Salmonella enterica serovars Typhimurium and Enteritidis causing mixed infections in febrile children in Mozambique

Isolation and characterization of duck sewage source Salmonella phage P6 and antibacterial activity for recombinant endolysin LysP6

Salmonella is a globally prevalent foodborne pathogen, and adverse events caused by S. Enteritidis and S. Typhimurium are extremely common. With the emergence of drug resistance, there is an urgent need for efficient and specific lytic bacteriophages as alternative to antibiotics in clinical practice. In this study, phage P6 was isolated and screened from effluent and fecal samples from duck farm environments to specifically lyse the duck sources S. Typhimurium and S. Enteritidis. Phage P6 belongs to the genus Lederbergvirus, unclassified Lederbergvirus species. The phage P6 genome did not contained non-coding RNA, virulence genes and drug resistance genes, indicating that phage P6 was biologically safe for clinical applications. Phage P6 lysed 77.78% (28/36) of multidrug-resistant Salmonella and reduced biofilms formed by S. Enteritidis CVCC 3377, 4, and 24, and S. Typhimurium 44 by 44% to 75% within 3 h, and decreased Salmonella in duckling feces by up to 1.64 orders of magnitude. Prokaryotic expression of endolysin LysP6 lysed the chloroform-treated bacterial outer membrane from different serotypes of duck-derived Salmonella and E. coli standard strain ATCC 25922. The host range was expanded compared to phage P6, and the growth of Salmonella was effectively inhibited by LysP6 in conjunction with the membrane permeabilizer EDTA within 24 h. Therefore, phage P6 and phage-derived endolysins LysP6 are suitable for application as potent biocontrol agents to improve poultry health and food safety.

The prevalence of antimicrobial drug resistance of non-typhoidal Salmonella in human infections in sub-Saharan Africa: a systematic review and meta-analysis

INTRODUCTION

Non-typhoidal Salmonella (NTS) bacteremia is common in sub-Saharan Africa. We examined the prevalence of antibiotic resistance to fluoroquinolones, third-generation cephalosporins, and multi-drug resistance (MDR) in NTS human isolates from sub-Saharan Africa.

METHODS

A systematic review was conducted using a search in Ovid Medline, Embase, and African Index Medicus of publications between 2000 and 2021. A random-effects model meta-analysis was performed using data from 66 studies that included 29,039 NTS blood and 1,065 stool isolates.

RESULTS

The pooled prevalence proportions of MDR were 0.685 (95% CI 0.574-0.778) and 0.214 (0.020-0.785) in blood vs. stool isolates. The corresponding estimates of fluoroquinolones resistance were 0.014 (0.008-0.025) vs. 0.021 (0.012-0.036) and third-generation cephalosporins resistance 0.019 (0.012-0.031) vs. 0.035 (0.006-0.185). Similar results were found for children and adults. Resistance prevalence to these antibiotics in blood isolates increased between 2000-2010 and 2011-2021. The guidelines employed to determine antimicrobial resistance and epidemiological characteristics (e.g. sample size, study duration) correlated with the resistance prevalence.

CONCLUSIONS

The prevalence of MDR and resistance to fluoroquinolones and third-generation cephalosporins in NTS in sub-Saharan Africa is alarming.

EXPERT OPINION

Standardized surveillance of antimicrobial drug resistance in NTS in sub-Saharan Africa is warranted to guide healthcare policymaking and antibiotic stewardship programs.

Salmonella Broiler Meat's Contamination in Tunisia: Prevalence, Serotypes, Antimicrobial Resistance and Molecular Characterization of Isolated Strains

This study was conducted in north-eastern Tunisia to estimate the contamination prevalence of Salmonella in broilers' meat, to rank serotypes and to characterize the isolated multidrug-resistant (MDR) strains. A total number of 1288 meat samples were collected from 322 broiler batches; Salmonella isolates were identified by the alternative technique VIDAS Easy Salmonella. The susceptibility of Salmonella isolates was assessed against 21 antimicrobials using the disc diffusion method on Mueller-Hinton agar. Some antimicrobial resistance genes were identified using Polymerase Chain Reaction (PCR). The prevalence rates of Salmonella in the neck skin and the breast muscle contamination were estimated at 11.8% (38/322) and 0.9% (3/322), respectively. The prevalence rate of Salmonella in meat cutting parts contamination was estimated at 5.1% (33/644). Eight serotypes of Salmonella were identified, namely S. Enteritidis, S. Kentucky, S. Anatum, S. Infantis, S. Mbandaka, S. Zanzibar, S. Hadar and S. Agona. High rate of resistance was identified against amoxicillin (91.9%), nalidixic acid (83.8%), tetracycline (75.7%), streptomycin (73%), ciprofloxacin (70%), sulfamides (68.9%), cefalotin (68.9%), cefotaxim (67.6%) and cefoxitin (60.8%). The majority (90.5%; 67/74) of isolated strains was recognized as MDR. Nine MDR strains were identified as Extended-Spectrum β-Lactamase (ESBL) producers. The bla_CTX-M gene was identified by PCR in all the nine ESBL strains. TetA, tetB and dfrA1 genes were amplified in 3.6% (2/56), 1.8% (1/56) and 19.3% (5/26) of tetracycline and trimethoprim-resistant strains, respectively. The integrase gene (class 2) was identified in only 8.1% (6/74) of the Salmonella-isolated strains. Our findings highlight the emergence of MDR Salmonella isolates in Tunisia.

Prevalence, Risk Factors, Antimicrobial Resistance and Molecular Characterization of Salmonella in Northeast Tunisia Broiler Flocks

This study was conducted in northeastern Tunisia to estimate both the prevalence and the risk factors of Salmonella in broiler flocks as well as to characterize the isolated multidrug-resistant (MDR) Salmonella strains. In the present study, a total number of 124 farms were sampled; Salmonella isolates were identified by the alternative technique VIDAS Easy Salmonella. The susceptibility of Salmonella isolates was assessed against 21 antimicrobials using the disk diffusion method on Mueller–Hinton agar using antimicrobial discs. Some antimicrobial resistance genes were identified using PCR. The prevalence rate of Salmonella infection, in the sampled farms, was estimated at 19.9% (64/322). Moreover, a total number of 13 different serotypes were identified. High rate of resistance was identified against nalidixic acid (82.85%), amoxicillin (81.25%), streptomycin (75%), and ciprofloxacin (75%). Alarming level of resistance to ertapenem (12.5%) was noticed. A total of 87.5% (56/64) of isolated strains were recognized as MDR. Three MDR strains were extended-spectrum β-lactamases (ESBL)-producers and three MDR strains were cephalosporinase-producers. The bla_CTX-M gene was amplified in all the three ESBL strains. The qnrB gene was not amplified in fluoroquinolones-resistant strains. The tetA and tetB genes were amplified in 5% (2/40) and 2.5% (1/40) of tetracycline-resistant strains, respectively. The dfrA1 gene was amplified in five of the 20 trimethoprim-resistant strains. The mcr-1, mcr-2, mcr-3, mcr-4, and mcr-5 genes were not amplified in any of the phenotypically colistin-resistant strains. In terms of integrase genes int1 and int2, only gene class 2 was amplified in 11% (7/64) of analyzed strains. Risk factors, such as the poor level of cleaning and disinfection, the lack of antimicrobial treatment at the start of the breeding, and a crawl space duration lower than 15 days, were associated with high Salmonella infection in birds. These data should be considered when preparing salmonellosis control programs in Tunisian broiler flocks.

Pathogenic signature of invasive non-typhoidal Salmonella in Africa: implications for vaccine development

Invasive non-typhoidal Salmonella (iNTS) infections are a leading cause of bacteremia in Sub-Saharan Africa (sSA), thereby representing a major public health threat. Salmonella Typhimurium clade ST313 and Salmonella Enteriditis lineages associated with Western and Central/Eastern Africa are among the iNTS serovars which are of the greatest concern due to their case-fatality rate, especially in children and in the immunocompromised population. Identification of pathogen-associated features and host susceptibility factors that increase the risk for invasive non-typhoidal salmonellosis would be instrumental for the design of targeted prevention strategies, which are urgently needed given the increasing spread of multidrug-resistant iNTS in Africa. This review summarizes current knowledge of bacterial traits and host immune responses associated with iNTS infections in sSA, then discusses how this knowledge can guide vaccine development while providing a summary of vaccine candidates in preclinical and early clinical development.

Serotype distribution and antimicrobial resistance of human Salmonella enterica in Bangui, Central African Republic, from 2004 to 2013

Background

Limited epidemiological and antimicrobial resistance data are available on Salmonella enterica from sub-Saharan Africa. We determine the prevalence of resistance to antibiotics in isolates in the Central African Republic (CAR) between 2004 and 2013 and the genetic basis for resistance to third-generation cephalosporin (C3G).

Methodology/Principal findings

A total of 582 non-duplicate human clinical isolates were collected. The most common serotype was Typhimurium (n = 180, 31% of the isolates). A randomly selected subset of S. Typhimurium isolates were subtyped by clustered regularly interspaced short palindromic repeat polymorphism (CRISPOL) typing. All but one invasive isolate tested (66/68, 96%) were associated with sequence type 313. Overall, the rates of resistance were high to traditional first-line drugs (18–40%) but low to many other antimicrobials, including fluoroquinolones (one resistant isolate) and C3G (only one ESBL-producing isolate). The extended-spectrum beta-lactamase (ESBL)-producing isolate and three additional ESBL isolates from West Africa were studied by whole genome sequencing. The bla_CTX-M-15 gene and the majority of antimicrobial resistance genes found in the ESBL isolate were present in a large conjugative IncHI2 plasmid highly similar (> 99% nucleotide identity) to ESBL-carrying plasmids found in Kenya (S. Typhimurium ST313) and also in West Africa (serotypes Grumpensis, Havana, Telelkebir and Typhimurium).

Conclusions/Significance

Although the prevalence of ESBL-producing Salmonella isolates was low in CAR, we found that a single IncHI2 plasmid-carrying bla_CTX-M-15 was widespread among Salmonella serotypes from sub-Saharan Africa, which is of concern.

Salmonella enterica infections are common causes of bloodstream infection in sub-Saharan Africa and associated with a high mortality rate. Levels of multidrug resistance have become alarmingly high. Then, third-generation cephalosporin (C3G) and fluoroquinolones have become standard for first-line empirical treatment. Recently, C3G-resistant Salmonella populations have emerged and spread over all continents. This resistance is mainly mediated by acquired extended-spectrum beta-lactamase (ESBL) genes carried by mobile genetic elements such as plasmids. We report here the prevalence of resistance to antibiotics in isolates in the Central African Republic (CAR) between 2004 and 2013 and the genetic basis for resistance to C3G. Overall, resistance rates to antimicrobials were low during the study period, for all classes other than conventional antimicrobials, confirming recommendations for first-line treatment based on C3G and fluoroquinolones. Only one ESBL-producing isolate was recovered. The ESBL gene and the majority of antimicrobial resistance genes found were present in a large plasmid highly similar to ESBL-carrying plasmids found in East and West Africa, highlighting its significant role in the spread of ESBL genes in Salmonella isolates in sub-Saharan Africa. These finding have implications for treatment of salmonellosis and support the growing necessity for increased microbiological surveillance based on networks of clinical laboratories in order to control dissemination of antibiotic resistance among Salmonella isolates.

Non-typhoidal Salmonella blood stream infection in Kuwait: Clinical and microbiological characteristics

Non-typhoidal Salmonella (NTS) bacteremia is a significant cause of morbidity and mortality worldwide. It is considered to be an emerging and neglected tropical disease in Africa. We studied this in two tertiary hospitals–Al Farwaniya and Al Amiri–in Kuwait, a subtropical country, from April 2013-May 2016. NTS bacteremia was present in 30 of 53,860 (0.75%) and 31 of 290,36 (1.33%) blood cultures in the two hospitals respectively. In Al Farwaniya hospital, one-third of the patients were from some tropical developing countries of Asia. About 66% of all patients (40/61) had diarrhea, and of these, 65% had the corresponding blood serovar isolated from stool culture. A few patients had Salmonella cultured from urine. Patients were either young or old. Most of the patients had co-morbidities affecting the immune system. Two patients each died in both hospitals. The number of different serovars cultured in each hospital was 13, and most infections were due to S. Enteritidis (all sequence type [ST]) 11) and S. Typhimurium (all ST19) except in a subgroup of expatriate patients from tropical developing countries in Al Farwaniya hospital. About a quarter of the isolates were multidrug-resistant. Most patients were treated with a cephalosporin with or without other antibiotics. S. Enteritidis and S. Typhimurium isolates were typed by pulsed field-gel electrophoresis (PFGE) and a selected number of isolates were whole-genome sequenced. Up to four different clades were present by PFGE in either species. Whole-genome sequenced isolates showed antibiotic-resistance genes that showed phenotypic correlation, and in some cases, phenotypes showed absence of specific genes. Whole-genome sequenced isolates showed presence of genes that contributed to blood-stream infection. Phylogeny by core genome analysis showed a close relationship with S. Typhimurium and S. Enteritidis from other parts of the world. The uniqueness of our study included the finding of a low prevalence of infection, mortality and multidrug-resistance, a relatively high prevalence of gastrointestinal infection in patients, and the characterization of selected isolates of S. Typhimurium and S. Enteritidis serovars by whole-genome sequencing that shed light on phylogeny, virulence and resistance. Similarities with studies from developing countries especially Africa included infection in patients with co-morbidities affecting the immune system, predominance of S. Typhimurium and S. Enteritidis serovars and presence of drug-resistance in isolates.

Salmonella organisms are classified into typhoidal Salmonella (causing enteric fever) and non-typhoidal Salmonella (NTS) (causing infections other than enteric fever). Apart from causing other infections, NTS causes blood-stream infection (bacteremia and septicemia). NTS blood stream infection (NTS-BI) is considered to be an emerging and neglected tropical disease in Africa. It causes a very high morbidity and mortality in Africa. The individuals affected in Africa are children, malnourished people, patients with malaria or HIV etc. These conditions affect the immune system and make them vulnerable to infection with NTS. In these patients, diarrheal disease due to NTS is rare. The majority of infections are due to two types of NTS: Typhimurium and Enteritidis. There is a very high prevalence of multidrug-resistance in NTS making the infection difficult to treat. NTS-BI is also present in other parts of the world including developed countries albeit at a lower prevalence. Kuwait is a high-income, subtropical country in transition (from a developing to developed country), located in the Middle East. We studied NTS-BI in Al Farwaniya and Al Amiri hospitals in Kuwait during April 2013 to May 2016. Out of nearly 30,000 to more than 50,000 blood cultures done in these hospitals, NTS was present in 0. 75 to 1.33% of blood cultures, representing a very small proportion of blood cultures, unlike in Africa. This showed that 31 patients in Al Farwaniya hospital and 30 patients in Al Amari hospital had NTS-BI. Most of these patients had underlying illnesses such as diabetes, lung infection, cancer etc. that affect the immune system, as in Africa. Many patients also had diarrheal disease caused by the same NTS that caused blood stream infection, unlike in Africa. Only two patients in each hospital died, a low mortality, unlike in Africa. The majority of the isolates belonged to Typhimurium and Enteritidis as in Africa. Even though resistance to drugs was a problem, about quarter of the isolates only were multidrug-resistant, a lower prevalence compared to in Africa. In Kuwait, we performed a detailed genetic study of a selected number of Typhimurium and Enteritidis isolates by a modern technique called whole genome sequencing. This revealed genetic determinants encoding drug-resistance and virulence causing blood-stream infection. This type of study was not performed in African isolates. Thus, our study revealed similarities and differences with studies of NTS-BI in Africa.

Lysis Profiles of Salmonella Phages on Salmonella Isolates from Various Sources and Efficiency of a Phage Cocktail against S. Enteritidis and S. Typhimurium

Salmonella enterica serovar Enteritidis and Salmonella enterica serovar Typhimurium are major foodborne pathogens of concern worldwide. Bacteriophage applications have gained more interest for biocontrol in foods. This study isolated 36 Salmonella phages from several animal farms in Thailand and tested them on 47 Salmonella strains from several sources, including farms, seafood processing plant and humans in Thailand and USA. Phages were classified into three major groups. The estimated phage genome size showed the range from 50 ± 2 to 200 ± 2 kb. An effective phage cocktail consisting of three phages was developed. Approximately 4 log CFU/mL of S. Enteritidis and S. Typhimurium could be reduced. These phages revealed a burst size of up to 97.7 on S. Enteritidis and 173.7 PFU/cell on S. Typhimurium. Our phage cocktail could decrease S. Enteritidis on chicken meat and sunflower sprouts by 0.66 log CFU/cm² and 1.27 log CFU/g, respectively. S. Typhimurium on chicken meat and sunflower sprouts were decreased by 1.73 log CFU/cm² and 1.17 log CFU/g, respectively. Overall, animal farms in Thailand provided high abundance and diversity of Salmonella phages with the lysis ability on Salmonella hosts from various environments and continents. A developed phage cocktail suggests a potential biocontrol against Salmonella in fresh foods.