E. coli outbreak in a neonate intensive care unit in a general hospital in Mexico City

Nosocomial infections are a major cause of morbidity and mortality among neonates admitted to neonatal intensive care units (NICUs). The aim of this paper was to describe an outbreak of Escherichia coli among infants admitted to the NICU of the General Hospital “Dr. Manuel Gea Gonzalez” in May of 2008. The isolated E. coli strains were identified using standard biochemical methods. The susceptibilities of these strains were analysed by determining their minimal inhibitory concentrations. Following this, their molecular relationships to each other were assessed by pulsed field gel electrophoresis (PFGE) analysis and corroborated by serology. Twelve E. coli strains were isolated from blood, urine, or indwelling catheter samples from five cases of preterm infants within a 3-day period. Patients were admitted to the NICU of the general hospital and, during the outbreak, developed sepsis caused by E. coli. For four of the patients, the average age was 23 days, while one patient was a 3-month-old infant. Prior to sepsis, the infants had received assisted ventilation and hyperalimentation through a central venous catheter. Two profiles were observed by PFGE; profile A was identified as the outbreak’s cause and an outcome of cross-infection, while profile B showed genetic differences but serologically it was identified as part of the same serotype. We conclude that E. coli colonised the patients through horizontal transmission. A focal source of the microorganism in this outbreak was not identified, but cross-transmission through handling was the most probable route.     

Plasmid distribution in Escherichia coli urinary isolates with special reference to aerobactin and colicin production

Plasmids were detected in 31 out of 35 strains of Escherichia coli isolated from unclassified cases of urinary tract infection at a median value of 1.88 plasmid bands per isolate. The isolates showed an association of aerobactin and colicin production with the distribution of plasmid bands having a median value of 2.33 and 1.72 (plasmid bands per isolate) in aerobactin-positive and aerobactin-negative strains respectively. For colicin producers, the median plasmid bands per isolate was 3.66 compared to 1.80 for colicin-negative strains.     

Enterohemolysin production is associated with a temperate bacteriophage in Escherichia coli serogroup O26 strains.

A temperate bacteriophage that determines the expression of enterohemolysin was isolated from Escherichia coli O26 strain C3888. The genetic determinant associated with enterohemolysin production (E-Hly determinant) was cloned from EcoRI-digested bacteriophage DNA in vector plasmid pUC8. pUC8 recombinant plasmid pEO19 carries a 3.7-kb EcoRI insert of phage DNA, and enterohemolysin was expressed in E. coli K-12 after transformation. Hemolysin-negative derivatives of pEO19 were generated by transposon mutagenesis with Tn1725. By subcloning, the phage E-Hly determinant was assigned to a 2,150-bp piece of DNA which is flanked by EcoRI and AccI restriction sites. The enterohemolysin-producing recombinant strains and wild-type strain C3888 express a 60-kDa protein which was detected in the bacterial outer membrane by Western immunoblotting. Biologically active enterohemolysin was detected only in bacteria grown to the stationary phase, and the hemolysin was not released into the culture medium. Lysis of erythrocytes was inhibited by 30 mM dextran 4, which functions as an osmotic protectant without destroying the enterohemolysin itself.