Diversity of aminoglycoside modifying enzyme genes among multidrug resistant Acinetobacter baumannii genotypes isolated from nosocomial infections in Tehran hospitals and their association with class 1 integrons

The aim of the present study was to investigate, for the first time, the diversity of the genes encoding aminoglycoside-modifying enzymes (AME) and their association with class 1 integrons in Iranian Acinetobacter baumannii strains. A total of 100 multidrug resistant A. baumannii, isolated from eight distinct hospitals in Tehran, were enrolled in this study. Susceptibility of these isolates to antimicrobial agents including gentamicin and amikacin was determined by E-test. Aminoglycoside resistant isolates were then tested by PCR for AME genes, including aphA6, aacC1, aacC2, aacA4, aadB, aadA1, classes 1 integron, 5'-CS-3' and typed by RAPD PCR. The rate of resistance to imipenem, meropenem, gentamicin and amikacin were 39%, 39%, 38% and 32%, respectively. Intermediate resistance phenotype to gentamicin and amikacin was observed in 2% and 5% of all the isolates, respectively. After aph6 with 90% (n = 36/40), aadA1, aacC1 and aadB with 82.5% (n = 33/40), 65% (n = 26/40) and 20% (n = 8/40) were the most prevalent AME genes among aminoglycosides resistant A. baumannii isolates. A combination of two to four different resistance genes was observed in 39 of 40 strains (97.5%), with a total of 7 different combinations. PCR of integrase genes revealed that AME gene was associated with 67% of class 1 integrons. RAPD analysis showed three predominant genotypes A (n = 20), B (n = 10) and 10 unrelated genotypes. The occurrence of identical resistance genes, gene combinations and class 1 integrons associated with these genes in clonally distinct strains indicates that horizontal gene transfer plays a major role in the dissemination of aminoglycoside resistance in A. baumannii.     

Antibiotic resistance of Salmonella strains isolated from children living in the wastewater-spreading field of Marrakesh city (Morocco)

A total of 813 Salmonella strains isolated from raw wastewater and stool specimens of inpatient children, living in the wastewater-spreading field of Marrakesh city, were examined for their susceptibility to 15 antimicrobial agents. All the isolates were susceptible to cefotaxime, and almost of them showed susceptibility to gentamicin (99.88%), trimethoprim-sulphamethoxazole (98.04%), nalidixic acid (98.04%), kanamycin (97.30%), trimethoprim (97.18%), and chloramphenicol (96.07%). The highest levels of antibiotic resistance were obtained for cephalothin (29.27%), amoxicillin (26.44%), sulphamethoxazole (26.07%), and ampicillin (25.21%). The strains from the serogroup B showed the highest antibiotic resistance frequencies. The percentage of polyresistant strains (36.09%) was significantly higher than that of monoresistant isolates (15.49%). The incidence of drug resistance in Salmonella isolates from stools was significantly higher than in those isolated from wastewater.     

Inhibition of HIV-1 replication by amphotericin B methyl ester: selection for resistant variants

Membrane cholesterol plays an important role in human immunodeficiency virus type 1 (HIV-1) particle production and infectivity. Here, we have investigated the target and mechanism of action of a cholesterol-binding compound, the polyene antifungal antibiotic amphotericin B methyl ester (AME). We found that AME potently inhibited the replication of a highly divergent panel of HIV-1 isolates in various T-cell lines and primary cells irrespective of clade or target cell tropism. The defects in HIV-1 replication caused by AME were due to profoundly impaired viral infectivity as well as a defect in viral particle production. To elucidate further the mechanism of action of AME, we selected for and characterized AME-resistant HIV-1 variants. Mutations responsible for AME resistance mapped to a highly conserved and functionally important endocytosis motif in the cytoplasmic tail of the transmembrane glycoprotein gp41. Interestingly, truncation of the gp41 cytoplasmic tail in the context of either HIV-1 or rhesus macaque simian immunodeficiency virus also conferred resistance to AME. The infectivity of HIV-1 virions bearing murine leukemia virus or vesicular stomatitis virus glycoproteins was unaffected by AME. Our data define the target and mechanism of action of AME and provide support for the concept that cholesterol-binding compounds should be pursued as antiretroviral drugs to disrupt HIV-1 replication.     

Taxonomic spectrum and antibiotic resistance of Enterobacteriaceae isolated from bile of patients with cholangitis]

The data on the taxonomic structure and antibiotic resistance of Enterobacteriaceae isolated from bile of patients with various clinical variants of cholangitis are presented. It was shown that bacteriocholia was registered in 53.3-90.9% of the patients during operations and in 88.9-100% of the patients during the postoperative period. Among bilicultures enterobacteria dominated (93.4% of the cases) with predominance of E. coli and Klebsiella spp. (the total about 70%). The enterobacteria isolates were frequently resistant to ampicillin and amoxycillin/clavulanate (92.6 and 70.4% of the strains respectively), gentamicin and amikacin (74.1 and 22.2%), cefazolin and cefotaxime (88.9 and 37.0%). The resistance to imipenem and ciprofloxacin (7.4%) was rare, that should be considered while prescribing drugs for empirical antimicrobial chemotherapy.     

Mercury resistance among clinical isolates of Escherichia coli

The use of organomercurials in liquid detergents and disinfectants promoted resistance to mercury among bacteria. Dental amalgam and industries using mercury are the main source of human exposure to mercury vapor. Release of mercury from dental amalgam contributes to the enrichment of the intestinal flora with mercury resistance plasmids which may be associated with antibiotic resistance. The aim of our study was to evaluate the frequency of E. coli strains resistant to mercury and other antimicrobial agents currently used in therapy. The bacterial mercury and ampicillin, cephalexin, cefotaxime, gentamicin, tetracycline and chloramphenicol resistance was tested against 363 E. coli strains obtained from faeces and urine between 1999-2000. According to the guidelines suggested by NCCLS (1998), minimum inhibitory concentrations (MICs) were determined on Mueller-Hinton agar, using the dilution technique with an inoculum of about 10(5) CFU. The MICs were read after 18 h incubation at 37 degrees C as the lowest concentration that inhibited the development of visible growth. Plasmids in enterobacteria may carry genes encoding resistance to both mercury and antibiotics. Among the tested E. coli strains, mercury resistance rose to 29.2%. Mercury resistance in E. coli is significantly linked to multiresistance to antimicrobial agents. Between 91.5-23.6 of mercury chloride resistant isolates were also resistant to the tested antibiotics. The increased use of non antibiotic antimicrobial agents is a possible selection factor for antibiotic-resistant strains in clinical and domestic environments.     

Evaluation of the Short-Term Effects of Antimicrobial Stewardship in the Intensive Care Unit at a Tertiary Hospital in China

Antibiotic abuse can lead to antibiotic resistance, which is a severe problem in China. The purpose of this study is to evaluate the short-term effects of antimicrobial stewardship strategies, including formulary restriction, preauthorization, perioperative quinolone restriction, and control of total antibiotic consumption in the ICU at a tertiary hospital in China. After implementation of antimicrobial stewardship, the total antibiotic consumption in the ICU significantly decreased. The defined daily doses (DDDs) per 100 patient-days decreased from 197.65 to 143.41; however, the consumption of cephalosporins increased from 53.65 to 63.17 DDDs. Significant improvements in resistance to amikacin, gentamicin, ciprofloxacin, ofloxacin, ceftriaxone, ceftazidime, and piperacillin in Enterobacteriaceae and resistance to ceftazidime, imipenem, and meropenem in non-fermenting Gram-negative rods were observed. In addition, the initial use of no antibiotics or of a single antibiotic significantly increased (P<0.001) and the use of two antibiotics in combination significantly decreased (P<0.001). Our results demonstrate that implementation of antimicrobial stewardship in a short period in the ICU dramatically reduced antibiotic consumption and significantly improved antibiotic resistance, which leads to more reasonable antibiotic selections by ICU physicians.     

High antimicrobial resistance among bacterial isolates of blood stream infections (BSI) in a Nigerian University Teaching Hospital

The antimicrobial resistance profile of 220 bacteria isolated from 1,006 episodes of blood stream infections (BSI) between January 2004 and December 2005 in a University Teaching Hospital, Southwestern Nigeria, were analyzed. Gram positive bacteria constituted 47.3% while Gram negative constituted 52.7%. The most common organisms were Staphylococcus aureus (37.3%), Klebsiella (30%), Pseudomonas (8.2%), Proteus (6.4%), Escherichia coli (5.5%) and coagulase negative staphylococci (4.6%). The cumulative resistance of all the bacteria isolates to ampicillin was 79%, gentamicin 51%, ceftazidime 11% and ciprofloxacin 6%. About 85% of the Gram positive bacteria were resistant to penicillinG, 79% to methicillin and 37% to erythromycin while 74% of the Gram negative bacteria were resistant to cotrimoxazole, 69% to tetracycline and 38% to chloramphenicol. Among the 7 antibiotics tested for each group, 7 patterns of antibiotic resistance were observed for each; 6 were multi-drug pattern with number of antibiotics ranging from 2 to 7. This study demonstrates high antimicrobial resistance among clinical bacterial isolates of BSI to commonly prescribed antibiotics most especially penicillinG, ampicillin, methicillin, cotrimoxazole, tetracycline and gentamicin. Based on the result of this study, it is suggested that the combination of ampicillin and gentamicin normally employed for empirical treatment of BSI in our hospital should be stopped.     

Variations in antibiotic resistance profile in Enterobacteriaceae isolated from wild Australian mammals

We carried out a retrospective analysis of 946 strains of Enterobacteriaceae isolated from wild Australian mammals between 1993 and 1997. The prevalence of resistance to fixed concentrations of 32 antimicrobial agents was determined, and the respective roles that taxonomic family of the host, state of origin and bacterial species play in defining prevalence and range of resistance were investigated. Our results demonstrated a low but widespread prevalence of antimicrobial resistance in wild isolates. Only amikacin, ciprofloxacin, meropenem and gentamicin inhibited growth in all 946 samples. There was extensive variation in the combination of antibiotics to which isolates were resistant, and multiple antibiotic resistance was common. Geographical location and host group significantly influenced the antibiotic resistance profile of an isolate, whereas bacterial species influenced both the resistance profile of an isolate and the number of antibiotics it was resistant to. The role of these factors in determining observed antibiotic resistance profiles suggests that any study measuring resistance in wild isolates should include the broadest possible range of bacterial species, host species and sampling locations. As such, this study provides an important new baseline for future measurements of antibiotic resistance in the Australian environment.     

A set of novel multiplex Taqman real-time PCRs for the detection of diarrhoeagenic Escherichia coli and its use in determining the prevalence of EPEC and EAEC in a university hospital

Background

Escherichia coli isolates of equine faecal origin were investigated for antibiotic resistance, resistance genes and their ability to perform horizontal transfer.

Methods

In total, 264 faecal samples were collected from 138 horses in hospital and community livery premises in northwest England, yielding 296 resistant E. coli isolates. Isolates were tested for susceptibility to antimicrobial drugs by disc diffusion and agar dilution methods in order to determine minimum inhibitory concentrations (MIC). PCR amplification was used to detect genes conferring resistance to: ampicillin (TEM and SHV beta-lactamase), chloramphenicol (catI, catII, catIII and cml), tetracycline (tetA, tetB, tetC, tetD, tet E and tetG), and trimethoprim (dfrA1, dfrA9, dfrA12, dfrA13, dfr7, and dfr17).

Results

The proportion of antibiotic resistant isolates, and multidrug resistant isolates (MDR) was significantly higher in hospital samples compared to livery samples (MDR: 48% of hospital isolates; 12% of livery isolates, p < 0.001). Resistance to ciprofloxacin and florfenicol were identified mostly within the MDR phenotypes. Resistance genes included dfr, TEM beta-lactamase, tet and cat, conferring resistance to trimethoprim, ampicillin, tetracycline and chloramphenicol, respectively. Within each antimicrobial resistance group, these genes occurred at frequencies of 93% (260/279), 91%, 86.8% and 73.5%, respectively; with 115/296 (38.8%) found to be MDR isolates. Conjugation experiments were performed on selected isolates and MDR phenotypes were readily transferred.

Conclusions

Our findings demonstrate that E. coli of equine faecal origin are commonly resistant to antibiotics used in human and veterinary medicine. Furthermore, our results suggest that most antibiotic resistance observed in equine E. coli is encoded by well-known and well-characterized resistant genes common to E. coli from man and domestic animals. These data support the ongoing concern about antimicrobial resistance, MDR, antimicrobial use in veterinary medicine and the zoonotic risk that horses could potentially pose to public health.     

In vitro selection of resistance in <Emphasis Type="Italic">Escherichia coli</Emphasis> and <Emphasis Type="Italic">Klebsiella</Emphasis> spp. at <Emphasis Type="Italic">in vivo</Emphasis> fluoroquinolone concentrations

Background  

Fluoroquinolones are potent antimicrobial agents used for the treatment of a wide variety of community- and nosocomial- infections. However, resistance to fluoroquinolones in Enterobacteriaceae is increasingly reported. Studies assessing the ability of fluoroquinolones to select for resistance have often used antimicrobial concentrations quite different from those actually acquired at the site of infection. The present study compared the ability to select for resistance of levofloxacin, ciprofloxacin and prulifloxacin at concentrations observed in vivo in twenty strains of Escherichia coli and Klebsiella spp. isolated from patients with respiratory and urinary infections. The frequencies of spontaneous single-step mutations at plasma peak and trough antibiotic concentrations were calculated. Multi-step selection of resistance was evaluated by performing 10 serial cultures on agar plates containing a linear gradient from trough to peak antimicrobial concentrations, followed by 10 subcultures on antibiotic-free agar. E. coli resistant strains selected after multi-step selection were characterized for DNA mutations by sequencing gyrA, gyrB, parC and parE genes.     

Detection of Salmonella spp. in retail raw food samples from Vietnam and characterization of their antibiotic resistance

A study was conducted to examine the levels of Salmonella spp. contamination in raw food samples, including chicken, beef, pork, and shellfish, from Vietnam and to determine their antibiotic resistance characteristics. A total of 180 samples were collected and examined for the presence of Salmonella spp., yielding 91 Salmonella isolates. Sixty-one percent of meat and 18% of shellfish samples were contaminated with Salmonella spp. Susceptibility of all isolates to a variety of antimicrobial agents was tested, and resistance to tetracycline, ampicillin/amoxicillin, nalidixic acid, sulfafurazole, and streptomycin was found in 40.7%, 22.0%, 18.7%, 16.5%, and 14.3% of the isolates, respectively. Resistance to enrofloxacin, trimethoprim, chloramphenicol, kanamycin, and gentamicin was also detected (8.8 to 2.2%). About half (50.5%) of the isolates were resistant to at least one antibiotic, and multiresistant Salmonella isolates, resistant to at least three different classes of antibiotics, were isolated from all food types. One isolate from chicken (serovar Albany) contained a variant of the Salmonella genomic island 1 antibiotic resistance gene cluster. The results show that antibiotic resistance in Salmonella spp. in raw food samples from Vietnam is significant.     

Plasmid macroevolution in a nosocomial environment: demonstration of a persistent molecular polymorphism and construction of a cladistic phylogeny on the basis of restriction data

Summary Descendants of a gentamicin resistance plasmid first isolated from the Minneapolis Veterans Administration Hospital in 1975 persisted at the hospital until 1983. During this extended period of time several macroevolutionary variants arose and two classes of variants were shown to persist with the initial plasmid. It was possible to construct a cladistic phylogeny on the basis of restriction endonuclease cleavage patterns of the initial and variant plasmids. Additionally, a plasmid polymorphism comprised of members of the plasmid classes was shown to persist at the hospital throughout the endemic period.     

Analysis of plasmid profile of antibiotic-resistant Enterobacteriaceae circulating in hospitals

Certain pheno- and genotype properties of S. typhimurium and some other representatives of Enterobacteriaceae resistant to antimicrobial drugs were studied. The strains were isolated from children with salmonellosis within 4 months when an infection hospital was subjected to microbiological observation. It was shown that by their antibiotic resistance, phagovars and molecular weights of the plasmid DNas, the strains S. typhimurium were similar to those isolated during hospital infections. The conjugative plasmids responsible for antibiotic resistance in some strains did not differ in their molecular weights and antibiotic resistance markers. The strains S. typhimurium similar in their pheno- and genotype properties were isolated only from 2 patients which allowed one to consider it possible that the patients were infected by the strains of common genesis. Analysis of nonpathogenic representatives of Enterobacteriaceae isolated from the patients along with the S. typhimurium strains confirmed the fact that the patients were infected with the same pathogenic strain.     

Bacteriophage-mediated transduction of antibiotic resistance in enterococci

Aims: Temperate bacteriophages are bacterial viruses that transfer genetic information between bacteria. This phenomenon is known as transduction, and it is important in acquisition of bacterial virulence genes and antimicrobial resistance determinants. The aim of this study was to demonstrate the role of bacteriophages in gene transfer (antibiotic resistance) in enterococci. Methods and Results: Three bacteriophages from environmental samples isolated on pig host strains of Enterococcus gallinarum and Enterococcus faecalis were evaluated in transduction experiments. Antibiotic resistance was transferred from Ent. gallinarum to Ent. faecalis (tetracycline resistance) and from Ent. faecalis to Enterococcus faecium, Enterococcus hirae/durans and Enterococcus casseliflavus (gentamicin resistance). Conclusions: Bacteriophages play a role in transfer of antibiotic resistance determinants in enterococci. Significance and Impact of the Study: This study confirms previous suggestions on transduction in enterococci, in particular on interspecies transduction. Interspecies transduction is significant because it widens the range of recipients involved in antimicrobial resistance transfer.     

Antimicrobial resistance of Enterococcus sp. isolated from the intestinal tract of patients from a university hospital in Brazil

This study reports the results about antimicrobial resistance of Enterococcus spp. isolated from intestinal tract of patients from a university hospital in Brazil. The identification of strains at species level was performed by conventional biochemical tests, API 20 Strep (bioMérieux), and polymerase chain reaction assay. The species distribution was E. faecium (34%), followed by E. faecalis (33%), E. gallinarum (23.7%), E. casseliflavus (5.2%), E. avium (1%), and E. hirae (1%). Intrinsic resistance to vancomycin characterized by presence of vanC genes was found in E. gallinarum and E. casseliflavus. The high prevalence of VanC phenotype enterococci is very important because these species have been reported as causing a wide variety of infections. Vancomycin-resistant E. faecium or E. faecalis were not found and no one isolate of these species was a beta-lactamase producer. Thirteen clinical isolates of enterococci (13.4%) showed multiresistance patterns, which were defined by resistance to three classes of antibiotics plus resistance to at least one aminoglycoside (gentamicin and/or streptomycin). The resistance to several antimicrobials shown by enterococcal strains obtained in this study is of concern because of the decrease in the therapeutic options for treatment of infections caused by enterococci.     

Bacteriophage types of methicillin--resistant Staphylococcus aureus strains isolated in 2005-2006 in the Gdańsk area and their resistance to other antibiotics

The phage type of 38 methicillin--resistant Staphylococcus aureus strains isolated from clinical samples in 5 hospitals in the Gdańsk area in 2005-2007 was determined and antibiotic resistance of obtained phage types was analysed. Phage typing was performed using set of 10 phages as following: MR8, MR12, MR25, 30, 33, 38, M3, M5, 622, 56B. Drug resistance was determined by the disc--diffusion method. There were 12 phage types observed. The most frequent (28.9%) was 56B type which was present in 3 hospitals and in one hospital was found to be predominated. The studied strains were most frequent (23.7%) resistant to erythromycin, clindamycin, ciprofloxacin, trimethoprim/sulfamethoxazole, tetracycline and gentamicin. This resistance pattern predominated in strains belonging to 56B type.     

Daptomycin treatment impacts resistance in off-target populations of vancomycin-resistant Enterococcus faecium

The antimicrobial resistance crisis has persisted despite broad attempts at intervention. It has been proposed that an important driver of resistance is selection imposed on bacterial populations that are not the intended target of antimicrobial therapy. But to date, there has been limited quantitative measure of the mean and variance of resistance following antibiotic exposure. Here we focus on the important nosocomial pathogen Enterococcus faecium in a hospital system where resistance to daptomycin is evolving despite standard interventions. We hypothesized that the intravenous use of daptomycin generates off-target selection for resistance in transmissible gastrointestinal (carriage) populations of E. faecium. We performed a cohort study in which the daptomycin resistance of E. faecium isolated from rectal swabs from daptomycin-exposed patients was compared to a control group of patients exposed to linezolid, a drug with similar indications. In the daptomycin-exposed group, daptomycin resistance of E. faecium from the off-target population was on average 50% higher than resistance in the control group (n = 428 clones from 22 patients). There was also greater phenotypic diversity in daptomycin resistance within daptomycin-exposed patients. In patients where multiple samples over time were available, a wide variability in temporal dynamics were observed, from long-term maintenance of resistance to rapid return to sensitivity after daptomycin treatment stopped. Sequencing of isolates from a subset of patients supports the argument that selection occurs within patients. Our results demonstrate that off-target gastrointestinal populations rapidly respond to intravenous antibiotic exposure. Focusing on the off-target evolutionary dynamics may offer novel avenues to slow the spread of antibiotic resistance.

This study shows that systemic daptomycin use causes selection for daptomycin resistance in gastrointestinal populations of vancomycin-resistant Enterococcus faecium, highlighting the importance of off-target selection on the evolution of antimicrobial resistance.     

Antimicrobial resistance and virulence determinants in European Salmonella genomic island 1-positive Salmonella enterica isolates from different origins

Salmonella genomic island 1 (SGI1) contains a multidrug resistance region conferring the ampicillin-chloramphenicol-streptomycin-sulfamethoxazole-tetracycline resistance phenotype encoded by bla(PSE-1), floR, aadA2, sul1, and tet(G). Its increasing spread via interbacterial transfer and the emergence of new variants are important public health concerns. We investigated the molecular properties of SGI1-carrying Salmonella enterica serovars selected from a European strain collection. A total of 38 strains belonging to S. enterica serovar Agona, S. enterica serovar Albany, S. enterica serovar Derby, S. enterica serovar Kentucky, S. enterica serovar Newport, S. enterica serovar Paratyphi B dT+, and S. enterica serovar Typhimurium, isolated between 2002 and 2006 in eight European countries from humans, animals, and food, were subjected to antimicrobial susceptibility testing, molecular typing methods (XbaI pulsed-field gel electrophoresis [PFGE], plasmid analysis, and multilocus variable-number tandem-repeat analysis [MLVA]), as well as detection of resistance and virulence determinants (PCR/sequencing and DNA microarray analysis). Typing experiments revealed wide heterogeneity inside the strain collection and even within serovars. PFGE analysis distinguished a total of 26 different patterns. In contrast, the characterization of the phenotypic and genotypic antimicrobial resistance revealed serovar-specific features. Apart from the classical SGI1 organization found in 61% of the strains, seven different variants were identified with antimicrobial resistance properties associated with SGI1-A (S. Derby), SGI1-C (S. Derby), SGI1-F (S. Albany), SGI1-L (S. Newport), SGI1-K (S. Kentucky), SGI1-M (S. Typhimurium), and, eventually, a novel variant similar to SGI1-C with additional gentamicin resistance encoded by aadB. Only minor serovar-specific differences among virulence patterns were detected. In conclusion, the SGI1 carriers exhibited pathogenetic backgrounds comparable to the ones published for susceptible isolates. However, because of their multidrug resistance, they may be more relevant in clinical settings.     

Isolation and evaluation of probiotic potential of lactic acid bacteria isolated from poultry intestine

The gut is a source of lactic acid bacteria with remarkable functional and technologies properties as well as a potential source of probiotics. In the present study, 13 strains of Lactobacillus were isolated from poultry intestine and identified according to their 16S rDNA sequences, as well as the evaluation of their probiotic potential. The probiotic properties were tested in aspects of antibiotic susceptibility, antimicrobial activity, exopolysaccharide production, lysozyme tolerance, gut condition tolerance (low pH, bile salt tolerance) and adhesion to human colorectal adenocarcinoma cell line (Caco-2). Most isolates were resistance to streptomycin (10 μg/mL), gentamicin (10 μg/mL), kanamycin (30 μg/mL), penicillin (10 μg/mL) and chloramphenicol (30 μg/mL). Isolates shows strong abilities to adhere to Caco-2 cell in the range of (76 to 85%). Isolates SHA101 to SHA113 showed high survival rate under gastrointestinal tract condition (>80%), indicating their potential in application of probiotics. The results of these tests indicate that the lactic acid bacteria isolated from poultry intestine have potential use as probiotic in various products.     

Anaerobic transfer of antibiotic resistance from Pseudomonas aeruginosa

Pseudomonas aeruginosa, an opportunistic pathogen that often initiates infections from a reservoir in the intestinal tract, may donate or acquire antibiotic resistance in an anaerobic environment. Only by including nitrate and nitrite in media could antibiotic-resistant and -sensitive strains of P. aeruginosa be cultured in a glove box isolator. These anaerobically grown cells remained sensitive to lytic phage isolated from sewage. After incubation with a phage lysate derived from P. aeruginosa 1822, anaerobic transfer of antibiotic resistance to recipients P. aeruginosa PS8EtBr and PS8EtBrR occurred at frequencies of 6.2 x 10(-9) and 5.0 x 10(-8) cells per plaque-forming unit, respectively. In experiments performed outside the isolator, transfer frequencies to PS8EtBr and PS8EtBrR were higher, 1.3 x 10(-7) and 6.5 x 10(-8) cells per plaque-forming unit, respectively. When P. aeruginosa 1822 was incubated aerobically with Escherichia coli B in medium containing nitrate and nitrite, the maximum concentration of carbenicillin-resistant E. coli B reached 25% of the total E. coli B population. This percentage declined to 0.01% of the total E. coli B population when anaerobically grown P. aeruginosa 1822 and E. coli B were combined and incubated in the glove box isolator. The highest concentration of the recipient population converted to antibiotic resistance occurred after 24 h of aerobic incubation, when an initially high donor/recipient ratio (>15) of cells was mixed. These data indicate that transfer of antibiotic resistance either by transduction between Pseudomonas spp. or by conjugation between Pseudomonas sp. and E. coli occurs under strict anaerobic conditions, although at lower frequencies than under aerobic conditions.