Methicillin-resistant Staphylococcus aureus as a cause of invasive infections in Central Africa: a case report and review of the literature

Causative agents and antimicrobial resistance patterns of human skin and soft tissue infections in Bagamoyo, Tanzania

Few epidemiological studies have been carried out to assess the aetiology and antimicrobial susceptibility patterns of pathogens giving rise to skin and soft tissue infections (SSTIs) in sub-Saharan Africa. In the present study from six healthcare facilities in Bagamoyo, Tanzania, wound swabs from outpatients with SSTIs were analysed by a suite of methods, including microbiological culture techniques, matrix-assisted laser desorption/ionisation time-of-flight mass spectrometry and resistance testing. Among 185 patients with SSTIs, 179 (96.8%) swabs showed microbiological growth. In total, 327 organisms were found, of which 285 were of potential aetiological relevance. Staphylococcus aureus was the predominant pathogen (prevalence: 71.4%), followed by the Gram-negative bacteria Enterobacter cloacae complex (14.6%), Klebsiella pneumoniae (12.4%) and Pseudomonas aeruginosa (11.8%). While one out of three isolates of S. aureus showed resistance to macrolides, tetracyclines, cotrimoxazole and clindamycin, only a single methicillin-resistant S. aureus (MRSA) strain was found. In Gram-negative bacteria, resistance to ampicillin and cotrimoxazole was common, while extended-spectrum beta-lactamases were rarely detected (<1%). We conclude that S. aureus was the most frequently detected pathogen in community-acquired SSTIs in Bagamoyo, Tanzania. Resistance to commonly prescribed oral antibiotics was considerable, but multi-resistant strains were rarely encountered. Monitoring of antibiotic susceptibility patterns in SSTIs is important to provide specific data for tailoring treatment recommendations.

Methicillin-Resistant Staphylococcus aureus: Molecular Characterization, Evolution, and Epidemiology

Staphylococcus aureus, a major human pathogen, has a collection of virulence factors and the ability to acquire resistance to most antibiotics. This ability is further augmented by constant emergence of new clones, making S. aureus a "superbug." Clinical use of methicillin has led to the appearance of methicillin-resistant S. aureus (MRSA). The past few decades have witnessed the existence of new MRSA clones. Unlike traditional MRSA residing in hospitals, the new clones can invade community settings and infect people without predisposing risk factors. This evolution continues with the buildup of the MRSA reservoir in companion and food animals. This review focuses on imparting a better understanding of MRSA evolution and its molecular characterization and epidemiology. We first describe the origin of MRSA, with emphasis on the diverse nature of staphylococcal cassette chromosome mec (SCCmec). mecA and its new homologues (mecB, mecC, and mecD), SCCmec types (13 SCCmec types have been discovered to date), and their classification criteria are discussed. The review then describes various typing methods applied to study the molecular epidemiology and evolutionary nature of MRSA. Starting with the historical methods and continuing to the advanced whole-genome approaches, typing of collections of MRSA has shed light on the origin, spread, and evolutionary pathways of MRSA clones.

Origin, evolution, and global transmission of community-acquired Staphylococcus aureus ST8

USA300 is a hypervirulent, community-acquired, multidrug-resistant Staphylococcus aureus clone that started to spread in the United States around 17 years ago. Many studies detected it also in South America, Europe, and the Asia-Pacific region. In this study, we show that USA300 is also circulating in sub-Saharan Africa. Locating the temporal and spatial origin of clonal lineages is important with respect to epidemiology and molecular evolution of pathogens. We show that USA300 evolved from a less virulent and less resistant ancestor circulating in Central Europe around 160 years ago. Constant surveillance of pathogen transmission routes is vital to prevent and control potential outbreaks. Whole genome sequencing proved to be a useful tool for epidemiological surveillance.

USA300 is a pandemic clonal lineage of hypervirulent, community-acquired, methicillin-resistant Staphylococcus aureus (CA-MRSA) with specific molecular characteristics. Despite its high clinical relevance, the evolutionary origin of USA300 remained unclear. We used comparative genomics of 224 temporal and spatial diverse S. aureus isolates of multilocus sequence type (ST) 8 to reconstruct the molecular evolution and global dissemination of ST8, including USA300. Analyses of core SNP diversity and accessory genome variations showed that the ancestor of all ST8 S. aureus most likely emerged in Central Europe in the mid-19th century. From here, ST8 was exported to North America in the early 20th century and progressively acquired the USA300 characteristics Panton–Valentine leukocidin (PVL), SCCmec IVa, the arginine catabolic mobile element (ACME), and a specific mutation in capsular polysaccharide gene cap5E. Although the PVL-encoding phage ϕSa2USA was introduced into the ST8 background only once, various SCCmec types were introduced to ST8 at different times and places. Starting from North America, USA300 spread globally, including Africa. African USA300 isolates have aberrant spa-types (t112, t121) and form a monophyletic group within the clade of North American USA300. Large parts of ST8 methicillin-susceptible S. aureus (MSSA) isolated in Africa represent a symplesiomorphic group of ST8 (i.e., a group representing the characteristics of the ancestor), which are rarely found in other world regions. Isolates previously discussed as USA300 ancestors, including USA500 and a “historic” CA-MRSA from Western Australia, were shown to be only distantly related to recent USA300 clones.

Community-Associated Staphylococcus aureus from Sub-Saharan Africa and Germany: A Cross-Sectional Geographic Correlation Study

Clonal clusters and gene repertoires of Staphylococcus aureus are essential to understand disease and are well characterized in industrialized countries but poorly analysed in developing regions. The objective of this study was to compare the molecular-epidemiologic profiles of S. aureus isolates from Sub-Saharan Africa and Germany. S. aureus isolates from 600 staphylococcal carriers and 600 patients with community-associated staphylococcal disease were characterized by DNA hybridization, clonal complex (CC) attribution, and principal component (PCA)-based gene repertoire analysis. 73% of all CCs identified representing 77% of the isolates contained in these CCs were predominant in either African or German region. Significant differences between African versus German isolates were found for alleles encoding the accessory gene regulator type, enterotoxins, the Panton-Valentine leukocidin, immune evasion gene cluster, and adhesins. PCA in conjunction with silhouette analysis distinguished nine separable PCA clusters, with five clusters primarily comprising of African and two clusters of German isolates. Significant differences between S. aureus lineages in Africa and Germany may be a clue to explain the apparent difference in disease between tropical/(so-called) developing and temperate/industrialized regions. In low-resource countries further clinical-epidemiologic research is warranted not only for neglected tropical diseases but also for major bacterial infections.

Bromomethylthioindole Inspired Carbazole Hybrids as Promising Class of Anti-MRSA Agents

Series of N-substituted carbazole analogues bearing an indole ring were synthesized as anti-methicillin-resistant Staphylococcus aureus (MRSA) agents from a molecular hybridization approach. The representative compound 19 showed an MIC = 1 μg/mL against a panel of MRSA clinical isolates as it possessed comparable in vitro activities to that of vancomycin. Moreover, compound 19 also exhibited MIC = 1 μg/mL activities against a recent identified Z172 MRSA strain (vancomycin-intermediate and daptomycin-nonsusceptible phenotype) and the vancomycin-resistant Enterococcus faecalis (VRE) strain. In a mouse model with lethal infection of MRSA (4N216), a 75% survival rate was observed after a single dose of compound 19 was intravenously administered at 20 mg/kg. In light of their equipotent activities against different MRSA isolates and VRE strain, the data underscore the importance of designed hybrid series for the development of new N-substituted carbazoles as potential anti-MRSA agents.

Management of severe non-TB bacterial infection in HIV-infected adults

Despite widespread antiretroviral therapy use, severe bacterial infections (SBI) in HIV-infected adults continue to cause significant morbidity and mortality globally. Four main pathogens account for the majority of documented SBI: Streptococcus pneumoniae, non-typhoidal strains of Salmonella enterica, Escherichia coli and Staphylococcus aureus. The epidemiology of SBI is dynamic, both in developing countries where, despite dramatic successes in antiretroviral therapy, coverage is far from complete, and in settings in both resource-poor and resource-rich countries where antiretroviral therapy failure is becoming increasingly common. Throughout the world, this complexity is further compounded by rapidly emerging antimicrobial resistance, making management of SBI very challenging in these vulnerable patients. We review the causes and treatment of SBI in HIV-infected people and discuss future developments in this field.

Missense mutations of PBP2a are associated with reduced susceptibility to ceftaroline and ceftobiprole in African MRSA

OBJECTIVES

Ceftaroline and ceftobiprole are new cephalosporins, which are active against MRSA by inhibiting PBP2a. Recently, high rates of resistance to ceftaroline were reported from Ghana. The objective of this study was to assess rates of resistance to ceftaroline and ceftobiprole in MRSA from Africa and to describe potential missense mutations of PBP2a.

METHODS

MRSA isolates derived from Staphylococcus aureus colonization (n = 37) and infection (n = 23) and were collected in Côte d'Ivoire (n = 17), DR Congo (n = 6), Gabon (n = 21) and Nigeria (n = 16). The MICs were determined by the broth microdilution method. The mecA gene was sequenced and missense mutations were associated with the corresponding MLST ST.

RESULTS

In total, 16.7% (n = 10) and 15% (n = 9) of isolates were resistant to ceftaroline and ceftobiprole, respectively. The corresponding MICs of ceftaroline and ceftobiprole correlated significantly (r = 0.92). Isolates belonging to ST241 harboured a triple mutation of PBP2a (N146K-N204K-G246E), which was associated with high rates of resistance to ceftaroline (90.9%) and ceftobiprole (81.8%).

CONCLUSIONS

Resistances to ceftaroline and ceftobiprole were only detected in Nigeria and were associated with ST241 and a triple mutation of PBP2a.

Methicillin-Resistant Staphylococcus aureus in the Community in Luanda, Angola: Blurred Boundaries with the Hospital Setting

Although the nosocomial prevalence of methicillin-resistant Staphylococcus aureus (MRSA) in Angola is over 60% and one of the highest in Africa, the extent of MRSA in the community is unknown. To fill this gap, we conducted a hospital-based study in which 158 children attending the emergency ward and ambulatory services of a pediatric hospital in Luanda, the capital of Angola, were screened for S. aureus nasal colonization. Overall, 70 (44.3%) individuals were colonized with S. aureus, of which 20 (28.6%) carried MRSA, resulting in a prevalence of 12.7% (20/158) of MRSA in the population screened. Molecular characterization by pulsed-field gel electrophoresis (PFGE), spa typing, multilocus sequence typing, and SCCmec typing distributed the isolates into two major MRSA clones and one dominant methicillin-susceptible S. aureus (MSSA) lineage, corresponding to the main clones circulating in hospitals in Luanda. The MRSA isolates mainly belonged to clones A (PFGE type A, spa type t105, ST5-IVa-65%) and B (PFGE B, t3869, ST88-IVa-30%), while MSSA isolates mainly belonged to clone L (PFGE type L, t861, ST508-42%). S. aureus isolates showed resistance to penicillin (96%), rifampin (87%), and trimethoprim-sulfamethoxazole (21%). In conclusion, the prevalence of MRSA among children in the community in Luanda is high and seems to originate from hospitals, warranting continuous monitoring and implementation of additional infection control measures.

The Challenge of Diagnosing and Treating Staphylococcus aureus Invasive Infections in a Resource-limited Sub-Saharan Africa Setting: A Case Report

BACKGROUND

Community-acquired methicillin-sensitive Staphylococcus aureus (CA-MSSA) is responsible for the majority of skin and soft-tissue infections. CA-MSSA can also cause life-threatening infections, possibly in relation to particular virulence factors, including Panton-Valentine leukocidin (PVL).

METHODS

We describe a severe CA-MSSA necrotizing pneumonia complicated with multifocal osteomyelitis, pericardial effusion and endocarditis in a 6-year-old boy admitted to a Mozambican hospital. Staphylococcus aureus isolation and antibiotic susceptibility testing were performed by conventional microbiology. Additionally, microarray assay was used for molecular characterization.

RESULTS

Blood culture confirmed the presence of S. aureus susceptible to most antimicrobial agents, including methicillin. Molecular characterization confirmed the presence of PVL, together with alpha and beta haemolysin genes.

CONCLUSIONS

To our knowledge, this is the first reported case of disseminated CA-MSSA disease with confirmed PVL exotoxin in sub-Saharan Africa. PVL-positive CA-MSSA should be considered in the differential diagnosis of community-acquired pneumonia, making laboratory testing a higher priority.

Molecular epidemiology of Methicillin-resistant Staphylococcus aureus in Africa: a systematic review

Methicillin-resistant Staphylococcus aureus (MRSA) infections are a serious global problem, with considerable impact on patients and substantial health care costs. This systematic review provides an overview on the clonal diversity of MRSA, as well as the prevalence of Panton-Valentine leukocidin (PVL)-positive MRSA in Africa. A search on the molecular characterization of MRSA in Africa was conducted by two authors using predefined terms. We screened for articles published in English and French through to October 2014 from five electronic databases. A total of 57 eligible studies were identified. Thirty-four reports from 15 countries provided adequate genotyping data. CC5 is the predominant clonal complex in the healthcare setting in Africa. The hospital-associated MRSA ST239/ST241-III [3A] was identified in nine African countries. This clone was also described with SCCmec type IV [2B] in Algeria and Nigeria, and type V [5C] in Niger. In Africa, the European ST80-IV [2B] clone was limited to Algeria, Egypt and Tunisia. The clonal types ST22-IV [2B], ST36-II [2A], and ST612-IV [2B] were only reported in South Africa. No clear distinctions were observed between MRSA responsible for hospital and community infections. The community clones ST8-IV [2B] and ST88-IV [2B] were reported both in the hospital and community settings in Angola, Cameroon, Gabon, Ghana, Madagascar, Nigeria, and São Tomé and Príncipe. The proportion of PVL-positive MRSA carriage and/or infections ranged from 0.3 to 100% in humans. A number of pandemic clones were identified in Africa. Moreover, some MRSA clones are limited to specific countries or regions. We strongly advocate for more surveillance studies on MRSA in Africa.