Antimicrobial Susceptibility Pattern of Fosfomycin in Various Clinical Isolates

Humaira Zafar1*,  Nouman Noor2, Kiran Tauseef Bukhari3, Sadaf Humayun2, Noor Khan Lakhnana4

1Department of Microbiology, Al Nafees Medical College & Hospital, Islamabad

2Department of Dentistry, Rawal Dental College, Rawal Institute of Health Sciences, Islamabad

3Department of Haematology, Al Nafees Medical College & Hospital, Islamabad

4Department of Pathology, Al Nafees Medical College, Islamabad.

Received: 10-Feb-2017 , Accepted: 26-Jun-2017

Keywords: Fosfomycin sensitivity, Gram negative, Gram positive

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To identify the susceptibility pattern of Fosfomycin in various clinical isolates by estimating the frequency in terms of percentages. A convenient sampling technique was adopted for study proceedings. Total 748(n) specimens for culture and sensitivity were received in the microbiology section of pathology department. Out of these 748(n) specimens, positive cultures were seen in 144(n). For culture and sensitivity proceedings, the recommended CLSI – 2014 (clinical and laboratory standard institute) guidelines were followed. The bacterial isolation was done by biochemical tests. The zone diameter of >16 mm for 50µgm fosfomycin disc was considered as sensitive zone. While <15-12mm was considered as intermittent one and

1 Introduction

Fosfomycin belongs to the group of phosphonic acid derivatives. It is available in tablets and sachets preparation. The sachets have been given a license by food & drug administration of United States for the management of complicated and uncomplicated UTIs1. The drug harbors a wide spectrum against many gram positive and gram negative bacteria2. Moreover, various multi drug resistant pathogens especially the carbapenam resistant Pseudomonas aeruginosa, Klebsiella pneumonia, extended-spectrum β-lactamase (ESBL) producing bacteria and the vancomycin resistant enterococci (VRE)3, 4

Many researches are available regarding the importance of fosfomycin usage in urinary tract infection5. However, the studies on its efficacy for the isolates of other specimens like pus, stool, high vaginal swabs and blood are deficient.

In view of all this, current study was designed to identify the sensitivity pattern of fosfomycin for both gram positive and gram negative isolates in various specimens.

2 Materials and Methods

The study was done at Microbiology (Pathology) Department of Al Nafees Medical College & Hospital, Islamabad, Pakistan. The study was carried out over the period of two years i.e 01st Oct 2015 to 20th Jan 2017. For ethical considerations informed consent was taken from all the enrolled participants.

A Convenient sampling technique was adopted for this study. All the indoor and outdoor specimens received for culture and sensitivity were included in the study. While the samples sent in wrong containers, dry swabs, or delay in specimen sending to laboratory (without preservatives) were excluded from the study.

The CLSI-2014 guidelines were followed for microbiological sample processing. Three days proceedings were done for the processing of urine, high vaginal swabs (HVS), pus, stool, and sputum specimens. While Blood cultures were followed for 07 days. 

CLED (cysteine lysine electrolyte deficient media) was used for urine cultures. While for rest of all specimens Macconkey’s agar and Blood agar were used. Nutrient agar was used for obtaining the drug susceptibility of fosfomycin.

The first day inoculation for pus, blood, sputum, HVS, and stool specimens were done on Macconkey’s and Blood agar. CLED agar was used for first day inoculation of urine specimens. Bacteriuric strips were used for the purpose and to count the number of bacteria per ml. The inoculated plates were incubated at 370C for 24 hours. The remaining urine specimens were then transferred to the disposable test tubes for centrifugation at 3000rpm/05minutes. The number of pus cells were identified by direct microscopy of deposits and correlated with bacteriuria afterwards. 

On second day the morphology of colonies were assessed. Further identification of bacteria was done by gram staining and biochemical tests.  The fosfomycin with a disc potency of 50µgm was used to detect the susceptibility pattern on Nutrient agar on same day.

On third day, interpretation of biochemical tests and drug susceptibility were done as per recommended CLSI guidelines. According to which, fosfomycin disc with a clearing zone of >16mm was considered sensitive. A zone diameter of >12-15mm was considered as intermittently sensitive and

All the blood cultures were processed accordingly (recommended protocols) uptil 07 days.

Frequencies and percentages were the numerical variables extracted by using the SPSS version 20. Mean zone diameters along with standard deviation were assessed as well.

3 Results

Total 748 (n) specimens received in microbiology section of pathology department from 01st Oct 2015 to 20th Jan 2017. Out of which 207(n) yielded significant growth. The positive urine cultures were seen in 70.04% (n=145) cases, followed by pus i.e 12.5% (n=26), high vaginal swabs (HVS) i.e 7.72% (n=16), sputum i.e 4.83% (n=10), blood i.e 2.8% (n=6), and lastly the stool i.e 1.9% (n=04). This is shown in table 1.

In case of positive urine cultures 70.04 (n=145), Escherichia coli was seen in 57.9% (n=84), followed by Klebsiella pneumoniae i.e 14.4 % (n=21), Pseudomonas aeruginosa i.e 11% (n=16), Satphylococcus saprophyticus i.e 5.5 (n=08), Proteus vulgaris i.e 04% (n=06), Morganella marganii i.e 3.44% (n=05), Serratia marcecens i..e  2.75%(n=04), and Citrobacter freundii i.e 0.68% (n=01). This is shown in table - 2.

In nineteen 12.5% (n=26) positive pus specimens, Staphylococcus aureus was seen in 38.46% (n=10), followed by Pseudomonas aeruginosa i.e 19.2% (n=05), Klebsiella pneumonia i.e 15.3%(n=04), Proteus vulgaris & Escherichia coli i.e 11.53% (n=03), each. While Morganella morganii was seen in only 3.84% (n=01).

In sixteen 7.7% (n=16) positive HVS specimens, Pseudomonas aeruginosa, Klebsiella pneumoniae and Escherichia coli were seen in 25% (n=04) each. Next in sequence were Proteus vulgaris 18.7% (n=03) and Streptococcus agalactiae in 6.2% (n=01).

Amongst nine positive sputum specimens 4.83% (n=10), Klebsiella pneumoniae was present in 50% % (n=05).  It was followed by Morganella morganii i.e 30% (n=03), and Moraxella catarrhalis in 20% (n=02).

Amongst six positive blood cultures 2.83% (n=06), Salmonella typhi was seen in 100% (n=06) cases. 

In case of four positive stool cultures 1.9% (n=04), Escherichia coli was present in 100% (n=04) specimens. This is shown in table 2.

The total distribution revealed that 90.8% (n=188) isolates were gram negative, while 17% (n=19) were gram positive. The mean zone diameter in mm (SD) for gram negative organisms was 17.34+1.03. However for gram positive organisms it was 17.6+1.01. This is shown in table 3.

Amongst the gram negative organisms, 76.06% (n=143) were sensitive to fosfomycin. While 68.42% (n=13) gram positive organisms were sensitive to fosfomycin..

For gram negative organisms highest sensitivityof 100% was seen for Citrobacter freundii and Pseudomonas aeruginosa. Next in sequence was Salmonella typhi (83.3%), Escherichia coli (67.5%), Klebsiella pneumonia (55.8%), Morganella morganii (55.5%), Moraxella catarrhalis (50%), Proteus vulgaris (41.6%), and Serratia marcescens  (25%) respectively. 

For gram positive isolates highest sensitivity was seen i.e 100% for each, Staphylococcus saprophyticus and Streptococcus agalactiae. This was followed by Staphylococcus aureus (40%) including the methicillin resistant Staphylococcus aureus (MRSA). This is shown in table 3.

4 Discussions

Literature review highlights the facts that there is increased incidence of drug resistance cases like the methicillin resistant Staphylococcus aureus (MRSA), vancomycin resistant Staphylococcus aureus (VRSA) or extended spectrum beta lactamases (ESBL). The reported incidence of such cases in Japan, Korea and China is about 60%. In Europe it is 35%6, 7. While in Pakistan it is 36.1%.  Hence, the management of simple infections is becoming challenging for the health care professionals globally8. Falagas ME etal in 2010 described that besides treatment for urinary tract infection, this drug can be used for the management of systemic infections as well9.

As mentioned in the results of current study, a wide spectrum of susceptibility was observed for fosfomycin for various isolates in different specimens. It was assessed from the current study results that, 76.06% (n=143) gram negative organisms, and 68.42% (n=13) gram positive organisms. This is in favor of two studies conducted by Falagas ME etal in 2008 & 2010. He narrated that fosfomycin harbors good efficacy against various gram positive cocci like the Staphylococcus aureus and Enterococcus faecalis. While for gram negative organisms like Enterobacteriaceae family members and Pseudomonas aeruginosa, it has yielded good results10, 11.

Amongst the gram negative isolates highest sensitivity was seen for Pseudomonas aeruginosa (100%), Citrobacter freundii (100%), Salmonella typhi (83.3%), Escherichia coli (67.5%), Klebsiella pneumonia (55.8%), and Morganella morganii (55.5%). This is different from the study results by Samonis etal (2010). He narrated in his published research that almost all Escherichia coli are susceptible to fosfomycin. However, all Salmonella typi are found susceptible, just like the results of our study. Considerable susceptibility was observed for Klebsiella pneumoniae, Pseudomonas aeruginosa and Enterobacter. This supports the findings of current study12.

Regarding the susceptibility pattern of gram positive isolates, highest sensitivity was seen i.e 100% for each, Staphylococcus saprophyticus and Streptococcus agalactiae. It was followed by Staphylococcus aureus (40%). His is different from the study results by Falagas etal (2010). He concluded that highest efficacy amongst gram positive organisms is for Staphylococcus aureus (MSSA), followed by penicillin-resistant Streptococcus pneumonia, MRSA, Enterococci and lastly for vancomycin resistant enterococci (VRE)13. Maviglia R etal (2009) also supports the finding of current study that fosfomycin is amongst promising management options for Staphylococcus saprophyticus and enterococci14. Samonis etal (2010) described that the efficacy of drug for Streptococcus agalactiae is there but to lesser extent as compared to other gram positive organisms. This is a different finding form current study results12.

The mean zone diameter for gram negative isolates is 17.34±1.03. While for gram positive isolates, it was 17.6±1.01. The literature review is deficient for justification of specific finding of current study. 

The susceptibility pattern of fosfomycin extracted from current study will be a guide for initiating the prophylactic management decisions in various clinical sittings.

5 Conclusion

Besides the urine isolates, wide spectrum of susceptibility is observed for fosfomycin. The efficacy of fosfomycin is more for gram negative 76% (n=143) as compared to gram positive organisms 68.4% (n=13).

6 Recommendations

  • Fosfomycin can be used for the management of either gram negative or gram positive severe infections.
  • The studies with larger sample size are required to assess the efficacy of fosfomycin.
  • Fosfomycin can be considered as a good option for the management infections like methicillin resistant Staphylococcus aureus (MRSA) or extended spectrum beta lactamases (ESBL)

7 Limitations of study

  • Small sample size
  • Anaerobic culture and sensitivity not performed
  • Study is conducted in one setting only

8 Acknowledgements

Mr Arshad; for performing culture and sensitivities of maximum specimens

Mr Murtaza; for facilitating the lab technicalities

9 Conflicts of Interests

There are no conflicts of interests regarding publication of this manuscript in UKJPB

10 Author’s contributions

HZ: Provoking the idea of study, corresponding author, Abstract, Methodology & Result writing, along with final formatting of entire manuscript.

NN: Data gathering and analysis

KTB: Introduction writing, Summarizing the tables for Results, Collection of latest references for discussion.

SH: Data gathering and analysis

NKL: Supervising all laboratory technicalities and final proof reading of manuscript.

11 References

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  2. Maraki S.. Susceptibility of urinary tract bacteria to fosfomycin. Antimicrob. Agents Chemother. 2009; 53(3):4508–4510.
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