Resistance to Aminoglycosides of Methicillin-Resistant Strains of Staphylococcus aureus, Originating in the Surgical and Transplantation Wards of the Warsaw Clinical Center-A Retrospective Analysis.

INTRODUCTION: Aminoglycoside resistance (AR) is common in health care-associated methicillin-resistant Staphylococcus aureus (HA-MRSA). AR is most often associated with the production of antibiotic modifying enzymes: bidomain AAC(6')-Ie/APH(2″)-Ia acetyltransferase and phosphotransferase, ANT(4')-Ia nucleotidyltransferase, and APH(3″)-IIIa phosphotransferase. AIM: Determination of aminoglycoside sensitivity, presence of genes encoding enzymes, and molecular typing of HA-MRSA strains derived from patients hospitalized in surgical and transplantation wards. MATERIALS AND METHODS: Fifty-four HA-MRSA strains, isolated from various materials from patients in the surgical and transplantation wards of Warsaw's clinical hospital, hospitalized between 1991 and 2007. The MIC values of gentamicin-GEN/tobramycin-TOB/amikacin-AK/netilmicin-NET were determined by the E-test (CLSI/EUCAST). Genes mecA/aacA-aphD/aadD/aph(3″)-IIIa were detected using PCR. SCCmec types were determined according to the Oliveira method and the sequence type (ST)/clonal complex (CC) by the MLST method. RESULTS: Of the isolates tested, 36 (66.7%) showed resistance to at least one aminoglycoside: TOB (57.4%), GEN (53.7%), AK (55.6%), NET (24.1%). The aacA-aphD gene was present in 29 MRSA-GEN-R (most often in combination with aadD, 15/29 or aph(3″)-IIIa, 10/29); the aacA-aphD gene was the only determinant of resistance in 1 isolate. The AR variants mainly belonged to the CC8 clonal complex (ST239/247/241/254/8) and most frequently contained SCCmec type III (3A) cassettes. CONCLUSIONS: Resistance to at least one aminoglycoside was present in 66.7% of HA-MRSA and in more than 22% to all of them. The presence of the aacA-aphD gene was sufficient to express the resistance phenotype to GEN/TOB/AK/NET. Resistant isolates were closely related to each other.

Effect of Selective Antibiotic Pressure on the MLS-B Phenotype in Methicillin-Resistant Staphylococcus aureus Strains Originating From Patients From Transplantation Wards: 24 Years of Observations.

INTRODUCTION: Staphylococcus aureus infection, and health care-associated-methicillin resistant S aureus (HA-MRSA) in particular, is a serious risk for patients treated with organ transplantation. The frequent combined resistance of these bacteria to macrolides, lincosamides, and streptogramin-B (MLS-B) limits the use of these drugs in therapy. AIM: Evaluation of the mechanism of MLS-B resistance among HA-MRSA strains derived from patients treated in surgical-transplantation wards, over a 24-year period, and assessment of correlation of clindamycin use and resistance phenotype. MATERIALS AND METHODS: One hundred and twelve HA-MRSA strains from patients in surgical-transplantation wards (clinical hospital, Warsaw), hospitalized in the period from 1991 to 2014. Methicillin-resistance was determined using phenotypic and genetic methods by detecting the mecA gene. Erythromycin/clindamycin resistance was determined by E-test, the iMLS-B (inductive) and cMLS-B (constitutive) phenotypes by the D-test method. The number of defined daily doses (DDD), statistically per 1000 person-days, was calculated in accordance with the WHO guidelines. RESULTS: Resistance to erythromycin/clindamycin in MRSA strains increased from 1991 to 2004-2007 from 64.7/11.8% to 100/76.9%, respectively. The frequency of the cMLS-B phenotype in the years 1991/2010-2011/2012 was 5.9%/76.9%/69.7%, respectively, and correlated with the increased use of clindamycin in the examined wards. In 2012, the percentage of MLS-B-sensitive isolates increased from 3.9 to 21.7%, while constitutive resistance decreased to 69.7%, which correlated with a decrease in the use of clindamycin. CONCLUSIONS: The proportion of cMLS-B to iMLS-B phenotypes in HA-MRSA is related to the amount of clindamycin used in hospital wards. Limiting the selection pressure of antibiotics can lead to complete loss of resistance or return to the inductive mechanism of its regulation.

Significance of Screening Tests and the Incidence of New Delhi Metallo-beta-lactamase-Producing Gram-negative Bacilli in the Surgery and Transplantation Wards of a Warsaw Medical Center During the Period From April 2014 to May 2017.

BACKGROUND: The first New Delhi metallo-beta-lactamase (NDM)-producing bacteria were isolated in 2008 in the world, and in 2011 in Poland. Due to the high clonal diversity (17 types) of their blaNDM gene, encoded on (Tn125-like) mobile genetic elements, these strains usually exhibit resistance to nearly all available antibiotics, which is particularly dangerous for organ transplant recipients. PURPOSE: To assess of the prevalence of Gram-negative NDM-positive bacilli in surgery/transplantation wards of a teaching hospital in Warsaw and to ascertain the significance of screening tests on the rates and nature of colonization. MATERIALS AND METHODS: The evaluated strains were isolated from 30 patients (between April 2014 and May 2017). The species were identified with VITEK-MS, antibiotic susceptibility was determined with VITEK 2, disk-diffusion, and/or E-test methods, according to EUCAST guidelines. The presence of the blaNDM-1 gene was confirmed using the polymerase chain reaction technique. RESULTS AND CONCLUSIONS: There were 77 blaNDM-1-positive Klebsiella pneumoniae strains isolated from 30 patients. Cultures from individual patients, mainly from rectal swabs (53.9%) and urine samples (39.8%), yielded 1-11 isolates. Fifteen patients were already colonized on admission, and the other 15 developed a symptomatic infection. In total, 24 (80%) patients were carriers, and their colonizations persisted for <1-20 months. Most isolates were susceptible only to colistin, gentamicin, amikacin, tigecycline, and/or sulfamethoxazole/trimethoprim. Gastrointestinal-tract-colonizing K pneumoniae are the main reservoir of the blaNDM-1 gene. Following the introduction of on-admission mandatory screening for carbapenem-resistant strains, the rates of NDM-producing K pneumoniae isolation increased (7.5-fold), while the rates of isolation from patients with symptomatic infections considerably decreased (2.8-fold).

Significant increase in the isolation of glycopeptide-resistant enterococci from patients hospitalized in the transplant surgery ward in 2004-2005.

Enterococci despite their low pathogenicity are the third cause of hospital infections. Enterococci resistant to glycopeptides present special risks. The aim of this work was to determine the frequency of isolates of all enterococci versus enterococci resistant to glycopeptides from patients in the Transplant Surgery Ward. Moreover, vancomycin-resistant enterococci (VRE) were characterized with respect to the type of van and ddl genes as well as vancomycin and teicoplanin MIC values. Among 160 enterococcal strains isolated in 2004, only 2 were resistant to glycopeptides (1.3%). In 2005, among 244 enterococci, 44 strains were resistant (18%). All resistant strains were Enterococcus faecium, as confirmed by detection of the ddl gene specific for E. faecium. Moreover, among all enterococci isolated from these patients, E. faecium dominated (over 50% in 5 subsequent years). All examined VRE possessed VanA type of resistance with high vancomycin and teicoplanin MIC values. All of them possessed the vanA ligase gene. The investigated VRE were characterized by high resistance to most antibiotics: penicillin and amoxicillin, rifampicin, ciprofloxacin, and high concentrations of streptomycin, but susceptible to linezolid and quinupristine/dalfopristine. Strains differed in their susceptibility to tetracycline, nitrofurantoin, and high concentrations of gentamicin.

Serratia marcescens isolated in 2005 from clinical specimens from patients with diminished immunity.

Serratia marcescens is an important agent in hospital infections. The aim of this paper was to compare the resistance patterns of S. marcescens strains isolated during 1 year from patients of various wards of the Institute of Transplantology. The mechanisms of beta-lactam antibiotic resistance were of especial interest. We investigated the 81 strains of S. marcescens, isolated during 2005 from patients on 3 wards and 1 clinic of the Transplantation Institute. An unusually high resistance to most antibiotics was observed among S. marcescens strains. Extended spectrum beta-lactamases (ESBLs) were probably produced by 63.2% to 84.6% of strains, depending on the ward. Additionally, about 30% of them were probably derepressed AmpC producers. The patterns of resistance indicated that at least 2 resistant clones of S. marcescens spread among the patients. One of the clones demonstrated both ESBL and derepressed AmpC production and was susceptible only to carbapenems. The second, producing ESBL, was susceptible to piperacillin/tazobactam and carbapenems. All investigated strains were resistant to nitrofurantoin. Strains of the second group were rarely susceptible to other antibiotics: aminoglycosides, ciprofloxacin, cotrimoxazole, or fosfomycin.

Occurrence of glycopeptide-resistant enterococci in transplant medicine internal wards in 2001-2005.

The appearance of vancomycin-resistant enterococci (VRE) has caused serious therapeutic problems. In Poland, the frequency of VRE isolation is lower than in the United States or some other European countries. The aim of our work was to analyze the occurrence and characterization of VRE isolated from patients of 2 transplant medicine wards. These wards contained liver or kidney transplant patients. This study examined 5 years, including 235 to 313 enterococcal isolates per year. In 2001-2002, none of the isolated enterococci was confirmed as VRE, which appeared in 2003 (11 strains) and continued on a similar level (from 4% to 6%) in the next 2 years. Among all isolated enterococci, Enterococcus faecalis predominated. In 2003 and 2004, the numbers of E. faecium and E. faecalis among isolated VRE strains were similar, but in 2005, we observed significant predominance of E. faecium. Among VRE strains examined by polymerase chain reaction for the presence of vanA, vanB, vanD, vanE, and vanG ligases, only vanA was found in all cases. The examined strains represented several patterns of resistance to other antibiotics.

Drug Susceptibility Assessment in Stenotrophomonas Maltophilia Strains Isolated From the Blood of Organ Transplantation Recipients in a Warsaw Teaching Hospital During 2011 to 2014.

BACKGROUND: Blood infections with multidrug-resistant Gram-negative carbapenem-resistant bacilli are particularly dangerous and challenging to treat in organ transplant recipients. Resistance to carbapenems may be acquired, for example, in Enterobacteriaceae, Pseudomonas, or Acinetobacter spp. or innate, for example, in Stenotrophomonas maltophilia. The purpose of this study was to analyze blood infections caused by S maltophilia in organ transplant recipients and to compare drug susceptibility of these bacteria and the same species isolated from the blood of other inpatients. METHODS: A total of 26 S maltophilia strains isolated from blood samples of 26 patients (including 14 liver or kidney transplant recipients) hospitalized during 2011 to 2014 were evaluated in this study. Antibiotic susceptibility was determined via E-test and disk diffusion methods. RESULTS: Stenotrophomonas maltophilia strains isolated from blood exhibited sensitivity to trimethoprim/sulfamethoxazole (100%), levofloxacin (96.2%), ciprofloxacin (92.3%), ticarcillin/clavulanic acid (80.8%), and ceftazidime (53.9%). CONCLUSIONS: Because appropriate antibiotic therapy in the case of S maltophilia differs from the standard empirical therapy administered in the case of most other Gram-negative bacilli, early identification of this pathogen is of particular significance. The use of antibiotics to which this pathogen is sensitive eliminates the infection and helps avoid graft loss.

Epidemiological and Drug-Resistance Types of Methicillin-Resistant Staphylococcus Aureus Strains Isolated From Surgical and Transplantation Ward Patients During 2010 to 2011.

BACKGROUND: The increasing prevalence of multi-drug-resistant methicillin-resistant Staphylococcus aureus (MRSA) is a substantial problem in hospitals worldwide, especially in wards with immunocompromised patients undergoing organ transplant. Epidemiological characteristics and antibiotic susceptibility profiles of hospital-acquired (HA) MRSA strains isolated from surgical/transplantation ward patients were studied. METHODS: We analyzed 26 HA-MRSA strains isolated from 22 patients hospitalized at 3 different surgical and transplantation wards at a Warsaw clinical hospital during 2010 to 2011. Eleven patients were MRSA-asymptomatic carriers. Strain relatedness was evaluated through the use of multi-locus sequence typing (MLST), multi-locus variable-number tandem repeat analysis (MLVA), and random amplified polymorphic DNA/arbitrarily primed PCR (RAPD) methods. Antibiotic susceptibility was assessed the use of routine diagnostic methods. RESULTS: The evaluated strains belonged to 4 clonal complexes (CCs) and 4 sequence types (STs): CC30/ST36 (65.4%), CC8/ST8 (15.4%), CC5/ST1827 (11.5%), and CC1/ST1 (7.7%). Six MLVA types and 6 RAPD types were isolated. A ciprofloxacin-, erythromycin-, and clindamycin-resistant CC30/ST36 clone (MLVA type 1, RAPD type 1A) was isolated in all wards. The isolated HA-MRSA strains were most often resistant to ciprofloxacin (100%), erythromycin (96.2%), clindamycin (84.6%), and gentamycin (30.8%). CONCLUSIONS: A ciprofloxacin-, erythromycin-, and clindamycin-resistant HA-MRSA ST36 CC30 clone, which prevailed on transplantation wards in the years 2010 to 2011, is probably one of the international epidemic clones named UK EMRSA-16 or USA200.

Epidemiological aspects of antibiotic resistance in respiratory pathogens.

Respiratory infections are the most frequent reason for primary health care consultation. The main causes of respiratory tract infections in children are viruses and the most common types are upper respiratory tract infections: common cold, pharyngitis, otitis media and sinusitis. Pneumonia is much more serious. As well as viruses, bacteria are often involved in respiratory tract infections. Three bacterial species are most commonly isolated: Streptococcus pneumoniae, non-encapsulated Haemophilus influenzae and Moraxella (Branhamella) catarrhalis. The most common bacterial cause of pharyngitis is Streptococcus pyogenes. Bacteria isolated from community-acquired infection usually are sensitive to the majority of suitable drugs, but during the past two decades, significant antibiotic resistance has emerged. Resistance to penicillins has spread among H. influenzae and S. pneumoniae. The mechanism of penicillin resistance in H. influenzae is mainly by production of beta-lactamases TEM-1 and ROB-1, whereas in S. pneumoniae resistance is an effect of the changes in penicillin binding proteins. Among respiratory pathogens, resistance to tetracyclines, macrolides, trimethoprim-sulphamethoxazole and fluoroquinolones has also appeared. Several mechanisms depending on changes in target, active efflux and modifying enzymes are involved.

Antibiotic resistance in Gram-positive cocci.

Gram-positive cocci still predominate as a cause of nosocomial- and community-acquired infections. These organisms frequently reveal a high natural, intrinsic resistance to antimicrobials. Additionally, these bacteria are able to acquire resistance to frequently used drugs rapidly through selective pressure of the environment and via the genetic evolution of bacteria. The wide application of antimicrobials in medical and veterinary practice, usage of antibiotics in agriculture and common usage of antiseptics and disinfectants result in selective pressure. The use of antibiotics directly selects resistant variants to different antibiotics or disinfectants. The same genetic element (e.g. qac or smr) conferring resistance to some disinfectants are often present on the same plasmid conferring resistance to antibiotics. Selection of resistant variants occurs most frequently in the hospital environment. Staphylococcus aureus and enterococci are the most commonly isolated bacteria causing nosocomial infections. Among those giving therapeutic problems are methicillin-resistant staphylococci and vancomycin-resistant enterococci. Resistance to high levels of aminoglycosides or penicillins among hospital enterococcal strains can completely abolish synergism of the drugs. In these cases glycopeptides will be the drugs of choice in the treatment of serious infections. Recently S. aureus strains with decreased susceptibility to vancomycin has appeared. A mechanism for this elevated resistance, although intensively investigated, still remains unknown.

Epidemiology of methicillin-resistant Staphylococcus aureus in a Warsaw hospital.

Methicillin-resistant Staphylococcus aureus (MRSA) isolates were collected during two eight-month periods in 1991 and 1994, respectively. In order to study the epidemiology, all 74 strains were characterized by phage-typing, antibiotic resistance patterns and DNA-restriction map after cleavage with SmaI enzyme, and pulsed-filed gel electrophoresis (PFGE). These investigations confirmed that MRSA in the hospital, 1991 and 1994, was not due to the spread of one or two clones, but by the simultaneous occurrence of a few well characterized strains and sporadic, occurring strains of different phage-types. Some of these might have developed from the more commonly occurring strains. Isolates from 1994 were more resistant to antibiotics in vitro, than the 1991 isolates. The typing results also indicated that whilst most of the MRSA strains in 1994 were different compared with those of 1991, some of the strains might have been present in both years. The PFGE-typing was more discriminatory and gave a higher typability than the phage-typing, especially among the multiply resistant isolates of MRSA from 1994. Among the less resistant strains the phage-typability was high and with only few exceptions, there was a good correlation between PFGE-type and phage-type.

[Genetic transfer of methycilline resistance in Staphylococus epidermidis and Staphylococcus aureus strains in mixed cultures]. / Przekazywanie genów opornosci na metycyline miedzy szczepami Staphylococcus epidermidis i Staphylococcus aureus w hodowlach mieszanych.

In mixed cultures of staphylococci a transfer of the resistance to methicillin and penicillinase plasmids as well as tetracycline and chloramphenicol plasmids was investigated. It was shown that the resistance to methicillin was transferred in mixed cultures from one strain of S. aureus to another and from S. epidermidis to S. aureus. In both cases transfer of methicillin resistance required, the presence of penicillinase plasmid in recipient or donor strain. In the case of other markers transmission was independent. Moreover it was shown that the transfer of resistance genes in mixed cultures was mediated by bacteriophage of the serologic group A.

[Bacteriophages of serologic group B converting synthesis of fibrinolysin in S. aureus]. / Bakteriofagi grupy serologicznej B konwertujace synteze fibrynolizyny u S. aureus.

On the basis of the length of tail, two morphological types of S. aureus bacteriophages of the serogroup B converting fibrinolysine were shown. The properties of the 22 S. aureus bacteriophages of the serologic group B were investigated. All of the investigated bacteriophages were classified as the morphological group II of the family Styloviridae on the basis of electron microscope analysis. The size of capsids of the examined bacteriophages was 53.85 +/- 1.05 nm and the tail length varied from 135.4 nm to 170.5 nm. All of them had the tail terminated in the basal plate. The lytic properties of the investigated bacteriophages were not identical. 7 of them showed features of lytic group I and 15 of lytic group III. The members of lytic group III had apparently a longer tail than bacteriophages of lytic group I.

[Bacteriophages of serologic group F converting synthesis of fibrinolysin and beta toxin in S. aureus]. / Bakteriofagi grupy serologicznej F konwertujace synteze fibrynolizyny i toksyny beta u S. aureus.

The properties of the 18 S. aureus bacteriophages of the serogroup F were investigated. The chosen bacteriophages were able to convert production of fibrinolysine inhibited synthesis of beta toxin. All of the investigated bacteriophages were classified as morphological group II of the family Styloviridae on the basis of the electron microscope analysis. The size of capsids of the examined bacteriophages was 54.10 +/- 0.80 nm and the tail length was from 206.1 nm to 311.9 nm. Most of them (15 bacteriophages) had the tail terminated in the basal plate. The lytic properties of the investigated bacteriophages were not identical. 11 of them showed features of lytic group III and 7 of lytic group V (miscellaneous).

[Characteristics of penicillinase plasmids from Staphylococcus aureus strains]. / Charakterystyka plazmidów penicylinazowych u szczepów Staphylococcus aureus.

Penicillinase plasmids are present in most MRSA strains. They are very varying in their genotype and phenotype they confer. Penicillinase plasmids were transduced from 80 hospital MRSA strains to NCTC 8325 and the phenotype as well as the incompatibility group of plasmid were determined. Resistance to cadmium (high and low level), resistance to organic and nonorganic mercury compounds, arsenate/arsenite/antimonium resistance, resistance to bismuth and hypersensitivity to bismuth, resistance to macrolides as well as beta-lactamase production and its inductibility were checked. Among the examined strains 20 different phenotypes of penicillinase plasmids were found. Patterns of penicillinase plasmids were compared to DNA patterns of the investigated strains after digestion with SmaI and separation in pulsed field electrophoresis (PFGE). It was shown that strains with the same PFGE pattern often differ in the type of their penicillinase plasmid. Determining of penicillinase plasmid phenotype could be useful in differentiating S. aureus strains sharing the same pattern of PFGE.

[Localization of genes conferring resistance to selected groups of antibiotics in methicillin-resistant strains of Staphylococcus aureus]. / Lokalizacja genów opornosci na wybrane grupy antybiotyków u metycylinoopornych szczepów Staphylococcus aureus.

Localization of genes conferring resistance to MLS, tetracyclines, chloramphenicol, gentamycin and neomycin in 80 MRSA strains isolated from hospital specimens was determined. The obtained results were compared to DNA patterns of the examined strains after digestion with SmaI and separation in pulsed field electrophoresis (PFGE). It was shown that genes of resistance to MLS (ErmI+) in the case of 13 strains were located on chromosome and in the case of 37 strains on plasmids (16 strains had ErmI+ and 21 strains had ErmI-). Genes determining resistance to tetracyclines were localised on chromosome in the case of 39 (23 strains possessed TetK, 11 strains had TetM and 5 strains possessed both TetK and TetM determinants) and in the case of 32 strains on plasmids. Chloramphenicol resistance genes were localised on plasmids in all 30 resistant strains. Genes conferring resistance to gentamycin were present in 31 of the investigated strains on chromosome and in two strains on plasmids. Neomycin resistance genes were plasmid in 34 strains. It was shown that the localization of the resistance genes and the PFGE patterns of the investigated strains were highly correlated.

[Use of pulse-field electrophoresis for intraspecies differentiation of methycillin-resistant, coagulase-negative strains of Staphylococcus aureus (MRSA-CN)]. / Zastosowanie pulsacyjnej elektroforezy do wewnatrzgatunkowego róznicowania metycylino-opornych, koagulazo-ujemnych szczepów Staphylococcus aureus (MRSA-CN).

Strains showing a negative reaction in tube test for coagulase accounted 10 to 20% of all Staphylococcus aureus isolated from patients of PSK No. 1 in Warsaw. They are MRSA as well as MSSA strains. 37 coagulase-negative isolates of MRSA were examined using the method depending on digestion of whole cell DNA with SmaI enzyme and electrophoretic separation of the obtained fragments in the pulsed field (PFGE). It was shown that majority of the strains (26 from 37) had individual, unique patterns of bands. However, the two groups of strains were also observed showing a great similarity. The larger group contained 8 strains which were obtained from patients from different wards and the smaller group contained 3 strains obtained from patients from one hospital ward. The obtained results showed that among coagulase-negative MRSA strains are not only sporadic strains but also strains with probably epidemic properties, derived from different clones.

[Characteristics of the MRSA clone with reduced susceptibility to vancomycin]. / Charakterystyka klonu MRSA o obnizonej wrazliwosci na wankomycyne.

The MIC of vancomycin was determined for all S. aureus strains isolated during 1997 in one hospital. MIC values for most isolates were in the range of 0.5-2 mg/l. In 18 strains, MIC was = 6 mg/L. All these strains were MRSA. Recently described VISA strains possessed MIC values for vancomycin equal or higher than 8 mg/l and such strains were not detected in the investigated group. Although strains with MIC = 6 mg/l are not VISA, but they are candidate for reduced vancomycin susceptibility, e.g. during therapy in compromised patients. Analysis of DNA of these strains by pulsed-field gel electrophoresis (PFGE) revealed that 15 of them shared a significant similarity, allowing to place them in the same group. The comparison data of phage patterns as well as antibiotic resistance patterns strongly suggest that all these strains were derivatives of a single clone.

[Evaluation of susceptibility of methicillin resistant Staphylococcus aureus strains to vancomycin]. / Ocena wrazliwosci metycylinoopornych szczepów Staphylococcus aureus na wankomycyne.

Susceptibility to vancomycin and teicoplanin was studied in the most frequently isolated Staphylococcus species isolated in the State Hospital Clinic Nr 1 in Warsaw in 1994. No strains resistant to vancomycin were found in two Staphylococci most frequently isolated from clinical material: S. aureus and S. epidermidis. Occurrence of this resistance is very rare and is restricted only to coagulase-negative Staphylococci such as S. xylosus, S. capitis, S. lentus and S. cohni. Resistance to teicoplanin was observed more often (1.4% in S. aureus and from 11.8% to 39.3% in 9 species of coagulase-negative Staphylococci). For the majority of methicillin-susceptible clinical strains (80%), the MBC value did not exceed 4.0 mcg/ml of vancomycin while for almost half of the strains in the population of methicillin-resistant strains MBC values ranged from 32.0 to 128 mcg/ml of vancomycin. Moreover, vancomycin-tolerant strains were found eight times more often in the studied MRSA (26.7%) population than in MSSA strains (3.3%).

[Lysogenic conversion as a factor influencing tolerance to vancomycin in Staphylococcus aureus]. / Konwersja lizogenna jako czynnik wplywajacy na zjawisko tolerancji na wankomycyne u Staphylococcus aureus.

The standard, non-lysogenic, bacteriophage-free S. aureus NCTC 8325-4 strain was lysogenized with 15 different, obtained in our laboratory staphylokinase-converting bacteriophages belonging to serological groups A, B and F. MIC and MBC of vancomycin as well as the ratio of MBC to MIC were evaluated for all 15 lysogenic derivatives. The obtained results were compared with those for maternal strain. In the case of eight strains the ratio MBC/MIC showed the presence of tolerance to vancomycin (MBC/MIC > or = 32). Four of the vancomycin-tolerant derivatives were lysogenized with bacteriophages belonging to the serological group A, two were members of group B and two belonged to group F.