Serum resistance among Escherichia coli strains causing urinary tract infection in relation to O type and the carriage of hemolysin, colicin, and antibiotic resistance determinants

Fimbriation, surface hydrophobicity and serum resistance in uropathogenic strains of Escherichia coli

A total of 80 Escherichia coli strains were examined for expression of P-fimbriae, mannose-sensitive haemagglutination (MSHA) and mannose-resistant haemagglutination (MRHA) of human group A erythrocytes and guinea pig erythrocytes, cell surface hydrophobicity and resistance to serum bactericidal activity. Isolates were obtained from urine of children and adults, either with acute pyelonephritis (n = 15 and n 12) or lower urinary tract infection (UTI) (n = 30 and n = 23, respectively). Results obtained showed that, in E. coli strains isolated both from children and adults with lower UTI, significant differences were not found concerning the incidence of P-fimbriae, cell surface hydrophobicity and serum resistance. In pyelonephritogenic E. coli isolated from children and adults, the incidence of P-fimbriae and cell surface hydrophobicity was associated more frequently with the former (87% vs. 42% and 100% vs. 67%, P < 0.05), while serum resistance was associated with the latter (47% vs. 67%, P < 0.05).

pap-and pil-related DNA sequences and other virulence determinants associated with Escherichia coli isolated from septicemic chickens and turkeys

Escherichia coli isolates from septicemic or healthy chickens and turkeys from Quebec were serotyped, examined genotypically by using DNA probes specific for the pil and pap fimbrial systems and the aerobactin siderophore system, and examined phenotypically for lethality in day-old chicks, hemagglutination, serum resistance, and aerobactin production. Serogroups O78 and O1 were most common in septicemic chickens and turkeys. pap+ isolates from chickens were associated with septicemia, and pap+ isolates from turkeys were associated with lethality in day-old chicks. Four of nine pap+ isolates from septicemic turkeys expressed P adhesin, whereas all pap+ isolates from septicemic chickens were negative for P adhesin. The pil+ genotype was associated with septicemia in chickens and with serum resistance in isolates from turkeys. Mannose-sensitive hemagglutination of guinea pig erythrocytes was associated with septicemia in chickens and turkeys, although this phenotype was not associated with pil+ isolates from turkeys. Serum resistance was associated with isolates from septicemic turkeys and with lethality in isolates from chickens. The aerobactin system was associated with isolates from septicemic chickens and turkeys. Overall, results indicated that (i) genotypic examination may reveal virulence-associated traits which differ from the typically expected phenotype and/or are not readily expressed in vitro, and (ii) certain phenotypic and genotypic traits associated with E. coli causing extraintestinal disease in humans and animals are also associated with E. coli causing avian septicemia.

Influence of cefpodoxime on selected immunological functions and bacterial pathogenicity factors in vitro

The influence of a new oral cephalosporin cefpodoxime, on several interactions of the host-parasite relationship was investigated. Pretreatment of polymorphonuclear granulocytes (PNG) with cefpodoxime at therapeutical dosage in vitro did not have a significant effect on chemotaxis and luminol-dependent chemiluminescence. On the other hand, human serum did not exert a considerable effect on the bactericidal activity of cefpodoxime on Klebsiella pneumoniae and Staph. aureus. Serum resistance of Klebsiella pneumoniae was not altered after pretreatment with cefpodoxime 1/16 MIC (0.03 micrograms/ml) for 3 to 27 hours.

Etiology and pathophysiology of pyelonephritis

Escherichia coli is the most frequent cause of pyelonephritis. Its possible virulence factors include the ability to adhere and colonize the urinary tract, an important initiating factor in all urinary tract infections (UTIs). The importance of P fimbriae in this adhesion is stressed and the evidence for its importance in pyelonephritis is presented in epidemiologic studies of patients, as well as in animal studies. It appears that both host receptor density and the nonsecretor state is responsible for susceptibility to urinary tract infection. Vesicoureteral reflux can be responsible for ascending upper tract infection, but infection with P-fimbriated E coli may lead to ascending pyelonephritis without reflux because of the paralytic effect of lipid A on ureteral peristaltic activity. Renal ischemia leads to renal damage following infection by reperfusion damage due to the release of superoxide. Experimentally, this ischemic damage can be prevented by allopurinol, a xanthine oxidase inhibitor. The acute inflammatory response can produce renal damage because of the respiratory burst of phagocytosis, which while killing phagocytosed bacteria also damages renal tubules. An amelioration of the inflammatory response by treatment with superoxide dismutase or corticosteroids has been shown to modulate renal damage. Vaccination with P fimbriae has been shown experimentally to prevent the initiation of the disease. However, since vaccines are not clinically available, the clinical and animal studies on therapy of acute disease are stressed. Acute pyelonephritis during the first 3 years of life more often produced the renal damage that could lead to end-stage renal disease.(ABSTRACT TRUNCATED AT 250 WORDS)

Virulence factors in Escherichia coli urinary tract infection

Uropathogenic strains of Escherichia coli are characterized by the expression of distinctive bacterial properties, products, or structures referred to as virulence factors because they help the organism overcome host defenses and colonize or invade the urinary tract. Virulence factors of recognized importance in the pathogenesis of urinary tract infection (UTI) include adhesins (P fimbriae, certain other mannose-resistant adhesins, and type 1 fimbriae), the aerobactin system, hemolysin, K capsule, and resistance to serum killing. This review summarizes the virtual explosion of information regarding the epidemiology, biochemistry, mechanisms of action, and genetic basis of these urovirulence factors that has occurred in the past decade and identifies areas in need of further study. Virulence factor expression is more common among certain genetically related groups of E. coli which constitute virulent clones within the larger E. coli population. In general, the more virulence factors a strain expresses, the more severe an infection it is able to cause. Certain virulence factors specifically favor the development of pyelonephritis, others favor cystitis, and others favor asymptomatic bacteriuria. The currently defined virulence factors clearly contribute to the virulence of wild-type strains but are usually insufficient in themselves to transform an avirulent organism into a pathogen, demonstrating that other as-yet-undefined virulence properties await discovery. Virulence factor testing is a useful epidemiological and research tool but as yet has no defined clinical role. Immunological and biochemical anti-virulence factor interventions are effective in animal models of UTI and hold promise for the prevention of UTI in humans.

Bacterial adherence in urinary tract infections: preliminary studies in a primate model

Escherichia coli with both P and type 1 fimbriae caused vaginal colonization in the female green monkey, while only the P-fimbriated bacteria frequently caused ascending bladder infection. Bladder inoculation caused only short-lived bladder infection from type 1 fimbriated E. coli, but those with P-fimbriae caused acute pyelonephritis even in the absence of vesicoureteral reflux. Thus, type 1 fimbriae of E. coli, while causing vaginal colonization, did not often cause ascending infection in the non-compromised host as did P-fimbriated bacteria.

Type 1 fimbriate strains of Escherichia coli initiate renal parenchymal scarring

The renal scarring which characterizes chronic pyelonephritis is initiated by bacterial infection and is independent on the activation of an inflammatory response. Although the presence of polymorphonuclear leukocytes (PMN) is essential for initiating the scarring process, the bacterial structures responsible for their activation have not been investigated. In an animal model of chronic pyelonephritis the surface area of the renal scars produced by Type 1 fimbriate escherichia coli (E. coli) was significantly greater than that of those produced by P fimbriate and non-fimbriate strains (P less than 0.01). The activation of human PMN by the same Type 1 fimbriate organisms resulted in a significant release of lysosomal neutral protease activity (P less than 0.001) and activation of the respiratory burst (P less than 0.01). The neutral protease release in response to P fimbriate and non-fimbriate organisms was not significantly increased. The extent of renal scarring also correlated with the release of neutral protease activity (P less than 0.02) and with the degree of activation of the respiratory burst (P less than 0.05). These results demonstrate that the ability of E. coli strains to cause renal scars may be related to their capacity to express Type 1 fimbria, which may be a causative factor in the in vivo activation of the inflammatory response.

Hydrophobic properties of Escherichia coli causing acute pyelonephritis

Cell surface hydrophobic properties and expression of P-fimbriae were examined in 130 strains of Escherichia coli derived from women (n = 66) and children (n = 64) with acute non-obstructive pyelonephritis and in 170 faecal strains of E. coli from healthy adults (n = 103) and children (n = 67) by use of the salt aggregation test and the P-fimbriae-specific particle agglutination test. The strains of E. coli isolated were aggregated in salt solutions of varying molarity (0.001-1.6 M final concentration). Patients with predisposing medical or urological conditions in the urinary tract were excluded. Pyelonephritic strains of E. coli from the women and children had a higher degree of cell surface hydrophobicity (80 and 98% respectively) than faecal strains from healthy adults and children (57 and 82% respectively, P less than 0.01 and P less than 0.01). Both pyelonephritic and faecal strains of E. coli from the children were more often salt aggregation positive (hydrophobic) than faecal strains of E. coli from healthy adults (P less than 0.01 and P less than 0.001, respectively). Pyelonephritic strains of E. coli from women and children were more often P-fimbriated (79 and 84% respectively) than faecal control strains from women and children (15 and 33%, P less than 0.001 and P less than 0.001, respectively) but there was no significant correlation between expression of P-fimbriae and cell surface hydrophobicity.

[Urinary tract infection following kidney allotransplantation: differentiation between bacterial colonization and bacterial infection]

Among 124 recipients of a renal allotransplant (22 men, 52 women), 60 patients (27 men, 33 women) showed more than 10(6) colony-forming units/ml midstream urine on one or several occasions. 26 patients (10 men, 16 women) did not present with leucocyturia whereas 23 (10 men, 13 women) did so. Urine samples were examined 1/2 to 5 1/2 years after transplantation. The comparison of the 2 groups of patients with and without leucocyturia revealed the following: there was no age difference; during the first year after grafting, bacteriuria with leucocyturia was more common; recurrent and de novo infections, dysuria, pyelonephritis and demonstration of E. coli were more frequent. Therapy was more effective in cases of bacteriuria without leucocyturia; the serum creatinine was more seldom elevated above the normal range and complications with ureters, bladder emptying or stenoses of the urethra were more seldomly observed.

Incidence of aerobactin-positive Escherichia coli strains in patients with symptomatic urinary tract infection

A total of 323 Escherichia coli strains from children with primary acute non-obstructive pyelonephritis (n = 144) or cystitis (n = 56) and from adults with acute non-obstructive pyelonephritis (n = 66) or cystitis (n = 57) were examined for presence of the aerobactin-mediated iron uptake system and expression of P-fimbriae. Overall, pyelonephritogenic Escherichia coli strains were significantly more often aerobactin-positive (72%) than cystitis strains (42%) (p less than 0.001). Seventy-three percent of the isolates from children with acute pyelonephritis were aerobactin-positive compared to 54% of the cystitis strains (p less than 0.05). Pyelonephritogenic Escherichia coli strains from adults were also significantly more often aerobactin-positive (70%) than cystitis strains (30%) (p less than 0.001). The cystitis strains from children were more often aerobactin-positive than cystitis strains from adult patients (p less than 0.05). There was a significant correlation between presence of the aerobactin-mediated iron uptake system and expression of P-fimbriae in all strains (p less than 0.001).

Toxins and serotypes of faecal non-enterotoxigenic and non-enteropathogenic Escherichia coli strains causing mannose-resistant haemagglutination: relation with haemagglutination patterns

Forty-three faecal non-enterotoxigenic and non-enteropathogenic human Escherichia coli strains causing mannose-resistant haemagglutination (MRHA) were tested for production of cytotoxic necrotizing factor (CNF), haemolysis (Hly), Verotoxin (VT) and lethal activity for mice. The serotypes of the strains were also determined. Of the total strains investigated, 49% synthesized CNF, 53% were haemolytic and 40% were lethal for mice. No strain producing VT was detected. Striking differences in the production of Hly and CNF were observed when MRHA strains were grouped according to their lethal or non-lethal activity. Thus, 82% of lethal strains produced Hly and/or CNF whereas only 35% (p less than 0.01) and 27% (p less than 0.01) of non-lethal strains produced Hly and CNF, respectively. The production of toxins was specially associated with strains possessing defined MRHA types. Thus, 100%, 82% and 50% of strains belonging to MRHA types III, IVa and V, respectively, were toxigenic, whereas no toxigenic strains from MRHA types IVb and VI were detected. The majority (77%) of MRHA strains possessed typical O groups usually reported to be present in pathogenic extraintestinal E. coli or in facultatively enteropathogenic E. coli. Furthermore, these O groups were more frequently detected in toxigenic (93%) than in non-toxigenic (47%) strains (p less than 0.01). Our results suggest that faecal non-enterotoxigenic E. coli strains belonging to MRHA types III, IVa and V may be responsible for extraintestinal infections as well as for sporadic intestinal infections, and that certain O groups are specially associated with E. coli strains belonging to particular MRHA types.

The hemolysin of Escherichia coli

Many strains of E. coli elaborate a hemolysin which is responsible for the zone of beta-hemolysis surrounding bacterial colonies on blood agar. The significance of this cytolysin as a determinant of bacterial pathogenicity has been established in animal models with the use of genetically engineered, isogenic bacterial strains. An analogous role in human infections has been inferred from the high association of hemolysin production with disease. Studies at a molecular genetical level have defined 4 genes that are required for the synthesis, post-translational modification and secretion of the hemolysin. The structural gene hlyA encodes for a 107-110,000 polypeptide, which must be modified in an unknown manner to its active form by the product of the neighboring hlyC gene. Genes hlyB and hlyD encode for proteins that export the molecule to the extracellular medium. The signal for secretion is contained in the C-terminal portion of the toxin molecule. The secreted hemolysin attacks plasma membranes of target mammalian cells by inserting as a monomer into the bilayer and generating hydrophilic transmembrane pores of approximately 2 nm effective diameter. The pores display a marked selectivity for cations over anions and pore-opening is dependent on the presence of a correct transmembrane potential. Binding to a membrane target does not require the presence of a specific receptor, and pores may be generated in planar lipid membranes consisting solely of phosphatidylcholine. Pore formation in nucleated cells can trigger secondary reactions such as stimulation of arachidonate metabolism with release of lipid mediators, probably initiated by passive influx of extracellular Ca2+.(ABSTRACT TRUNCATED AT 250 WORDS)

Type 1 fimbriate Escherichia coli stimulates a unique pattern of degranulation by human polymorphonuclear leukocytes

Uropathogenic strains of Escherichia coli bearing mannose-sensitive (type 1) fimbriae promote a unique pattern of degranulation from human polymorphonuclear leukocytes (PMN). Significant quantities of the primary (1 degree) and tertiary (3 degree) granule markers, neutral protease-myeloperoxidase and N-acetyl-beta-D-glucosaminidase, respectively, were released by PMN in a dose- and time-dependent manner when stimulated by these defined bacterial strains. Organisms bearing mannose-resistant (P) fimbriae promoted release of only the secondary (2 degree) granule marker, vitamin B12-binding protein. When this pattern of degranulation was compared to that produced by PMN in response to a variety of soluble and particulate stimuli, only the calcium ionophore A23187 similarly triggered 1 degree and 3 degree granule marker release. All the other stimuli tested--zymosan, serum-treated and unopsonized; n-formylmethionyl-leucyl-phenylalanine; and phorbol myristate acetate--promoted release of only the 2 degree granule marker. These results demonstrate selectivity of PMN degranulation in response to a number of transmembrane signals. In addition, the capacity of E. coli to promote PMN degranulation is dependent on its phenotypic fimbrial expression, a surface characteristic which correlates significantly with its relative surface hydrophobicity as measured by binding to octyl Sepharose. Those bacteria demonstrating the greatest hydrophobicity were capable of triggering discharge of all three granule marker proteins. Thus, the mannose-sensitive fimbriae of uropathogenic E. coli may contribute significantly to their potential pathophysiologic role in renal scarring.

Comparison of virulence factors and antibiotic resistance profiles of Escherichia coli strains from humans and dogs with urinary tract infections

The purpose of this study was to compare virulence factors and antibiotic resistance profiles of Escherichia coli strains isolated from dogs and humans with urinary tract infections. Factors studied included resistance to antibiotics and the transferability of R-plasmids to a recipient E. coli; production of colicins, hemolysins, beta-lactamase, and urease; hemagglutination of erythrocytes; and fermentation of dulcitol. The canine E. coli isolates had a wider range of antibiotic resistance and a higher R-plasmid transmissibility rate. A higher percentage of the canine isolates produced colicins (40% vs. 24%), hemolysins (44% vs. 16%), beta-lactamase (52% vs. 4%), and fermented dulcitol (84% vs. 80%) as compared with the human isolates. The human isolates had a greater ability to hemagglutinate erythrocytes as compared with the canine isolates (24% vs. 8%). None of the isolates produced urease.

Occurrence and properties of hly-plasmids in E. coli from patients of the Berne area

1818 E. coli wild-type strains from patients of the region of Berne were screened for their haemolytic property and for carriage of hly-plasmids. Among 885 strains of fecal and 993 strains of urinary tract isolates 136 (15%) and 259 (28%) were haemolytic respectively. In five fecal, but none of the urinary strains the haemolytic activity was encoded by transmissible plasmids. In spite of independent origin, the five isolated hly-plasmids proved to be very similar. They all showed a high transfer-frequency according to their derepressed state and coded for F-sexpili. Four belonged to the rare F VI- and one to the F IV-incompatibility group. Restriction patterns after Eco R1- and Hind III-digestion were identical in three and similar in the other two plasmids. Comparing the plasmids from Berne with hly-plasmids isolated in Essex, similarities as well as specific differences were detected.

Escherichia coli in extra-intestinal infections

When Theodor Escherich (1885a, b) first describedEscherichia colihe looked on it as a saprophytic organism. Soon several investigators found that colibacteria could be isolated from intestinal infections and from many infections outside the intestine, like urinary tract infections (UTI), cholecystitis, wound infections, meningitis, septicaemia, pulmonary infections, and many more. Uhlenhuth (1897) showed that coli strains from pathological processes were more pathogenic in animal experiments than strains isolated from the normal intestine. Smith (1927), who examined strains from white scours in calves, showed that spontaneous acapsular mutants could be obtained from certain colibacteria, and that such mutants were less virulent when injected intra-peritoneally into guinea-pigs.

Genetic organization of the afimbrial adhesin operon and nucleotide sequence from a uropathogenic Escherichia coli gene encoding an afimbrial adhesin

The uropathogenic Escherichia coli KS52 strain expresses a mannose-resistant hemagglutinin AFA-I, which recognizes a human erythrocyte site distinct from the alpha-digalactoside glycosphingolipid receptor common to uropathogenic E. coli strains specifying a P adhesin. A 6.7-kilobase chromosomal DNA fragment was cloned from KS52 into pBR322 and was shown to be necessary for host cell mannose-resistant hemagglutination expression and uroepithelial cell adherence (Labigne-Roussel et al., Infect. Immun. 46:251-259, 1984). The genetic organization of the 6.7-kilobase DNA fragment was investigated by generating derivative plasmids, and the polypeptides encoded by those plasmids in isolated minicells were analyzed on polyacrylamide gel. The 6.7-kilobase insert expresses five polypeptides of molecular mass 13,000, 16,000, 18,500, 30,000, and 100,000 daltons encoded, respectively, by the afaA, afaE, afaD, afaB, and afaC genes. The five genes were localized and were shown to belong to the same transcriptional unit. The afaB, afaC, and afaE gene products are required for mannose-resistant hemagglutination expression, whereas mutations in or deletions of either afaA or afaD do not modify host mannose-resistant hemagglutination expression. The afaE gene was identified as the structural gene encoding hemagglutinin. The gene has been sequenced; it encodes a 152-residue protein containing a typical 21-residue procaryote signal sequence and a 131-residue mature polypeptide, the AFA-I adhesin.

Experimental pyelonephritis in the monkey. VII. Ascending pyelonephritis in the absence of vesicoureteral reflux

Six adult male nonrefluxing monkeys were experimentally infected by inoculation of P-fimbriated E. coli into the bladder. Eight control monkeys were inoculated with a non-P-fimbriated E. coli strain. Inoculation with the P-fimbriated E. coli resulted in marked leukocytosis, prolonged bacteriuria and loss of renal function with a 66 per cent incidence of pyelonephritis. Death secondary to bilateral pyelonephritis was seen in 2 monkeys inoculated with P-fimbriated E. coli. Pyelonephritis was not seen in any of the monkeys inoculated with non-P-fimbriated E. coli. The study shows that ascending pyelonephritis can occur in monkeys in the absence of vesicoureteral reflux.

Expression and regulation of the plasmid-encoded hemolysin determinant of Escherichia coli

As a first approach towards studying the regulation of hemolysin synthesis in Escherichia coli, we have fused lacZ into the four hly genes (hlyC, hlyA, hlyBa and hlyBb) using the Mud-1 (Mu::lacZ, Y, Apr) phage. The sites of insertion of Mud-1 within the various hly genes of the Hly plasmid pHly152 were determined by the hemolytic phenotype of the Hly- mutants (Hly-ex/Hly-in or Hly-ex/Hly+in) and by complementation of these Hly- mutants with recombinant plasmids carrying cloned hly genes. It was found that hlyC, hlyA and hlyBa are transcribed from a relatively weak promoter (hlypL) located in front of hlyC. The activity of beta-galactosidase is considerably lower when Mud-1 is integrated in hlyBa than when it is inserted in hlyC, suggesting a considerable decline in hly gene expression from hlyC to hlyBa. The DNA sequence upstream of the coding region of hlyC was found to promote galK gene expression when a fragment covering this region was inserted into the promoter-probe vector pKO-11. A putative promoter sequence, which could correspond to hlypL, was identified in this sequence. The hlyBb gene appears to be transcribed from a different promoter and the direction of transcription seems to be opposite to that of the hlyC, A, Ba operon. The strength of this promoter (hlypR), based on the level of beta-galactosidase activity of Mud-1 insertion mutants in hlyBb, is considerably higher than that of hlypL.(ABSTRACT TRUNCATED AT 250 WORDS)

Cloning and expression of an afimbrial adhesin (AFA-I) responsible for P blood group-independent, mannose-resistant hemagglutination from a pyelonephritic Escherichia coli strain

The uropathogenic Escherichia coli KS52 strain expresses a mannose-resistant hemagglutinin involving an erythrocyte recognition site distinct from the alpha-digalactoside glycosphingolipid receptor identified for the uropathogenic E. coli strains specifying a P adhesin. The KS52 strain showed three major properties. (i) It agglutinated human erythrocytes of all tested blood groups. (ii) Hemagglutinin activity was found both in the supernatant fluid L-broth cultures and in cells grown on L-agar plates. (iii) No fimbriae in organisms grown on L-agar plates were detected by electron microscopy. Whole-cell DNA from the KS52 strain was size fractionated and cloned into the pHC79 cosmid vector. Three recombinant cosmids expressing a mannose-resistant hemagglutination (MRHA) phenotype were characterized and used to subclone the smallest DNA fragment able to confer the same MRHA properties as the parent strain. A 6.7-kilobase chromosomal DNA fragment cloned in pBR322 (pIL14) was shown to be necessary for host-cell MRHA expression and uroepithelial cell adherence. The insert encoded the production of a 16,000-dalton hemagglutinin. This polypeptide could be detected in culture supernatant fluids, in E. coli minicells harboring the pIL14 plasmid, and, by immunoblotting, in the KS52 strain and E. coli whole cells harboring the pIL14 plasmid. No homology was detected by Southern hybridization between the cloned insert and the DNA of the operon responsible for MRHA in the P-specifying, fimbriate strains (pap operon).

Survey of drug and phage resistance and colicin and hemolysin production among coliforms isolated in the Ivory Coast

Analysis of 178 strains isolated as total and fecal coliforms in the Ivory Coast revealed that (i) hemolytic activity was scarce (0.6%) among this bacterial population; (ii) the most prevalent colicins detected were, in decreasing order, E, I, A, and G; (iii) the frequency of coliphage and drug resistance was similar to that observed in other countries, except for those of drug-resistant strains in animal feces, which were lower than in countries where animals are antibiotic fed; and (iv) one of the drug resistance plasmids seemed to possess a restriction-modification system and another seemed to code for capsular material.

Serum resistance encoded by colicin V plasmids in Escherichia coli and its relationship to the plasmid transfer system

Eight colicin V plasmids were conjugated into a plasmidless Escherichia coli (K-12) strain that was susceptible to the bactericidal effects of normal rabbit serum. The resulting colicin V-positive strains were examined for their capacity to resist the lethal effects of serum. Serum resistance was assessed as growth of the bacterial strain in medium containing 5% normal rabbit serum inoculated from a culture in the early exponential phase. Only three of the eight colicin V plasmids were found to confer the serum resistance phenotype on the host strain. Derepression of the transfer system was associated with serum resistance in two of the plasmids. Two other derepressed plasmids did not confer serum resistance on the host bacterium. Therefore, such derepression alone was insufficient to produce serum resistance. The factor(s) encoded by colicin V plasmids and responsible for the serum resistance of the bacterial strains bearing the plasmids was shown to be a property associated with the cell and not an extracellular factor excreted into the growth medium.

Transport of hemolysin across the outer membrane of Escherichia coli requires two functions

Among a large collection of hemolysis-negative mutants obtained by mutagenesis of the Hly plasmid pHly152 with Tn5, we have isolated two classes of mutants which are defective in the transport of hemolysin across the outer membrane. The two cistrons (hylBa and hlyBb) which are affected in these mutants are located adjacent to each other on the hly determinant but are transcribed from different promoters. Recombinant plasmids were constructed which carry the two functions as combined or separated cistrons. These were shown to complement the two types of transport mutants. Studies on the compartmentation of hemolysin in these two classes of mutants indicate that most hemolysin (greater than 70%) in hlyBa mutants is located in the periplasmic space, whereas in hlyBb mutants a larger portion of hemolysin is associated with the outer membrane fraction. The phenotypic appearance of colonies from hlyBb mutants is that of beta-hemolytic Escherichia coli strains, indicating that a substantial portion of hemolysin has already reached the outside of the outer membrane without being released into the medium. Release was achieved readily when hlyBb mutants were complemented with a recombinant plasmid carrying hlyBb.

Bactericidal and bacteriolytic activity of serum against gram-negative bacteria

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Hemolysin production as a virulence marker in symptomatic and asymptomatic urinary tract infections caused by Escherichia coli

Potential virulence, as defined by combined levels of adhesion to urinary epithelial cells, serum resistance, and mouse toxicity, was assessed for Escherichia coli strains causing symptomatic and asymptomatic urinary tract infections in relation to the carriage of hemolysin and other suspected virulence determinants. Hemolysin production (Hly), associated with certain O (O4, O6, O18, and O75), K (5), and hemagglutination (VI and VII) antigenic types but not colicin V production (Cva), was evident in 83 and 60% of isolates in groups possessing high potential virulence and in only 11 and 6% of those with low virulence. Strains of particular O-types were not more virulent per se, but among the serotypes, specific combinations of virulence factors appeared decisive, e.g., O18 HAVI B/D/G Hly(+) K5(+/-) and O18 HAIII/IVB/V Hly(-) Cva(+/-) K1(+/-) strains were, respectively, of high and low potential virulence. Isolates with high potential virulence were found to a similar extent in symptomatic and asymptomatic infections.

Relationship between plasmid and chromosomal hemolysin determinants of Escherichia coli

Plasmid hemolysin (hly) determinants have been shown previously to comprise three cistrons (hlyA, hlyB, hlyC), coding for the synthesis and transport of hemolysin. Using recombinant plasmids as specific probes for these cistrons, we were able to analyze the chromosomal hly determinants of nine Escherichia coli strains which belonged to serotypes O4, O6, O18, and O75 and were isolated from urinary tract infections and fecal flora. The chromosomal hly genes shared extensive sequence homology with the cloned plasmid hly determinant. Nevertheless, small differences were observed, and these were found to lie mainly within cistron A (hlyA), which has been shown to determine the hemolysin protein itself. These fine variations were not specific for the O-serotype.

Transport of hemolysin by Escherichia coli

The hemolytic phenotype in Escherichia coli is determined by four genes. Two (hlyC and hlyA) determine the synthesis of a hemolytically active protein which is transported across the cytoplasmic membrane. The other two genes (hlyBa and hlyBb) encode two proteins which are located in the outer membrane and seem to form a specific transport system for hemolysin across the outer membrane. The primary product of gene hlyA is a protein (protein A) of 106,000 daltons which is nonhemolytic and which is not transported. No signal peptide can be recognized at its N-terminus. In the presence of the hlyC gene product (protein C), the 106,000-dalton protein is processed to the major proteolytic product of 58,000 daltons, which is hemolytically active and is transported across the cytoplasmic membrane. Several other proteolytic fragments of the 106,000-dalton protein are also generated. During the transport of the 58,000-dalton fragment (and possible other proteolytic fragments of hlyA gene product), the C protein remains in the cytoplasm. In the absence of hlyBa and hlyBb the entire hemolytic activity (mainly associated with the 58,000-dalton protein) is located in the periplasm: Studies on the location of hemolysin in hlyBa and hlyBb mutants suggest that the gene product of hlyBa (protein Ba) binds hemolysin and leads it through the outer membrane whereas the gene product of hlyBb (protein Bb) releases hemolysin from the outer membrane. This transport system is specific for E coli hemolysin. Other periplasmic enzymes of E coli and heterologous hemolysin (cereolysin) are not transported.

Cloning of the chromosomal determinants encoding hemolysin production and mannose-resistant hemagglutination in Escherichia coli

We have cloned the chromosomal hemolysin determinants from Escherichia coli strains belonging to the four O-serotypes O4, O6, O18, and O75. The hemolysin-producing clones were isolated from gene banks of these strains which were constructed by inserting partial Sau3A fragments of chromosomal DNA into the cosmid pJC74. The hemolytic cosmid clones were relatively stable. The inserts were further subcloned either as SalI fragments in pACYC184 or as BamHI-SalI fragments in a recombinant plasmid (pANN202) containing cistron C (hlyC) of the plasmid-encoded hemolysin determinant. Detailed restriction maps of each of these determinants were constructed, and it was found that, despite sharing overall homology, the determinants exhibited minor specific differences in their structure. These appeared to be restricted to cistron A (hlyA), which is the structural gene for hemolysin. In the gene banks of two of these hemolytic strains, we could also identify clones which carried the genetic determinants for the mannose-resistant hemagglutination antigens Vb and VIc. Both of these fimbrial antigens were expressed in the E. coli K-12 clones to an extent similar to that observed in the wild-type strains. These recombinant cosmids were rather unstable, and, in the absence of selection, segregated at a high frequency.