Chloramphenicol Susceptibility Research Articles

Membranome-based identification of amino acid substitution in Haemophilus influenzae multidrug efflux pump HmrM for reduced chloramphenicol susceptibility.

A decreased chloramphenicol susceptibility in Haemophilus influenzae is commonly caused by the activity of chloramphenicol acetyltransferases (CATs). However, the involvement of membrane proteins in chloramphenicol susceptibility in H. influenzae remains unclear. In this study, chloramphenicol susceptibility testing, whole-genome sequencing, and analyses of membrane-related genes were performed in 51 H. influenzae isolates. Functional complementation assays and structure-based protein analyses were conducted to assess the effect of proteins with sequence substitutions on the minimum inhibitory concentration (MIC) of chloramphenicol in CAT-negative H. influenzae isolates. Six isolates were resistant to chloramphenicol and positive for type A-2 CATs. Of these isolates, A3256 had a similar level of CAT activity but a higher chloramphenicol MIC relative to the other resistant isolates; it also had 163 specific variations in 58 membrane genes. Regarding the CAT-negative isolates, logistic regression and receiver operator characteristic curve analyses revealed that 48T > G (Asn16Lys), 85C > T (Leu29Phe), and 88C > A (Leu30Ile) in HI_0898 (emrA), and 86T > G (Phe29Cys) and 141T > A (Ser47Arg) in HI_1177 (artM) were associated with enhanced chloramphenicol susceptibility, whereas 997G > A (Val333Ile) in HI_1612 (hmrM) was associated with reduced chloramphenicol susceptibility. Furthermore, the chloramphenicol MIC was lower in the CAT-negative isolates with EmrA-Leu29Phe/Leu30Ile or ArtM-Ser47Arg substitution and higher in those with HmrM-Val333Ile substitution, relative to their counterparts. The Val333Ile substitution was associated with enhanced HmrM protein stability and flexibility and increased chloramphenicol MICs in CAT-negative H. influenzae isolates. In conclusion, the substitution in H. influenzae multidrug efflux pump HmrM associated with reduced chloramphenicol susceptibility was characterised.

Molecular basis of the persistence of chloramphenicol resistance among Escherichia coli and Salmonella spp. from pigs, pork and humans in Thailand.

This study aimed to investigate the potential mechanisms associated with the persistence of chloramphenicol (CHP) resistance in Escherichia coli and Salmonella enterica isolated from pigs, pork, and humans in Thailand. The CHP-resistant E. coli (n = 106) and Salmonella (n = 57) isolates were tested for their CHP susceptibility in the presence and absence of phenylalanine arginine β-naphthylamide (PAβN). The potential co-selection of CHP resistance was investigated through conjugation experiments. Whole genome sequencing (WGS) was performed to analyze the E. coli (E329, E333, and E290) and Salmonella (SA448, SA461, and SA515) isolates with high CHP MIC (32-256 μg/mL) and predominant plasmid replicon types. The presence of PAβN significantly reduced the CHP MICs (≥4-fold) in most E. coli (67.9%) and Salmonella (64.9%). Ampicillin, tetracycline, and streptomycin co-selected for CHP-resistant Salmonella and E. coli-transconjugants carrying cmlA. IncF plasmids were mostly detected in cmlA carrying Salmonella (IncFIIAs) and E. coli (IncFIB and IncF) transconjugants. The WGS analysis revealed that class1 integrons with cmlA1 gene cassette flanked by IS26 and TnAs1 were located on IncX1 plasmid, IncFIA(HI1)/HI1B plasmids and IncFII/FIB plasmids. IncFIA(HI1)/HI1B/Q1in SA448 contained catA flanked by IS1B and TnAs3. In conclusion, cross resistance through proton motive force-dependent mechanisms and co-selection by other antimicrobial agents involved the persistence of CHP-resistance in E. coli in this collection. Dissemination of CHP-resistance genes was potentially facilitated by mobilization via mobile genetic elements.

Ciprofloxacin and Azithromycin Susceptibility in Salmonella Causing Bloodstream Infection in a Tertiary Care Hospital in South India

Enteric fever is a major health concern worldwide, especially in tropical countries. Enteric fever caused by Salmonella enterica is a gastrointestinal tract disease to begin with and later involving many systems,. After the advent of multidrug resistant Salmonellae, ciprofloxacin became the focus of its treatment. Azithromycin is widely being used for the prevention and treatment of Enteric fever. Of late, there are reports in literature to support that Salmonella have regained susceptibility to Ampicillin, Cotrimaxazole and Chloramphenicol. Therefore, this study undertaken aims to find out the antimicrobial susceptibility of Salmonella isolates to conventional drugs like Ampicillin, Cotrimaxazole and Chloramphenicol and find out susceptibility pattern of Ciprofloxacin that is over used for treatment of enteric fever and Azithromycin, most often used in children. As there is no disc diffusion method as per CLSI 2019 guidelines to detect the susceptibility to ciprofloxacin, ciprofloxacin resistance was determined by minimum inhibitory concentration(MIC)by E-test.Kirby-Bauer disk diffusion technique was used to monitor Azithromycin resistance among Salmonella entericaserovarTyphi as per CLSI 2019 guidelines. METHODS:The Prospective study was conducted over a period of 8 months (May 2019- December 2019) with the clinical samples yielding the growth of Salmonella from blood. These strains were screened for Ciprofloxacin susceptibility by E-test. Azithromycin,Ampicillin, Co-Trimaxazole and Chloramphenicol susceptibility were detected by Kirby-Bauer disc diffusion technique. RESULTS: Of the 80 isolates that were screened, 52 (65%) were resistant, 24 (30%) were intermediate susceptible and remaining 4(5%) were sensitive to ciprofloxacin by MIC detection. 69 (86.25%) of the isolates were sensitive and 11 (13.75%) were resistant to Azithromycin by disc diffusion technique. All isolates (100%)were found to be susceptible to Ampicillin, Co-Trimaxazole and Chloramphenicol CONCLUSION:The current study shows a high prevalence of resistance to ciprofloxacin in Salmonella species isolated in and around Mysuru district in southern India. Detection of ciprofloxacin resistance by the Kirby Bauer disk diffusion method is less effective, so it is advised that MIC of ciprofloxacin must be regularly done in the diagnostic laboratories for all strains. The findings from our study also showed low level resistance (13.75%) to Azithromycin. It is advised that Azithromycin can be used as a therapeutic agent only if it is reported to be sensitive by the susceptibility test. Conventional agents like Ampicillin, Co-Trimaxazole and Chloramphenicol can be reconsidered for treatment of Enteric fever.

Trend of Changes in Chloramphenicol Resistance during the Years 2017–2020: A Retrospective Report from Israel

Resistant bacteria limit treatment options. This challenge has awakened interest in antibiotics that are no longer in use due to side effects, such as chloramphenicol. This work investigated trends in chloramphenicol resistance rates during 2017-2020 in bacteria isolated from diverse clinical samples at the Baruch Padeh Medical Center, Poriya, Israel. Bacteria were isolated from 3873 samples and identified using routine methods, including matrix-assisted laser desorption ionization-time of flight (MALDI-TOF) technology. Chloramphenicol susceptibility was tested using a VITEK II instrument or by the Kirby-Bauer disk-diffusion test. The average chloramphenicol resistance rate was 24%, with no significant differences between study years. Chloramphenicol resistance was associated with sample origin (p < 0.001); isolates originating from sputum samples showed 49.8% resistance rate, compared to 2.3% of the body fluid isolates, 10.4% of the ear/eye isolates and 22.5% of the blood isolates. Furthermore, there was a significant decrease in chloramphenicol resistance among blood and ear/eye isolates during the study period (p = 0.01, p < 0.001, respectively). The highest resistance rate was among Pseudomonas aeruginosa isolates (50.5%). In conclusion, since chloramphenicol susceptibility seems to be retained, its comeback to the clinical world should be considered.

Cluster analysis of oxytetracycline and chloramphenicol susceptibility in Aeromonas spp. and Escherichia coli from the aquaculture environment

Cluster analysis of oxytetracycline and chloramphenicol susceptibility in Aeromonas spp. and Escherichia coli from the aquaculture environment

Modulation of antimicrobial resistance in clinical isolates of Enterobacter aerogenes: A strategy combining antibiotics and chemosensitisers.

The main focus of this study was to evaluate the antimicrobial susceptibility profiles of a number of human clinical isolates of Enterobacter aerogenes isolates and to explore the effects of selected chemosensitisers on reversal of the resistant phenotype of these isolates. This study design was accomplished by: (i) characterising several multidrug-resistant (MDR) E. aerogenes clinical isolates; (ii) evaluating the contribution of target gene mutations to the resistance phenotype, focusing on fluoroquinolones and chloramphenicol only; (iii) evaluating the contribution of membrane permeability and efflux to the MDR phenotype; (iv) assessing the combined action of selected antimicrobials and chemosensitisers in order to identify combinations with synergistic effects able to reduce the minimum inhibitory concentration (MIC); and (v) understanding how these combinations can modulate the permeability or efflux of these isolates. Resistance to ciprofloxacin could not be totally reversed owing to pre-existing mutations in target genes. Chloramphenicol susceptibility was efficiently restored by the addition of the selected chemosensitisers. From the modulation kinetics it was clear that phenothiazines were able to increase the accumulation of Hoechst dye. Modulation of permeability and efflux in the presence of chemosensitisers can help us to propose more appropriate chemotherapeutic combinations that can set the model to be used in the treatment of these and other MDR infections.

4-Hydroxybenzaldehyde sensitizes Acinetobacter baumannii to amphenicols.

Bacterial metabolism modulated by environmental chemicals could alter antibiotic susceptibility. 4-Hydroxybenzaldehyde (4-HBA), which cannot support the growth of Acinetobacter baumannii, exhibited synergism only with amphenicol antibiotics including chloramphenicol (CAM) and thiamphenicol. Interestingly, this synergistic effect was not observed with other growth-supporting, structurally similar compounds such as 4-hydroxybenzoate. Transcriptomic analysis demonstrated that genes involved in protocatechuate metabolism (pca genes) and osmotic stress (bet genes) were significantly upregulated by 4-HBA and CAM treatment. The 14C-labeled CAM influx was lower in a pcaK1 (encoding a transporter of protocatechuate) deletion mutant and was higher in the pcaK1 overexpressing cells relative to that in the wild type upon 4-HBA treatment. Our kinetic data using 14C-labeled CAM clearly showed that CAM uptake is possibly through facilitated diffusion. Deletion of pcaK1 did not result in the elimination of CAM influx, indicating that CAM does not enter only through PcaK1. The amount of 4-HBA in the culture supernatant was, however, unaffected during the test conditions, validating that it was not metabolized by the bacteria. CAM resistant A. baumannii cells derived by serial passages through CAM-amended media exhibited lower level of pcaK1 gene expression. These results led us to conclude that the activation of PcaK1 transporter is probably linked to cellular CAM susceptibility. This is the first report showing a relationship between CAM influx and aromatic compound metabolism in A. baumannii.

Antimicrobial susceptibility profile, treatment outcome and serotype distribution of clinical isolates of Salmonella enterica subspecies enterica: a 2-year study from Kerala, South India.

Background/purposeTyphoid and paratyphoid fever continue to be important causes of illness and death in parts of Asia, being associated with poor sanitation and consumption of unsafe food and water. Antimicrobial resistance has emerged to traditional first-line drugs, namely, the fluoroquinolones, as well as to third-generation cephalosporins, posing challenges to treatment. Azithromycin has proven to be an effective alternative for treatment of uncomplicated typhoid fever. The purpose of this study was to determine the antimicrobial susceptibility, clinical outcome and serotype distribution pattern of clinical isolates belonging to Salmonella enterica subspecies enterica.MethodologyAll clinical isolates of S. enterica obtained from blood, sterile body fluids, as well as stool and urine samples at Amrita Institute of Medical Sciences and Research Centre, Kerala, India, between August 2011 and July 2013 were included in the study and processed based on standard microbiology protocols.ResultsA total of 118 isolates of Salmonella were obtained during the study period. Out of these, 79 were of S. Typhi (66.95%), followed by isolates of S. Paratyphi A (22; 18.64%) and S. Typhimurium 12 (10.17%). Five isolates could not be identified further. There was 100% susceptibility to ceftriaxone in all S. enterica subspecies. Ciprofloxacin susceptibility was 32.91% for S. Typhi and 40.90% for S. Paratyphi A as determined by the disk diffusion method. The susceptibility profile of S. Typhi isolates to different antimicrobials was as follows: chloramphenicol (94.93%), ampicillin (77.21%), cotrimoxazole (75.94%) and azithromycin (78.48%). For S. Typhi, the minimum inhibitory concentration (MIC) of ciprofloxacin required to inhibit the growth of 50% of organisms was 0.5 μg/mL (intermediate) and MIC required to inhibit the growth of 90% of organisms was 1 μg/mL (resistant). S. Typhimurium was 100% susceptible to cotrimoxazole, ampicillin, ceftriaxone, chloramphenicol, ofloxacin and azithromycin. Susceptibility to ciprofloxacin was 66.66%. Patients from whom S. Typhimurium was isolated had comorbidities with documented risk. Of the 118 patients, 3 expired. Two had typhoid fever and were in sepsis at admission. One had S. Typhimurium and was suffering from multiple myeloma.ConclusionS. Typhi was the predominant isolate. All isolates were susceptible to ceftriaxone. Chloramphenicol susceptibility was >90%. No multidrug-resistant Salmonella strains were isolated. Susceptibility to ciprofloxacin for S. Typhi was 33%. Recovery rate was 97%.

Chloramphenicol - A Potent Armament Against Multi-Drug Resistant (MDR) Gram Negative Bacilli?

Multidrug-resistant gram-negative bacteria cause infections which are hard to treat and cause high morbidity and mortality. Due to limited therapeutic options there is a renewed interest upon older antimicrobials which had fallen into disuse as a result of toxic side effects. One such antibiotic is chloramphenicol which was sidelined due to reports linking its use with the development of aplastic anaemia. A study was conducted to evaluate the susceptibility of chloramphenicol in light of the emerging problem of multi-drug resistant gram negative bacteria (MDR GNB). A total of 483 MDR GNB of the 650 consecutive Gram Negative Bacteria isolated from various clinical samples of patients admitted at a tertiary care hospital in Jaipur between January-June 2014 were screened for chloramphenicol susceptibility by the disc diffusion method as per CLSI guidelines. The MDR GNB isolates were obtained from 217 (45%) urine, 163 (34%) from respiratory samples, 52(11%) from pus, 42 (9%) from blood and 9 (2%) from body fluids. A 68% of the MDR GNB isolates were found to be sensitive to chloramphenicol. Clinicians should always check for the local susceptibility of Gram-negative bacteria to chloramphenicol. This antibiotic has a potential to play a role in the therapeutic management of infections due to MDR GNB pathogens.

First evidence of antibacterial and synergistic effects of Thymus riatarum essential oil with conventional antibiotics

The in vitro antibacterial activity of Thymus riatarum essential oil was evaluated in the present study using different assays toward human pathogenic isolates collected during serious infections.The phytochemical analysis of T. riatarum essential oil (EO) indicated the presence of 20 components, including mainly borneol (41.67%), terpinen-4-ol (8.65%), and trans-caryophyllene (7.59%). Determination of antibacterial activity showed that the EO possesses a noticeable potential of inhibiting the growth of tested strains with Minimum Inhibitory Concentrations (MICs) ranging from 3.57mL/L to 7.5mL/L. However, Pseudomonas aeruginosa showed the least sensitivity and was only inhibited with high concentrations (MIC>7.5mL/L). The release of cytoplasmic material absorbing at 260nm, measured in the presence of T. riatarum EO, increased in response to oil concentration.The ability of T. riatarum EO to block efflux pumps systems of resistant Gram-negative bacteria was also studied. The results indicated that the EO activity was significantly enhanced in the presence of an efflux pump inhibitor such as phenylalanine arginyl ß-naphthylamide (PAßN). In addition, the tested EO, used at MIC/4, was able to increase chloramphenicol susceptibility of several resistant isolates.These results demonstrated that T. riatarum EO could permeabilize bacterial membrane impairing efflux pump activity and may be used in combination with conventional antibiotics against multidrug-resistant bacteria. To our knowledge, this is the first report about the antibacterial activity and the mode of action of T. riatarum EO.

Antibiotic resistance of Staphylococcus aureus in children with atopic dermatitis in 2002-2004 versus 2007-2009 years

Background. Staphylococus aureus (S. aureus) colonization is revealed in 80-84% of patients with atopic dermatitis (AD). There are no results on S. aureus susceptibility to antibiotics in children with AD within the period 2002-2004 to 2007-2009 years. Methods. S. aureus susceptibility to antibiotics was evaluated in 62 children with AD in 2002-2004 years and in 199 children in 2007-2009 years. S. aureus susceptibility and resistance to antibiotics were evaluated as frequencies (q) and their 95% confidential intervals (CI 95%) with MS «Excell». results. S. aureus antibiotic susceptibility in AD children is increased to ciprofloxacin since 2002-2004 to 2007-2009 [0,54 (0,42..0,67) /0,85 (0,80..0,91)] and is not changed to ceftriaxone [0,57 (0,44..0,70) /0,64 (0,57..0,71)], oxacillin [0,75 (0,64..0,86)/0,71 (0,64..0,78)] and cefuroxime [0,61 (0,49..0,74)/0,58 (0,36..0,80)]. Erythromycin susceptibility of S. aureus is 7 times reduced [0,71 (0,60..0,82)/0,10 (0,06..0,14)]; chloramphenicol susceptibility is 2 times reduced [0,79 (0,69..0,90)/0,33 (0,09..0,57)]. There is a decline of S. aureus antibiotic susceptibility to penicillin, ampicillin, linkomycin. Conclusion. Ceftriaxone may be the antibiotic of choice in children with severe infected AD. Oxacillin and cefuroxime should be recommended as an alternative choice.

Antibiogram of Salmonella Isolates from Blood with an Emphasis on Nalidixic Acid and Chloramphenicol Susceptibility in a Tertiary Care Hospital in Coastal Karnataka: A Prospective Study

Background:Enteric fever is caused by the serotypes Salmonella Typhi, Salmonella Paratyphi A, Salmonella Paratyphi B and Salmonella Paratyphi C. After emergence of multidrug resistant Salmonellae Ciprofloxacin, a fluorquinolone antibiotic was the first-line therapy. Treatment failure was observed with Ciprofloxacin soon and such strains showed in-vitro resistance to Nalidixic acid. Recent reports suggest re-emergence of Chloramphenicol sensitive strains and increasing Nalidixic acid resistance. This study is aimed at detecting the current trend in the antibiogram of Salmonella isolates from blood culture in coastal Karnataka, with an emphasis on antibiotic susceptibility of Nalidixic acid and Chloramphenicol and evaluate, if there is a need to modify the strategies in the antibiotic therapy for enteric fever.Materials and Methods:Blood samples received for culture in the laboratory between June 2009 and August 2011 was cultured in Brain Heart infusion broth, bile broth or in a commercial BACTEC culture media. The growth from blood cultures were processed for identification and antibiotic susceptibility as per standard methods. Antibiotic susceptibility for Ampicillin, Trimethoprim-sulphamethoxazole, Chloramphenicol, Ciprofloxacin, Ceftriaxone and Nalidixic acid were noted.Results:Out of 9053 blood culture specimens received, Salmonella was isolated from 103 specimens. There were 85 Salmonella Typhi isolates, 16 Salmonella Paratyphi A and two Salmonella Paratyphi B. Salmonella Typhi and Salmonella Paratyphi A showed the highest resistance to Nalidixic acid. Salmonella Typhi showed highest susceptibility to Ceftriaxone and Salmonella Paratyphi A to trimethoprim-sulphamethoxazole and Chloramphenicol. Two isolates were multidrug resistant. One Salmonella Paratyphi A was resistant to Ceftriaxone.Conclusion:Routine screening of Nalidixic acid susceptibility is practical to predict fluorquinolone resistance in Salmonella and preventing therapeutic failure while treating with it. It is worthwhile to consider replacing fluorquinolones with Chloramphenicol or Ceftriaxone as the first line of therapy for enteric fever. Periodic analysis of Salmonella antibiogram should be done to formulate the best possible treatment strategies.

Essential oils from Moroccan plants as potential chemosensitisers restoring antibiotic activity in resistant Gram-negative bacteria

Bacterial drug resistance is a worrying public health problem. Antibiotic efflux is a major non-specific resistance mechanism used by bacteria, and efflux pumps are involved in the low-level susceptibility of various important Gram-negative pathogens. Use of molecules that can block bacterial pumps is an attractive strategy, but several studies report only partial efficacy owing to limits of these molecules (stability, selectivity, bioavailability, toxicity, etc.). The objective of this study was to search for natural sources of molecules able to inhibit efflux pump systems of resistant Gram-negative bacteria (Escherichia coli, Enterobacter aerogenes, Klebsiella pneumoniae, Salmonella enterica serotype Typhimurium and Pseudomonas aeruginosa). The results indicate that the studied essential oils exhibit interesting activity against the tested bacteria. This activity was significantly enhanced in the presence of an efflux pump inhibitor such as phenylalanine arginyl β-naphthylamide (PAβN). The role of lipopolysaccharide (LPS) structure in the effect of essential oils was also reported in Salmonella LPS deep-rough mutants. In addition, essential oils of Thymus maroccanus and Thymus broussonetii, used at a low concentration (a fraction of the minimum inhibitory concentration), are able to significantly increase chloramphenicol susceptibility of several resistant isolates. These results demonstrate that these essential oils can alter efflux pump activity and may be attractive candidates to develop new drugs for chemosensitising multidrug-resistant strains to clinically used antibiotics.

Mortality in Penicillin-Resistant Pneumococcal Meningitis

To the Editors: In developing countries, penicillin and chloramphenicol remain widely used to treat meningitis, and few data are available to assess the impact of antibiotic resistance on the outcome of this therapy. In the early 1990s it was shown that mortality and sequelae were increased when children treated with penicillin and chloramphenicol had pneumococcal meningitis caused by intermediately penicillin-resistant strains.1 Poor outcome was consistent with relatively limited penetration of penicillin into the cerebrospinal fluid and lack of inhibition of chloramphenicol on pneumococci at achievable CSF concentrations.1 We have recently analyzed the outcome of children with pneumococcal meningitis treated with penicillin and chloramphenicol (benzylpenicillin 200 000 IU/kg per 24 hours and chloramphenicol 100 mg/kg per 24 hours every 6 hours) in a randomized trial of dexamethazone therapy in Malawi.2 Penicillin and chloramphenicol susceptibility were assessed by disk diffusion. Although the chloramphenicol disk test discriminates between chloramphenicol intermediate and resistant strains, the oxacillin disk can only identify strains as penicillin–nonsusceptible. Nonetheless, it is likely that most strains found to be nonsusceptible in Blantyre by the oxacillin disk test, are intermediately resistant, as in a previous study from Blantyre, all of 8 meningeal, 1 empyema, and 21 carriage isolates nonsusceptible by this disk test were intermediately resistant,3 as were 95% of 146 penicillin–nonsusceptible strains from rural Malawian children.4 Of 229 pneumococcal meningitis isolates available for susceptibility testing, 39 (17%) were nonsusceptible to chloramphenicol (1 intermediate) and 47 nonsusceptible to penicillin (20%).2 In this study, mortality was not influenced by randomization to the dexamethazone group in the children treated with penicillin and chloramphenicol, so the analysis of mortality by resistance is for all the children regardless of their randomization. The risk of death was increased (RR: 1.55; 95% CI: 1.06–2.28; P = 0.03) in children with penicillin nonsusceptible, but chloramphenicol susceptible isolates: 22/45 (48%) versus children infected with fully susceptible strains 45/143 (31%). These data support the previous observation that penicillin plus chloramphenicol fail in the treatment of intermediately penicillin–resistant pneumococcal meningitis.1 Although statistically nonsignificant, there was also an increased death rate 16/35 (46%) associated with chloramphenicol–nonsusceptibility despite penicillin susceptibility (RR: 1.45; 95% CI: 0.94–2.24; P = 0.11). In 2 patients, the strain was nonsusceptible to both drugs; 1 died, and 1 survived with sequelae. Mortality associated with nonsusceptibility to either drug 39/82 (48%) was associated with significantly increased mortality (RR: 1.51; 95% CI: 1.08–2.11; P = 0.016). Survival with sequelae was common in all 3 groups—penicillin and chloramphenicol susceptible (29%), penicillin nonsusceptible only (24%), and chloramphenicol nonsusceptible only (26%). These data suggest that combination therapy (organism susceptible to both drugs) may be superior to monotherapy (resistance to 1 drug) for therapy for pneumococcal meningitis. We caution physicians and pediatricians against the use of penicillin plus chloramphenicol to treat pneumococcal meningitis, as the distribution of inter-mediate penicillin resistance among pneumococci is global. Keith P. Klugman, MBBCh, PhD Medical Research Council University of the Witwatersrand/National Institute for Communicable Diseases Respiratory and Meningeal Pathogens Research Unit Johannesburg, South Africa; and The Rollins School of Public Health Emory University Atlanta, GA Amanda L. Walsh, MSc Amos Phiri, MSc Malawi Liverpool Wellcome Trust Research Laboratories Blantyre, Malawi Elizabeth M. Molyneux, FRCPCH Pediatric Department College of Medicine Blantyre, Malawi

Invasive Gram-negative bacilli are frequently resistant to standard antibiotics for children admitted to hospital in Kilifi, Kenya

To determine the pattern of resistance among Gram-negative bacilli causing invasive bacterial disease for the antibiotics that are already in common use in Kilifi, Kenya and for two potential alternatives, ciprofloxacin and cefotaxime. Also, to determine whether prevalence and severity of resistance was increasing over time, to identify patients who are particularly at risk of resistant infections, and to explore which factors are associated with the development of resistance in our setting. We used Etest to study antibiotic susceptibility patterns of 90 Gram-negative bacilli cultured in blood or CSF from paediatric inpatients over 8 years. Susceptibility to amoxicillin 28%, cefotaxime 95% and ciprofloxacin 99% did not vary significantly with age. Susceptibilities for isolates from children aged less than 14 days were: chloramphenicol, 81%; trimethoprim/sulfamethoxazole, 71%; and gentamicin, 91%. From older children, susceptibilities were: chloramphenicol, 62%; trimethoprim/sulfamethoxazole, 39%; and gentamicin, 73%. Chloramphenicol susceptibility was significantly more common among non-typhi salmonellae than other species (79% versus 53%, P < 0.0005). The combination of gentamicin and chloramphenicol covered 91% of all isolates. The prevalence of resistance did not increase over time and was not more common in patients with HIV or malnutrition. Age was the only clinical feature that predicted resistance. Gentamicin or chloramphenicol alone was suboptimal therapy for Gram-negative sepsis, although in this retrospective study, there was no association between resistance and mortality.

Trends of multiple-drug resistance among Salmonella serotype Typhi isolates during a 14-year period in Egypt.

A total of 853 isolates of Salmonella serotype Typhi recovered from patients with typhoid fever who were admitted to a major infectious disease hospital in Cairo, Egypt, from 1987 through 2000 underwent antibiotic susceptibility testing to determine multiple-drug resistance. The observed resurgence of chloramphenicol susceptibility (P=.002) may suggest reuse of this drug for the treatment of typhoid fever in Egypt.

Antimicrobial resistance in anaerobes.

The development of antibiotic resistance in anaerobic bacteria has a tremendous impact on the selection of antimicrobial agents for empirical therapy. Susceptibility studies have documented the emergence of antimicrobial resistance and indicate distinct differences in resistance patterns related to individual hospitals, geographic regions, and antibiotic-prescribing regimens. Resistance to beta-lactam drugs, clindamycin, tetracyclines, and 5-nitroimidazoles (metronidazole) has been observed. The prime mechanism for resistance to beta-lactam agents is the production of beta-lactamases. Resistance to clindamycin is mediated by modification of the ribosome. Tetracycline resistance is mediated by both tetracycline efflux and ribosomal protection. 5-Nitroimidazole resistance appears to be caused by a combination of decreased antibiotic uptake and decreased nitroreductase activity. The level of chloramphenicol susceptibility remains quite high, whereas uniform resistance to aminoglycosides and quinolones is observed. Understanding the mechanisms of resistance is critical for both informed selection of antimicrobial therapy and the design of new antimicrobial agents.

A multicenter study of the antimicrobial susceptibility of community-acquired lower respiratory tract pathogens in the United States, 1992–1994: The Alexander Project

A multicenter, collaborative study was performed over a three-year period (1992–1994) to determine the antimicrobial susceptibilities of isolates of Haemophilus influenzae, Moraxella catarrhalis, and Streptococcus pneumoniae from community-acquired lower respiratory tract infections. Isolates were collected from five geographically separated medical centers in the United States and sent to a central laboratory for antimicrobial susceptibility testing. Of 350, 536, and 372 isolates of H. influenzae collected from the five centers in 1992, 1993, and 1994, 26.3%, 28.2%, and 30.1%, respectively, were β-lactamase-positive. All isolates of H. influenzae remained susceptible to ceftriaxone, doxycycline, ciprofloxacin, and ofloxacin over the three-year period. Between 95 and 100% of isolates of H. influenzae remained susceptible to amoxicillin-clavulanic acid cefixime, clarithromycin, and chloramphenicol over this same period. The prevalence of β-lactamase-positive isolates of M. catarrhalis increased from 92.1% in 1992 to 93.8% in 1993 and to 96.5% in 1994; however, isolates of this species were highly susceptible to amoxicillin-clavulanic acid, the cephalosporins, the macrolides, the fluoroquinolones, chloramphenicol, doxycycline, and trimethoprim-sulfamethoxazole. The prevalence of penicillin-intermediate isolates of S. pneumoniae decreased from 16% in 1992 to 8.2% in 1994, whereas that of penicillin-resistant isolates increased from 5.6% to 10.9% in the same period. Ceftriaxone susceptibility declined from 95.2% to 88.4% over the three years, whereas chloramphenicol susceptibility declined from 98.4% to 90.5% and that of trimethoprim-sulfamethoxazole declined from 85.6% to 68.7%. Macrolide activity remained unchanged.

Application of a modified disc diffusion technique to antimicrobial susceptibility testing of Vibrio anguillarum and Aeromonas salmonicida clinical isolates

Two techniques for antimicrobial susceptibility testing of Vibrio anguillarum and Aeromonas salmonicida strains were compared. The first method was the reference test that determines Minimal Inhibitory Concentrations (MIC); the second was a modified diffusion test that measures the Inhibitory Concentrations in Diffusion (ICD) by carrying out the diffusion test with five discs of differing contents. ICD measurement was not applicable for the susceptibility testing of oxytetracycline and sulfadimethoxine. On the other hand, a good correlation between the MICs and the ICDs was observed for oxolinic acid, sarafloxacin, chloramphenicol and trimethoprim. Moreover, the ICD values were close to those obtained for the MIC values. A. salmonicida resistant strains were detected by ICD determination. Thus, ICD could be used instead of MIC for oxolinic acid, sarafloxacin, trimethoprim and chloramphenicol susceptibility testings. The ICD technique is easy to carry out and is not dependent on the growth characteristics of bacteria.

Failure of chloramphenicol therapy in penicillin-resistant pneumococcal meningitis

First-line therapy for meningitis is often penicillin plus chloramphenicol. Penicillin-resistant Streptococcus pneumoniae (PRSP) infections are increasing world wide, but the efficacy of chloramphenicol for PRSP meningitis is unknown. We therefore prospectively assessed children with pneumococcal meningitis treated with penicillin plus chloramphenicol over 27 months to compare outcome of penicillin-susceptible S pneumoniae(PSSP) meningitis with that of PRSP meningitis. 68 children with pneumococcal meningitis who survived 24 hours were evaluated, of whom 25 had chloramphenicol-susceptible PRSP meningitis that was treated initially with chloramphenicol. 20 (80%) of these 25 children had an unsatisfactory outcome (death, serious neurological deficit, or poor clinical response). By contrast, 14 (33%) of 43 children with PSSP meningitis (treated with benzylpenicillin) had an adverse outcome (p<0·001). Despite similar zone sizes on antibiotic disc testing (indicating chloramphenicol susceptibility) the chloramphenicol minimum bactericidal concentrations (MBCs) of PRSP isolates were significantly higher than those of PSSP isolates. The higher chloramphenicol MBCs resulted in borderline cerebrospinal-fluid bactericidal activity in many cases of PRSP meningitis and frequent treatment failure. Current definitions of chloramphenicol susceptibility of S pneumoniae may be inappropriate for management of pneumococcal meningitis. We suggest that chloramphenicol should not be used for the management of PRSP meningitis; alternative agents, such as third-generation cephalosporins, are more appropriate.