Prevalence and chemosusceptibility of Neisseria meningitidis and Haemophilus influenzae in a population of central Italy

The purpose of this study was to determine the prevalence of nasopharyngeal carriers of Neisseria meningitidis and Haemophilus influenzae, and to evaluate their chemoresistance. N. meningitidis was more frequently isolated in adolescents (10-15 years). All of meningococci were susceptible to ceftriaxone and rifampin, only one isolate showed reduced susceptibility to chloramphenicol and four strains showed reduced penicillin susceptibility. The results show that these drugs are still effective for prophylaxis and treatment in our area. All strains of H. influenzae were susceptible to penicillin, ceftriaxone, chloramphenicol, rifampin, azithromicin and gentamicin. 6 nontypeable strains were resistant to sulfamethoxazole-trimethoprim, 7 strains of type a and c-f, and 3 non-typeable strains showed reduced susceptibility to tetracycline. In contrast with the current trend in the world, in our area the susceptibility of H. influenzae to betalactams was 100%, therefore these antibiotics are still the drugs of choice for treatment of invasive diseases.     

Drug resistance and R plasmids in Escherichia coli strains isolated from broilers

In 1978, 1,021 Escherichia coli strains were isolated from 105 field broilers (F) and 1,058 strains from 106 broilers in a zootechnical experiment station (Z), and their drug-resistance patterns and the presence of conjugative R plasmids were compared. The resistance markers examined were tetracycline (TC), chloramphenicol (CM), streptomycin (SM), sulfonamides (SA), kanamycin (KM), and ampicillin (APC). The populations of individuals that excreted resistant strains were 100% in F and 58% in Z. Frequencies of isolation of drug-resistant strains among the total isolates were 93% in F and 36% in Z, indicating that the resistant strains are a rather high proportion of the intestinal flora in F but are slightly less prevalent in Z. The resistance pattern to (TC.SM.SA.KM) was seen at the highest frequency in both groups. Conjugative R plasmids were demonstrated more frequently in field broilers (F). The results reflect the wide use of antibiotics in the livestock industry, resulting in the appearance of drug-resistant strains mostly due to the presence of R plasmids.     

Characterization of plasmids that confer inducible resistance to 14-membered macrolides and streptogramin type B antibiotics in Staphylococcus aureus

During a period from 1978 to 1989, 413 Staphylococcus aureus strains were isolated at 27 different geographical regions in Hungary; they exhibited an inducible resistance to the 14-membered macrolides and streptogramin type B antibiotics, but not to the 16-membered macrolides and lincosamides: this resistance is referred to as PMS resistance phenotype. The isolates were mostly associated with patients suffering from staphylococcal diseases and with hygienic screenings in hospitals and closed communities. They were rarely isolated from food-poisoning cases, food hygienic screenings, or animal sources. Strains with PMS resistance phenotype were resistant to penicillin (99.0%), tetracycline (78.7%), and chloramphenicol (63.0%); however, they were susceptible to oxacillin. Most of them (94.2%) belonged to the phage type 52-complex. The determinant for PMS phenotype was located on plasmids, which also encoded beta-lactamase production and cadmium ion resistance, but not arsenate resistance. Three types of plasmid with molecular size of 50 kilobases (kb), 23.8 kb, and 16.8 kb, were found among the strains with PMS resistance phenotype, and the 50 kb and 23.8 kb plasmids also encoded mercury resistance. The 16.8 kb and 23.8 kb plasmids belonged to incompatibility group 1.     

Biological characteristics of Staphylococcus aureus isolated from nude mice

The characteristics of 50 strains of Staphylococcus aureus isolated from BALB/c nude mice (nu/nu, nu/+) with or without subcutaneous abscesses [13] were examined. All the 50 strains belonged to biotype B according to the classification by Hájek and Marsálek. All of them were phage typable, showing a single phage pattern of 52A/79/47/53/77/83A/85. The coagulase type was classified as VII. All of the 50 strains were highly sensitive to penicillin, methylphenylisoxazolyl penicillin, erythromycin, spiramycin, lincomycin, chloramphenicol, tetracycline, kanamycin, gentamicin and cephaloridine, but were resistant to sulfisoxazole. Two S. aureus strains isolated from the nostril and finger of one person working in the mouse colony were identified as the same biotype as the murine strains but different in phage type, coagulase type and drug resistance pattern.     

Dynamics of drug resistance of Vibrio cholerae isolated from surface water reservoirs in Siberia and the Soviet Far East in 1976-1990]

In the study on antibiotic resistance 1383 strains of El Tor Vibrio cholerae isolated from surface water reservoirs in 12 administrative territories of the Siberia and Far East within a period of 15 years were tested. The following antibiotics were used: ampicillin, streptomycin, monomycin, polymyxin, tetracycline, chloramphenicol, rifampicin and nalidixic acid. The resistance was unstable and its pattern was wave-like according to annual changes in the biological cycle. It was especially evident in regard to ampicillin, streptomycin, monomycin and polymyxin. The highest numbers of the strains were resistant to polymyxin, ampicillin and streptomycin (up to 100 per cent in some years). The lowest numbers of the strains were resistant to chloramphenicol (0.4 per cent) and tetracycline (1.9 per cent). No strains resistant to rifampicin and nalidixic acid were isolated. In some cases the antibiotic resistance level depended on the geographical zone where the strain was isolated. A direct quantitative dependence of the resistance level on the MIC was observed: the lower the MIC of the drug was, the lower the number of the strains resistant to it was. Within the 15-year period there was no general tendency to increase the resistance in V. cholerae to the antibiotics used.     

Changes in antibiotic sensitivity in strains of Staphylococcus aureus, 1952-78.

Two hundred strains of Staphylococcus aureus isolated from outpatients with infections of the skin and subcutaneous tissues were tested for sensitivity to penicillin, erythromycin, tetracycline, sodium fusidate, methicillin, clindamycin, chloramphenicol, and gentamicin. One hundred and sixty-three (81.5%) of the strains were resistant to penicillin and 16 (8%) resistant to tetracycline. Incidence of resistance to other antibiotics was low. No strain was resistant to chloramphenicol, gentamicin, or methicillin. When compared with results of earlier studies, there was an increase in the incidence of resistance to penicillin and tetracycline, but no appreciable increase in resistance to other antibiotics.     

Antimicrobial Susceptibility of Clostridium difficile from Different Sources

A total of 79 Clostridium difficile strains from healthy young and elderly adults, elderly patients without gastrointestinal disease, elderly patients receiving antibiotics without gastrointestinal complications, and elderly patients with antibiotic-associated diarrhea or pseudomembranous colitis were tested for their susceptibilities to 24 antimicrobial agents. All of the 79 strains were inhibited by low concentrations of rifampicin, metronidazole, fusidic acid, vancomycin, ampicillin, and penicillin G. The strains were highly resistant to aminoglycosides, trimethoprim, sulfamethoxazole, nalidixic acid, and cycloserine and often resistant to neomycin, cefoxitin, and cefalexin. Wide variations in the susceptibility of C. difficile strains to erythromycin, clindamycin, lincomycin, chloramphenicol, and tetracycline were found. Strains resistant to erythromycin, clindamycin, and lincomycin were more frequently found among strains isolated from elderly adults than those isolated from young adults, with particularly high frequency among strains isolated from elderly patients receiving antibiotics. None of the 23 strains isolated from healthy young adults was resistant to chloramphenicol. All of the 14 strains resistant to erythromycin, clindamycin, lincomycin, and chloramphenicol were sensitive to tetracycline and all of the 15 strains resistant to erythromycin, clindamycin, lincomycin, and tetracycline were sensitive to chloramphenicol. Only one out of 19 tetracycline-resistant strains was highly toxigenic, whereas 42 (70%) of 60 sensitive strains were highly toxigenic.     

Worldwide distribution of the conjugative Clostridium perfringens tetracycline resistance plasmid, pCW3

The aim of this study was to test the hypothesis that all conjugative R-plasmids of Clostridium perfringens are closely related to the previously characterized tetracycline resistance plasmid, pCW3. Fourteen conjugative R-plasmids derived from 11 C. perfringens strains isolated in Australia, the United States, France, Belgium, and Japan were analyzed. Eleven of the plasmids encoded tetracycline resistance while three carried both tetracycline and chloramphenicol resistance. Each of these plasmids was compared, by restriction analysis, to the reference plasmid, pCW3. Seven of the tetracycline resistance plasmids had EcoRI, XbaI, and ClaI restriction profiles that were identical to those of the corresponding pCW3 digests. The seven remaining R-plasmids were different from pCW3. Comparison of partial restriction maps of these plasmids with a complete map of pCW3 indicated that they contained at least 17 kb of DNA that also was present in pCW3. Hybridization analysis confirmed that these plasmids shared substantial homology with pCW3. The three tetracycline and chloramphenicol resistance plasmids frequently lost a 6-kb chloramphenicol resistance segment during conjugation. Cloning experiments showed that the chloramphenicol resistance determinant was expressed in Escherichia coli and that the chloramphenicol resistance gene of one of these plasmids, pIP401, was contained within a 1.5-kb region of the 6-kb deletion segment. Hybridization analysis indicated that the deletion segment of pIP401 was related to those of the other two chloramphenicol resistance plasmids. During the course of this study, conjugative R-plasmids which appear to be identical to pCW3 or closely related to pCW3 were identified from C. perfringens strains from human, animal and environmental sources in five countries. It is concluded that C. perfringens strains in humans and animals throughout the world have overlapping gene pools and that all the conjugative C. perfringens R-plasmids examined probably evolved from a pCW3-like element.     

A comprehensive evaluation of the biological properties of the causative agents of typhoid fever isolated from patients and carriers

The biological properties of 106 S. typhi cultures were studied; of these, 59 cultures were isolated from 45 chronic carriers and 47 cultures, from 23 typhoid fever patients. According to the degree of their virulence (CPD50 in the continuous cell-line culture Hep-2), the strains isolated from the patients were more virulent than those isolated from the chronic carriers. The mean value of lg CPD50 was 5.76 +/- 0.04 for the patients and 6.86 +/- 0.03 for the chronic carriers. The strains isolated from the patients showed greater variability in the degree of their virulence. The study of the plasmid spectrum showed that 9.4 +/- 5.6% of the strains contained plasmids. From the patients plasmid-containing strains were isolated more frequently than from the carriers (14.9 +/- 2.5% and 5.1 +/- 2.9%). Multiresistance to antibiotics in combination with the presence of plasmids was detected in 6 strains isolated from the typhoid patients with morbidity having the character of outbreaks.     

Conjugative R plasmids isolated from hospital strains of Pseudomonas aeruginosa]

It was shown that Pseudomonas aeruginosa hospital strains isolated from patients and environment in the Republican Centre of Burns in Tbilisi contained conjugative R plasmids. The plasmids were marked pM15 and pM19, respectively. The plasmid pM15 determined resistance to carbenicillin, kanamycin and tetracycline and plasmid pM19 determined resistance to carbenicillin, kanamycin, tetracycline, chloramphenicol, gentamicin and streptomycin. Plasmid pM15 had a molecular weight of 45.8 MD and seven sites for EcoRI, six sites for HindIII and five sites for Hpa-I-restrictase. This plasmid, as others, belongs to the Inc-P1 incompatibility group.     

Naturally occurring drug resistance plasmids in hospital strains of Staphylococcus aureus

A genetic analysis of multiply inorganic salts and antibiotic--resistant strains of Staphylococcus aureus was performed. Experiments designed to show reversion of organisms to antibiotic and inorganic salt susceptibility, as well as studies on the influence of ultraviolet irradiation of phage on the transduction frequencies of the resistance markers, indicated that determinants of chloramphenicol, tetracycline, aminoglycoside antibiotics, inorganic salts, and penicillin resistance in hospital strain are present on separate plasmids. Transduced by us plasmids pN742 and pN794 determined resistance to neomycin, kanamycin, paromomycin, lividomycin and streptomycin.     

Sensitivity to antibacterial preparations of the pathogenic staphylococci isolated from carriers]

After discontinuation of the use of antibiotics for sanation of the carriers of pathogenic staphylococci among the staff of a maternity unit, the number of the strains resistant to penicillin, streptomycin, chlortetracycline, tetracycline, levomycetin, erythromycin, monomycin and neomycin decreased 1.3, 2.9, 10,4.3,5.5,1.5,3.9 and 2.4 times respectively. The differences were statistically reliable. The causes of the antibiotic resistance decrease require further investigation.     

Transduction of penicillinase production in Staphylococcus epidermidis and nature of the genetic determinant.

Four strains of Staphylococcus epidermidis from clinical sources were capable of serving as donors for the transduction of either penicillinase production, ethidium bromide resistance, or tetracycline resistance. Three typing phages served as transducing phages and, depending upon the combination of transducing phage, donor strain, and recipient strain, the rates of transduction ranged between 10(-5) and 10(-9). In one strain, cotransduction of penicillinase production and ethidium bromide resistance was observed. Although ultraviolet irradiation kinetics indicated that both the tetracycline resistance and the penicillin resistance determinants were located on plasmids, only resistance to tetracycline could be eliminated by growth in the presence of curing agents or at elevated temperature. However, evidence was obtained by agarose gel electrophoretic studies that both the tetracycline resistance and the penicillin resistance determinants are located on separate plasmids in this organism.     

The sensitivity of phage DNA and plasmid DNA for a restriction enzyme from Staphylococcus aureus

In Staphylococcus aureus transduction of different tetracycline and chloramphenicol plasmids with a group I/III modification was possible to group I and III strains. Group II strains, containing a restriction endonuclease, had a restriction both for the phage and the plasmids: two restriction-deficient group II strains were good acceptors for these plasmids.     

Analysis of integrons in human isolates of Salmonella enterica serovar typhimurium isolated in the Slovak Republic

About 110 sporadic, epidemiologically unrelated Salmonella enterica serovar typhimurium strains isolated in the Slovak Republic were analyzed for the presence of integrons. Of these 110 examined strains, 47 were of definitive phage type DT104 and 63 were strains of various phage type, RDNC and untypeable, designated here as non-DT104 strains. All isolates were also tested for antimicrobial resistance to 10 antibiotics as well as for the presence of virulence plasmid. Of 63 non-DT104 strains, 15 isolates were multiple-resistant, independently from phage type, other strains were resistant to one, two or three drugs. Resistance to ampicillin, streptomycin, tetracycline and sulfisoxazole was most frequently observed. Among the DT104 isolates up 65.9% exhibited characteristic pentaresistance--ACSSuT phenotype. The integron content was studied in PCR experiments using a 5'-CS/3'-CS primer pair. Fourteen non-DT104 strains, independently from phage type, were found to carry integrons with amplicons 650-1900 bp in size. Thirty-six DT104 strains contained integrons of 1000 and 1200 bp and 31 of they exhibited the ACSSuT phenotype. No integron was found in 10 DT104 strains, which included strains mostly resistant only to streptomycin, tetracycline and sulfisoxazole. The majority of non-DT104 strains did not possess any integrons. Our findings show the widespread existence of both resistant and multiple-resistant epidemiologically unrelated Salmonella typhimurium strains and suggest that integrons contribute to this antimicrobial resistance. The presence of 90-kb virulence plasmid in the 54 non-DT104 and in the all DT104 strains was found.     

Frequency of R Factor-mediated Multiple Drug Resistance in Klebsiella and Aerobacter

A comparative study was done on the transfer frequency of R factors from 90 strains of multiple drug-resistant Aerobacter and 81 strains of Klebsiella to Escherichia coli CSH-2 (F(-), met(-), pro(-), Nal-r). The most common resistance patterns for the Aerobacter isolants were ampicillin streptomycin chloramphenicol tetracycline and ampicillin streptomycin chloramphenicol tetracycline kanamycin neomycin; for the Klebsiella isolants, the most common resistance pattern was ampicillin kanamycin streptomycin tetracycline chloramphenicol neomycin. R factors were isolated from 14.1% of the Aerobacter strains; 61.5% of these R factors harbored R determinants for ampicillin streptomycin tetracycline. R factors were isolated from 79.1% of the Klebsiella strains; four R factors were isolated with significant frequency; streptomycin chloramphenicol kanamycin neomycin, 37.5%; ampicillin streptomycin tetracycline kanamycin neomycin, 14.1%; ampicillin streptomycin tetracycline, 12.5%; and streptomycin chloramphenicol tetracycline, 12.5%.Chloramphenicol, kanamycin, and neomycin resistance was rarely transferred from the Aerobacter strains, although over 50% of the clinical isolants possessed resistance to these antibiotics. In contrast, over 75% of the Klebsiella strains transferred resistance to chloramphenicol, kanamycin, neomycin. Highest frequency of transferred resistance to individual drugs in the Aerobacter strains was to streptomycin (14.8%), whereas in the Klebsiella group resistance to four drugs was transferred at a very high frequency: streptomycin (80.8%), chloramphenicol (78.5%), kanamycin (76.4%), and neomycin (75.9%).     

Phage types of Staphylococcus aureus strains and their antibiotic resistance in carriers of medical students population

The phage types of 78 S. aureus strains isolated from nose swabs obtained from a medical students in 2005 -2006 was determined and antibiotic resistance of the phage types was analysed. 680 students were tested in order to obtain the strains and 11.5% of them were carriers of S. aureus. Phage typing was performed using basic set of23 phages and 3 additional phages: 88, 89 and 187. Drug resistance was determined by the disc-diffusion method. The most frequent in studied population were the group III (21.8%) and strains lysed by phages belonging to varied groups (21.8%). Highly different phage patterns were observed among strains belonging to each of the group. Strains belonging to the group III as the strains lysed by phages from varied groups were most frequently resistant only to penicillin (52,9% respectively). Resistance to penicillin was also most often observed in the strains belonging to another groups and phage types. Usefulness of the additional phages 88,89 and 187 was in the investigations as no more than 51% of strains was lysed by this phages.     

Antibiotic sensitivity of Shigella isolated from patients from 1974-1985

Antibiotic sensitivity of 3524 Shigella cultures isolated from patients in 1974-1982 and 414 cultures isolated in 1983-1985 was assayed with standard paper disks. The isolates of 1974-1982 were mostly responsive to ampicillin, carbenicillin, kanamycin, gentamicin, monomycin, neomycin and chloramphenicol. Certain differences in the level of the antibiotic resistance were observed in the Shigella isolates belonging to diverse species. Polyresistant cultures of Shigella amounted to 96.5% and ranged from 88.5 to 99.4% in different years. The number of the cultures with multiple resistance among Shigella sonnei was somewhat higher than that among the Flexneri and Newcastle bacilli. The Shigella isolates of 1983-1985 were mostly responsive to gentamicin, carbenicillin, neomycin, kanamycin and monomycin. 55.5% of the Shigella isolates were responsive to chloramphenicol and only 3.1% to tetracycline. Almost all the causative agents of dysentery isolated within that period were polyresistant. Phenotypic characteristics of multiple resistance in the Shigella cultures were studied.     

Energy metabolism in Staphylococci containing plasmids of resistance to a number of antibiotics]

Activity patterns of membrane-bound enzymes of an antibiotic sensitive strain of Staphylococcus aureus 8325-4 and its variants containing the plasmids of resistance to penicillin, tetracycline, erythromycin and chloramphenicol were studied. It was shown that acquiring of resistance to the above mentioned antibiotics influenced cellular energy metabolism. The resistant strains exhibited an increase in the specific activity of NADN, malate and succinate oxidases, intensification of the ATP-hydrolyzing activity, changes in the activity of definite dehydrogenases and a decrease in the specific content of cytochromes. No changes in the composition of respiration carriers were detected.     

Resistance of Shigella to antibiotics

Antibiotic sensitivity of 104 Shigella clinical strains and 104 Escherichia coli strains isolated from patients with acute dysentery not treated with antibiotics in 1986-1987 was studied. It was shown that 100 per cent of the dysentery pathogens and colon bacilli were antibiotic resistant. Strains resistant simultaneously to chloramphenicol, ampicillin, streptomycin, tetracycline, monomycin and kanamycin were the most frequent among the dysentery pathogens. Colon bacilli and dysentery pathogens isolated from the same patient had specific sets of antibiotic resistance markers. Pathogenetic therapy of dysentery and exclusion of antibiotic use for several years did not result in lower numbers of Shigella antibiotic resistant strains.