Antigenic relationships among type strains of Yersinia enterocolitica and those of Escherichia coli, Salmonella spp., and Shigella spp

The antigenic type strains for Yersinia enterocolitica antigens O:1 to O:34 were examined and their antigenic relationships with the type strains of Escherichia coli, Shigella spp., and Salmonella spp. were determined. Y. enterocolitica O:5,27 was antigenically identical to E. coli O97 and Y. enterocolitica O:11 was antigenically identical to E. coli O98.     

Correlation of in vitro susceptibility results for amoxicillin-clavulanate and ampicillin-sulbactam tested against Escherichia coli.

The results of amoxicillin-clavulanate (AUG) and ampicillin-sulbactam (A/S) susceptibility testing by three different susceptibility testing methods, the MicroScan, Etest, and Kirby-Bauer methods, for 61 consecutive isolates of ampicillin-resistant Escherichia coli from different patients were compared. There was poor correlation of results for the two agents, the most and least marked discrepancies being observed by the MicroScan method (86.9% susceptible to AUG and 4.9% susceptible to A/S) and the Kirby-Bauer method (39.4% susceptible to AUG and 32.8% susceptible to A/S), respectively. More organisms were susceptible to AUG than A/S, regardless of the susceptibility testing methodology. The results from a College of American Pathologists survey with one E. coli isolate tested at different institutions also indicated greater susceptibility to AUG than to A/S. These agents are thought to be equally efficacious clinically. The discrepancies observed among methods for each antimicrobial inhibitor combination and the discrepancies observed between the two agents by each testing method suggest that the breakpoints for these agents need to be reevaluated.     

Enzymatic resistance to cefotaxime in 56 strains of Klebsiella spp., Escherichia coli and Salmonella spp. at a Tunisian hospital (1984-1988)

The enzymatic and plasmid-encoded resistance towards oxyimino-beta-lactams has been recently reported as related to the production of an extended-spectrum beta-lactamase (e.g. SHV-2, CTX-1 or TEM-3), in particular in our hospital since 1984. The prevalence of that resistance has been examined from January 1984 to December 1988 in function of specimen, unit and type of enzyme among 8,421 isolates of Klebsiella spp., E. coli, Salmonella spp. Each isolate showing a diameter of inhibition zone size inferior or equal to 25 mm for cefotaxime, the double disk synergy test was performed between a disk of amoxicillin and a clavulanic acid disk of cefotaxime, ceftriaxone, ceftazidime and aztreonam. In case of synergy, sonicated extracts have been prepared and examined by isoelectrofocusing with the detection of beta-lactamase activity by ceftriaxone and nitrocefin. 56 isolates (K. pneumoniae, K. oxytoca, E. coli, S. wien, S. typhimurium scored positive including 27 in pediatrics, 18 in surgery, and 8 in medicine. 41% of isolates have been obtained from blood cultures and 26.8% from urines. A majority of isolates (49/56) produced the SHV-2 type, but other types mediating the resistance phenotype CTX have been individualized initially by their isoelectric points e.g. 5.4 (TEM-20 in K. pneumoniae in July 1986), 6.4 (TEM-21 in E. coli, 1 K. pneumoniae in July 1988). The prevalence of resistance to cefotaxime from 1984 to 1988 has increased (from 0.3 to 1.4%), the highest rate being observed in pediatrics (5.6% in 1984 and 22.1% in 1988).     

Bactericidal, bacteriolytic and opsonic activity of human serum against Escherichia coli

The effect of human serum on Escherichia coli was studied with serum-sensitive and serum-resistant strains. The bactericidal effect of human serum on serum-sensitive strains of E. coli depended on the activation of the classical complement pathway. The role of activation of the alternative pathway was less important. After incubation in sub-bactericidal concentrations of serum these strains were also easily phagocytosed by polymorphonuclear leukocytes (PMNL). Strains of E. coli of certain O-types required not only an intact classical pathway but also the presence of specific antibodies for effective killing by serum and effective phagocytosis by PMNL, despite rapid activation of complement and rapid deposition of C3 on the bacterial surface in the absence of antibody. Capsulate strains O1K1 and O78K80 resisted the bactericidal effect of serum even in the presence of specific antibodies; phagocytosis by PMNL only occurred after opsonisation with specific antibodies.     

Bactericidal activity of human eosinophilic granulocytes against Escherichia coli

Eosinophils participate in allergic inflammation and may have roles in the body's defense against helminthic infestation. Even under noninflammatory conditions, eosinophils are present in the mucosa of the large intestine, where large numbers of gram-negative bacteria reside. Therefore, roles for eosinophils in host defenses against bacterial invasion are possible. In a system for bacterial viable counts, the bactericidal activity of eosinophils and the contribution of different cellular antibacterial systems against Escherichia coli were investigated. Eosinophils showed a rapid and efficient killing of E. coli under aerobic conditions, whereas under anaerobic conditions bacterial killing decreased dramatically. In addition, diphenylene iodonium chloride (DPI), an inhibitor of the NADPH oxidase and thereby of superoxide production, also significantly inhibited bacterial killing. The inhibitor of nitric oxide (NO) production L-N(5)-(1-iminoethyl)-ornithine dihydrochloride did not affect the killing efficiency, suggesting that NO or derivatives thereof are of minor importance under the experimental conditions used. To investigate the involvement of superoxide and eosinophil peroxidase (EPO) in bacterial killing, EPO was blocked by azide. The rate of E. coli killing decreased significantly in the presence of azide, whereas addition of DPI did not further decrease the killing, suggesting that superoxide acts in conjunction with EPO. Bactericidal activity was seen in eosinophil extracts containing granule proteins, indicating that oxygen-independent killing may be of importance as well. The findings suggest that eosinophils can participate in host defense against gram-negative bacterial invasion and that oxygen-dependent killing, i.e., superoxide acting in conjunction with EPO, may be the most important bactericidal effector function of these cells.     

Comparative activity of linezolid against staphylococci and enterococci isolated in Italy

The activity of linezolid, a new oxazolidinone, was tested against 862 Gram-positive cocci isolated in Italy and compared with the activities of 12 antibiotics. Overall, MIC₉₀s for linezolid (2–4 mg/L) indicated an in vitro activity comparable to that of vancomycin in methicillin-resistant Staphylococcus aureus (4 mg/L), S. epidermidis (2 mg/L) and methicillin-susceptible strains. Enterococcus faecalis strains were susceptible to linezolid (MIC₉₀ 2–4 mg/L), glycopeptides and β -lactams. In E. faecium , only glycopeptides (MIC₉₀ 2 mg/L) and linezolid (MIC₉₀ 2 mg/L) were active. Linezolid was the only drug active against two strains of Enterococcus showing a VanA phenotype. Owing to its antibacterial profile, linezolid represents a promising drug for the treatment of Gram-positive infections.     

Characterization of antimicrobial resistance among Escherichia coli O111 isolates of animal and human origin

Fifty isolates of Escherichia coli serogroup O111 recovered from humans and various animal species over a 24-year period (1976-1999) were examined for typical virulence-associated factors and susceptibilities to antimicrobials of human and veterinary significance. Nine H (flagellar) types were identified including nonmotile (n = 24), 32 (n = 12), negative (n = 5), and 56 (n = 3). Thirty-five (70%) isolates possessed at least one Shiga-toxin-producing E. coli (STEC)-associated virulence determinants (eae, stxl, stx2, hlyA) via PCR analysis. Of these 35 isolates, 20 possessed eae, stxl, and hlyA genes, whereas three isolates possessed eae, stxl, stx2, and hylA genes. Multiple antibiotic resistance was observed in 70% of the 50 E. coli O111 isolates. The majority of isolates displayed resistance to streptomycin, sulfamethoxazole, tetracycline, and kanamycin. Bacterial resistance to ampicillin, gentamicin, chloramphenicol, trimethoprim and apramycin was also observed. Integrons were identified in 23 (46%) of the E. coli isolates assayed, with a 1-kb amplicon being most frequently observed. DNA sequencing of these integrons revealed the presence of the aadA gene, encoding resistance to streptomycin. Two integrons of 1.5 and 2 kb contained the aadA2 and either dfrI or dfrXII genes, encoding resistance to streptomycin and trimethoprim, respectively. Integrons were also identified from isolates dating back to 1982. Isolates were further genetically characterized via ribotyping, which identified 15 distinct ribogroups, with 62% of isolates clustering into four major ribogroups. Certain riboprint patterns from different animal species, including humans, were observed in isolates spanning the 24-year collection period, suggesting the dissemination of specialized pathogenic O111 clones.     

Comparative in vitro activity of LY146032 (Daptomycin) against gram-positive cocci

The in vitro activity of LY146032 was compared with those of seven other antimicrobial agents against gram-positive cocci. MICs of LY146032 were lowest for Streptococcus pneumoniae and methicillin-susceptible Staphylococcus epidermidis (0.25 mg/l).For methicillin-resistant Staphylococcus epidermidis and Staphylococcus aureus the MICs were 1 mg/l, for Enterococcus faecalis 2 mg/l and for Enterococcus faecium 4 mg/l. The activity of LY146032 was in general higher than that of vancomycin. Time-kill studies showed LY146032 had higher bactericidal activity than vancomycin against a methicillin-resistant Staphylococcus aureus strain, and bactericidal activity against Enterococcus faecalis and Enterococcus faecium.     

Heterogeneity among virulence and antimicrobial resistance gene profiles of extraintestinal Escherichia coli isolates of animal and human origin

Extraintestinal pathogenic Escherichia coli (ExPEC) isolates collected from different infected animals and from human patients with extraintestinal infections in 2001 were characterized for their phenotypic and genotypic antimicrobial resistance profiles, genotypes, and key virulence factors. Among the 10 antimicrobial agents tested, resistance to ampicillin, tetracycline, and sulfonamides was most frequent. Multiresistant strains were found in both the animal and the human groups of isolates. Resistance gene distribution was assessed by colony hybridization. Similar antibiotic resistance patterns could be observed in the animal and the human isolates. Although some resistance genes, such as bla(TEM), sulI, and sulII, were equally represented in the animal and human ExPEC isolates, differences in the distributions of tetracycline [tet(D)], chloramphenicol (catI, catIII, and floR), and trimethoprim (dhfrI, dhfrV, dhfrVII, and dhfrXIII) resistance genes were observed between the animal and the human isolates. Approximately one-third of the ExPEC isolates possessed a class 1 integron. The four major different variable regions of the class 1 integron contained aminoglycoside (aadA1, aadA2, aadA5, and aadA6) and/or trimethoprim (dhfrIb, dhfrXII, and dhfrXVII) resistance genes. The ExPEC strains belonged to different phylogenetic groups, depending on their host origin. Strains isolated from animal tissues belonged to either a commensal group (group A or B1) or a virulent group (group B2 or D), while the majority of the human isolates belonged to a virulent group (group B2 or D). Although the limited number of isolates evaluated in the present study prevents firm epidemiological conclusions from being made, on a more global scale, these data demonstrate that extraintestinal isolates of E. coli can possess relatively distinct intra- and intergroup resistance gene profiles, with animal isolates presenting a more heterogeneous group than human isolates.     

Genetic characterization of glycopeptide-resistant enterococci of human and animal origin from mixed pig and poultry farms

Glycopeptide resistant enterococci (GRE) isolated from animals and humans were characterised using both AFPL typing and genetic characterisation of the glycopeptide resistance transposon Tn1546. All isolates were collected in 1997 when the glycopeptide avoparcin was still being used as growth promoter. All investigated animal isolates were from mixed pig and poultry farms in the Netherlands and the human isolated from the farmers of these farms. A total of 24 isolates were investigated. AFLP and Tn1546 typing revealed that both pig and poultry related enterococcal and vanA transposon genotypes were found among the human isolates indicating spread of glycopeptide resistance from both pig and poultry to the farmers. These findings contradict previous finding that showed that GRE recovered from the general population were genotypically undistinguishable from GRE isolated from pigs but are in line with other studies that demonstrated spread of GRE from poultry to farmers in poultry farms.     

Bactericidal activity and synergy studies of BAL9141, a novel pyrrolidinone-3-ylidenemethyl cephem, tested against streptococci, enterococci and methicillin-resistant staphylococci

BAL9141 has been reported to have inhibitory activity against methicillin-resistant Staphylococcus aureus (MRSA), many enterococci, and streptococci with various resistant patterns. BAL9141 potency was assessed by time–kill curves alone or with subinhibitory concentrations of gentamicin (MIC/4). BAL9141 exhibited bactericidal activity alone against all the streptococci and staphylococci. Among ampicillin-susceptible enterococci, BAL9141 was bactericidal against some strains, but no BAL9141 inhibition was observed of ampicillin-resistant Enterococcus faecium . The activity of BAL9141 with gentamicin was slightly enhanced (not synergy) or indifferent against staphylococci. BAL9141 demonstrated bactericidal action alone against Enterococcus faecalis and some E. faecium strains (− 4.8 to −6.0 log₁₀ CFU/mL), but static effects were also noted. Drug interactions with gentamicin showed early synergy (4–8 h) for all enterococci, and indifference or synergy at 24 h (no antagonism). BAL9141 (≤8 mg/L) showed promising bactericidal activity alone and synergy with gentamicin against some of the vancomycin-resistant enterococci tested.     

In vitro activity of dalbavancin against enterococci isolates from wild animals, pets, poultry and humans in Portugal

Dalbavancin is a new new semisynthetic teicoplanin-related lipoglycopeptide with activity against gram-positive organisms. We investigated the activity of dalbavancin against faecal enterococci isolates from wild animals, pets, poultry and healthy humans in Portugal. The in vitro activity of dalbavancin was determined by the microbroth dilution method according to the Clinical Laboratory Standards Institute (CLSI) guidelines in 589 enterococci of different species and origins. All vancomycin-susceptible Enterococcus spp. were inhibited by < or =0.25 mg/l dalbavancin. Although vancomycin-resistant-enterococci (VRE) showed higher dalbavancin MIC values (16 mg/l), the isolates that exhibited the VanC resistance phenotype were inhibited at dalbavancin concentrations < or =0.125 mg/l. Only van A isolates were not inhibited by low concentrations of dalbavancin since van A strains showed higher dalbavancin MIC values (16 mg/l).     

Drug resistance and colicin production among various serotypes of Escherichia coli of animal origin

One hundred and twenty two strains of E. coli isolated from clinical conditions of animals were studied for the production of colicins and their sensitivity behaviour towards 16 antibiotics and trimethoprim-sulphamethoxazole. Out of 122 strains, 27 (22.1%) were found colicinogenic and 25 (93%) of these colicinogenic strains were found resistant to one or more of drugs in various combinations. All the 27 colicinogenic strains could be typed into 15 serogroups. Serogroup 084 was found predominant. Transfer of R-plasmids and Col-plasmids were observed in 5 (18.5%) strains individually. In one strain both drug resistance and colicin production determinants were transferred enblock. Such transconjugants will be more invasive and virulent and will create serious chemotherapeutic problems.     

Inhibitor-based methods for detection of plasmid-mediated AmpC beta-lactamases in Klebsiella spp., Escherichia coli, and Proteus mirabilis

Non-beta-lactam inhibitor-based methods were evaluated for detecting plasmid-mediated AmpC beta-lactamases in Klebsiella spp., Escherichia coli, and Proteus mirabilis. Using CLSI methodology and disks containing cefotetan alone and in combination with 400 mug of boronic acid, 9 of 10 positive control strains and 54 of 55 AmpC-PCR-positive clinical isolates were detected. Importantly 71% and 40% of these clinical isolates were susceptible by routine testing to ceftriaxone and ceftazidime, respectively. Boronic acid disks also enhanced detection of expanded-spectrum beta-lactamases in AmpC producers.     

Ureolytic Escherichia coli of human origin: serological, epidemiological, and genetic analysis.

Forty-five strains of ureolytic Escherichia coli of human origin, isolated in the United States between 1956 and 1977, were characterized by geographical distribution, site of infection, serotype, resistance to antibiotics, and biochemical reactions. All strains were studied for the ability to generate clones of nonureolytic E. coli (segregants), and a subset of these were selected for plasmid analysis and a variety of bacterial matings. There did not appear to be a common geographical distribution, serotype, antibiogram, or other aberrant biochemical reactions other than the hydrolysis of urea among these strains. The predominance of urinary tract isolates (46.7% total) may reflect a relationship between urea hydrolysis and pathogenesis at this site. Ten of the strains (22.2%) did segregate nonureolytic E. coli colonies, and all possessed at least one common plasmid species with a molecular weight of about 65 X 10(6). Only strain 1138-77 serotype O16:H6 conjugally transfered the ability to hydrolyze urea, ferment sucrose, and resist inhibition by sulfadiazide simultaneously. The resulting, recombination-deficient E. coli K-12 tranconjugant was found to possess a plasmid with a molecular weight of about 80 X 10(6) to 90 X 10(6).     

IncI1 plasmids associated with the spread of CMY-2, CTX-M-1 and SHV-12 in Escherichia coli of animal and human origin

Fourteen plasmids carrying bla_CTC-M-1, bla_SHV-12 or bla_CMY-2 genes from Escherichia coli of both avian and human origin were analysed. IncI1 plasmids were largely predominant. Plasmid mutilocus sequence typing and comparative analysis revealed that the bla_CMY-2-ST12-IncI1 plasmids from avian E. coli were identical to those previously found in Salmonella from humans, but different to those associated with human E. coli. The IncI1-ST3 plasmids carrying bla_CTX-M-1 or bla_SHV-12 were related to those previously identified in avian E. coli, but different to those identified in human E. coli. Overall, no plasmids shared by E. coli of both origin (human/avian) were identified; however, further investigations are needed.     

The effects of ethyleneglycoltetra-acetic acid on bactericidal activity of human serum against Escherichia coli

The effects of ethyleneglycoltetra-acetic acid (EGTA) and EGTA + magnesium (MgEGTA) on the viable counts of 10 strains of Escherichia coli O6 have been studied in normal human serum (NHS), heat-inactivated serum (HIS) and in culture media with and without the addition of a beta-lactam antibiotic. The addition of EGTA to NHS largely prevented bactericidal activity against serum-sensitive strains while, in contrast, it reduced the growth of a serum-resistant strain. These apparently paradoxical effects are due to the lower growth rate permitted by the reduced amount of available magnesium in the presence of EGTA. Experiments with equimolar concentrations of EGTA and magnesium indicated that whilst MgEGTA is a reagent allowing alternative complement-pathway activity, such activity must be determined by comparison with results in HIS + MgEGTA rather than in HIS alone, classical-pathway activity being taken as the difference between the results in NHS and in NHS + MgEGTA. By these criteria, prompt killing by serum was found to occur via the classical pathway while delayed serum bactericidal activity occurred by the alternative pathway in some strains and by the classical pathway in others.     

Comparative in vitro activity of cefepime (BMY 28142) against multiresistant nosocomial isolates ofPseudomonas aeruginosa

The in vitro activity of a new parenteral cephalosporin cefepime (BMY 28142) was compared with that of ceftazidime, cefotaxime, piperacillin, imipenem, gentamicin, amikacin and ciprofloxacin against 173 recent multiresistantPseudomonas aeruginosa isolates of nosocomial origin using an agar dilution technique with an inoculum of 10⁴ CFU per spot. The activity of cefepime was comparable to that of ceftazidime, superior to that of cefotaxime, piperacillin, gentamicin and amikacin, but inferior to that of imipenem and ciprofloxacin. Cross-resistance ofPseudomonas aeruginosa to ceftazidime and cefepime occurred in nearly 50% of the cefepime resistant strains and 61.5% of the ceftazidime resistant strains respectively.