Minimum inhibitory concentration of carbapenems and tigecycline against Salmonella spp

Clinical and antimicrobial susceptibility profile of typhoid fever in children in the era of antibiotic resistance

Enteric fever remains a significant public health problem in low- and middle-income countries with further challenges from emerging antimicrobial resistance. Our prospective study evaluated the current clinical and antimicrobial susceptibility profile of enteric fever in 88 children and compared it to previously established literature. Enteric fever usually presents with nonspecific signs and symptoms, with predominant respiratory complaints. A paradigm shift in the antimicrobial sensitivity pattern has been noted, with increasing resistance for first-line antibiotics and older antibiotics such as ampicillin, cotrimoxazole, and chloramphenicol showing good sensitivity. Thus, the introduction of the latter merits consideration.

Defying the odds: Determinants of the antimicrobial response of Salmonella Typhi and their interplay

Salmonella Typhi, the invasive serovar of S. enterica subspecies enterica, causes typhoid fever in healthy human hosts. The emergence of antibiotic-resistant strains has consistently challenged the successful treatment of typhoid fever with conventional antibiotics. Antimicrobial resistance (AMR) in Salmonella is acquired either by mutations in the genomic DNA or by acquiring extrachromosomal DNA via horizontal gene transfer. In addition, Salmonella can form a subpopulation of antibiotic persistent (AP) cells that can survive at high concentrations of antibiotics. These have reduced the effectiveness of the first and second lines of antibiotics used to treat Salmonella infection. The recurrent and chronic carriage of S. Typhi in human hosts further complicates the treatment process, as a remarkable shift in the immune response from pro-inflammatory Th1 to anti-inflammatory Th2 is observed. Recent studies have also highlighted the overlap between AP, persistent infection (PI) and AMR. These incidents have revealed several areas of research. In this review, we have put forward a timeline for the evolution of antibiotic resistance in Salmonella and discussed the different mechanisms of the same availed by the pathogen at the genotypic and phenotypic levels. Further, we have presented a detailed discussion on Salmonella antibiotic persistence (AP), PI, the host and bacterial virulence factors that can influence PI, and how both AP and PI can lead to AMR.

Enteric Fever: Diagnostic Challenges and the Importance of Early Intervention

Enteric fever is a systemic infection caused by highly virulent Salmonella enterica serovars: Typhi and Paratyphi. Diagnosis of enteric fever is challenging due to a wide variety of clinical features which overlap with other febrile illnesses. The current diagnostic methods are limited because of the suboptimal sensitivity of conventional tests like blood culture in detecting organisms and the invasive nature of bone marrow culture. It emphasizes the need to develop improved and more reliable diagnostic modalities. The rising rates of multidrug-resistant Salmonella strains call for an accurate understanding of the current management of the disease. Proper public health measures and large-scale immunization programs will help reduce the burden of the disease. A comprehensive surveillance system can help detect the chronic carrier state and is crucial in understanding antibiotic susceptibility patterns. We conducted an all-language literature search on Medline, Cochrane, Embase, and Google Scholar till May 2022. The following search words and medical subject headings (MeSH) were used: "enteric fever," "Salmonella Typhi," "multidrug-resistant Salmonella," chronic carrier state," "Salmonella detection, "and "typhoid vaccine." We reviewed the literature on clinical features, pathophysiology, new diagnostic tests, and interventions to prevent the disease. This article explores enteric fever and its various clinical features and addresses the emerging threat of multidrug resistance. It focuses on novel methods for diagnosis and prevention strategies, including vaccines and the use of surveillance systems employed across different parts of the world.

Salmonella Shedding in Slaughter Pigs and the Use of Esterified Formic Acid in the Drinking Water as a Potential Abattoir-Based Mitigation Measure

Pigs shedding Salmonella at slaughter are considered a source of carcass contamination and human infection. To assess this potential risk, the proportion of Salmonella shedders that arrive for slaughter was evaluated in a population of 1068 pigs from 24 farms. Shedding was present in 27.3% of the pigs, and the monophasic variant of Salmonella Typhimurium, an emerging zoonotic serotype, was the most prevalent (46.9%). Antimicrobial resistance (AMR) in Salmonella isolates was common, but few isolates showed AMR to antimicrobials of critical importance for humans such as third-generation cephalosporins (5%), colistin (0%), or carbapenems (0%). However, AMR to tigecycline was moderately high (15%). The efficacy of an esterified formic acid in the lairage drinking water (3 kg formic acid/1000 L) was also assessed as a potential abattoir-based strategy to reduce Salmonella shedding. It was able to reduce the proportion of shedders (60.7% in the control group (CG) vs. 44.3% in the treatment group (TG); p < 0.01). After considering clustering and confounding factors, the odds of shedding Salmonella in the CG were 2.75 (95% CI = 1.80−4.21) times higher than those of the TG, suggesting a potential efficacy of reduction in shedding as high as 63.6%. This strategy may contribute to mitigating the burden of abattoir environmental contamination.

Evaluation of Antimicrobial Susceptibility Profile in Salmonella Typhi and Salmonella Paratyphi A: Presenting the Current Scenario in India and Strategy for Future Management

Background

Systematic studies to estimate the disease burden of typhoid and paratyphoid in India are limited. Therefore, a multicenter study on the Surveillance of Enteric Fever in India was carried out to estimate the incidence, clinical presentation, and antimicrobial resistance (AMR) trend. The data presented here represent the national burden of AMR in Salmonella Typhi and Salmonella Paratyphi A.

Methods

Antimicrobial susceptibility testing was performed for S. Typhi and S. Paratyphi A (n = 2373) isolates collected prospectively during a 2-year period from November 2017 to January 2020.

Results

Of 2373 Salmonella isolates, 2032 (85.6%) were identified as S. Typhi and 341 (14.4%) were S. Paratyphi A. Approximately 2% of S. Typhi were multidrug-resistant (MDR), whereas all 341 (100%) of S. Paratyphi A isolates were sensitive to the first-line antimicrobials. Among 98% of ciprofloxacin nonsusceptible isolates, resistance (minimum inhibitory concentration [MIC] &gt;0.5 µg/mL) was higher in S. Typhi (37%) compared with S. Paratyphi A (20%). Azithromycin susceptibility was 99.9% and 100% with a mean MIC of 4.98 μg/mL for S. Typhi and 7.39 μg/mL for S. Paratyphi A respectively. Ceftriaxone was the only agent that retained 100% susceptibility. Moreover, beta-lactam/beta-lactamase inhibitors showed potent in vitro activity against the study isolates.

Conclusions

Data obtained from this systematic surveillance study confirms the declining trend of MDR Salmonella isolates from India. The higher prevalence of ciprofloxacin nonsusceptibility enforces to limit its use and adhere to the judicious usage of azithromycin and ceftriaxone for enteric fever management.

Genomic Characterization of Antimicrobial Resistance in Food Chain and Livestock-Associated Salmonella Species

The rising trend of antimicrobial resistance (AMR) by foodborne bacteria is a public health concern as these pathogens are easily transmitted to humans through the food chain. Non-typhoid Salmonella spp. is one of the leading foodborne pathogens which infect humans worldwide and is associated with food and livestock. Due to the lack of discovery of new antibiotics and the pressure exerted by antimicrobial resistance in the pharmaceutical industry, this review aimed to address the issue of antibiotic use in livestock which leads to AMR in Salmonella. Much attention was given to resistance to carbapenems and colistin which are the last-line antibiotics used in cases of multi drug resistant bacterial infections. In the present review, we highlighted data published on antimicrobial resistant Salmonella species and serovars associated with livestock and food chain animals. The importance of genomic characterization of carbapenem and colistin resistant Salmonella in determining the relationship between human clinical isolates and food animal isolates was also discussed in this review. Plasmids, transposons, and insertion sequence elements mediate dissemination of not only AMR genes but also genes for resistance to heavy metals and disinfectants, thus limiting the therapeutic options for treatment and control of Salmonella. Genes for resistance to colistin (mcr-1 to mcr-9) and carbapenem (blaVIM-1, blaDNM-1, and blaNDM-5) have been detected from poultry, pig, and human Salmonella isolates, indicating food animal-associated AMR which is a threat to human public health. Genotyping, plasmid characterization, and phylogenetic analysis is important in understanding the epidemiology of livestock-related Salmonella so that measures of preventing foodborne threats to humans can be improved.

Resistance to colistin and production of extended-spectrum β-lactamases and/or AmpC enzymes in Salmonella isolates collected from healthy pigs in Northwest Spain in two periods: 2008-2009 and 2018

Salmonellosis is a common subclinical infection in pigs and therefore apparently healthy animals may represent a reservoir of antibiotic-resistant Salmonella for humans. This study estimates and characterizes resistance to two classes of antimicrobials considered of the highest priority within the critically important antimicrobials for humans, i.e. colistin (CR) and 3rd generation cephalosporins (3GC), on a collection of Salmonella isolates from pigs from two periods: between 2008 and 09, when colistin was massively used; and in 2018, after three years under a National Plan against Antibiotic Resistance. Prevalence of CR was low (6 out of 625; 0.96%; 95%CI: 0.44-2.1) in 2008-09 and associated mostly to the mcr-1 gene, which was detected in four S. 4,5,12:i:- isolates. Polymorphisms in the pmrAB genes were detected in a S. 9,12:-:- isolate. No CR was detected in 2018 out of 59 isolates tested. Among 270 Salmonella isolates considered for the assessment of resistance to 3GC in the 2008-2009 sampling, only one Salmonella Bredeney (0.37%; 95%CI: 0.07-2.1) showed resistance to 3GC, which was associated with the bla_CMY-2 gene (AmpC producer). In 2018, six isolates out of 59 (10.2%; 95%CI: 4.7-20.5) showed resistance to 3GC, but only two different strains were identified (S. 4,12:i:- and S. Rissen), both confirmed as extended-spectrum β-lactamases (ESBL) producers. The bla_CTX-M-3 and bla_TEM-1b genes in S. 4,12:i:- and the bla_TEM-1b gene in S. Rissen seemed to be associated with this resistance. Overall, the prevalence of CR in Salmonella appeared to be very low in 2008-2009 despite the considerable use of colistin in pigs at that time, and seemed to remain so in 2018. Resistance to 3GC was even lower in 2008-2009 but somewhat higher in 2018. Resistance was mostly coded by genes associated with mobile genetic elements. Most serotypes involved in these antimicrobial resistances displayed a multidrug resistance pattern and were considered zoonotic.

Progress in the overall understanding of typhoid fever: implications for vaccine development

INTRODUCTION

Typhoid fever continues to have a substantial impact on human health, especially in Asia and sub-Saharan Africa. Access to safe water, and adequate sanitation and hygiene remain the cornerstone of prevention, but these are not widely available in many impoverished settings. The emergence of antibiotic resistance affects typhoid treatment and adds urgency to typhoid control efforts. Vaccines provide opportunities to prevent and control typhoid fever in endemic settings.

AREAS COVERED

Literature search was performed looking for evidence concerning the global burden of typhoid and strategies for the prevention and treatment of typhoid fever. Cost of illness, available typhoid and paratyphoid vaccines and cost-effectiveness were also reviewed. The objective was to provide a critical overview of typhoid fever, in order to assess the current understanding and potential future directions for typhoid treatment and control.

EXPERT COMMENTARY

Our understanding of typhoid burden and methods of prevention has grown over recent years. However, typhoid fever still has a significant impact on health in low and middle-income countries. Introduction of typhoid conjugate vaccines to the immunization schedule is expected to make a major contribution to control of typhoid fever in endemic countries, although vaccination alone is unlikely to eliminate the disease.

Drug-resistant enteric fever worldwide, 1990 to 2018: a systematic review and meta-analysis

BACKGROUND

Antimicrobial resistance (AMR) is an increasing threat to global health. There are > 14 million cases of enteric fever every year and > 135,000 deaths. The disease is primarily controlled by antimicrobial treatment, but this is becoming increasingly difficult due to AMR. Our objectives were to assess the prevalence and geographic distribution of AMR in Salmonella enterica serovars Typhi and Paratyphi A infections globally, to evaluate the extent of the problem, and to facilitate the creation of geospatial maps of AMR prevalence to help targeted public health intervention.

METHODS

We performed a systematic review of the literature by searching seven databases for studies published between 1990 and 2018. We recategorised isolates to allow the analysis of fluoroquinolone resistance trends over the study period. The prevalence of multidrug resistance (MDR) and fluoroquinolone non-susceptibility (FQNS) in individual studies was illustrated by forest plots, and a random effects meta-analysis was performed, stratified by Global Burden of Disease (GBD) region and 5-year time period. Heterogeneity was assessed using the I2 statistics. We present a descriptive analysis of ceftriaxone and azithromycin resistance.

FINDINGS

We identified 4557 articles, of which 384, comprising 124,347 isolates (94,616 S. Typhi and 29,731 S. Paratyphi A) met the pre-specified inclusion criteria. The majority (276/384; 72%) of studies were from South Asia; 40 (10%) articles were identified from Sub-Saharan Africa. With the exception of MDR S. Typhi in South Asia, which declined between 1990 and 2018, and MDR S. Paratyphi A, which remained at low levels, resistance trends worsened for all antimicrobials in all regions. We identified several data gaps in Africa and the Middle East. Incomplete reporting of antimicrobial susceptibility testing (AST) and lack of quality assurance were identified.

INTERPRETATION

Drug-resistant enteric fever is widespread in low- and middle-income countries, and the situation is worsening. It is essential that public health and clinical measures, which include improvements in water quality and sanitation, the deployment of S. Typhi vaccination, and an informed choice of treatment are implemented. However, there is no licenced vaccine for S. Paratyphi A. The standardised reporting of AST data and rollout of external quality control assessment are urgently needed to facilitate evidence-based policy and practice.

TRIAL REGISTRATION

PROSPERO CRD42018029432.

Typhoid and paratyphoid fever: a call to action

Purpose of review

Enteric fever remains a major global-health concern, estimated to be responsible for between 11.9 and 26.9 million cases annually. Long-term prevention of enteric fever will require improved access to safe drinking water combined with investment in sanitation and hygiene interventions. In the short-to-medium term, new control strategies for typhoid fever have arrived in the form of typhoid Vi-conjugate vaccines (TCVs), offering hope that disease control can be achieved in the near future.

Recent findings

The diagnosis of enteric fever is complicated by its nonspecific clinical presentation, coupled with the low sensitivity of commonly used diagnostics. Investment in diagnostics has the potential to improve management, to refine estimates of disease burden and to facilitate vaccine impact studies. A new generation of reliable, diagnostic tests is needed that are simultaneously accessible, cost-effective, sensitive, and specific. The emergence and global dissemination of multidrug-resistant, fluoroquinolone-resistant, and extensively drug-resistant (XDR) strains of Salmonella Typhi emphasizes the importance of continued surveillance and appropriate antibiotic stewardship, integrated into a global strategy to address antimicrobial resistance (AMR). Current empirical treatment guidelines are out of date and should be updated to respond to local trends in AMR, so as to guide treatment choices in the absence of robust diagnostics and laboratory facilities. In September 2017, the WHO Strategic Advisory Group of Experts (SAGE) immunization recommended the programmatic use of TCVs in high burden countries. Ongoing and future studies should aim to study the impact of these vaccines in a diverse range of setting and to support the deployment of TCVs in high-burden countries.

Summary

The advent of new generation TCVs offers us a practical and affordable public-health tool that – for the first time – can be integrated into routine childhood immunization programmes. In this review, we advocate for the deployment of TCVs in line with WHO recommendations, to improve child health and limit the spread of antibiotic-resistant S. Typhi.

Introductory Article on Global Burden and Epidemiology of Typhoid Fever

This article is the introduction to a 12-paper supplement on global trends in typhoid fever. The Tackling Typhoid (T2) project was initiated in 2015 to synthesize the existing body of literature on typhoidal salmonellae and study national and regional typhoid fever trends. In addition to a global systematic review, eight case studies were undertaken to examine typhoid and paratyphoid fever trends in endemic countries alongside changes in relevant contextual factors. Incidence variations exist both within and between regions with large subnational differences as well, suggesting that public health changes impacting typhoid and paratyphoid fevers in one setting may not have similar impacts in another. This supplement also brings to light the lack of national typhoid fever surveillance systems, inconsistencies in diagnostics, and the lack of typhoid fever associated morbidity and mortality data in many countries, making it difficult to accurately quantify and track burden of disease. To better understand typhoid fever there is a need for more high-quality data from resource-poor settings. The implementation of typhoid surveillance systems alongside the transition to blood-culture confirmation of cases, where possible, would aid in the improvement of data quality in low-income settings. The following supplement includes the results of our global systematic review, eight-country case study articles, a qualitative article informed by semistructured interviews, and a conclusion article on potential ways forward for typhoid control.

The evolution of antimicrobial resistance in Salmonella Typhi

PURPOSE OF REVIEW

Increasing antimicrobial resistance in Salmonella Typhi is a serious public health concern, especially in industrializing countries. Here we review recent clinical and laboratory data concerning the evolution of antimicrobial resistance, with particular reference to the emergence resistance against fluoroquinolones, third generation cephalosporins, and azithromycin.

RECENT FINDINGS

The last 40 years have witnessed the sequential emergence of resistance to all first-line antimicrobials used in the treatment of S. Typhi infections. Multidrug resistance (MDR), defined by resistance to chloramphenicol, amoxicillin, and co-trimoxazole, emerged in the 1990s, followed rapidly by reduced susceptibility to fluoroquinolones. In the current decade, high-level fluoroquinolone resistance has emerged in south Asia and threatens to spread worldwide. Increasing reliance is now being placed on the activity of third generation cephalosporins and azithromycin, but resistance against these agents is developing. Carbapenems and tigecycline may be alternatives, although clinical data are sparse, and in some settings reversion to chloramphenicol and co-trimoxazole susceptibility is occurring. Therefore, older drugs may yet have a role in the treatment of S. Typhi infections.

SUMMARY

Good surveillance, improved diagnostics, more prudent use of antimicrobials, and effective vaccines will all be critical to reducing the burden of disease caused by S. Typhi.

Non-typhoidal Salmonella infections in children: Review of literature and recommendations for management

Non-typhoidal Salmonellae are a major cause of infectious diarrhoea worldwide and can cause invasive diseases, including bacteraemia, meningitis and osteomyelitis. Young or immunocompromised children and those with underlying conditions such as sickle cell disease are particularly vulnerable to invasive disease. There has been an increase in the rate of resistant non-typhoidal Salmonella, which is associated with invasive disease and hospitalisation. The intracellular nature of non-typhoidal Salmonella protects against extracellular antibiotics and can facilitate disease relapse, particularly meningitis. Effective antimicrobial agents with good intracellular penetration include azithromycin, fluoroquinolones and third-generation cephalosporins. Antibiotic treatment of non-typhoidal Salmonella gastroenteritis is only indicated if there are risk factors for invasive disease as it can prolong excretion and does not shorten the duration of gastrointestinal symptoms. Optimal choice and length of therapy for gastroenteritis and invasive disease in children is not clear. Here, we provide a review of the literature and treatment recommendations.

Epidemiology, Clinical Presentation, Laboratory Diagnosis, Antimicrobial Resistance, and Antimicrobial Management of Invasive Salmonella Infections

Salmonella enterica infections are common causes of bloodstream infection in low-resource areas, where they may be difficult to distinguish from other febrile illnesses and may be associated with a high case fatality ratio. Microbiologic culture of blood or bone marrow remains the mainstay of laboratory diagnosis. Antimicrobial resistance has emerged in Salmonella enterica, initially to the traditional first-line drugs chloramphenicol, ampicillin, and trimethoprim-sulfamethoxazole. Decreased fluoroquinolone susceptibility and then fluoroquinolone resistance have developed in association with chromosomal mutations in the quinolone resistance-determining region of genes encoding DNA gyrase and topoisomerase IV and also by plasmid-mediated resistance mechanisms. Resistance to extended-spectrum cephalosporins has occurred more often in nontyphoidal than in typhoidal Salmonella strains. Azithromycin is effective for the management of uncomplicated typhoid fever and may serve as an alternative oral drug in areas where fluoroquinolone resistance is common. In 2013, CLSI lowered the ciprofloxacin susceptibility breakpoints to account for accumulating clinical, microbiologic, and pharmacokinetic-pharmacodynamic data suggesting that revision was needed for contemporary invasive Salmonella infections. Newly established CLSI guidelines for azithromycin and Salmonella enterica serovar Typhi were published in CLSI document M100 in 2015.

Typhoid fever

Control of typhoid fever relies on clinical information, diagnosis, and an understanding for the epidemiology of the disease. Despite the breadth of work done so far, much is not known about the biology of this human-adapted bacterial pathogen and the complexity of the disease in endemic areas, especially those in Africa. The main barriers to control are vaccines that are not immunogenic in very young children and the development of multidrug resistance, which threatens efficacy of antimicrobial chemotherapy. Clinicians, microbiologists, and epidemiologists worldwide need to be familiar with shifting trends in enteric fever. This knowledge is crucial, both to control the disease and to manage cases. Additionally, salmonella serovars that cause human infection can change over time and location. In areas of Asia, multidrug-resistant Salmonella enterica serovar Typhi (S Typhi) has been the main cause of enteric fever, but now S Typhi is being displaced by infections with drug-resistant S enterica serovar Paratyphi A. New conjugate vaccines are imminent and new treatments have been promised, but the engagement of local medical and public health institutions in endemic areas is needed to allow surveillance and to implement control measures.

Antimicrobial resistance pattern and in-vitro activity of azithromycin in Salmonella isolates [corrected]

We evaluated antimicrobial susceptibility pattern of 42 Salmonella isolates from February 2012 through January 2013. We also determined the minimum inhibitory concentrations (MICs) of azithromycin against Salmonella isolates and compared them with corresponding disc diffusion sizes. Entire 42 isolates were sensitive to chloramphenicol, 41 (97.6%) were sensitive to cotrimoxazole and amoxicillin each. MICs for azithromycin ranged from 2 μg/ml to 24 μg/ml, corresponding zone diameters ranged from 15 mm to 33 mm and the two were significantly correlated (P = 0.001). Our results indicate that whereas, azithromycin is a potential therapeutic option, the sensitivity to the first line drugs and absence of multidrug resistance reinforce the concept of antimicrobial recycling.

Failure of oral antibiotic therapy, including azithromycin, in the treatment of a recurrent breast abscess caused by Salmonella enterica serotype Paratyphi A

We report a case of recurrent, multifocal Salmonella enterica serotype Paratyphi A breast abscesses, resistant to ciprofloxacin, which relapsed despite surgery, aspiration and multiple courses of antibiotics, including co-trimoxazole and azithromycin. The patient was cured after a prolonged course of intravenous ceftriaxone.

Increasing antimicrobial resistance and narrowing therapeutics in typhoidal salmonellae

Multidrug-resistant typhoid fever (MDRTF) is a major public health problem in developing countries and is an emerging problem in the developed world. Because of the difficulties in preventing typhoid by public health measures or immunization in developing countries, great reliance is placed on antimicrobial chemotherapy. The treatment should commence as soon as the clinical diagnosis is made rather than after the results of antimicrobial susceptibility tests but the existence of MDRTF poses a serious clinical dilemma in the selection of empiric antimicrobial therapy. With the widespread emergence and spread of strains resistant to chloramphenicol, ampicillin and trimethoprim, ciprofloxacin became the drug of choice for the treatment of typhoid fever. However, of late the efficacy of fluoroquinolones too has been questioned, mainly due to increasing reports of increasing defervescence time and poor patient response. This indicates that the organism has begun to develop resistance to fluoroquinolones, and is corroborated by a steady increase in Minimum Inhibitory Concentration (MIC) of ciprofloxacin. The therapeutics of ciprofloxacin-resistant enteric fever narrows down to third- and fourth-generation cephalosporins and azithromycin. However, the emergence of extended-spectrum b-lactamases (ESBLs) in typhoidal Salmonellae poses a new challenge and would greatly limit the therapeutic options leaving only tigecycline and carbepenems as secondary antimicrobial drugs. This increasing resistance is alarming and emphasizes the need of effective preventive measures to control typhoid and to limit the unnecessary use of antibiotics.

Rationale of azithromycin prescribing practices for enteric fever in India

PURPOSE

The present study was performed to assess the current susceptibility pattern of blood isolates of Salmonella spp from a super specialty hospital in North India against nalidixic acid, ciprofloxacin and azithromycin and compare the in vitro and in vivo response against azithromycin.

MATERIALS AND METHODS

We evaluated the minimum inhibitory concentration's (MIC's) of 107 blood isolates of Salmonella spp against nalidixic acid, azithromycin and ciprofloxacin and correlated in vitro and in vivo response of azithromycin from the treatment and discharge summaries from the Hospital Information System (HIS) software.

RESULTS

Among the 107 isolates evaluated, 94 (87.8%) were nalidixic acid-resistant (NAR) Salmonella and 36 were resistant to azithromycin by MIC testing. The MIC 90 value for azithromycin was 24 μg/mL. Among the 57 treatment histories evaluated using the HIS software, 19 (33%) patients had documented clinical non-response to azithromycin which required change of therapy.

CONCLUSIONS

The present study observed a higher MIC 90 values for azithromycin compared to Salmonella isolates from Western studies. There was also a documented clinical non-response against azithromycin. The in vitro and in vivo findings in this study suggest a guarded use of azithromycin for cases of enteric fever in India. The study also augments the reversal of resistance pattern in favour of chloramphenicol, ampicillin and trimethoprim - sulfamethoxazole.

Use of Carbapenems against clinical, nontyphoid Salmonella isolates: results from in vitro and in vivo animal studies

The emergence of multidrug-resistant Salmonella isolates has created the need for new therapeutic agents. We evaluated the intracellular activity of four carbapenem compounds against clinical nontyphoid Salmonella (NTS) isolates in vitro and ex vivo. Subsequently, the efficacy of carbapenem treatment against selected Salmonella isolates in vivo was assessed using a murine peritonitis model. The MIC(50) and MIC(90) for doripenem, ertapenem, imipenem, and meropenem against 126 NTS isolates were found to be 0.062 and 0.062, 0.015 and 0.015, 0.5 and 1, and 0.031 and 0.031 μg/ml, respectively. The intracellular killing effect of ertapenem was sustained for 24 h and was superior to that of imipenem, meropenem, and doripenem; its effect was comparable to that of ceftriaxone. Ertapenem demonstrated an excellent pharmacokinetic profile with a percent time above the MIC of 75.5% and an area under the concentration-time curve/MIC ratio of 20,733. When peritoneal exudate cells were examined directly ex vivo from mice with Salmonella-induced peritonitis, cells from mice treated with ertapenem and ceftriaxone had intracellular and extracellular bacterial counts reduced 10(2)- to 10(4)-fold and exhibited killing effects similar to each other. The survival rates of mice inoculated with 1 × 10(5) and 10(6) CFU of a ceftriaxone-susceptible Salmonella isolate that were subsequently treated with ertapenem or ceftriaxone were 100% and 90%, respectively. When mice were inoculated with 5 × 10(4) and 10(5) CFU of a ceftriaxone-resistant and ciprofloxacin-resistant Salmonella isolate, mice treated with ertapenem had a higher survival rate than mice treated with ceftriaxone (70% versus 0% and 50% versus 0%, respectively; P < 0.001). Our results suggest that ertapenem is at least as effective as ceftriaxone in treating murine Salmonella infections and show that further clinical investigations on the potential use of ertapenem in treatment of human Salmonella infections are warranted.

Antimicrobial susceptibility of bacterial isolates from community acquired infections in Sub-Saharan Africa and Asian low and middle income countries

OBJECTIVE

Antimicrobial resistance has arisen across the globe in both nosocomial and community settings as a consequence of widespread antibiotic consumption. Poor availability of laboratory diagnosis means that resistance frequently goes unrecognised and may only be detected as clinical treatment failure. In this review, we provide an overview of the reported susceptibility of common community acquired bacterial pathogens in Sub-Saharan Africa and Asia to the antibiotics that are most widely used in these areas.

METHODS

We reviewed the literature for reports of the susceptibility of prevalent pathogens in the community in SSA and Asia to a range of commonly prescribed antibiotics. Inclusion criteria required that isolates were collected since 2004 and that they were obtained from either normally sterile sites or urine. The data were aggregated by region and by age group.

RESULTS

Eighty-three studies were identified since 2004 which reported the antimicrobial susceptibilities of common bacterial pathogens. Different methods were used to assess in-vitro susceptibility in the different studies. The quality of testing (evidenced by resistance profiles) also varied considerably. For Streptococcus pneumoniae and Neisseria meningitidis most drugs maintained relatively high efficacy, apart from co-trimoxazole to which there were high levels of resistance in most of the pathogens surveyed.

CONCLUSIONS

Compared with the enormous infectious disease burden and widespread use of antibiotics there are relatively few reliable data on antimicrobial susceptibility from tropical Asia and Africa upon which to draw firm conclusions, although it is evident that many commonly used antibiotics face considerable resistance in prevalent bacterial pathogens. This is likely to exacerbate morbidity and mortality. Investment in improved antimicrobial susceptibility testing and surveillance systems is likely to be a highly cost-effective strategy and should be complemented by centralized and readily accessible information resources.

Quinolone and cephalosporin resistance in enteric Fever

Enteric fever is a major public health problem in developing countries. Ciprofloxacin resistance has now become a norm in the Indian subcontinent. Novel molecular substitutions may become frequent in future owing to selective pressures exerted by the irrational use of ciprofloxacin in human and veterinary therapeutics, in a population endemic with nalidixic acid-resistant strains. The therapeutics of ciprofloxacin-resistant enteric fever narrows down to third- and fourth-generation cephalosporins, azithromycin, tigecycline and penems. The first-line antimicrobials ampicillin, chloramphenicol and co-trimoxazole need to be rolled back. Antimicrobial surveillance coupled with molecular analysis of fluoroquinolone resistance is warranted for reconfirming novel and established molecular patterns for therapeutic reappraisal and for novel-drug targets. This review explores the antimicrobial resistance and its molecular mechanisms, as well as novel drugs in the therapy of enteric fever.

Susceptibility of bacterial isolates from community-acquired infections in sub-Saharan Africa and Asia to macrolide antibiotics

OBJECTIVE

To review the literature on the susceptibility of common community pathogens in sub-Saharan Africa and Asia to the macrolide antibiotics.

METHODS

Inclusion criteria required that isolates were collected since 2004 to ensure results were of contemporary relevance. The data were aggregated by region, age group and sterility of site of culture sample.

RESULTS

A total of 51 studies were identified, which reported the macrolide antimicrobial susceptibilities of common bacterial pathogens isolated since 2004. In general, there was less macrolide resistance in African than in Asian isolates. Most African studies reported high levels of macrolide susceptibility in Streptococcus pneumoniae, whereas most Chinese studies reported high levels of resistance. There was very little information available for Gram-negative organisms.

CONCLUSIONS

Susceptibility of the pneumococcus to macrolides in SSA remains high in many areas, and good activity of azithromycin has been shown against Salmonellae spp. in Asia. In urban areas where high antibiotic consumption is prevalent, there was evidence of increased resistance to macrolides. However, there is no information on susceptibility from large areas in both continents.