Virulence factors of lactose-negative Escherichia coli strains isolated from children with diarrhea in Somalia

Abstract

Lactose-negative Escherichia coli strains were isolated at high frequency from children with diarrhea in Somalia during a 2-year study on diarrheal diseases. Sixty-four of these strains, considered to be a representative sample, were characterized for virulence factors, plasmid profiles, and antibiotic resistance. Of these strains, 5 were recognized as enteroinvasive E. coli (they were serotyped as 0135:K-:H-), 6 belonged to classical enteropathogenic E. coli serotypes, 9 were able to adhere to tissue culture cells (of these, 4 showed a pattern of localized adherence and 1 was an enteropathogenic strain), 18 were both adherent and hemolytic, and 8 were simply hemolytic. None hybridized with 32P-labeled heat-labile or heat-stable (a and b) enterotoxin gene probes or produced moderate or high-level cytotoxic effects on HeLa cells. Of the 64 strains examined, 24 produced mannose-resistant hemagglutination with human, chicken, and monkey erythrocytes. One of these was serotyped as 04:K-:H8, and a rabbit O antiserum raised against this strain allowed us to establish that 23

Contribution of the RsaL global regulator toPseudomonas aeruginosavirulence and biofilm formation

“…Hemolytic activity was basically performed as described previously (Nicoletti et al, 1988). Five hundred microliters of sheep erythrocytes (Oxoid) suspended in phosphate buffer, pH 7.4, were mixed with 10 mL of P. aeruginosa cultures grown in LB at 37 1C, to an A 600 nm of 3.0.…”

Organization of aerobactin, hemolysin, and antibacterial resistance genes in lactose-negative Escherichia coli strains of serotype O4 isolated from children with diarrhea

“…They (i) had an 04 serotype, (ii) produced mannose-resistant hemagglutination with human, chicken, and monkey erythrocytes, (iii) adhered to HeLa and HEp-2 cells grown in culture, and (iv) were hemolytic and produced hydroxamate-type siderophores. Also, intact bacteria were able to destroy HeLa cell monolayers very rapidly (27). None of them contained heat-labile or heat-stable enterotoxin genes or had enterotoxic effects in rabbit ileal loop assays.…”

“…Bacterial cell extracts or culture supernatants did not produce high-level cytotoxic effects on HeLa cells. Moreover, these strains were multiply antibiotic resistant, and the identity of the plasmid profile in strains isolated over a period of years led us to postulate the epidemiological importance of these strains and propose a possible clonal origin (27).…”

“…In order to better understand the role, if any, of NLF 04 E. coli strains as the causative agents of diarrheal diseases, we have further characterized the high-molecular-weight plasmids harbored by these strains for replication properties as well as for the presence of antibiotic resistance genes and we have studied the genetic locations and organization of the hemolysin (hly) and aerobactin (aer) operons. Moreover, to ascertain whether factors other than hemolysin were responsible for the cytotoxic effect that we previously reported for these strains (27), we isolated Wy-negative mutant strains by transposon insertion mutagenesis and tested them for cytotoxicity with HeLa cell monolayers.…”

Persistent diarrhea: a persistent infection with enteropathogens or a gut commensal dysbiosis?

“…One might ask why many PD patients show secondary lactose intolerance if E. coli could digest lactose. This observation could find an explanation by the fact that 10% of E. coli strains, particularly from diarrhea patients are lactose nonfermenting strains (Nicoletti et al, 1988).…”