Bactericidal activities of chloramphenicol and eleven other antibiotics against Salmonella spp

Bacillus subtilis produces (p)ppGpp in response to the bacteriostatic antibiotic chloramphenicol to prevent its potential bactericidal effect

Antibiotics combat bacteria through their bacteriostatic (by growth inhibition) or bactericidal (by killing bacteria) action. Mechanistically, it has been proposed that bactericidal antibiotics trigger cellular damage, while bacteriostatic antibiotics suppress cellular metabolism. Here, we demonstrate how the difference between bacteriostatic and bactericidal activities of the antibiotic chloramphenicol can be attributed to an antibiotic-induced bacterial protective response: the stringent response. Chloramphenicol targets the ribosome to inhibit the growth of the Gram-positive bacterium Bacillus subtilis. Intriguingly, we found that chloramphenicol becomes bactericidal in B. subtilis mutants unable to produce (p)ppGpp. We observed a similar (p)ppGpp-dependent bactericidal effect of chloramphenicol in the Gram-positive pathogen Enterococcus faecalis. In B. subtilis, chloramphenicol treatment induces (p)ppGpp accumulation through the action of the (p)ppGpp synthetase RelA. (p)ppGpp subsequently depletes the intracellular concentration of GTP and antagonizes GTP action. This GTP regulation is critical for preventing chloramphenicol from killing B. subtilis, as bypassing (p)ppGpp-dependent GTP regulation potentiates chloramphenicol killing, while reducing GTP synthesis increases survival. Finally, chloramphenicol treatment protects cells from the classical bactericidal antibiotic vancomycin, reminiscent of the clinical phenomenon of antibiotic antagonism. Taken together, our findings suggest a role of (p)ppGpp in the control of the bacteriostatic and bactericidal activity of antibiotics in Gram-positive bacteria, which can be exploited to potentiate the efficacy of existing antibiotics.

A Quantitative Survey of Bacterial Persistence in the Presence of Antibiotics: Towards Antipersister Antimicrobial Discovery

Background: Bacterial persistence to antibiotics relates to the phenotypic ability to survive lethal concentrations of otherwise bactericidal antibiotics. The quantitative nature of the time-kill assay, which is the sector's standard for the study of antibiotic bacterial persistence, is an invaluable asset for global, unbiased, and cross-species analyses. Methods: We compiled the results of antibiotic persistence from antibiotic-sensitive bacteria during planktonic growth. The data were extracted from a sample of 187 publications over the last 50 years. The antibiotics used in this compilation were also compared in terms of structural similarity to fluorescent molecules known to accumulate in Escherichia coli. Results: We reviewed in detail data from 54 antibiotics and 36 bacterial species. Persistence varies widely as a function of the type of antibiotic (membrane-active antibiotics admit the fewest), the nature of the growth phase and medium (persistence is less common in exponential phase and rich media), and the Gram staining of the target organism (persistence is more common in Gram positives). Some antibiotics bear strong structural similarity to fluorophores known to be taken up by E. coli, potentially allowing competitive assays. Some antibiotics also, paradoxically, seem to allow more persisters at higher antibiotic concentrations. Conclusions: We consolidated an actionable knowledge base to support a rational development of antipersister antimicrobials. Persistence is seen as a step on the pathway to antimicrobial resistance, and we found no organisms that failed to exhibit it. Novel antibiotics need to have antipersister activity. Discovery strategies should include persister-specific approaches that could find antibiotics that preferably target the membrane structure and permeability of slow-growing cells.

The Cephalosporin Antibiotic Agents — II. First- and Second-Generation Agents

The first article in this series discussed the cephalosporin antibiotic agents as a class, including the similarities in their structure, antimicrobial action, and toxicity. Part II focuses on the difference between commercially available first- and second-“generation” agents.

The cephalosporins are classified using various criteria, including vulnerability to beta-lactamase hydrolysis and antibacterial activity. The latter classification is based on the in vitro activity of the individual agents, with each succeeding “generation” possessing a greater spectrum of activity than the previous generation(s).

Treatment of Salmonella meningitis: two case reports and a review of the literature

BACKGROUND

Salmonella species now represent a leading cause of Gram-negative bacterial meningitis in the developing world. Various drugs have been used for the treatment of Salmonella meningitis over the past decades, but mortality, neurologic sequelae and relapse rates remain high. In this report we describe two children aged 8 and 9 months who presented within a week to our hospital with Salmonella meningitis. They were treated with penicillin and chloramphenicol but progressed rapidly to death within 48 h.

AIM

The aim of this article is to review all published English literature on the treatment of Salmonella meningitis and identify the best drug option for its treatment. This was done by comparing the outcomes such as cure, failure, relapse, and death rates.

METHOD

A Medline electronic search was carried out to find and retrieve articles that have been published since 1987, when the last review of Salmonella meningitis was done.

RESULTS

Salmonella typhimurium was the commonest organism reported, and 89.7% of infections occurred in children less than 1 year old. Fluoroquinolones had a cure rate of 88.9%, while the third-generation cephalosporins had a cure rate of 84.6%. Conventional antibiotics (chloramphenicol, ampicillin, and cotrimoxazole) had a cure rate of 41.2%, a relapse rate of 11.8%, and an associated mortality of 44.7%. Treatment with fluoroquinolone and imipenem resulted in no deaths. There were, however, only two cases that were treated with imipenem.

CONCLUSION

When Salmonella meningitis is suspected, third-generation cephalosporins, with or without a fluoroquinolone, may be the best option for treatment.

Salmonella meningitis and its complications in infants

OBJECTIVE

To review the presenting features, complications and outcome of infants with Salmonella meningitis.

METHODOLOGY

Retrospective review of all cultures of cerebrospinal fluid positive for bacteria in children below 12 years of age, processed at the Department of Medical Microbiology, University of Malaya Medical Centre, Kuala Lumpur from 1973 to 1997. Records of all cases positive for Salmonella species were retrieved and studied.

RESULTS

Thirteen infants aged 3 days to 9 months with Salmonella meningitis were included. The median age of onset of symptoms was 4 months. The clinical and laboratory features were similar to other causes of bacterial meningitis. Salmonella enteritidis was the commonest serotype isolated. Nine infants developed fits, six of which were difficult to control. Other complications noted were hydrocephalus (five), subdural effusions (four), empyema (three), ventriculitis (two), intracranial haemorrhage and cerebral abscess (one each). The use of ampicillin and/or chloramphenicol and inadequate duration of therapy resulted in recrudescence or relapse in five infants. The overall mortality was 18%. The presence of empyema, intracerebral abscess, ventriculitis, hydrocephalus, and intracranial haemorrhage were associated with adverse neurodevelopmental sequelae or death. More than half of those who survived had normal long-term outcome.

CONCLUSION

Infants who developed neurological complications as a result of Salmonella meningitis had significant mortality and adverse long-term neurodevelopment outcome.

Therapy of experimental meningitis due to Salmonella enteritidis

In many areas of the developing world, Salmonella spp. account for greater than 50% of the gram-negative enteric organisms isolated from cerebrospinal fluid (CSF). The response of Salmonella meningitis to conventional therapy (chloramphenicol and/or ampicillin) is slow, complications arise frequently, and mortality rates of 60 to 80% are common. Two newer agents, ceftriaxone and imipenem, were compared with ampicillin, chloramphenicol, and trimethoprim-sulfamethoxazole (TMP-SMX) in the therapy of experimental Salmonella meningitis beginning 14 h after intracisternal inoculation and continued by constant intravenous infusion for 8 h. Drug concentrations in serum and CSF closely approximated those achieved in the sera and CSF of humans receiving standard parenteral regimens. Penetration into purulent CSF [(concentration of drug in CSF/concentration of drug in serum) x 100] ranged from 18 to 41%. The rate of bacterial killing in CSF was significantly (P less than 0.001) more rapid during therapy with ceftriaxone and imipenem than it was during therapy with chloramphenicol or TMP-SMX. Ceftriaxone and imipenem sterilized the CSF of six of seven animals at 8 h, whereas it sterilized the CSF of three of eight animals treated with ampicillin (P = 0.18), one of eight animals treated with chloramphenicol, and none of seven animals treated with TMP-SMX (P less than or equal to 0.01; ceftriaxone or imipenem versus chloramphenicol or TMP-SMX). New beta-lactams, including ceftriaxone and imipenem, appear to be effective therapy against Salmonella spp. in this animal model and deserve further evaluation in humans.

Ceftriaxone treatment of multidrug-resistant Salmonella osteomyelitis

Empiric treatment of serious Salmonella infections has been complicated by the emergence of strains resistant to multiple antimicrobial agents, including ampicillin, chloramphenicol, and trimethoprim/sulfamethoxazole. Recent reports suggest that the third-generation cephalosporins may be effective therapy for Salmonella infections. This report describes a case of antibiotic-resistant Salmonella heidelberg prosthetic hip infection successfully treated with prosthesis removal and once-daily ceftriaxone. Tube dilution sensitivity testing of the organism demonstrated minimal inhibitory and minimal bactericidal concentrations of 0.12 microgram/ml. Serum bactericidal activity, 30 minutes after infusion, was inhibitory and bactericidal at 1:512. It is concluded that the favorable preliminary results reported in the literature and the outcome in this patient suggest that the third-generation cephalosporins may be effective therapy for Salmonella infections and should undergo clinical trials.

Imipenem/cilastatin. A review of its antibacterial activity, pharmacokinetic properties and therapeutic efficacy

Imipenem is the first available semisynthetic thienamycin and is administered intravenously in combination with cilastatin, a renal dipeptidase inhibitor that increases urinary excretion of active drug. In vitro studies have demonstrated that imipenem has an extremely wide spectrum of antibacterial activity against Gram-negative and Gram-positive aerobic and anaerobic bacteria, even against many multiresistant strains of bacteria. It is very potent against species which elaborate beta-lactamases. Imipenem in combination with equal doses of cilastatin has been shown to be generally well tolerated and an effective antimicrobial for the treatment of infections of various body systems. It is likely to be most valuable as empirical treatment of mixed aerobic and anaerobic infections, bacteraemia in non-neutropenic patients and serious hospital-acquired infections.

Aztreonam. A review of its antibacterial activity, pharmacokinetic properties and therapeutic use

Aztreonam (azthreonam; SQ 26,776) is the first member of a new class of beta-lactam antibiotics, the monobactams. Aztreonam is selectively active against Gram-negative aerobic bacteria and inactive against Gram-positive bacteria. Thus, in vitro, aztreonam is inhibitory at low concentrations (MIC90 less than or equal to 1.6 mg/L) against Enterobacteriaceae except Enterobacter species, and is active against Pseudomonas aeruginosa, 90% of pseudomonads being inhibited by 12 to 32 mg/L. Aztreonam is inactive against Gram-positive aerobic bacteria and anaerobes, including Bacteroides fragilis. Therefore, when administered alone, aztreonam has minimal effect on indigenous faecal anaerobes. Aztreonam must be administered intravenously or intramuscularly when used to treat systemic infections, since absolute bioavailability is very low (about 1%) after oral administration. Since elimination half-life is less than 2 hours, 6- or 8-hourly administration is used in the treatment of moderately severe or severe infections, although 12-hourly injection is adequate in less severe systemic and some urinary tract infections. Therapeutic trials have shown aztreonam to be effective in Gram-negative infections including complicated infections of the urinary tract, in lower respiratory tract infections and in gynaecological and obstetric, intra-abdominal, joint and bone, skin and soft tissue infections, uncomplicated gonorrhoea and septicaemia. In comparisons with other antibiotics, aztreonam has been at least as effective or more effective than cefamandole in urinary tract infections and similar in efficacy to tobramycin or gentamicin. Where necessary, aztreonam and the standard drug have both been combined with another antibiotic active against Gram-positive and/or anaerobic bacteria. Aztreonam has been effective in eradicating pseudomonal infections in most patients (except in patients with cystic fibrosis), but the inevitably limited number of pseudomonal infections available for study prevents any conclusions as to the relative efficacy of aztreonam compared with other appropriate regimens against these infections. Thus, with an antibacterial spectrum which differs from that of other antibiotics, aztreonam should be a useful alternative to aminoglycosides or 'third generation' cephalosporins in patients with proven or suspected serious Gram-negative infections.

Norfloxacin. A review of its antibacterial activity, pharmacokinetic properties and therapeutic use

Norfloxacin is one of the new 4-quinolone antibacterial agents. A fluorinated piperazinyl-substituted congener of nalidixic acid, it demonstrates a much wider in vitro antibacterial spectrum and greater potency than the parent compound. Its antibacterial activity against most Gram-negative pathogens is enhanced in comparison to nalidixic acid, but is similar to that of some of the other new 4-quinolones like enoxacin, and slightly less than that of ciprofloxacin. Unlike nalidixic acid, norfloxacin is also active against Pseudomonas aeruginosa and some Gram-positive organisms. In acute or uncomplicated urinary tract infections, norfloxacin has repeatedly been shown to be as effective as co-trimoxazole. Single studies have demonstrated a significantly better bacteriological cure rate with norfloxacin than with pipemidic acid, and similar cure rates with norfloxacin and both a nalidixic acid/sodium citrate mixture and amoxycillin. Similar results were found in a few studies comparing norfloxacin to pipemidic acid or amoxycillin in patients with chronic and/or complicated urinary tract infections. Norfloxacin is as effective as spectinomycin in gonorrhoea due to penicillin-resistant N. gonorrhoeae, and cures bacterial gastroenteritis caused by several gastrointestinal pathogens. Norfloxacin appears to be well tolerated and may have a low propensity to select for bacterial resistance during clinical use, although the latter needs further confirmation.

Ceftazidime. A review of its antibacterial activity, pharmacokinetic properties and therapeutic use

Ceftazidime is a new 'third generation' cephalosporin administered intravenously or intramuscularly. Similarly to other third generation cephalosporins it has a broad spectrum of in vitro activity against Gram-positive and Gram-negative aerobic bacteria, is particularly active against Enterobacteriaceae (including beta-lactamase-positive strains) and is resistant to hydrolysis by most beta-lactamases. Importantly, in vitro ceftazidime is presently the most active cephalosporin available against Pseudomonas aeruginosa, but it is less active against Staphylococcus aureus than first and second generation cephalosporins. Only larger comparative trials are likely to discern any statistically significant differences in clinical efficacy which may exist between ceftazidime and other antibiotics, but ceftazidime appears to be similar in efficacy to 'standard' comparative drugs in lower respiratory tract infections and complicated and/or chronic urinary tract infections among debilitated or hospitalised patients. Thus, in patients having Gram-negative infections at these sites and in whom the potential toxicity of the aminoglycosides is a concern, ceftazidime may be a valuable alternative in that it apparently lacks serious side effects and does not require routine drug plasma concentration monitoring. In fibrocystic patients having acute respiratory tract infections, ceftazidime is highly effective at both reducing symptoms of infection and temporarily reducing the sputum counts of Pseudomonas species. However, in these patients resistance to ceftazidime may develop, as seen with other beta-lactam antibiotics. In the treatment of fever of unknown origin or documented infections in immunocompromised adults and children, ceftazidime appears to be similar in efficacy to various 2- or 3-drug combinations. Nevertheless, the coadministration of an antibiotic having greater efficacy against Gram-positive bacteria should be considered in immunocompromised patients. Results from a small number of comparative trials suggest that ceftazidime may be as effective as the aminoglycosides in intra-abdominal, obstetric and gynaecological, and skin and soft tissue infections. However, further clinical experience, particularly a few well designed comparative studies, is needed to clarify the comparative efficacy in these conditions as well as in septicaemia/bacteraemia, meningitis, and bone and joint infections.