The normal microbial flora

Bacterial interference among nasal inhabitants: eradication of Staphylococcus aureus from nasal cavities by artificial implantation of Corynebacterium sp

To evaluate the role of normal flora in the nares in preventing Staphylococcus aureus colonization, we conducted a replacement study in vivo. Staphylococcus epidermidis (rate of colonization: 100%), various species of corynebacteria (52.5%) and S. aureus (25.%) were the major bacterial inhabitants in the nares of 156 healthy volunteers. The low incidence of S. aureus colonization in the carriers with corynebacteria (8.5%), compared to non-carriers (44. 5%) indicated the possibility of competition for survival between S. aureus and corynebacteria. To confirm this hypothesis, we artificially implanted a strain of Corynebacterium sp (API Coryne bioprofile; 5100304), denoted as Co304 into the nares of 17 S. aureus carriers. S. aureus was completely eradicated in 71% of carriers by up to 15 inoculations of Co304. However, similar doses of 0.9% NaCl or S. epidermidis into the nares of 10 volunteers did not eradicate S. aureus. No bacteriocin-like activity against S. aureus was detectable, even after mitomycin C stimulation of Co304. Thus Co304 interfered with S. aureus by a different mechanism to a bacteriocin-like activity.

Bacterial diversity within the human subgingival crevice

Molecular, sequence-based environmental surveys of microorganisms have revealed a large degree of previously uncharacterized diversity. However, nearly all studies of the human endogenous bacterial flora have relied on cultivation and biochemical characterization of the resident organisms. We used molecular methods to characterize the breadth of bacterial diversity within the human subgingival crevice by comparing 264 small subunit rDNA sequences from 21 clone libraries created with products amplified directly from subgingival plaque, with sequences obtained from bacteria that were cultivated from the same specimen, as well as with sequences available in public databases. The majority (52.5%) of the directly amplified 16S rRNA sequences were <99% identical to sequences within public databases. In contrast, only 21.4% of the sequences recovered from cultivated bacteria showed this degree of variability. The 16S rDNA sequences recovered by direct amplification were also more deeply divergent; 13.5% of the amplified sequences were more than 5% nonidentical to any known sequence, a level of dissimilarity that is often found between members of different genera. None of the cultivated sequences exhibited this degree of sequence dissimilarity. Finally, direct amplification of 16S rDNA yielded a more diverse view of the subgingival bacterial flora than did cultivation. Our data suggest that a significant proportion of the resident human bacterial flora remain poorly characterized, even within this well studied and familiar microbial environment.

Antibacterial prophylaxis in children with urinary tract infection

The aim, in conservative management of vesico-ureteric reflux by antimicrobial prophylaxis, is to prevent recurrent febrile urinary tract infections and consequent renal scarring. However, the effects of this prophylactic strategy are difficult to evaluate, since the required studies comparing children on prophylaxis with controls (without prophylaxis but under careful supervision) are lacking. Furthermore, the optimal length of prophylaxis needs to be defined. Since risk of renal scarring is believed to occur more frequently in young people, and since recurrent urinary infections mainly affect girls, the age and sex of subjects are important in the design of a prophylactic regimen. Nitrofurantoin and trimethoprim are the most common agents used for long-term, low-dose antibacterial prophylaxis. Break-through infections still result from non-compliance and from development of bacterial resistance, the latter mainly arising with trimethoprim. Few studies of prophylactic drugs are available that adequately define patient materials and include a random allocation to the different agents. Further studies of the effects of alternative prophylactic agents are called for, preferably combined with fresh insight into the ecological impact on the bowel and periurethral floras.

Human cytokine responses induced by gram-positive cell walls of normal intestinal microbiota

The normal microbiota plays an important role in the health of the host, but little is known of how the human immune system recognizes and responds to Gram-positive indigenous bacteria. We have investigated cytokine responses of peripheral blood mononuclear cells (PBMC) to Gram-positive cell walls (CW) derived from four common intestinal indigenous bacteria, Eubacterium aerofaciens (Eu.a. ), Eubacterium limosum (Eu.l.), Lactobacillus casei (L.c.), and Lactobacillus fermentum (L.f.). Our results indicate that Gram-positive CW of the normal intestinal microbiota can induce cytokine responses of the human PBMC. The profile, level and kinetics of these responses are similar to those induced by lipopolysaccharide (LPS) or CW derived from a pathogen, Streptococcus pyogenes (S.p.). Bacterial CW are capable of inducing production of a proinflammatory cytokine, tumour necrosis factor-alpha (TNF-alpha), and an anti-inflammatory cytokine, IL-10, but not that of IL-4 or interferon-gamma (IFN-gamma). Monocytes are the main cell population in PBMC to produce TNF-alpha and IL-10. Induction of cytokine secretion is serum-dependent; both CD14-dependent and -independent pathways are involved. These findings suggest that the human cytokine responses induced by Gram-positive CW of the normal intestinal microbiota are similar to those induced by LPS or Gram-positive CW of the pathogens.

Gastrointestinal flora and its alterations in critical illness

The normal indigenous flora of the human gastrointestinal tract comprises a remarkably complex yet stable colony of more than 400 separate species, living in a symbiotic relationship with the human host. Stability of that flora is accomplished by multiple mechanisms including gastric acidity, gut motility, bile, products of immune cells in the gut epithelium, and competition between microorganisms for nutrients and intestinal binding sites. The indigenous flora influences multiple aspects of physiologic homeostasis and forms a key component of normal host defenses against infection by exogenous pathogens. Critical illness is associated with striking changes in patterns of microbial colonization, best described in the oropharynx and upper gastrointestinal tract. Pathological colonization occurs with the same species that is predominate in nosocomial infections, and descriptive studies suggest that such colonization is a risk factor for infection. Moreover, prophylactic measures that prevent pathological gut colonization in experimental circumstances reduce rates of nosocomial infection in critically ill patients and, in the case of selective decontamination of the digestive tract, reduce mortality risk. Conventional approaches to infectious diseases have conceptualized microorganisms as inimical and focused on eradicating them as rapidly and fully as possible. Insights from the study of critically ill patients suggest that that relationship is better understood as a symbiotic one and that preservation, rather than elimination, of the indigenous flora provides the greatest promise of clinical benefit to this vulnerable population.

Pulmonary host defenses. Implications for therapy

Pulmonary host defenses comprise a redundant system of protective mechanisms against invasion of the lungs by pathogenic microbes. The upper and lower airways are uniquely suited to contain and remove organisms that gain access to the respiratory mucosa. If the balance between host and organism is disputed, however, microbial clearance may be ineffective, and infection established. Pulmonary host defense mechanisms, which provide the basis for several current therapeutic strategies, are reviewed.

Review of probiotics available to modify gastrointestinal flora

There is evidence that the oral consumption of micro-organisms produces a protective effect on the gut flora. A significant number of studies suggests that probiotics might have beneficial effects on several microbial disorders of the gut, but it is very difficult to define the clinical efficacy of such products. In this review, we report the results of studies on traveller's diarrhoea (TD), antibiotic associated diarrhoea (AAD) and acute diarrhoea (AD) in which various probiotic preparations have been used in controlled trials and been shown to have a beneficial therapeutic or prophylactic effect.

Oral ecology and person-to-person transmission of Actinobacillus actinomycetemcomitans and Porphyromonas gingivalis

The ecological characteristics of the oral cavity are dissimilar for A. actinomycetemcomitans and for P. gingivalis, as judged by differences in their colonization preferences and patterns, associations with periodontal disease parameters, relationships with the subgingival microbiota and the type of periodontitis and their clonal persistence in the oral cavity. These features also suggest that as a periodontal pathogen, A. actinomycetemcomitans is different from P. gingivalis. Probably in most infected individuals, low levels of A. actinomycetemcomitans can persist for years in equilibrium with the host and the resident oral microbiota. However, it is well established that A. actinomycetemcomitans can cause disease in some individuals or in some circumstances when the regulatory mechanisms are unable to maintain homeostasis in the ecosystem. Elevated A. actinomycetemcomitans proportions of the biota can be regarded as a sign of ecological imbalance, leading to increased risk of periodontal destruction. There is also evidence showing elevated pathogenic potential of certain A. actinomycetemcomitans clones. Although A. actinomycetemcomitans seems to be relatively rarely transmitted between cohabiting adults, transmission can occur to periodontally healthy children of A. actinomycetemcomitans-positive parents. Parents and children may share factors that promote successful oral colonization of A. actinomycetemcomitans, or the window of opportunity is in childhood. Therefore, to prevent parent-child transmission of A. actinomycetemcomitans, bacterium-positive parents of young children are optimal targets for enhanced information and treatment. In selected populations, screening for specific clones of A. actinomycetemcomitans has been employed in prevention of peridontitis. Future research aiming at finding the reasons which cause the changes in the oral homeostasis to allow the growth of A. actinomycetemcomitans may give insight into novel prevention strategies for A. actinomycetemcomitans-associated periodontitis. Compared with A. actinomycetemcomitans, P. gingivalis shows a different pattern of coexistence with the host. In periodontal health or in children, P. gingivalis is absent or only rarely detected. When present, P. gingivalis is commonly recovered in high numbers from dentitions exhibiting inflamed periodontitis and poor oral hygiene. Contrary to A. actinomycetemcomitans, the data on the vertical transmission of P. gingivalis are limited. The major infection route of P. gingivalis seems to be between adults, indicating that P. gingivalis commonly colonizes in an established oral microbiota. These characteristics suggest that the degree of tolerance between P. gingivalis and the host is inferior to that between A. actinomycetemcomitans and the host. It appears that the association of P. gingivalis with disease is a rule rather than an accidental incident. On these grounds, it seems that the host-P. gingivalis relationship approaches antibiosis. Since P. gingivalis infection is related to a typical periodontal eco-pathology, the susceptibility to person-to-person transmission of this pathogen may be controlled by periodontal treatment and emphasizing the significance of high standard oral hygiene.

Risk factors for carriage of respiratory pathogens in the nasopharynx of healthy children. Ascanius Project Collaborative Group

OBJECTIVES

To assess risk factors for nasopharyngeal carriage of Streptococcus pneumoniae, Haemophilus influenzae and Moraxella catarrhalis in a large sample of healthy children.

METHODS

In this point prevalence survey nasopharyngeal specimens were obtained from 1723 healthy children, ages 1 to 7 years, attending day-care centers or schools in 18 Italian cities. Written questionnaires for obtaining information about the demographics and medical history of the children were completed by the parents in the presence of a pediatrician.

RESULTS

The overall carrier rate of respiratory pathogens was 17.9% (S. pneumoniae, 3.5%; H. influenzae, 11.9%; M. catarrhalis, 4.1%). Only 5% of S. pneumoniae strains were penicillin-resistant whereas approximately 40% were erythromycin-resistant. Beta-lactamase production was found in 5.8% of H. influenzae and 88.7% of M. catarrhalis isolates. By multivariate analysis age (< or = 3 years), having older siblings, a history of prolonged full-time day-care attendance and living in a rural area significantly influenced the odds of carrying nasopharyngeal respiratory pathogens, particularly in children ages 1 to 5 years. Sex, breastfeeding, passive smoking and recent upper respiratory tract infections were not significant variables. Antibiotic treatment in the previous 3 months did not affect nasopharyngeal carriage, whereas repeated treatments with a macrolide were associated with carriage of S. pneumoniae.

CONCLUSIONS

Our results suggest that there is a strong and long term relationship between exposure to large numbers of children in the first years of life and nasopharyngeal carriage of all respiratory pathogens. In addition antimicrobial restrictive guidelines should be tailored to local microbiologic sceneries.

Defense mechanisms against infections

Respiratory infections remain common and may be more difficult to treat because new microbes have been identified; commensal flora can become pathogens; and antibiotic resistance is developing, especially to Streptococcus pneumoniae. Contributing to the severity of pneumonia is the increasing number of more susceptible hosts--immunodeficient patients, created as a by-product of modern medical therapy or from infection with HIV, and elderly patients who have associated illnesses. Better strategies to replete immunocompromised hosts are required. Vaccination to modify infection with S. pneumoniae must be given higher priority by health care providers. New means to immunize the respiratory mucosal surface are needed. Research approaches to consider involve 1) targeting (carrying) relevant antigens to appropriate antigen-processing cells in the airways, eg, dendritic cells; and 2) coupling the immunomodulatory effects of cytokines, eg, interleukin-12. Interleukin-12, for example, can stimulate mucosal antibody responses producing S-IgA and IgG and cause T lymphocytes to produce interferon-gamma that can enhance microbial killing by macrophages.

Stool microflora in extremely low birthweight infants

AIM

To serially characterise aerobic and anaerobic stool microflora in extremely low birthweight infants and to correlate colonisation patterns with clinical risk factors.

METHODS

Stool specimens from 29 infants of birthweight <1000 g were collected on days 10, 20, and 30 after birth. Quantitative aerobic and anaerobic cultures were performed.

RESULTS

By day 30, predominant species were Enterococcus faecalis, Escherichia coli, Staphylococcus epidermidis, Enterbacter cloacae, Klebsiella pneumoniae, and Staphylococcus haemolyticus. Lactobacillus and Bifidobacteria spp were identified in only one infant. In breast milk fed (but not in formula fed) infants, the total number of bacterial species/stool specimen increased significantly with time (2.50 (SE 0.34) on day 10; 3.13 (0.38) on day 20; 4.27 (0.45) on day 30) as did quantitative bacterial counts; Gram negative species accounted for most of the increase. On day 30, significant inverse correlations were found between days of previous antibiotic treatment and number of bacterial species (r=0.491) and total organisms/g of stool (r=0.482). Gestational age, birthweight, maternal antibiotic or steroid treatment, prolonged rupture of the membranes, and mode of delivery did not seem to affect colonisation patterns.

CONCLUSIONS

The gut of extremely low birthweight infants is colonised by a paucity of bacterial species. Breast milking and reduction of antibiotic exposure are critical to increasing fecal microbial diversity.

Lactobacillus species prevents colitis in interleukin 10 gene-deficient mice

BACKGROUND & AIMS

Intestinal luminal microflora, or their products, are likely an important initiating factor in the pathogenesis of inflammatory bowel disease. The aim of this study was to determine the role of colonic aerobic luminal bacteria and Lactobacillus species in the development of colitis in interleukin (IL)-10 gene-deficient mice.

METHODS

Intestine from 2-16-week-old mice was scored histologically and cultured for bacteria. Lactobacillus sp. repopulation of the colonic lumen was achieved via daily rectal delivery of Lactobacillus reuteri or oral lactulose therapy.

RESULTS

At 2 weeks of age, IL-10 gene-deficient mice showed no colonic injury but did display abnormal colonic bacterial colonization with increased colonic mucosal aerobic adherent and translocated bacteria in conjunction with reduced Lactobacillus sp. levels. In association with the abnormal colonic bacterial colonization, colitis developed by 4 weeks of age. Restoring Lactobacillus sp. to normal levels reduced levels of colonic mucosal adherent and translocated bacteria and attenuated the development of the colitis.

CONCLUSIONS

In the neonatal period, IL-10 gene-deficient mice have decreased levels of colonic Lactobacillus sp. and an increase in colonic mucosal adherent and translocated bacteria. Normalizing Lactobacillus sp. levels reduced colonic mucosal adherent and translocated bacteria and prevented colitis.

Crossreactive recognition of viral, self, and bacterial peptide ligands by human class I-restricted cytotoxic T lymphocyte clonotypes: implications for molecular mimicry in autoimmune disease

The immunodominant, CD8(+) cytotoxic T lymphocyte (CTL) response to the HLA-B8-restricted peptide, RAKFKQLL, located in the Epstein-Barr virus immediate-early antigen, BZLF1, is characterized by a diverse T cell receptor (TCR) repertoire. Here, we show that this diversity can be partitioned on the basis of crossreactive cytotoxicity patterns involving the recognition of a self peptide-RSKFRQIV-located in a serine/threonine kinase and a bacterial peptide-RRKYKQII-located in Staphylococcus aureus replication initiation protein. Thus CTL clones that recognized the viral, self, and bacterial peptides expressed a highly restricted alphabeta TCR phenotype. The CTL clones that recognized viral and self peptides were more oligoclonal, whereas clones that strictly recognized the viral peptide displayed a diverse TCR profile. Interestingly, the self and bacterial peptides equally were substantially less effective than the cognate viral peptide in sensitizing target cell lysis, and also resulted only in a weak reactivation of memory CTLs in limiting dilution assays, whereas the cognate peptide was highly immunogenic. The described crossreactions show that human antiviral, CD8(+) CTL responses can be shaped by peptide ligands derived from autoantigens and environmental bacterial antigens, thereby providing a firm structural basis for molecular mimicry involving class I-restricted CTLs in the pathogenesis of autoimmune disease.

The role of anaerobes in patients with ventilator-associated pneumonia and aspiration pneumonia: a prospective study

CONTEXT

Aspiration of oropharyngeal material, with its high concentration of anaerobic bacteria, has been implicated in the pathogenesis of both ventilator-associated pneumonia (VAP) and aspiration pneumonitis (AP). Consequently, patients with these disorders are usually treated with antimicrobial agents with anaerobic activity.

OBJECTIVE

To determine the incidence of anaerobic bacteria in patients with VAP and AP.

DESIGN

Prospective, nonrandomized, interventional study.

SETTING

University-affiliated community teaching hospital.

PATIENTS AND INTERVENTIONS

We performed sequential blind protected specimen brush (PSB) sampling and mini-BAL in 143 patients with 185 episodes of suspected VAP and 25 patients with AP who required mechanical ventilation. Quantitative aerobic and anaerobic cultures were performed on all specimens. Pneumonia was considered to be present when either > 500 cfu/mL cultured from blind PSB sampling or > 5,000 cfu/mL cultured from mini-BAL were present.

RESULTS

Using the predefined criteria, bacterial pneumonia was diagnosed in 63 of 185 suspected VAP episodes (34%) and 12 of 25 patients with AP (48%). At least one dose of an antibiotic was given in the 24 h prior to bacteriologic sampling in 106 suspected VAP episodes (57%) and in 12 patients with AP (48%). More than one pathogen was isolated from 11 VAP and four AP patients. Pseudomonas aeruginosa, Staphylococcus aureus, and enteric Gram-negative organisms were isolated most frequently from patients with VAP. In the patients with AP, enteric Gram-negative organisms were isolated in patients with GI disorders and Streptococcus pneumoniae and Haemophilus influenzae predominated in patients with "community-acquired" aspiration. Only one anaerobic organism was isolated from the entire group of patients; Veillonella paravula was isolated from a blind PSB specimen in a patient with suspected aspiration pneumonia.

CONCLUSION

Despite painstaking effort, we were able to isolate only one anaerobic organism (nonpathogenic) from this group of patients. The spectrum of aerobes in patients with VAP was similar to that reported in the literature. The organisms found in patients with AP was a reflection of the organisms likely to colonize the oropharynx. The use of antibiotics with anaerobic coverage may not be necessary in patients with suspected VAP and AP. Furthermore, penicillin G and clindamycin may not be the antibiotics of choice in patients with AP.

Innate immunity, cytokines, and pulmonary host defense

Effective host defense against bacterial infection is dependent on the activation and recruitment of phagocytic cells. The initiation, maintenance, and resolution of this inflammatory response in the setting of bacterial pneumonia is dependent on the expression of cytokines. As the complexities of the host-pathogen interaction are further dissected and unraveled, immunologic manipulation of cytokine expression will likely become an important adjuvant therapy in the treatment of serious lung infections.

Microbial factors leading to recurrent upper respiratory tract infections

The treatment or prophylaxis of upper respiratory tract infections such as otitis media, sinusitis and tonsillitis with penicillins can generate bacterial resistance caused by production of beta-lactamase or changes in the penicillin-binding proteins. This resistance can spread in the community even to untreated individuals. The prevalence of resistant organisms tends to increase in the winter months. Beta-lactamase-producing bacteria may interfere with the eradication of penicillin-susceptible organisms and may account for substantial numbers of therapeutic failures among cases of otitis media, sinusitis and tonsillitis. The presence of normal flora that possess interfering capabilities against potential pathogens is beneficial to the host. Such flora may enhance recovery and prevent infections of the tonsils by group A beta-hemolytic streptococci. Therapeutic use of antimicrobial agents that preserve the normal flora but overcome penicillin-susceptible or -resistant pathogens may enhance recovery from upper respiratory tract infections.

Role of endogenous and exogenous nitric oxide on intestinal mucosa and microflora in the rat

In the present study the effects of exogenous and endogenous nitric oxide (NO) on intestinal bacteria and on the intestinal tissue integrity have been investigated in healthy rats and in rats receiving bacterial endotoxin (LPS). A segment of jejunum was taken in order to evaluate tissue damage and hematoxylin-eosin staining; microbiological studies were carried out collecting stool samples. Administration of LPS (5 mg kg-1 i.v.) induced a moderate jejunal damage, which was completely prevented by NG-nitro-L-arginine methyl ester (L-NAME), 5 mg kg-1 s.c.), thus suggesting a damage of endogenous NO on the intestinal mucosa; sodium nitroprusside (SNP, 10 mg kg-1 os) reduced significantly jejunal damage induced by LPS. Endogenous NO produced by the administration of LPS resulted to be cytotoxic for all examined aerobic and anaerobic bacteria, while exogenous NO, released from SNP, showed an inhibitory effect only on Entero. faecalis and E. coli growth. From our data, it seems reasonable to conclude that high local levels of NO are required in order to observe jejunal damage and cytotoxic effects on aerobic and anaerobic faecal flora.

A prospective survey for central line skin-site colonization by the pathogen Malassezia furfur among hospitalized adults receiving total parenteral nutrition

BACKGROUND

Over 50 case reports suggest that Malassezia furfur is an emerging systemic pathogen in neonates who receive IV lipid emulsions. Because isolation of this fungus requires special culture techniques, which are not routinely used, the authors of many case reports of M. furfur infections in adults question whether infections caused by this organism are being underdiagnosed in older patients.

METHODS

Catheter insertion site colonization rates in adults receiving total parenteral nutrition (TPN) were prospectively evaluated in 149 hospitalized patients with 928 cultures handled specifically for M. furfur detection. Positive control samples consisted of M. furfur cultures in neonates and in adults, who had not been enrolled in the study, and of a separate positive culture obtained from a skin site inoculated with M. furfur.

RESULTS

M. furfur was not cultured from any of the 928 study samples (95% confidence interval [CI] -0.4% to +0.4%).

CONCLUSIONS

These results suggest that M. furfur is less of a threat to hospitalized adults receiving TPN than has been otherwise postulated. These data do not support the inclusion of special cultures for M. furfur in routine skin-site surveillance programs among hospitalized adults receiving TPN.

Overview of the etiology of wound infections with particular emphasis on community-acquired illnesses

Wound cultures represent a general catchall category for a group of extremely diverse anatomic samples that range from superficial specimens of cutaneous structures (folliculitis, cellulitis) to specimens revealing invasive infections involving deep fascial planes and muscle (myonecrosis). Because of the complex nature of these infective processes, the terminology associated with such infections is often imprecise and confusing. Wounds are the result of trauma, either intentionally or accidentally induced. Nosocomial wound infections result primarily from surgical procedures, the development of pressure sores, or catheterization. Community-acquired wound infections are often preceded by injuries resulting from occupational exposure or recreational activities and are associated with a greater diversity of microorganisms due to the exposure of open wounds to inhabitants of the microbial biosphere. This review provides a general overview of the categories of wound infections and describes their acquisition and clinical significance. Particular emphasis is placed on selected community-acquired wound infections and the etiologic agents associated with such conditions.

Prophylactic antibiotics in cataract operations

The rationale for prophylactic antibiotics in cataract operations must be continually reevaluated in light of cost-effectiveness and adverse reactions. The principles learned from wound infections associated with general surgical procedures should be applied to the limited knowledge about the rare event of endophthalmitis. Herein the literature on experimental and clinical wound infections in general surgical procedures is reviewed, with analysis of microbial flora, pathophysiology of wound infections, and pharmacokinetics of antibiotics. Experimental and clinical studies on prophylactic antibiotics to prevent endophthalmitis are reviewed, including information on topically applied antibiotics, chemical antisepsis, and administration of subconjunctival, intracameral, and systemic antibiotics. In addition, the benefits, limitations, and risks of the various types of prophylactic antibiotics are discussed. Because of the limited data on prophylactic antibiotics in cataract operations, providing dogmatic statements is difficult. General recommendations are offered based on the currently available literature, and a stratified approach is suggested based on wound construction and number of anterior segment maneuvers.

Enteric bacteria: friend or foe?

The normal gastrointestinal tract contains an enormous number of aerobic and anaerobic bacteria which normally enjoy a symbiotic relationship with the host but can have adverse effects with local and systemic consequences. The small intestine constitutes a zone of transition between the sparsely populated stomach and the luxuriant bacterial flora of the colon. Regulation of the intestinal flora depends on complex interactions between many factors including secretion of gastric acid, intestinal motility, biliary and pancreatic secretions, local immunity, the surface glycocalyx and mucus layer, and diet. Microbial interactions are also important, and can involve alterations in redox potential, substrate depletion and production of substances such as bacteriocins that inhibit bacterial growth. The beneficial effect of the normal enteric flora include the competitive exclusion of potentially pathogenic organisms, and the production of nutrients such as short-chain fatty acids (which represent an important energy source for the colonic mucosa) and vitamins. Detrimental effects of the enteric flora include competition for calories and essential nutrients, particularly by bacteria located in the small intestine, and a capacity to damage the mucosa, in some circumstances causing or contributing to inflammatory bowel disease. These problems can be accentuated by interference with the physiological regulation of intraluminal bacteria allowing overgrowth by a normal resident, or colonisation by transient pathogens. The pathophysiological consequences may involve direct damage to the intestinal mucosa, and bacterial metabolism of intraluminal constituents, for example forming deconjugated bile acids and hydroxylated fatty acids which stimulate fluid secretion. Additional problems arise if there is interference with the mucosal barrier since this can result in increased passage of bacteria and bacterial products stimulating mucosal inflammation, while bacterial translocation can result in bacteraemia and septicaemia. Problems associated with bacterial pathogens are illustrated by the properties of the spectrum of pathogenic Escherichia coli, some of which facilitate long-term colonisation by adherence to the surface or invasion of enterocytes.

Nosocomial acquisition of Escherichia coli by infants delivered in hospitals

The delivery of infants in hospitals is desirable for obstetric reasons, but exposes the neonates to the microbiological hazards of a maternity unit. When neonates are born and cared for in hospital, the Escherichia coli strains that colonize the intestine tend to be acquired from the environment or from other babies, and are potentially pathogenic. The colonization of the infant with maternal flora should be promoted by strict rooming-in of mother and baby, or by delivery at home.

Spondylarthropathies: from gut to target organs

Recent studies strongly support the concept that gut and joint inflammation are closely related. Progress also has been made in identifying individual mechanisms that contribute to the pathogenesis of joint disease in IBD and in undifferentiated SpAs. However, the interrelationship of these mechanisms that result in chronic disease manifestations at a site distant from the initiating event remain to be elucidated. The local absence of homing molecule receptors in the gut wall combined with an expression of these receptors in target organs can be responsible for the transformation of the synovial membrane and/or the enthesis into an aberrant tertiary lymphoid organ of the gut.

Respiratory infections: community-acquired pneumonia and newer microbes

Respiratory infections, especially community-acquired forms of pneumonia (CAP), are challenging for clinicians because (1) a causative microorganism can only be found in about 50% of cases; (2) initial therapy, therefore, must be based on a probable or most likely etiology in the context of the patient's overall medical condition; and (3) new microbes or those considered previously as normal flora or less virulent forms seem responsible for some cases. It is important to be acquainted with new causes of infection which include Legionella species, Chlamydia pneumoniae, diphtheroids in certain instances (Corynebacterium pseudodiphtheriticum), and viruses such as the Hanta strains. Infections with Bordetella pertussis are increasing. However, the ever present and most common cause of CAP, Streptococcus pneumoniae, continues to present problems because of increasing antibiotic resistance, the high case fatality rate when bacteremia accompanies pneumonia, and the inability to give prophylactic immunization to all people with risk factors for this infection.

Turnover of nonencapsulated Haemophilus influenzae in the nasopharynges of otitis-prone children

Restriction enzyme analysis of total genomic DNA was applied to study the epidemiology of nontypeable Haemophilus influenzae (NTHI) isolated from the nasopharynges of children with recurrent acute otitis media (AOM). The turnover of strains, as judged from genetic fingerprinting of a total of 213 H. influenzae isolates collected prospectively during a 2-year study period from 38 children under 3 years of age, was examined in relation to episodes of AOM as well as to courses of antibiotic treatment. The children were selected if they had had at least one episode of AOM before 1 year of age and if more than two nasopharyngeal isolates of H. influenzae were recovered. The 213 H. influenzae isolates (90% NTHI) recovered corresponded to 128 different DNA fingerprints. Fifty-eight percent of the fingerprints were observed only once, whereas 42% appeared on two or more occasions in isolates from the same individual or in close relatives, i.e., brothers and sisters. Sixty-seven percent of these strains had a minimum colonization period of 2 months or less. Intermittent nasopharyngeal colonization periods longer than 5 months could be demonstrated for 13% of the strains. The present data suggest that intermittent colonization is due to endogenous reinfections. Genetically identical NTHI strains from unrelated individuals were never identified. As expected from the observation of a relatively high proportion of persistent colonizations, no correlation was found between episodes of AOM and the acquisition of new strains of H. influenzae, nor was any direct relation between antimicrobial therapy and the elimination of nasopharyngeal colonization with a particular strain of H. influenzae observed.

[Laboratory diagnostic peculiarities of mycoses in immunosuppressed patients]

Domestic invasive mycoses are typically present as secondary diseases in patients definitely immunocompromised. This truth should not obscure the fact that a transient overload of the immune system, e.g. in the polytrauma patients, may likewise favour the development of mycoses. The two groups of patients show a comparable course of infection and, to some extent, diagnostic signs: surveillance cultures and monitoring of antibodies are more helpful with trauma patients and less reliable in the typically immunocompromised patients. In the latter, however, antigen tests may yield more reliable results than in the trauma patients. The different functional capacities of the immune system in the two groups of patients may also affect the appearance of fungal elements, particularly of aspergilli, in secretions and biopsies.

The occurrence of duplicate lysyl-tRNA synthetase gene homologs in Escherichia coli and other procaryotes

The lysyl-tRNA synthetase (LysRS) system of Escherichia coli K-12 consists of two genes, lysS, which is constitutive, and lysU, which is inducible. It is of importance to know how extensively the two-gene LysRS system is distributed in procaryotes, in particular, among members of the family Enterobacteriaceae. To this end, the enterics E. coli K-12 and B; E. coli reference collection (ECOR) isolates EC2, EC49, EC65, and EC68; Shigella flexneri; Salmonella typhimurium; Klebsiella pneumoniae; Enterobacter aerogenes; Serratia marcescens; and Proteus vulgaris and the nonenterics Pseudomonas aeruginosa and Bacillus megaterium were grown in AC broth to a pH of 5.5 or less or cultured in SABO medium at pH 5.0. These growth conditions are known to induce LysRS activity (LysU synthesis) in E. coli K-12. Significant induction of LysRS activity (twofold or better) was observed in the E. coli strains, the ECOR isolates, S. flexneri, K. pneumoniae, and E. aerogenes. To demonstrate an association between LysRS induction and two distinct LysRS genes, Southern blotting was performed with a probe representing an 871-bp fragment amplified from an internal portion of the coding region of the lysU gene. In initial experiments, chromosomal DNA from E. coli K-12 strain MC4100 (lysS+ lysU+) was double digested with either BamHI and HindIII or BamHI and SalI, producing hybridizable fragments of 12.4 and 4.2 kb and 6.6 and 5.2 kb, respectively. Subjecting the chromosomal DNA of E. coli K-12 strain GNB10181 (lysS+ delta lysU) to the same regimen established that the larger fragment from each digestion contained the lysU gene. The results of Southern blot analysis of the other bacterial strains revealed that two hybridizable fragments were obtained from all of the E. coli and ECOR collection strains examined and S. flexneri, K. pneumoniae, and E. aerogenes. Only one lysU homolog was found with S. typhimurium and S. marcescens, and none was obtained with P. vulgaris. A single hybridizable band was found with both P. aeruginose and B, megaterium. These results show that the dual-gene LysRS system is not confined to E. coli K-12 and indicate that it may have first appeared in the genus Enterobacter.

Pulmonary host defenses

Well functioning host defenses in the respiratory tract effectively remove microbes and other debris that reach the conducting airways and alveoli, and this usually prevents infections. People with acute and chronic illnesses can experience failure of any number of these defense mechanisms that allow pneumonia (and bacteremia) to occur, often with considerable morbidity and mortality. People with alcohol-related illnesses are a susceptible group for infections, and many strategies are needed to help them such as moderating alcohol abuse and dependence, providing timely immunizations to create antibody against encapsulated bacteria, anticipating microbial colonization of mucosal areas that can promote infection, giving excellent supporting medical care in crisis situations, and prescribing appropriate antibiotics. New approaches to boosting inflammatory reactions to control lung infections better with cytokines and new immunomodulator therapies must be investigated now.

Host-microbe interaction in the gastrointestinal tract

In order for an infection to occur, the target organ must come in contact with sufficient microbes, the microbe must possess specific virulence factors, these virulence factors must be expressed, and the defenses of the organ system must be overcome. This dynamic process, which is ongoing in all living entities, can be described by the following relationship: [formula: see text] The establishment of infection first occurs in a particular organ. This phenomenon is known as tissue trophism and the association of microbes with organ systems governs the practice of clinical microbiology and infectious disease. With some microbes (e.g., Giardia, Cryptosporidium) the interaction with the particular organ is so specific that infections are almost always confined to one site; with others (e.g., Salmonella, enterovirus) the microbe has the potential to become systemic. When attempting to establish health risk assessment from microbes by contact with food and drinking water, one must therefore consider that the gastrointestinal tract is a complex organ system with a variety of specific host defense mechanisms. It is only when the microbe has particular virulence factors for sites in gastrointestinal tract, and the specific host defense mechanisms in the gastrointestinal tract are breached, that infection of this organ system occurs. Therefore, the general terms "immunosuppression" or "immunocompromise" are meaningless unless the specific immune defect is known. A description of the microbial virulence factors active against the gastrointestinal tract and the defense mechanisms of this organ system are reviewed to provide a biological basis health risk assessment and future food and drinking water regulations.

Host defenses against respiratory infection

The respiratory tract is protected from infection by its formidable mechanical and cellular defenses, supplemented when necessary by inflammatory and immune responses. Impairments in these defenses develop as a result of underlying disease and therapeutic interventions. Specific defects in host defenses often predispose to infection with particular etiologic agents. New opportunities for the therapeutic augmentation of defenses are emerging that may be particularly helpful in the care of immunocompromised patients.

Host defence capacities of pulmonary surfactant: evidence for 'non-surfactant' functions of the surfactant system

The most well characterized function of pulmonary surfactant is its ability to reduce surface tension at the alveolar air-liquid interface, thereby preventing lung collapse. However, several lines of evidence suggest that surfactant may also have 'non-surfactant' functions: specific components of surfactant (proteins and phospholipids) may interact with different alveolar cells, inhaled particles and micro-organisms modulating pulmonary host defence systems. SP-A, the most abundant surfactant protein, binds to alveolar macrophages via a specific surface receptor with high affinity [128]. Such binding effects the release of reactive oxygen species from resident alveolar macrophages if SP-A is properly presented to the target cell. SP-A also stimulates chemotaxis of alveolar macrophages [142], and serves as an opsonin in the phagocytosis of herpes simplex virus [161] Candida tropicalis [138] and various bacteria [137]. In addition, SP-A enhances the uptake of particles by monocytes and culture-derived macrophages [140] and improves bacterial killing. SP-D, another hydrophobic surfactant-associated protein, might interact with alveolar macrophages as well, stimulating the release of oxygen radicals [148], while for the hydrophilic surfactant proteins SP-B and SP-C no macrophage interactions have been described so far. SP-A and SP-D are members of the so-called 'collectins', pattern recognition molecules involved in first line defence. While some surfactant proteins appear to stimulate certain macrophage defence functions, surfactant phospholipids seem to inhibit those of lymphocytes. Suppressed lymphocyte functions include lymphoproliferation in response to mitogens and alloantigens, B cell immunoglobulin production and natural killer cell cytotoxicity. Concerning surfactant's phospholipid composition phosphatidylglycerol is more suppressive than phosphatidylcholine on a molar basis [38]. Bovine surfactant has an immunosuppressive effect on the development of hypersensitivity pneumonitis in a guinea pig model [150]. Despite these interesting observations, several important questions concerning the interactions of surfactant components with pulmonary host defence systems remain unanswered. Sufficient host defence in the lungs works through various humoral-cellular systems in conjunction with the specific anatomy of the airways and the gas exchange surface--how does the surfactant system fit into this network? Surfactant and alveolar cells are both altered during lung injury--is there a relationship between alveolar cells from RDS patients and the endogenous surfactant isolated from such patients? How does exogenous surfactant as used for substitution therapy modulate the defence system of the host? Some of those artificial surfactants have been shown to inhibit the endotoxin-alveolar macrophages, PMNs and monocytes including IL-1, IL-6 and TNF [139,152].(ABSTRACT TRUNCATED AT 400 WORDS)

Piperacillin/tazobactam in the treatment of polymicrobial infections

Polymicrobial infections are characterized by the presence of micro-organisms from more than one group of bacteria. Empirical treatment of polymicrobial infections requires an agent active against both anaerobic and aerobic/facultative bacteria. An aminoglycoside used in combination with an anti-anaerobe agent is commonly used to treat polymicrobial infections. However, aminoglycoside nephrotoxicity and treatment failures raise questions about the use of such regimens. Among non-aminoglycoside treatment regimens such as penicillin and cephalosporins, effectiveness has been compromised by bacteria producing extended spectrum beta-lactamases. Cefoxitin shows satisfactory results for treatment of intra-abdominal infections. Other studies have shown good results with imipenem, cefotetan and piperacillin used as single agents. Piperacillin/tazobactam, a new combination broad-spectrum antibiotic and potent beta-lactamase inhibitor, can be used for the treatment of infections caused by piperacillin-sensitive micro-organisms as well as beta-lactamase-producing, piperacillin-resistant organisms. This broad-spectrum activity is appropriate for infections traditionally treated empirically by double or triple antibiotic therapy.

Oral and oropharyngeal prevalence of Enterobacteriaceae in humans: a review

Members of the Enterobacteriaceae family are widely distributed in nature and exhibit substantial diversity in ecology, host range and pathogenic potential for man. While wide discrepancies in methodology exist between epidemiological studies, the available data indicate an increased prevalence of oral and/or oropharyngeal Enterobacteriaceae carriage in patients with illnesses of varying severity compared with healthy subjects. This paper reviews the prevalence of Enterobacteriaceae in the oral and oropharyngeal region of healthy human subjects and those affected by different disease entities, and discusses the complexities associated with collating and interpreting such data. The effect of antimicrobials and antiseptics on oral and oropharyngeal Enterobacteriaceae has also been reviewed, while highlighting the gaps in knowledge and future research directions.

Oropharyngeal flora in asthma and in chronic obstructive pulmonary disease. Indigenous oropharyngeal microorganisms in outpatients with asthma or chronic obstructive pulmonary disease

In vitro and in vivo studies have shown that various strains of "viridans streptococci" (nongroupable alpha-hemolytic streptococci) inhabiting the oropharynx suppress the growth of gram-positive and gram-negative microorganisms. We conducted an inventory of the oropharyngeal flora from ambulatory asthma and chronic obstructive pulmonary disease (COPD) patients and a control group to examine the interaction between viridans streptococci and potential pathogens in vivo. In addition, the difference in colonization patterns of these bacteria was studied. Oral washings from 195 patients, 48 asthma (24.6%), 147 COPD (75.4%), and 157 control subjects were examined microbiologically on two occasions with a 2-wk interval, resulting in a total of 384 and 295 oral washings, respectively. All patients were in a stable phase of disease throughout the study. The distribution of low (< or = 10(4)/ml) or high (> or = 10(5)/ml) concentrations of viridans streptococci did not differ substantially between asthma or COPD patients and control subjects. Potentially pathogenic microorganisms found in a low (< or = 10(4)/ml) or high (> or = 10(5)/ml) concentration were equally distributed between the two groups. Staphylococcus aureus and beta-hemolytic streptococci were found significantly less often in the asthma and COPD group (p < 0.005 and p < 0.0005, respectively), but the prevalence of Enterobacteriaceae species was significantly higher (p < 0.0005). No correlation was found between the concentration of viridans streptococci and the prevalence of gram-negative microorganisms. These findings suggest that viridans streptococci are probably not responsible for growth control of gram-negative microorganisms in vivo.(ABSTRACT TRUNCATED AT 250 WORDS)

Pathogenesis of urinary tract infection--experimental studies of vaginal resistance to colonization

The review summarizes studies of vaginal colonization resistance against Escherichia coli in a primate model. The genital flora surrounding the urethral orifice exerts a strong colonization resistance. Amoxicillin profoundly disturbs the normal vaginal microflora, reduces its adherence to vaginal epithelial cells in vivo and promotes a persistent vaginal E. coli colonization. Certain cephalosporins may have a similar effect. The induced ecological changes mimic those seen in patients with recurrent urinary tract infections (UTI). Amoxicillin also promotes the spread of E. coli from rectum to vagina, which may be of clinical significance. Trimethoprim and nitrofurantoin do not have these effects. The natural colonization resistance could not clearly be correlated with the presence of lactobacilli, which were only transiently reduced by amoxicillin. The colonization resistance against E. coli could only partly be restored by vaginal instillation of lactobacilli, but was fully restored by flushing of the whole vaginal flora from a healthy monkey. Clinical observations suggest that accumulation of E. coli around the urethral orifice increases the risk of UTI. We conclude that antibiotics and other compounds that interfere with the normal genital flora may increase the risk of UTI. This should influence the choice of antibiotics in the treatment of UTI.

Diagnosis of invasive mycoses in severely immunosuppressed patients

In compromised patients, invasive mycoses are being observed at an increasing frequency and with a broadening spectrum of causative fungi. The rapid and definitive diagnosis of such opportunistic mycoses requires the synoptical consideration of predisposing clinical conditions, of culture isolates, and of the results of nonculture techniques. At present, the latter comprise the monitoring of specific antibodies and of fungal antigens, and the microscopical examination of suspected biopsies. The validity of the individual techniques (e.g., the monitoring of antibodies or antigens) varies with individual mycoses. Alternative methods for monitoring fungal metabolites or nucleic acids are still in the developmental stage. Particularly the amplification of DNA by the polymerase chain reaction (PCR) has a high diagnostic potential. However, at present, it is uncertain whether PCR allows the necessary distinction between colonization and truly invasive infection, and whether PCR can be simplified sufficiently to allow the continuous surveillance of high-risk patients.

Micro-ecology of the nasopharyngeal bacterial flora in otitis-prone and non-otitis-prone children

The quantitative bacteriology of the adenoid was studied in otitis-prone and non-otitis-prone children. alpha-hemolytic Streptococci (Viridans Streptococci) appeared to be predominant normal flora in the healthy nasopharynx. There was a decrease in alpha-hemolytic Streptococci in the otitis-prone child compared to the non-otitis-prone child. Concomitantly, there appears to be an increase in both nontypable Haemophilus influenzae (NTHI) and S. pneumoniae in the nasopharyngeal flora in the otitis-prone child. The mechanisms responsible for this alteration of the micro-ecology of bacteria of the nasopharynx may be related, in part, to factors that alter mucociliary function. These factors could be viral infection, allergy, local and systemic immunological deficiency and the indiscriminate use of antibiotics. An understanding of the relationship between the normal flora and the potential pathogens may be important in the understanding of both the pathogenesis of otitis media (OM) and possibly the treatment of this disease entity.

Immune response to outer membrane antigens of Moraxella catarrhalis in children with otitis media

The systemic and local antibody responses to homologous strains of Moraxella catarrhalis were investigated in 14 children with otitis media. A total of 8 children (57%) demonstrated a rise in serum antibody of the immunoglobulin G (IgG) (5 of 14), IgM (5 of 14), or IgA (6 of 14) classes of immunoglobulin to outer membrane antigens. Local antibody consisted of IgG (100%), IgM (29%), and IgA (71%). The IgG and IgA specific antibody present in middle-ear effusions appeared to represent local production rather than passive diffusion from the systemic circulation. These data suggest that young children develop an antibody response to M. catarrhalis in the middle ear during otitis media but fail to develop systemic antibody in a uniform manner.