Characterization of escherichia coli and klebsiella pneumoniae isolated from neonates in a nursery ward using dna probes, plasmid profiles, and antimicrobial susceptibility patterns
A laboratory investigation of lactose positive enterobacteria isolated from neonates in the course of several cases of gastroenteritis in a nursery ward is described. During a period of 4 weeks, 30 neonates were involved and 5 of these died. A stool sample was taken from each of the 30 neonates regardless of their clinical status. Ten colonies of lactose positive enterobacteria were obtained from each neonate and identified as Escherichia coli (229 isolates) and Klebsiella pneumoniae (65 isolates). Six strains were lost during laboratory handling. The pathogenic potential of the strains was examined using an enteropathogenic E. coli adherence factor (EAF) DNA probe. Colony hybridization of DNA from the 294 isolates was performed using the 1 megadalton radiolabelled EAF probe. The EAF probe hybridized with DNA from 78 of the 229 E. coli strains and with none of the DNA from K. pneumoniae strains. The EAF probe positive strains were found in 13 neonates. Colony hybridization tests of DNA from all the E. coli and K. pneumoniae strains using alkaline phosphatase-labelled oligonucleotide probes specific for enterotoxins LT and ST1 of E. coli gave negative results. There were 28 and 8 different plasmid profile groups of E. coli and K. pneumoniae (xiii) respectively. A total of 78 strains of E. coli were shown to belong to one particular plasmid profile group possessing plasmids of molecular weight 65, 1.9, 1.7, and 1.4 megadaltons (MDa). All these strains gave positive results with the EAF probe which was shown to hybridize with the 65 MDa plasmid. Seven of the EAF probe positive and 6 EAF probe negative E. coli strains were further characterized at Centers for Disease Control, Atlanta, Georgia, USA. The 7"EAF probe positive strains were found to be 0111:HNT (NT=Nontypable). They adhered locally to HeLa cells, and did not produce Vero cell cytotoxins. The 6 EAF probe negative strains all belonged to serotypes other than 0111:HNT, and they neither adhered to HeLa cells nor elaborated Vero cell cytotoxins. Twenty neonates yielded pure cultures of E. coli, 5 had Klebsiella pneumoniae only, while 5 were positive for both species. The case fatality rates of neonates who harboured EAF probe positive E. coli, EAF probe negative E. coli, and K. pneumoniae were 30.8%, 7.7% and 0% respectively. Both E. coli and K. pneumoniae strains were resistant to most of the 16 antimicrobial agents tested. In general there was no marked difference in the antimicrobial susceptibility patterns of EAF probe positive and EAF probe negative E. coli strains. However, a lower percentage (10.3%) of the (xiv) EAF positive strains were resistant to gentamycin than the EAF negative ones (39.7%). Seventy percent of K. pneumoniae strains were resistant to gentamycin as compared to 30% of E. coli strains. None of the bacterial isolates examined was resistant to cefatoxime, but the majority of the strains (64-99%) were resistant to sulphonamides, trimethoprimsulfamethoxazole, chloramphenicol, oxytetracycline, erythromycin, penicillin, and ampicillin. A few strains (1-18.5%) were resistant to cefazolin, cefamandole, amikacin, nalidixan, and nitrofurantoin. No correlation between plasmid profiles and antibiotic resistance pattern was found.