In vivo evidence that bacteria in urinary tract infection grow under iron-restricted conditions

Relevance of iron metabolic genes in biofilm and infection in uropathogenic Proteus mirabilis

The microorganisms are found in the environment, forming sessile communities embedded in an extracellular matrix of their own production, called biofilm. These communities have a great relevance in the clinical context, since they are associated with infections caused by biofilm in medical implants, such as urinary catheters. The development of biofilms is a complex process where a great diversity of genes participate. The present work is based on the study of genes related to iron metabolism and its implication in the development of P. mirabilis biofilms and pathogenicity. For this study, two mutant strains defective in biofilm formation were selected, generated by the interruption of genes that encoded non-heme ferritin and TonB-dependent receptor. The mutations influence on the development of the biofilm was evaluated by different approaches. The complexity of the biofilm was analyzed using Confocal Laser Microscopy and image analysis. The mutants infectivity potential was assessed in two experimental mice models of urinary tract infection. The results obtained in the present work show us the role of the ferritin and a TonB-associated porin protein over the initial and later stages of biofilm development. Moreover, in the ascending UTI mouse model, both mutants failed to colonize the urinary tract. In CAUTI models, ferritin mutant damaged the bladder similarly to wild type but the Ton-B mutant was unable to generate infection in the urinary tract. The results obtained in the present work confirm the relevant role that iron metabolism genes have in P. mirabilis biofilm development and for infection in the urinary tract.

An Organ System-Based Synopsis of Pseudomonas aeruginosa Virulence

Driven in part by its metabolic versatility, high intrinsic antibiotic resistance, and a large repertoire of virulence factors, Pseudomonas aeruginosa is expertly adapted to thrive in a wide variety of environments, and in the process, making it a notorious opportunistic pathogen. Apart from the extensively studied chronic infection in the lungs of people with cystic fibrosis (CF), P. aeruginosa also causes multiple serious infections encompassing essentially all organs of the human body, among others, lung infection in patients with chronic obstructive pulmonary disease, primary ciliary dyskinesia and ventilator-associated pneumonia; bacteremia and sepsis; soft tissue infection in burns, open wounds and postsurgery patients; urinary tract infection; diabetic foot ulcers; chronic suppurative otitis media and otitis externa; and keratitis associated with extended contact lens use. Although well characterized in the context of CF, pathogenic processes mediated by various P. aeruginosa virulence factors in other organ systems remain poorly understood. In this review, we use an organ system-based approach to provide a synopsis of disease mechanisms exerted by P. aeruginosa virulence determinants that contribute to its success as a versatile pathogen.

Pathogenesis of Proteus mirabilis Infection

Proteus mirabilis, a Gram-negative rod-shaped bacterium most noted for its swarming motility and urease activity, frequently causes catheter-associated urinary tract infections (CAUTIs) that are often polymicrobial. These infections may be accompanied by urolithiasis, the development of bladder or kidney stones due to alkalinization of urine from urease-catalyzed urea hydrolysis. Adherence of the bacterium to epithelial and catheter surfaces is mediated by 17 different fimbriae, most notably MR/P fimbriae. Repressors of motility are often encoded by these fimbrial operons. Motility is mediated by flagella encoded on a single contiguous 54-kb chromosomal sequence. On agar plates, P. mirabilis undergoes a morphological conversion to a filamentous swarmer cell expressing hundreds of flagella. When swarms from different strains meet, a line of demarcation, a "Dienes line," develops due to the killing action of each strain's type VI secretion system. During infection, histological damage is caused by cytotoxins including hemolysin and a variety of proteases, some autotransported. The pathogenesis of infection, including assessment of individual genes or global screens for virulence or fitness factors has been assessed in murine models of ascending urinary tract infections or CAUTIs using both single-species and polymicrobial models. Global gene expression studies performed in culture and in the murine model have revealed the unique metabolism of this bacterium. Vaccines, using MR/P fimbria and its adhesin, MrpH, have been shown to be efficacious in the murine model. A comprehensive review of factors associated with urinary tract infection is presented, encompassing both historical perspectives and current advances.

Impact of polymicrobial biofilms in catheter-associated urinary tract infections

Recent reports have demonstrated that most biofilms involved in catheter-associated urinary tract infections are polymicrobial communities, with pathogenic microorganisms (e.g. Escherichia coli, Pseudomonas aeruginosa, Klebsiella pneumoniae) and uncommon microorganisms (e.g. Delftia tsuruhatensis, Achromobacter xylosoxidans) frequently co-inhabiting the same urinary catheter. However, little is known about the interactions that occur between different microorganisms and how they impact biofilm formation and infection outcome. This lack of knowledge affects CAUTIs management as uncommon bacteria action can, for instance, influence the rate at which pathogens adhere and grow, as well as affect the overall biofilm resistance to antibiotics. Another relevant aspect is the understanding of factors that drive a single pathogenic bacterium to become prevalent in a polymicrobial community and subsequently cause infection. In this review, a general overview about the IMDs-associated biofilm infections is provided, with an emphasis on the pathophysiology and the microbiome composition of CAUTIs. Based on the available literature, it is clear that more research about the microbiome interaction, mechanisms of biofilm formation and of antimicrobial tolerance of the polymicrobial consortium are required to better understand and treat these infections.

Interaction between atypical microorganisms and E. coli in catheter-associated urinary tract biofilms

Most biofilms involved in catheter-associated urinary tract infections (CAUTIs) are polymicrobial, with disease causing (eg Escherichia coli) and atypical microorganisms (eg Delftia tsuruhatensis) frequently inhabiting the same catheter. Nevertheless, there is a lack of knowledge about the role of atypical microorganisms. Here, single and dual-species biofilms consisting of E. coli and atypical bacteria (D. tsuruhatensis and Achromobacter xylosoxidans), were evaluated. All species were good biofilm producers (Log 5.84-7.25 CFU cm(-2) at 192 h) in artificial urine. The ability of atypical species to form a biofilm appeared to be hampered by the presence of E. coli. Additionally, when E. coli was added to a pre-formed biofilm of the atypical species, it seemed to take advantage of the first colonizers to accelerate adhesion, even when added at lower concentrations. The results suggest a greater ability of E. coli to form biofilms in conditions mimicking the CAUTIs, whatever the pre-existing microbiota and the inoculum concentration.

Regulatory and metabolic networks for the adaptation of Pseudomonas aeruginosa biofilms to urinary tract-like conditions

Biofilms of the Gram-negative bacterium Pseudomonas aeruginosa are one of the major causes of complicated urinary tract infections with detrimental outcome. To develop novel therapeutic strategies the molecular adaption strategies of P. aeruginosa biofilms to the conditions of the urinary tract were investigated thoroughly at the systems level using transcriptome, proteome, metabolome and enzyme activity analyses. For this purpose biofilms were grown anaerobically in artificial urine medium (AUM). Obtained data were integrated bioinformatically into gene regulatory and metabolic networks. The dominating response at the transcriptome and proteome level was the adaptation to iron limitation via the broad Fur regulon including 19 sigma factors and up to 80 regulated target genes or operons. In agreement, reduction of the iron cofactor-dependent nitrate respiratory metabolism was detected. An adaptation of the central metabolism to lactate, citrate and amino acid as carbon sources with the induction of the glyoxylate bypass was observed, while other components of AUM like urea and creatinine were not used. Amino acid utilization pathways were found induced, while fatty acid biosynthesis was reduced. The high amounts of phosphate found in AUM explain the reduction of phosphate assimilation systems. Increased quorum sensing activity with the parallel reduction of chemotaxis and flagellum assembly underscored the importance of the biofilm life style. However, reduced formation of the extracellular polysaccharide alginate, typical for P. aeruginosa biofilms in lungs, indicated a different biofilm type for urinary tract infections. Furthermore, the obtained quorum sensing response results in an increased production of virulence factors like the extracellular lipase LipA and protease LasB and AprA explaining the harmful cause of these infections.

Proteobactin and a yersiniabactin-related siderophore mediate iron acquisition in Proteus mirabilis

Proteus mirabilis causes complicated urinary tract infections (UTIs). While the urinary tract is an iron-limiting environment, iron acquisition remains poorly characterized for this uropathogen. Microarray analysis of P. mirabilis HI4320 cultured under iron limitation identified 45 significantly upregulated genes (P ≤ 0.05) that represent 21 putative iron-regulated systems. Two gene clusters, PMI0229-0239 and PMI2596-2605, encode putative siderophore systems. PMI0229-0239 encodes a non-ribosomal peptide synthetase-independent siderophore system for producing a novel siderophore, proteobactin. PMI2596-2605 are contained within the high-pathogenicity island, originally described in Yersinia pestis, and encodes proteins with apparent homology and organization to those involved in yersiniabactin production and uptake. Cross-feeding and biochemical analysis shows that P. mirabilis is unable to utilize or produce yersiniabactin, suggesting that this yersiniabactin-related locus is functionally distinct. Only disruption of both systems resulted in an in vitro iron-chelating defect; demonstrating production and iron-chelating activity for both siderophores. These findings clearly show that proteobactin and the yersiniabactin-related siderophore function as iron acquisition systems. Despite the activity of both siderophores, only mutants lacking the yersiniabactin-related siderophore have reduced fitness in vivo. The fitness requirement for the yersiniabactin-related siderophore during UTI shows, for the first time, the importance of siderophore production in vivo for P. mirabilis.

Zinc uptake contributes to motility and provides a competitive advantage to Proteus mirabilis during experimental urinary tract infection

Proteus mirabilis, a Gram-negative bacterium, represents a common cause of complicated urinary tract infections in catheterized patients or those with functional or anatomical abnormalities of the urinary tract. ZnuB, the membrane component of the high-affinity zinc (Zn(2+)) transport system ZnuACB, was previously shown to be recognized by sera from infected mice. Since this system has been shown to contribute to virulence in other pathogens, its role in Proteus mirabilis was investigated by constructing a strain with an insertionally interrupted copy of znuC. The znuC::Kan mutant was more sensitive to zinc limitation than the wild type, was outcompeted by the wild type in minimal medium, displayed reduced swimming and swarming motility, and produced less flaA transcript and flagellin protein. The production of flagellin and swarming motility were restored by complementation with znuCB in trans. Swarming motility was also restored by the addition of Zn(2+) to the agar prior to inoculation; the addition of Fe(2+) to the agar also partially restored the swarming motility of the znuC::Kan strain, but the addition of Co(2+), Cu(2+), or Ni(2+) did not. ZnuC contributes to but is not required for virulence in the urinary tract; the znuC::Kan strain was outcompeted by the wild type during a cochallenge experiment but was able to colonize mice to levels similar to the wild-type level during independent challenge. Since we demonstrated a role for ZnuC in zinc transport, we hypothesize that there is limited zinc present in the urinary tract and P. mirabilis must scavenge this ion to colonize and persist in the host.

Urinary tract infections caused by Pseudomonas aeruginosa: a minireview

Urinary tract infections (UTIs) are a serious health problem affecting millions of people each year. Infections of the urinary tract are the second most common type of infection in the body. Catheterization of the urinary tract is the most common factor, which predisposes the host to these infections. Catheter-associated UTI (CAUTI) is responsible for 40% of nosocomial infections, making it the most common cause of nosocomial infection. CAUTI accounts for more than 1 million cases in hospitals and nursing homes annually and often involve uropathogens other than Escherichia coli. While the epidemiology and pathogenic mechanisms of uropathogenic Escherichia coli have been extensively studied, little is known about the pathogenesis of UTIs caused by other organisms like Pseudomonas aeruginosa. Scanty available information regarding pathogenesis of UTIs caused by P. aeruginosa is an important bottleneck in developing effective preventive approaches. The aim of this review is to summarize some of the advances made in the field of P. aeruginosa induced UTIs and draws attention of the workers that more basic research at the level of pathogenesis is needed so that novel strategies can be designed.

Outer membrane antigens of the uropathogen Proteus mirabilis recognized by the humoral response during experimental murine urinary tract infection

Proteus mirabilis, a gram-negative bacterium, is a frequent cause of complicated urinary tract infections in those with functional or anatomical abnormalities or those subject to long-term catheterization. To systematically identify surface-exposed antigens as potential vaccine candidates, proteins in the outer membrane fraction of bacteria were separated by two-dimensional gel electrophoresis and subjected to Western blotting with sera from mice experimentally infected with P. mirabilis. Protein spots reactive with sera were identified by mass spectrometry, which in conjunction with the newly completed genome sequence of P. mirabilis HI4320, was used to identify surface-exposed antigens. Culture conditions that may mimic in vivo conditions more closely than Luria broth (growth in human urine and under iron limitation and osmotic stress) were also used. Thirty-seven antigens to which a humoral response had been mounted, including 23 outer membrane proteins, were identified. These antigens are presumably expressed during urinary tract infection. Protein targets that are both actively required for virulence and antigenic may serve as protective antigens for vaccination; thus, five representative antigens were selected for use in virulence studies. Strains of P. mirabilis with mutations in three of the corresponding genes (the PMI0047 gene, rafY, and fadL) were not attenuated in the murine model of urinary tract infection. Putative iron acquisition proteins PMI0842 and PMI2596, however, both contribute to fitness in the urinary tract and thus emerge as vaccine candidates.

An iron-regulated outer-membrane protein of Proteus mirabilis is a haem receptor that plays an important role in urinary tract infection and in in vivo growth

Proteus mirabilis, a common cause of urinary tract infections, expresses iron-regulated outer-membrane proteins (OMPs) in response to iron restriction. It has been suggested that a 64 kDa OMP is involved in haemoprotein uptake and that this might have a role in pathogenesis. In order to confirm this hypothesis, this study generated a P. mirabilis mutant strain (P7) that did not express the 64 kDa OMP, by insertion of the TnphoA transposon. The nucleotide sequence of the interrupted gene revealed that it corresponded to a haemin receptor precursor. Moreover, in vitro growth assays showed that the mutant was unable to grow using haemoglobin and haemin as unique iron sources. The authors also carried out in vivo growth and infectivity assays and demonstrated that P7 was not able to survive in an in vivo model and was less efficient than wild-type strain Pr 6515 in colonizing the urinary tract. These results confirmed that the P. mirabilis 64 kDa iron-regulated OMP is a haem receptor that has an important role for survival and multiplication of these bacteria in the mammalian host and in the development of urinary tract infection.

Complicated catheter-associated urinary tract infections due to Escherichia coli and Proteus mirabilis

Catheter-associated urinary tract infections (CAUTIs) represent the most common type of nosocomial infection and are a major health concern due to the complications and frequent recurrence. These infections are often caused by Escherichia coli and Proteus mirabilis. Gram-negative bacterial species that cause CAUTIs express a number of virulence factors associated with adhesion, motility, biofilm formation, immunoavoidance, and nutrient acquisition as well as factors that cause damage to the host. These infections can be reduced by limiting catheter usage and ensuring that health care professionals correctly use closed-system Foley catheters. A number of novel approaches such as condom and suprapubic catheters, intermittent catheterization, new surfaces, catheters with antimicrobial agents, and probiotics have thus far met with limited success. While the diagnosis of symptomatic versus asymptomatic CAUTIs may be a contentious issue, it is generally agreed that once a catheterized patient is believed to have a symptomatic urinary tract infection, the catheter is removed if possible due to the high rate of relapse. Research focusing on the pathogenesis of CAUTIs will lead to a better understanding of the disease process and will subsequently lead to the development of new diagnosis, prevention, and treatment options.

Quantitative profile of the uropathogenic Escherichia coli outer membrane proteome during growth in human urine

Outer membrane proteins (OMPs) of microbial pathogens are critical components that mediate direct interactions between microbes and their surrounding environment. Consequently, the study of OMPs is integral to furthering the understanding of host-pathogen interactions and to identifying key targets for development of improved antimicrobial agents and vaccines. In this study, we used two-dimensional polyacrylamide gel electrophoresis (2D-PAGE) and tandem mass spectrometry to characterize the uropathogenic Escherichia coli (UPEC) outer membrane subproteome; 30 individual OMPs present on the bacterial surface during growth in human urine were identified. Fluorescence difference gel electrophoresis was used to identify quantitative changes in levels of UPEC strain CFT073 OMPs during growth in urine; six known receptors for iron compounds were induced in this environment, i.e., ChuA, IutA, FhuA, IroN, IreA, and Iha. A seventh putative iron compound receptor, encoded by CFT073 open reading frame (ORF) c2482, was also identified and found to be induced in urine. Further, the induction of these seven iron receptors in human urine and during defined iron limitation was verified by using quantitative real-time PCR (qPCR). An eighth iron receptor, fepA, displayed similar induction levels under these conditions as measured by qPCR but was not identified by 2D-PAGE. Addition of 10 microM FeCl(2) to human urine repressed the transcription of all eight iron receptor genes. A number of fecal-commensal, intestinal pathogenic, and uropathogenic E. coli strains all displayed similar growth rates in human urine, showing that the ability to grow in urine per se is not a urovirulence trait. Thus, human urine is an iron-limiting environment and UPEC enriches its outer membrane with iron receptors to contend with this iron limitation.

Serum concentrations of GM-CSF and G-CSF correlate with the Th1/Th2 cytokine response in cystic fibrosis patients with chronic Pseudomonas aeruginosa lung infection

The inflammation in cystic fibrosis (CF) patients with chronic Pseudomonas aeruginosa lung infection is dominated by polymorphonuclear neutrophils (PMNs). There seems to be a relationship between the PMN-dominated inflammation, pronounced antibody production and a Th2-dominated response. Apart from mobilizing monocytes and PMNs from the bone marrow, GM-CSF, G-CSF and IL-3 select subsets of dendritic cells, which subsequently induce distinct Th responses. Therefore, the present study examines the correlation between the mobilizing cytokines in serum and the Th responses. The IFN-gamma and IL-4 production by peripheral blood mononuclear cells, and the concentrations of GM-CSF and G-CSF in serum as well as lung function, were determined in 37 CF patients with and 6 CF patients without chronic P. aeruginosa lung infection. The GM-CSF/G-CSF ratio correlated both with the IFN-gamma production and good lung function. In addition, an inverse correlation between IL-3 and IFN-gamma was observed. The results indicate involvement of endogenous GM-CSF, G-CSF and IL-3 in the skewed Th response in CF, and change to a Th1-dominated response might be achieved with GM-CSF treatment.

Protection mediated by antibodies to iron-regulated outer-membrane proteins of S. typhi in a mouse peritonitis model

Iron limitation induces the expression of iron-regulated outer-membrane proteins, which are not expressed under iron sufficient growth conditions. In the present study, these proteins were purified in order to evaluate their protective potential in the experimental model. Anti IROMPs antiserum was raised in rabbits. In mice, passively transferred anti-IROMPs antibodies provided 60% protection against the serovar Typhi challenge dose (9.6 LD50). The hyperimmune serum containing anti-IROMPs antibodies were also found to be bactericidal in the presence of complement whereas no bacterial killing was observed with pre-immunized serum. Bactericidal titre of anti-IROMPs serum was fond to be 2000 as more than 50% killing was observed with serum diluted to 1:2000. The role of IROMPs was assessed in actively-immunized mice followed by challenge with serovar Typhi. These proteins provided protection in 90% mice against challenge (480 LD50) with the pathogen. The levels of isotypes of antibodies (IgG, IgM & IgA) in the sera and secretory antibodies (sIgA) in the gut fluid of immunized mice correlated with the protection. This study, thus indicates that anti IROMPs antibodies may play an important role in providing protection at systemic as well as at mucosal level.

Outer membrane proteins: key players for bacterial adaptation in host niches

Outer membrane proteins (OMPs) of Gram-negative bacteria have diverse functions and are directly involved in the interaction with various environments encountered by pathogenic organisms. Thus, OMPs represent important virulence factors and play essential roles in bacterial adaptation to host niches, which are usually hostile to invading pathogens. Understanding the structure and functions of bacterial OMPs will facilitate the design of antimicrobial drugs and vaccines. In this paper, we will present a brief review on OMPs that contribute to bacterial adaptive responses including iron uptake, antimicrobial peptide resistance, serum resistance, and drug/bile resistance.

Improved outcome of chronic Pseudomonas aeruginosa lung infection is associated with induction of a Th1-dominated cytokine response

Repeated challenge with antigen is involved in the pathogenesis of a variety of pulmonary diseases. Patients with cystic fibrosis (CF) experience recurrent pulmonary colonization with Pseudomonas aeruginosa before establishment of chronic lung infection. To mimic recurrent lung infections in CF patients, the lungs of susceptible BALB/c mice were re-infected with P. aeruginosa 14 days after the initial infection. Singly-infected BALB/c mice, as well as non-infected mice, were used as controls. Decreased mortality and milder lung inflammation in re-infected BALB/c mice, as well as a tendency for improved clearance of bacteria, was observed when compared with singly-infected mice. The improved outcome in re-infected mice correlated with changes in CD4 cell numbers. Surface expression of LFA-1 on pulmonary CD4 cells was increased in re-infected compared with singly-infected mice. Moreover, resistance to re-infection was paralleled by a shift towards a Th1-dominated response and increased IL-12 production. No significant increase in serum IgG was observed in the re-infected mice. In conclusion, these results indicate a protective role for a Th1-dominated response, independent of antibody production, in chronic P. aeruginosa lung infection in CF.

Early immune response in susceptible and resistant mice strains with chronic Pseudomonas aeruginosa lung infection determines the type of T-helper cell response

Most cystic fibrosis (CF) patients become chronically infected with Pseudomonas aeruginosa in the lungs. The infection is characterized by a pronounced antibody response and a persistant inflammation dominated by polymorphonuclear neutrophils. Moreover a high antibody response correlates with a poor prognosis. We speculated that a change from this Th2-like response to a Th1-like response might decrease the lung inflammation and thus improve the prognosis in CF patients. To investigate this, we infected C3H/HeN and BALB/c mice intratracheally with P. aeruginosa. In addition, we studied the early immune response leading to different Th responses. Mortality was lower in the C3H/HeN mice (p<0.005), they cleared the bacteria faster (day 3 p<0.01, day 7 p<0.02), had a milder lung inflammation (day 7 p<0.01, day 14 p< or =0.0005) and had a Th1-like IgG subclass switch. At day 3, the C3H/HeN mice produced less NO and TNF-alpha, (p<0.01 and p<0.03) and had the lowest IL-10/IL-12 ratio (p< or =0.05). At day 7, the C3H/HeN mice had the highest IFN-gamma (p<0.02), and the lowest IL-4 (p<0.02) production in the lungs. In conclusion, these results show that the Th1-reacting C3H/HeN mice with chronic P. aeruginosa lung infection have a better disease outcome compared to the Th2-reacting BALB/c mice, indicating that a Th1 response might be beneficial in CF patients with chronic P. aeruginosa lung infection.

The biology of cystitis: host and bacterial factors

Cystitis is caused by a relatively small number of bacterial species. To colonize and grow in the urinary tract, these organisms have developed and acquired special properties (virulence factors) that allow them to overcome the defences of the urinary tract, particularly clearance by urine flow. These virulence factors are unlikely to be required during transmission from host to host, and sometimes their constitutive expression may actually be disadvantageous. Such factors are therefore regulated by the environment and in a coordinate manner to ensure their most appropriate expression for the conditions encountered. This review focuses on the biology of the urinary tract and the bacterial properties necessary to cause cystitis. The regulation of virulence factors at the different stages of the infection is considered, and a general model for the pathogenesis of urinary tract infection is proposed.

Vibrio cholerae O1 strain TSI-4 produces the exopolysaccharide materials that determine colony morphology, stress resistance, and biofilm formation

Vibrio cholerae O1 strain TSI-4 (El Tor, Ogawa) can shift to a rugose colony morphology from its normal translucent colony morphology in response to nutrient starvation. We have investigated differences between the rugose and translucent forms of V. cholerae O1 strain TSI-4. Electron microscopic examination of the rugose form of TSI-4 (TSI-4/R) revealed thick, electron-dense exopolysaccharide materials surrounding polycationic ferritin-stained cells, while the ferritin-stained material was absent around the translucent form of TSI-4 (TSI-4/T). The exopolysaccharide produced by V. cholerae TSI-4/R was found to have a composition of N-acetyl-D-glucosamine, D-mannose, 6-deoxy-D-galactose, and D-galactose (7.4:10.2:2.4:3.0). The expression of an amorphous exopolysaccharide promotes biofilm development under static culture conditions. Biofilm formation by the rugose strain was determined by scanning electron microscopy, and most of the surface of the film was colonized by actively dividing rod cells. The corresponding rugose and translucent strains were compared for stress resistance. By having exopolysaccharide materials, the rugose strains acquired resistance to osmotic and oxidative stress. Our data indicated that an exopolysaccharide material on the surface of the rugose strain promoted biofilm formation and resistance to the effects of two stressing agents.

Identification of iron-regulated outer membrane proteins in uropathogenic Proteus mirabilis and its relationship with heme uptake

The effect of iron deprivation on the expression of outer membrane proteins and the ability to use heme as an iron source by uropathogenic Proteus mirabilis, Pr 6515, was studied. Examination of iron-restricted bacteria showed three outer membrane proteins ranging from 66 to 75 kDa to be affected by iron restriction, as well as a newly expressed 64-kDa protein. These proteins were induced within 15 minutes of iron-deprivation. The strain grew in the presence of ferric citrate, hemin and hemoglobin as iron sources, but could not use transferrin, lactoferrin or siderophores from exogenous sources. The 64- and 66-kDa proteins showed hemin-binding activity by affinity chromatography, and both reacted in Western blots with sera from mice transurethrally infected with the same strain. We suggest that P. mirabilis expresses iron-regulated outer membrane proteins that could be involved in heme uptake and may have a role in pathogenesis.

Siderophore production by Staphylococcus aureus and identification of iron-regulated proteins

Siderophore activity of Staphylococcus aureus was detected in an iron-restricted chemically defined medium. The molecular mass of this siderophore, called aureochelin, was 577 Da. Surface-associated proteins of 120, 88, 57, 35, and 33 kDa were mainly expressed under iron restriction conditions. Results showed a relationship between siderophore production and the existence of the 120- and 88-kDa proteins. Western blotting of surface-associated proteins revealed that these proteins were recognized both by patients sera and polyclonal rabbit serum.

Relative importance of three iron-regulated outer membrane proteins for in vivo growth of Vibrio cholerae

Iron is an essential nutrient to support the growth of most bacterial species. However, iron is not easily available to microorganisms infecting mammalian hosts, because it is largely sequestered by iron-binding proteins, such as transferrin or lactoferrin, or complexed to heme. In response to environmental iron stress, Vibrio cholerae produces the siderophore vibriobactin as well as a number of iron-induced outer membrane proteins. Previous data on the role of iron acquisition systems for the intraintestinal growth of mucosal pathogens such as V. cholerae are conflicting. In this report, we isolated mutants of V. cholerae with TnphoA fusions in each of viuA, hutA, and irgA, as well as strains mutant in each pair of these genes and all three simultaneously, to analyze the role of these iron-induced outer membrane protein receptors for in vivo growth of V. cholerae. The fusion between hutA and TnphoA in a single copy on the chromosome allowed the study of in vitro regulation of hutA in response to iron, fur, and irgB; transcription of hutA was tightly iron regulated (70-fold) and dependent on a functional Fur but did not require IrgB. To investigate the effects of mutations in these iron-induced outer membrane proteins on in vivo growth, we inoculated ileal loops in a rabbit model of infection. This avoids exposure of organisms to the potential killing effects of gastric acid, allows several logarithmic increases in growth in the in vivo environment, and facilitates direct comparison of multiple strains in the same animal to avoid any differences between animals. We grew each mutant to be tested in competition with the wild-type strain in the same loop, to provide an internal control. We confirmed that the inocula for these experiments were grown under conditions of iron stress prior to in vivo inoculation, by measuring the alkaline phosphatase activity of the iron-regulated fusion in each strain. The results confirmed that mutation of irgA produced a much more substantial in vivo growth defect than mutation of either hutA or viuA alone. Double mutants of irgA with either viuA or hutA, or the strain mutant in all three genes, showed an in vivo growth defect comparable to the strain mutant in irgA only, suggesting that mutation of irgA was the most relevant for in vivo growth. The strain mutant in both hutA and viuA was also markedly impaired for in vivo growth, suggesting that mutation of both of these iron uptake systems simultaneously can also produce a substantial in vivo growth defect.

Production of superoxide dismutases from Proteus mirabilis and Proteus vulgaris

Proteus mirabilis and Proteus vulgaris expressed a combination of superoxide dismutase (Sod) activities, which was assigned to FeSod1, FeSod2 and MnSod for P. mirabilis, and FeSod, MnSod and CuZnSod for P. vulgaris. Production of the Sod proteins was dependent on the availability of iron, whether cells were grown under anaerobiosis or aerobiosis and growth phase. Nalidixic acid and chloramphenicol inhibited cell growth and the iron- and dioxygen-dependent production of Sod. These results support the involvement of metal ions and redox status in the production of Proteus Sods.

Constituents of human urine alter siderophore production of Escherichia coli

Four uroisolates and four faecal isolates of Escherichia coli were randomly selected for studying the siderophore production in an iron-deficient, chemically defined, medium. Glucose, lactose, urea and creatinine were added individually, as well as in combination, to estimate their influence on siderophore production. No difference in siderophore production was observed between stool and urinary isolates of E. coli. Alterations in phenolate production were observed to be constituent-dependent while a uniformly significant increase in hydroxamate production (p < 0.05) was recorded after addition of the constituents, either each individually or in combination.

Proteus mirabilis amino acid deaminase: cloning, nucleotide sequence, and characterization of aad

Proteus, Providencia, and Morganella species produce deaminases that generate alpha-keto acids from amino acids. The alpha-keto acid products are detected by the formation of colored iron complexes, raising the possibility that the enzyme functions to secure iron for these species, which do not produce traditional siderophores. A gene encoding an amino acid deaminase of uropathogenic Proteus mirabilis was identified by screening a genomic library hosted in Escherichia coli DH5 alpha for amino acid deaminase activity. The deaminase gene, localized on a cosmid clone by subcloning and Tn5::751 mutagenesis, was subjected to nucleotide sequencing. A single open reading frame, designated aad (amino acid deaminase), which appears to be both necessary and sufficient for deaminase activity, predicts a 473-amino-acid polypeptide (51,151 Da) encoded within an area mapped by transposon mutagenesis. The predicted amino acid sequence of Aad did not share significant amino acid sequence similarity with any other polypeptide in the PIR or SwissProt database. Amino acid deaminase activity in both P. mirabilis and E. coli transformed with aad-encoding plasmids was not affected by medium iron concentration or expression of genes in multicopy in fur, cya, or crp E. coli backgrounds. Enzyme expression was negatively affected by growth with glucose or glycerol as the sole carbon source but was not consistent with catabolite repression.

Effects of ciprofloxacin and protamine sulfate combinations against catheter-associated Pseudomonas aeruginosa biofilms

Infection is a common complication associated with the use of transcutaneous and implanted medical devices. These infections are generally difficult to treat and frequently require removal of the biomaterial before the infection can be completely eradicated. The presence of a bacterial biofilm recalcitrant to treatment often mediates these infections. We studied the influence of a polycationic protein, protamine sulfate, on the efficacy of the fluoroquinolone ciprofloxacin against a clinical isolate of Pseudomonas aeruginosa. A P. aeruginosa biofilm was developed on 1-cm sections of red rubber catheter material and then treated with various combinations of protamine sulfate and ciprofloxacin. The present work demonstrated that ciprofloxacin in combination with protamine was more effective against biofilms than was ciprofloxacin alone. Protamine sulfate at 50 micrograms/ml combined with antibiotic at 0.5 microgram/ml reduced the number of viable cells by an average of 98.97%, while protamine sulfate at 50 micrograms/ml alone resulted in an average 107.8% increase and antibiotic alone resulted in an average 58.6% reduction after 24 h. Furthermore, protamine sulfate, in combination with ciprofloxacin, inhibited P. aeruginosa in a dose-dependent fashion. It was further observed that treatment with the combination of protamine sulfate and ciprofloxacin had a more drastic effect on planktonic organisms as compared with the P. aeruginosa biofilms; the MBC was reduced to < 0.05 microgram/ml in the presence of 25 micrograms of protamine sulfate per ml. These findings were substantiated by ultrastructure studies of treated cells using scanning and transmission electron microscopy. The synergism between ciprofloxacin and protamine sulfate significantly enhanced the efficacy of ciprofloxacin against planktonic and biofilm P. aeruginosa.

Glycosaminoglycans and struvite calculi

Glycosaminoglycans (GAGs) are suspended in urine and are present on tissue surfaces in the urinary tract. Consequently, they have the potential to influence any pathological disorder in this environment, including urinary tract infections by Proteus mirabilis and struvite (NH4MgPO4.6H2(0)) urolithiasis. Although GAGs, suspended in urine, may inhibit the formation of other types of calculus minerals, no such effect has been reported in struvite calculi. Nevertheless, GAGs are a major component of the organic matrix of all types of urinary calculi. In contrast, there is evidence that the GAG layer on the bladder surface may act as a defence mechanism against infection by inhibiting bacterial adhesion. More studies are needed to elucidate fully the role of GAGs in urinary infections and struvite urolithiasis.

Novel antigens expressed by Aeromonas salmonicida grown in vivo

Virulent and avirulent Aeromonas salmonicida strains grown inside intraperitoneal implants in Rainbow trout (Oncorhynchus mykiss) were examined for unique antigen expression. Western blots (immunoblots), performed with immune rabbit serum raised against in vivo-grown cells, revealed several unique antigens. With the exception of lipopolysaccharide (LPS), these novel antigens were destroyed after proteinase K treatment. The majority of these antigens were not induced in vitro in response to either iron limitation or anaerobiosis. In addition, electron microscopy demonstrated the presence of a putative capsule on in vivo-grown cells. Purification and fractionation of this carbohydrate material from cells grown in carbon-rich synthetic media resulted in the isolation and separation of an antigenically distinct LPS not seen with cells grown in standard media. Antiserum raised against in vivo-grown cells recognized both this LPS and the typical LPS of A. salmonicida apparent in in vitro-grown cells. Antiserum raised against in vitro-grown cells recognized only the LPS expressed in vitro. Antiserum directed against in vivo-grown cells was approximately 10 times more sensitive than serum directed against in vitro-grown cells in detecting A. salmonicida in infected fish kidney tissue.

Iron uptake mechanisms of pathogenic bacteria

Most of the iron in a mammalian body is complexed with various proteins. Moreover, in response to infection, iron availability is reduced in both extracellular and intracellular compartments. Bacteria need iron for growth and successful bacterial pathogens have therefore evolved to compete successfully for iron in the highly iron-stressed environment of the host's tissues and body fluids. Several strategies have been identified among pathogenic bacteria, including reduction of ferric to ferrous iron, occupation of intracellular niches, utilisation of host iron compounds, and production of siderophores. While direct evidence that high affinity mechanisms for iron acquisition function as bacterial virulence determinants has been provided in only a small number of cases, it is likely that many if not all such systems play a central role in the pathogenesis of infection.

Inhibitory effect against pathogenic and spoilage bacteria of Pseudomonas strains isolated from spoiled and fresh fish

The antibacterial effects of 209 Pseudomonas strains isolated from spoiled iced fish and newly caught fish were assessed by screening target organisms in agar diffusion assays. One-third (67 strains) inhibited the growth of one or several of six target organisms (Escherichia coli, Shewanella putrefaciens, Aeromonas sobria, Pseudomonas fluorescens, Listeria monocytogenes, and Staphylococcus aureus), of which S. aureus and A. sobria were the most sensitive. The inhibitory action was most pronounced among the strains producing siderophores, and the presence of iron eliminated the antibacterial effect of two-thirds of the inhibitory strains. Siderophore-mediated competition for iron may explain the inhibitory activity of these strains. All but nine of the inhibiting strains were found to inhibit the growth of 38 psychrotrophic S. putrefaciens strains isolated from spoiling fish and fish products. Siderophore-containing Pseudomonas culture supernatants inhibited growth of S. putrefaciens, as did the addition of iron chelators (ethylenediamine dihydroxyphenylacetic acid [EDDHA]). In particular, Pseudomonas strains isolated from newly caught and spoiled Nile perch (Lates niloticus) inhibited S. putrefaciens. This suggests that microbial interaction (e.g., competition or antagonism) may influence the selection of a microflora for some chilled food products.

Differences in protein expression of Haemophilus somnus grown under conditions of iron-restriction

Outer membrane protein profiles were compared in 14 H. somnus strains isolated from brain and lung lesions as well as from the genital tract of asymptomatic carriers during in vitro growth under iron-restricted conditions. Ethylenediamine-di-O-hydroxyphenyl acetic acid (EDDA) was used to obtain iron-restricted conditions in media used for this study. The outer membrane protein profiles were studied by the discontinuous sodium dodecyl sulfate-polyacrylamide gel electrophoretic system (SDS-PAGE), and the proteins were stained with silver or transferred to nitrocellulose sheets and western blots conducted. Growth under iron-restricted conditions resulted in the induction of outer membrane proteins in most H. somnus strains examined. Studies also indicated differences among H. somnus strains in the number of induced proteins and their molecular weights but the results did not indicate a specific relationship between these strain-dependent differences and tissue trophism. Western blot analysis revealed a high degree of immunological relatedness among strains of H. somnus in their iron-regulated proteins. However, hyperimmune serum used in these assays failed to recognize certain iron-regulated proteins expressed by some H. somnus strains, a finding which may have important implications for the induction of protective immunity in cattle against this bovine pathogen.

Determination of IgG subclass antibodies to Pseudomonas aeruginosa outer membrane proteins in cystic fibrosis lung infection using immunoblotting and enzyme-linked immunosorbent assay

IgG subclass antibodies to Pseudomonas aeruginosa outer membrane proteins (OMP) were investigated in serum from cystic fibrosis (CF) patients by immunoblotting and enzyme-linked immunosorbent assay (ELISA). Fifteen patients (eight in good and seven in poor clinical condition) have been followed for an average of 13 years with multiple serum samples covering the preinfection, and early and late stages of chronic infection. Laser-scanning densitometry of photographs taken from immunoblots was used to quantify antibody level and compare with ELISA titres. The earliest anti-OMP antibodies to appear were of the IgG1 subclass. There was no significant difference in IgG subclass antibody levels to OMPs between patients in relatively good and poor clinical condition. Data presented indicate a high positive correlation among measurements of IgG subclass antibodies to P. aeruginosa OMPs using ELISA and immunoblotting.

Modulation of surface antigen expression by Klebsiella pneumoniae in response to growth environment

Growth in pooled human body fluids [urine, serum and peritoneal dialysate (HPD)] modulated the expression of cell envelope antigens in virulent (serotype O1:K1) and avirulent (serotype O1:K66) Klebsiella pneumoniae strains. Marked variations in the outer membrane protein (OMP) and lipopolysaccharide (LPS) profiles were noted when broth-grown cells were compared with those of bacteria cultured in body fluids. In particular, for the O1:K1 serotype strain, growth in the latter resulted in: (a) the expression of at least five iron-regulated OMPs in the 74-87 kDa range, the pattern of which was medium dependent; (b) alterations in the migration of the LPS core polysaccharide; and (c) the reversion of isogenic O-:K+ and O-:K- mutants to the O+ phenotype after growth in fresh serum but not in heat-inactivated serum, urine or HPD. Similar results were obtained for the O1:K66 serotype, although no variation in the migration of the LPS core was noted. For both O1:K1 and O1:K66 serotypes, neither the surface exposure of O1 serotype LPS nor the production of K-antigen (capsular polysaccharide) was affected by growth in body fluids. No reversion of K- mutants to the K+ phenotype was observed. These data illustrate the phenotype flexibility of this opportunistic pathogen and emphasise the crucial role of the O- rather than the K-antigen in protecting K. pneumoniae from complement-mediated serum killing.

Effect of porphyrins and host iron transport proteins on outer membrane protein expression in Porphyromonas (Bacteroides) gingivalis: identification of a novel 26 kDa hemin-repressible surface protein

Porphyromonas gingivalis is capable of in vitro growth when iron sources are either complexed to hemin or host iron transport proteins, or exist in an inorganic form. This study examined the effect of these iron sources on outer membrane protein (OMP) expression in P. gingivalis W50. Hemin (iron) starved P. gingivalis was transferred into growth medium containing hemin, hemoglobin, hemin-saturated human serum albumin, hemin-free human serum albumin, transferrin, lactoferrin, or inorganic iron. Surface proteins were identified by 125I-labeling and resolved by SDS-PAGE and autoradiography. When grown under hemin starved conditions, P. gingivalis W50 and related strains expressed a major 26 kDa OMP, as revealed by 125I-autoradiography. Autoradiographic analysis demonstrated the absence of this 26 kDa OMP from the P. gingivalis surface in hemin-containing environments. Growth of P. gingivalis W50 in the presence of host iron transport proteins (hemin-free) or inorganic iron resulted in surface expression of a 26 kDa OMP. The presence of protoporphyrin IX or substitution of hemin-associated iron with zinc, resulted in continued surface expression of the 26 kDa OMP, indicating that repressibility of this OMP required the coordination of iron to the protoporphyrin IX molecule (i.e. hemin). A survey of 125I-labeled OMPs from several hemin starved P. gingivalis and related strains, demonstrated that a hemin-repressible 26 kDa OMP occurred only in P. gingivalis. We report here a newly described 26 kDa hemin-regulated surface protein occurring in several strains of P. gingivalis which is expressed on the cell surface in hemin starved conditions and is lost from the cell surface in response to an environment containing iron coordinated specifically to protoporphyrin IX (i.e. hemin).

Role of aerobactin in systemic spread of an opportunistic strain of Escherichia coli from the intestinal tract of gnotobiotic lambs

To assess the role of the aerobactin-related system in the virulence of bovine opportunistic Escherichia coli, and to determine the stage(s) of the overall infectious process at which it is acting, germfree lambs were mixedly infected orally with two derivative strains of this bacterium differing in their ability (Iut+) or inability (Iut-) to express a functional aerobactin-mediated iron transport system. The Iut- strain was compared with the Iut+ strain for colonization of the gut, translocation to the mesenteric lymph nodes (MLN), and spread to other organs and to the body fluids of diassociated lambs. The Iut- mutant was found in smaller numbers in the duodenum, suggesting that aerobactin conferred a significant selective advantage for colonization of this intestinal segment. Although the two challenge strains translocated to MLN, the population level in the MLN was always higher for the Iut+ strain. Moreover, experimental infections resulted in recovery of only the Iut+ strain in the organs other than the MLN and in the body fluids. These results indicate a role for aerobactin in promoting systemic spread of the bacteria from the intestine. Direct evidence was obtained that aerobactin secretion occurred in vivo at both intestinal and extraintestinal sites of infection. In contrast to enterobactin, aerobactin was detected in the duodenum, jejunum, ileum, cecum, liver, spleen, kidney, urine, cerebrospinal fluid, and bile. The highest concentration of aerobactin was found in the urine, even when the samples were devoid of infecting bacteria. All of these findings suggest that aerobactin is released in vivo in a diffusible form and that it may be an important step in the production of disease by intestinal opportunistic E. coli.

Cell envelope proteins of Staphylococcus epidermidis grown in vivo in a peritoneal chamber implant

Staphylococcus epidermidis was grown in vivo in chambers implanted intraperitoneally in rats. The cell wall and cytoplasmic membrane protein profiles of the in vivo-grown organisms were compared with those of S. epidermidis grown in vitro in nutrient broth (NB), in iron-restricted NB, or in pooled human peritoneal dialysate (HPD). Compared with growth in broth and in common with growth in HPD, growth in vivo in chambers resulted in the repression of many S. epidermidis wall proteins, with proteins of 27, 42, 54, and 70 kDa predominating. Growth in vivo also resulted in the induction of two iron-repressible cytoplasmic membrane proteins of 32 and 36 kDa, which were also present in staphylococci grown in HPD and in iron-restricted NB. Immunoblotting experiments revealed that in sera taken 21 days after inoculation of the intraperitoneal chambers, the predominant antibody response to cell envelope proteins was directed against the 32- and 36-kDa iron-repressible membrane proteins.

Virulence determinants in Pseudomonas aeruginosa strains from urinary tract infections

A total of 121 uropathogenic Pseudomonas aeruginosa strains were examined for production of several virulence-related factors. These strains were distributed in five predominant O-serotypes, i.e. O 4, O 12, O 11, O 6 and O 5, which accounted respectively for 23.9, 23.1, 12.3, 8.2 and 5.7% of isolates. Pyochelin and pyoverdin siderophores were produced by most of the isolates, defective variants occurring at very low frequency (2.4% for pyochelin and 7.4% for pyoverdin). Adherence to uroepithelial cells and production of cytotoxins was demonstrated in 52.8 and 67.7% of the strains, respectively, with higher frequencies for epidemiologically related strains belonging to serotypes O 4 and O 12. Titration of total proteases, elastase and phospholipase C revealed a high degree of heterogeneity among isolates. However, examination of individual O-serotypes by exoenzyme production showed that elevated levels of total proteases and elastase were characteristics of serotypes of minor numerical importance, i.e. O 1, O 10, O 11 and O 17, whilst low levels of elastase were produced by strains belonging to the predominant serotypes, namely O 4 and O 12. Moreover, epidemiologically related strains belonging to serotypes O 4 and O 12 appeared more homogeneous than the whole serogroup, when compared with other groups on the basis of exoenzyme levels.

The immunogenicity of outer membrane proteins of haemin-depleted Porphyromonas (Bacteroides) gingivalis W50 in periodontal disease

The antigens from outer membrane protein extracts of Porphyromonas gingivalis (W50), grown under different haemin concentrations, were examined for binding with serum antibodies from patients with severe progressive periodontitis or from periodontally healthy control subjects. P. gingivalis was grown under haemin limitation (0.33 micrograms/ml) and haemin excess (2.5 micrograms/ml) conditions in a chemostat at a mean generation time of 6.9 h, at pH 7.5. Sarkosyl-insoluble fractions of outer membrane proteins from P. gingivalis were prepared, and analysed by sodium dodecyl sulphate-polyacrylamide gel electrophoresis (SDS-PAGE) and immunoblot techniques. The SDS-PAGE analysis of the outer membrane of haemin-limited P. gingivalis identified several new protein components, or changed expression of bands compared with cells grown under haemin excess. Immunoblot analysis showed IgG antibodies to 2 haemin deprivation-induced proteins in patients with severe progressive periodontitis, but not in the control sera. These results confirm the immunogenicity of some of the haemin-regulated outer membrane proteins of P. gingivalis in severe progressive periodontitis.

Bacterial colonization behaviour: a new virulence strategy in urinary infections?

The urinary bladder resists bacterial colonization and infection by a number of mechanisms, one of which involves the sloughing of colonized uroepithelial cells. Pathogens which thus become detached from bladder tissue are rapidly eliminated upon voiding of urine. During a recent study of bacterial colonization by the urinary pathogen, Proteus mirabilis, we noted that it colonized glass surfaces such that organisms became widely and evenly dispersed over the surface. In contrast, Pseudomonas fluorescens, a non-pathogen in the urinary tract, did not disperse over the surface but colonized and grew in such a manner as to form small clumps or microcolonies. Other investigators have also shown that Escherichia coli, a common urinary pathogen, initially colonizes bladders in a random, widely-dispersed fashion. We propose that successful bladder pathogens will predominantly adopt colonization behaviour that enables them to widely disperse over bladder tissue and, in so doing, avoid being cleared by the desquamation of uroepithelial cells. Colonization behaviour would therefore represent a previously uncharacterized virulence strategy.

Antibiotic-induced release of endotoxin in chronically bacteriuric patients

A novel in vivo model for the study of antibiotic-induced release of endotoxin from gram-negative bacteria is described. The model uses the chronically colonized urinary tracts of patients whose spinal cords have been injured. At baseline, the organisms were present in the range of 1 x 10(3) to 2 x 10(7) CFU/ml, and the concentration of endotoxin ranged from 2 x 10(-1) to 1 x 10(3) ng/ml in 44 studies. In 10 control studies, the concentration of endotoxin and the numbers of viable gram-negative bacteria over time changed by an average of less than 0.15 log10 units from the baseline values. At 2 h after antibiotic administration, the average decrease in CFU was 0.93 log10 units, and because antibiotics cause the release of endotoxin, an average increase in endotoxin concentration of 0.59 log10 units was noted in 21 studies with susceptible bacteria. Similar changes in response to antibiotic exposure were seen in studies with susceptible Pseudomonas bacteria in comparison with those seen in studies with susceptible members of the family Enterobacteriaceae. These results provide evidence that this novel model may be useful for comparing the effects of antibiotics with different modes of action, both as single agents and in combination, on the concentration of endotoxin in relation to changes in the numbers of bacteria, under conditions of bacterial replication and antibiotic exposure more closely resembling those found in vivo than is possible in other models.

Phenotypic variation in the outer membrane protein composition of Actinobacillus (Haemophilus) pleuropneumoniae: non-specific effect of exogenous pyridine nucleotide supply

Actinobacillus pleuropneumoniae, grown in batch culture, was provided with pyridine nucleotides at concentrations that limited the final growth yield (pyridine nucleotide-deficient cultures) or did not determine the final extent of growth (pyridine nucleotide-sufficient cultures). Sarkosyl-extracted outer membranes from stationary phase, pyridine nucleotide-sufficient organisms contained 23,000 Mr and 43,000 Mr polypeptides that were absent (23,000 Mr) or barely detectable (43,000 Mr) in outer membranes from stationary phase, pyridine nucleotide-deficient organisms or exponential phase organisms. When growth ceased due to exhaustion of pyridine nucleotide, the ratio of the major outer membrane polypeptides (31,000, 38,000 and 69,000 Mr) was altered, becoming more like the ratio found with exponential phase organisms. Similar results were obtained when growth ceased due to glucose exhaustion at low biomass concentrations demonstrating that diverse nutrient deprivations can induce similar changes in outer membrane protein profile. All of these polypeptides were recognized by porcine immune sera indicating their production by A. pleuropneumoniae growing in vivo.