Identification of PSE and OXA beta-lactamase genes in Pseudomonas aeruginosa using PCR-restriction fragment length polymorphism

OBJECTIVE

A method using PCR-restriction fragment length polymorphism was developed to identify Pseudomonas aeruginosa beta-lactamase genes.

METHODS

Two hundred and fifty-nine P. aeruginosa isolates were screened by PCR with 11 primer pairs designed to detect genes encoding PSE, OXA, TEM and SHV enzymes. PSE and OXA gene variants were distinguished by restriction of PCR products with endonucleases recognizing sites involved in point mutations. Nucleotide sequences were verified for a few isolates by sequencing the PCR products.

RESULTS

Four isolates produced extended-spectrum beta-lactamases (ESBLs) according to the double disc synergy test. PCR detecting bla(PSE) genes was positive in 162 (62.5%) isolates: 151 carried bla(PSE-1) and 11 carried a variant encoding an enzyme differing from PSE-1 by a single amino acid substitution (Pro102 to Ser). PCR detecting sequences for enzymes of the OXA-10 group was positive in 68 (26.3%) isolates: 31 carried bla(OXA-10), one carried bla(OXA-14) and 36 carried a new variant intermediate between bla(OXA-13) and bla(OXA-19). The bla(OXA-2) gene was identified in 13 (5%) isolates. Two other isolates carried bla(OXA-2) variants encoding ESBLs differing from OXA-2 by a single amino acid substitution (Asp150 to Tyr and Trp159 to Cys, respectively). PCR detecting sequences for enzymes of the OXA-1 group was positive in 12 (4.6%) isolates. A bla(TEM) gene was identified in five (1.9%) isolates (three bla(TEM-1), one bla(TEM-2), one bla(TEM-4)).

CONCLUSION

This approach is effective for screening P. aeruginosa for beta-lactamase gene carriage in epidemiological studies and for detecting new variants.

Identification of the hemolysis-associated protein 1 as a cross-protective immunogen of Leptospira interrogans by adenovirus-mediated vaccination

New vaccine strategies are needed for the prevention of leptospirosis, a widespread human and animal disease caused by pathogenic leptospires. Our previous work determined that a protein leptospiral extract conferred cross-protection in a gerbil model of leptospirosis. The 31- to 34-kDa protein fraction of Leptospira interrogans serovar autumnalis was shown sufficient for this purpose. In the present study, N-terminal sequencing of a 32-kDa fraction and Southern blotting of genomic DNA with corresponding degenerated oligonucleotide probes identified two of its constituents: hemolysis-associated protein 1 (Hap1) and the outer membrane Leptospira protein 1 (OmpL1). Adenovirus-mediated Hap1 vaccination induces significant protection against a virulent heterologous Leptospira challenge in gerbils, whereas a similar OmpL1 construct failed to protect the animals. These data indicate that Hap1 could be a good candidate for developing a new generation of vaccines able to induce broad protection against leptospirosis disease.

Evidence of cross-protection within Leptospira interrogans in an experimental model

Killed whole-cell preparations were used as bacterins against leptospirosis. As this type of protection is considered to be serogroup-specific, several serogroups were added to the usual vaccines, and the most pathogenic serovar was chosen for each group. Different leptospire extracts were evaluated for their protective capacity against acute lethal leptospirosis in gerbils (Meriones unguiculatus). Total extracts induced complete protection against homologous challenges and partial protection against heterologous challenges. LPS fractions protected against homologous but not heterologous challenges, whereas protein extract induced significant protection against both types of challenge. Thus, cross-protection within L. interrogans was related to the protein extract.

TEM-24 extended-spectrum beta-lactamase-producing Enterobacter aerogenes: long-term clonal dissemination in French hospitals

OBJECTIVE

To investigate interstrain relatedness of TEM-24-producing Enterobacter aerogenes clinical strains isolated between 1993 and 1998 in 10 French hospitals from nine areas by pulsed-field gel electrophoresis (PFGE) and plasmid patterns.

METHODS

Fifteen TEM-24-producing strains and a set of 16 control strains having various other antibiotic resistance phenotypes were genotyped by PFGE. Plasmid DNA from TEM-24-producing strains and transconjugants was analyzed.

RESULTS

Analysis of XbaI macrorestriction patterns revealed only minor variations, and showed that all 15 TEM-24-producing strains were closely related. Some isolates originating from distant areas had indistinguishable patterns. According to their clustering correlation coefficients, they were also genomically distant from the control strains. Two plasmid patterns were observed in TEM-24-producing strains, one of them in 13 of the strains. Large plasmids of 85 kb encoding TEM-24 beta-lactamase were present in all isolates and, in all except one strain, could be transferred with high frequency by conjugation.

CONCLUSIONS

These results confirm that the spread of the TEM-24 extended-spectrum beta-lactamase in France was essentially due to the dissemination of a single clone.

Long-term investigation of the clonal dissemination of Klebsiella pneumoniae isolates producing extended-spectrum beta-lactamases in a university hospital

Seventy isolates of Klebsiella pneumoniae with extended-spectrum beta-lactamases (ESBLs) were compared. These were isolated from 51 patients on 10 separate wards in one hospital over an 18-month period between 1992 and 1994. Antibiograms were determined and the isolates were typed by pulsed-field gel electrophoresis of their DNA digestion with XbaI. The isolates were compared to three genotypically different epidemic strains responsible for previous outbreaks at the hospital between 1988 and 1991. Isolates from 84% of the present patients had closely related XbaI patterns, and most (74%) produced an ESBL with an iso-electric point (pI) of 7.0. A similar pattern was found for one of the previous epidemic strains, but it produced an ESBL with a pI of 7.8; isolates with this latter enzyme variant were found only in six of the present patients. The two other previous epidemic strains had ESBLs with a pI of 6.3 and organisms related to them were found in one and two of the present patients, respectively.

Purulent pleurisy caused by Campylobacter lari

An 80-year-old debilitated patient developed purulent pleurisy caused by a Campylobacter lari isolate. The patient underwent surgical drainage and received antibiotic therapy with amoxicillin/clavulanic acid and ofloxacin. Antibiotic susceptibility data showed that the isolate was fully sensitive to clarithromycin, tetracycline, aminoglycosides. and ciprofloxacin. Imipenem and amoxicillin plus clavulanic acid were the most active beta-lactam agents.

Differentiation of human and animal strains of Streptococcus dysgalactiae by pulsed-field gel electrophoresis

The genetic diversity among 54 human isolates and 33 animal isolates belonging to the species Streptococcus dysgalactiae (20 alpha-haemolytic Streptococcus dysgalactiae, 23 Streptococcus equisimilis, 43 group G streptococci and one group L streptococcus) was evaluated by macrorestriction analysis of chromosomal DNA with SmaI and resolution by pulsed-field gel electrophoresis. This technique revealed a high degree of intraspecies polymorphism, leading to the differentiation of 80 distinct banding patterns, and identified the presence of two major clusters, one containing isolates of human origin and the other isolates of animal origin. These results suggest than human and animal isolates of S.dysgalactiae are genetically distinct, and support the recent proposal of the subspecies S. dysgalactiae subsp. equisimilis for human isolates. The heterogeneity revealed within isolates from the same host type indicates that pulsed-field gel electrophoresis is a powerful epidemiological tool for studying S. dysgalactiae infections.

Epidemiological typing of extended-spectrum beta-lactamase-producing Klebsiella pneumoniae isolates responsible for five outbreaks in a university hospital

Thirty-seven isolates of extended-spectrum beta-lactamase-producing (ESBL) Klebsiella pneumoniae implicated in five nosocomial outbreaks (I-V) on three distinct wards of our hospital were compared using capsular typing, biotyping, antibiotyping, enzyme electrophoresis typing and DNA macrorestriction analysis with Xba I resolved by pulsed-field gel electrophoresis. The isolates from each outbreak had common phenotypic and genotypic characteristics indicating that they were related epidemiologically. Isolates from outbreaks I (four patients) and V (13 patients), although they occurred in two different wards (neurology and surgery) and three years apart, produced the same ESBL with a pI of 7.8 (SHV-4) and were of serotype K25. The Xba I patterns were closely related. The isolates of outbreaks II (seven patients), III (four patients) and IV (seven patients), which occurred in a single surgical intensive care unit, produced an ESBL with a pI of 6.3 (TEM-3). Isolates from outbreaks III and IV, which occurred six months apart, were of serotype K68 and had similar Xba I patterns suggesting that the two outbreaks were due to a single strain which persisted endemically in the ward. The isolates from outbreak II were of serotype K62, and had distinct characteristics from the two later outbreaks. The Xba I patterns of the isolates from outbreaks "I and V', II and "III and IV' had Dice similarity coefficients under 40% showing that the three groups were genetically distant. DNA macrorestriction analysis was a useful complement to phenotypic methods for identifying K. pneumoniae strains responsible for outbreaks harbouring a common ESBL.

Pulsed-field gel electrophoresis is more discriminating than multilocus enzyme electrophoresis and random amplified polymorphic DNA analysis for typing pyogenic streptococci

The SmaI restriction endonuclease digestion patterns of chromosomal DNAs from 99 pyogenic streptococci belonging to Lancefield group A (41 Streptococcus pyogenes), group C (seven S.dysgalactiae, 11 "S. equisimilis", three S. equi, eight S. zooepidemicus) and group G (25 human group G Streptococcus, four S. canis) were analyzed by pulsed-field gel electrophoresis (PFGE), and the results were compared with those previously obtained by multilocus enzyme electrophoresis (MLEE) and random amplified polymorphic DNA analysis (RAPD). PFGE revealed 93 distinct types among the 99 strains, and no patterns were common to strains of different species. The discriminatory power of PFGE was greater than that of MLEE and RAPD for groups A and G streptococci. The polymorphism among group C streptococci was similar with the three techniques. PFGE is, therefore, the most efficacious method for epidemiological typing of pyogenic streptococci.

Arbitrary primed PCR rules out Clostridium difficile cross-infection among patients in a haematology unit

Eight out of 20 (40%) patients with haematological malignancies hospitalized in the same unit of our hospital from 24 January to 24 April 1995, suffered from diarrhoea due to Clostridium difficile. The C. difficile isolates were characterized by serotyping and by arbitrary primed polymerase chain reaction (AP-PCR) using three different 10-mer oligonucleotides. It was found by serotyping that five patients had non-typeable isolates and three had serogroup H isolates. The AP-PCR typed all the isolates and yielded various patterns suggesting that there had been no cross-transmission between the patients. Control faecal sample cultures showed that two patients were still carrying the same isolates after specific treatment with vancomycin or metronidazole, and that one patient had acquired an isolate with a new AP-PCR type. AP-PCR was found to be a rapid, effective discriminative method for the immediate epidemiological tracking of hospital-acquired infections due to C difficile.

Elution of six antibiotics bonded to polyethylene vascular grafts sealed with three proteins

The elution of six antistaphylococcal antibiotics from vascular polyethylene grafts sealed with albumin, gelatin, or collagen were studied in an in vitro system. The antibiotics tested were pefloxacin, vancomycin, teicoplanin, fusidic acid, pristinamycin, and rifampicin. The grafts were impregnated by simple soaking in antibiotic (1 mg/ml). The data were fitted to an exponential model and antibiotic half-lives (t1/2) were calculated from the regression lines. All the antibiotics tested were bound to the protein sealants. Antibiotic release varied with the type of antibiotic and the sealant. Rifampicin was eluted most slowly, particularly with albumin- and gelatin-sealed grafts, with t1/2 at 4-5.5 hr and antibiotic activity was still found at 48 hr. The glycopeptides were also eluted more slowly from albumin or gelatin sealant than from collagen. Although large quantities of glycopeptides were initially bound, they were quickly eluted (t1/2 = 30-44 min) and there was no residual antibiotic activity at 24 hr. Pefloxacin, pristinamycin, and fusidic acid bound to collagen or gelatin sealants were the most rapidly eluted, with t1/2 of 3-14 min, but they were eluted more slowly from albumin-sealed grafts, with t1/2 of 22-90 min. In vitro studies can be useful for evaluating the binding of antibiotics to protein-sealed grafts before animal experiments or human testing.

Activities of piperacillin, ceftazidime, cefepime and cefpirome against Pseudomonas aeruginosa strains with intrinsic ticarcillin resistance

The in vitro activities of cefepime and cefpirome against 44 intrinsically ticarcillin-resistant strains of Pseudomonas aeruginosa were compared to their activities against 20 ticarcillin-susceptible strains by MIC determination and the disk test. Time-killing curves were constructed for piperacillin, ceftazidime, cefepime and cefpirome against two susceptible and two resistant strains. The activities of cefepime and cefpirome against the resistant strains were impaired, and most of the strains were of intermediate sensitivity to these agents. The time-killing curves of the four beta-lactams were similar, with a modest decline in viable cell counts over the first 6 h followed by regrowth. There was no difference between the susceptible and resistant strains.

Persistence of Staphylococcus aureus strains among cystic fibrosis patients over extended periods of time

Pulsed-field gel electrophoresis (PFGE) of SmaI macrorestriction fragments of chromosomal DNA was used to confirm the persistence of methicillin-sensitive Staphylococcus aureus isolates in the sputum of 25 cystic fibrosis patients in five French hospitals. Three-to-eight consecutive isolates, with the same esterase electrophoretic type isolated from each patient over a period of 12-28 months, were analysed. Consecutive isolates with indistinguishable PFGE profiles were found in 12 patients (48%) and consecutive isolates with similar PFGE profiles showing minor differences of one-to-four fragments (similarity coefficient >/=84%) were found in 11 patients. Consecutive isolates with different PFGE profiles were obtained from only two patients, but the profiles found in each patient were more closely related to each other than to other profiles. The results were in agreement with esterase electrophoretic typing for 23 patients, and we considered that those patients were infected with a single persistent strain. For any given patient, variations in antibiotypes and phage types of consecutive isolates were not associated with major genotypic variations. PFGE is useful in confirming the persistence of S. aureus strains in cystic fibrosis patients over long periods.

Analysis of genetic relationships among strains of groups A, C and G streptococci by random amplified polymorphic DNA analysis

Random amplified polymorphic DNA (RAPD) analysis was evaluated for its capacity to distinguish species and strains within species of groups A, C and G streptococci. The 99 strains tested, previously typed by multilocus enzyme electrophoresis (MLEE), included 41 group A streptococci (Streptococcus pyogenes), 25 group G Streptococcus spp. (GGS), seven S. dysgalactiae, 11 S. equisimilis, four S. canis, three S. equi and eight S. zooepidemicus. The combined data obtained with three single primers distinguished 82 types. RAPD analysis provided taxonomic results that were in general agreement with previous species classification based on DNA-DNA homology and MLEE. The intraspecies typing efficiency of the technique was significantly improved by the parallel use of several primers. RAPD analysis had greater discriminatory power than MLEE for GAS and GGS. There was not total agreement between the two techniques as RAPD distinguished strains with identical electrophoretic types, whereas MLEE differentiated strains with identical PCR types. RAPD analysis did not distinguish all GAS strains with different biotypes and its already high discriminatory power was further enhanced by concomitant biotyping.

[Comparison of the activity of beta-lactams against Pseudomonas aeruginosa according to phenotypes of resistance]

The in vitro activity of ticarcillin, ticarcillin-clavulanic acid, piperacillin, piperacillin-tazobactam, cefsulodin, ceftazidime, cefepime, cefpirome and aztreonam was evaluated against 130 isolates of Pseudomonas aeruginosa with various beta-lactam phenotypes. MICs were determined by the agar dilution method and inhibition method and inhibition zones by the disk test. The resistance mechanisms were characterized by the iodometric method. The activity of cefepime was greater than that of cefpirome whatever the resistance phenotype. Some ticarcillin-susceptible strains were intermediate to cefepime and cefpirome. Most strains with a penicillinase or "intrinsic resistance" phenotype were susceptible to ceftazidime but intermediate to cefepime and cefpirome. Only 10% of cephalosporinase-over-producing strains remained susceptible to cefepime.

Synthesis of 4'-iodo-5-methoxy-valerophenone O-(2-aminoethyl)oxime as an agent for exploration of serotoninergic transporter

The serotonin reuptake process is observed in the central nervous system and in cells derived from the neural crest. It would therefore be of great interest to visualize this reuptake for brain exploration and to visualize the tumors derived from these cells (Apudome). Fluvoxamine has been described as a specific uptake inhibitor for serotonin uptake and we therefore supposed that an iodinated derivative of this compound would be a suitable tracer for this purpose. We had shown by computer-assisted investigation that the trifluoromethyl group of fluvoxamine can be replaced by iodine without changing the steric hindrance of the structure. We therefore expected that this result would allow the development of a new iodinated ligand for human exploration by SPECT which would inhibit for the serotoninergic transporter. This new ligand is 4'-iodo-5-methoxyvalerophenone O-(2-aminoethyl)oxime in its E configuration. In vitro binding studies demonstrated that this iodinated ligand has a weaker affinity for the serotonin uptake sites than fluvoxamine. Steric hindrance is not sufficient to predict affinity, other structural factors such as electronic density and dipole moment must be considered to explain the biological difference between fluvoxamine and its iodinated analog.

Epidemiology of Staphylococcus aureus in patients with cystic fibrosis

Seven hundred and thirty-four isolates of Staphylococcus aureus, recovered from the sputum of 238 cystic fibrosis patients in six French hospitals, were characterized by esterase electrophoretic typing, capsular polysaccharide serotyping and phage typing and tested against 14 antibiotics for sensitivity. Thirty-four esterase electrophoretic types were found with a genotypic diversity coefficient of 0.91. Five hundred and forty-eight (78.7%) isolates produced capsular polysaccharide and 350 (50.3%) were type 8. Four hundred and sixty isolates (66.6%) were phage typable and 202 (28.2%) were lysed by group III bacteriophages. No esterase electrophoretic type, capsular type or phage type was specific to cystic fibrosis. Isolates belonged to a wide range of types, similar to strains acquired outside hospitals. Eighty-five patients had three or more consecutive isolates over at least 6 months. The ability of S. aureus to persist for long periods of time has been demonstrated in 73% of them. Methicillin-resistance was encountered among 73 strains (9.8%) which were also multiresistant. Two hundred and eighty-nine (39.9%) strains were sensitive to all antibiotics tested except to penicillin. Pristinamycin and co-trimoxazole were the most effective antibiotics. These results could contribute to the elaboration of a rational approach to the prophylaxis and therapy of respiratory staphylococcal infections in cystic fibrosis patients.

[Epidemiological studies of the susceptibility of Pseudomonas aeruginosa to antibiotics]

The susceptibility to antibiotics of 1367 non-replicate strains of Pseudomonas aeruginosa isolated at Beaujon Hospital between 1990 and 1992 was investigated and compared with the serogroup O and the strain origin (ward, sample). Five betalactam resistance patterns were distinguished according to susceptibility to ticarcillin, piperacillin, ceftazidime and aztreonam,: 1 = SSSS, 2 = RRSS, 3 = RRRR, 4 = RSSR, 5 = RRSR. The other antibiotics studied were imipenem, tobramycin, amikacin, ciprofloxacin and fosfomycin. Resistance to all antibiotics, fosfomycin excepted, was higher in intensive care units than in other wards. The respective frequencies of the phenotypes were: 70.3%, 4.3%, 11.8%, 10.2% and 3.4%. The frequency of pattern 3 steadily increased between 1990 and 1992 at the expense of pattern 1, whereas patterns 2, 4 and 5 remained stable. The most common serogroups were O6 (15.8%), O11 (14.5%) and O1 (9.9%). The O11 strains were more widespread in intensive care units than in other wards and were more resistant to antibiotics. Most of the O12 strains displayed pattern 2 and were highly resistant to antibiotics.