In vitro activity of fleroxacin against multiresistant gram-negative bacilli isolated from patients with nosocomial infections

Molecular Detection of the Virulent ExoU Genotype of Pseudomonas aeruginosa Isolated from Infected Surgical Incisions

BACKGROUND

Pseudomonas aeruginosa is one of the major pathogens responsible for hospital-acquired infections, which harbor a wide array of virulence factors. The main aim of this study was to determine the frequency of the virulent ExoU genotype in relation to the ExoS genotype among isolated P. aeruginosa from infected surgical incisions, followed by phylogenetic analysis.

METHODS

A total of 66 P. aeruginosa isolates were identified by cultural and biochemical characteristics. All isolates were tested for antimicrobial susceptibility against the following antimicrobial agents: imipenem, amikacin, gentamicin, amoxycillin, cefotaxime, cefepime, and levofloxacin. Molecular detection of the ExoS and ExoU as well as two other virulence genes was done by polymerase chain reaction (PCR). Sequencing of ExoU gene and phylogenetic analysis was performed.

RESULTS

Approximately 81% of the isolated P. aeruginosa were multi-drug resistant. The ExoS genotype was more prevalent (63%) among the isolates than the ExoU genotype (18%), with 9% of the isolates possessing both toxins. LasB and AprA were detected in 63.6% and 27.2% of the isolates, respectively. An association was observed between the number of virulence genes and the presence of multi-drug resistance. All the ExoU were multi-drug resistant (MDR), whereas 71% of the ExoS were MDR. Phylogenetic analysis of ExoU gene showed a 99% similarity with four different strains.

CONCLUSION

Despite the greater frequency of the ExoS genotype, the presence of the virulent MDR ExoU genotype isolates from surgical site infections is an alarming sign requiring further intervention and investigations.

Simultaneous Presence of blaTEM and blaSHV Genes on a Large Conjugative Plasmid Carried by Extended-Spectrum β-Lactamase-Producing Klebsiella pneumoniae

BACKGROUND

Among members of the family Enterobacteriaceae, the production of plasmid-mediated extended-spectrum beta-lactamases (ESbetaLs) has emerged as an important mechanism of the resistance to beta-lactams.

METHODS

The molecular basis of extended-spectrum beta-lactamase in 48 strains of Klebsiella pneumoniae, recovered from neonatal patients with nosocomial septicemia during an outbreak that occurred in November 2000 at a Neonatal Intensive Care Unit of The Andes University Hospital in Venezuela, were investigated.

RESULTS

The isolates were resistant to expanded-spectrum cephalosporins, aztreonam, gentamicin, kanamycin, tetracycline, and chloramphenicol, but remained susceptible to cefoxitin, imipenem, amikacin, and tobramycin. Production of ESbetaL activity was confirmed by restoring susceptibility to ceftazidime in the presence of clavulanic acid. All isolates harbored an 87-kilobase plasmid. Analysis of the outer membrane protein patterns did not reveal relevant changes of the porins profile. All resistance markers were transferable to Escherichia coli by conjugation and were lost en bloc after treatment with acridine orange. Isoelectric focusing for beta-lactamases was performed on transconjugants, obtaining 2 bands with isoelectric points of 5.4 and 8.2. Genes encoding both enzymes are located on the single, self-transferable 87-kilobase plasmid pKAM542. Analysis of the plasmid by hybridization revealed the presence of both blaTEM and blaSHV determinants. Cloning and sequencing identified them as blaTEM-1 and blaSHV-5, respectively; the latter was responsible for the ESbetaL activity among nosocomial isolates of K pneumoniae.

CONCLUSIONS

Microbiologists, epidemiologists, and clinicians must be aware of potential ESbetaL-encoding organisms to assess proper antimicrobial managements and effective infection controls.