Sources of intrapopulation variability in causative agents of nosocomial infection.

The mechanisms of heterogeneity of S. aureus and P. aeruginosa populations of pathological foci in patients with wound, traumatic, and burns infections were studied. It has been established that populations of the mentioned species in the sources of infection (patients and carriers) are pronouncedly heterogeneous and objects in the external environment serving as factors of transmission are contaminated with a whole complex of diverse variants. The conclusion can therefore be drawn that the first source of intrapopulation variability of wound populations of microbes is the presence of varying strains and variants in the infecting dose of the causative agent. The second source consists in repeated superinfection (immigration) of pathological processes by new, usually nosocomial, strains and variants of the same species with their subsequent selection during the patients' stay in the health-service establishment. Other sources of population variability, such as mutation and recombination, are of minor importance. With respect to the obtained results it is necessary to increase the volume of the representative sample of cultures in bacteriological diagnosis of open processes, to protect them reliably from superinfection, to follow up dynamically changes in the composition of causative agents and to provide for suitable correction of chemotherapy.

[Interpopulation variability of Staphylococcus aureus]. / Mezhpopuliatsionnaia izmenchivost' Staphylococcus aureus.

The comparative study of 830 hospital and 181 extrahospital S. aureus strains has revealed the existance of the interpopulation (group, geographic) variability of this species. Hospital strains differ from those inhabiting other places by the composition of phago- and resistovars, greater resistance to antibiotics, antiseptic and disinfecting agents, the inhibiting action of antagonist, as well as by pronounced antagonistic activity. The biological characteristics of such strains allow one to classify them with the hospital ecological variants (ecovars) of S. aureus. These properties of hospital strains give them selective advantages in hospitals over extrahospital strains, and the latter are thus ousted from the skin surface, mucous membranes, wound surfaces. The measures taken to prevent hospital infections must be aimed mainly against the hospital ecovars of these bacteria.

[Antibiotic resistance of Pseudomonas aeruginosa strains isolated from patients with infected burns]. / Ustoichivost' k antibiotikam shtammov Pseudomonas aeruginosa, vydelennykh ot bol'nykh s infitsirovannymi ozhogami.

Sensitivity to 15 drugs of 248 P. aeruginosa strains isolated from patients with infected burns was studied by the method of agar dilution. All of the strains were resistant to polymyxin M, ceporin, erythromycin and oleandomycin. Most of the strains were resistant to streptomycin, monomycin, ampicillin and rifadin. Moderate resistance of the strains to carbenicillin, morphocycline, vibramycin, kanamycin, tetraolean and tetracycline was observed: the maximum concentrations of these antibiotics (128 microgram/ml) inhibited the growth of 85, 69, 63, 51.8, 43.6 and 41.2 per cent of the strains respectively. Gentamicin proved to be most active against the strains of P. aeruginosa and inhibited 87 per cent of the strains when used in the therapeutic doses. The study provided recomendation of the drugs for parenteral and local use in treatment of burns infected with P. aeruginosa.

[Antagonistic activity as 1 of the properties of hospital strains of Staphylococcus aureus]. / Antagonisticheskaia aktivnost' kak odno iz svoistv gospital'nykh shtammov Staphylococcus aureus.

The frequency of antagonistic activity in S. aureus strains depended on the source from which the strains had been isolated. Antagonistic strains were most frequently detected in the departments of traumatology and orthopedy, as well as in the departments of routine and urgent surgery.

[Variability of the microfloral makeup of the pathological focus in suppurative infection]. / Izmenchivost' sostava mikroflory patologicheskogo ochaga u bol'nykh gnoinoi infektsiei.

During the period of hospital treatment a change in the composition of would microflora in 145 patients was found to occur, which affected the characteristics of microflora in respect of species, types and strains. This change consisted in the appearance of new (secondary) species, variants and strains and in the disappearance of some original (primary) ones. The populations of staphylococci were found to vary in the level and spectrum of their resistance to antibiotics (resistovars) and in the degree and spectrum of their sensitivity to staphylococcal typing phages (phagovars). Changes in the populations of staphylococci were caused mainly by the cange of S. aureus or by the additional appearance of their new variants which belonged, as a rule, to phage group II, had multiple resistance to antibiotics and corresponded to the phagovars of the hospital flora. The development of hospital variants in open wounds led to an increased general level of resistance of staphylococcal populations to antibiotics.