Reasons for the Emergence of Antibiotic Resistance

Short chain fatty acids inhibit corneal inflammatory responses to TLR ligands via the ocular G-protein coupled receptor 43

PURPOSE

Short chain fatty acids (SCFAs) produced by gut microbiota are known to play primary roles in gut homeostasis by immunomodulation partially through G-protein coupled receptors (GPR) 43. Using mouse models of TLR ligand induced keratitis, we investigated whether SCFAs and GPR43 play any regulatory roles in the pathogenesis of inflammatory responses in the eye.

METHODS

Both human and mouse eyes were labeled with a specific antibody for GPR43 and imaged by a laser scanning confocal microscope. Corneal cups from naïve C57BL/6J (B6) and GPR43 knockout (KO) mice were stimulated with TLR ligands in the presence or absence of sodium butyrate overnight and then processed for RT-PCR assay for expression of GPR43 and cytokines. Keratitis was induced by Poly I:C in wild type (WT) B6, GPR43KO and chimeric mice and the disease severity was evaluated by the corneal fluorescein staining test, and infiltrating cell staining and calculating in corneal whole mount.

RESULTS

GPR43 is expressed in both human and mouse eyes and the expression is bidirectionally regulated by TLR ligands and butyrate. Butyrate significantly inhibited inflammation caused by several TLR ligands such as Poly I:C, Flagellin, and CpG-ODN (TLR-3, 5 and 9 agonists, respectively) in WT, but not GPR43KO, mice. Butyrate inhibition of TLR-induced keratitis is mediated by the GPR43 expressed in tissue but not hematopoietic, cells.

CONCLUSIONS

This is the first report to demonstrate of the protective effect of SCFAs on microbial keratitis, and the dynamic expression and anti-inflammatory function of GPR43 in the eye. SCFAs can modulate inflammation and immunity in the eye through GPR43.

Surgical site infection after 769 Tibial Plateau Leveling Osteotomies

Objective

To report surgical site infections (SSI) after Tibial Plateau Leveling Osteotomy (TPLO), treatment course, associated risk factors, bacterial isolates and antimicrobial resistance.

Study design

Retrospective clinical cohort study.

Study population

Six hundred and twenty seven dogs and 769 TPLO procedures.

Methods

Data from electronic medical records of dogs undergoing TPLO between 2005 and 2015 at a single institution have been retrospectively reviewed. A generalized mixed logistic regression was used to determine possible risk factors. The Chi-Square test of independence was used to examine the relationship between the isolation of multidrug-resistant (MDR) bacteria and the development of major infections undergoing additional surgical treatment. To assess the correlation between number of SSI and number MDR isolate per year, Pearson's correlation coefficient was calculated.

Results

The overall complication rate was 19.3% (n = 149). SSI was most frequent with 8.5% (n = 65). Major SSI occurred in 6.8% (n = 52) TPLO (80.0% SSI). Staphylococcus (S.) pseudintermedius (n = 37) and S. aureus (n = 10) were most frequently isolated. Multidrug-resistant bacteria were identified in 2.7% (n = 21) TPLO (32.3% SSI) but were not associated with major SSI (p = 0.426). There was a strong positive correlation between number of MDR isolates per year and number of SSI per year [r ₍₉₎ = 0.79, p = 0.004]. Factors associated with SSI were previous TPLO in the contralateral stifle (p = 0.02, OR = 2.01, 95% CI = 1.11-3.64) and German Shepherd dogs (p = 0.035, OR = 4.41, 95% CI = 1.11-17.54). The use of non-locking implants was found to be protective (p = 0.02, OR = 0.179, 95% CI = 0.18-0.77).

Clinical significance

Infection with multidrug-resistant bacteria is an emerging problem in veterinary practice and treatment is challenging. The incidence of major SSI was found to be high but was not associated with the isolation of MDR bacteria.

Correlation Between Individual Child-Level Antibiotic Consumption and Antibiotic-Resistant Among Commensal Escherichia coli: Results from a Cohort of Children Aged 1-3 Years in Rural Ujjain India

Background

The global expansion of antibiotic-resistant bacteria is a serious concern and is increasing worldwide in both pathogenic and commensal bacteria. The study determined the correlation between individual child-level antibiotic consumption and antibiotic resistance among the commensal Escherichia coli (E.coli) in a cohort of 125 children in rural Ujjain, India.

Methods

During a two-year period between August 2014 and September 2016, stool samples were collected at seven-time points from a cohort of 125 children; aged 1–3. A total of six colonies of E.coli per stool sample were collected for antibiotic susceptibility testing. Antibiotic consumption data was collected during the healthcare-seeking follow–up done during the same period. At each of the seven-time points correlation between antibiotic consumption (Defined Daily Dose-DDD/100 patient-days) and antibiotic resistance (number of resistant isolates) was analyzed independently using the Spearman correlation coefficient. Further, mixed-effects logistic regression models were built to study correlation between child-level consumption of penicillin with the number of E.coli isolates resistant to ampicillin, consumption of cephalosporin with resistance to cefotaxime and ceftazidime, consumption of fluoroquinolones with resistance to nalidixic acid and consumption of cotrimoxazole with resistance to cotrimoxazole.

Results

Out of 756 illness episodes reported in 125 children 42% were with antibiotic prescriptions and reported a total antibiotic consumption of 55DDD/100 patient-days. The most common antibiotics used were cefixime (J01DD08;72 DDD/100patient/days) followed by ofloxacin (J01MA01;51DDD/100patient-days), cefpodoxime (J01DD13;38DDD/100patient-days) and amoxicillin (J01CA04;28DDD/100patient-days). The highest percentage of resistance was found to the ampicillin (67%) followed by nalidixic acid (52%) and cefotaxime (44%) and when summarized, more than 90% were resistant to cefotaxime, ceftazidime, and co-trimoxazole in commensal E.coli isolates. The consumption of cephalosporins showed weak positive correlation with the resistance to cefotaxime (Coefficient±SE=0.13 ± 0.09,p<0.001).

Conclusion

Our findings showed no correlation between individual-level antibiotic consumption and resistance development in commensal E.coli in a rural community environment.

Evidence of Community-Wide Spread of Multi-Drug Resistant Escherichia coli in Young Children in Lusaka and Ndola Districts, Zambia

Increased antimicrobial resistance (AMR) has been reported for pathogenic and commensal Escherichia coli (E. coli), hampering the treatment, and increasing the burden of infectious diarrhoeal diseases in children in developing countries. This study focused on exploring the occurrence, patterns, and possible drivers of AMR E. coli isolated from children under-five years in Zambia. A hospital-based cross-sectional study was conducted in the Lusaka and Ndola districts. Rectal swabs were collected from 565 and 455 diarrhoeic and healthy children, respectively, from which 1020 E. coli were cultured and subjected to antibiotic susceptibility testing. Nearly all E. coli (96.9%) were resistant to at least one antimicrobial agent tested. Further, 700 isolates were Multi-Drug Resistant, 136 were possibly Extensively-Drug Resistant and nine were Pan-Drug-Resistant. Forty percent of the isolates were imipenem-resistant, mostly from healthy children. A questionnaire survey documented a complex pattern of associations between and within the subgroups of the levels of MDR and socio-demographic characteristics, antibiotic stewardship, and guardians’ knowledge of AMR. This study has revealed the severity of AMR in children and the need for a community-specific-risk-based approach to implementing measures to curb the problem.

The impact of therapeutic-dose induced intestinal enrofloxacin concentrations in healthy pigs on fecal Escherichia coli populations

BACKGROUND

Knowledge of therapy-induced intestinal tract concentrations of antimicrobials allows for interpretation and prediction of antimicrobial resistance selection within the intestinal microbiota. This study describes the impact of three different doses of enrofloxacin (ENR) and two different administration routes on the intestinal concentration of ENR and on the fecal Escherichia coli populations in pigs. Enrofloxacin was administered on three consecutive days to four different treatment groups. The groups either received an oral bolus administration of ENR (conventional or half dose) or an intramuscular administration (conventional or double dose).

RESULTS

Quantitative analysis of fecal samples showed high ENR concentrations in all groups, ranging from 5.114 ± 1.272 μg/g up to 39.54 ± 10.43 μg/g at the end of the treatment period. In addition, analysis of the luminal intestinal content revealed an increase of ENR concentration from the proximal to the distal intestinal tract segments, with no significant effect of administration route. Fecal samples were also screened for resistance in E. coli isolates against ENR. Wild-type (MIC≤0.125 μg/mL) and non-wild-type (0.125 < MIC≤2 μg/mL) E. coli isolates were found at time 0 h. At the end of treatment (3 days) only non-wild-type isolates (MIC≥32 μg/mL) were found.

CONCLUSIONS

In conclusion, the observed intestinal ENR concentrations in all groups showed to be both theoretically (based on pharmacokinetic and pharmacodynamic principles) and effectively (in vivo measurement) capable of significantly reducing the intestinal E. coli wild-type population.

Investigation of plasmid-mediated resistance in E. coli isolated from healthy and diarrheic sheep and goats

Escherichia coli is zoonotic bacteria and the emergence of antimicrobial-resistant strains becomes a critical issue in both human and animal health globally. This study was therefore aimed to investigate the plasmid-mediated resistance in E. coli strains isolated from healthy and diarrheic sheep and goats. A total of 234 fecal samples were obtained from 157 sheep (99 healthy and 58 diarrheic) and 77 goats (32 healthy and 45 diarrheic) for the isolation and identification of E. coli. Plasmid DNA was extracted using the alkaline lysis method. Phenotypic antibiotic susceptibility profiles were determined against the three classes of antimicrobials, which resistance is mediated by plasmids (Cephalosporins, Fluoroquinolone, and Aminoglycosides) using the disc-diffusion method. The frequency of plasmid-mediated resistance genes was investigated by PCR. A total of 159 E. coli strains harbored plasmids. The isolates antibiogram showed different patterns of resistance in both healthy and diarrheic animals. A total of (82; 51.5%) E. coli strains were multidrug-resistant. rmtB gene was detected in all Aminoglycoside-resistant E. coli, and the ESBL-producing E. coli possessed different CTX-M genes. Similarly, fluoroquinolone-resistant E. coli possessed different qnr genes. On the analysis of the gyrB gene sequence of fluoroquinolone-resistant E. coli, multiple point mutations were revealed. In conclusion, a high prevalence of E. coli with high resistance patterns to antimicrobials was revealed in the current study, in addition to a wide distribution of their resistance determinants. These findings highlight the importance of sheep and goats as reservoirs for the dissemination of MDR E. coli and resistance gene horizontal transfer.

Antimicrobial resistance of pathogenic Aeromonas spp. isolated from marketed Pacific abalone (Haliotis discus hannai) in Korea

AIMS

The object of this study was to identify potential health concerns of the Aeromons spp. isolated from marketed Pacific abalone (Haliotis discus hannai) with respect to their virulence and antimicrobial resistance patterns.

METHODS AND RESULTS

We identified 29 strains of aeromonads consisting of five species; Aeromonas hydrophila (n = 9), Aeromonas enteropelogenes (n = 14), Aeromonas veronii (n = 3), Aeromonas salmonicida (n = 2) and Aeromonas sobria (n = 1), by employing series of biochemical tests and gene sequencing. In the phenotypic virulence assays, all isolates showed gelatinase and caseinase activities, while lipase formation (69%), phospholipase production (90%), DNase formation (82%), slime production (49%) and haemolysis activity (α = 18% and β = 82%) were also detected among isolates. Prevalence of virulence genes; aerA (100%), fla (66%), ahyB (73%), act (52%), alt (42%), ast (35%), ser (52%), gcat (69%), ascV (43%), hlyA (83%), lip (52%) and exu (59%) were detected by PCR assays. In disc diffusion test, 100% resistance was detected against ampicillin while cephalothin, rifampicin, oxytetracycline, colistine sulphate, nalidixic acid and piperaciliin were resisted by 86, 73, 42, 35, 28, 20 and 20% of the isolates respectively. Thirteen (45%) of the isolates showed multiple antimicrobial resistance (MAR) indices ≥ 0·2.

CONCLUSIONS

Our findings suggest that the potential health risk posed by the abalone-borne Aeromonas spp. should not be underestimated.

SIGNIFICANCE AND IMPACT OF THE STUDY

This is the first time to evaluate possible public health risks upon consumption of abalone harbored Aeromonas spp. and also to isolate potential pathogenic and multidrug-resistant Aeromonas spp. from Pacific abalone in Korea.

High levels of drug resistance in commensal E. coli in a cohort of children from rural central India

The world is experiencing crisis of antibiotic resistance not only in pathogenic but also in commensal bacteria. We determine the prevalence of antibiotic resistance in commensal Escherichia coli in young children in rural setting of central India and search for its correlations with demographic and behavioral factors. At seven time points during a period of 2 years we collected stool samples from 125 children; aged 1–3 in a rural area of Madhya Pradesh. We isolated six isolates of E. coli per stool sample and subjected them to antibiotic susceptibility testing. We found resistance to ampicillin, quinolones, cephalosporins, sulfamethoxazole, co-trimoxazole, in at least one isolate from 89% to 100% of children. Extended spectrum beta lactamase producing E. coli were identified in all but one child and multidrug resistance was identified in isolates from all children. Female gender (p = 0.04) and higher wealth (p = 0.03) was significantly correlated with less antibiotic resistance. Thus, the high prevalence of antibiotic resistance in commensal E. coli in rural community from India needs urgent measures to control the growing antibiotic resistance crisis.

Advances in antimicrobial photodynamic inactivation at the nanoscale

The alarming worldwide increase in antibiotic resistance amongst microbial pathogens necessitates a search for new antimicrobial techniques, which will not be affected by, or indeed cause resistance themselves. Light-mediated photoinactivation is one such technique that takes advantage of the whole spectrum of light to destroy a broad spectrum of pathogens. Many of these photoinactivation techniques rely on the participation of a diverse range of nanoparticles and nanostructures that have dimensions very similar to the wavelength of light. Photodynamic inactivation relies on the photochemical production of singlet oxygen from photosensitizing dyes (type II pathway) that can benefit remarkably from formulation in nanoparticle-based drug delivery vehicles. Fullerenes are a closed-cage carbon allotrope nanoparticle with a high absorption coefficient and triplet yield. Their photochemistry is highly dependent on microenvironment, and can be type II in organic solvents and type I (hydroxyl radicals) in a biological milieu. Titanium dioxide nanoparticles act as a large band-gap semiconductor that can carry out photo-induced electron transfer under ultraviolet A light and can also produce reactive oxygen species that kill microbial cells. We discuss some recent studies in which quite remarkable potentiation of microbial killing (up to six logs) can be obtained by the addition of simple inorganic salts such as the non-toxic sodium/potassium iodide, bromide, nitrite, and even the toxic sodium azide. Interesting mechanistic insights were obtained to explain this increased killing.

Effect of administration route and dose alteration on sulfadiazine-trimethoprim plasma and intestinal concentrations in pigs

Potentiated sulfonamides, such as sulfadiazine-trimethoprim (SDZ-TRIM), are frequently used antimicrobials in both human and veterinary medicine. To optimise their use in relation to the emerging problem of resistance selection, this paper studied the impact of dose and administration route of SDZ-TRIM on the exposure of the gut microbiota to these antimicrobials. An animal experiment was conducted with 36 pigs, divided into six different treatment groups (n = 6). Three different administration routes were outlined: oral (PO) gavage, intramuscular (IM) injection and medicated feed, with 5-day therapy duration. Conventional dosing (30 mg SDZ-TRIM/kg bodyweight [BW]) and half dosing (15 mg SDZ-TRIM/kg BW) was performed for the oral routes in two applications per day. For the IM route, a conventional dose of 15 mg SDZ-TRIM/kg BW or a double dose of 30 mg SDZ-TRIM/kg BW was administered once daily. After daily collection of blood and faeces, the intestinal content of all animals was sampled in different gastrointestinal tract (GIT) segments, and SDZ and TRIM were quantified. Remarkably, SDZ accumulated in distal GIT segments, independently of the administration route. High concentrations (mean ± standard deviation) up to 26.93 ± 8.36 µg/g, 11.15 ± 3.78 µg/g and 19.36 ± 1.86 µg/g after PO gavage, IM administration and medicated feed, respectively, were measured for SDZ. In contrast, TRIM concentrations decreased from proximal to distal segments and were mostly below the limit of quantification (0.025 µg/g). The high oral bioavailability of SDZ indicates gastrointestinal secretion is a substantial elimination route for SDZ.

Antibiotic Resistance in an Indian Rural Community: A 'One-Health' Observational Study on Commensal Coliform from Humans, Animals, and Water

Antibiotic-resistant bacteria are an escalating grim menace to global public health. Our aim is to phenotype and genotype antibiotic-resistant commensal Escherichia coli (E. coli) from humans, animals, and water from the same community with a ‘one-health’ approach. The samples were collected from a village belonging to demographic surveillance site of Ruxmaniben Deepchand (R.D.) Gardi Medical College Ujjain, Central India. Commensal coliforms from stool samples from children aged 1–3 years and their environment (animals, drinking water from children's households, common source- and waste-water) were studied for antibiotic susceptibility and plasmid-encoded resistance genes. E. coli isolates from human (n = 127), animal (n = 21), waste- (n = 12), source- (n = 10), and household drinking water (n = 122) carried 70%, 29%, 41%, 30%, and 30% multi-drug resistance, respectively. Extended spectrum beta-lactamase (ESBL) producers were 57% in human and 23% in environmental isolates. Co-resistance was frequent in penicillin, cephalosporin, and quinolone. Antibiotic-resistance genes bla_CTX-M-9 and qnrS were most frequent. Group D-type isolates with resistance genes were mainly from humans and wastewater. Colistin resistance, or the mcr-1 gene, was not detected. The frequency of resistance, co-resistance, and resistant genes are high and similar in coliforms from humans and their environment. This emphasizes the need to mitigate antibiotic resistance with a ‘one-health’ approach.

Current Issues in Gram-Negative Resistance: Extended-Spectrum Beta-Lactamases and Inducible Beta-Lactamases

The production of beta-lactamases is the most common cause of antimicrobial resistance in gram-negative bacilli. Two beta-lactamases, extended-spectrum beta-lactamases (ESBLs) and inducible beta-lactamases (IDBLs), are presently seen with increasing frequency. Treatment of severe infections due to gram-negative bacilli producing these beta-lactamases is problematic. In vitro susceptibility testing of ESBL-producing organisms remains difficult to interpret; clinical isolates sensitive to a particular antimicrobial agent at standard inoculum may become resistant when a higher inoculum is employed. Laboratory detection of IDBL-producing organisms is not yet commercially available. Due to the lack of sufficient outcome data, clinicians often have no choice but to use carbapenems empirically for the treatment of severe infections caused by organisms suspected of producing these enzymes. The widespread empiric use of carbapenems is of concern and may potentially precipitate increased bacterial resistance to this class of antimicrobial agents.

Effect of administration route and dose escalation on plasma and intestinal concentrations of enrofloxacin and ciprofloxacin in broiler chickens

Background

The (mis)use of fluoroquinolones in the fowl industry has led to an alarming incidence of fluoroquinolone resistance in pathogenic as well as commensal bacteria. Next to simply reducing antimicrobial consumption, optimizing dosage regimens can be regarded as a suitable strategy to reduce antimicrobial resistance development without jeopardizing therapy efficacy and outcome. A first step in order to limit antimicrobial resistance is to assess the exposure of the intestinal microbiota to enrofloxacin after different treatment strategies. Therefore, a study was conducted in broiler chickens to assess the effect of route of administration (oral versus intramuscular) and dose escalation (10 and 50 mg/kg body weight) on plasma and intestinal concentrations of enrofloxacin and its main metabolite ciprofloxacin after treatment with enrofloxacin once daily for five consecutive days. Four different parts of the intestinal tract were sampled: ileum, cecum, colon and cloaca. A liquid chromatography-tandem mass spectrometry (LC-MS/MS) method was developed to quantify both analytes in plasma and intestinal content. Sample preparation prior to LC-MS/MS analysis consisted of extraction with ethyl acetate. For intestinal content samples PBS buffer was added before extraction. The supernatant was evaporated to dryness and resuspended in water prior to analysis.

Results

The results in plasma and intestinal content demonstrated that biotransformation of enro- to ciprofloxacin in broiler chickens is limited. In general, the intestinal microbiota in cecum and colon is exposed to significant levels of enrofloxacin after conventional treatment (21–130 μg/g). A clear increase of intestinal concentrations was demonstrated after administration of a five-fold higher dose (31–454 μg/g). After intramuscular administration, intestinal concentrations were comparable, except for the higher levels in cloaca due to the complete bioavailability and urinary excretion.

Conclusions

The intestinal microbiota is exposed to high levels of the antimicrobial, after oral as well as parenteral therapy. Furthermore, a dose and time dependent correlation was observed. The impact of the detected intestinal levels on resistance selection in the intestinal microbiota has to be further investigated.

Electronic supplementary material

The online version of this article (doi:10.1186/s12917-014-0289-1) contains supplementary material, which is available to authorized users.

Antibiotic resistance in pediatric urology

Antibiotics are a mainstay in the treatment of bacterial infections, though their use is a primary risk factor for the development of antibiotic resistance. Antibiotic resistance is a growing problem in pediatric urology as demonstrated by increased uropathogen resistance. Lack of urine testing, nonselective use of prophylaxis, and poor empiric prescribing practices exacerbate this problem. This article reviews antibiotic utilization in pediatric urology with emphasis on modifiable practice patterns to potentially help mitigate the growing rates of antibiotic resistance. This includes urine testing to only treat when indicated and tailor broad-spectrum therapy as able; selective application of antibiotic prophylaxis to patients with high-grade vesicoureteral reflux and hydronephrosis with counseling regarding the importance of compliance; and using local antiobiograms, particularly pediatric-specific antiobiograms, with inpatient versus outpatient data.

Antibiotic administration routes significantly influence the levels of antibiotic resistance in gut microbiota

This study examined the impact of oral exposure to antibiotic-resistant bacteria and antibiotic administration methods on antibiotic resistance (AR) gene pools and the profile of resistant bacteria in host gastrointestinal (GI) tracts using C57BL/6J mice with natural gut microbiota. Mice inoculated with a mixture of tet(M)-carrying Enterococcus spp. or blaCMY-2-carrying Escherichia coli were treated with different doses of tetracycline hydrochloride (Tet) or ampicillin sodium (Amp) and delivered via either feed or intravenous (i.v.) injection. Quantitative PCR assessment of mouse fecal samples revealed that (i) AR gene pools were below the detection limit in mice without prior inoculation of AR gene carriers regardless of subsequent exposure to corresponding antibiotics; (ii) oral exposure to high doses of Tet and Amp in mice inoculated with AR gene carriers led to rapid enrichment of corresponding AR gene pools in feces; (iii) significantly less or delayed development of AR in the GI tract of the AR carrier-inoculated mice was observed when the same doses of antibiotics were administered via i.v. injection rather than oral administration; and (iv) antibiotic dosage, and maybe the excretion route, affected AR in the GI tract. The shift of dominant AR bacterial populations in the gut microbiota was consistent with the dynamics of AR gene pools. The emergence of endogenous resistant bacteria in the gut microbiota corresponding to drug exposure was also observed. Together, these data suggest that oral administration of antibiotics has a prominent effect on AR amplification and development in gut microbiota, which may be minimized by alternative drug administration approaches, as illustrated by i.v. injection in this study and proper drug selection.

Office-related antibiotic prescribing for Medicaid-enrolled children

BACKGROUND

Prudent antibiotic prescribing practices are essential to limiting antibiotic resistance.

OBJECTIVE

To assess the trend in percentage of office visits for acute respiratory infections (ARIs) linked with an antibiotic prescription.

METHODS

Retrospective analysis of Montana Medicaid billing claims data for each year, 1999 to 2010, was done. Participants included continuously enrolled children aged ≤14 years. Primary outcomes were ARI-related office visits and filled antibiotic prescriptions within 10 days of the office visit.

RESULTS

Of the 873 244 office visits identified, 116 962 (13%) had an ARI as the primary diagnosis. Among ARI-related office visits, 64 250 (55%) were linked with an antibiotic prescription. From 1999 to 2010, the odds of ARI-related visits being linked with an antibiotic prescription did not change (odds ratio = 1.00; 95% confidence interval = 0.995-1.002).

CONCLUSIONS

The percentage of ARI-related visits linked with an antibiotic prescription did not decrease from 1999 to 2010. Further efforts are needed to reduce antibiotic treatment for ARIs.

Rational design of engineered cationic antimicrobial peptides consisting exclusively of arginine and tryptophan, and their activity against multidrug-resistant pathogens

The emergence of multidrug-resistant (MDR) pathogens underscores the need for new antimicrobial agents to overcome the resistance mechanisms of these organisms. Cationic antimicrobial peptides (CAPs) provide a potential source of new antimicrobial therapeutics. We previously characterized a lytic base unit (LBU) series of engineered CAPs (eCAPs) of 12 to 48 residues demonstrating maximum antibacterial selectivity at 24 residues. Further, Trp substitution in LBU sequences increased activity against both P. aeruginosa and S. aureus under challenging conditions (e.g., saline, divalent cations, and serum). Based on these findings, we hypothesized that the optimal length and, therefore, the cost for maximum eCAP activity under physiologically relevant conditions could be significantly reduced using only Arg and Trp arranged to form idealized amphipathic helices. Hence, we developed a novel peptide series, composed only of Arg and Trp, in a sequence predicted and verified by circular dichroism to fold into optimized amphipathic helices. The most effective antimicrobial activity was achieved at 12 residues in length (WR12) against a panel of both Gram-negative and Gram-positive clinical isolates, including extensively drug-resistant strains, in saline and broth culture and at various pH values. The results demonstrate that the rational design of CAPs can lead to a significant reduction in the length and the number of amino acids used in peptide design to achieve optimal potency and selectivity against specific pathogens.

Single intraoperative intravenous Co-Amoxiclav versus postoperative full oral course in prevention of postadenotonsillectomy morbidity: a randomised clinical trial

Background

Adenotonsillectomy results in postoperative morbidity which otolaryngologists attempt to reduce by use of antibiotics. The regimes used as quite varied with some opting for a full oral course postoperatively while others prefer prophylactic doses. This randomised clinical trial done in Kenyatta National Hospital, Kenya had the aim of comparing the efficacy of Co-Amoxiclav given as a single intravenous dose with a full oral course in the prevention of post adenotonsillectomy morbidity.

Methods

126 patients below 12 years scheduled to undergo adenotonsillectomy were randomised into two groups. 63 were given a single intravenous dose of Enhancin [Co-Amoxiclav] at induction while the remaining half received a five days oral course of the same postoperatively. All received oral Pacimol [Paracetamol] in the postoperative period. Analysis was done and comparison made between the two groups with regards to pain, fever and diet tolerated in the postoperative period with a follow up period of seven days.

Results

There was no statistical significant difference between the two groups with regards to postoperative pain, fever and diet tolerated. All had a P-value > 0.2. Postoperative pain was highest in the first postoperative day and reduced progressively to the lowest level on the 7^th postoperative day. As pain reduced, patients were able to tolerate a more solid diet with all but 6 tolerating their usual diet. 4 patients developed fever in the 1^st postoperative day which did not progress to the next day. One patient had fever on the 4^th and 7^th postoperative day and was admitted in the paediatrics' ward with a chest infection. All these patients with history of fever were in the group that was on oral postoperative Co-Amoxiclav.

Conclusion

A single intraoperative dose of Co-Amoxiclav given intravenously at induction was found to be just as effective as a full oral course of the same given postoperatively in the prevention of post adenotonsillectomy morbidity. The prophylactic dose is favoured over the later as it is cheaper, ensures compliance and relieves off the need for refrigeration of the oral suspension as not all have access to refrigeration in low economy countries as ours.

Trial registration

ClinicalTrials.gov: NCT01267942

Are physicians with better clinical skills on licensing examinations less likely to prescribe antibiotics for viral respiratory infections in ambulatory care settings?

BACKGROUND

Viral respiratory infections (VRIs) are a common reason for ambulatory visits, and 35% are treated with an antibiotic. Antibiotic use for VRIs is not recommended, and it promotes antibiotic resistance. Effective patient-physician communication is critical to address this problem. Recognizing the importance of physician communication skills, licensure examinations were reformed in the United States and Canada to evaluate these skills.

OBJECTIVE

To assess whether physician clinical and communication skills, as measured by the Canadian clinical skills examination (CSE), predict antibiotic prescribing for VRI in ambulatory care.

RESEARCH DESIGN AND SUBJECTS

A total of 442 Quebec general practitioners and pediatricians who wrote the CSE in 1993-1996 were followed from 1993 to 2007, and their 159,456 VRI visits were identified from physician claims.

MEASURES

The outcome was an antibiotic prescription from a study physician dispensed within 7 days of the VRI visit. Multivariate logistic regression analyses were used to estimate the association between antibiotic prescribing for VRI and CSE score, adjusting for physician, patient, and encounter characteristics.

RESULTS

Better clinical and communication skills were associated with a reduction in the risk of antibiotic prescribing, but only for female physicians. Every 1-standard deviation increase in CSE score was associated with a 19% reduction in the risk of antibiotic prescribing (risk ratio, 0.81; 95% confidence interval, 0.68-0.97). Better clinical skills were associated with an even greater reduction in risk among female physicians with higher workloads (risk ratio, 0.48; 95% confidence interval, 0.29-0.79).

CONCLUSION

Physician clinical and communication skills are important determinants of antibiotic prescribing for VRI and should be targeted by future interventions.

Methicillin-resistant Staphylococcus aureus (MRSA) in food production animals

Until recently, reports on methicillin-resistant Staphylococcus aureus (MRSA) in food production animals were mainly limited to occasional detections in dairy cattle mastitis. However, since 2005 a MRSA clone, CC398, has been reported colonizing pigs, veal calves and broiler chickens and infecting dairy cows. Many aspects of its prevalence in pigs remain unclear. In other livestock, colonizing capacity and reservoir status still require elucidation. MRSA CC398 has also been detected in meat, but, as for other MRSA, the risk this poses is somewhat unclear. Currently, the most worrying aspect of MRSA CC398 appears to be its capacity to spread to humans. This might complicate MRSA control measures in human healthcare, urging research into risk factors and transmission routes. Although infections with MRSA CC398 are much less reported than carriage, more investigation into its pathogenic potential is required. Moreover, the origin and evolution of this clone remain unknown.

Occurrence of resistance to antibiotics, UV-B, and arsenic in bacteria isolated from extreme environments in high-altitude (above 4400 m) Andean wetlands

High-altitude Andean wetlands are pristine environments with extreme conditions such as high UV radiation, high heavy metal content (mainly arsenic), high salinity, and oligotrophy. In this paper, the UV-B resistance and tolerance to arsenic of phylogenetically characterized bacteria (Actinobacteria [six isolates], Firmicutes [four isolates], and gamma-Proteobacteria [three isolates]) isolated from Laguna Vilama (4400-m altitude) and Laguna Azul (4560 m) were determined. In addition, given that multiple antibiotic resistances were also determined, a relationship between antibiotic resistances as a consequence of mutagenic ability or in relation to metal resistance is proposed. High UV-B resistances were found, since after 30 min (0.7 KJ m(-2)) and 60 min (1.4 KJ m(-2)) of irradiation, most of the studied bacteria did not show a decreased survival; what is more, many of them had an improved survival with the increased doses. Augmentations in mutagenesis rates were observed after UV-B irradiation in only 4 of the 13 tested isolates. Arsenite tolerance was also established in 8 of the 13 tested strains: Staphylococcus saprophyticus A3 and Micrococcus sp. A7, which were able to grow in media containing up to 10 mM As(III). Finally, predominance of antibiotic resistances (azithromycin, erythromycin, clarithromycin, roxithromycin, streptomycin, chloramphenicol, gentamycin, kanamycin, tetracycline, and ampicillin) was found, in all the isolated strains from both wetlands, with unexpectedly high minimal inhibitory concentrations (MICs; >2 mg mL(-1)) for macrolides. These results demonstrate that in extreme environments like high-altitude wetlands there is a correlation of multiresistances to UV-B radiation and arsenic, and that antibiotic resistances are also widespread in these pristine environments, where antibiotic selective pressure is supposed to be absent.

Determinants of carriage of resistant Escherichia coli in the Indonesian population inside and outside hospitals

OBJECTIVES

Antibiotic resistance is a worldwide healthcare problem exacerbated by antibiotic use and transmission of resistant bacteria. Not much is known about resistance in commensal flora and about determinants for resistance in Indonesia. This study analysed recent antibiotic use as well as demographic, socioeconomic, disease-related and healthcare-related determinants of rectal carriage of resistant Escherichia coli in the community and in hospitals in Indonesia.

METHODS

Carriers of susceptible E. coli were compared with carriers of E. coli with resistance to any of the tested antibiotics. Logistic regression analysis was performed to determine which variables were associated with carriage of resistant E. coli. Individuals in the community with varying levels of contact with healthcare institutions and hospitalized patients were analysed as separate populations.

RESULTS AND CONCLUSIONS

Of 3275 individuals (community 2494, hospital 781), 54% carried resistant E. coli. Recent antibiotic use was the most important determinant of resistance in both populations [community: odds ratio (OR) 1.8, 95% confidence interval (95% CI) 1.5-2.3; hospital: OR 2.5, 95% CI 1.6-3.9]. In the community, hospitalization (OR 2.4, 95% CI 2.0-3.0), diarrhoeal symptoms (OR 1.9, 95% CI 1.3-2.7) and age under 16 years (adults: OR 0.4, 95% CI 0.3-0.5) were associated with carriage of resistant E. coli. For hospitalized patients, having no health insurance was associated with less resistance (OR 0.6, 95% CI 0.4-0.9) and differences were observed between hospitals (Semarang: OR 2.2, 95% CI 1.5-3.3) and departments (Paediatrics: OR 4.3, 95% CI 1.7-10.7). Further research is needed to investigate whether transmission is responsible for these differences.

Selection of antibiotic-resistant pathogens in the community

In recent years, the importance of the community as a breeding ground for antibiotic-resistant pathogens is being recognized. Prescription of antimicrobial drugs for viral infections, inadequate dosage, use of long-acting macrolides and broad-spectrum antibiotics, and accessibility of over-the-counter antibiotics in many countries are the main drivers of increasing resistance. Education of physicians and the public on the correct use of antibiotics, introduction of rapid and reliable laboratory methods to distinguish between viral and bacterial infections, and offering economic incentives to the pharmaceutical industry to develop new drugs appear to be key issues in the confrontation with this serious public health problem.

Application of molecular techniques to the study of hospital infection

Nosocomial infections are an important source of morbidity and mortality in hospital settings, afflicting an estimated 2 million patients in United States each year. This number represents up to 5% of hospitalized patients and results in an estimated 88,000 deaths and 4.5 billion dollars in excess health care costs. Increasingly, hospital-acquired infections with multidrug-resistant pathogens represent a major problem in patients. Understanding pathogen relatedness is essential for determining the epidemiology of nosocomial infections and aiding in the design of rational pathogen control methods. The role of pathogen typing is to determine whether epidemiologically related isolates are also genetically related. To determine molecular relatedness of isolates for epidemiologic investigation, new technologies based on DNA, or molecular analysis, are methods of choice. These DNA-based molecular methodologies include pulsed-field gel electrophoresis (PFGE), PCR-based typing methods, and multilocus sequence analysis. Establishing clonality of pathogens can aid in the identification of the source (environmental or personnel) of organisms, distinguish infectious from noninfectious strains, and distinguish relapse from reinfection. The integration of molecular typing with conventional hospital epidemiologic surveillance has been proven to be cost-effective due to the associated reduction in the number of nosocomial infections. Cost-effectiveness is maximized through the collaboration of the laboratory, through epidemiologic typing, and the infection control department during epidemiologic investigations.

A survey on antibiotic usage in dairy herds in Pennsylvania

A survey was conducted (July 2001 to June 2002) on antibiotic usage of 113 dairy herds from 13 counties in Pennsylvania. Fifty percent of dairy farms surveyed maintained antibiotic treatment records. Only 21% of dairy producers had written plans for treating sick animals. Thirty-two percent of dairy producers sought veterinarian advice before administering antibiotics and on most farms (93%), antibiotics were administered by the owner/manager or designated herdsman. Twenty-four percent of the dairy producers said they always completed the course of antibiotic treatment. Any extra-label use of antibiotics was administered only on the guidelines of a veterinarian on majority of the farms. Comprehensive records from 33 dairy farms indicated that antibiotic usage was largest for calves with enteritis (36%) followed by pneumonia in calves (25%) and foot rot in cattle (16%). Twenty-four antibiotics including beta-lactams, spectinomycin, florfenicol, and tetracyclines were used on these farms. Beta-lactam antibiotics were used mostly for dry cow therapy, clinical mastitis, and on some farms for pneumonia and metritis. On 18% of the dairy herds surveyed, ceftiofur was used in an extra-label manner to treat mastitis in lactating cattle. On 70% of farms, calves were fed medicated milk replacers containing oxytetracycline and neomycin. The results of this study suggest that antibiotics are used extensively on dairy herds for both therapeutic and prophylactic purposes. Beta-lactams and tetracyclines were the most widely used antibiotics. There is considerable variation in the management practices associated with antibiotic use on dairy farms. It is anticipated that the findings of this survey will permit developing new strategies for prudent use of antibiotics on dairy herds.

An outcome-based approach for teaching prudent antimicrobial prescribing to undergraduate medical students: report of a Working Party of the British Society for Antimicrobial Chemotherapy

Antibiotic resistance is on the increase. This is evidenced by the almost daily publication of related articles in both professional journals and the media. The Department of Health and the Scottish Executive have published strategies and action plans that highlight the need for prudent use of antimicrobials. A key strategy in facilitating prudent prescribing is the early introduction of the relevant knowledge concepts and skills into the undergraduate medical curriculum. This reflects the need to ensure graduating doctors are fit for practice (General Medical Council) in accordance with evidence-based antibiotic policies. Outcome-based education has gained increasing credibility as an explicit and systematic approach to developing standards for undergraduate prescribing education. This approach enables performance to be measured accurately. This paper provides an introduction to understanding outcome-based education and how it has been applied in the context of prudent antimicrobial prescribing for undergraduate medical education as defined by an expert working party. In addition, the paper shares how this has then been implemented through the development of a new teaching resource custom designed to assist with teaching the skills of antimicrobial prescribing using an outcome framework. To avoid the increase of antibiotic resistance we advocate that the educational approach to prescribing should be one of achieving shared predetermined outcomes, and that the purpose-designed Appropriate Antimicrobial Prescribing for Tomorrow's Doctors (APT) teaching resource should be referred to and used by students, teachers, assessors, curriculum planners and anyone involved in antimicrobial prescribing.

Vancomycin-resistant enterococci: a road map on how to prevent the emergence and transmission of antimicrobial resistance

Nosocomial acquisition of microorganisms resistant to multiple antibiotics represents a threat to patient safety. Here we review the mechanisms that have allowed highly resistant strains belonging to the Enterococcus genus to proliferate within our health-care institutions. These mechanisms indicate that decreasing the prevalence of resistant organisms requires active surveillance, adherence to vigorous isolation, hand hygiene and environmental decontamination measures, and effective antibiotic stewardship. We suggest how to tailor such a complex, multidisciplinary program to the needs of a particular health-care setting so as to maximize cost-effectiveness.

Deadweight loss of bacterial resistance due to overtreatment

Widespread use of antibiotics is considered the major driving force behind the development of antibiotic resistance. The benefits of exceeding the welfare-maximizing level of antibiotic use are below the costs of resistance created by this excess quantity of antibiotics used, thereby resulting in a welfare deadweight loss. This paper uses a simple economic model to examine the theoretical and empirical aspects of the welfare loss generated by resistance and analyzes its policy implications. The annual deadweight loss associated with outpatient prescriptions for amoxicillin in the United States is estimated at US dollars 225 million.

Antimicrobial Use and Resistance

As antimicrobial use continues to rise, we are experiencing a concomitant rise in the prevalence of antimicrobial resistance. The precise relationship between use and resistance, however, has been challenging to define. Although the selection pressure exerted by antibiotic therapy appears to be the primary force promoting resistance, it is clear that the pathway to resistance is different for various organisms and antimicrobial agents. By understanding the mechanisms by which resistance emerges and spreads, it should be possible to design intervention strategies to slow or halt the process. This review summarizes some of our current understandings about the development and transmission of antibiotic-resistant bacteria, some of the control measures designed to interrupt the process, and how mathematical modeling can help us to better understand these complex pathways.

Etiology of fever and opportunities for reduction of antibiotic use in a pediatric intensive care unit

OBJECTIVE

To determine the cause of fever in critically ill children and to identify opportunities for reducing antibiotic use in this population.

DESIGN

Prospective case series.

SETTING

A tertiary-care medical-surgical pediatric intensive care unit (PICU).

PATIENTS

Children admitted to the PICU who experienced fever (axillary temperature >38.3 degrees C).

MEASUREMENTS

Consecutive children who were febrile at any point in their PICU stay were investigated over two winter seasons. Etiology of the fever was determined by physical examination and routine microbiology and radiographic tests. Three subgroups were reviewed to approximate the number of antibiotic-days that could have been reduced; namely, those with an indeterminate source, those with a documented viral infection, and those receiving a prolonged course of antibiotics. A set of standards reflecting common antibiotic use then was applied to these three patient groups.

RESULTS

Of 211 subjects, the majority (83.3%) had either a definitive or suspected focus for their fever, and nearly all of these patients were judged to have an infectious etiology. The study population received a total of 2,036 antibiotic-days. Despite the high incidence of infectious causes of fever in our subjects, however, approximately 15% of total antibiotic-days could have been reduced by applying common-use standards.

CONCLUSIONS

Fever in the PICU was usually of defined focus and infectious in origin. However, among febrile patients in the PICU, substantial opportunity exists for reduction of antibiotic use. Trials determining the safety of antibiotic reduction in this population should be pursued vigorously.

Antimicrobial management strategies for Gram-positive bacterial resistance in the intensive care unit

This article summarizes the current situation with Gram-positive infections, including the two primary consequences-failure to cure and resistance-relevant to the intensive care unit. The past few years have seen Enterococcus faecium resistance to vancomycin increase from 10% of strains to approaching 60% of strains in some centers. Failure is now so frequent that vancomycin can no longer be safely used. This has lead to use of two new antibiotics, quinupristin/dalfopristin (Synercid), first marketed in the United States in September 1999, and linezolid (Zyvox), which reached the U.S. market in May 2000. Both of these agents are being used to treat culture-proven vancomycin-resistant E. faecium. The calculated areas under the inhibitory curve (AUIC) values of vancomycin, even when its minimal inhibitory concentration (MIC) is 4.0 microg/mL, show almost all vancomycin-resistant E. faecium have AUICs <125. This explains failure, as well as the further selection of this bacteria into subpopulations with progressively higher MICs. Less well defined, but potentially an even greater problem, is the poor efficacy of vancomycin against multiresistant Staphylococcus aureus. Here, there is evidence of clinical failure in lower respiratory tract infection patients, but in most cases the MIC values of the organism have not risen to the point where AUICs are <125. However, the minimum bactericidal concentration of this organism may be considerably higher than its MIC, and in other cases there may be a high inoculum effect or a protein-binding effect to explain the failure of vancomycin to kill multiresistant S. aureus. Besides the increasing use of the new agents, strategies to manage these two increasingly resistant Gram-positive infections include cephalosporin restriction, switch and streamlining when cultures come back from the lab, combination regimens, and cycling in selected intensive care units.

Antimicrobial management measures to limit resistance: A process-based conceptual framework

To curb the trend toward increasingly resistant microorganisms, we must at least ensure that antibiotics are used in accordance with the best available scientific evidence. Here we review the control and streamlining measures aimed at optimizing the use of antibiotics, placing an emphasis on their demonstrated effectiveness in the intensive care unit environment. Because of their wide variety, the measures have been organized along the process of choosing, dosing, delivering, and then adjusting the initial antibiotics according to the culture results. By clarifying the range of options available, this process-based conceptual framework assists in best adapting a creative mixture of control measures to a particular healthcare system. The framework also facilitates the overview of a proposed multidisciplinary antibiotic management program, thereby helping to secure the administrative and local provider support necessary for its implementation and continued improvement.

A prospective study of antibiotic use and associated infections in young children

This study examines antibiotic usage and associated infections in infants and young children in Iowa. Longitudinal data were collected using a cohort recruited at birth from eight hospitals in eastern Iowa. Parents of recruited children were mailed questionnaires at 6 weeks, and 3, 6, 9, 12, 16, and 20 months of age. The cumulative incidence of antibiotic use and associated infections was determined using Kaplan-Meier survival analysis. There were data on 1,368 children. Antibiotic use was common in our cohort and increased with age. Beginning at age 3 months, approximately 50% of the cohort was exposed to an antibiotic during each reporting period. Otitis media was the most common indication and was responsible for 67.3% of antibiotic use. Children were most frequently treated with amoxicillin, followed by the cephalosporins and sulphonamides. By 12 and 20 months of age 79.0% and 92.5% of the children, respectively, had been treated with at least one course of antibiotics. Children received antibiotics for a median of 43 days by 20 months of age. Males were more likely to experience any antibiotic exposure than females (hazard ratio = 1.18) and showed a trend for more days of use (P = 0.052). There was a small but significant variation in antibiotic usage in the different recruitment communities (P = 0.02).

Use of RAPD-ALF analysis for investigating the frequency of bacterial cross-transmission in an adult intensive care unit

Bacterial cross-transmission was investigated during a 12-month period in an adult intensive care unit (ICU) by the generation of random amplified polymorphic DNA (RAPD) fingerprinting profiles, combined with automated laser fluorescence (ALF) analysis. The potential episodes of cross-transmission identified, were compared with those detected by the conventional first-line screen of antibiogram typing. Over the year, 215 primary gram-negative bacterial isolates were obtained from 160 patients. In total, 22 possible episodes of cross-transmission, involving 70 (44%) of the 160 patients, were identified by RAPD-ALF analysis, and 19 of these were substantiated with epidemiological evidence. Conversely, 31 possible episodes were identified on the basis of antibiogram data, but only three of these episodes, two involving Acinetobacter baumannii and one involving Serratia marcescens, correlated with those identified by RAPD-ALF analysis. It was concluded that analysis of antibiogram data alone is an unreliable method for assessing bacterial cross-transmission, unless the organism involved has a particularly stable or unusual resistance pattern. In contrast, the technique of RAPD-ALF analysis may provide a rapid and simple technique for obtaining an insight into the population dynamics of gram-negative bacteria in adult ICUs.

Strategies for study of the role of cycling on antimicrobial use and resistance

Resistant bacteria usually are seen first in the intensive care unit and other acute-care areas. Thus, strategies to control these organisms often are first tested in these healthcare settings. Frequent among these strategies are attempts to improve antimicrobial use. One proposed method to decrease resistance in special settings like the intensive care unit is the cycling or rotation of antimicrobials. This intervention must be evaluated in the context of other concomitant attempts to improve antimicrobial usage and must take into account other factors influencing resistance. Until such studies are done, the value of cycling and other efforts to limit prescribers' choices of drugs in endemic settings will be unclear. Studies to evaluate cycling will have to be of large scale to produce useful data. It is unlikely that many hospitals or healthcare systems will have sufficient resources on their own to develop studies of sufficient power to be applied widely. Thus, cooperative studies to provide data on this important issue should be an international priority.

Combinatorial discovery process yields antimicrobial peptoids

N-alkylated glycine trimers are generically referred to as peptoids. The identification of antimicrobial peptoids from a statistically unbiased diverse combinatorial chemistry library led to the design of the optimization peptoid library that we describe in this manuscript. This optimization library was designed using structural information from the most active peptoids in the unbiased library. Screening of the optimization library for antimicrobial activity identified a single pool of peptoids with activity against both Staphylococcus aureus and Escherichia coli. The active peptoids from this pool were active against drug sensitive and drug resistant organisms and represent novel antibacterial compounds.

Studies of antibiotic resistance within the patient, hospitals and the community using simple mathematical models

The emergence of antibiotic resistance in a wide variety of important pathogens of humans presents a worldwide threat to public health. This paper describes recent work on the use of mathematical models of the emergence and spread of resistance bacteria, on scales ranging from within the patient, in hospitals and within communities of people. Model development starts within the treated patient, and pharmacokinetic and pharmacodynamic principles are melded within a framework that mirrors the interaction between bacterial population growth, drug treatment and the immunological responses targeted at the pathogen. The model helps identify areas in which more precise information is needed, particularly in the context of how drugs influence pathogen birth and death rates (pharmacodynamics). The next area addressed is the spread of multiply drug-resistant bacteria in hospital settings. Models of the transmission dynamics of the pathogen provide a framework for assessing the relative merits of different forms of intervention, and provide criteria for control or eradication. The model is applied to the spread of vancomycin-resistant enterococci in an intensive care setting. This model framework is generalized to consider the spread of resistant organisms between hospitals. The model framework allows for heterogeneity in hospital size and highlights the importance of large hospitals in the maintenance of resistant organisms within a defined country. The spread of methicillin resistant Staphylococcus aureus (MRSA) in England and Wales provides a template for model construction and analysis. The final section addresses the emergence and spread of resistant organisms in communities of people and the dependence on the intensity of selection as measured by the volume or rate of drug use. Model output is fitted to data for Finland and Iceland and conclusions drawn concerning the key factors determining the rate of spread and decay once drug pressure is relaxed.

The transmission dynamics of antibiotic-resistant bacteria: the relationship between resistance in commensal organisms and antibiotic consumption

We propose a mathematical model of the transmission dynamics of colonization by commensal bacteria within a human community subject to varying levels of antibiotic use designed to control morbidity induced by pathogenic strains of the normally commensal organisms. Colonization is assumed not to induce morbidity in the majority of cases, and antibiotic use is assumed to be related to the arrival and growth of pathogenic strains that give rise to infections including clinical symptoms of disease. In the absence of antibiotic resistance, the model shows how the pattern of antibiotic prescription and use can eliminate the non-pathogenic commensal strains from the host community if the fraction of people taking antibiotics with a defined efficacy exceeds some critical level. The model is extended to take account of the evolution of antibiotic resistance in the commensal population. We assume resistance may be either plasmid-mediated or conferred by selection of low-level pre-existing mutants, and that resistant organisms may experience reduced reproductive fitness. Invasion of the host community by drug-resistant commensals is possible if certain antibiotic prescribing patterns pertain. We calculate these conditions in terms of the transmission parameter of the organism and the level of antibiotic prescription and use. The model is employed to address the issues of how best to use antibiotics in populations harbouring resistant organisms, and when resistant bacteria will out-compete sensitive strains.

Molecular diagnostics of infectious diseases

Over the past several years, the development and application of molecular diagnostic techniques has initiated a revolution in the diagnosis and monitoring of infectious diseases. Microbial phenotypic characteristics, such as protein, bacteriophage, and chromatographic profiles, as well as biotyping and susceptibility testing, are used in most routine laboratories for identification and differentiation. Nucleic acid techniques, such as plasmid profiling, various methods for generating restriction fragment length polymorphisms, and the polymerase chain reaction (PCR), are making increasing inroads into clinical laboratories. PCR-based systems to detect the etiologic agents of disease directly from clinical samples, without the need for culture, have been useful in rapid detection of unculturable or fastidious microorganisms. Additionally, sequence analysis of amplified microbial DNA allows for identification and better characterization of the pathogen. Subspecies variation, identified by various techniques, has been shown to be important in the prognosis of certain diseases. Other important advances include the determination of viral load and the direct detection of genes or gene mutations responsible for drug resistance. Increased use of automation and user-friendly software makes these technologies more widely available. In all, the detection of infectious agents at the nucleic acid level represents a true synthesis of clinical chemistry and clinical microbiology techniques.

Selective compartments for resistant microorganisms in antibiotic gradients

The development of bacterial resistance to antibiotics is one of the best documented examples of contemporary biological evolution. Variability in the mechanisms of resistance depends on the diversity of genotypes in the huge bacterial populations, and also on the diversity of selective pressures that are produced along the antibiotic concentration gradients formed in the highly compartmentalized human body during therapy. These antibiotic gradients can be conceived as comprising selective compartments, each one of them defined as the concentration able to select a particular genetic variant. In vitro experimental models confirm that some antibiotic resistant variants are selected only at certain selective concentrations of antibiotics. The correspondence between selective compartments and selectable variants could offer a way of describing more accurately the antibiotic selective landscapes and for taking measures to prevent the development of a major threat to the future of modern medicine.

The antibiotic selective process: concentration-specific amplification of low-level resistant populations

The biochemistry and genetics of antibiotic resistance are far better known than the equally important events underlying the selection of resistant populations. The hidden selection of low-level resistant variants may be a key process in the emergence of high-level antibiotic resistance. Different low-level resistant bacterial subpopulations may be specifically selected by different low antibiotic concentrations. The space in the environment (human body) where a given selective concentration exists represents the selective compartment. For pharmacokinetic reasons, low antibiotic concentrations occur in a larger selective compartment and persist longer than high antibiotic concentrations. The specific selection of low-level variants by low concentrations of antibiotic can be reproduced in experimental in vitro models using mixtures of susceptible and low-level resistant populations. We demonstrated this in Escherichia coli strains harbouring TEM-1, TEM-12 and TEM-10 beta-lactamases challenged by cefotaxime, and also Streptococcus pneumoniae strains with various levels of penicillin resistance challenged by amoxicillin or cefotaxime. In both cases, four hours of antibiotic challenge produced selective peaks of low-level resistant variant populations at low-level antibiotic concentrations. We conclude that variants with small decreases in antibiotic susceptibility may be fully selectable under in vivo circumstances; on the other hand, low-level antibiotic concentrations may have a considerable selective effect on the emergence of antibiotic resistance.