Characterization of plasmids which mediate resistance to multiple antibiotics in gram-negative bacteria of nosocomial origin

BACKGROUND: The genetic and molecular mechanisms involved in antimicrobial resistance of 10 strains of gramnegative bacilli (1 Serratia marcescens; 2 Escherichia coli; 1 Proteus mirabilis; 4 Klebsiella pneumoniae; 1 Enterobacter cloacae y 1 Alcaligenes faecalis), isolated from adult patients with nosocomial pulmonary infection at the in-patient facilities of the University Hospital of Los Andes, Mérida, Venezuela, have been studied. METHODS: The antimicrobial susceptibility was determined by minimum inhibitory concentrations using the dilution method in agar. The study of extrachromosomal genes was carried out by conjugation, bacterial infection with the bacteriophage M13 and curing of plasmid by acridine orange. The plasmids were isolated by alkaline lysis and analysis of restriction endonuclease digestion was carried out separately using the enzymes EcoRI and HindIII. A DNA probe, derived from the region which encodes the TEM-1 beta-lactamase of the plasmid pBR322 was used for dot-blot hybridization tests. RESULTS: All of the gramnegative bacilli showed resistance to ampicillin, carbenicillin and cephalothin (> 128 micrograms/ml) and 3 strains also showed resistance to gentamicin (> 64 micrograms/ml). Genetic and molecular procedures showed the presence of conjugative plasmids of approximately 54 kb in all the 10 strains. The restriction patterns obtained by using EcoRI and HindIII indicated common DNA fragments in most of the plasmids studied. The dot-blot hybridization tests confirmed homology between the plasmids and the DNA probe used (TEM-1 beta-lactamase). CONCLUSIONS: In this study, the gramnegative bacteria of nosocomial origin harbored self-transferable plasmids of approximately 54 kb, which mediate resistance to gentamicin and encode a beta-lactamase of the TEM group.     

Evaluation of the usefulness of tests for production of Beta-D-glucuronidase and propylene glycol utilization for the differentiation of enterobacteriaceae rods

The aim of the study was to inquire about the diagnostic usefulness of determining the activity of glucuronidase and utilisation of propylene glycol in Enterobacteriaceae rods. The study included 1511 strains: 411- E. coli, 278 - Klebsiella, 231 - Salmonella, 159 - Yersinia, 97 - Citrobacter, 75 - Shigella and 260 strains representing 6 other kinds of enteric rods. Determination was performed in a liquid medium containing in 1 ml 25 mcg MUG and 100 mcg ONPG. Propylene glycol (PG) utilisation was observed in peptone water with 2% of the substrate and with the Andrade indicator. In comparative tests Rambach commercial medium and MacConkey agar from the Fluorocult series were used. In the test with MUG a positive result was obtained from 81.8% E. coli, 65% - Shigella and 13% - Salmonella subgenus I. Only exceptionally was this test positive with Providencia, Enterobacter and Yersinia strains (1-5%) but negative with Citrobacter, Klebsiella, Serratia, Hafnia, Proteus and Morganella strains. Glucuronidase production is not sufficiently characteristic of E. coli strains isolated from humans to be the only basis for the preliminary differentiation of these rods from other Enterobacteriaceae. The test with ONPG was positive from 95-100% E. coli, Yersinia, Citrobacter, Klebsiella, Enterobacter and Hafnia strains; 61% - Shigella, 9% - Salmonella and 3% - Providencia, but negative with Serratia, Proteus and Morganella strains. Propylene glycol was decomposed by 74% Salmonella strains of subgenus I, 65-94% - Klebsiella, Yersinia and Citrobacter. Shigella, Enterobacter, Serratia, Proteus, Providencia and Morganella rods did not decompose propylene glycol. Evidence that among strains non-decomposing propylene glycol were all the studied S. typhi, S. paratyphi A, S. paratyphi C, S. choleraesuis, S. virchow and S. gallinarum strains as well as a significant percentage of strains representing 8 other Salmonella serotypes frequently detected allows to believe that the use of activity against propylene glycol even simultaneously with the test for galactosidase as basis for the differentiation of Salmonella rods of subgenus I from other Enterobacteriaceae can lead to errors already at the onset of diagnostic procedure.     

The treatment of squint-amblyopia with eccentric fixation (author''s transl)

The antimicrobial activity of netilmicin, a new semisynthetic aminoglycosidic aminocyclitol, was determined against 123 recent gram-negative clinical isolates susceptible to gentamicin and 60 isolates resistant to either sisomicin, gentamicin, or tobramycin. The minimal inhibitory concentrations and minimal bactericidal concentrations of netilmicin, sisomicin, gentamicin, and tobramycin against Pseudomonas, Escherichia coli, Klebsiella, Enterobacter, Proteus mirabilis, and indole-positive Proteus were, in general, quite similar. Gentamicin was the most active against Serratia. A total of 54, 67, and 88% of gentamicin-resistant Pseudomonas, Serratia, and Klebsiella, respectively, were susceptible to netilmicin. Strains of indole-positive Proteus, Acinetobacter, Providencia, and E. coli resistant to gentamicin were likely to be resistant also to netilmicin.     

Antimicrobial activity of fluoroquinolones and other antibiotics on 1,116 clinical gram-positive and gram-negative isolates

A total of 1,116 clinically isolated strains belonging to Staphylococcus aureus (200), Staphylococcus epidermidis (200), Streptococcus pneumoniae (20), Escherchia coli (200), Klebsiella spp. (177), Serratia marcescens (22), Pseudomonas aeruginosa (224), Haemophilus influenzae (35) and Salmonella (38) from the Department of Infectious Diseases, La Sapienza University in Rome (Italy) were tested against three fluoroquinolones (ofloxacin, ciprofloxacin and levofloxacin) and 10 other antibiotics (augmentin, ampicillin, cefaclor, cefixime, cefotaxime, cotrimoxazole, gentamicin, minocycline, oxacillin and vancomycin). Fluoroquinolones inhibited essentially about 100% of H. influenzae, Salmonella and S. pneumoniae, more than 75% of Staphylococcus including methicillin-resistant strains, and about 90% of Enterobacteriaceae and 50% of P. aeruginosa. Minimal inhibitory concentration values ranged from < 0.015 to > 32 micrograms/ml for Klebsiella, S. aureus and epidermidis, E. coli and P. aeruginosa; from < 0.015 to 2 micrograms/ml for Salmonella; from 0.03 to 16 micrograms/ml for Serratia; from < 0.015 to 1 microgram/ml for Haemophilus; and from 0.5 to 2 micrograms/ml for S. pneumoniae. Levofloxacin and to a lesser extent ofloxacin and ciprofloxacin, generally exhibited a greater activity than the other agents against both Gram-positive and Gram-negative bacteria. Regarding the distribution of resistant strains in Italy, we found a peculiar pattern of resistance as far as E. coli and P. aeruginosa were concerned. Quality control parameters are also summarized. S. epidermidis resulted as a new emergent pathogen especially in immunocompromised patients and its level of sensitivity has been modified over the last few years. In fact, the percentage of resistant strains to antibiotics or the percentage of methicillin-resistant isolates (in our study 35%), has gradually increased. Levofloxacin and ofloxacin showed good activity against staphylococcal strains compared with the majority of other antibiotics. These results suggest that the newer quinolones are promising antimicrobial agents for various infections.     

Comparison of activity of sisomicin and gentamicin in mouse protection tests with gram-negative bacilli

The efficacy of sisomicin and gentamicin was compared in mouse protection studies against strains of Escherichia coli, Klebsiella sp., Enterobacter aerogenes, Serratia marcescens, Proteus mirabilis, and Pseudomonas aeruginosa. There was no significant difference in mortality of the mice in any of the protocol groups when five different dosages of sisomicin and gentamicin given by three separate schedules were compared for each bacterial inoculum in each antibiotic protocol. The mean protective dose values of sisomicin were at least one-half those of gentamicin for each protocol against Pseudomonas aeruginosa.     

In vitro antimicrobial activity of fluoroquinolones against clinical isolates obtained in 1989 and 1990

The in vitro activity of nine fluoroquinolones, enoxacin, norfloxacin, ofloxacin, ciprofloxacin, lomefloxacin, tosufloxacin, sparfloxacin, fleroxacin and levofloxacin, and two earlier quinolones, nalidixic acid and pipemidic acid, against 1,346 bacterial strains isolated clinically between 1989 and 1990, was evaluated by agar dilution method. The bacteria studied were Staphylococcus aureus (including methicillin-susceptible and -resistant strains), Staphylococcus epidermidis, Enterococcus species (including high-level gentamicin-resistant strains), Escherichia coli, Salmonella species, Proteus mirabilis, Proteus vulgaris, Morganella morganii, Klebsiella pneumoniae, Enterobacter cloacae, Serratia marcescens, Citrobacter spp., Pseudomonas aeruginosa, Pseudomonas cepacia, Acinetobacter baumannii, and Bacteroides fragilis. In contrast to the moderate to poor activity of two earlier quinolones, the fluoroquinolones acted well against most Enterobacteriaceae and A. baumannii. The minimum inhibitory concentrations for 90% of the drug strains (MIC90s) were < 1 microgram/mL against most tested species. Ciprofloxacin, tosufloxacin, sparfloxacin, and levofloxacin were more effective against multi-drug-resistant nosocomial pathogens. All fluoroquinolones assayed were very active against methicillin-susceptible S. aureus, with MIC90s < or = 1 microgram/mL. For methicillin-resistant strains, on the other hand, the MIC90s were > or = 4 micrograms/mL. There was no significant difference in fluoroquinolone susceptibility between methicillin-susceptible and -resistant S. epidermidis. Sparfloxacin, tosufloxacin, ciprofloxacin and levofloxacin were more active against enterococci. Most fluoroquinolones were relatively inactive against B. fragilis, with the exception of tosufloxacin, sparfloxacin and levofloxacin. The MIC90s of most quinolones assayed against K. pneumoniae, Citrobacter spp., E. cloacae, S. aureus and S. epidermidis were at least four-fold higher in our study. Therefore, it is important for physicians to use fluoroquinolones carefully so as to prevent or delay the emergence of resistant strains.     

Comparison of the antibacterial activity of nine cephalosporins against Enterobacteriaceae and nonfermentative gram-negative bacilli

The in vitro antibacterial activity of nine cephalosporins (cephalothin, cephaloridine, cephalexin, cefazolin, cefamandole, cefuroxime, cefatrizine, cefoxitin, and cefazaflur) was determined against 344 strains of Enterobacteriaceae and 99 nonfermentative gram-negative bacilli. Cefamandole, cefazaflur, and cefuroxime were the most active cephalosporins against the Enterobacteriaceae (with the exception of Serratia marcescens). However, cefoxitin was the only cephalosporin that inhibited all 30 S. marcescens strains in a concentration of 16 mug/ml and was by far the most active compound against selected cephalothin-resistant strains of Escherichia coli, Klebsiella, and Proteus mirabilis. Acinetobacter spp. were inhibited best by cefuroxime, but none of the cephalosporins had appreciable activity against the Pseudomonas spp.     

In vitro antimicrobial activities of lactoferrin, its concomitant use with cefpodoxime proxetil and clinical effect of cefpodoxime proxetil

As one of the biodefense mechanisms, lactoferrin (LFN) in the secreta of female genital organ may be an interesting biological material in view of its antimicrobial activity. In the present study, we investigated antimicrobial activities of LFN and its combination with cefpodoxime proxetil (CPDX-PR), we also as evaluated clinical effect of CPDX-PR. The following results were obtained. 1. Antimicrobial activities of LFN were tested against 15 strains of 10 species of bacteria, and potent activities against Staphylococcus aureus 209P, Escherichia coli, Klebsiella pneumoniae and Proteus spp. were found. 2. In a concomitant use of LFN with CPDX-PR (a checkerboard method), synergistic actions were observed against S. aureus 209P, E. coli STf, K. pneumoniae 602 and Pseudomonas aeruginosa 1046, and additive actions against E. coli NIHJ and Providencia rettgeri 1603. In 3 strains, the MICs of CPDX-PR in the presence of LFN were reduced to < 1/64. 3. In the evaluation of clinical effect of CPDX-PR, efficacy rates were 53/57 (92.9%) in a patient group with infections. The incidence of adverse reaction was 0/57.     

Ceftezole, a new cephalosporin C derivative I. In vitro and in vivo antimicrobial activity

Ceftezole, a new cephalosporin antibiotic similar to cefazolin, has the following chemical structure: (6R,7R)-8-oxo-7[2-(1H-tetrazol-1-yl)acetamido]-3-[(1,3,4-thiadiazol-2-ylthio)methyl]-5-thia-1-azabicyclo[4.2.0]oct-2-ene-carboxylic acid. Ceftezole was found to be a broad-spectrum antibiotic, active in vitro against many species of gram-positive and gram-negative bacteria except Pseudomonas aeruginosa, Serratia marcescens and Proteus vulgaris. The activity of ceftezole against clinical isolates of Escherichia coli and Klebsiella spp. appeared to be nearly equal to that of cefazolin and higher than those of cephaloridine and cephalothin. Cross-resistance was observed between ampicillin and cephaloridine, but not between ampicillin and ceftezole, in susceptibility tests on clinical isolates of P. mirabilis. The in vitro activity was little affected by the inoculum size, the presence of human serum or the test medium. Ceftezole exhibited apparent bactericidal activity at the concentrations above the minimum inhibitory concentration (MIC) against both S. aureus and E. coli. The development in vitro of resistance by S. aureus 209p and E. coli NIHJ to ceftezole after 16 transfers was similar to or somewhat slower than that to other drugs tested. Ceftezole was relatively stable in nutrient broth and minimally degraded in the serum or tissue homogenates of rats. Ceftezole, in a single subcutaneous administration, exhibited somewhat less efficacy in mice against intraperitoneal infections with Streptococcus pyogenes, S. pneumoniae, E. coli, K. pneumoniae or P. mirabilis than either cephaloridine or cefazolin. However, ceftezole exhibited efficacy similar to that of cephaloridine or cefazolin when administered in three doses. Furthermore, ceftezole was as effective as cefazolin in the treatment of experimental abscesses in mice caused by subcutaneous inoculation with S. aureus.     

Quantitative bacterial ecology of normal nasal mucosa

A quantitative research into the aerobic bacteria of human nasal cavities has been carried out; 183 healthy individuals observed, negative results 18 (9.83%). Streptococcus, Enterococcus, Staphylococcus aureus, Staphylococcus epidermidis, Micrococcus, Streptococcus pneumoniae, Neisseria, were numerically determined and the incidence of each single species or genus exactly specified. Among gram-negative bacteria, Enterobacter, Providencia, Proteus, Citrobacter freundii, Haemophilus influenzae, Klebsiella pneumoniae, Escherichia coli, Serratia, Herella, Pseudomonas, and among the Hyphomycetes, Candida albicans have been identified and their number calculated. Diphteroid bacteria were also detected and counted; among them, the Corynebacterium pseudodiphtheriticum seemed to be the most frequent and numerous species. Finally, interference phenomena in vivo by Staphylococcus aureus and environmental and nourishment competition by Staphylococcus epidermidis, Streptococcus and Diphtheroids were noted.     

Characterization of ceftriaxone-resistant Enterobacteriaceae: a multicentre study in 26 French hospitals. Vigil'Roc Study Group

During a multicentre study performed in 26 French hospitals, 287 (3.2%) of 9038 Enterobacteriaceae isolated, mainly Enterobacter spp., Serratia spp., Citrobacter spp. and Klebsiella spp. were classified as ceftriaxone resistant on the basis of an MIC > 4 mg/L or the presence of an extended-spectrum beta-lactamase. Extended-spectrum beta-lactamase was present mainly in Klebsiella pneumoniae (65 strains, 10.2%) and very rarely in Escherichia coli, Proteus mirabilis, Klebsiella oxytoca, Citrobacter spp. and Enterobacter spp. The extended-spectrum beta-lactamases conferred low-level resistance to ceftriaxone in nearly 60% of the strains harbouring them, emphasizing the need for routine testing for the presence of these enzymes. Among transconjugants three types of extended-spectrum beta-lactamase were identified. Those resembling TEM-3 were the most common, but TEM-21, and SHV-4 were also found. Clavulanate and to a lesser extent sulbactam inhibited all the extended-spectrum beta-lactamases encountered in this study.     

Antigenic crossreactivity and lipopolysaccharide neutralization properties of bovine immunoglobulin G

We investigated a possible mechanism by which immunization against core and lipid A determinants of lipopolysaccharide reduced clinical cases of mastitis and symptoms commonly associated with heterologous Gram-negative IMI. The IgG fraction of sera from cows immunized with either Escherichia coli J5 bacterin, E. coli J5 lipopolysaccharide conjugate vaccine, or unimmunized controls was purified by precipitation with caprylic acid and ammonium sulfate. The degree of IgG crossreactivity with Gram-negative bacteria that were isolated from clinical quarters was greater than that with Gram-positive isolates of Staphylococcus aureus. The highest magnitude of crossreactivity was against smooth strain E. coli isolates, followed by heterologous species of Enterobacter, Serratia, and Klebsiella isolates. Serum IgG from cows immunized with conjugate was highly crossreactive to E. coli J5, E. coli O111:B4, Serratia marcescens, Klebsiella pneumoniae, and Salmonella typhimurium lipopolysaccharides. The magnitude of antibody crossreactivity with lipopolysaccharides coincided with the ability of IgG to suppress the mitogenic effect of lipopolysaccharides on bovine lymphocytes.     

A gene (wbbL) from Serratia marcescens N28b (O4) complements the rfb-50 mutation of Escherichia coli K-12 derivatives

A cosmid-based genomic library of Serratia marcescens N28b was introduced into Escherichia coli DH5alpha, and clones were screened for serum resistance. One clone was found resistant to serum, to bacteriocin 28b, and to bacteriophages TuIa and TuIb. This clone also showed O antigen in its lipopolysaccharide. Subcloning and sequencing experiments showed that a 2,124-bp DNA fragment containing the rmlD and wbbL genes was responsible for the observed phenotypes. On the basis of amino acid similarity, we suggest that the 288-residue RmlD protein is a dTDP-L-rhamnose synthase. Plasmid pJT102, containing only the wbbL gene, was able to induce O16-antigen production and serum resistance in E. coli DH5alpha. These results suggest that the 282-residue WbbL protein is a rhamnosyltransferase able to complement the rJb-50 mutation in E. coli K-12 derivatives, despite the low level of amino acid identity between WbbL and the E. coli rhamnosyltransferase (24.80%). S. marcescens N28b rmlD and wbbL mutants were constructed by mobilization of suicide plasmids containing a portion of rmlD or wbbL. These insertion mutants were unable to produce O antigen; since strain N28b produces O4 antigen, these results suggest that both genes are involved in O4-antigen biosynthesis.     

Canadian Pseudomonas aeruginosa susceptibility study from 48 medical centers: focus on ciprofloxacin

The carbapenem-induced endotoxin release was evaluated using experimental models of gram-negative bacterial sepsis in Wistar rats. Infections with Escherichia coli, Serratia marcescens, Klebsiella pneumoniae, Pseudomonas aeruginosa, Proteus vulgaris and Proteus mirabilis resulted in an increase of the plasma endotoxin concentration after treatment with ceftazidime and carbapenems including imipenem, panipenem, meropenem and biapenem. Except for P. aeruginosa, the plasma endotoxin concentrations after carbapenem treatment were significantly lower than those after ceftazidime treatment. It is noteworthy that treatment of P. aeruginosa sepsis with meropenem or biapenem induced significantly more endotoxin release than other carbapenems and the endotoxin concentrations induced by these carbapenems reached those of ceftazidime treatment. The plasma endotoxin concentrations appeared to correlate with the reduction of platelet counts and the elevation of both glutamic oxaloacetic transaminase and glutamic pyruvic transaminase values.     

Ciprofloxacin resistance in gram negative bacilli. Epidemiologic aspects

BACKGROUND: The aim of the present was to study the resistance to ciprofloxacin (CIP) in gram negative bacilli (April 1990-March 1992) and to determine the temporary distribution of the resistant strains by species, samples and departments. METHODS: Seven thousand four hundred seventy-eight samples were studied. The identification and determination of the sensitivity was performed by the PASCO (Difco) system. Haemophilus spp. and Campylobacter spp. were excluded from the study. The microorganisms with CIM 2 mg/l were considered as resistant (CIPr). RESULTS: Four hundred eighty-one CIPr isolations were identified (6.4%). With regard to the percentage of resistant strains, the species with the highest were: Providencia stuartii (50%); Pseudomonas cepacia (44.4%); Xanthomonas maltophilia (26.9%); Acinetobacter baumannii (25.8%); Pseudomonas aeruginosa (16%); Citrobacter freundii (12.5%); Serratia marcescens (8.4%); Enterobacter cloacae (5.8%) and Escherichia coli (4.3%). With respect to the absolute number of resistant strains, the most frequent resistant strains were: P. aeruginosa (205), E. coli (144), and A. baumannii (41). Isolation of E. coli and A. baumannii CIPr increased over the study period. Forty-four point five percent of the E. coli CIPr were of extrahospitalary origin; most of the A. baumannii (92.9%) and P. aeruginosa (77.6%) in contrast were of intrahospitalary origin. CONCLUSIONS: P. aeruginosa, E. coli, and A. baumannii are the most frequently resistant species. The frequency of isolation of resistant strains of E. coli and A. baumannii significantly increased (p < 0.001) over the two years of the study.     

Antimicrobial activities of major oral antibacterial agents against clinically isolated microbial strains from inpatients]

Antimicrobial activities were examined for major antibacterial agents against clinically isolated microbial strains which were isolated and identified from materials collected from inpatients with various infections in 1988, 1989 and 1990, and the following conclusions were obtained. 1. Among strains isolated each year, methicillin-resistant Staphylococcus aureus (MRSA) were found frequently. 2. CEPs-resistant Escherichia coli strains were observed among strains isolated each year. 3. Increasing tendencies in resistances of Citrobacter freundii, Enterobacter spp., Serratia marcescens to cephems and new quinolones were observed. 4. Increasing tendencies in resistances of Proteus vulgaris to ceftazidime (CAZ) and new quinolones appeared to exist. 5. Among strains isolated each year, resistances of Pseudomonas aeruginosa to CAZ and quinolones were observed in high rates, but also their resistances to imipenem appeared to increase. 6. Many of recently increasing multiple resistant bacteria seem to have different sites of drug action and/or to have non-hydrolytic modes of resistance.     

Diagnostic imaging and therapeutic implications in lung infections in patients with HIV-1 infection

We studied retrospectively 132 episodes of infectious pneumonias in 89 patients examined from 1990 to 1995. Pneumocystis carinii was found to be the most common cause of pneumonia (33 patients). The other causes were: Streptococcus pneumoniae (15), Mycobacterium tuberculosis (14), Pseudomonas aeruginosa (8), Staphylococcus aureus (5), Cytomegalovirus (4), Haemophilus influentiae (4), Mycobacterium avium intracellulare (2), Klebsiella pneumoniae (2), E. coli (2), Serratia marcescens (1). No etiologic agent was found in 40 cases. We stress the need of a more frequent use of invasive diagnostic procedures in the study of focal lung consolidations because this radiologic sign is highly aspecific and may be caused by too many different pathogenic agents, needing different therapies-i.e., Streptococcus pneumoniae (15 cases), Pseudomonas aeruginosa (8), Staphylococcus aureus (5), Klebsiella pneumoniae (2), Escherichia coli (2), Pneumocystis carinii, Serratia marcescens and Haemophilus influentiae (1). Since there is an increase in mortality among patients treated with empiric antibiotic therapy, we stress the need of the routinary use of bronchoalveolar lavage in HIV+ patients with lung consolidation to perform specific therapy. Moreover, Pneumocystis carinii is by far the most frequent cause of diffuse interstitial infiltrates, and PCP has very suggestive clinical (dyspnea), radiologic (diffuse perihilar interstitial infiltrates; ground glass opacities; pneumatoceles) and laboratory (CD3+CD4 < 200/mcl; LDH > 600 UI/dl; PO2 < 70 mmHg) patterns, always related to the discovery of Pneumocystis carinii in escreatum. Thus, we decided to treat 15 patients with specific therapy for Pneumocystis carinii pneumonia with the above diagnostic algorithm, obtaining in all of them complete clinical and radiologic recovery. To conclude, in critical patients, invasive procedures should be performed only in the cases in which PCP is clinically improbable.     

Demodex folliculorum and topical treatment: acaricidal action evaluated by standardized skin surface biopsy

Resistance to third-generation cephalosporins mediated by beta-lactamases is an increasing problem for clinical therapeutics. A wide range of Enterobacteriaceae produce these AmpC enzymes (Bush-Jacoby-Medeiros group 1), including Enterobacter spp., Citrobacter freundii, Morganella morganii, Providencia spp., and Serratia marcescens. Resistance via this mechanism has been shown to be statistically correlated with the use of some third-generation cephalosporins, and the infections caused by these stably derepressed enzyme-producing species seem to occur most frequently in the seriously ill. More recently the genes encoding this enzyme have been documented on plasmids capable of transfer into other species such as Klebsiella pneumoniae. Fourth-generation cephalosporins, with stability and low affinity for the Amp C beta-lactamases and the ability to penetrate rapidly into the periplasmic space of Gram-negative organisms, offer a viable alternative in the treatment of these infections or as empiric regimens. Furthermore, these compounds (example: cefpirome) possess greater potency against the frequently occurring Gram-positive cocci such as oxacillin-susceptible staphylococci and the streptococci (including some penicillin-resistant strains) as compared to previously used anti-pseudomonal cephalosporias, ceftazidime.     

Plasmid-mediated gentamicin resistance of Pseudomonas aeruginosa and its lack of expression in Escherichia coli

We isolated 11 nonconjugative plasmids mediating resistance to aminoglycoside antibiotics, including gentamicin, from Pseudomonas aeruginosa strains. Their genetic properties were investigated in both P. aeruginosa and Escherichia coli transformants. The plasmid molecular weights ranged from 11 x 10(6) to 24 x 10(6). A low level or complete absence of gentamicin resistance was observed when these plasmids were introduced into E. coli, but gentamicin resistance was restored when the plasmids were transferred back to P. aeruginosa from E. coli. Aminoglycoside-modifying enzyme activity was detected in P. aeruginosa harboring these plasmids, but was absent or greatly reduced in E. coli strains. This lack of expression may explain the observed decrease in aminoglycoside resistance.     

N-formimidoyl-thienamycin: in vitro activity in bacteria with resistance to beta-lactam antibiotics or gentamicin

The minimum inhibitory concentration (MIC) and the minimum bactericidal concentration (MBC) of N-formimidoyl-thienamycin were determined for 25 strains each of Escherichia coli, Klebsiella pneumoniae, Enterobacter cloacae, Serratia marcescens and Pseudomonas aeruginosa which were resistant to gentamicin and/or acylureido penicillins or cefotaxime, cefoperazone or moxalactam, and for 38 strains of the group D streptococci. The drug was very active against the most frequently encountered gram-negative resistant causative organisms of nosocomial infections. The MIC ranged from 0.25-1 mg/l for multiresistant Enterobacteriaceae, and from 0.5-4 mg/l for multiresistant P. aeruginosa. The group D streptococci (enterococci) showed a low MIC (median: 0.75 mg/l); the median of the MBC was greater than 64 mg/l, however.