Sensitivity of serologically classified strains of escherichia coli of human origin to the serum bactericidal system

Host heterogeneity in humoral bactericidal activity can be complement independent

Background

Humoral bactericidal activity was first recognized nearly a century ago. However, the extent of inter-individual heterogeneity and the mechanisms underlying such heterogeneity beyond antibody or complement systems have not been well studied.

Methods

The plasma bactericidal activity of five healthy volunteers were tested against 30 strains of Gram-negative uropathogens, Klebsiella pneumoniae and Escherichia coli, associated with bloodstream infections. IgG and IgM titers specific to K. pneumoniae strains KP13883 and KPB1 were measured by ELISA, and complement inhibitor was used to measure the contribution of complement-induced killing. Furthermore, MALDI-TOF mass spectrometry was conducted to determine the metabolomic components of plasma with bactericidal properties in 25 healthy individuals using Bayesian inference of Pearson correlation between peak intensity and colony counts of surviving bacteria.

Results

Plasma bactericidal activity varied widely between individuals against various bacterial strains. While individual plasma with higher IgM titers specific to K. pneumoniae strain KP13883 showed more efficient killing of the strain, both IgM and IgG titers for K. pneumoniae strain KPB1 did not correlate well with the killing activity. Complement inhibition assays elucidated that the complement-mediated killing was not responsible for the inter-individual heterogeneity in either isolate. Subsequently, using MALDI-TOF mass spectrometry on plasmas of 25 healthy individuals, we identified several small molecules including gangliosides, pediocins, or saponins as candidates that showed negative correlation between peak intensities and colony forming units of the test bacteria.

Conclusion

This is the first study to demonstrate the inter-individual heterogeneity of constitutive innate humoral bactericidal function quantitatively and that the heterogeneity can be independent of antibody or the complement system.

Antimicrobial Activity in Continuous Ambulatory Peritoneal Dialysis

The antimicrobial activity of serum and dialysate from patients on continuous ambulatory peritoneal dialysis (CAPD) was assessed by performing bactericidal assays on serum and both fresh and spent dialysate. Fresh dialysate, whether lactate or acetate based, displayed significant bactericidal activity, which could be abolished by the addition of serum or albumin but not urea. Most patients on CAPD lost that killing activity sometime during the course of their dialysis, but a few retained this capability. Serum bactericidal activity was decreased in CAPD patients when compared to that of normal controls or patients on hemodialysis. These studies suggest the need for further work to assess the relationship of such findings to the pathogenesis of peritonitis in patients on CAPD.

Anti-endotoxin vaccines: back to the future

Gram-negative bacterial (GNB) infections are a leading cause of serious infections both in hospitals and the community. The mortality remains high despite potent antimicrobials and modern supportive care. In the last decade invasive GNB have become increasingly resistant to commonly used antibiotics, and attempts to intervene with novel biological therapies have been unsuccessful. Earlier studies with antibodies directed against a highly conserved core region in the GNB lipopolysaccharide (LPS, or endotoxin) suggested that this approach may have therapeutic benefit, and led to the development of a subunit vaccine that has progressed to phase 1 clinical testing. Since only a few serogroups of GNB cause bacteremia, O-specific vaccines had been developed, but these were not deployed because of the availability of other therapeutic options at the time. Given the likelihood that new antibiotics will not be soon available, the development of vaccines and antibodies directed against endotoxin, both O and core antigens, deserves a “second look”.

Klebsiella spp. as nosocomial pathogens: epidemiology, taxonomy, typing methods, and pathogenicity factors

Bacteria belonging to the genus Klebsiella frequently cause human nosocomial infections. In particular, the medically most important Klebsiella species, Klebsiella pneumoniae, accounts for a significant proportion of hospital-acquired urinary tract infections, pneumonia, septicemias, and soft tissue infections. The principal pathogenic reservoirs for transmission of Klebsiella are the gastrointestinal tract and the hands of hospital personnel. Because of their ability to spread rapidly in the hospital environment, these bacteria tend to cause nosocomial outbreaks. Hospital outbreaks of multidrug-resistant Klebsiella spp., especially those in neonatal wards, are often caused by new types of strains, the so-called extended-spectrum-beta-lactamase (ESBL) producers. The incidence of ESBL-producing strains among clinical Klebsiella isolates has been steadily increasing over the past years. The resulting limitations on the therapeutic options demand new measures for the management of Klebsiella hospital infections. While the different typing methods are useful epidemiological tools for infection control, recent findings about Klebsiella virulence factors have provided new insights into the pathogenic strategies of these bacteria. Klebsiella pathogenicity factors such as capsules or lipopolysaccharides are presently considered to be promising candidates for vaccination efforts that may serve as immunological infection control measures.

Complement component C9 enhances the capacity of beta-lactam antibiotics to kill Escherichia coli in vitro and in vivo

Complement component C9 is required for rapid complement-mediated killing of Escherichia coli. In this report, the influence of supplemental C9 on the bactericidal and protective effects of beta-lactam antibiotics in neonates was assessed. By rocket immunoelectrophoresis, the intrinsic C9 concentrations of pooled serum from both human and rat neonates was less than 20% of adult levels. Supplemental C9 purified from human plasma enhanced the capacity of ampicillin-treated serum from human neonates to impair the survival of E coli O7:K1:NM (P < 0.02). Similarly, supplemental C9 enhanced the capacity of cefotaxime-treated neonatal rat serum to impair the survival of E coli O1:K1:NM (P < 0.05). Moreover, the intraperitoneal administration of C9 enhanced the survival of cefotaxime-treated neonatal rats that were septic with E coli (P < 0.05). These observations may contribute to the development of new strategies, such as augmentation of complement component serum concentrations, to reduce the morbidity and mortality of neonatal E coli sepsis.

The administration of complement component C9 enhances the survival of neonatal rats with Escherichia coli sepsis

To determine the significance of neonatal C9 deficiency, an animal model was developed in the rat. By rocket immunoelectrophoresis, the concentration of C9 in pooled adult rat serum was 224 +/- 7.2 microg/mL. In contrast, the concentration of C9 in pooled serum from 1-d-old rats was only 43 +/- 3.8 microg/mL and increased during the first 3 wk of life to 170 +/- 20 microg/mL. Similarly, the capacities of neonatal rat serum to kill two pathogenic strains of Escherichia coli and to lyse sensitized sheep erythrocytes were diminished compared with adult serum but increased during the first 3 wk of life. Supplemental human C9 significantly enhanced the bactericidal and hemolytic activity of neonatal rat serum. The capacity of neonatal rats to survive after the intrapulmonary injection of E. coli was positively correlated with the serum C9 concentration, bactericidal activity, and hemolytic activity. In 2-d-old rats infected with E. coli, the intraperitoneal administration of human C9 significantly enhanced survival and also enhanced the protective effect of intraperitoneal human IgG antibodies. The data indicate that C9 deficiency predisposed neonatal rats to invasion by E. coli. The neonatal rat appears to be a suitable model with which to investigate the significance of C9 deficiency.

The O4 specific antigen moiety of lipopolysaccharide but not the K54 group 2 capsule is important for urovirulence of an extraintestinal isolate of Escherichia coli

Group 2 capsules and lipopolysaccharides are regarded as important virulence factors in extraintestinal isolates of Escherichia coli, but their specific contributions to bladder and renal infections, if any, are unknown. Proven isogenic derivatives deficient in the K54 antigen alone (CP9.137), the O4 antigen alone (CP921), or both the K54 and O4 antigens (CP923) were compared with their wild-type parent (CP9 [O4/K54JH5]) for growth in human urine in vitro and for virulence in vivo in a mouse model of ascending urinary tract infection (UTI). Growth of CP9.137 and CP921 was equivalent to that of CP9 in human urine. CP923 demonstrated a small but reproducible decrease in log-phase growth but achieved the same plateau density. In the mouse model of UTI, the isogenic mutant deficient in the 04 antigen alone (CP921) and, to a greater degree, the derivative deficient in both the K54 and O4 antigens (CP923) were significantly less virulent in nearly all parameters measured. In contrast, the K54 knockout derivative was as virulent as its parent, CP9, in causing bladder infection and nearly as virulent in causing renal infection. These results demonstrate an important role for the O4 antigen moiety of lipopolysaccharide in the pathogenesis of UTI. The possibility that the K54 antigen also plays a minor role cannot be excluded.

Serum response of Escherichia coli strains causing dyspepsia and urinary tract infection: relation to alpha-hemolysin production and O type

A total of 109 alpha-hemolytic and 104 nonhemolytic Escherichia coli isolates from children with dyspepsia and urinary tract infections were investigated for resistance to the bactericidal activity of human serum. A significantly higher proportion of serum resistance was found in alpha-hemolytic E. coli isolates than in nonhemolytic isolates (P < 0.01). An association between the titer of alpha-hemolysin produced and serum resistance was found.

Comparative virulence of blood and stool isolates of Shigella sonnei

Shigellemia is rare in developed countries and might result from the emergence of unusually virulent strains. We compared systemic invasiveness markers of isolates from the blood of 3 temporally clustered patients with Shigella sonnei bacteremia in Boston with those of 11 unrelated contemporaneous strains from stools of people in New England. We found no difference between the two groups in O-chain length by sodium dodecyl sulfate-polyacrylamide gel electrophoresis, mouse 50% lethal dose, in vivo response to iron, and susceptibility to serum, which varied from moderately susceptible to ultrasusceptible. Mean intraperitoneal 50% lethal doses of smooth form I colonies for mice were equally low (10(5.8) CFU) in both groups, and the 50% lethal doses were lowered equally further in the two groups by predosing with iron to levels useful in mouse model sepsis studies. S. sonnei bacteremia may reflect compromised host defenses, not bacterial virulence.

TnphoA-mediated disruption of K54 capsular polysaccharide genes in Escherichia coli confers serum sensitivity

To assess whether non-K1, group 2 capsular serotypes are important in conferring serum resistance to extraintestinal isolates of Escherichia coli, a K54 blood isolate (CP9) was evaluated as a model pathogen. Transposon mutagenesis (TnphoA) was used to generate isogenic capsule-negative mutants. CP9 was resistant to the bactericidal effects of serum, growing in 80% serum. In contrast, all of the capsule-negative mutants had an increased sensitivity to 80% normal human serum, undergoing a 2- to 3-log kill over 3 h when starting inocula of 10(4) to 10(7) CFU/ml were used. The killing of the capsule-negative strains was mediated through the alternative complement pathway and not by lysozyme or beta-lysins. The protective effect of the K54 capsule against the bactericidal activity of serum was not through inhibition of the complement cascade, nor did it appear to be through a difference in the binding of C3.

Inhibition of bactericidal activity of anticapsular antibody by nonspecific antibodies reactive with surface-exposed antigenic determinants on Actinobacillus pleuropneumoniae

In an attempt to understand the mechanism of serum resistance in Actinobacillus pleuropneumoniae, in the present study we examined various interactions among the bacterial surface constituents, serum antibodies, and complement. Analysis of swine sera revealed the presence of anticapsular antibodies in convalescent-phase sera but not in preimmune sera. Both types of sera contained antibodies which reacted with each of 14 polypeptides present in saline extracts of the bacteria. Absorption of the preimmune sera with intact bacteria depleted antibodies to two of the polypeptides (27 and 32 kDa) and high-molecular-weight (greater than 97.4,000) components which did not stain with Coomassie blue. Data derived from complement consumption and C3-binding experiments indicated that the organism was capable of initiating complement activation and binding C3 during incubation in preimmune and immune sera. Experiments designed to evaluate the bactericidal effectiveness of anticapsular antibody revealed that the purified antibody was bactericidal only when preimmune sera absorbed with intact bacteria were used as a source of complement. The bactericidal effects of anticapsular antibody and absorbed preimmune sera were inhibited in a dose-dependent manner by heat-inactivated preimmune sera and immunoglobulin G derived from the sera. The inhibitory activity of the preimmune sera was neutralized by preincubating the sera with column fractions of the saline extract which contained either the 27- or the 32-kDa polypeptide. These results indicate that serum resistance in A. pleuropneumoniae 4074 could be related to inhibition of the bactericidal action of anticapsular antibody by nonspecific antibodies which recognize surface-exposed epitopes on the polypeptides.

Serum resistance in different serotypes of Escherichia coli

Resistance to complement-mediated serum activity is an important virulence factor in E. coli isolated from extraintestinal infections. Because there are no reports about the percentage of serum-resistant E. coli strains in common O serogroups, the study was carried out using Taylor's method (75% serum) for the determination of serum resistance of 253 E. coli strains, which had been isolated from urinary tract infections. The strains belonged to 8 common serogroups (O1, O2, O4, O6, O9, O16, O18, and O75) with a frequency of 6 to 24%, 218 (86%) were encapsulated. Among 26 different K antigens, K1 and K5 could be found in 32 and 33%. 25% of all strains investigated were found to be serum-resistant. The percentage of serum-resistant strains was between 11% and 63% in the different O serotypes, the highest frequency was found in O6 (63%) and O2 strains (43%). Among all serum-resistant strains carrying 13 different K antigens, K1 and K5 were the most common ones, with a percentage of 62% altogether. Serum resistance can be expected in strains from urinary tract infections, with a quite varying frequency depending on the O serotype, certain K antigens and other factors.

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.

Role of bacterial and host factors in the pathogenesis of Shigella septicemia

To determine the role of bacterial and host factors in the pathogenesis of shigellemia, blood and fecal Shigella isolates were compared for serum resistance and siderophore production, and shigellemic patients were examined for decreased serum bactericidal activity or increased serum transferrin saturation compared to control patients with non-bacteremic shigellosis. The majority of both blood (36/38) and fecal (36/48) Shigella isolates were sensitive to normal serum (greater than 2 log kill/60 min). Shigella dysenteriae type 1 strains were the most sensitive, and Shigella sonnei strains were the most resistant. Siderophore production was species- and serotype-dependent. Shigella dysenteriae type 1 produced only enterochelin; most Shigella flexneri expressed only aerobactin, and Shigella sonnei secreted both types of siderophores. No difference in siderophores was noted between blood and fecal strains within a given serotype. In contrast, shigellemic patients exhibited a 43-fold decrease in serum bactericidal activity and a two-fold increase in transferrin saturation compared to well-nourished control patients. These results indicate that the pathogenesis of Shigella septicemia is not related to serum resistance or siderophore production but may involve serum abnormalities associated with malnutrition.

Determination of serum bactericidal activity against Escherichia coli by an automated photometric method

The resistance of gram-negative bacteria to complement-mediated serum activity is supposedly an important virulence factor. However, the lack of standardization in the methods used to determine serum activity and the many definitions applied make the comparisons between studies very difficult. We developed a rapid photometric method that we compared with a classical killing one. Escherichia coli in the exponential phase of growth in brain heart infusion broth (final inoculum, 10(7) CFU/ml) at 35 degrees C was added to 50% human serum in Veronal buffer. Viable counts and automatic recording of the variations in the optical densities were obtained for 40 E. coli strains isolated from the stools of healthy adults. With the viable count method, 17 (42.5%) were susceptible (at least a 1 log CFU/ml decrease), 17 (42.5%) were resistant (a 0.6 log CFU/ml increase), 4 (10%) were intermediate (poorly growing inoculum or a decrease of less than 1 log CFU/ml), and 2 could not be classified (nonreproducible results). Agreement between both methods was observed for 87.5% of the stool strains. Eight reference strains of known susceptibilities were classified identically by both methods, leading to a final concordance rate of 89.6%. A total of 129 blood isolates were tested by the photometric method: 64 (49.6%) were resistant, 50 (38.8%) were susceptible 5 (3.9%) showed early regrowth, and 10 (7.7%) were not perfectly reproducible. Of these 129 blood isolates, 5 were also tested by the killing method: 37 (49%) were resistant, 32 (43%) were susceptible, and 6 (8%) were intermediate. The concordance rate between both assays was 89% for the blood isolates; when the minor discordances were ruled out, it was 97%. This automated method could be a useful screening tool for detecting resistance to serum in clinical trials and for studying the in vitro variations of this property.

Resistance of Pseudomonas pseudomallei to normal human serum bactericidal action

The effect of human normal serum (HNS) on Pseudomonas pseudomallei was determined. It is apparent from our data that the organism is resistant to the normal serum bactericidal mechanism. Ancillary experiments to confirm this serum-resistant property of P. pseudomallei were done by examining the effects of growth phase conditions of the bacteria (i.e., logarithmic and stationary phases) and different buffered systems used as diluent in our bactericidal assay. Results obtained showed similar degree of resistance to serum bactericidal killing by 5 strains of the organisms tested. The possible survival advantage of serum-resistance property to P. pseudomallei as bacterial pathogens known to invade the blood stream is discussed.

Experimental Escherichia coli endocarditis in rats: roles of serum bactericidal activity and duration of catheter placement

Studies were undertaken to investigate the relationship of the sensitivity of Escherichia coli to the bactericidal properties of serum and the ability of different strains to induce and sustain endocardial infection in rats. Strains of E. coli demonstrated different degrees of serum sensitivity, as determined by a method which employed concentrations of serum from 10 to 95% and periods of incubation as long as 24 h. The greater the serum sensitivity of the E. coli strain, the less able it was to initiate infection and the more rapidly it was spontaneously eliminated from established infections. Endocardial infection with E. coli was established by intravenous challenge in rats with polyethylene catheters passing through the aortic valve into the left ventricle. An E. coli strain of low serum sensitivity was used; the initiation of infection depended upon the length of time the catheter had been in place and, in addition, whether the catheter was in place at the time of bacterial challenge. Removal of the catheter permitted spontaneous sterilization of the endocardial vegetations. The time necessary for sterilization was in direct proportion to the length of time the catheter remained in place following bacterial challenge. If the catheter was not removed, sterilization of the endocardial vegetations did not take place. These studies suggest that serum bactericidal activity is an important host defense mechanism, acting to prevent the initiation of endocarditis in the case of highly serum-sensitive E. coli and to sterilize experimentally induced endocarditis in the case of less-serum-sensitive bacteria. The catheter used to induce nonbacterial endocardial vegetations favored the colonization of vegetations by E. coli, and it delayed the spontaneous sterilization of infected vegetations which occurred in relation to the susceptibility of the strain to the bactericidal properties of the serum. This effect of the catheter was not attributable to bacteria remaining viable in its lumen, nor was it attributable to inhibition of the bactericidal capacity of the serum as measured in vitro. Whatever the mechanism responsible for the catheter effect, experimental studies of the evolution of infections established with this technique must take into consideration the duration of catheter placement and whether and for how long it was present before or after inoculation with test bacteria.

Controlled evaluation of modified radiometric blood culture medium supplemented with gelatin for detection of bacteremia and fungemia

Although the addition of 1.2% gelatin to broth blood culture media containing sodium polyanetholesulfonate has been shown to enhance detection of certain bacteria, including Neisseria meningitidis, N. gonorrhoeae, Peptostreptococcus anaerobius, and Gardnerella vaginalis, the effect of such supplementation on the detection of other microorganisms causing bacteremia and fungemia is not known. Therefore, we studied BACTEC 6B medium with and without gelatin in 6,833 paired comparisons to examine the effects of supplementation on both the yield and the speed of detection of sepsis. More aerobic and facultative bacteria grew in the 6B than in the 6B-gelatin medium (P less than 0.001), especially staphylococci (P less than 0.01), Escherichia coli (P less than 0.01), other members of the family Enterobacteriaceae (P less than 0.05), and Acinetobacter spp. (P less than 0.05). When microorganisms grew in both bottles, they did so earlier in 6B than in 6B-gelatin (P less than 0.001). We conclude that the 6B medium in its present formulation is superior to 6B medium supplemented with 1.2% gelatin.

Lipopolysaccharide size and distribution determine serum resistance in Salmonella montevideo

The survival of Salmonella montevideo during serum treatment depends on the presence of an O antigen (O-Ag) associated with the lipopolysaccharide molecule. In this organism, the O antigen is a polysaccharide composed of 0 to more than 55 subunits, each containing 4 mannose residues together with glucose and n-acetylglucosamine. We used a mutant strain of S. montevideo that requires exogenous mannose for the synthesis of O-Ag. Lipopolysaccharide (LPS) was prepared from these cells grown under three different conditions where the availability of exogenous mannose was regulated such that the average number of O-Ag units per LPS molecule, the percentage of LPS molecules bearing long O-Ag side chains, and the percentage of lipid A cores bearing O-Ag were all varied. These changes in LPS profiles were monitored on sodium dodecyl sulfate-polyacrylamide gels, and cells with different LPS profiles were tested for their ability to survive treatment with pooled normal human serum. Survival in serum was associated with LPS that contained an average of 4 to 5 O-Ag units per LPS molecule, and 20 to 23% of the LPS molecules had more than 14 O-Ag units per LPS molecule. Serum survival was less clearly associated with the percentage of lipid A cores covered with O-Ag. We propose, based on these data and on previous work, that the O-Ag polysaccharide provides the cell protection from serum killing by sterically hindering access of the C5b-9 complex to the outer membrane and that a critical density of long O-Ag polysaccharide is necessary to provide protection.

Role of lipopolysaccharide and complement in susceptibility of Haemophilus ducreyi to human serum

The role of lipopolysaccharide (LPS) in the susceptibility of Haemophilus ducreyi to human serum and the mechanism of complement activation by serum-susceptible (Sers) strains were investigated. Serum treated with 2 mM Mg2+ and 20 mM ethylene glycol-bis(beta-aminoethyl ether)-N,N,N',N'-tetraacetic acid was nonbactericidal, but inulin-treated serum remained bactericidal. Absorption of serum with heat-killed whole cells of an Sers strain removed its bactericidal activity against the absorbing strain and also against other Sers strains. LPS obtained from Sers strains inhibited the bactericidal activity of serum against all Sers strains, whereas LPS from serum-resistant (Serr) strains and an Serr isogenic strain did not. However, high concentrations of LPS from the Serr strain inhibited the bactericidal activity of serum, an indication that part of the structural site involved in serum susceptibility is retained in the LPS of this strain. The LPS of Sers strains exhibited higher anticomplement activity than the LPS of Serr strains. These findings suggest that the classical pathway of complement activation is involved in the serum killing of H. ducreyi and that LPS composition may contribute to their susceptibility to complement-mediated serum bactericidal activity.

Gal-Gal binding and hemolysin phenotypes and genotypes associated with uropathogenic Escherichia coli

To determine whether uropathogenic strains of Escherichia coli exhibit a distinctive constellation of phenotypes, we examined 44 urinary isolates from women with radiologically normal urinary tracts and pyelonephritis, cystitis, or asymptomatic bacteriuria and 73 fecal isolates from healthy control subjects. The strains were characterized by their O serogroup, by their binding specificity (as determined by adhesins), and by their production of hemolysin and colicin V. In addition, the strains were assessed for homologous gene sequences by means of DNA-hybridization probes prepared from cistrons that encode hemolysin and the Gal-Gal binding adhesin--two determinants of virulence, which cause tissue injury and promote bacterial colonization of uroepithelia, respectively. In contrast to most isolates from normal feces and from the urine of patients with asymptomatic bacteriuria, pyelonephritis strains belong to a small number of O serogroups; all express the Gal--Gal binding adhesin and 75 per cent are hemolytic. A gene probe for the Gal--Gal binding adhesin, derived from the chromosome of one strain from a patient with pyelonephritis, hybridized with the DNA of all other pyelonephritis strains. The probe for the hemolysin gene hybridized with DNA from all other hemolytic strains. These data indicate that most cases of pyelonephritis are due to a small number of pathogenic clones that express critical determinants of virulence, and that the nucleotide sequences for hemolysin and the Gal--Gal binding adhesin in heterologous strains share homology. We are tempted to speculate that the gene products of these shared regions of the genome might form the basis for a vaccine against pyelonephritis.

Serum sensitivity of a Pseudomonas aeruginosa mucoid strain

The susceptibility of Pseudomonas aeruginosa 144M (a mucoid strain isolated from the sputum of a cystic fibrosis patient) to the bactericidal activity of pooled fresh normal human serum (FHS) was examined. FHS at concentrations of greater than or equal to 2.5% was capable of killing greater than 95% of strain 144M. Strain 144M was killed by FHS in a dose-dependent manner. Although either immunoglobulin M (IgM) or IgG was bactericidal in the presence of complement, IgM was about 10 times as effective as IgG. However, optimal killing activity required both IgM and IgG and complement, activated by the classical pathway. A role for lysozyme in the killing of 144M was demonstrated only when low concentrations of FHS were used. In contrast to 144M, P. aeruginosa strains 144NM and 144M(SR) were totally resistant to FHS at all of the concentrations tested (up to 50%). Neither the FHS susceptibility of 144M nor the FHS resistance of 144NM or 144M(SR) was altered by choice of growth medium, growth phase, or temperature of growth. Results of absorption studies with whole organisms, isolated outer membrane preparations, or lipopolysaccharide (LPS) from each strain suggest that the antigen(s) which binds the bactericidal immunoglobulins is accessible on the surface of 144M but not on the surface of 144NM or 144M(SR), is insensitive to trypsin treatment, and is believed to be LPS. Sodium dodecyl sulfate-polyacrylamide gel electrophoresis of the three LPS preparations demonstrated that 144M LPS contained primarily lipid-A-core polysaccharide components, whereas the LPS from 144NM and 144M(SR) were heterogeneous, with various degrees of O-side-chain substitution. These results suggest that at least one target for bactericidal antibody on the surface of 144M is contained in the rough LPS of this strain.

The serum sensitivity, colonial morphology, serogroup specificity, and outer membrane protein of Pseudomonas aeruginosa strains isolated from several clinical sites

Ninety-three strains of Pseudomonas aeruginosa, isolated from 68 patients hospitalized with respiratory tract infections, burns, urinary tract infections, and other illnesses, were examined for: 1) sensitivity to the bactericidal activity of fresh normal human serum (FHS); 2) colonial morphology; 3) serogroup designation; and 4) outer membrane protein (OMP) profile. The purpose of this study was to determine if there was any relationship between any of these microbial characteristics and the propensity of this microorganism to infect a specific clinical site or tissue. The results of this study can be summarized as follows: 1) slime-producing strains were generally more serum-sensitive than non-slime producers, although serum sensitivity was not related to slime production per se; 2) CF strains were much more serum-sensitive than non-CF strains; 3) the clinical isolation site appeared to be the predominant determinant of a strain's sensitivity to FHS; 4) the ability of P. aeruginosa to colonize/infect a specific clinical site or resist the bactericidal activity of FHS was generally unrelated to serogroup specificity; and 5) whereas the OMP profile of a particular strain does not appear to correlate with its response to the bactericidal effect of FHS, it does appear to be related to its clinical isolation site.

Bactericidal and bacteriolytic activity of serum against gram-negative bacteria

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Phagocytosis and intracellular killing of the contagious equine metritis organism by equine neutrophils in serum

Equine neutrophils were combined with Haemophilus equigenitalis (contagious equine metritis organism; CEMO) or Escherichia coli in low- and high-antibody-titer serum to evaluate the neutrophils ability to phagocytize and kill these bacteria. More E. coli than CEMO were phagocytized at each time period. After 120 min in low-antibody-titer serum, 56.3% of the E. coli and 34.3% of the CEMO were phagocytized. A total of 45% of CEMO and 74.9% of E. coli were phagocytized by 120 min when neutrophils were in high-antibody-titer serum. More than 75% of the ingested E. coli and 90% of the ingested CEMO were killed within 210 min of incubation. Fewer E. coli than CEMO were killed at any given time period. Ultrastructural examination showed CEMO to be degraded in the neutrophil. Degradation was the most extensive in neutrophils in high-titer serum. It is suggested that CEMO is a pathogenic extracellular bacterium incapable of prolonged intracellular survival and that it is slower to be phagocytized than a nonpathogenic E. coli.

Bactericidal effect of pooled human serum on Bacteroides melaninogenicus, Bacteroides asaccharolyticus and Actinobacillus actinomycetemcomitans

Bacteria belonging to the species B. melaninogenicus ss. melaninogenicus (two strains), B. melaninogenicus ss. intermedius (five strains), B. asaccharolyticus (seven strains), and Actinobacillus actinomycetemcomitans (four strains) were tested under anaerobic conditions for their sensitivity to the bactericidal effect of pooled human serum. The A. actinomycetemcomitans strains were not killed to any extent by the serum. Both B. melaninogenicus ss. melaninogenicus strains were killed by serum. The sensitivity to serum among the strains of B. asaccharolyticus and B. melaninogenicus ss. intermedius was diverse. There was no correlation between the sensitivity to serum among the strains and the levels of specific antibodies in the serum. The bactericidal activity of serum was only effective if the complement system was present in serum. All strains initiated activation of complement and binding of a C3 component to the cell surface both in normal and MgEGTA chelated serum. The possible role of serum bactericidal activity in the pathogenesis of oral infections is unclear.

Serum-induced lysis of Pseudomonas aeruginosa

The sensitivity of 12 Pseudomonas aeruginosa strains (5 mucoid and 7 non-mucoid strains) to serum and the interaction of these strains with the complement system was studied. Five strains (4 mucoid and 1 non-mucoid strains) were lysed in 20% normal serum as measured by the release of radiolabelled material from 3H-adenine labelled bacteria. Three of these strains were also lysed in MgEGTA chelated serum. All strains activated complement via the classical pathway, and six strains were able to activate the alternative complement pathway as well. Slime production did not interfere with bacteriolysis and complement consumption.

Hemolysin and K antigens in relation to serotype and hemagglutination type of Escherichia coli isolated from extraintestinal infections

Escherichia coli isolated from cases of bacteremia and from a variety of urinary tract infections were characterized according to serotype (O:H antigenicity), K type (possession of K1, K2, K3, K12, or K13), hemagglutination (HA) type, and production of beta-hemolysin. Results obtained with the bacteremia and urinary tract infection isolates were similar except for more hemolytic isolated from urine than from blood (42 versus 29%) and more K1+ isolates from blood than from urine (50 versus 29%). A close correlation was found between Ha type VI (production of fimbriae which mediate mannose-resistant HA of human and African green monkey erythrocytes) and the production of hemolysin or K1 capsular antigen or both. Most (95 of 98, or 95%) of the HA type VI+ blood isolates and most (146 of 164, or 89%) of the HA type VI+ urine isolates produced hemolysin or K1 or both, in contrast to 22 and 26%, respectively, of those belonging to HA types other than HA type VI. Also, 76% of all hemolytic and 70% of all K1+ isolates belonged to HA type VI. Remarkably few of the HA type VI+ isolates (13%) and even fewer of the HA type VI- isolates (3%) produced both K1 and hemolysin; these belonged mainly to serotypes O16:H6, O18:H7 and O2:H4. Other major serogroups were usually K1+/hemolysin- (O1, O7) or K1-/hemolysin+ (O2, O4, O6). At least 74% (262 of 351) and possibly as many as 83% (293 of 351) of those isolates which produced mannose-resistant HA of human erythrocytes were classified as HA type VI+; 31 isolates produced mannose-resistant HA with all erythrocytes tested. Taking serogroup and serotype into consideration, we conclude that the E. coli fimbrial hemagglutinin(s) responsible for the HA type VI phenotype will prove to be the same as the virulence-associated mannose-resistant adhesins of uropathogenic E. coli which other investigators have characterized as unique fimbrial antigens detectable by mannose-resistant HA of human erythrocytes.

Modification of bacterial serum susceptibility by rifampin

A subinhibitory concentration of rifampin converted a strain of Escherichia coli from serum resistant to serum susceptible. When continually cultured in nutrient broth containing 1.5 microgram of rifampin per ml, this strain of E. coli became susceptible to killing by both normal human serum and normal rabbit serum. Copared to the original strain, the rifampin-treated E. coli displayed no detectable change in adherence capability, but appeared less virulent in the rabbit model of endocarditis. A rifampin-resistant mutant of the E. coli strain was not found to undergo conversion to serum susceptibility upon culture in rifampin.

Gram-negative bacteremia. III. Reassessment of etiology, epidemiology and ecology in 612 patients

Evaluation of 612 episodes of gram-negative bacteremia over a 10-year period demonstrated its progressively increasing frequency. This increase was associated with an increasing proportion of patients with more severe underlying disease, increasing patient age, increasing frequency of cardiac surgery and manipulative procedures, and increasing frequency of treatment with antibiotics, corticosteroids and antimetabolites in patients with bacteremia. Fatality rates paralleled the severity of the host's underlying disease as noted in previous reports. The urinary tract was the most frequent source of bacteremia, but in 30 per cent of the patients, predominantly those with more severe underlying disease, the original source could not be identified. Of all blood cultures obtained in these patients, 72 per cent were positive. Bacteremia was of low magnitude with 77 per cent of the patients have quantitative blood cultures with less than 10 gram-negative bacilli per milliliter of blood. Escherichia coli was the most frequent etiologic agent followed in frequency by Klebsiella-Enterobacter-Serratia species, Pseudomonas aeruginosa, Proteus and Providencia species, and species of Bacteroides. Sixteen per cent of the bacteremias were polymicrobic. K and O-antigen typing of Escherichia coli and capsular typing of K. pneumoniae demonstrated that a large number of serologic types of these strains were responsible for bacteremia. Over-all, bacteremia caused by multiple species of bacteria was associated with higher fatality rates, but no significant differences in fatality rates could be demonstrated for bacteremias caused by individual species of gram-negative bacilli when comparisons were made between patients with underlying diseases of similar severity. The presence or type of K-antigen did not influence the lethality of Esch. coli infections. Although some O-antigen types, 0:4, 0:6 and 0:8, were associated with higher fatality rates than other O-antigen types, "rough" or autoagglutinable Esch. coli were as lethal as smooth strains. These findings indicate that bacterial factors, other than antibiotic resistance, have little influence on the outcome of gram-negative bacteremia and that gram-negative bacilli function primarily as "opportunistic" pathogens.

The significance of serum-sensitive bacilli in gram-negative bacteremia

Clinical findings from 76 patients (median age 67 years) with gram-negative bacteremia were analysed and related to the sensitivity of the blood isolates to the bactericidal activity of normal human serum. 28 strains (37%) were resistant, an equal number intermediately sensitive and 20 markedly sensitive (26%). No correlation was found between serum sensitivity and origin of the bacteremia, presence of fever or blood granulocyte count. The frequency of shock in immunocompromised patients with serum-resistant strains was 60% (6/10); in those with intermediately or markedly sensitive strains it was 44% (8/18). In the non-immunocompromised patients with resistant strains the frequency of shock was 33 (6/18) versus 10% (3/30) in those without such strains. Thus the risk of developing shock with gram-negative bacteremia seems to depend on both parasite and host factors, although in this study only the latter were statistically significant. We conclude that serum-sensitive strains can invade the blood stream in spite of the serum bactericidal activity and cause severe disease in some patients.

Antibody levels to enteric bacteria in juvenile rheumatoid arthritis

In order to determine the immunologic status and possible susceptibility to bacterial infection in children with juvenile rheumatoid arthritis (JRA), titer of hemagglutingating antibodies to E coli 055, E coli 086, common antigen, and Shigella polyvalent antigen were measured. Immunoglobulin G was the predominant antibody. IgA antibodies were found in higher titer in children with JRA. No significant differences were found between children with JRA do not have any deficit in antibody production to specific bacterial antigens, and any increased appearance of infection in these children is more probably due to deficiencies in cellular factors.

Interaction of E. coli strains with human serum: lack of relationship to K1 antigen

Twenty-eight strains of E. coli isolated from infants were compared with respect to opsonic requirements, sensitivity to serum, and ability to activate serum chemotactic factors. Six of the strains were isolated from stools of healthy newborn infants; 22 were isolated from the cerebrospinal fluid or blood of infants with meningitis and/or septicemia. Eighteen of the strains had K1 polysaccharide antigen. Fourteen of the strains (seven with K1 antigen) activated complement via the alternative pathway and all of these strains were well opsonized in 4% pooled human serum. A higher concentration of serum was necessary to opsonize 12 of the 14 strains that did not activate the alternative pathway. A wide variation was also found in opsonic requirements of E. coli strains isolated from healthy and sick infants. There was no relationship of the K1 antigen to opsonic requirements, to capacity to activate complement via the alternative pathway, to generation of chemotactic factors, or to sensitivity to serum cidal activity. Therefore, the association of E. coli with K1 antigen and neonatal meningitis did not appear to be related to these bacteria-serum interactions.

Gonococci causing disseminated gonococcal infection are resistant to the bactericidal action of normal human sera

The susceptibility of strains of Neisseria gonorrhoeae to the bactericidal action of normal human sera was determined for isolates from patients with disseminated gonococcal infection and uncomplicated gonorrhea. Serum susceptibility was correlated with penicillin susceptibility and auxotype. 38 of 39 strains (97%) of N. gonorrhoeae from Seattle patients with disseminated gonococcal infection were resistant to the complement-dependent bactericidal action of normal human sera. 36 of these were inhibited by less than or equal to mug/ml of penicillin G and required arginine, hypoxanthine, and uracil for growth on chemically defined medium (Arg-Hyx-Ura- auxotype). 12 of 43 isolates from patients with uncomplicated gonorrhea were also of the Arg-Hyx-Ura-auxotype, inhibited by less than or equal to 0.030 mug/ml of penicillin G, and serum resistant. Of the 31 remaining strains of other auxotypes isolated from patients with uncomplicated gonorrhea, 18 (58.1%) were sensitive to normal human sera in titers ranging from 2 to 2,048. The bactericidal action of normal human sera may prevent the dissemination of serum-sensitive gonococci. However, since only a small proportion of individuals infected by serum-resistant strains develop disseminated gonococcal infection, serum resistance appears to be a necessary but not a sufficient virulence factor for dissemination. Host factors such as menstruation and pharyngeal gonococcal infection may favor the dissemination of serum-resistant strains. Since serum-resistant Arg-Hyx-Ura strains are far more frequently isolated from patients with disseminated gonococcal infection than serum-resistant strains of other auxotypes, Arg-Hyx-Ura-strains may possess other virulence factors in addition to serum resistance.