Characterisation of staphylococcus aureus bacteraemia at Tygerberg hospital

An overview of antimicrobial resistance surveillance among healthcare-associated pathogens in South Africa

Healthcare-associated infections are a serious public health concern resulting in morbidity and mortality particularly in developing countries. The lack of information from Africa, the increasing rates of antimicrobial resistance and the emergence of new resistance mechanisms intensifies this concern warranting the need for vigorous standardised surveillance platforms that produce reliable and accurate data which can be used for addressing these concerns. The implementation of national treatment guidelines, policies, antimicrobial stewardship programmes and infection prevention and control practices within healthcare institutions require a platform from which it can draw information and direct its approach. In this review, the importance of standardised surveillance systems, the challenges faced in the application of a surveillance system and the condition (existence and nonexistence) of such systems in African countries is discussed. This review also reports on some South African data.

A small proportion of community-associated methicillin-resistant Staphylococcus aureus bacteraemia, compared to healthcare-associated cases, in two South African provinces

We compared the proportion of cases of community-associated and healthcare-associated methicillin-resistant Staphylococcus aureus (CA-MRSA and HA-MRSA, respectively) bacteraemia among patients at five hospitals in the Gauteng and Western Cape provinces in South Africa and described the molecular characteristics and antimicrobial susceptibility trends. This was a cross-sectional study using data collected by enhanced surveillance for S. aureus bacteraemia. A total of 2511 cases of S. aureus bacteraemia were identified from January 2013 to January 2016. Among 1914 cases of S. aureus, 557 (29.1%) cases were identified as MRSA infection. Forty-four cases (44/1914 [2.3%] of all S. aureus cases) were considered CA-MRSA infection and 513/1914 (26.8% of all cases) had HA-MRSA infection; the majority were neonates. CA-MRSA constituted 7.9% (44/557) of all cases of MRSA infection. Staphylococcus aureus isolates demonstrated significantly reduced susceptibility to the following classes of antimicrobial agents: macrolides, tetracyclines, aminoglycosides and cotrimoxazole, in 2015 compared to 2013 (p < 0.05). Of the 557 MRSA isolates, 484 (87%) were typed for SCCmec elements and spa types: the most common SCCmec type was type III (n = 236, 48.76%), followed by type IV (n = 144, 29.76%). The most common spa types were t037 (n = 229, 47.31%) and t1257 (n = 90, 18.60%). Of 28 isolates selected for multilocus sequence typing (MLST), the most common sequence types (STs) were ST239 and ST612 of clonal complex 8 (CC8) (n = 8 each) and a novel ST (ST4121) was obtained for one isolate. This study demonstrates that S. aureus bacteraemia is common in South African academic centres and characterised by HA-MRSA SCCmec types III and IV. A small proportion of CA-MRSA cases were caused by a few different sequence types.

Molecular Characterization of Community Acquired Staphylococcus aureus Bacteremia in Young Children in Southern Mozambique, 2001-2009

Background: The emergence of community-acquired Staphylococcus aureus infections is increasingly recognized as life threating problem worldwide. In Manhiça district, southern Mozambique, S. aureus is the leading cause of community-acquired bacteremia in neonates. Methods: Eighty-four S. aureus isolates from children less than 5 years admitted to Manhiça District Hospital from 2001 to 2009 were randomly selected and genetically characterized by DNA microarray and spa typing. Antimicrobial susceptibility was determined by VITEK 2. Results: Thirty-eight different spa types and 14 clonal complexes (CC) were identified. Spa-type t084 (n = 10; 12%) was the most predominant while CC8 (n = 18; 21%) and CC15 (n = 14; 16%) were the most frequent CCs. Mortality tended to be higher among children infected with CC45 (33.3%, 1/3) and CC8 (27.8%, 5/18). The majority of isolates possessed the accessory gene regulator I (45%) and belonged to either capsule type 8 (52%) or 5 (47%). Panton valentine leukocidin (PVL) encoding genes were detected in 30%. Antibiotic resistance was high for penicillin (89%), tetracycline (59%) and Trimethoprim Sulfamethoxazole (36%) while MRSA was uncommon (8%). Conclusions: Although MRSA were uncommon, we found high genetic diversity of methicillin susceptible S. aureus causing bacteremia in Mozambican children, associated with high resistance to the most available antibiotics in this community. Some CCs are likely to be more lethal indicating the need for prompt recognition and appropriate treatment.

Prevalence and Trends of Staphylococcus aureus Bacteraemia in Hospitalized Patients in South Africa, 2010 to 2012: Laboratory-Based Surveillance Mapping of Antimicrobial Resistance and Molecular Epidemiology

INTRODUCTION

We aimed to obtain an in-depth understanding on recent antimicrobial resistance trends and molecular epidemiology trends of S. aureus bacteraemia (SAB).

METHODS

Thirteen academic centres in South Africa were included from June 2010 until July 2012. S. aureus susceptibility testing was performed on the MicroScan Walkaway. Real-time PCR using the LightCycler 480 II was done for mecA and nuc. SCCmec and spa-typing were finalized with conventional PCR. We selected one isolate per common spa type per province for multilocus sequence typing (MLST).

RESULTS

S. aureus from 2709 patients were included, and 1231 (46%) were resistant to methicillin, with a significant decline over the three-year period (p-value = 0.003). Geographical distribution of MRSA was significantly higher in Gauteng compared to the other provinces (P<0.001). Children <5 years were significantly associated with MRSA with higher rates compared to all other age groups (P = 0.01). The most prevalent SCCmec type was SCCmec type III (531 [41%]) followed by type IV (402 [31%]). Spa-typing discovered 47 different spa-types. The five (87%) most common spa-types were t037, t1257, t045, t064 and t012. Based on MLST, the commonest was ST612 clonal complex (CC8) (n = 7) followed by ST5 (CC5) (n = 4), ST36 (CC30) (n = 4) and ST239 (CC8) (n = 3).

CONCLUSIONS

MRSA rate is high in South Africa. Majority of the isolates were classified as SCCmec type III (41%) and type IV (31%), which are typically associated with hospital and community- acquired infections, respectively. Overall, this study reveals the presence of a variety of hospital-acquired MRSA clones in South Africa dominance of few clones, spa 037 and 1257. Monitoring trends in resistance and molecular typing is recommended to detect changing epidemiological trends in AMR patterns of SAB.

Biofilm formation in invasive Staphylococcus aureus isolates is associated with the clonal lineage

The contribution of the genetic background of Staphylococcus aureus to biofilm formation is poorly understood. We investigated the association between the genetic background and the biofilm forming ability of clinical invasive S. aureus isolates. Secondary objectives included investigating any correlation with biofilm formation and methicillin resistance or the source of bacteraemia. The study was conducted at a 1300-bed tertiary hospital in Cape Town, South Africa. S. aureus isolates obtained from blood cultures between January 2010 and January 2012 were included. Genotypic characterization was performed by PFGE, spa typing, SCCmec typing and MLST. Thirty genotypically unique strains were assessed for phenotypic biofilm formation with the microtitre plate assay. All isolates were tested in triplicate and an average optical density, measured at a wavelength of 490 nm, was determined. The biofilm forming ability of isolates with A490 ≤ 0.17 were considered non-adherent, A490 > 0.17 'weak positive' and A490 > 0.34 'strong positive'. Fifty seven percent of isolates formed biofilms. Weak biofilm formation occurred in 40% (n = 12) and strong biofilm formation in 17% (n = 5) of isolates. All 5 isolates capable of strong biofilm formation belong to one spa clonal complex (spa-CC 064). Strains from spa-CC 064 were capable of higher biofilm formation than other spa clonal complexes (p = 0.00002). These 5 strains belonged to MLST CC5 and CC8. Biofilm formation correlates with the spa clonal lineage in our population of invasive S. aureus strains. Biofilm formation did not correlate with methicillin resistance and was not related to the source of bacteraemia.