samples of serum and synovial fluid (SF) were taken over 36 hours through indwelling cannulae. No morbidity was experienced either during or after this procedure. Satisfactory antistaphylococcal concentrations in SF were achieved with sodium fusidate (500 mg 8 hourly) and amoxycillin (250 mg 8 hourly). Cephradine (500 mg 6 hourly) frequently failed to reach the minimum inhibitory concentration for Staphylococcus aureus in the SF, and flucloxacillin (250 mg 6 hourly) was unpredictable in its penetration of the synovial space. Wide interpatient variation of both serum and SF concentrations was found. Our results indicate that sodium fusidate is an appropriate early treatment for a nonresistant staphylococcal joint infection. Amoxycillin is a suitable alternative or second antistaphylococcal drug and would also be appropriate initial therapy when the infecting organism is unknown. We strongly recommend that SF antibiotic concentrations be measured, to ensure adequate penetration of the synovial cavity, in the treatment of septic arthritis.