CYP broth: a tool for Yersinia pestis isolation in ancient culture collections and field samples.

We developed a simple new selective LB-based medium, named CYP broth, suitable for recovering long-term stored Y. pestis subcultures and for isolation of Y. pestis strains from field-caught samples for the Plague surveillance. It aimed to inhibit the growth contaminating microorganisms and enrich Y. pestis growth through iron supplementation. The performance of CYP broth on microbial growth from different gram-negative and gram-positive strains from American Type Culture Collection (ATCC®) and other clinical isolates, field-caught rodent samples, and more importantly, on several vials of ancient Y. pestis subcultures was evaluated. Additionally, other pathogenic Yersinia species such as Y. pseudotuberculosis and Y. enterocolitica were also successfully isolated with CYP broth. Selectivity tests and bacterial growth performance on CYP broth (LB broth supplemented with Cefsulodine, Irgasan, Novobiocin, nystatin and ferrioxamine E) were evaluated in comparison with LB broth without additive; LB broth/CIN, LB broth/nystatin and with traditional agar media including LB agar without additive, and LB agar and Cefsulodin-Irgasan-Novobiocin Agar (CIN agar) supplemented with 50 µg/mL of nystatin. Of note, the CYP broth had a recovery twofold higher than those of the CIN supplemented media or other regular media. Additionally, selectivity tests and bacterial growth performance were also evaluated on CYP broth in the absence of ferrioxamine E. The cultures were incubated at 28 °C and visually inspected for microbiological growth analysis and O.D.625 nm measurement between 0 and 120 h. The presence and purity of Y. pestis growth were confirmed by bacteriophage and multiplex PCR tests. Altogether, CYP broth provides an enhanced growth of Y. pestis at 28 °C, while inhibiting contaminant microorganisms. The media is a simple, but powerful tool to improve the reactivation and decontamination of ancient Y. pestis culture collections and for the isolation of Y. pestis strains for the Plague surveillance from various backgrounds. KEY POINTS: • The newly described CYP broth improves the recuperation of ancient/contaminated Yersinia pestis culture collections • CYP broth was also efficient in reducing environmental contamination in field-capture samples, improving Y. pestis isolation • CYP broth can also be used for the isolation of Y. enterocolitica and Y. pseudotuberculosis.

Supervised molecular dynamics for exploring the druggability of the SARS-CoV-2 spike protein.

The recent outbreak of the respiratory syndrome-related coronavirus (SARS-CoV-2) is stimulating an unprecedented scientific campaign to alleviate the burden of the coronavirus disease (COVID-19). One line of research has focused on targeting SARS-CoV-2 proteins fundamental for its replication by repurposing drugs approved for other diseases. The first interaction between the virus and the host cell is mediated by the spike protein on the virus surface and the human angiotensin-converting enzyme (ACE2). Small molecules able to bind the receptor-binding domain (RBD) of the spike protein and disrupt the binding to ACE2 would offer an important tool for slowing, or even preventing, the infection. Here, we screened 2421 approved small molecules in silico and validated the docking outcomes through extensive molecular dynamics simulations. Out of six drugs characterized as putative RBD binders, the cephalosporin antibiotic cefsulodin was further assessed for its effect on the binding between the RBD and ACE2, suggesting that it is important to consider the dynamic formation of the heterodimer between RBD and ACE2 when judging any potential candidate.

SPOR Proteins Are Required for Functionality of Class A Penicillin-Binding Proteins in Escherichia coli.

Sporulation-related repeat (SPOR) domains are present in many bacterial cell envelope proteins and are known to bind peptidoglycan. Escherichia coli contains four SPOR proteins, DamX, DedD, FtsN, and RlpA, of which FtsN is essential for septal peptidoglycan synthesis. DamX and DedD may also play a role in cell division, based on mild cell division defects observed in strains lacking these SPOR domain proteins. Here, we show by nuclear magnetic resonance (NMR) spectroscopy that the periplasmic part of DedD consists of a disordered region followed by a canonical SPOR domain with a structure similar to that of the SPOR domains of FtsN, DamX, and RlpA. The absence of DamX or DedD decreases the functionality of the bifunctional transglycosylase-transpeptidase penicillin-binding protein 1B (PBP1B). DamX and DedD interact with PBP1B and stimulate its glycosyltransferase activity, and DamX also stimulates the transpeptidase activity. DedD also binds to PBP1A and stimulates its glycosyltransferase activity. Our data support a direct role of DamX and DedD in enhancing the activity of PBP1B and PBP1A, presumably during the synthesis of the cell division septum.IMPORTANCEEscherichia coli has four SPOR proteins that bind peptidoglycan, of which FtsN is essential for cell division. DamX and DedD are suggested to have semiredundant functions in cell division based on genetic evidence. Here, we solved the structure of the SPOR domain of DedD, and we show that both DamX and DedD interact with and stimulate the synthetic activity of the peptidoglycan synthases PBP1A and PBP1B, suggesting that these class A PBP enzymes act in concert with peptidoglycan-binding proteins during cell division.

Identification of Inhibitors of Integrin Cytoplasmic Domain Interactions With Syk.

Leukocyte inflammatory responses require integrin cell-adhesion molecule signaling through spleen tyrosine kinase (Syk), a non-receptor kinase that binds directly to integrin ß-chain cytoplasmic domains. Here, we developed a high-throughput screen to identify small molecule inhibitors of the Syk-integrin cytoplasmic domain interactions. Screening small molecule compound libraries identified the ß-lactam antibiotics cefsulodin and ceftazidime, which inhibited integrin ß-subunit cytoplasmic domain binding to the tandem SH2 domains of Syk (IC50 range, 1.02-4.9 µM). Modeling suggested antagonist binding to Syk outside the pITAM binding site. Ceftazidime inhibited integrin signaling via Syk, including inhibition of adhesion-dependent upregulation of interleukin-1ß and monocyte chemoattractant protein-1, but did not inhibit ITAM-dependent phosphorylation of Syk mediated by FcγRI signaling. Our results demonstrate a novel means to target Syk independent of its kinase and pITAM binding sites such that integrin signaling via this kinase is abrogated but ITAM-dependent signaling remains intact. As integrin signaling through Syk is essential for leukocyte activation, this may represent a novel approach to target inflammation.

Single-molecule imaging reveals modulation of cell wall synthesis dynamics in live bacterial cells.

The peptidoglycan cell wall is an integral organelle critical for bacterial cell shape and stability. Proper cell wall construction requires the interaction of synthesis enzymes and the cytoskeleton, but it is unclear how the activities of individual proteins are coordinated to preserve the morphology and integrity of the cell wall during growth. To elucidate this coordination, we used single-molecule imaging to follow the behaviours of the two major peptidoglycan synthases in live, elongating Escherichia coli cells and after perturbation. We observed heterogeneous localization dynamics of penicillin-binding protein (PBP) 1A, the synthase predominantly associated with cell wall elongation, with individual PBP1A molecules distributed between mobile and immobile populations. Perturbations to PBP1A activity, either directly through antibiotics or indirectly through PBP1A's interaction with its lipoprotein activator or other synthases, shifted the fraction of mobile molecules. Our results suggest that multiple levels of regulation control the activity of enzymes to coordinate peptidoglycan synthesis.

Interactions of release factor RF3 with the translation machinery.

The bacterial release factor RF3 is a GTPase that has been implicated in multiple, incompletely understood steps of protein synthesis. This study explores the genetic interaction of RF3 with other components of the translation machinery. RF3 contributes to translation termination by recycling the class I release factors RF1 and RF2 off post-termination ribosomes. RF3 has also been implicated in dissociation of peptidyl-tRNAs from elongating ribosomes and in a post-peptidyltransferase quality control (post-PT QC) mechanism that selectively terminates ribosomes carrying erroneous peptides. A majority of the in vivo studies on RF3 have been carried out in K-12 strains of Escherichia coli which carry a partially defective RF2 protein with an Ala to Thr substitution at position 246. Here, the contribution of the K-12 specific RF2 variant to RF3 activities has been investigated. Strain reconstruction experiments in both E. coli and Salmonella enterica demonstrate that defects in termination and post-PT QC that are associated with RF3 loss, as well as phenotypes uncovered by phenotypic profiling, are all substantially ameliorated when the incompletely active K-12-specific RF2 protein is replaced by a fully active Ala246 RF2. These results indicate that RF3 loss is well tolerated in bacteria with fully active class I release factors, but that many of the previously reported phenotypes for RF3 deletion strains have been compromised by the presence of a partially defective RF2.

Evaluation of a modified Cefsulodin-Irgasan-Novobiocin agar for isolation of Yersinia spp.

Y. enterocolitica and Y. pseudotuberculosis are important food borne pathogens. However, the presence of competitive microbiota makes the isolation of Y. enterocolitica and Y. pseudotuberculosis from naturally contaminated foods difficult. We attempted to evaluate the performance of a modified Cefsulodin-Irgasan-Novobiocin (CIN) agar in the differentiation of Y. enterocolitica from non-Yersinia species, particularly the natural intestinal microbiota. The modified CIN enabled the growth of Y. enterocolitica colonies with the same efficiency as CIN and Luria-Bertani agar. The detection limits of the modified CIN for Y. enterocolitica in culture medium (10 cfu/ml) and in artificially contaminated pork (10(4) cfu/ml) were also comparable to those of CIN. However, the modified CIN provided a better discrimination of Yersinia colonies from other bacteria exhibiting Yersinia-like colonies on CIN (H2S-producing Citrobacter freundii, C. braakii, Enterobacter cloacae, Aeromonas hydrophila, Providencia rettgeri, and Morganella morganii). The modified CIN exhibited a higher recovery rate of Y. enterocolitica from artificially prepared bacterial cultures and naturally contaminated samples compared with CIN. Our results thus demonstrated that the use of modified CIN may be a valuable means to increase the recovery rate of food borne Yersinia from natural samples, which are usually contaminated by multiple types of bacteria.

A novel peptidoglycan binding protein crucial for PBP1A-mediated cell wall biogenesis in Vibrio cholerae.

The bacterial cell wall, which is comprised of a mesh of polysaccharide strands crosslinked via peptide bridges (peptidoglycan, PG), is critical for maintenance of cell shape and survival. PG assembly is mediated by a variety of Penicillin Binding Proteins (PBP) whose fundamental activities have been characterized in great detail; however, there is limited knowledge of the factors that modulate their activities in different environments or growth phases. In Vibrio cholerae, the cause of cholera, PG synthesis during the transition into stationary phase is primarily mediated by the bifunctional enzyme PBP1A. Here, we screened an ordered V. cholerae transposon library for mutants that are sensitive to growth inhibition by non-canonical D-amino acids (DAA), which prevent growth and maintenance of cell shape in PBP1A-deficient V. cholerae. In addition to PBP1A and its lipoprotein activator LpoA, we found that CsiV, a small periplasmic protein with no previously described function, is essential for growth in the presence of DAA. Deletion of csiV, like deletion of lpoA or the PBP1A-encoding gene mrcA, causes cells to lose their rod shape in the presence of DAA or the beta-lactam antibiotic cefsulodin, and all three mutations are synthetically lethal with deletion of mrcB, which encodes PBP1B, V. cholerae's second key bifunctional PBP. CsiV interacts with LpoA and PG but apparently not with PBP1A, supporting the hypothesis that CsiV promotes LpoA's role as an activator of PBP1A, and thereby modulates V. cholerae PG biogenesis. Finally, the requirement for CsiV in PBP1A-mediated growth of V. cholerae can be overcome either by augmenting PG synthesis or by reducing PG degradation, thereby highlighting the importance of balancing these two processes for bacterial survival.

Sub-inhibitory cefsulodin sensitization of E. coli to ß-lactams is mediated by PBP1b inhibition.

The combination of antibiotics is one of the strategies to combat drug-resistant bacteria, though only a handful of such combinations are in use, such as the ß-lactam combinations. In the present study, the efficacy of a specific sub-inhibitory concentration of cefsulodin with other ß-lactams was evaluated against a range of Gram-negative clinical isolates. This approach increased the sensitivity of the isolates, regardless of the ß-lactamase production. The preferred target and mechanism of action of cefsulodin were identified in laboratory strains of Escherichia coli, by examining the effects of deleting the penicillin-binding protein (PBP) 1a and 1b encoding genes individually. Deletion of PBP1b was involved in sensitizing the bacteria to ß-lactam agents, irrespective of its O-antigen status. Moreover, the use of a sub-inhibitory concentration of cefsulodin in combination with a ß-lactam exerted an effect similar to that one obtained for PBP1b gene deletion. We conclude that the identified ß-lactam/cefsulodin combination works by inhibiting PBP1b (at least partially) despite the involvement of ß-lactamases, and therefore could be extended to a broad range of Gram-negative pathogens.

Distinct single-cell morphological dynamics under beta-lactam antibiotics.

The bacterial cell wall is conserved in prokaryotes, stabilizing cells against osmotic stress. Beta-lactams inhibit cell-wall synthesis and induce lysis through a bulge-mediated mechanism; however, little is known about the formation dynamics and stability of these bulges. To capture processes of different timescales, we developed an imaging platform combining automated image analysis with live-cell microscopy at high time resolution. Beta-lactam killing of Escherichia coli cells proceeded through four stages: elongation, bulge formation, bulge stagnation, and lysis. Both the cell wall and outer membrane (OM) affect the observed dynamics; damaging the cell wall with different beta-lactams and compromising OM integrity cause different modes and rates of lysis. Our results show that the bulge-formation dynamics are determined by how the cell wall is perturbed. The OM plays an independent role in stabilizing the bulge once it is formed. The stabilized bulge delays lysis and allows recovery upon drug removal.

High-resolution dose-response screening using droplet-based microfluidics.

A critical early step in drug discovery is the screening of a chemical library. Typically, promising compounds are identified in a primary screen and then more fully characterized in a dose-response analysis with 7-10 data points per compound. Here, we describe a robust microfluidic approach that increases the number of data points to approximately 10,000 per compound. The system exploits Taylor-Aris dispersion to create concentration gradients, which are then segmented into picoliter microreactors by droplet-based microfluidics. The large number of data points results in IC(50) values that are highly precise (± 2.40% at 95% confidence) and highly reproducible (CV = 2.45%, n = 16). In addition, the high resolution of the data reveals complex dose-response relationships unambiguously. We used this system to screen a chemical library of 704 compounds against protein tyrosine phosphatase 1B, a diabetes, obesity, and cancer target. We identified a number of novel inhibitors, the most potent being sodium cefsulodine, which has an IC(50) of 27 ± 0.83 µM.

[A simple disk diffusion test to identify beta-lactamase-negative, ampicillin-resistant Haemophilus influenzae--application of cephalexin, cefsulodin and cefaclor disks].

Currently, beta-lactamase-negative (BLN) ampicillin-resistant (AR) strains of Haemophilus influenzae are prevalent in Japan. BLNAR strains are defined by the presence of specific mutation(s) in the ftsI gene but are not phenotypically distinguishable by ampicillin (ABPC) susceptibility. In the present study, we showed that cephalexin (CEX), cefsulodin (CFS), and cefaclor (CCL) disk diffusion tests can be effectively used to identify BLNAR strains. A total of 169 clinical isolates of BLN H. influenzae, consisting of 113 of BLNAR and 56 of BLN, ampicillin-susceptible (AS), were included. All the isolates were genetically defined by detection of the TEM gene and partial sequencing of the ftsI gene. The Clinical and Laboratory Standards Institute (CLSI) standard broth microdilution and disk diffusion tests for ABPC provided 20% and 19% false susceptible rates, respectively. Alternatively, 34 cephem agents were tested using disk diffusion. Of the agents tested, CEX, CFS, and CCL disks could effectively discriminate between BLNAR and BLNAS isolates. All the BLNAS isolates showed visible growth inhibitory zones around CEX and CFS disks, but 108 (95.6%) and 106 (93.8%) BLNAR isolates did not. The results indicated 100% predictive values (PVs) for BLNAR and PVs for BLNAS were 91.8% for CEX and 88.9% for CFS. The CLSI-based interpretations for CCL (> or =20 mm) also highly correlated with BLNAR and BLNAS, PVs for BLNAR and for BLNAS being 100% and 93.3%, respectively. With simplicity and discriminability of the test method, we recommend a CEX disk diffusion test in combination with a rapid beta-lactamase test to identify BLNAR isolates in clinical laboratories.

The Rcs phosphorelay is a cell envelope stress response activated by peptidoglycan stress and contributes to intrinsic antibiotic resistance.

Gram-negative bacteria possess stress responses to maintain the integrity of the cell envelope. Stress sensors monitor outer membrane permeability, envelope protein folding, and energization of the inner membrane. The systems used by gram-negative bacteria to sense and combat stress resulting from disruption of the peptidoglycan layer are not well characterized. The peptidoglycan layer is a single molecule that completely surrounds the cell and ensures its structural integrity. During cell growth, new peptidoglycan subunits are incorporated into the peptidoglycan layer by a series of enzymes called the penicillin-binding proteins (PBPs). To explore how gram-negative bacteria respond to peptidoglycan stress, global gene expression analysis was used to identify Escherichia coli stress responses activated following inhibition of specific PBPs by the beta-lactam antibiotics amdinocillin (mecillinam) and cefsulodin. Inhibition of PBPs with different roles in peptidoglycan synthesis has different consequences for cell morphology and viability, suggesting that not all perturbations to the peptidoglycan layer generate equivalent stresses. We demonstrate that inhibition of different PBPs resulted in both shared and unique stress responses. The regulation of capsular synthesis (Rcs) phosphorelay was activated by inhibition of all PBPs tested. Furthermore, we show that activation of the Rcs phosphorelay increased survival in the presence of these antibiotics, independently of capsule synthesis. Both activation of the phosphorelay and survival required signal transduction via the outer membrane lipoprotein RcsF and the response regulator RcsB. We propose that the Rcs pathway responds to peptidoglycan damage and contributes to the intrinsic resistance of E. coli to beta-lactam antibiotics.

Unstable Escherichia coli L forms revisited: growth requires peptidoglycan synthesis.

Growing bacterial L forms are reputed to lack peptidoglycan, although cell division is normally inseparable from septal peptidoglycan synthesis. To explore which cell division functions L forms use, we established a protocol for quantitatively converting a culture of a wild-type Escherichia coli K-12 strain overnight to a growing L-form-like state by use of the beta-lactam cefsulodin, a specific inhibitor of penicillin-binding proteins (PBPs) 1A and 1B. In rich hypertonic medium containing cefsulodin, all cells are spherical and osmosensitive, like classical L forms. Surprisingly, however, mutant studies showed that colony formation requires d-glutamate, diaminopimelate, and MurA activity, all of which are specific to peptidoglycan synthesis. High-performance liquid chromatography analysis confirmed that these L-form-like cells contain peptidoglycan, with 7% of the normal amount. Moreover, the beta-lactam piperacillin, a specific inhibitor of the cell division protein PBP 3, rapidly blocks the cell division of these L-form-like cells. Similarly, penicillin-induced L-form-like cells, which grow only within the agar layers of rich hypertonic plates, also require d-glutamate, diaminopimelate, and MurA activity. These results strongly suggest that cefsulodin- and penicillin-induced L-form-like cells of E. coli-and possibly all L forms-have residual peptidoglycan synthesis which is essential for their growth, probably being required for cell division.

Growth studies of plasmid bearing and plasmid cured Yersinia enterocolitica GER O:3 in the presence of cefsulodin, irgasan and novobiocin at 25 and 37 degrees C.

AIM: In this study, the growth characteristics of Yersinia enterocolitica biotype 4, GER O:3 plasmid bearing (P+) and plasmid cured (P-) strain types were evaluated in brain heart infusion broth supplemented with cefsulodin, irgasan, and novobiocin alone or in combination. METHODS AND RESULTS: Growth curves were obtained for the two strain types in broth supplemented with selective agents at 25 or 37 degrees C for 32 h to obtain data on the lag phase durations and growth rates of the strains. Generally, the lag times and growth rates of the P+ and P- strains were similar for cultures incubated at 25 degrees C regardless of the selective agent added and where plasmid replication and expression were not under any significant burden. However, where the lag times and growth rates of the strains were examined at 37 degrees C, significant differences were observed in the lag phase durations of the plasmid bearing strain type compared the plasmid cured strain, an effect that was due to the burden of the plasmid and the influence of selective agents. Generally, when two or more agents were present, lag phase durations were longer for the plasmid bearing strain. Some exceptions noted where in the presence of irgasan or full selective agent (CIN) the opposite case was observed. When growth rates were compared, the plasmidless strain type was typically faster than the plasmid bearing strain in the presence of most selective agents at 37 degrees C and the growth rates of both strain types at 25 degrees C were similar where the temperature appeared to negate the effects of plasmid. CONCLUSIONS: The data obtained in these studies suggest that selective agents (in particular irgasan) and incubation temperature play a significant role in influencing the growth characteristics of plasmid bearing and plasmid cured strains of Y. enterocolitica. SIGNIFICANCE AND IMPACT OF THE STUDY: This data presented in this study has significant implications for enrichment methods used in the detection or recovery of plasmid bearing Y. enterocolitica strains from food, environmental or clinical samples.

[Pseudomonas aeruginosa: a multicentric study of antibiotic resistance (1999-2000)]. / Pseudomonas aeruginosa: étude multicentrique de la résistance aux antibiotiques (1999-2000).

A retrospective multicentric study was carried out over a period of 2 years (1999-2000). 2659 strains of Pseudomonas aeruginosa were collected from 4 university hospitals (Charles Nicolle Hospital, Pediatric Hospital and National Centre of Bone Marrow Transplantation in Tunis, Habib Bourguiba Hospital in Sfax). Epidemiological profile and antibiotic susceptibility were analysed. All bacteria were identified by conventional methods and antibiotic susceptibility tests were performed according to CA-SFM guidelines. The strains were recovered essentially from surgical wards (33%) and intensive care units (22%). Pseudomonas aeruginosa was isolated mainly from pus (36%), urine (32%) and respiratory samples (18%). 25% of strains were resistant to ticarcilline, 18% to cefsulodine, 9% to ceftazidime, 14% to imipenem and amikacin and 25% to ciprofloxacin. Moreover, the resistance rates varied from hospital to hospital and from unit to another. The resistant strains were isolated particularly from urology and intensive care units: respectively 62% and 39% for ticarcilline; 26% and 13% for ceftazidime. The acquired resistance to b-lactams seems largely due to penicillinase production. The frequency of resistance to ceftazidime was the lowest and seems associated to chromosomal cephalosporinase over production.

Fast lysis of Escherichia coli filament cells requires differentiation of potential division sites.

Periodic activation of zonal peptidoglycan (murein) synthesis at division sites in Escherichia coli has been reported recently. Zonal synthesis is responsible for septum formation, whereas elongation of the cell sacculus is performed by diffuse insertion of precursors. Zonal synthesis can be triggered in ftsA, ftsQ and ftsI (pbpB) division mutants growing as filaments at the restrictive temperature, but not in ftsZ mutant strains. The lytic response to beta-lactams of cells able or unable to periodically trigger a zonal mode of murein synthesis could be substantially different. Therefore, we investigated the response to the bacteriolytic beta-lactam cefsulodin of ftsZ and ftsI mutants growing at the restrictive (42 degrees C) temperature. The ftsI cells lysed early and quickly after addition of the antibiotic. Sacculi of lysed cells were transversely cut in a very sharp way. In contrast the ftsZ strain lysed late and slowly after addition of the antibiotic and sacculi showed a generalized weakening of the murein network and extended breaks with a frayed appearance. No transversely cut sacculi comparable to those seen in the ftsI samples were found. Our results strongly support that beta-lactam-induced lysis occurs preferentially at division sites because of the activation of zonal murein synthesis at the initiation of septation.

Effects of antibiotics on adherence of Pseudomonas aeruginosa and Pseudomonas fluorescens to human fibronectin.

The effect of subminimal inhibitory concentration (1/2 MIC) of antimicrobial agents on the adherence of fluorescent Pseudomonas to human fibronectin (FN) was investigated by examining two Pseudomonas fluorescens and four Pseudomonas aeruginosa strains. The Escherichia coli (MC1061 and JM109) strains, used as negative controls, adhered poorly to FN immobilized on microtiter wells (adherence indices of 0.04 +/- 0.02 and 0.03 +/- 0.01 10(5) CFU/well, respectively). Two P. aeruginosa strains (NK125502 and ER82483) were highly adherent to FN (adherence indices of 3.22 +/- 0.75 10(5) and 3.08 +/- 1.42 10(5) CFU/well, respectively), the two others (ER98513 and ER92581) adhered less efficiently (adherence indices of 0.91 +/- 0.05 10(5) and 0.45 +/- 0.23 10(5) CFU/well, respectively). The two P. fluorescens strains (MF0 and ER74508) were highly adherent to fibronectin (adherence indices of 7.06 +/- 1.00 10(5) and 2.08 +/- 0.67 10(5) CFU/well, respectively). Cefsulodin was the only antimicrobial agent tested that decreased the FN adherence of the majority of the strains: decrease in adherence highly significant (p < 0.01) for the P. fluorescens MF0 strain, significant (p < 0.05) for the P. aeruginosa NK125502, ER98513 and the P. fluorescens ER74508 strains, and not significant for the P. aeruginosa ER92581 strain. The effects of chloramphenicol and polymyxin B on the adherence of Pseudomonas were strain dependent. Gentamicin had no statistically significant effect on bacterial adherence. We conclude that, in addition to its antibacterial activity, cefsulodin could be effective in preventing the adherence of fluorescent Pseudomonas to FN, an important property in the presence of injured epithelium and coated biomaterials.