Gentamicin-resistantPseudomonas aeruginosa: Concepts regarding their evolution and attenuated virulence

Pseudomonas aeruginosa, a free-living bacterial species, is a major nosocomial pathogen, especially of compromised patients within medical facilities. Numerous factors contribute to the ecological selection of this bacterial species within the hospital environment, among which the expression of newly acquired or quiescent enzymatic capability seems par-amount. The emergence of pathogenic strains ofP. aeruginosa appears to be gradual, embodying a transition of strains from their natural aquatic environment, to establishing inanimate (hospital) and animate (human) reservoirs. In this stepwise transition, subsets ofP. aeruginosa may evolve which express a survival trait, for example, gentamicin resistance, but concomitantly suffer a loss of invasive potential. In this study,P. aeruginosa strains from natural [22], hospital [11], and stool [17] sources were evaluated for their physiological and exoenzymatic activity and compared with gentamicin-resistantP. aeruginosa (GRPA) strains [49] of clinical origin. As a whole, environmental and hospital isolates showed reduced enzymatic potential, for example, frequency of production of elastase, lipase, deoxyribonuclease, and pyocyanin production. Human fecal isolates most closely resembled the prototype of human invasiveP. aeruginosa in their gentamicin susceptibility (95%) and increased frequencies of exoenzymes, including elastase production. On the other hand, GRPA were frequently apyocyanogenic (9/49), lacked extracellular enzymes correlated with pathogenicity, and were rarely isolated from systemic sites. When encountered, these strains appeared to represent colonization of a body site rather than incitants of overt infection. As a subset ofP. aeruginosa, gentamicin resistance was seen predominantly among serotype 11 strains, and encountered most frequently from patients with localized urinary tract infections.     

Mechanistic understanding of Phenyllactic acid mediated inhibition of quorum sensing and biofilm development in Pseudomonas aeruginosa

Pseudomonas aeruginosa depends on its quorum sensing (QS) system for its virulence factors’ production and biofilm formation. Biofilms of P. aeruginosa on the surface of indwelling catheters are often resistant to antibiotic therapy. Alternative approaches that employ QS inhibitors alone or in combination with antibiotics are being developed to tackle P. aeruginosa infections. Here, we have studied the mechanism of action of 3-Phenyllactic acid (PLA), a QS inhibitory compound produced by Lactobacillus species, against P. aeruginosa PAO1. Our study revealed that PLA inhibited the expression of virulence factors such as pyocyanin, protease, and rhamnolipids that are involved in the biofilm formation of P. aeruginosa PAO1. Swarming motility, another important criterion for biofilm formation of P. aeruginosa PAO1, was also inhibited by PLA. Gene expression, mass spectrometric, functional complementation assays, and in silico data indicated that the quorum quenching and biofilm inhibitory activities of PLA are attributed to its ability to interact with P. aeruginosa QS receptors. PLA antagonistically binds to QS receptors RhlR and PqsR with a higher affinity than its cognate ligands N-butyryl-l-homoserine lactone (C₄–HSL) and 2-heptyl-3,4-dihydroxyquinoline (PQS; Pseudomonas quinolone signal). Using an in vivo intraperitoneal catheter-associated medaka fish infection model, we proved that PLA inhibited the initial attachment of P. aeruginosa PAO1 on implanted catheter tubes. Our in vitro and in vivo results revealed the potential of PLA as anti-biofilm compound against P. aeruginosa.

     

Murein degradation inEscherichia coli infected with bacteriophage ϕX174

LY 127935 (moxalactam), a new 1-oxa cephalosporin, was evaluated in vitro in agar dilution testing against 177 different clinical isolates of cephalothin-resistant Enterobacteriaceae andPseudomonas aeruginosa in parallel with amikacin, cephalothin, cefoxitin, and cefamandole. Ninety percent of the isolates were also gentamicin-resistant by disk testing. LY 127935 showed a very high degree of activity against cephalothin-resistant organisms but amikacin was more active in vitro, particularly againstP. aeruginosa. Cefoxitin and cefamandole were consistently less active than either LY 127935 or amikacin.     

Characterisation of potential virulence markers in <Emphasis Type="Italic">Pseudomonas aeruginosa</Emphasis> isolated from drinking water

Pseudomonas aeruginosa isolates from tap water, mineral water, and artesian well water were investigated for their ability to produce different potential virulence factors or markers such as hemolysins, hemaglutinins, cytotoxins and their ability to adhere to epithelial cells and to abiotic surfaces. The susceptibility to antibiotics, human serum sensitivity and the survival of P. aeruginosa isolates in a chlorinated environment were also examined. Of the 30 isolates tested, 16 possessed the capacity to adhere to abiotic surfaces, and 28 to adhere to epithelial cells; 30 were capable of producing hemolysins, 27 produced cytotoxins, 9 hemagglutinins, and 18 were classified as serum-resistant. For the lowest concentration of chlorine (0.2 mg/l) tested, no killing of biofilm bacteria could be discerned, even after prolonged exposure to the agent. Although all the drinking water isolates were susceptible to aztreonam, cefepime, ceftazidime, ciprofloxacin, imipenem, meropenem, piperacillin-tazobactam, and polymyxin, the P. aeruginosa isolates were resistant to one or more antibiotics. The increasing prevalence of resistance in the isolates from environmental sources may have important therapeutic implications. A notable proportion of the P. aeruginosa isolates from drinking water were able to develop virulence factors, and the incidence of virulence properties was not statistically different among the three sources. A more extensive study of the virulence properties of this bacterium by toxic assays on animals should be explored. Still more interesting would be toxicity assays on immuno-deficient animals with isolates from drinking water in order to better understand the health risk these bacteria may present.     

Resistance ofPseudomonas aeruginosa to sodium dimethyldithiocarbamate by adaptation

Resistance and the development thereof inPseudomonas aeruginosa to the bactericide sodium dimethyldithiocarbamate (SMT) was investigated.P. aeruginosa was cultured in nutrient-poor broth in the presence of subinhibitory concentrations of SMT. It adapted over 21 days of exposure from 250 g·ml^–1 to 490 g·ml^–1. The initial high MIC was ascribed to exclusion of SMT by the lipopolysaccharide layer, since removal thereof by EDTA rendered cells highly susceptible. The alginate-producing mutant PAO 579 was much more susceptible to SMT than was its parent PAO 381, indicating that extracellular polysaccharide does not act as an exclusion barrier to SMT. Following 24 h of exposure to SMT,P. aeruginosa had an altered profile of outer membrane proteins as determined by SDS-PAGE. Resistant cells had a further altered profile. Resistance ofP. aeruginosa is ascribed to a change in the outer membrane protein profile, leading to improved exclusion of SMT.     

Mutual Influences of Pseudomonas aeruginosa and Desulfovibrio desulfuricans on their Adhesion to Stainless Steel

The mutual influences of Pseudomonas aeruginosa PAO1 and Desulfovibrio desulfuricans subsp. desulfuricans (ATCC 29577) on their adhesion to stainless steel were investigated in batch and column experiments. It was found that P. aeruginosa promoted the adhesion of D. desulfuricans under conditions of turbulence, but not under quiescent conditions. The enhancement involved the alignment of most D. desulfuricans along P. aeruginosa cells and was attributed to the additional interaction surface area provided by adhered P. aeruginosa to aligning D. desulfuricans cells. A slightly positive effect of pre-adhered D. desulfuricans on the adhesion of P. aeruginosa was found. Under condition of laminar flow, substantially better adhesion of D. desulfuricans to confluent P. aeruginosa biofilms than to steel was observed. The mutual influences are discussed in terms of more favorable adhesion energies and the influence of changed hydraulic conditions due to the roughness of P. aeruginosa biofilms.     

Comparative in vitro activity of moxalactam (LY127935), other beta-lactam antibiotics,and aminoglycosides

Moxalactam (LY127935), a novel beta-lactam antibiotic, was compared with semisynthetic penicillins, cephalosporins, and aminoglycosides by the agar dilution method against 5,317 recent clinical isolates of facultative and anaerobic bactria. At 0.5 μg/ml, moxalactam inhibited 90% of all Gram-negative bacilli tested except forPseudomonas aeruginosa (81% inhibited by 32 μg/ml) andAcinetobacter calcoaceticus (88% inhibited by 32 μg/ml). More than 90% ofBacteroides fragilis andStaphylococcus aureus were inhibited by 4 μg/ml and 8 μg/ml, respectively. Moxalactam was at least 16-fold more active by weight than cephalothin, cefamandole, and cefoxitin forEscherichia coli, Klebsiella pneumoniae, andEnterobacter species, and 2- to 4-fold more active than cefoxitin forB. fragilis. Moxalactam was 4-fold less active than cefamandole and cephalothin forS. aureus and 2- to 4-fold less active than piperacillin forP. aeruginosa. Moxalactam was as active or more active than the aminoglycosides for all facultative Gram-negative bacilli except forP. aeruginosa. Moxalactam was inhibitory (minimal inhibitory concentration <16 μg/ml) for 20/27 gentamicin-resistant isolates and 8/13 amikacin-resistant organisms. Moxalactam’s in vitro activity against Gram-negative bacilli is markedly superior to presently available cephalosporins and, except forP. aeruginosa, is comparable to the aminoglycosides.     

Relationship between cystic fibrosis respiratory tract bacterial communities and age,genotype, antibiotics and Pseudomonas aeruginosa

Polymicrobial bronchopulmonary infections in cystic fibrosis (CF) cause progressive lung damage and death. Although the arrival of Pseudomonas aeruginosa often heralds a more rapid rate of pulmonary decline, there is significant inter‐individual variation in the rate of decline, the causes of which remain poorly understood. By coupling culture‐independent methods with ecological analyses, we discovered correlations between bacterial community profiles and clinical disease markers in respiratory tracts of 45 children with CF. Bacterial community complexity was inversely correlated with patient age, presence of P. aeruginosa and antibiotic exposure, and was related to CF genotype. Strikingly, bacterial communities lacking P. aeruginosa were much more similar to each other than were those containing P. aeruginosa, regardless of antibiotic exposure. This suggests that community composition might be a better predictor of disease progression than the presence of P. aeruginosa alone and deserves further study.     

Mapping QTLs for pre-harvest sprouting tolerance on chromosome 2D in a synthetic hexaploid wheat×common wheat cross

Based on segregation distortion of simple sequence repeat (SSR) molecular markers, we detected a significant quantitative trait loci (QTL) for pre-harvest sprouting (PHS) tolerance on the short arm of chromosome 2D (2DS) in the extremely susceptible population of F₂ progeny generated from the cross of PHS tolerant synthetic hexaploid wheat cultivar ‘RSP’ and PHS susceptible bread wheat cultivar ‘88–1643’. To identify the QTL of PHS tolerance, we constructed two SSR-based genetic maps of 2DS in 2004 and 2005. One putative QTL associated with PHS tolerance, designatedQphs.sau-2D, was identified within the marker intervalsXgwm261-Xgwm484 in 2004 and in the next year, nearly in the same position, between markerswmc112 andXgwm484. Confidence intervals based on the LOD-drop-off method ranged from 9 cM to 15.4 cM and almost completely overlapped with marker intervalXgwm261-Xgwm484. Flanking markers near this QTL could be assigned to the C-2DS1-0.33 chromosome bin, suggesting that the gene(s) controlling PHS tolerance is located in that chromosome region. The phenotypic variation explained by this QTL was about 25.73–27.50%. Genotyping of 48 F₆ PHS tolerant plants derived from the cross between PHS tolerant wheat cultivar ‘RSP’ and PHS susceptible bread wheat cultivar ‘MY11’ showed that the allele ofQphs.sau-2D found in the ‘RSP’ genome may prove useful for the improvement of PHS tolerance.     

Cultivar response against root-infecting fungi and efficacy of Pseudomonas aeruginosa in controlling soybean root rot

Abstract

A study was conducted in the greenhouse to examine the resistance of three soybean cultivars against root-infecting fungi, and to determine the role of five strains of Pseudomonas aeruginosa in protecting the roots from these fungal pathogens. In this study soybean cv RAWAL was found to be less susceptible against charcoal rot fungus Macrophomina phaseolina than cvs PARC and BRAGG. Most of the strains of P. aeruginosa used as seed dressing significantly reduced M. phaseolina and Rhizoctonia solani infection on all three cvs PARC, BRAGG and RAWAL (p < 0.05). Most of the strains of P. aeruginosa were effective on cv PARC against Fusarium solani infection, while on cv BRAGG P. aeruginosa strain Pa₃, and on cv RAWAL strain Pa₅ were effective. Both strains Pa₃ and Pa₂₂ gave maximum plant height and fresh weight of shoots, respectively on cvs PARC and BRAGG than other strains. These characteristics make these P. aeruginosa strains good candidates for use as biocontrol agents against soil-borne plant pathogens.     

Q pili enhance the attachment of Moraxella bovis to bovine corneas in vitro

Moraxella bovis, the causative agent of infectious bovine keratoconjunctivttis, exhibits several virulence factors, including pili, haemotysin, leukotoxin, and proteases. The pili are filamentous appendages which mediate bacterial adherence. Prior studies have shown that Q-piliated M. bovis Epp63 are more infectious and more pathogenic than l-piliated and nonpiliated isogenic variants, suggesting that Q pili perse or traits associated with Q-pilin expression, promote the early association of Q-pillated bacteria with bovine corneal tissue. In order to better evaluate the role of Q pili in M. bovis attachment, several M. bovis strains and a recombinant P. aeruginosa strain which elaborates M. bovis Q pili but not P. aeruginosa PAK pili, were evaluated using an in vitro corneal attachment assay. For each strain tested, piliated organisms attached better than non-piliated bacteria. M. bovis Epp63 Q-piIiated bacteria adhered better than either the l-piliated or non-piliated isogenic variants. Finally, recombinant P. aeruginosa organisms elaborating M. bovis Q pili adhered better than the parent P. aeruginosa strain which did not produce M. bovis pili. These results indicate that the presence of pili, especially Q pili, enhances the attachment of bacteria to bovine cornea In vitro.     

Molecular epidemiology of pseudomonas aeruginosa clinical isolates from Portuguese Central Hospital

The relatedness between clinical isolates of P. aeruginosa obtained from patients during their stay in a Portuguese Central Hospital was evaluated. Genotypic fingerprinting (M13-PCR), phenotypic methods (biotyping and antibiotyping) and epidemiological information (spatial and temporal links) were used to evaluate the relatedness between 88 clinical isolates (68 patients), selected randomly out of 189. Sixty-two M13 types were found, 12 of them containing isolates from more than one patient. Thirty-four antibiotypes were found, as well as a significant association (p < 0.05) between epidemic isolates and multiresistance patterns. The nosocomial transmission of P. aeruginosa strains may be limited since M13 typing demonstrated a high degree of diversity among all the isolates, suggesting the occurrence of mainly independent infectious episodes. The results show the possible occurrence of cross-acquisition, cross-colonization and cross-infection and suggest an epidemic population structure for P. aeruginosa in this hospital.     

The effects of glutaraldehyde on the control of single and dual biofilms of Bacillus cereus and Pseudomonas fluorescens

Glutaraldehyde (GLUT) was evaluated for control of single and dual species biofilms of Bacillus cereus and Pseudomonas fluorescens on stainless steel surfaces using a chemostat system. The biofilms were characterized in terms of mass, cell density, total and matrix proteins and polysaccharides. The control action of GLUT was assessed in terms of inactivation and removal of biofilm. Post-biocide action was characterized 3, 7, 12, 24, 48 and 72 h after treatment. Tests with planktonic cells were also performed for comparison. The results demonstrated that in dual species biofilms the metabolic activity, cell density and the content of matrix proteins were higher than those of either single species. Planktonic B. cereus was more susceptible to GLUT than P. fluorescens. The biocide susceptibility of dual species planktonic cultures was an average of each single species. Planktonic cells were more susceptible to GLUT than their biofilm counterparts. Biofilm inactivation was similar for both of the single biofilms while dual biofilms were more resistant than single species biofilms. GLUT at 200 mg l^?1 caused low biofilm removal (<10%). Analysis of the post-biocide treatment data revealed the ability of biofilms to recover their activity over time. However, 12 h after biocide application, sloughing events were detected for both single and dual species biofilms, but were more marked for those formed by P. fluorescens (removal >40% of the total biofilm). The overall results suggest that GLUT exerts significant antimicrobial activity against planktonic bacteria and a partial and reversible activity against B. cereus and P. fluorescens single and dual species biofilms. The biocide had low antifouling effects when analysed immediately after treatment. However, GLUT had significant long-term effects on biofilm removal, inducing significant sloughing events (recovery in terms of mass 72 h after treatment for single biofilms and 42 h later for dual biofilms). In general, dual species biofilms demonstrated higher resistance and resilience to GLUT exposure than either of the single species biofilms. P. fluorescens biofilms were more susceptible to the biocide than B. cereus biofilms.     

Role of Pseudomonas aeruginosa lipopolysaccharides in modulation of biofilm and virulence factors of Enterobacteriaceae

Enterobacteriaceae members are largely distributed in the environment and responsible for a wide range of bacterial infections in hospitalized patients. Pseudomonas aeruginosa (P. aeruginosa) causes severe nosocomial infections associated with severe inflammation due to its potent virulent factors including lipopolysaccharide (LPS). The aim of this study is to assess the bacterial LPS effect on Enterobacteriaceae biofilm and other virulence factors in vitro. The effect of P. aeruginosa LPS on biofilm formation of two other species of Enterobacteriaceae (Escherichia coli and Klebsiella pneumoniae) was assessed using a standard biofilm assay. PCR was performed on genes of biofilm and virulence factors. Expression of biofilm, type-1-fimbriae and serum resistance genes in treated and untreated cells was measured with RT-PCR. P. aeruginosa LPS has the ability to stimulate biofilm formation and stabilize the already formed biofilm significantly in all tested strains. In addition, LPS significantly increased the level of expression of Bss, FimH, and Iss genes when measured by RT-PCR. P. aeruginosa LPS has a direct stimulatory effect on the biofilm formation, type-1-fimbriae, and serum resistance in both E. coli and K. pneumoniae. So, the presence of P. aeruginosa in mixed infection with Enterobactereacea leads to increase their virulence.

     

Widespread Emergence of Multidrug Resistant <Emphasis Type="Italic">Pseudomonas aeruginosa</Emphasis> Isolated from CSF Samples

Bacterial infections of the central nervous system, especially acute infections such as bacterial meningitis require immediate, invariably empiric antibiotic therapy due to the widespread emergence of resistance among bacterial species. Nosocomial infections by Pseudomonas aeruginosa have been described with an increasing trend towards multidrug resistance. P. aeruginosa isolates n = 53 (66%) isolated from the cerebrospinal fluid (CSF) were used for this study. Antibiotic resistance in 53 P. aeruginosa clinical isolates from 80 CSF samples were evaluated. Of these, n = 42 (80%) of the isolates showed multidrug resistance to more than eight antibiotics and n = 17 (32%) isolates were found to be imipenem resistant P. aeruginosa (IMPR-Pa). Genotypical examination by ERIC based PCR revealed minor genetic variations. Polymicrobial infections are common in the CSF samples. However, high prevalence of P. aeruginosa as an opportunistic pathogen has been developing with increased resistance to antimicrobial agents and thus becoming a significant threat.     

Evaluation of a FRET-Peptide Substrate to Predict Virulence in Pseudomonas aeruginosa

Pseudomonas aeruginosa produces a number of proteases that are associated with virulence and disease progression. A substrate able to detect P. aeruginosa-specific proteolytic activity could help to rapidly alert clinicians to the virulence potential of individual P. aeruginosa strains. For this purpose we designed a set of P. aeruginosa-specific fluorogenic substrates, comprising fluorescence resonance energy transfer (FRET)-labeled peptides, and evaluated their applicability to P. aeruginosa virulence in a range of clinical isolates. A FRET-peptide comprising three glycines (3xGly) was found to be specific for the detection of P. aeruginosa proteases. Further screening of 97 P. aeruginosa clinical isolates showed a wide variation in 3xGly cleavage activity. The absence of 3xGly degradation by a lasI knock out strain indicated that 3xGly cleavage by P. aeruginosa could be quorum sensing (QS)-related, a hypothesis strengthened by the observation of a strong correlation between 3xGly cleavage, LasA staphylolytic activity and pyocyanin production. Additionally, isolates able to cleave 3xGly were more susceptible to the QS inhibiting antibiotic azithromycin (AZM). In conclusion, we designed and evaluated a 3xGly substrate possibly useful as a simple tool to predict virulence and AZM susceptibility.     

Antibiofilm activity of <Emphasis Type="Italic">Andrographis paniculata</Emphasis> against cystic fibrosis clinical isolate <Emphasis Type="Italic">Pseudomonas aeruginosa</Emphasis>

Respiratory tract and device associated infections caused by biofilm forming Pseudomonas aeruginosa play a primary role in the pathogenesis and prognosis of cystic fibrosis (CF) diseases. The biofilm formed by these pathogens attributes to the antibiotic resistance and protection from host immune response. Once established, the pathogens respond poorly to therapeutic agents. Recently medicinal plants are largely explored as potential source of bioactive agents. In this context the present study reports the antibiofilm activity of the folkloric medicinal plant Andrographis paniculata against biofilm forming CF causative Pseudomonas aeruginosa isolated from CF sputum. P. aeruginosa was also assessed for their growth and development of the biofilm, phylogenetic relationship and antibiotic susceptibility. Antibiogram of the strains indicated that they were resistant to more than one antibiotic. Six extracts of A. paniculata showed significant antibiofilm activity. P. aeruginosa strains, KMS P03 and KMS P05, were found to be maximally inhibited by the methanol extract to an extent of 88.6 and 87.5% respectively. This is the first report on antibiofilm activity of A. paniculata extracts, and our results indicate scope for development of complementary medicine for biofilm associated infections.     

Effect of nutrient availability on the C, N, and P elemental ratios in the cyanobacterium Microcystis aeruginosa

To clarify whether nutrients limit the growth of Microcystis aeruginosa (Kütz.) Kütz during the growing season in Lake Yogo, we examined the cellular ratios of carbon (C), nitrogen (N), and phosphorus (P) in the populations of M. aeruginosa from August to December 2001. We also measured cellular C, N, and P ratios of M. aeruginosa under batch culture conditions. The cellular levels of N and P of M. aeruginosa in natural population changed more than twofold. The atomic N: C ratio of natural populations of Microcystis fluctuated from 0.11 to 0.26. The atomic P: C ratio fluctuated from 0.0080 to 0.024. The N: C, P: C, and N: P ratios of exponentially growing M. aeruginosa in N-and P-rich medium were 0.19, 0.013, and 15 on average. The growth of M. aeruginosa was suppressed below the N: C ratio of 0.13 under the N-free condition and below the P: C ratio of 0.0026 in the P-free condition. In the natural population, the N: C ratio was low on August 1-2 (0.11) and the P: C ratio was low (less than 0.011) until September. The Microcystis population on August 1-2 was N limited, judging from the results of the culture experiment. In other periods, the population seemed to be supplied with a sufficient amount of N. Although the P: C ratio was low (approximately 0.01) during August and September, it was several times larger than the value of the reduction of growth rate that occurred in culture. P limitation did not occur during the study period. N became more of a limiting factor than P for the formation of blooms of Microcystis. No blooms were observed in August and September, in spite of the increase of cellular levels of N. The formation of Microcystis blooms in Lake Yogo seems to be affected by artificial manipulations such as pumping from Lake Biwa and outflow.     

Pathogenicity ofPseudomonas aeruginosa and its relationship to the choline metabolism through the action of cholinesterase,acid phosphatase,and phospholipase C

The increase of cholinesterase (ChE), acid phosphatase (Ac.Pase), and phospholipase C (PLC) activities byPseudomonas aeruginosa was associated with the choline consumption in growth media of varied composition (high or low P_i concentrations, presence or absence of ammonium ion, amino acids, polyamines, peptone, or tricarboxylic acid cycle intermediates). The highest production of the three enzymes occurred in the late stationary growth phase. The simultaneous presence of alkaline phosphatase (Alk.Pase) and the above enzymes was noted when the bacteria were grown in low P_i medium plus choline, in the absence of a preferred carbon source. The importance of choline in the production of ChE, Ac.Pase, and PLC was observed in either clinical isolates or collection strains ofP. aeruginosa. These enzymes catalyze the hydrolysis of acetylcholine, phosphorylcholine, and phosphatidylcholine. Through their action the bacteria may break down various compounds (e.g., acetylcholine, from the corneal epithelium; lung surfactant dipalmitoylphosphatidylcholine; phosphorylcholine, a product of the PLC action) or cell membranes through the coordinated action of PLC and Ac.Pase or Alk.Pase. The final consequence of the action of these enzymes is an increase of the free choline concentration. Extrapolated to an in vivo situation, if the stationary growth phase resembles the conditions thatP. aeruginosa encounters in its natural environments, then it is possible to include choline among the factors promoting the pathogenicity of this bacterium.