Staphylococcus species are a major component of the human skin and mucosa microbiota. Also, fecal carriage of staphylococci is widespread in humans, although the number of bacteria detectable in stool samples is usually low (Akinkunmi and Lamikanra, 2012). Commensal staphylococci can become pathogenic when there is a break in the skin or mucosal barrier as well as during the insertion of indwelling medical devices (Kateete et al., 2020). Staphylococci were previously categorized as coagulase-negative or coagulase-positive based on their ability to produce the coagulase enzyme (Gómez-Sanz et al., 2019), and the term coagulase-negative staphylococci became widely used to encompass all staphylococci other than the well-recognized human pathogen Staphylococcus aureus. However, due to the coagulase-variable nature of some species, the term staphylococci other than Staphylococcus aureus (SOSA) has been introduced to better differentiate S. aureus and other (“non-aureus”) staphylococci (Humphries et al., 2021).

Neonates may be colonized with SOSA through breastfeeding, and high rates of colonization ranging from 92.9%–98.9% have been reported (Soeorg et al., 2017).

Antibiotic resistance (ABR) is a worldwide and common problem in staphylococci, including SOSA. The prevalence of colonization with methicillin-resistant SOSA (MR-SOSA) ranges widely from 30.2% to as high as 89.3% in healthy individuals in Nigeria (Akinkunmi and Lamikanra, 2010) and Brazil (Ternes et al., 2013). SOSA are often considered a reservoir for ABR and virulence genes, which can be transferred to other pathogenic bacteria such as S. aureus (Nemeghaire et al., 2014). Colonization by resistant SOSA could therefore facilitate the spread of ABR genes into other species and contribute to the general infection burden by antibiotic resistant bacteria (Jamaluddin et al., 2008). The staphylococcal cassette chromosome mec (SCCmec) are mobile genetic elements which usually carry mec genes (i.e., mecA, mecB, mecC) that encode alternative penicillin-binding proteins, mediating resistance to nearly all β-lactam antibiotics (Saber et al., 2017). SCCmec elements have their evolutionary origin most likely in Mammaliicoccus sciuri (previously known as Staphylococcus sciuri) and have been transferred to S. aureus and other SOSA species. Fourteen SCCmec types (I–XIV) have been described in S. aureus (Urushibara et al., 2019), of which SCCmec types I–IX have been reported in SOSA, mostly in Staphylococcus epidermidis, Staphylococcus haemolyticus, and Staphylococcus hominis. However, the majority of SCCmec elements in SOSA are non-typeable using available methods, due to the high recombination rates in SOSA (Miragaia, 2018), which increases their diversity.

Apart from S. epidermidis for which surveillance data are well established (Thomas et al., 2007), there is limited multi-locus sequence typing (MLST) information and molecular epidemiology data available for SOSA. Nevertheless, S. haemolyticus ST239 has been associated with SCCmec type III (Lin et al., 2022; Montelongo et al., 2022) and S. hominis ST16 and ST23 have been identified in outbreaks in Spain (Zhang et al., 2013). These STs were reported in pathogenic SOSA, but there is a lack of information on the distribution of STs in commensal SOSA in Africa and in Sub-Saharan Africa. With this study we would like to fill this knowledge gap and analyse the gastrointestinal carriage and population structure of ABR SOSA isolates in healthy children in Cape Town communities.

In this study, phenotypic and genotypic methods were used to characterize SOSA isolates. The whole genome sequencing analysis has provided additional information on antibiotic resistance genes, strain types and speciation.

High rates of colonization with SOSA have been reported in healthy children: 37%–42% in Nigeria (Akinkunmi and Lamikanra, 2010), and in Scotland (Jackson et al., 2000). Of the children included in this study, 33.3% were colonized by SOSA. The species of SOSA isolated from this study were similar to those isolated by Domínguez et al. (2002) in Spanish children and Akinkunmi and Lamikanra (2010) in Nigerian children; however those studies also identified S. warneri and S. caprae, and S. schleiferi, S. lugdunesis and unspeciated SOSA, respectively. In both studies, S. epidermidis was the most common SOSA colonizing children, Nigeria (30.2%) and Spain (38.5%), while in our study S. haemolyticus was the most commonly isolated (25.3%). This demonstrates that carriage of SOSA species in the faecal samples of children/humans may differ between geographical locations. Together with S. capitis, which was also reported in all three studies, these SOSA have been implicated in nosocomial infections associated with high rates of antibiotic resistance (Decalonne et al., 2020).

Due to the small numbers of the other SOSA isolated in this study, the discussion will focus on S. haemolyticus. S. haemolyticus and S. borealis are discussed together due to the inability of commonly used species identification methods to distinguish them. All S. haemolyticus isolates (100.0%) from this study were methicillin resistant. This is higher than the 46.2% (n = 12) seen in Nigeria, 50.0% (n = 1) in Spain and 10.0% in public settings in London (Domínguez et al., 2002; Akinkunmi and Lamikanra, 2010; Xu et al., 2018). This high methicillin resistance rate threatens empiric treatment practices in Cape Town, South Africa. This may also highlight the need to review the use of antibiotics in Cape Town communities.

The tetracycline resistance rate in S. haemolyticus (39.0%) is similar to that described in carriage isolates in Nigeria (30.8%). Although tetracycline is not approved for use in children, the high resistance rates seen in Nigeria and South Africa may reflect the use of this antibiotic in adult populations, as well as food animals and agriculture in Africa (Mshana et al., 2021).

Resistance to erythromycin (50.6%) was similar to what was reported in Nigeria (53.8%). Resistance to trimethoprim-sulfamethoxazole (31.2%) was lower than the 53.8% reported in Nigeria while clindamycin resistance was slightly higher (18.2% vs. 11.5%). The lower rate of resistance of S. haemolyticus to trimethoprim-sulfamethoxazole in this study is surprising since trimethoprim-sulfamethoxazole is one of the commonest antibiotics used extensively for prophylaxis in HIV infected individuals in South Africa (Takuva et al., 2019). In this study, all isolates were susceptible to vancomycin, which is similar to what was reported by Domínguez et al. (2002) in Spanish children, however 15.4% vancomycin resistance was reported in Nigeria (Akinkunmi and Lamikanra, 2010).

High rates (30%) of multidrug-resistant SOSA (MDR-SOSA) colonization have also been reported in neonates in Brazil (Ternes et al., 2013), this is higher than the 18.6% observed in this study.

The methicillin resistance gene mecA was detected in only 65.3% of S. haemolyticus isolates, despite all being methicillin resistant. The mecA detection rate was higher than 22.2% reported in non-healthcare settings in the United Kingdom (Xu et al., 2018). Resistance to β-lactams such as oxacillin has been associated with mecA and rarely mecC. The absence of mecA in 34.7% of methicillin-resistant S. haemolyticus may be due to challenges in using cefoxitin and oxacillin for screening for methicillin resistance in non-aureus staphylococci, as described by Yang et al. (2022) and Humphries et al. (2021). Other novel resistance mechanisms may be involved, such as elevated expression of blaZ, which has been shown in some SOSA isolates, although this has not been conclusively linked to methicillin resistance (Black et al., 2011).

This study is the first to identify S. borealis in Africa. S. borealis shares 861 core genes with S. haemolyticus, representing 34.6% of its genome (Pain et al., 2020). S. borealis cannot be distinguished from S. haemolyticus using the three bacterial identification system commonly used globally (MALDI-TOF, Vitek AES system, and 16S RNA sequencing) which raises the possibility that S. borealis may be wrongly identified as S. haemolyticus. However, Pain et al. (2020) described distinctive phenotypic characteristics of S. borealis using strains from Norway, which may be useful in distinguishing the species. The high clindamycin resistance in S. borealis is concerning and its impact on public health deserves further investigation. We recommend a future study using a large sample size, describing the distribution, antibiotic resistance, and virulence of S. borealis in South Africa and globally.

The study reveals the limitations of strain typing in SOSA globally. We identified novel strain types of S. haemolyticus, S. hominis and S. sciuri, but due to the limited S. borealis isolates which have been described, no typing system is available for this species. SCCmec types could only be assigned to 42.8% of methicillin resistant isolates, across all species. SCCmec type VIII is most common in S. haemolyticus in our setting, however, SCCmec type VIII has only been reported in clinical S. hominis and S. epidermidis in Tunisia and Malaysia, respectively (Bouchami et al., 2011; Sani et al., 2014). Majority of SCCmec elements from methicillin resistant SOSA (57.1%) were non-typeable; this not surprising due to the high recombination rate in SOSA and partly because the current SCCmec typing scheme is dedicated to S. aureus and therefore not ideal for SOSA (Ternes et al., 2013; Ikhimiukor et al., 2023). The International Working Group on the Staphylococcal Cassette Chromosome elements⁵ does not annotate SCCmec types in SOSA due to the high complexity of the elements found in SOSA. We, therefore, recommend that new approaches be explored to characterize/type SCCmec elements in SOSA to better represent the SCCmec structures in Staphylococcus other than S. aureus (SOSA). The use of AST profiles to identify potential strain differences among the isolated staphylococci has many limitations, but it was a pragmatic approach to focus the molecular analysis of isolates with a likelihood of being different. It is encouraging that of the 14 participants who had multiple isolates with different AST profiles, 10 were confirmed to be different STs. However, we cannot comment on the possibility that isolates with the same AST profile from the same participant may have belonged to different STs.

The findings suggests that children in Cape Town are colonized by multidrug resistant SOSA. This increases the risk of dissemination into clinical settings and poses a risk to empiric treatment practices. The study highlights the need for improving speciation and epidemiological tools such as multilocus sequence typing (MLST) and SCCmec typing to better describe the population structure of SOSA which can help in designing effective ABR surveillance and control strategies.

The novel sequence types presented in this study can be found in online repositories. The names of the repository/repositories and accession number(s) can be found at: https://www.ncbi.nlm.nih.gov/, PRJNA980213.

This study was approved by Health Research Ethics Committee (HREC), Stellenbosch University. Written informed consent to participate in this study was provided by the participants’ legal guardian/next of kin.

RO contributed to the conceptualisation and design of the study, performed laboratory work, whole genome sequence data analysis and interpretation, and wrote the manuscript. MN-F, AW, and WZ contributed to the conceptualisation and design of the study and provided critical feedback on the manuscript. All authors contributed to the article and approved the submitted version.

This study was supported by the German Research Council (DFG) through grant ZI665/3-1 and the German Federal Ministry of Education and Research (BMBF) through grant number 01KI2009E and the Harry Crossley foundation.

The authors declare that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest.

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