Strains Of Gram-negative Bacilli Research Articles

Antimicrobial Activity and Spectrum Investigation of Eight Broad-Spectrum β-Lactam Drugs: A 1997 Surveillance Trial in 102 Medical Centers in the United States

Because antimicrobial agents become less effective after the emergence of resistance mechanisms in clinically prevalent pathogens, physicians must utilize local, regional, and national antimicrobial susceptibility surveillance data to assist in choices of appropriate agents. An investigation of the spectrum and potency of eight broad-spectrum β-lactam drugs (cefepime, cefotaxime, ceftazidime, ceftriaxone, imipenem, piperacillin with or without tazobactam, and ticarcillin/clavulanic acid) was performed using a common protocol and method (Etest; AB BIODISK, Solna, Sweden) in 102 clinical microbiology laboratories in the United States. A total of 9777 strains of Gram-negative bacilli were tested from late 1996 through April 1997. Quality assurance measures using three control strains observed quality control failures in 13 laboratories (usually ticarcillin/clavulanic acid or piperacillin), but only 2% of results required deletion. A total of 33.4% of Enterobacter spp. (1977 strains) were either resistant or intermediately susceptible to ceftazidime. Only imipenem (99.6% susceptible) and cefepime (99.1%) remained highly active against strains of Enterobacter, as well as Citrobacter freundii, indole-positive Proteae, and Serratia spp. Ceftazidime-resistant Escherichia coli and Klebsiella pneumoniae were detected at rates of 10.3% and 23.8%, respectively. Although these were participant-selected strains, only imipenem and cefepime had broad-spectrum coverage (≥97.1%) against these extended-spectrum β-lactamase phenotypes. A dominant number of these extended-spectrum β-lactamase phenotypes were reported from medical centers in the Northeast, but a nationwide distribution was observed. Among the nonenteric Gram-negative bacilli (4057 strains), the rank order of susceptibility (percent inhibited at published breakpoint concentrations) was: imipenem (86.1%) > piperacillin/tazobactam (80.1%) > cefepime (77.1%) > ceftazidime = piperacillin (74.9%) > ticarcillin/clavulanic acid (61.6%) > cefotaxime (18.2%) > ceftriaxone (12.9%). The cephalosporins, cefepime and ceftazidime, had rates of resistance for the 3005 Pseudomonas aeruginosa isolates of 10.1% and 14.4%, respectively. For all Gram-negative strains tested, only two contemporary β-lactam antimicrobials exhibited >90% inhibition of strains, imipenem at 93.6% and cefepime at 90.2%. These drugs were superior to the other tested compounds (48.8–84.3%). Ticarcillin/clavulanic acid had the narrowest spectrum of activity (48.8% of isolates susceptible). These results indicate that carbapenems and a new fourth-generation cephalosporin, cefepime, possess usable in vitro potencies against current clinical strains of Gram-negative bacilli, many of which harbored resistance to other antimicrobial agents.

Endogenous source of bacteria in tracheal tube and proximal ventilator breathing system in intensive care patients

Although bacteria from both the ventilator breathing system and the gastrointestinal tract have been implicated in the pathogenesis of ventilator-associated pneumonia, an endogenous source of bacteria in the proximal respiratory breathing system has yet to be demonstrated conclusively. We investigated a potential route of bacterial colonization from the stomach contents to the efferent limb of the ventilator breathing system by bacterial culture of daily specimens from six sites in 20 surgical intensive care patients. Gram-negative bacilli were isolated in a progressively increasing proportion of samples at successive sampling points, consistent with an endogenous-to-external route of spread (patients, chi-square = 14.12, P < 0.02; samples, chi-square = 106.15, P < 0.001). Identical strains of gram-negative bacilli, confirmed by REPS typing, were found at two or more sites in seven patients. In all seven, gram-negative bacilli were first isolated from a site in the patient. In none of the 20 patients was there evidence of a sequence of colonization from the ventilator tubing or Y-piece connector towards the patient. Probable colonization sequences plotted from the time of first isolation supported the proposed sequence in six patients, and in five began with the stomach contents. Isolation sequences contrary to the proposed direction of colonization involved four bacterial species and two patients, and did not extend beyond two sample sites. These findings imply that the retrograde route of bacterial colonization of the ventilated lung extends into the proximal respiratory breathing system and may help to identify additional targets for preventive intervention.

Aminoglycoside resistance. Enzymatic mechanisms in clinical bacterial strains in Slovakia during the last decade

We determined the importance and dissemination of enzymatic mechanisms of aminoglycoside resistance in 239 gentamicin-resistant strains of Gram-negative bacilli isolated in Slovakia during the past decade. Over the past 5 years, the resistance to tobramycin has risen by 1.1%, to netilmicin by 27.4%, to amikacin by 78.3%, and resistance to isepamicin was high too (81.9%). Sixteen different aminoglycoside-modifying enzymes were detected and their significance for resistance to aminoglycosides was confirmed. It is evident that within the past 5 years gentamicin-resistant bacteria have obtained genetic information on resistance to the other aminoglycosides tested and the percentage of strains with different enzyme combinations has risen. These observations confirm the continuously increasing complexity of antibiotic resistance in clinical bacterial isolates under study in Slovakia during the last decade.

Aminoglycoside resistance. Enzymatic mechanisms in clinical bacterial strains in Slovakia during the last decade.

We determined the importance and dissemination of enzymatic mechanisms of aminoglycoside resistance in 239 gentamicin-resistant strains of Gram-negative bacilli isolated in Slovakia during the past decade. Over the past 5 years, the resistance to tobramycin has risen by 1.1% to netilmicin by 27.4%, to amikacin by 78.3%, and resistance to isepamicin was high too (81.9%). Sixteen different aminoglycoside-modifying enzymes were detected and their significance for resistance to aminoglycosides was confirmed. It is evident that within the past 5 years gentamicin-resistant bacterial have obtained genetic information on resistance to the other aminoglycosides tested and the percentage of strains with different enzyme combinations has risen. These observations confirm the continuously increasing complexity of antibiotic resistance in clinical bacterial isolates under study in Slovakia during the last decade.

Antimicrobial activity of RU-66647, a new ketolide

A new macrolide subclass called ketolides, possess a mode of action similar to the macrolide-lincosamide-streptogramin (MLS) compounds. Utilizing reference in vitro tests, the in vitro activity of RU-66647 (a ketolide) was compared to other MLS compounds against 376 Gram-positive organisms and over 400 representative strains of Gram-negative bacilli. The ketolide's spectrum was most similar to clindamycin and an earlier drug in the series (RU-64004 or RU-004) against staphylococci and streptococci. However, RU-66647 was more active than erythromycin and azithromycin against oxacillin-resistant Staphylococcus spp. and vancomycin-resistant enterococci. Ketolide activity was more potent than other MLS drugs against vancomycin-susceptible enterococci (MIC 90′, 3.25–4 μg/ml) and all streptococci (MICs, ⩽0.25 μg/ml). Erythromycin-resistant (constitutive) strains were generally inhibited by ⩽2 μg RU-66647/ml (staphylococci, 31 to 36%; streptococci, 100%; enterococci, 72%). RU-66647 was active against Haemophilus influenzae (MIC 90′, 2 μg/ml), Moraxella catarrhalis (MIC 90, 0.12 μg/ml), and pathogenic Neisseria spp. (MIC 90 0.5 μg/ml). The ketolide failed to inhibit Enterobacteriaceae, nonfermentative Gram-negative bacilli, and Bacteroides fragilis group strains. RU-66647 was observed to be a promising new compound directed toward some organisms resistant to other MLS-class drugs.

Infection surveillance and antibiotic utilization in a community-based skilled nursing facility.

To survey the types of suspect infections, the antibiotic utilization and the patterns of antibiotic resistance among bacterial pathogens in a community Skilled Nursing Facility (SNF), we conducted a 20-month prospective observational surveillance program comprising all 585 patients admitted to a 149-bed private community SNF. Data were collected form medical charts, laboratory reports and nurses reports. Overall, 41% of the patients developed at least one presumptive nosocomial infection, and 54% of the patients received one or more antibiotic treatments. The overall presumptive nosocomial infection rate was 7.2 per 1000 patient days. The most common sites of presumptive nosocomial infection were the urinary tract (38%) and the respiratory tract (28%). The most common pathogens overall were E. coli (25%). Antibiotic groups used most frequently were the quinolones (22% of prescriptions). Thirty-nine percent of the Staphylococcus aureus isolates associated with suspected infections were resistant to methicillin, and of these 94% were also resistant to ciprofloxacin. Most of the resistant S. aureus isolates were from indwelling catheter-associated with UTIs. Infections associated with quinolone resistant strains of gram-negative bacilli were infrequent. No epidemiologic evidence of nosocomial clustering was apparent.

Activity of sucralfate (sucrose octa-sulphate), an anti-ulcer agent, against opportunistic gram-negative bacilli.

The in-vitro activity of sucralfate (sucrose octa-sulphate) in suspension was examined against 128 strains of Gram-negative bacilli. Inhibitory activity was demonstrated against all isolates and bactericidal activity was demonstrated for 68. Sucralfate has inhibitory and bactericidal antibacterial activity which may contribute to its in-vivo clinical efficacy.

Study on the bacteriological examination of sputum and bronchoscopy specimens from 31 cases with pneumonia due to Chlamydia psittaci

We carried out the bacteriological examination of sputum and bronchoscopy specimens from 31 cases with pneumonia due to C. psittaci. The results obtained were as follows: 1. The positive culture of sputum and bronchoscopy specimens were 38.7% (12/31). 2. The organisms detected from them were 13 strains of gram-negative bacilli, 2 of gram-positive cocci and one gram-positive bacillus. 3. Significant differences were observed in the white blood cell count between the cases of positive culture and those of normal upper respiratory tract flora (p less than 0.05). From the results we conclude that it would be better that we add the proper antimicrobial drugs to chlamydial antibiotics in the treatment of patients with leukocytosis.

Cefpodoxime: Comparative antibacterial activity, influence of growth conditions, and bactericidal activity

The antimicrobial activity of cefpodoxime, the active metabolite of the new cephalosporin ester cefpodoxime proxetil, in comparison to cefixime, cefotiam, cefuroxime, and cefotaxime was determined against a broad spectrum of freshly isolated gram-positive and gram-negative bacterial strains. Cefpodoxime was demonstrated to be inhibitory at concentrations of less than or equal to 1 mg/l against 90% of strains of Moraxella catarrhalis, Haemophilus influenzae, Escherichia coli (beta-lactamase- negative strains), Klebsiella spp., Serratia spp., Proteus mirabilis, Proteus vulgaris, Providencia spp., and Salmonella spp. This antimicrobial activity of cefpodoxime was generally superior to that of cefuroxime and similar to that of cefixime. Cefpodoxime was active at less than or equal to 1 mg/l against 50% of the members of beta-lactamase-producing Escherichia coli, Enterobacter cloacae, Enterobacter aerogenes, Citrobacter spp., and Morganella morganii. Cefpodoxime proved to be highly inhibitory against group A, B, and G streptococci and Streptococcus pneumoniae (MIC90 less than 0.015 mg/l). The MICs of cefpodoxime and those of the other cephalosporins were less than 2 mg/l for greater than or equal to 90% of the strains of Staphylococcus aureus and Staphylococcus epidermidis, with the exception of cefixime which had no activity with MICs below 8 mg/l against these bacteria. Pseudomonas spp., Acinetobacter spp., and Enterococcus spp. were resistant to cefpodoxime. The antibacterial activity of cefpodoxime was only to a minor degree influenced by different growth conditions with the exception of high inoculum sizes against some beta-lactamase producing strains of gram-negative bacilli.(ABSTRACT TRUNCATED AT 250 WORDS)

Comparison of microbiologic assay methods for hemodialysis fluids

To help prevent pyrogenic reactions and bacteremia in hemodialysis patients, the Association for the Advancement of Medical Instrumentation and the Centers for Disease Control recommend microbiologic assay of hemodialysis fluids at least monthly. Five commercially available assay systems were evaluated by using the membrane filtration technique with standard methods agar and trypticase soy agar as the standards for comparison. Each assay system was challenged with dialysate and reverse-osmosis water from local dialysis centers, aqueous suspensions of eight laboratory strains of gram-negative bacilli and nontuberculous mycobacteria, and a mixed microbial flora inoculated into reverse-osmosis water and laboratory-prepared dialysate. Mean viable counts from triplicate samples were obtained after incubation at 37 degrees C for up to 72 h. The efficiency of recovery varied with the specific type of microbial challenge. The SPC water sampler (Millipore Corp., Bedford, Mass.) was the most consistent in obtaining the highest viable counts. Other commercial systems were comparable to each other in overall performance. All assay systems tested provided an acceptable balance between microbial recovery and required sampling time, equipment, and expertise.

In vitro Activity of Cefepime, a New Parenteral Cephalosporin, against Recent European Blood Isolates and in Comparison with Piperacillin/Tazobactam

Cefepime, a new parenteral cephalosporin with broad antibacterial spectrum and stability to the hydrolysis to many bacterial beta-lactamases, was tested against recent blood culture isolates (369 strains of gram-negative bacilli and 131 strains of staphylococci) collected in 29 European laboratories by the microdilution method in Mueller-Hinton broth. Cefepime was very active against the gram-negative bacilli (MIC50 less than or equal to 0.016-0.064 mg/l; MIC90 0.064-4 mg/l) and less active against Pseudomonas (MIC50 4 mg/l; MIC90 greater than 16 mg/l) or Acinetobacter (MIC50 and MIC90 greater than 16 mg/l). The staphylococci were also inhibited (MIC50 8 mg/l; MIC90 16 mg/l). Cefepime was very active against bacteria producing different plasmid-encoded beta-lactamases (MIC 0.016-0.5 mg/l). Piperacillin was not active against the latter strains (MIC from 2 to greater than 64 mg/l), but the presence of the beta-lactamase inhibitor tazobactam restored the activity of piperacillin. The bactericidal activity of cefepime and piperacillin/tazobactam against beta-lactamase-producing strains was confirmed by the killing curve technique.

Construction of a probe for the aminoglycoside 3-V-acetyltransferase gene and detection of the gene among endemic clinical isolates.

A recent surveillance study at Vanderbilt University Medical Center indicated that 8.5% of the gram-negative bacilli isolated were resistant to gentamicin. To determine what proportion of current gentamicin-resistant isolates elaborated aminoglycoside 3-V-acetyltransferase [AAC(3)-V], a probe for this gene was constructed from a 975-base-pair PstI-SalI fragment of the nonconjugative R plasmid pCER954b. This plasmid was first isolated at Vanderbilt University Medical Center from epidemic strains of Serratia marcescens. Nineteen isolates determined to produce AAC(3)-V by MIC profile all reacted with the probe. The probe did not hybridize with DNA from organisms producing 10 other aminoglycoside-modifying enzyme types. With this probe, 30 (36%) of 84 gentamicin-resistant, gram-negative bacilli elaborated AAC(3)-V. Of these 30 isolates, 25 contained a conjugative plasmid that transferred gentamicin resistance. In contrast to other medical centers, at Vanderbilt a sizable number of gentamicin-resistant, gram-negative bacilli produced AAC(3)-V. This resistance determinant, initially identified in an epidemic Serratia strain, has persisted and become incorporated into currently isolated endemic strains of gram-negative bacilli.

A clinical study on imipenem/cilastatin sodium in the field of pediatrics

A clinical study on imipenem/cilastatin sodium (MK-0787/MK-0791) was carried out and the following results were obtained. MK-0787/MK-0791 was used for treatment of a total of 33 patients and clinical effectiveness, bacteriological efficacy and adverse reactions were evaluated. The clinical effects were excellent in 1 case, good in 21 cases and fair in 2 cases in a total of 24 cases with respiratory tract infections, were excellent in 5 cases and good in 1 case in a total of 6 cases with urinary tract infections, and were good in 2 cases and fair in 1 case in a total of 3 cases with gastroenteritis. Causative organisms isolated from 11 patients were 1 strain of Gram-positive cocci and 10 strains of Gram-negative bacilli. Ten out of 11 strains were eradicated for an eradication rate of 91%. The clinical efficacy was confirmed in 11 cases for an efficacy rate of 100%. The bacteriological study has shown that MK-0787/MK-0791 has a strong antimicrobial activity. No side effects were observed. There was only one abnormal laboratory finding, i.e., a case of eosinophilia.

Antibiotic Resistance Patterns During Aminoglycoside Restriction

When amikacin first became available its use was restricted to prevent the emergence of resistant strains of gram-negative bacilli to this new agent. Gentamicin was the aminoglycoside most widely used at this time, and the incidence of gentamicin-resistant bacteria was 14%, while only 2.4% were resistant to amikacin. For a period of 15 months gentamicin use was restricted, and amikacin was used almost exclusively. Amikacin use was associated with a fall in the incidence of gentamicin-resistant bacteria to 9.2% (p less than .00005), while amikacin resistance remained unchanged at 2.2% (NS). During a period of 21 months after all aminoglycoside restrictions were lifted, gentamicin use again increased, and was accompanied by a return of gentamicin resistance to the baseline level of 15.3%. During this period, amikacin resistance also increased to 4.0% (p less than .0000001) but was due primarily to an increase in resistant Pseudomonas aeruginosa. Escherichia coli was the most frequently isolated gram-negative bacillus during all three periods, and it remained sensitive to both antibiotics regardless of the drug in use. In contrast, P. aeruginosa showed a high level of resistance to gentamicin, which fell when this antibiotic was restricted, only to return to a high level with reinstitution of gentamicin. While there was also an increase in amikacin resistant strains of P. aeruginosa with unrestricted aminoglycoside use, there was no apparent shift in the pattern of aminoglycoside modifying enzymes among a small random selection of amikacin-resistant bacteria. Impaired uptake of antibiotic was the predominant mechanism responsible for P. aeruginosa resistance among strains that did not produce aminoglycoside acetyltransferase (AAC)(6').

The in vitro activity of the newer β-lactam antibiotics against 124 strains of gram-negative bacilli

The MIC values of 99 isolates of Enterobacteriaceae to 11 of the newer beta-lactam antibiotics, and 25 isolates of Pseudomonas aeruginosa to 9 of these drugs were compared with representatives of the established beta-lactam antibiotics and gentamicin. The MIC values for the newer agents were significantly lower in comparison with the older reference compounds. The potential clinical use of these newer antibiotics is discussed.

Unpredictable interactions between cefotetan and penicillins or aminoglycosides

The bacteriostatic and bactericidal activity of gentamicin, amikacin, piperacillin, azlocillin, ampicillin, benzyl penicillin, and oxacillin against 85 selected isolates was measured alone and in the presence of subinhibitory concentrations of cefotetan. A potential for antagonistic interactions between cefotetan and acylamino penicillins (piperacillin > azlocillin > ampicillin) were observed with some strains; synergy was suggested with other isolates, however. Bacteriostatic and bactericidal activity of the two aminoglycosides was enhanced by cefotetan with most gram-negative bacilli, but bactericidal activity was significantly diminished with 4 of 65 strains. Piperacillin and cefotetan were clearly antagonistic with 11 of 44 strains and synergistic with 4 of 44 strains of gram-negative bacilli: the remaining 21 strains gave off scale end points and could not be analyzed in that way.

Netilmicin Sulfate: A Comparative Evaluation of Antimicrobial Activity, Pharmacokinetics, Adverse Reactions and Clinical Efficacy

Netilmicin, the 1-N-ethyl derivative of sisomicin, is a new aminoglycoside antibiotic that was recently marketed in the United States. Its role in therapeutics is not yet established. The pharmacokinetic profile of netilmicin is very similar to that of gentamicin. Its antimicrobial spectrum and clinical efficacy is similar to that of gentamicin, tobramycin and amikacin. It is less active in vitro against Pseudomonas aeruginosa that gentamicin and tobramycin, but in clinical trials the efficacy of netilmicin against the organism has been similar to other aminoglycosides. Netilmicin is active against some gentamicin and tobramycin-resistant strains of gram-negative bacilli, particularly those harboring adenylating and phosphorylation enzymes. Most of these strains are sensitive to amikacin as well, and amikacin is also active against most netilmicin-resistant strains of these bacteria. Therefore, amikacin remains the aminoglycoside of choice against gentamicin tobramycin and netilmicin-resistant gram-negative bacilli. In comparison to other currently available aminoglycosides, a lower frequency of nephrotoxicity and ototoxicity has been observed in laboratory animals given netilmicin. This has not been unequivocally demonstrated in humans. The frequency of nephrotoxicity in humans has been similar to that of other aminoglycosides. The frequency of ototoxicity associated with netilmicin in humans has been low but not significantly less than in other aminoglycosides, except in one trial. If further studies document a significantly lower frequency of ototoxicity with netilmicin, it may become the aminoglycoside of choice for patients with significant risk factors for ototoxicity, such as advanced age, renal impairment, concomitant ototoxic drug therapy and prolonged aminoglycoside administration.

Augmentin: laboratory studies.

Clavulanic acid is a beta-lactam antibiotic which, although it has little intrinsic activity, is a potent inhibitor of bacterial beta-lactamases. When combined with amoxycillin its range of activity includes penicillinase-producing strains of Staphylococcus aureus and many of the beta-lactamase-producing strains of Gram-negative bacilli. Bacteria sensitive to augmentin include amoxycillin-resistant strains of Haemophilus influenzae and Escherichia coli, in addition strains of Klebsiella aerogenes, Proteus mirabilis, Proteus vulgaris and Bacteroides fragilis are usually sensitive. The beta-lactamases produced by Enterobacter spp, Proteus morgani, Serratia marcescens and Pseudomonas aeruginosa are less susceptible to clavulanic acid and these bacteria are usually resistant to augmentin (1).

Bacterial colonization and infection in the neonate

The vast majority of healthy term neonates tolerate their abrupt introduction to the bacterial world with little risk of infection. However, infants who require a longer hospital stay are at greater risk of having an infection, particularly when intensive care is needed. In one study, 15.3 percent of the infants in an intensive care unit acquired a nosocomial infection. Gram-negative bacilli have emerged as the principle cause of nosocomial infection. Nosocomial infection due to gram-negative bacilli usually occurs in neonates already colonized with gram-negative bacilli in the pharynx or intestine, and the risk of colonization with hospital strains of gram-negative bacilli (which are often resistant to multiple antibiotics) increases dramatically the longer a baby stays in intensive care. The factors which predispose individual neonates to colonization and infection with gram-negative bacilli require further study, but gram-negative bacilli are most often transmitted among neonates on the hands of personnel. Neonates in whom intestinal colonization with gram-negative bacilli develops are a particularly important reservoir of gram-negative bacilli in the nursery; once colonized, infants may harbour antibiotic-resistant hospital strains of gram-negative bacilli in their stool for more than a year. Pharyngeal colonization with α streptococci appears to protect neonates from pharyngeal colonization with gram-negative bacilli, and bacterial interference may play an important role in regulating intestinal colonization as well. Investigation of the mechanisms of bacterial interference may lead to better understanding of the colonization process and development of alternatives to classic infection control methods.

The in-vitro activity of ceftazidime against clinically important pathogens

A total of 1414 strains of Gram-negative bacilli and 250 strains of Gram-positive cocci were tested for antimicrobial susceptibility using the broth dilution method. The strains were clinical isolates from 26 hospitals in the Rhein-Main area. All the strains were tested against ceftazidime and ten other cephalosporin antibiotics. Ceftazidime was found to exhibit an in-vitro activity against Enterobacteriaceae similar to that of cefotaxime, moxalactam and other new members of the cephalosporin class, but was more active against Acinetobacter species. Ceftazidime shows extremely high activity both against carbenicillin-sensitive and -resistant strains of Pseudomonas aeruginosa. Similarly, ampicillin-sensitive and -resistant strains of Haemophilus influenzae are susceptible to ceftazidime. The activity of ceftazidime against Staphylococcus aureus is limited and, like other cephalosporins, it is inactive against Streptococcus faecalis.