The two subspecies of Francisella tularensis, F. tularensis subsp. tularensis (type A) and F. tularensis subsp. palaearctica (type B), differ from each other in biochemistry and virulence. Strains of F. tularensis subsp. tularensis are believed to be confined to North America, whereas strains of F. tularensis subsp. palaearctica occur in Europe, in Asia, and in North America. Moreover, the existence of two other subspecies, designated F. tularensis subsp. mediaasiatica and F. tularensis subsp. palaearcitica japonica, has been suggested for strains of F. tularensis isolated in the central Asian focus of the Soviet Union and in Japan, respectively. In the present study, strains biochemically classified as F. tularensis subsp. mediaasiatica or F. tularensis subsp. palaearctica japonica have been investigated by hybridization with probes specific to 16S rRNAs of the two main subspecies. Furthermore, the virulence and biochemical characteristics of the strains were compared with those of strains belonging to F. tularensis subsp. palaearctica and F. tularensis subsp. tularensis. It was found that 16S rRNAs of F. tularensis subsp. mediaasiatica and F. tularensis subsp. palaearctica japonica hybridize with the probe specific to a genotype proposed herein, genotype A (F. tularensis subsp. tularensis), which shows that strains genetically related to this subspecies are found outside North America. However, the central Asian strains differed from F. tularensis subsp. palaearctica and F. tularensis subsp. tularensis strains when investigated by fermentation of glucose. The results of the biochemical tests could not be unambiguously used for differentiation of strains into F. tularensis subsp. palaearctica or F. tularensis subsp. tularensis. These drawbacks suggest that classification of strains of Francisella on the basis of 16S rRNA analysis may be preferable to classification on the basis of biochemical analysis.

Lipopolysaccharide and outer membranes from the three virulent encapsulated (Cap(+)) strains of three subspecies of Francisella tularensis and their isogenic avirulent capsule-deficient (Cap(-)) mutants were isolated. It was shown that the Cap cells and their outer membranes almost completely consumed the available complement of normal human serum whereas Cap(-) LPS (R-LPS), Cap(+) cells and their components activated the complement less effectively. Absorption of normal human serum with Cap(-) strain dramatically reduced the complement consumption for homologous strain and its surface structures. This reduction reflected the loss of bactericidal antibodies. Addition of antibodies to whole cells of F. tularensis completely restored complement activity. The cross-absorbing experiments demonstrated that Cap(-) cells more effectively deplete bactericidal antibodies than homologous virulent strain. From these results it can be concluded that normal human serum is bactericidal for serum-sensitive Cap(-) F. tularensis strains through the action of complement initiated by the classical complement pathway and serum resistance of virulent strains is not due to absence of targets for bactericidal antibodies, but is due to their low accessibility because of O-side chains of lipopolysaccharide.

Objective: comparative study of the etiological structure of community-acquired pneumonia in SARSCoV-2 “+”and SARS-CoV-2 “-“ patients who sought help from medical organizations in the Rostov Region.Materials and methods. Biological material from 508 patients diagnosed with community-acquired pneumonia who were on outpatient treatment or in hospitals in Rostov-on-Don was studied. Verification of respiratory viruses, including SARS-CoV-2 RNA, as well as M. pneumoniae, C. pneumoniae, and L. pneumophila was performed by polymerase chain reaction in nasopharyngeal smears. Bacteriological analysis of sputum was carried out using differential diagnostic media, identification of isolated pathogens was carried out using time-of-flight mass spectrometry on Autoflex (Bruker Daltonics) with BioTyper 3.0 software.Results and discussion. During the spread of a new coronavirus infection in the Rostov Region, the main etiological agent of community-acquired pneumonia is the new SARS-CoV-2 coronavirus. Specific character of pneumonia in patients with laboratory-confirmed COVID-19 is a higher incidence of mixed infection of both viral and bacterial etiology. Against the background of detection of a new coronavirus infection in patients with pneumonia, cases of detection of other types of coronaviruses have been registered (HKU-1,OC43, HL-63 and 229Е). The most common etiological agent of bacterial pneumonia in patients was Streptococcus spp., both in patients with COVID-19-associated pneumonia and in patients who tested negative for SARS-CoV-2. Coronavirus patients represent a high risk group for the development of mycotic lung lesions.

Актуальность. В условиях продолжающейся пандемии коронавирусной инфекции на фоне снижения иммунного статуса организма течение вирусной пневмонии достаточно часто осложняется присоединением бактериальной микрофлоры. Возбудители такой коинфекции могут проявлять множественную лекарственную резистентность, что существенно снижает эффективность этиотропной терапии. В этой связи целесообразным представляется микробиологическое сопровождение пациентов с целью выбора наиболее оптимальных схем лечения. Цель. Изучение видового состава бактериальных возбудителей внебольничных пневмоний (ВП) у коронапозитивных (Covid-19 +) и коронанегативных (Covid-19 -) пациентов и определение спектра их чувствительности/устойчивости к антибактериальным препаратам. Материал и методы. Исследован видовой состав микроорганизмов образцов мокроты от 723 пациентов с ВП, поступивших из ЛПО г. Ростова-на-Дону в августе и декабре 2020 года. Идентификацию выделенных культур проводили с помощью бактериологического и масс-спектрометрического методов. Чувствительность бактерий к антибиотикам определяли диско-диффузионным методом. Результаты. Показано, что в августе в спектре возбудителей ВП превалировали пневмококки и стафилококки, тогда как в декабре вырос процент выделений Acinetobacter spp. и S. haemolyticus. Обнаружена высокая степень изоляции различных видов дрожжей р. Candida, причем у Cov+ больных выявлена тенденция к большей обсемененности (≥104 м.кл./мл). Некоторые возбудители (A. baumannii, S. haemolyticus, P. aeruginosa, S. maltophilia) характеризуются полиантибиотикорезистентностью, а отдельные штаммы этих видов – панрезистентностью ко всем группам антибиотиков. Заключение. Полученные данные демонстрируют, что тяжелые формы внебольничной пневмонии могут быть обусловлены вирусо-бактериальными и вирусо-бактериально-дрожжевыми ассоциациями возбудителей, включая бактерии с узким спектром чувствительности к антибактериальным препаратам.

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