Skip to main content

Vancomycin heteroresistance in coagulase negative Staphylococcus blood stream infections from patients of intensive care units in Mansoura University Hospitals, Egypt



Vancomycin heteroresistance in coagulase negative Staphylococci (CoNS) is a recent health concern especially in serious infections like bloodstream infections as it may lead to failure of therapy. Little information is available about the prevalence vancomycin heteroresistance in CoNS causing bloodstream infections in intensive care units (ICUs) patients of Mansoura University Hospitals (MUHs).


This prospective study enrolled 743 blood samples collected from ICUs patients presented with clinical manifestations of bloodstream infections over the period extending from January 2014 to March 2016. Samples were processed, coagulase negative Staphylococci were identified by routine microbiological methods and the absence of coagulase activity. Species were identified by API Staph 32. Oxacillin resistant CoNS were identified by cefoxitin disc diffusion method. Susceptibility testing of isolated CoNS to vancomycin was carried out using vancomycin agar dilution method. Mec A gene detection by PCR was done for oxacillin resistant isolates. Screening for vancomycin heteroresistance was done on brain heart infusion (BHI) agar containing 4 μg/mL vancomycin. Confirmation of vancomycin heteroresistance was carried out by population analysis profile (PAP).


A total of 58 isolates were identified as CoNS from patients of clinically suspected bloodstream infections. The identified species were 33 (56.9%) Staphylococcus epidermidis, 12 (20.7%) Staphylococcus capitis, 7 (12.1%) Staphylococcus haemolyticus, and 3 isolates (5.2%) Staphylococcus lugdunesis. Three isolates were unidentified by API Staph 32. Forty-four (75.9%) isolates were oxacillin resistant. Mec A gene was detected in all oxacillin resistant isolates. All isolates had susceptible vancomycin MICs by agar dilution. Nine isolates (15.5%) could grow on BHI agar containing 4 μg/mL vancomycin. These isolates showed heterogeneous profile of resistance to vancomycin by population analysis profile.


Vancomycin heteroresistant CoNS causing bloodstream infections is growing unrecognized health hazard in ICUs patients. These isolates have susceptible vancomycin MICs. Screening methods are recommended and should be considered to improve clinical outcome in these high risk patients.


Coagulase-negative Staphylococci (CoNS) are considered as a major cause of bloodstream infections (BSIs) in intensive care units (ICUs) patients [1]. Glycopeptides especially vancomycin are frequently considered as the first choice for treatment of serious infections caused by CoNS due to rise in resistance to Beta lactam antibiotics [2].

Although, glycopeptides resistance in CoNS has been first detected in 1987 [3]. The increased use of glycopeptides leads to diminished glycopeptides susceptibility among CoNS [4]. Later, another type of resistance named heteroresistance has been also described in clinical CoNS isolates in which vancomycin-intermediate subpopulation of cells exist in susceptible microbial population [5, 6].

Although, there is decrease susceptibility to glycopeptides in CoNS [6, 7], little studies were conducted on heteroresistance to glycopeptides in CoNS in comparison to S. aureus [8,9,10]. The objective of the present study was to determine the prevalence of heteroresistance vancomycin coagulase negative Staphylococci among patients with BSIs in ICUs of Mansoura university hospitals.

Patients and methods

This study was conducted on patients who had BSI in the ICUs of Mansoura university hospitals from January 2014 to March 2016. Nine ICUs were included in this study; five medical and four surgical ICUs. Blood samples were collected from patients admitted to these ICUs and presented with symptoms with suspected bloodstream infections according to CDC criteria [11]. Blood stream infections caused by CoNS are considered only if at least two blood cultures positive for CoNS were collected within 5 days [12]. Staphylococci were identified by standard microbiological methods [13]. CONS was confirmed by negative coagulase (coa) gene [14]. Identification of Species was done by API Staph 32 (bioMérieux) according to the manufacture instructions.

The data including: sex, age, clinical diagnosis and systemic antimicrobial therapy were retrieved from the medical records.

Oxacillin susceptibility testing

Resistance to oxacillin was evaluated by cefoxitin (30 µg) (Mast Diagnostics, Merseyside-UK) disc diffusion method according to the Clinical and Laboratory Standards Institute (CLSI) criteria [15]. Oxacillin resistant CoNS isolates were tested for the presence of mecA gene. The PCR for mecA gene was done as previously described [16].

Vancomycin susceptibility testing

Agar dilution method was done to determine the vancomycin susceptibility according to CLSI guidelines [15]. Standard vancomycin susceptible S. aureus ATCC 29213 was included as quality control.

Isolated strains were evaluated for vancomycin heteroresistance using the brain heart infusion (BHI) screen agar method as formerly described [17]. Briefly, bacterial suspension of 0.5 McFarland turbidity was prepared from an overnight culture on blood agar plate. Four 10-µL drops of the suspension were dropped onto a BHI agar plate (Mast Diagnostics, Merseyside-UK) containing 4 µg/mL vancomycin (Sigma Chemical Co., St. Louis, Mo.). Plates were incubated at 35 °C ± 2 for 48 h; the number of colonies in each drop was counted. A strain was considered to be heteroresistant to vancomycin if ≥ 1 droplet had ≥ 2 colonies.

Population analysis profile (PAP) for vancomycin heteroresistance

The PAP method was used to confirm vancomycin heteroresistance in subpopulations. All isolates that grown on BHI screen agar plate were included in PAP experiments [18]. Inoculums of (100 μL) 0.5 McFarland turbidity bacterial suspension and serial tenfold dilutions were cultured on BHI agar plates containing vancomycin at the concentrations 2, 4, 6, 8, 10, 12, 14 and 16 μg/mL at 35 °C. After 48 h, the number of colonies on plate in each concentration of drug was counted. Each strain was tested twice.

Heteroresistant strain was defined as any CoNS strain that has a susceptible vancomycin MIC by agar dilution method, can grow on BHI with 4 µg/mL vancomycin and has by PAP susceptibility testing a MIC greater than or equal to 8 µg/mL in the two experiments [19].


Total of 743 of clinically suspected blood stream infections were involved in this study. Fifty-eight isolates of CoNS were detected by absence of coA gene. S. epidermidis was the most common isolated species. Distribution of CoNS was summarized in Fig. 1.

Fig. 1
figure 1

Distribution of CoNS species

Resistance rates of the isolated CoNS to oxacillin were reported to be 76.6% (36/47). All isolates were categorized as vancomycin susceptible using agar dilution method according to the CLSI guidelines [15]. The MICs of vancomycin range from 0.25 to 2 and 0.25 to 1 µg/mL in oxacillin resistant and oxacillin sensitive isolates respectively. Vancomycin MICs by agar dilution method among different CoNS species are shown in Table 1.

Table 1 Vancomycin MICs by agar dilution and species distribution of 58 CoNS strains isolated from blood stream infections

Nine of these CoNS isolates can grow on the BHI agar containing 4 μg/mL of vancomycin. vancomycin MICs ranged from (1–2 µg/mL) by agar dilution method. By PAP these nine isolates were in the vancomycin intermediate susceptibility zone ranging from 10 to 16 µg/mL. All these heteroresistant isolates were oxacillin resistant. Majority of heteroresistant strains were S. epidermidis (66.7%). The PAPs of these nine strains are shown in Fig. 2.

Fig. 2
figure 2

PAP analysis of nine strains can grow on BHI with 4 µg/mL Vancomycin

Most of heteroresistant isolates were isolated from patients with previous vancomycin exposure (6/9). The characteristics of the vancomycin heteroresistant CoNS isolates and Characteristics of patients are shown in Table 2.

Table 2 Characteristics of Vancomycin heteroresistant CoNS isolates and patients features


Coagulase-negative Staphylococci were considered as contaminants of bacterial cultures. However, this group especially S. epidermidis has emerged as an important pathogen and a major cause of serious infections in ICU patients [1, 20]. In this study, S. epidermidis was the most common isolated member of CoNS followed by S. capitis. This was in agreement with prior reports conducted in adult ICUs [5, 20].

In the current study, resistance of CoNS to oxacillin was 76.6%. Our study supports previous reports that show increased resistance of CoNS to oxacillin in which oxacillin resistance among CoNS reached 82.4% [21]. Owing to increased resistance to methicillin among CoNS, vancomycin is frequently considered as the first choice in antimicrobial therapy [22]. In contrast to oxacillin, all CoNS isolates in the present study were sensitive to vancomycin. This was in agreement with other studies conducted on different samples demonstrated that all isolates of CoNS were sensitive to vancomycin [23,24,25]. Vancomycin resistance is still infrequent in CoNS. However, heterogeneous resistance was reported among CoNS and was associated with failure of vancomycin therapy. These heteroresistant microcolonies may be a precursor of vancomycin resistance [5, 6]. These heterogeneous resistant strains have a susceptible vancomycin MIC, but they can grow in presence of 4 µg/mL vancomycin which is greater than their MIC [19].

Despite the presence of many methods for diagnosis of vancomycin heteroresistance in Staphylococci as modified E test, PAP, PAP-AUC and disc diffusion method [26,27,28], still PAP method is the most reliable method and considered as the gold standard for the detection of heteroresistant Staphylococci [29]. In the present study, nine isolates (15.5%) showed vancomycin heteroresistance profile identified by growth on BHI containing 4 µg/mL vancomycin and confirmed by PAP. The prevalence of heteroresistance was similar to previous reports that range from (7.4 to 18.3%) [28, 21]. All heteroresistant isolates were oxacillin resistant and most of them were associated previous vancomycin therapy. In spite of susceptibility of all isolates to vancomycin, there was an increase in vancomycin MIC range of oxacillin resistant isolates (.25–2 µg/mL) towards the intermediate cutoff. In prior studies, increase in vancomycin MIC and rise of heteroresistant Staphylococci among BSI was attributed to previous use of β lactams or glycopeptides, patients admission to ICU and high rate of oxacillin resistance [28, 4]. Many previous reports show the possible relation of reduced susceptibility to glycopeptides and methicillin resistant CoNS isolates [30]. More studies extending longer durations are needed to investigate if there is a gradual increase in vancomcin MICs in oxacillin resistant CoNS like vancomycin MICs creep in methicillin resistant S. aureus.


This study alerts about the emergence of oxacillin-resistant CoNS showed heteroresistance to vancomycin. These heteroresistance strains were susceptible to vancomycin and cannot be detected by conventional standard methods. This implies the need of screening test for heteroresistance to avoid therapeutic failure. So, we should be aware of the potential reduction in vancomycin susceptibility of this pathogen, and this should be considered in determination of both empirical and rational therapy.



coagulase negative Staphylococci


bloodstream infections


intensive care units


brain heart infusion


population analysis profile


  1. Stoll BJ, Hansen N, Fanaroff AA, Wright LL, Carlo WA, Ehrenkranz RA, Lemons JA, Donovan EF, Stark AR, Tyson JE, et al. Late-onset sepsis in very low birth weight neonates: the experience of the NICHD Neonatal Research Network. Pediatrics. 2002;110(2 Pt 1):285–91.

    Article  PubMed  Google Scholar 

  2. Venkatesh MP, Placencia F, Weisman LE. Coagulase-negative staphylococcal infections in the neonate and child: an update. Semin Pediatr Infect Dis. 2006;17(3):120–7.

    Article  PubMed  Google Scholar 

  3. Schwalbe RS, Stapleton JT, Gilligan PH. Emergence of vancomycin resistance in coagulase-negative Staphylococci. New Engl J Med. 1987;316(15):927–31.

    Article  CAS  PubMed  Google Scholar 

  4. Biavasco F, Vignaroli C, Varaldo PE. Glycopeptide resistance in coagulase-negative staphylococci. Eur J Clin Microbiol Infect Dis. 2000;19(6):403–17.

    Article  CAS  PubMed  Google Scholar 

  5. Garrett DO, Jochimsen E, Murfitt K, Hill B, McAllister S, Nelson P, Spera RV, Sall RK, Tenover FC, Johnston J, et al. The emergence of decreased susceptibility to vancomycin in Staphylococcus epidermidis. Infect Control Hosp Epidemiol. 1999;20(3):167–70.

    Article  CAS  PubMed  Google Scholar 

  6. Sieradzki K, Roberts RB, Serur D, Hargrave J, Tomasz A. Heterogeneously vancomycin-resistant Staphylococcus epidermidis strain causing recurrent peritonitis in a dialysis patient during vancomycin therapy. J Clin Microbiol. 1999;37(1):39–44.

    CAS  PubMed  PubMed Central  Google Scholar 

  7. Nunes AP, Teixeira LM, Iorio NL, Bastos CC, de Sousa Fonseca L, Souto-Padron T, dos Santos KR. Heterogeneous resistance to vancomycin in Staphylococcus epidermidis, Staphylococcus haemolyticus and Staphylococcus warneri clinical strains: characterisation of glycopeptide susceptibility profiles and cell wall thickening. Int J Antimicrob Agents. 2006;27(4):307–15.

    Article  CAS  PubMed  Google Scholar 

  8. Yusof A, Engelhardt A, Karlsson A, Bylund L, Vidh P, Mills K, Wootton M, Walsh TR. Evaluation of a new Etest vancomycin-teicoplanin strip for detection of glycopeptide-intermediate Staphylococcus aureus (GISA), in particular, heterogeneous GISA. J Clin Microbiol. 2008;46(9):3042–7.

    Article  CAS  PubMed  PubMed Central  Google Scholar 

  9. Sun W, Chen H, Liu Y, Zhao C, Nichols WW, Chen M, Zhang J, Ma Y, Wang H. Prevalence and characterization of heterogeneous vancomycin-intermediate Staphylococcus aureus isolates from 14 cities in China. Antimicrob Agents Chemother. 2009;53(9):3642–9.

    Article  CAS  PubMed  PubMed Central  Google Scholar 

  10. van Hal SJ, Wehrhahn MC, Barbagiannakos T, Mercer J, Chen D, Paterson DL, Gosbell IB. Performance of various testing methodologies for detection of heteroresistant vancomycin-intermediate Staphylococcus aureus in bloodstream isolates. J Clin Microbiol. 2011;49(4):1489–94.

    Article  PubMed  PubMed Central  Google Scholar 

  11. Horan TC, Andrus M, Dudeck MA. CDC/NHSN surveillance definition of health care-associated infection and criteria for specific types of infections in the acute care setting. Am J Infect Control. 2008;36(5):309–32.

    Article  PubMed  Google Scholar 

  12. Beekmann SE, Diekema DJ, Doern GV. Determining the clinical significance of coagulase-negative Staphylococci isolated from blood cultures. Infect Control Hosp Epidemiol. 2005;26(6):559–66.

    Article  PubMed  Google Scholar 

  13. Koneman E, Allen S, Janda W, Schreckenberger P, Winn Jr W. The Gram positive cocci. I. Staphylococci and related organisms. Color atlas and textbook of diagnostic microbiology, 5th ed. Lippincott/The Williams & Wilkins Co, Philadelphia, PA. 1997:539–576.

  14. Tiwari HK, Sapkota D, Sen MR. Evaluation of different tests for detection of Staphylococcus aureus using coagulase (coa) gene PCR as the gold standard. Nepal Med Coll J (NMCJ). 2008;10(2):129–31.

    CAS  Google Scholar 

  15. Wayne P. Clinical and laboratory standards institute: performance standards for antimicrobial susceptibility testing: twenty-fourth informational supplement, M100-S24. Clin Lab Stand Inst (CLSI). 2014;34(1):1–219.

    Google Scholar 

  16. Murakami K, Minamide W, Wada K, Nakamura E, Teraoka H, Watanabe S. Identification of methicillin-resistant strains of staphylococci by polymerase chain reaction. J Clin Microbiol. 1991;29(10):2240–4.

    CAS  PubMed  PubMed Central  Google Scholar 

  17. Satola SW, Farley MM, Anderson KF, Patel JB. Comparison of detection methods for heteroresistant vancomycin-intermediate Staphylococcus aureus, with the population analysis profile method as the reference method. J Clin Microbiol. 2011;49(1):177–83.

    Article  PubMed  Google Scholar 

  18. Kim MN, Pai CH, Woo JH, Ryu JS, Hiramatsu K. Vancomycin-intermediate Staphylococcus aureus in Korea. J Clin Microbiol. 2000;38(10):3879–81.

    CAS  PubMed  PubMed Central  Google Scholar 

  19. Hiramatsu K, Aritaka N, Hanaki H, Kawasaki S, Hosoda Y, Hori S, Fukuchi Y, Kobayashi I. Dissemination in Japanese hospitals of strains of Staphylococcus aureus heterogeneously resistant to vancomycin. Lancet. 1997;350(9092):1670–3.

    Article  CAS  PubMed  Google Scholar 

  20. Natoli S, Fontana C, Favaro M, Bergamini A, Testore GP, Minelli S, Bossa MC, Casapulla M, Broglio G, Beltrame A, et al. Characterization of coagulase-negative staphylococcal isolates from blood with reduced susceptibility to glycopeptides and therapeutic options. BMC Infect Dis. 2009;9:83.

    Article  PubMed  PubMed Central  Google Scholar 

  21. Nunes APF, Schuenck RP, Bastos CCR, Magnanini MMF, Long JB, Iorio NLP. Santos KRNd: heterogeneous resistance to vancomycin and teicoplanin among Staphylococcus spp. isolated from bacteremia. Braz J Infect Dis. 2007;11(3):345–50.

    Article  CAS  PubMed  Google Scholar 

  22. Ahlstrand E, Svensson K, Persson L, Tidefelt U, Soderquist B. Glycopeptide resistance in coagulase-negative staphylococci isolated in blood cultures from patients with hematological malignancies during three decades. Eur J Clin Microbiol Infect Dis. 2011;30(11):1349–54.

    Article  CAS  PubMed  Google Scholar 

  23. Al Tayyar IA, Al-Zoubi MS, Hussein E, Khudairat S, Sarosiekf K. Prevalence and antimicrobial susceptibility pattern of coagulase-negative staphylococci (CoNS) isolated from clinical specimens in northern of Jordan. Iran J Microbiol. 2015;7(6):294–301.

    PubMed  PubMed Central  Google Scholar 

  24. Soltani R, Khalili H, Abdollahi A, Rasoolinejad M, Dashti-Khavidaki S. Nosocomial Gram-positive antimicrobial susceptibility pattern at a referral teaching hospital in Tehran, Iran. Future Microbiol. 2012;7(7):903–10.

    Article  CAS  PubMed  Google Scholar 

  25. Tayebi Z, Seyedjavadi SS, Goudarzi M, Rahimi MK, Boromandi S, Bostanabad SZ, Mirzaii A, Mahdiyoun M. Frequency and antibiotic resistance pattern in gram positive uropathogenes isolated from hospitalized patients with urinary tract infection in Tehran, Iran. J Genes Microb Immun 2014;2014:1–9.

    Article  Google Scholar 

  26. Park KH, Kim ES, Kim HS, Park SJ, Bang KM, Park HJ, Park SY, Moon SM, Chong YP, Kim SH, et al. Comparison of the clinical features, bacterial genotypes and outcomes of patients with bacteraemia due to heteroresistant vancomycin-intermediate Staphylococcus aureus and vancomycin-susceptible S. aureus. J Antimicrob Chemother. 2012;67(8):1843–9.

    Article  CAS  PubMed  Google Scholar 

  27. El-Halfawy OM, Valvano MA. Antimicrobial heteroresistance: an emerging field in need of clarity. Clin Microbiol Rev. 2015;28(1):191–207.

    Article  PubMed  PubMed Central  Google Scholar 

  28. Wong SS, Ho PL, Woo PC, Yuen KY. Bacteremia caused by staphylococci with inducible vancomycin heteroresistance. Clin Infet Dis. 1999;29(4):760–7.

    Article  CAS  Google Scholar 

  29. Howden BP, Davies JK, Johnson PD, Stinear TP, Grayson ML. Reduced vancomycin susceptibility in Staphylococcus aureus, including vancomycin-intermediate and heterogeneous vancomycin-intermediate strains: resistance mechanisms, laboratory detection, and clinical implications. Clin Microbiol Rev. 2010;23(1):99–139.

    Article  CAS  PubMed  PubMed Central  Google Scholar 

  30. Del’ Alamo L, Cereda RF, Tosin I, Miranda EA, Sader HS. Antimicrobial susceptibility of coagulase-negative staphylococci and characterization of isolates with reduced susceptibility to glycopeptides. Diagn Microbiol Infect Dis. 1999;34(3):185–91.

    Article  PubMed  Google Scholar 

Download references

Authors’ contributions

GM and RE designed the study, carried out the microbiological tests, analyzed and interpreted data, contributed in writing the manuscript. All authors read and approved the final manuscript.


Not applicable.

Competing interests

The authors declare that they have no competing interests.

Availability of data and materials

Please contact author for data requests.

Consent for publication

Not applicable.

Ethics approval and consent to participate

The protocol was approved by the institutional research board at faculty of medicine, Mansoura University. consent to participate were taken from all participants.



Publisher’s Note

Springer Nature remains neutral with regard to jurisdictional claims in published maps and institutional affiliations.

Author information

Authors and Affiliations


Corresponding author

Correspondence to Rasha Hassan El-Mahdy.

Rights and permissions

Open Access This article is distributed under the terms of the Creative Commons Attribution 4.0 International License (, which permits unrestricted use, distribution, and reproduction in any medium, provided you give appropriate credit to the original author(s) and the source, provide a link to the Creative Commons license, and indicate if changes were made. The Creative Commons Public Domain Dedication waiver ( applies to the data made available in this article, unless otherwise stated.

Reprints and permissions

About this article

Check for updates. Verify currency and authenticity via CrossMark

Cite this article

Mashaly, G.ES., El-Mahdy, R.H. Vancomycin heteroresistance in coagulase negative Staphylococcus blood stream infections from patients of intensive care units in Mansoura University Hospitals, Egypt. Ann Clin Microbiol Antimicrob 16, 63 (2017).

Download citation

  • Received:

  • Accepted:

  • Published:

  • DOI: